1st step, damp your room. That will take care of the decay. Then add bandages, aka bass traps. Acoustic 001. Don't skip it on your way to Acoustic 101.
have you read this thread?1st step, damp your room. That will take care of the decay. Then add bandages, aka bass traps. Acoustic 001. Don't skip it on your way to Acoustic 101.
thats what ive been saying from the beginning. treat your room with bass traps and first reflection panels.
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not at all. this is false.
False? Not necessarily. You may be overlooking something really valuable here.
I agree with you that the multiple sub-woofer approach as championed by Geddes and Duke LeJeune generally has very poor ETC performance. There are cases where it improves it a bit, but not enough IMO
BUT
there IS another, PROVEN way which satisfies the ETC criteria AND has outstandingly flat bass response without the use of EQ or needing much in the way of room damping.
I'm trying to find the published info on this and will update later when I find it, but in Germany, someone put together a studio project that clearly demonstrates the advantages of active absorption. And it definitely satisfied even the most stringent ETC criteria.
AS I recall, it went like this:
1) "Plane-wave" bass radiating system at front wall of room, designed to emulate a single vibrating plane by using multiple bass drivers - this required with proper spacing between them and also relative to the wall dimensions. (IIRC the room was about 5m wide, 3m tall and 10m deep)
He placed multiple subs, arrayed vertically on the wall, I think he found he could manage with just 4 or of them, mounted about a meter away from the floor, adjoining walls and ceiling, in such a way that their combined output created something very close to a planar wave.
2) At the back of the room, he placed a "plane-wave" active absorption system, with four identical subs to the front, with inverted output, time delayed them and adjusted their output levels in such a way that when the pressure wave from the front system reached the back wall it was completely canceled (i.e. actively absorbed). Completely. As in zeroed out to some insanely low level, IIRC over 90 dB suppression.
3) The in-room measured results were outstanding: this approach yielded uniform bass response (IIRC better than +/- 1dB) anywhere in the room, no peaks or nulls whatsoever from the lower limits of the subs up to beyond 200Hz No standing waves or room modes at all, anywhere.
4) More importantly perhaps, the time-response curves seemed virtually perfect. When you don't have much in the way of reflections, well, I guess the ETC will show that, eh?
I'm sorry I can't find the bookmark I'd placed on the page that had this info. I will keep on searching for it.
Make of this what you will.
However, for those of you that prefer to keep an open mind, look for the information on this system! I also highly recommend Music and Design's (Kreskovsky) Tech Studies section, there are some other approaches to bass absorption using subwoofers as spaced dipoles, and these too look very interesting. look for Tech
In closing, while it is obvious you have a wealth of experience and knowledge... well..... it doesn't help when we let our opinions create a closed mindset.... even if/when our opinions are really well informed.
Opinions are based on what we have learned and observed. They can often become hard-set beliefs. But when something new comes along that seems to go against what we believe, does that mean it should be rejected out of hand?
In this instance, we have described a system which has been built, tested and proven to eliminate the majority of the standing wave and room resonance issue, AND with near perfect time response...
Ummm....Is it possible this was the type of system that Chris was referring to?
Your rather categorical and dismissive reply was: "not at all. this is false."
Listen, youknowyou...... I don't mean to be too harsh with you, but... WOW... wasn't that flippant response just a little over the top?
Especially when as in the system described above, what Chris said was possible has been proven?
As in realized, tested and verified to be a superior solution? Including for the ETC criteria?
I would urge you to soften your stance and have a close look at the information presented here, as you and many others here may benefit from it.
Will the room still need some damping? Almost certainly yes, as the main speakers or monitors will also influence the room response in a big way.
But I think where the main part of the bass is concerned, in a room such as described, we could pretty much dispense with lots of the ultra-thick damping and the bass-traps.
OK, so go look for this and have fun discovering this method.
What I want for next christmas is to have the funds necessary to buy a house and build a room such as described. Ha!
Thanks and Best Regards
very interesting. id love to know more.
howver, this method cannot solve reflexion from front and side walls, sbir behavior, and wont help for midrange and highs combfiltering. further wouldnt this method inly work for one specific place in the room?
i also wonder how it translate sq wise
it may work for bass but im highly perplexed. im not sure why not stick with proven method rather then cite exception.
howver, this method cannot solve reflexion from front and side walls, sbir behavior, and wont help for midrange and highs combfiltering. further wouldnt this method inly work for one specific place in the room?
i also wonder how it translate sq wise
it may work for bass but im highly perplexed. im not sure why not stick with proven method rather then cite exception.
Good questions. Let me respond to some of what you've said:
1) "this method cannot solve reflexion from front and side walls"
This statement holds true above a certain frequency, but at low frequencies, the design method does greatly solve this issue by creating a virtual plane wave.... the output from the spaced drivers sums to form something very close to a "single wave" that is moving out in near-planar rather than hemispherical fashion.
I was quite surprised this could be done with only 4 drivers, spaced as they were... intuitively I would have thought the whole wall would have to be woofers..... but the author stated that with only 4 woofers it acts as a virtual planar surface all the way up to 200Hz! (and the measured evidence supported that...)
So, if what we get is a virtual planar wave, traveling through the length of the room, then the side-wall, floor and ceiling reflections become negligible in the bass range.
And, when it gets to the back of the room, the planar pressure wave gets neatly swallowed up by the anti-phase pressure wave at the back... it's like having an infinitely long tube with a planar wave traveling through it.
The result is that you get uniform bass response at ANY point in the room, and near perfect ETC curves, limited only by the bass drivers qualities.
2) "sbir behavior"
Umm... what is "sbir behavior"???
3) "and wont help for midrange and highs combfiltering"
Completely agreed. I thought I addressed this when I wrote:
Will the room still need some damping? Almost certainly yes, as the main speakers or monitors will also influence the room response in a big way.
4) "further wouldnt this method inly work for one specific place in the room?"
No, if it is close to being a perfext planar wave, then it moves through the room (and then gets absorbed at the back) - no reflections & no standing waves - visualize how this wave simply arises, washes over the listener and keeps on going, never to return - and this happens at ANY point in the room.
5) "i also wonder how it translate sq wise"
According to the article (STILL searching for it!) the people who have heard this system said it is of the utmost transparency in the bass range, by far the best they had ever heard.
6) "it may work for bass but im highly perplexed. im not sure why not stick with proven method rather then cite exception."
WHY?
Because it could save you BOAT-LOADS of something we call MONEY!!Well, actually, I did mention that the room still needs to be treated due to the use of speakers/monitors along with the bass arrays... however, if crossing over with steep slopes, there is very little need to absorb frequencies much below 200Hz... okay, okay, you want to cross over at 100Hz? Make it 100Hz then....
Can't you see how much is saved by not needing uber-thick absorbent panels all over the room? Not to mention near zero need for bass traps? It allows for the use of much thinner acoustically absorbent pads... and as you probably know, 2" is about 6X cheaper than 12"
Also, it becomes a LOT easier to make the room aesthetically attractive.
And finally, because the bass performance approaches theoretical ideals both in frequency AND time-response.
I am not arguing against your position, I am advocating that you take a more open-minded stance and integrate this new information.
I firmly believe the combined approach of planar-wave front with active cancellation at the rear PLUS proper room damping for the 100Hz up is the way to go.
If you do, you may well get a mind-blowing system out of it.
BTW, I haven't mentioned this yet, but I did a very simple variant of this with two subwoofers, one at the front of the room and the time-delayed anti-phase at the back, and with minor eq the results in the listening area were utterly amazing both in measurement and in listening. And it was also quite good to excellent at nearly any "normal" listening position, seated or standing, even at the side-walls, nearly anywhere in the room. No bass-traps were needed.
Sorry, I don't have the measurements - all of that went when my old computer died - but it was pretty dang gooood!
So I submit all of this to you as food for thought. I have no agenda other than to let you and this forum know about this method, it can give truly excellent results and save tons of money, effort and time.
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hi
i personally also have no agenda. seriously treating my room has made the most impressive change to my system and only want to share
google sbir ( sound boundary interference response).
i will ask around about the method your describing! im far from a expert but in many ways? it sounds impossible to cancel the effect of the room with subwoofer for many reasons that come to mind: walls inequal behavior and resonance within the foundation which shows complex impedance, or simply sbir which before the lf frequencies hits the back wall they have already have been bouncing off the ceiling, floor, side walls + the direct sound from the speaker. the lf have already reflected and combine with the direct sound, i m not sure the method u describe can have any effect.
"By Wes Lachot
THE BOUNDARY EFFECT
One way of improving a room's bass response is to use certain room ratios (of height to width to depth), thus tuning the room's modal response. Although good ratios are very important, many instances of problematic bass are caused by the more general wave cancellation: When sound waves hit a wall, they reverse direction and recombine with the waves coming from the source. Room boundary-related wave cancellation, or the boundary effect, affects all sound waves, at all frequencies - not just frequencies that are mathematically related to the room dimensions. This phenomenon of sound waves mixing with their own reflections causes pressure build-ups (loudness) and cancellations (softness) at predictable distances from the wall, given a specific frequency. With bass notes, the problems are especially noticeable, since the wavelengths are longer and you can't simply move your head a couple of inches to compensate for the problem - something you probably do unconsciously for higher frequencies. This wavelength issue is the cause of many bass headaches, and understanding the boundary effect can help you to create more solid bass when mixing, even when working in a room with less than ideal modal ratios. Top
Let's take a moment to examine what happens when a speaker vibrates at 40 Hz. in a room. Forty times per second, the speaker cone thrusts forward, causing a compression "peak" to travel across the room at the speed of sound. In between each such forward peak, the speaker cone travels backward, creating rarefaction "valleys." The distance between one compression peak and the next is one cycle, hence 40 peaks in a second equals 40 cycles per second, or 40 Hz. Since sound travels through the air at a speed of approximately 1130 feet per second, and 40 waves are going past any given point in a second, each wave cycle will be 28 feet apart (1130 divided by 40 equals approximately 28). The distance between a peak and a valley will be half that: 14 feet. In a free field with no boundaries, you could stand at any reasonable distance from the speaker and hear flat, even bass, because the alternating peaks and valleys just keep going right past you, no matter where you stand.
In a room, on the other hand, a wave will hit a wall or other surface, reverse direction, and then this reflected wave will mix with the source wave coming from the speakers. Inside, as opposed to outside, speakers sound louder due to these reflections, as volume is not lost to "outer space." The downside is that in some places in the room, for a given note, compression meets compression, amplifying that frequency (constructive interference), and in other parts of the room, compression meets rarefaction, canceling at that frequency (destructive interference). Exactly where in the room this happens varies with which bass note is sounding, and this is what drives engineers nuts as they try to decide on the bass level, EQ, and compression. The volume of any given bass note is completely dependent upon where you are in the room; conversely, the amount of bass you perceive at any given point in the room is dependent upon what note is being played. Top
Figure 1: Five different phases of a 40 Hz. wave are shown, with the dotted line representing the reflection off the boundary to the right. The ear hears the wave by detecting variations in pressure from static pressure (represented by the horizontal line through the middle). At any given point in the room, the direct and reflected waves combine additively, with values above the horizontal line being positive, and those below the line being negative. Note that at the 7-foot point, or 1/4 wavelength, the net result is zero, regardless of which phase is hitting the wall, so the ear hears no pressure variations at this location. (Note: for visual clarity, the reflected waves are shown to have the same amplitude as the source waves. In reality, the reflected waves are several decibels lower in amplitude, due to reflection-related energy loss, so the nulls are actually less than total.) Click the image for a larger version.
i personally also have no agenda. seriously treating my room has made the most impressive change to my system and only want to share
google sbir ( sound boundary interference response).
i will ask around about the method your describing! im far from a expert but in many ways? it sounds impossible to cancel the effect of the room with subwoofer for many reasons that come to mind: walls inequal behavior and resonance within the foundation which shows complex impedance, or simply sbir which before the lf frequencies hits the back wall they have already have been bouncing off the ceiling, floor, side walls + the direct sound from the speaker. the lf have already reflected and combine with the direct sound, i m not sure the method u describe can have any effect.
"By Wes Lachot
THE BOUNDARY EFFECT
One way of improving a room's bass response is to use certain room ratios (of height to width to depth), thus tuning the room's modal response. Although good ratios are very important, many instances of problematic bass are caused by the more general wave cancellation: When sound waves hit a wall, they reverse direction and recombine with the waves coming from the source. Room boundary-related wave cancellation, or the boundary effect, affects all sound waves, at all frequencies - not just frequencies that are mathematically related to the room dimensions. This phenomenon of sound waves mixing with their own reflections causes pressure build-ups (loudness) and cancellations (softness) at predictable distances from the wall, given a specific frequency. With bass notes, the problems are especially noticeable, since the wavelengths are longer and you can't simply move your head a couple of inches to compensate for the problem - something you probably do unconsciously for higher frequencies. This wavelength issue is the cause of many bass headaches, and understanding the boundary effect can help you to create more solid bass when mixing, even when working in a room with less than ideal modal ratios. Top
Let's take a moment to examine what happens when a speaker vibrates at 40 Hz. in a room. Forty times per second, the speaker cone thrusts forward, causing a compression "peak" to travel across the room at the speed of sound. In between each such forward peak, the speaker cone travels backward, creating rarefaction "valleys." The distance between one compression peak and the next is one cycle, hence 40 peaks in a second equals 40 cycles per second, or 40 Hz. Since sound travels through the air at a speed of approximately 1130 feet per second, and 40 waves are going past any given point in a second, each wave cycle will be 28 feet apart (1130 divided by 40 equals approximately 28). The distance between a peak and a valley will be half that: 14 feet. In a free field with no boundaries, you could stand at any reasonable distance from the speaker and hear flat, even bass, because the alternating peaks and valleys just keep going right past you, no matter where you stand.
In a room, on the other hand, a wave will hit a wall or other surface, reverse direction, and then this reflected wave will mix with the source wave coming from the speakers. Inside, as opposed to outside, speakers sound louder due to these reflections, as volume is not lost to "outer space." The downside is that in some places in the room, for a given note, compression meets compression, amplifying that frequency (constructive interference), and in other parts of the room, compression meets rarefaction, canceling at that frequency (destructive interference). Exactly where in the room this happens varies with which bass note is sounding, and this is what drives engineers nuts as they try to decide on the bass level, EQ, and compression. The volume of any given bass note is completely dependent upon where you are in the room; conversely, the amount of bass you perceive at any given point in the room is dependent upon what note is being played. Top
Figure 1: Five different phases of a 40 Hz. wave are shown, with the dotted line representing the reflection off the boundary to the right. The ear hears the wave by detecting variations in pressure from static pressure (represented by the horizontal line through the middle). At any given point in the room, the direct and reflected waves combine additively, with values above the horizontal line being positive, and those below the line being negative. Note that at the 7-foot point, or 1/4 wavelength, the net result is zero, regardless of which phase is hitting the wall, so the ear hears no pressure variations at this location. (Note: for visual clarity, the reflected waves are shown to have the same amplitude as the source waves. In reality, the reflected waves are several decibels lower in amplitude, due to reflection-related energy loss, so the nulls are actually less than total.) Click the image for a larger version.
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Whatever the abstract benefits of multiple subs, in practice their location can be beneficially chosen to minimize stimulating the eigentones.
I've been wondering for the past 50 years if a motional feedback speaker in a corner can act like an active absorber? Since I believe this will eventually be a common feature of good music systems, it will help erase the sound of the room.
A lot of the ear-evaluation versus meter measurement debate comes home to roost in psychoacoustics where meter measurements are weak. A part of the problem is music is a complicated mix of short and long duration sounds (and part of the reason concert halls reverb times are adjusted for choirs, talk, movies, or different kinds of bands). So does that mean neither a FR nor a waterfall display captures the sound of music but some kind of N-dimensional display is needed that incorporates the duration or window of the stimulus sound? Does REW have a window adjustment when you do FRs?
Ben
I've been wondering for the past 50 years if a motional feedback speaker in a corner can act like an active absorber? Since I believe this will eventually be a common feature of good music systems, it will help erase the sound of the room.
A lot of the ear-evaluation versus meter measurement debate comes home to roost in psychoacoustics where meter measurements are weak. A part of the problem is music is a complicated mix of short and long duration sounds (and part of the reason concert halls reverb times are adjusted for choirs, talk, movies, or different kinds of bands). So does that mean neither a FR nor a waterfall display captures the sound of music but some kind of N-dimensional display is needed that incorporates the duration or window of the stimulus sound? Does REW have a window adjustment when you do FRs?
Ben
Maybe this is it (what Jack Caldwell was discussing), and it might be germane to this discussion, even though I agree that I don't completely understand it:
http://www.hannover-hardcore.de/infinity_classics/!!!/Dokumentation SBA-01.pdf
It's not cheap though with 18(!!) Peerless XXLS drivers! And a 2X3500watt amplifier (scroll to the bottom of the above link!).
Practical?
Best,
Anand.
http://www.hannover-hardcore.de/infinity_classics/!!!/Dokumentation SBA-01.pdf
It's not cheap though with 18(!!) Peerless XXLS drivers! And a 2X3500watt amplifier (scroll to the bottom of the above link!).
Practical?
Best,
Anand.
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Oh...and I just noticed that there is 1/6th octave smoothing everywhere! Oh well...I'm not impressed anymore. It's much easier to get +/- 1.5dB that way.
Best,
Anand.
This isn't the one... I can't read much German, but it doesn't look like this one has the back-wall active bass cancellation that I was referring to.
Right now I am REALLY wishing I could find that article! It would do a world of good if you could see for yourself what was achieved with the near-planar wave approach. Seriously, the measurements I saw there put nearly every other bass system I have seen to shame.
And yes I get the boundary effects and reflections business, especially with a single source that is generating spherical wave-fronts.
But please be aware boundary effects and reflections become much less problematic, (even non-problematic if you see that article!) when you are generating a virtual plane-wave which traverses the length of the room without bouncing and reflecting.
I was shocked when I saw the article, because I never would have thought one could build a near-planar wave system with drivers spaced the way they were - but the proof (measured proof, not anecdotal) showed otherwise.
I hope someone here can find or reference that article for us... I have NOT been able to find it...... sigh
Anand, sorry, this next line is not about you...it's dedicated to the guy that posted on Gear-slutz..
NO, this is NOT what I was referring to ... someone here assumed it was, copied what I had written before and associated this link to what I wrote and is asking if it would work ... on Gear-slutz of all places !!
Criminy !!! What are you thinking? Please, at least ASK before assuming and then posting wrong info!!
To be clear AGAIN: this link is NOT what I was referring to. This one does NOT have the back-wall active bass cancellation that I was referring to.
It does feature near plane-wave front bass response .... but it does NOT have the back wave cancellation array... making it a completely different kettle of fish.
AHA! I found part of it! It's not the full white paper I'd seen, but it's a start...
It's on AVS forum, author name Follgott, he called it the Double Bass Array. Here it is:
Double Bass Array (DBA) - The modern bass concept! - AVS Forum | Home Theater Discussions And Reviews
and here's part of the original research that led to this implementation (in German):
http://www.nubert.de/downloads/optimierung_der_tieftonwiedergabe.pdf?PHPSESSID=qctxokyy
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Hmm, ran a translate on the technical paper referenced in the last post...
here's an edited (corrected the english) version of a key concept
The placement of the subwoofers has to be such that the distance in any respective direction is not greater than half the wavelength of the highest desired frequency...
What remains are the natural frequencies of the listening room in the longitudinal direction, which usually have the strongest and most damaging impact on the bass reproduction. Instead of huge
acoustic absorbers, a second identical Bass array is used at the rear of the room... of paramount importance is the use of
second bass arrays with a very precise level and delay adjustment.
here's an edited (corrected the english) version of a key concept
The placement of the subwoofers has to be such that the distance in any respective direction is not greater than half the wavelength of the highest desired frequency...
What remains are the natural frequencies of the listening room in the longitudinal direction, which usually have the strongest and most damaging impact on the bass reproduction. Instead of huge
acoustic absorbers, a second identical Bass array is used at the rear of the room... of paramount importance is the use of
second bass arrays with a very precise level and delay adjustment.
Todd Welti from Harman describes DBA here and he does it well:
Comparison of Double Bass Array to Sound Field Management: Overview
Best,
Anand.
Comparison of Double Bass Array to Sound Field Management: Overview
Best,
Anand.
hi
when I saw that you said the link was not the one you were talking about, I edited the post and changed the link.
no biggy!
I hope we can have some good info about that method.
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Hey, thanks nycavsr2000, that's some great input.
Yes, looks like some researchers at Aalborg University took the DBA stuff and renamed it CABS (Controlled Acoustic Bass System)
Have a look at what Todd Welti (yes, he of major Harman white-paper fame) had to say about it: "Based on the simulations and actual room measurements done by Celestinos and Nielsen, the method seems to work very well."
Here's a link to that paper:
http://vbn.aau.dk/ws/files/62729103/LF_sound_reproduction.pdf
I find the CABS paper useful but also quite frustrating as the bulk of the CABS measurements and proof of concept are aimed at showing it can also be made to work well in an irregularly shaped room. While I think that's admirable, it doesn't show enough of the goodies where a simple rectangular room is concerned... and pays no attention whatsoever to the ETC curves...aaaargh
So, I 'm still searching for the more in-depth info that Follgott had presented... it's gotta be out there somewhere! Those measurements and ETC curves were a thing of beauty, almost worthy of framing and displaying in the listening room! (Yes, I confess... I too have a thing for curves...)
But now at least, we have enough proof of concept, along with critical "expert approval" by Todd Welti of Harman, who developed the multi-woofer approach at Harman and published extensively about it.
Either way, I think it's clear that whether called DBA or CABS, active bass absorption at the back wall works exceptionally well in rectangular rooms, and significantly reduce the material expense and effort where bass traps and absorbers are concerned.
At the very least try what I did, with one sub at the front and one active canceling sub at the back, time-delayed and level adjusted to absorb most of the bass waves as they got there. Also, I adjusted the delay on the main channels so that at the listener's seats the wave from the front sub and the main speakers arrived in sync. It works fabulously well, enough to where I never got around to treating the room any further.
Yes, looks like some researchers at Aalborg University took the DBA stuff and renamed it CABS (Controlled Acoustic Bass System)
Have a look at what Todd Welti (yes, he of major Harman white-paper fame) had to say about it: "Based on the simulations and actual room measurements done by Celestinos and Nielsen, the method seems to work very well."
Here's a link to that paper:
http://vbn.aau.dk/ws/files/62729103/LF_sound_reproduction.pdf
I find the CABS paper useful but also quite frustrating as the bulk of the CABS measurements and proof of concept are aimed at showing it can also be made to work well in an irregularly shaped room. While I think that's admirable, it doesn't show enough of the goodies where a simple rectangular room is concerned... and pays no attention whatsoever to the ETC curves...aaaargh
So, I 'm still searching for the more in-depth info that Follgott had presented... it's gotta be out there somewhere! Those measurements and ETC curves were a thing of beauty, almost worthy of framing and displaying in the listening room! (Yes, I confess... I too have a thing for curves...)
But now at least, we have enough proof of concept, along with critical "expert approval" by Todd Welti of Harman, who developed the multi-woofer approach at Harman and published extensively about it.
Either way, I think it's clear that whether called DBA or CABS, active bass absorption at the back wall works exceptionally well in rectangular rooms, and significantly reduce the material expense and effort where bass traps and absorbers are concerned.
At the very least try what I did, with one sub at the front and one active canceling sub at the back, time-delayed and level adjusted to absorb most of the bass waves as they got there. Also, I adjusted the delay on the main channels so that at the listener's seats the wave from the front sub and the main speakers arrived in sync. It works fabulously well, enough to where I never got around to treating the room any further.
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