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2 Attachment(s)
Re: Ask an Acoustic Engineer (me)
Question: I want to find the different in "box size" between no polyfill and a stuffed box. I have a Dayton DATS and ran the sweet for before and after.
What math can I use to determine the airspace for each? Or if not, the supposed gains the subwoofer sees in volume from the polyfill? I've found people mention you only need Qts and Fs, but others that say you need VAS, others say you need Qtc... Would love some input on that.
Attached is the screenshot difference between the same subwoofer and box, but with 4.5lbs of stuffing (as I calculated a very rough 4.5 cubes in my complex enclosure).
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Re: Ask an Acoustic Engineer (me)
Great response to my question Justin and thank you for taking the time to write that. I loved the driving analogy! I’m sure this will help many members here understand the theory. I couldn’t get the DIYMA link to work. I did a bunch of research into regulated vs non regulated amplifiers a long time ago. Not sure if it’s entirely accurate but the consensus was that non regulated power supplies gave amplifiers a slight edge in dynamic power over regulated power supplies but I’m not so sure that would be audible. Just think of the power drop you get when shutting off your engine with the audio playing. Your voltage could go from 14 volts to 12.5 volts yet you likely won’t notice a difference from the reduced power as a result.
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Re: Ask an Acoustic Engineer (me)
Quote:
Originally Posted by
JCsAudio
Great response to my question Justin and thank you for taking the time to write that. I loved the driving analogy! I’m sure this will help many members here understand the theory. I couldn’t get the DIYMA link to work.
I'm happy you were able to read that too. I know you were pretty bummed about not getting an answer earlier!
I fixed the link in the thing. Here it is again, just in case:
www.diymobileaudio.com/threads/how-does-rips-jl-audio-work.89221/page-2#post-1127909
And NoDestiny I'm thinking about your question. We do this at the office too.
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Re: Ask an Acoustic Engineer (me)
Thanks Justin, I just read that article now. Very good information there and now I know exactly how RIPS works. I was kind of bummed about the first question, lol. I was like......AHHHH man, lol. Seriously though it’s awesome that you come on here and share your knowledge like this and I really appreciate it. Reminiscent of that old post from msmith and many from Andy Wehmeyer from back in the day.
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Re: Ask an Acoustic Engineer (me)
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3 Attachment(s)
Re: Ask an Acoustic Engineer (me)
Quote:
Originally Posted by
NoDestiny
Question: I want to find the different in "box size" between no polyfill and a stuffed box. I have a Dayton DATS and ran the sweet for before and after.
What math can I use to determine the airspace for each? Or if not, the supposed gains the subwoofer sees in volume from the polyfill?
Attachment 10564
There are many ways to calculate this so you might be able to do it with Vas or Qts in a similar way. I like the method I came up with since it's really simple.
You need three measurements with the DATS system by pressing the "measure free air parameters" button, and record the resonant frequency fs for each:
1) measure woofer in free air without any enclosure
2) measure woofer in sealed box without any stuffing
3) measure woofer in sealed box with stuffing
To find the ratio of how much "bigger" the enclosure became from the stuffing that you added, the formula looks like this:
Attachment 10562
To find the air volume of the box, I usually measure the woofer with something like DATS and then simulate it in a sealed box. I change the air volume of the simulated box until the resonant frequency of the box Fc matches the resonant frequency when I measure the woofer in the box using DATS.
You can try to calculate it too, however you must make very careful measurement of the woofer when you do since any errors will multiply when you try to calculate the enclosure volume. The formula looks like this:
Attachment 10563
The units are MKS (meter-kilogram-second) so make sure you convert Sd from square centimeters to square meters, and convert Cms from mm/N to meters/newton and so on. The answer spits out cubic feet. By Fc I mean the resonant frequency of the woofer in the box.
Cool question, I enjoyed working through this one since I can use it at the office more often now : )
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1 Attachment(s)
Re: Ask an Acoustic Engineer (me)
Just wanted to interject with a video link that has an amp technician walking through to explain this technology.
Also wanted to raise an interesting aspect that relates to both subwoofers and amplifiers, that IMO makes the design of these "constant power" amplifiers actually even more remarkable:
Quote:
Originally Posted by
Justin Zazzi
I admit amplifier design is not my specialty...
Non-regulated power supplies will allow the rail voltages to increase or decrease as the battery voltage is increased or decreased...
Regulated power supplies will hold the rail voltages constant when the battery voltage changes...
I was going to write a big thing here but Manville Smith of JL Audio wrote a sweet post over at DIYMA about ten years ago.
How does RIPS (JL Audio) work? post #21
Please read Manville's post, it is really well written and it goes into a lot of really good detail.
In short, the output stage is usually made up of transistors that can supply the speaker with voltage up to the rail voltage limits that the power supply has. The speaker will present an impedance (or a load) and then current will flow.
To add complexity to the challenge - speaker's impedance isn't a constant, it's naturally different at different frequencies, and at a speaker's natural resonance can rise surprisingly high - let's say a 4 ohm subwoofer has an Re of 3.5 ohms and an Fs of 24hz, like this completely random sample I found just because it had a plot...
You can see that impedence rise at Fs - up to 100ohms, maybe more:
Attachment 10572
Want another wrench to throw in the works? That above plot - it completely changes as soon as you put a subwoofer in a box. In a sealed box, it shifts based on the size of your box. In a ported box, the vent has an impact on cone motion which in turn impacts impedance. You could change the height or width of that resonance, or you could add a second high-impedance spike on the plot, again depending on box size and tuning.
The point relative to this "constant power" amp design is - a sub's impedance is all over the place, dynamically, and (from the amp's perspective) unpredictably. That amp is designed to drive one sub in a box as well as another totally different sub in a totally different box, and not impart any false coloration on the frequency response of that sub playing.
Quote:
Originally Posted by
Justin Zazzi
Continuing with the car analogy, a given car can drive 65mph on the freeway if the road is flat. The same car will go much slower up a steep hill, even with the gas pedal on the floor. The same car can go much faster than 65mph if you're driving down a steep hill, so fast that it can easily loose control and crash into a fireball and cause the road to be closed and inconvenience literally everyone else in a supremely selfish act of dumbassery.
Relating the car to the amplifier: an amplifier can supply 100watts of power if the impedance of the speaker is a good match (like driving the speed limit on a flat highway). The same amplifier, using the same rail voltage, can supply less power if the speaker impedance is too high (like driving up a steep hill). The same amplifier can supply much more than rated power if the speaker impedance is too low (like driving down a steep hill) and if the impedance is too low then the amplifier can overheat and blow up (like the car going too fast and crashing).
I love the analogies. Definitely driving your amp at too low of a load can cause it to die... I'd call that a car wreck.
It might be fun to take a deeper dive into this "impedance rise" topic, as a lot of people refer to it these days...
I see a lot of SPL competitors these days are actually becoming aware of their impedance plots, and are saying to themselves "Wait up... if my box is tuned to 60hz, and I measured my 1 ohm sub's impedance rises to 16 ohms at 60hz in this box - if my 2000w amp is only making that power at 1 ohm... does that mean my amp is only making... hang on... 2 ohm... 4 ohm... 8 ohm..16 ohm... 125 watts when I'm burping?"
So lately I've seen people wiring to very, very low impedances - 1/4 ohm, I'm sure some people are trying less - so that their amp makes the power their sub can handle at (and ONLY at!!) their burp frequency.
Would be fun to take a deeper dive into the negative consequences - That they've literally created a one-note wonder that would fry it's amp if you fed it anything other than that specific test tone (do people still use "burp buttons"?), and to compound that problem - that they've frequently got to solder across their protection resistors to totally eliminate amp protection (for those amps of this class that have protection) for this to even work at all. But maybe a theoretical dive into the negatives from the speaker perspective?
Quote:
Originally Posted by
Justin Zazzi
Constant Power
To get constant power out of an amplifier at 1Ω and 2Ω and 4Ω, you need two main things: 1) enough voltage amplifier power supply so that the power can be realized on the highest impedance load and 2) a current sensing/limiting technique so that the amplifier doesn't overheat or fail when the lowest impedance load is used.
An example amplifier might claim:
100w @ 4Ω
100w @ 2Ω
100w @ 1Ω
To get 100w at 4Ω the rail voltage would have to be
Sam from BareVids is an awesome guy for anyone who wants to understand amplifiers better. I subscribe to his vids, watch them while I'm working - he's a huge distraction, honestly.:lol:
In this particular link, he looks inside a Taramps amp that has a "smart" circuit like the JL RIPS amps.
It's important to know that - for the reasons Justin already described - there's limits to this "smart" technology just like there are limits to normal amplifiers that don't have this kind of design.
So these amp ratings would look like BS to me:
100w @ 4Ω
100w @ 2Ω
100w @ 1Ω
...because that's a big range to actually maintain constant power across.
I'd be betting it would really dyno out more like this:
40w @ 8Ω
80w @ 4Ω
100w @ 2Ω
100w @ 1Ω
Check out Sam's dive into this smart technology - he brings up the waveforms on his scope, so you can actually see the technology work, can see the voltages change, and power change.
It sounds like a deep dive, but Sam does a great job explaining it at a layman level. Definitely worth a watch.
https://www.youtube.com/watch?v=DxMGPhNASl4&t=440s
Note that link is actually the 7:25 mark on a Williston Labs review - another guy worth subscribing to IMO - but I subscribe to Sam as well. His channel is "barevids" - don't worry, it's not what that looks like. Nothing NSFW. :lol:
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Re: Ask an Acoustic Engineer (me)
Quote:
Originally Posted by
ckirocz28
That's a really interesting question! I replied in your thread with a reason why it might not work, and a small tweak to make it work potentially, maybe.
That's freaking fascinating and I'm dying to see if it works!
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Re: Ask an Acoustic Engineer (me)
Quote:
Originally Posted by
geolemon
It might be fun to take a deeper dive into this "impedance rise" topic, as a lot of people refer to it these days...
I see a lot of SPL competitors these days are actually becoming aware of their impedance plots, and are saying to themselves "Wait up... if my box is tuned to 60hz, and I measured my 1 ohm sub's impedance rises to 16 ohms at 60hz in this box - if my 2000w amp is only making that power at 1 ohm... does that mean my amp is only making... hang on... 2 ohm... 4 ohm... 8 ohm..16 ohm... 125 watts when I'm burping?"
So lately I've seen people wiring to very, very low impedances - 1/4 ohm, I'm sure some people are trying less - so that their amp makes the power their sub can handle at (and ONLY at!!) their burp frequency.
I've heard people doing that too! But wait, there's more!
When playing a high-output burst the voice coil heats up which changes the impedance of the system, which changes the resonant frequency, and on and on. I met a competitor once who mapped this temperature rise and performance change vs time and then created a burp track that started at some frequency (maybe 52hz) and changed frequency over time to match the change in the performance of the system as it heats up over a very short time. This way the frequency of the tone is always matched to the instantaneous resonant frequency of the system for maximum output not just when it starts, but as the system continues pounding over time. This stuff is crazy!
Quote:
Originally Posted by
geolemon
Check out Sam's dive into this smart technology - he brings up the waveforms on his scope, so you can actually see the technology work, can see the voltages change, and power change.
It sounds like a deep dive, but Sam does a great job explaining it at a layman level. Definitely worth a watch.
https://www.youtube.com/watch?v=DxMGPhNASl4&t=440s
Thank you for the video link, that was nice to see! I like all the practical bits with the scope traces.
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Re: Ask an Acoustic Engineer (me)
So.... Just so I understand at a more "basic" level. :-)
- An amplifier with a "regulated" power supply will provide the same amount of power regardless of the speaker impedance.
- An amplifier with an "un-regulated" power supply will provide less power to speakers with higher impedance.
Are those two statements true?
The reason that I ask is because I'm still not clear why my JL XD600/6v2 (which does NOT have a RIPPS power supply) provides 100W RMS at 2 ohms, but 75W RMS at 4 ohms. Why is there such a small difference between the 2 and 4 ohm outputs? Don't most "un-regulated" amps provide twice the amount of power at 2 ohms (compared to 4 ohms)?
While the JL XD line of amps don't have the "RIPPS" power supplies, do they maybe have some "lesser" version of a regulated power supply instead? I honestly don't know if they are regulated or un-regulated.
Thanks - and sorry if this was already explained earlier - maybe I just didn't understand it.
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Re: Ask an Acoustic Engineer (me)
Quote:
Originally Posted by
jtrosky
So.... Just so I understand at a more "basic" level. :-)
- An amplifier with a "regulated" power supply will provide the same amount of power regardless of the speaker impedance.
- An amplifier with an "un-regulated" power supply will provide less power to speakers with higher impedance.
Are those two statements true?
Not quite.
Quote:
Originally Posted by
jtrosky
The reason that I ask is because I'm still not clear why my JL XD600/6v2 (which does NOT have a RIPPS power supply) provides 100W RMS at 2 ohms, but 75W RMS at 4 ohms. Why is there such a small difference between the 2 and 4 ohm outputs? Don't most "un-regulated" amps provide twice the amount of power at 2 ohms (compared to 4 ohms)?
While the JL XD line of amps don't have the "RIPPS" power supplies, do they maybe have some "lesser" version of a regulated power supply instead? I honestly don't know if they are regulated or un-regulated.
Thanks - and sorry if this was already explained earlier - maybe I just didn't understand it.
I'm not sure how the XD amplifier from JL works. However, the regulated vs non-regulated power supply usually means the power output can vary when the battery voltage changes. Usually, as I understand it, this effect will not show up in the specs when you look at power ratings vs impedance so the non-regulated nature of the amplifier isn't responsible for the 100w@2Ω vs 75w@4Ω thing. I think. Again, I can't speak for the JL line of amps.
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Re: Ask an Acoustic Engineer (me)
In an amplifier with a non regulated power supply if the power doesn’t double when the impedance load gets cut in half then it’s because the power supply isn’t designed for this and runs out of current capacity before it can. This is how I understand it. In the interest of efficiency and amplifier size reduction, plus cost savings, many of today’s modern amplifiers have power supplies that are on the small side of things compared to the golden age of huge surfboard class AB amplifiers from years ago.
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Re: Ask an Acoustic Engineer (me)
I guess I just assumed that a JL Audio XD amp wouldn't "skimp" on the power supply. I mean they are not "cheap" amps. Hell, I paid more $$$ for half the power (compared to an AudioControl LC-6.1200, for example). Kind of sucks that I only "gain" 25W going from 4 ohms to 2 ohms.
Looks like the AudioControl LC-6.1200 goes from 125W x 6 (4 ohms) to 200W x 6 (2 ohms). So I could have paid less $$$ and got twice the power (if running 2 ohms). Oh well... I do like the JL Audio XD amps otherwise - and it's not like I really need more volume - but I just think it would be nice to have a little more power for the midbass channels, which are the volume-limiting channels in my system.
Any thoughts on the JL XD series amp vs the AudioControl LC-series amps?
When trying to decide which amp to go with (JL X600/6v2 or AudioControl LC-6.1200), I decided on the JL Audio because of JL's reputation as well as the fact that the AudioControl had all kinds of features that I just didn't need since I was going to run fully active with a full DSP - and you couldn't bypass all of the high/low pass filters on all channels with the AudioControl. Not the end of the world, but I figured that the less "circuitry" the signal has to go through, the better chance of clean, noise-free output.
Thanks for all of the info!!
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Re: Ask an Acoustic Engineer (me)
Quote:
Originally Posted by
jtrosky
So.... Just so I understand at a more "basic" level. :-)
- An amplifier with a "regulated" power supply will provide the same amount of power regardless of the speaker impedance.
- An amplifier with an "un-regulated" power supply will provide less power to speakers with higher impedance.
Are those two statements true?
The reason that I ask is because I'm still not clear why my JL XD600/6v2 (which does NOT have a RIPPS power supply) provides 100W RMS at 2 ohms, but 75W RMS at 4 ohms. Why is there such a small difference between the 2 and 4 ohm outputs? Don't most "un-regulated" amps provide twice the amount of power at 2 ohms (compared to 4 ohms)?
While the JL XD line of amps don't have the "RIPPS" power supplies, do they maybe have some "lesser" version of a regulated power supply instead? I honestly don't know if they are regulated or un-regulated.
Thanks - and sorry if this was already explained earlier - maybe I just didn't understand it.
In the old days, an amplifier with a regulated power supply would produce the same amount of power at 12 volts as it would at 14 volts. It would just draw more current at the lower voltage. An amplifier with an unregulated power supply would produce more power at 14 volts than it would at 12 volts.
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Re: Ask an Acoustic Engineer (me)
Jtrosky, JL Audio amplifiers dyno really well so I think you’re getting more than what’s rated by a good margin plus there are things about amplifiers that are as important or more important than just the total power output. https://youtu.be/UsLUeO33DgE
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Re: Ask an Acoustic Engineer (me)
Quote:
Originally Posted by
jtrosky
I guess I just assumed that a JL Audio XD amp wouldn't "skimp" on the power supply. I mean they are not "cheap" amps. Hell, I paid more $$$ for half the power (compared to an AudioControl LC-6.1200, for example). Kind of sucks that I only "gain" 25W going from 4 ohms to 2 ohms.
Looks like the AudioControl LC-6.1200 goes from 125W x 6 (4 ohms) to 200W x 6 (2 ohms). So I could have paid less $$$ and got twice the power (if running 2 ohms). Oh well... I do like the JL Audio XD amps otherwise - and it's not like I really need more volume - but I just think it would be nice to have a little more power for the midbass channels, which are the volume-limiting channels in my system.
Any thoughts on the JL XD series amp vs the AudioControl LC-series amps?
When trying to decide which amp to go with (JL X600/6v2 or AudioControl LC-6.1200), I decided on the JL Audio because of JL's reputation as well as the fact that the AudioControl had all kinds of features that I just didn't need since I was going to run fully active with a full DSP - and you couldn't bypass all of the high/low pass filters on all channels with the AudioControl. Not the end of the world, but I figured that the less "circuitry" the signal has to go through, the better chance of clean, noise-free output.
Thanks for all of the info!!
I believe the "regulated" power supply is only regulating the power input, the "RIPS" was an output side regulation. I'm quite fond of the XD series, I've got two of the 400/4's. But I agree they're a little low on power for midbass duty, that's why I have 2 channels bridged on each mid.
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2 Attachment(s)
Re: Ask an Acoustic Engineer (me)
Hey Justin or any acoustic engineers,
I would like to hear more discussion or breakdown on stereo stages involving a 3rd center channel. Yes we know the standard 2 channel R and L stereo creates a proper center image when properly aligned. We know that when introducing a mono sum center R+L, the stage width will severely collapse due to the same R and L information coming from both the center and the sides speakers.
Attachment 10642
But with stronger DSP options becoming available I wanted to hear more about what the shortcomings of the following center channel schemes would present to listeners when compared to the standard 2 channel stereo scheme. We know the 1st scheme collapses the stereo stage width, but what can be generally expected from the last 3 schemes? I could be wrong but I believe the 2nd scheme is what Audiocontrol used to implement for their discontinued ESP-3 center channel processor. The last 2 schemes are assuming the center channel is derived via an up-mixer with an algorithm to steer only common information in both R and L to the C channel (like Logic 7, Pro Logic 2, or Helix RealCenter).
Attachment 10643
*For comparison sake, let’s assume the listener is in central listening position and all 3 speakers are the same.
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Re: Ask an Acoustic Engineer (me)
Quote:
Originally Posted by
Bnlcmbcar
Hey Justin or any acoustic engineers,
I would like to hear more discussion or breakdown on stereo stages involving a 3rd center channel.
Those are some good questions but they are beyond me for now. I recommend looking at the original Dolby Pro Logic circuits wince they are well documented and heavily discussed. There are also a lot of psychoacoustic studies done and published in the AES E-Journal that would be fun to read. If you find a couple papers that you'd like to read, let me know and I'll see if I can get them. Pro tip: the AES wants you to pay for the papers but you can contact the authors directly and if you ask nicely, they will send you a copy for free (I've done this a few times and made some good friends!).
I would like to learn more about this too.
Andy Wehmeyer has a lot more center-channel knowledge and he would be a good person to ask!
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Re: Ask an Acoustic Engineer (me)
Quote:
Originally Posted by
Justin Zazzi
When playing a high-output burst the voice coil heats up which changes the impedance of the system, which changes the resonant frequency, and on and on. I met a competitor once who mapped this temperature rise and performance change vs time and then created a burp track that started at some frequency (maybe 52hz) and changed frequency over time to match the change in the performance of the system as it heats up over a very short time. This way the frequency of the tone is always matched to the instantaneous resonant frequency of the system for maximum output not just when it starts, but as the system continues pounding over time. This stuff is crazy!
That actually makes me think of a certain manufacturer (coughDDcough) who disclaimers their specifications saying that they don't accurately represent how "their" drivers behave on power.
It's a different thing, but definitely in the same vein as "the deeper you dive, the more complex it gets":
Part of me wants to agree with them - I was lucky enough to get to personally visit DLC Labs to meet Dave Clark in person and have some of my prototype subs tested on their DUMAX machine - specifically because it actually manipulates the driver using vacuum across the whole excursion range, to not only provide small-signal specs at the "at rest" position, but also across the entire range, so you can see linearity. We were licensing XBL^2 back in the mid 90's, specifically for that linearity, and I wanted to see if the suspensions that I chose were a good match for a motor design we already settled on. We wanted to design a subwoofer that was linear - so the specs on that sheet WERE good, at least until you got to Xmax - which we wanted to be way out there.
Essentially, DD's statement is basically saying "our subs aren't linear", which - I mean, fine. I had a 9915 back in the day, and it literally had a stack of glued-together spiders to control all that moving mass that an SPL sub needs to have, on the power that they expect an SPL sub to be burped at... and no one cares about linearity in the lanes. You want BL... that basically means ALL the coils in the gap at rest! :lol:
And ironically in a different way, in a different DD "tech talk" post, they DO advocate breaking in a sub - which, while that wouldn't fix linearity issues, it would at least somewhat resolve the initial "at rest" vs "in motion" point that they are actually making. I wish there was a comment thread below their blog, for people to say "Just break in your subs, THEN measure the official specs!" ...but clearly I'm no fan of gluing together stacks of spiders - that's not how a "multi-layer spider" is supposed to be IMO.
Now, your comment does make me think though - even using a DUMAX machine, it's still small signal analysis - so, to your point - no heat.
I'm past my sub engineering days (IT consulting pays better), but it makes me wonder - if we did a second DUMAX run after running the sub at rated RMS power for 15 minutes or so to bring the temperature up to the rated maximum, and then measured it - how far would the parameters shift? :hmm:
Great point - and I'd expect those SPL nutcases to take those measurements after heat rise. It's actually the geek-level stuff that can make SPL fun. :cool: Well - to me. :nerd:
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Re: Ask an Acoustic Engineer (me)
Quote:
Originally Posted by
Bnlcmbcar
Hey Justin or any acoustic engineers,
I would like to hear more discussion or breakdown on stereo stages involving a 3rd center channel...
But with stronger DSP options becoming available I wanted to hear more about what the shortcomings of the following center channel schemes would present to listeners...
Attachment 10643
Quote:
Originally Posted by
Justin Zazzi
I would like to learn more about this too.
I would as well - and I'd also advocate Bnlcmbcar to do some searching some of the DIY audio forums that have home theater sections.
From the diagrams that you posted, I'd be concerned as you are (especially in a car) that you'd narrow the image, because you are pulling some of the L and R content into the center - which, most troublingly - brings some of the L content to your R side, if you are in the driver's seat. Conversely, for a passenger, brings some of the R content to the L of them. Eek.
What I'd like to see in a center channel for a car, would be "(L+R)-(L-R)". That way, it's only bringing the content from both speakers to the center, and even if there's a little content that's on both channels but simply louder on one than the other, it still mitigates that by attenuating that sound at the center channel. I'd believe that would at least help keep the stage width - hopefully as wide as with just a stereo pair.
But I think really, in a car, the KISS rule applies... there's already glass, and absorbant upholstery, and plastic, all pointing different directions - you could have ONE speaker in a car and end up with a nightmare of multiple pathlength distances, direct and reflected (with each of those having a 180 degree shift - plus pathlength difference offset!) creating anything but a flat response as it arrives at your ears. :lol:
So I subscribe to the "the fewer speakers the better" theory for car audio. There's exceptions - for example, three way components where you actually aim the mid and tweeter - can provide better imaging. But my default recommendation is simplicity over complexity, for those pathlength reasons.
I'm really interested in this myself, but in no way for creating a center channel (IMO, there's already enough direct and reflected pathlength sounds wreaking havoc on image-killing phase interactions as they all ultimately arrive at the listening position)...
I want to make a "L-(L+R)" channel and a "R-(L+R)" channel to add some rear fill (something I otherwise also don't believe in, for those same image-killing phase interaction reasons) plus some additional delay, so I'm going to be researching this soon myself. My DSP will only help with delay and passband. I'd be interested if you find any good threads.
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Re: Ask an Acoustic Engineer (me)
Quote:
Originally Posted by
JCsAudio
Great response to my question Justin and thank you for taking the time to write that. I loved the driving analogy! I’m sure this will help many members here understand the theory. I couldn’t get the DIYMA link to work. I did a bunch of research into regulated vs non regulated amplifiers a long time ago. Not sure if it’s entirely accurate but the consensus was that non regulated power supplies gave amplifiers a slight edge in dynamic power over regulated power supplies but I’m not so sure that would be audible. Just think of the power drop you get when shutting off your engine with the audio playing. Your voltage could go from 14 volts to 12.5 volts yet you likely won’t notice a difference from the reduced power as a result.
I hate to further complicate things, but :). Anyone remember the old Bob Carver amps that put out hellacious power in a tiny rack mount chassis? This was before the class D amplifier days. How did he do this? Regulated variable tracking power supplies. The power supply adjusts its rail voltage rapidly in sync with the incoming signal. This kept power supply switching losses to a minimum.
Here is some info off the internetwebthing"
1) Magnetic Field Power Amp = a fancy (maybe even copyrited) name just to stand out among other amps and dazzle (baffle) the uninformed consumer.
2) The only thing related to a magetic field is the use of a TRIAC plus additional circuitry to modulate the primary of the power transformer to limit power/secondary voltage. It doesn't appear to be very well regulated and only seems to "stiffen" the AC line under heavy loads. Not real fancy, not real effective, and can be very noisy due to the low frequency AC lines and spikes caused by high voltage switching.
3) All Carvers I've seen run 'Class G' (rail switching) circuitry in their output stage. They run low/med/high Vcc rails with the 'Class A' drivers running on the highest rails and the additional output devices connected to the higher rails by fast recovery diodes. The entire output stage is controlled by a single op-amp through global feedback. This gives the benifit of lower idle power thus the need for smaller heatsinks, along with high peak-power. The best example of this is their famous little cube amp rated at 200WPC with virtually no heatsink.
Today's pint sized amps use this same technology. Mix that with a multi-stage class D output stage and your overall losses are reduced to a bare minimum. Really cool stuff. It can't quite beat classic amp topologies in sound quality quite yet. But, you would be hard pressed to detect a 0.01% distortion vs 0.1%. The reduction in size is worth the trade-off to me in my daily driver.
Ge0
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Re: Ask an Acoustic Engineer (me)
Quote:
Originally Posted by
jtrosky
So.... Just so I understand at a more "basic" level. :-)
- An amplifier with a "regulated" power supply will provide the same amount of power regardless of the speaker impedance.
- An amplifier with an "un-regulated" power supply will provide less power to speakers with higher impedance.
Are those two statements true?
The reason that I ask is because I'm still not clear why my JL XD600/6v2 (which does NOT have a RIPPS power supply) provides 100W RMS at 2 ohms, but 75W RMS at 4 ohms. Why is there such a small difference between the 2 and 4 ohm outputs? Don't most "un-regulated" amps provide twice the amount of power at 2 ohms (compared to 4 ohms)?
While the JL XD line of amps don't have the "RIPPS" power supplies, do they maybe have some "lesser" version of a regulated power supply instead? I honestly don't know if they are regulated or un-regulated.
Thanks - and sorry if this was already explained earlier - maybe I just didn't understand it.
A regulated power supply will hold a constant voltage at its power supply rails regardless of small (or large) fluctuations in system voltage. For instance it will keep the rails at +/- 20V whether Vbat is at 9V or 15V. The power you supply to a fixed load will not vary.
An unregulated power supply can be considered an input voltage tracking supply. Say it is designed to produce +/- 20V at 13.5V. At 9v you may only get +/- 15V power supply rail voltage. At 15V maybe it's +/- 28V. The power you supply to a fixed load will vary in regards to vehicle system voltage.
This does not have much to do with amp protection circuitry. Each amp design has a maximum power envelop. This is dictated by power supply design and heat sink cooling capacity. Similar technology to what is used on modern video cards and microprocessors. The amp will protect itself when it gets near its thermal limits. Also, driving lower impedance loads raises current draw and thermal loss. So, doubling of power may not be possible by halving the load. The amp just couldn't deliver that much power safely so it throttles back. Hope this makes sense.
Ge0
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Re: Ask an Acoustic Engineer (me)
What you’re describing to me Ge0 sounds like a class H amplifier design which is a Class AB with variable power supply from my understanding. Arc Audio currently uses a variation of this technology in some of their amplifiers.
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Re: Ask an Acoustic Engineer (me)
@justin zazzi
I read a great discussion a few posts back and wanted to revise the topic of Loud Speaker Design and innovation.
Just curious on your thoughts/opinions on why we haven't seen anything like the phoenix gold cyclone or CV Strokers in today's car audio? I don't know what the PG performance was but CV did really well with that design.
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Re: Ask an Acoustic Engineer (me)
Quote:
Originally Posted by
geolemon
From the diagrams that you posted, I'd be concerned as you are (especially in a car) that you'd narrow the image, because you are pulling some of the L and R content into the center - which, most troublingly - brings some of the L content to your R side, if you are in the driver's seat. Conversely, for a passenger, brings some of the R content to the L of them. Eek.
Yes indeed. This is the case for scenario 1 in the diagram. I ‘illustrated’ what you described above in the first attachment where the stage collapses. But if all 3 speakers are the same can we get the stereo sum to sound wider with speaker placement by playing stereo differential signal from the R and L speakers (scheme 2)?
Quote:
Originally Posted by
geolemon
What I'd like to see in a center channel for a car, would be "(L+R)-(L-R)". That way, it's only bringing the content from both speakers to the center, and even if there's a little content that's on both channels but simply louder on one than the other, it still mitigates that by attenuating that sound at the center channel. I'd believe that would at least help keep the stage width - hopefully as wide as with just a stereo pair.
I know what you mean but it cannot be derived that way. There is complex math that needs to be crunched to calculate a center signal.
"(L+R)-(L-R)" = L+R-L+R = 2R (not desired center)
Even if you take it further to using L-R and R-L to extract center from combined L+R you wind up with L+R again:
(L+R) - [(L-R)+(R-L)] = L+R - L + R - R + L = L+R
Fear not though, you can actually have that center channel you describe with a select few DSP’s that have center channel processing based on calculations to deduce the common information from both the right and left channels and steer them to a center channel based on their proprietary algorithms.
Quote:
Originally Posted by
geolemon
But I think really, in a car, the KISS rule applies... there's already glass, and absorbant upholstery, and plastic, all pointing different directions - you could have ONE speaker in a car and end up with a nightmare of multiple pathlength distances, direct and reflected (with each of those having a 180 degree shift - plus pathlength difference offset!) creating anything but a flat response as it arrives at your ears. :lol:
So I subscribe to the "the fewer speakers the better" theory for car audio. There's exceptions - for example, three way components where you actually aim the mid and tweeter - can provide better imaging. But my default recommendation is simplicity over complexity, for those pathlength reasons.
I’m just very curious for information on the theories of whats achievable. The main premise and goal would ultimately be geared towards creating a stage for more than 1 passenger to enjoy.
Quote:
Originally Posted by
geolemon
I'm really interested in this myself, but in no way for creating a center channel (IMO, there's already enough direct and reflected pathlength sounds wreaking havoc on image-killing phase interactions as they all ultimately arrive at the listening position)...
I want to make a "L-(L+R)" channel and a "R-(L+R)" channel to add some rear fill (something I otherwise also don't believe in, for those same image-killing phase interaction reasons) plus some additional delay, so I'm going to be researching this soon myself. My DSP will only help with delay and passband. I'd be interested if you find any good threads.
Check out the miniDSP 8x12DL and the APL1012. These have some powerful features involving FIR filters to help account for the harsher environment of the car audio with its many reflections. The Helix Ultra DSP has a center channel algorithm in conjunction with a virtual channel architecture that enables varying degrees schemes like 3 and 4.
Eventually stronger processors/algorithms will emerge (or become cheaper) enabling more options to the table for car audio than whats more traditionally used.
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6 Attachment(s)
Re: Ask an Acoustic Engineer (me)
Quote:
Originally Posted by
Cutaway
@justin zazzi
I read a great discussion a few posts back and wanted to revise the topic of Loud Speaker Design and innovation.
Just curious on your thoughts/opinions on why we haven't seen anything like the phoenix gold cyclone or CV Strokers in today's car audio? I don't know what the PG performance was but CV did really well with that design.
Sorry to hijack - I happen to own two PG Cyclones (one broken), and had the honor of making pen-pals with Tom Danley back in the early '00s, with the goal of making my own rotary servo subwoofer (NOT to make a product to sell, just a fun one-off, for engineering bragging rights). Unfortunately my business partner (fellow audio tech geek) and I burned out the motors that Tom Danley personally had suggested to us, and we put it on the shelf to focus on other things... that would have been fun though. Basically I'd taken a flat bar stock for the center, and had my buddy CNC machine some motor mount adapters - I mounted one motor on each end, unlike the Cyclone with had one motor at one end. The motors were each about double the size of the Cyclone's, so I made a center vane out of foam core and kevlar, hollowed out with stiffening channels, and then vacuum-bagged it for a super light vane. Instead of a screw shaped wave guide, I was just going to build it into a quad-chamber box that would manage the wave phases. Would be fun to pull tat project off the shelf, but it was becoming an expensive experiment...
Anyway, I'm not seeing the similarity between the PG Cyclone and the CV Stroker:
The Cyclone was a remarkable one-of-a-kind joint effort between PG Cyclone, specifically licensing Tom Danley's patented servo-drive technology - interesting for that rotary implementation that ServoDrive doesn't even sell. It was a one of a kind.
I can tell you from my experience with the Cyclone, that it is good for about 40hz and down (way down), but basically then you need another more traditional subwoofer to pick up the 40hz and up to wherever your midbasses really pick up. It was also very expensive, to not do everything that a subwoofer of today can do. And the real advantage was displacement - this was before "high excursion" subs really existed. I'd have to find the specs again, but this was before subs like the W7 or XBL^2 existed, so they were advertising the Cyclone had 3x the displacement of a standard 12"... which is about what a W7 does, or a CSX-12, and even a W7 is less expensive.
Attachment 10757
The Cerwin Vega Stroker is basically just a traditional subwoofer. It had a unique little gimmick, but it isn't really wild or radical IMO: in place of a dustcap, they used a second spider, that clamped onto a rod that poked forward of the pole piece. I say "clamped" because there was a set screw that allowed you to slightly adjust the center "at rest" position of the cone unit in the magnetic gap - some say that was to compensate when you mounted the subwoofer horizontally, to actively avoid cone droop... but that's really solving something that isn't usually a problem anyway. It did make the suspension quite unique, because really there was both an upper and lower spider, and even the surround was spider-like. But essentially, it was a big, heavy SPL sub with a fancy dustcap. Definitely not as far-out as a Cyclone.
Attachment 10758
Do you mean "Why aren't there more unique subwoofers"?
There are, if you look past the kids who only care about "power handling" (despite the trade-offs in efficiency that imparts) from their salad-bar contract manufactured subwoofers, there's lots of unique geek stuff - that's the stuff I love.
I'd suggest reading up on:
- underhung vs overhung subwoofers (just as a baseline on motors - but underhung are far less common)
- optional components like shorting rings and sleeves (seeing DUMAX measurements of BL curves will help understand that topic - as well as the ones below: )
- the JBL GTi DDD motor - which had two separate magnetic gaps, and two opposite-wound windings on the former, to not only give it linearity, but a braking force if driven to over-excursion.
- the XBL^2 motors - essentially a groove in an underhung-sized top plate, with a voice coil winding length perfectly balanced so that as coils leave magnetic field 1, they enter magnetic field 2, keeping BL linear - but in a MUCH simpler way than JBL did
- Side note for googling: check out where the W7 is cross-drilled in it's long excursion motor, and it's winding length. Some say that's to create an XBL^2-like effect, without running afoul of the XBL^2 patents.
- Speaking of the W7 - it's own front suspension is very innovative, and allows for a larger cone - therefore more cone area, and a larger surround - therefore more excursion capability, previously somewhat mutually exclusive.
- Shallow subwoofers - some of these stuff the motor inside where the cone used to be - well done ones are interesting engineering, and worth looking into the trade-offs on excursion and how they overcome them.
If it's not just unique subwoofers you are interested in, search out:
- plasma tweeters. In pursuit of the lowest mass possible, it's literally sound from an electrical flame.
- Electrostatic drivers, and magnetic-planar drivers. It's a panel suspended in either a massively high-voltage static field, or a magnetic field, rather than a cone.
- Distributed Mode Loudspeakers. It's literally just a motor, designed to vibrate something that otherwise wouldn't be a speaker
- Even - phase plugs and whizzer cones on midranges. That search will get into a great discussion on speaker directionality.
- which also makes me think of compression drivers - in the late 80's and early 90's they were morphed into "waveguides" that dominated IASCA SQ competitions back then
I'm sure I could come up with others (I own a dome subwoofer with a 10" voice coil but that was never on anyone's radar), but if you are researching to understand them personally, and then to understand why these aren't all commercial successes, that list above will keep you busy for a couple years. :lol:
Usually though, commercial failure comes down to two things:
- Relatively unproven technology is uncomfortable to most people. That's a barrier to sales and to adoption rates.
- Low volume sellers, and complex assemblies, both add to cost. Expense is always a barrier. Even me - I'm personally a "bang for the buck" fan way more than I'm a "geek engineering" fan.
...and that always should make an engineer ask themselves:
- What is the goal we're trying to achieve? Speakers simulate air - is there something different you are trying to achieve? Why?
- Is there an existing way to achieve that goal, that reaches the limits we want, for less money? Then why engineer a more expensive way?
Sorry - /hijack. :nerd:
(EDIT for visuals: )
JBL GTi - really two opposing motors folded into one - you can see both coils, both magnetic gaps - which are opposite wound, because those gaps are opposite phase:
Attachment 10759
XBL^2 motor cutaway - showing "at rest" position, but as the cone moves in either direction, coils leave one gap and enter the other, leaving BL constant (linearity) while making huge excursion:
Attachment 10760
Compare that to those baseline "overhung" and "underhung" cutaways.
And the best I can find of the W7 internals... see that sneaky pole vent cross drilling in there? It's right at the center of where the coil is "at rest", having the same type of effect as XBL^2 [as that would weaken the field at that spot]... but also that innovative basket, suspension, all custom parts that the little guys just can't do:
Attachment 10761
EDIT edit: (apologies)
I can't mention ServoDrive and how different the Cyclone is, without showing what they actually sell:
Attachment 10762
It's interestingly a rotary servo motor at the top (blue, mostly hidden - looks like a shop tool motor) with a shaft that goes to that proprietary belt mechanism, which converts the rotary motion to linear motion - pushing two shafts that move two "traditional" 15' cone units in a linear way.
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Re: Ask an Acoustic Engineer (me)
@Geolemon -
That is some great information and will keep me busy in the "rabbit hole" for a long time. Even though i am familiar with a few of your examples (the popular ones) i guess i hadnt really considered those innovative and in reality they really are. I have tended to shy away from brands like JL, JBL and RF for really dumb reasons.
Your knowledge share is really appreciated.
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Re: Ask an Acoustic Engineer (me)
Question that someone might be able to answer on the constant power amps,
On a 4 channel amp, if channels 3 and 4 are 2ohms and 1 and 2 are 4 ohms, when the amp detects 2 ohms on channels 3 and 4, does it then only adjust those channels for 2 ohms or does it also adjust channels 1 and 2?
Just curious about that. I am assuming it only limits channels 3 and 4.
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Re: Ask an Acoustic Engineer (me)
Quote:
Originally Posted by
JCsAudio
What you’re describing to me Ge0 sounds like a class H amplifier design which is a Class AB with variable power supply from my understanding. Arc Audio currently uses a variation of this technology in some of their amplifiers.
It's not class H, it's Magnetic Field baby!!!
Seriously though, amp classifications are so misused by marketing departments these days I just ignore them. What's class GD or class HD? Then there was the Tri-path class T. Ughh...
Ge0
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Re: Ask an Acoustic Engineer (me)
Quote:
Originally Posted by
Ge0
It's not class H, it's Magnetic Field baby!!!
Seriously though, amp classifications are so misused by marketing departments these days I just ignore them. What's class GD or class HD? Then there was the Tri-path class T. Ughh...
Ge0
Tell me about it. In the end though I think most of these fall into a few categories and the manufacturers are just using marketing tactics to make it seem like their product is different or better. We’ve got class A, class B, Class AB, Class D (T is basically chip based D) and Class G and H and a combination of those two.
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Re: Ask an Acoustic Engineer (me)
Quote:
Originally Posted by
JCsAudio
Tell me about it. In the end though I think most of these fall into a few categories and the manufacturers are just using marketing tactics to make it seem like their product is different or better. We’ve got class A, class B, Class AB, Class D (T is basically chip based D) and Class G and H and a combination of those two.
WAYYYYY back in the day I used to do side jobs for Stillwater Designs (Kicker), Soundstream, and Directed Electronics. When my kids were born my primary career started to take off. I needed to drop my amplifier design and repair hobby + partial ownership of my car audio shop to focus on stable work.
A few years later I hired this kid just a few years out of college to help with automotive electronics design. I changed jobs a few times and brought him with me each time. We both enjoyed screwing around with car audio and did this together as a hobby. Then one day I was offered a management job at Harman International's car audio division. I took him with me again. However, my past employer offered me a hefty raise and promotion to stay with them. They treated me well and are one of the worlds largest suppliers of automotive electronics. I decided to stay even though working professionally in audio would be fun. I never started work at Harman but my friend did. He is now chief design engineer behind their car amplifier division. The guy who is now manager of their applications / calibration department (tuning) is also a friend and used to be a member in our local car audio club. We still keep in close touch. I enjoy hearing about some of the advanced designs they have in the pipeline. That, and if I had a car with a Harman system (Jeep Grand Cherokee) I had full access to their lab and equipment needed to tune subtle changes.
To make a long story short. Everything has gone to class D with class H type power supplies. Is that class DH or HD? Who knows. Harman calls it xAF and it is not tied to a specific hardware but a suit of hardware options.
Ge0
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Re: Ask an Acoustic Engineer (me)
Quote:
Originally Posted by
Jdunk54nl
Question that someone might be able to answer on the constant power amps,
On a 4 channel amp, if channels 3 and 4 are 2ohms and 1 and 2 are 4 ohms, when the amp detects 2 ohms on channels 3 and 4, does it then only adjust those channels for 2 ohms or does it also adjust channels 1 and 2?
Just curious about that. I am assuming it only limits channels 3 and 4.
JD, not really sure what you are asking...
Ge0
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Re: Ask an Acoustic Engineer (me)
Quote:
Originally Posted by
Ge0
JD, not really sure what you are asking...
Ge0
if an amp detects a 2 ohm load and is one of the ones that is 100w at 4 ohms or 2 ohms, when it adjusts (based on manville smiths description of the RIPS) to a 2 ohm load, so drops voltage but increases amps, does the entire amp adjust or just those specific channels or pairs of channels. Manville said the amp limits itself to a 2 ohm load until the next power cycle, I just wasn’t sure if all channels are then limited in voltage to a 2 ohm load or if just those specific channels.
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1 Attachment(s)
Re: Ask an Acoustic Engineer (me)
Quote:
Originally Posted by
Cutaway
@justin zazzi
I read a great discussion a few posts back and wanted to revise the topic of Loud Speaker Design and innovation.
Just curious on your thoughts/opinions on why we haven't seen anything like the phoenix gold cyclone or CV Strokers in today's car audio? I don't know what the PG performance was but CV did really well with that design.
GeoLemon knocks it out of the park with a great reply to your question. I'm quoting one spot:
Quote:
Originally Posted by
geolemon
I can tell you from my experience with the Cyclone, that it is good for about 40hz and down (way down), but basically then you need another more traditional subwoofer to pick up the 40hz and up to wherever your midbasses really pick up. It was also very expensive, to not do everything that a subwoofer of today can do. And the real advantage was displacement - this was before "high excursion" subs really existed. I'd have to find the specs again, but this was before subs like the W7 or XBL^2 existed, so they were advertising the Cyclone had 3x the displacement of a standard 12"... which is about what a W7 does, or a CSX-12, and even a W7 is less expensive.
If I had to guess, I would say there is less need for really creative bass drivers today because the traditional design has matured a lot and there is plenty of bass available for a reasonable price now. I feel there is still a niche for ultra-low-frequency drivers like the Eminent Technology rotary woofer since getting tons of bass below 30hz is still a challenge especially if you don't have much room to work with. This one seems best suited for an infinite-baffle setup in a house playing into the attic or the basement though.
Attachment 10780
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Re: Ask an Acoustic Engineer (me)
Quote:
Originally Posted by
Jdunk54nl
if an amp detects a 2 ohm load and is one of the ones that is 100w at 4 ohms or 2 ohms, when it adjusts (based on manville smiths description of the RIPS) to a 2 ohm load, so drops voltage but increases amps, does the entire amp adjust or just those specific channels or pairs of channels. Manville said the amp limits itself to a 2 ohm load until the next power cycle, I just wasn’t sure if all channels are then limited in voltage to a 2 ohm load or if just those specific channels.
If the mechanism is to lower the rail voltage like I think RIPS does, then I imagine it would affect all channels since they usually share one set of rails.
If the mechanism is something else, then .... maybe?
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Re: Ask an Acoustic Engineer (me)
Quote:
Originally Posted by
Justin Zazzi
This one seems best suited for an infinite-baffle setup in a house playing into the attic or the basement though.
Attachment 10780
That thing is fantastic looking and would be a great conversation piece during a boring gathering ...
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Re: Ask an Acoustic Engineer (me)
Quote:
Originally Posted by
Cutaway
That thing is fantastic looking and would be a great conversation piece during a boring gathering ...
I want to make one so bad it hurts!
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Re: Ask an Acoustic Engineer (me)
Quote:
Originally Posted by
Justin Zazzi
GeoLemon knocks it out of the park with a great reply to your question. I'm quoting one spot:
If I had to guess, I would say there is less need for really creative bass drivers today because the traditional design has matured a lot and there is plenty of bass available for a reasonable price now. I feel there is still a niche for ultra-low-frequency drivers like the Eminent Technology rotary woofer since getting tons of bass below 30hz is still a challenge especially if you don't have much room to work with. This one seems best suited for an infinite-baffle setup in a house playing into the attic or the basement though.
Attachment 10780
Speaking of alternative subwoofer designs. Have ever happened to that tech where the subwoofer driver was a cylinder with a number of diaphragms inside? It was an odd shaped sub to fit into a car. But, it was a very interesting tech.
I did my searching using google. However, after a few thousand irrelevant advertiser hits I decided to give up.
Ge0
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1 Attachment(s)
Re: Ask an Acoustic Engineer (me)
Quote:
Originally Posted by
Ge0
Speaking of alternative subwoofer designs. Have ever happened to that tech where the subwoofer driver was a cylinder with a number of diaphragms inside? It was an odd shaped sub to fit into a car. But, it was a very interesting tech.
I did my searching using google. However, after a few thousand irrelevant advertiser hits I decided to give up.
Ge0
The Tymphany LAT (linear array transducer)?
I got to play with those recently. Kinda neat but outrageously heavy for what they were.
Attachment 10781
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Re: Ask an Acoustic Engineer (me)
How deep and loud does the rotary subwoofer play? My 24s are flat to 7 Hz in-room at reference level. In one room I measured with the 24 placed in the corner, it was flat to 6 Hz. With conventional designs that capable, I agree it doesn’t make a lot of sense for these exotic designs that may not work as well or take a closet to work (rotary sub).