Whats your thoughts on passive room mode treatment?

mors

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Hi guys, I have been working on room mode for some time, my room is about 6m x 4m x 2.4m, and having first problematic mode at ~52hz, ~60z and ~90hz, and I almost tired every passive method, eg. >4in absorbent on wall, membrane type bass trap on wall, corner bass trap, but do not really help me out. You can find my room response below using REW.
32132



Then I started considering helmholtz resonator but I can only find one in Arqen, and tube trap (not helmholtz resonator), anyone has been using them and what is the outcome?

Mors
 

Marc Lombardi

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There's a limit to what you can do for resonance below 100Hz. I have many resistive bass traps 4" and 6", all four corners floor to ceiling, and others spaced a couple feet from the wall where I can. My 40Hz resonance persists. The problem is resistive traps are most efficient at 1/4 wavelength from the wall which in your case is nearly 6ft. I wondered about membrane and Helmholtz, but there's no way to know how many of these expensive devices will be needed. At this point your best bet is probably Parametric EQ with a miniDSP or something similar. Or Dirac room correction.
 

pseud

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Peq would be your best option but you need to be willing to experiment and keep tweaking. The peaks at 52 and 60 should be handled but it could also reduce your gain but will involve trial and error
 

Barry Rudolph

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I've had very good results with my two PSI Audio AVAA Active traps on the floor in the left ands right front corners. My mix room is 2.9-meters wide, 2.45 m high and 3.6-m long. I'm due to do some new measurements having replace my main monitors recently and I'll post those soon. With the AVAAs, I have, in the past gotten the room flat down to 30Hz, leaving only the floor-ceiling- 1st room mode node at 71Hz. So my next acoustic treatment will probably be a pair of tuned membrane traps mounted on the ceiling over the listening position (I havre a hardwood floor). I already have two very thick absorbers hanging as a cloud overhead so adding these two more panels will be it--no more space on the walls or ceiling as I have many absorption panels--to the point of over doing it.

So it possible to flatten out at some cost. I am trying to avoid using DIRAC or any electronic room correction if I can. I mix Pop music in this space and so far it has worked well!
 

bvocal

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In my efforts nothing passive actually works. If it does work it's more miracle than anything else, see, the problem with using so much passive absorption is that it's not/never linear through the frequencies, so you'll likely remove valuable musical tone before you effect a solution. The other solution is membrane traps, Helmholtz resonators and diaphragmatic units all emit noise of their own, and every one I tried that noise was audible and sucked.
Barry, right above, seems to have found a good solution, albeit an expensive one. What Barry found is very well hidden from the world... I've never found it before and I've looked pretty hard for active solutions ever since I 'invented' one myself. You see, I was looking to see if I could sell my 'invention', until I found the pro audio world already knew this solution...
Essentially, subwoofers with inverted phase placed after the listening position with the right amount of delay will do what or close to what Barry's PSI Audio AVAA Active traps do. The more the subs have the sonic signature of the mains the better. With either solution
I made the setup with two unused cabinets I had and some cheap woofers and a miniDSPHD. So my out of pocket, because I had 2 plate amps and 2 cabinets, was under $300.
It takes more messing around to get my budget solution dialed in than the PSI Audio AVAA Active traps, but with a savings of $3700/$7700 I'm cool with that, especially as I designed and built a whole new separate epic system for under that $3700....
 

Barry Rudolph

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Well I would disagree about you assessment of passive absorbers but that's another discussion really. You are incorrect it equating the PSI Audio AVAA units--to a phase-inverted subwoofers--in fact they emit no sound at all because they work on the build up of pressure at the boundaries--notably in the corners where I have them. I, along with Bob Katz and a few others, have these devices and I love mine!

Please read my review--the link is included in the the txt file.

Thanks
 

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bvocal

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My description was incomplete, regardless, what I am doing is exactly what that unit is doing, a mechanical air pump working opposite the sound signal to counter pressure build up, difference is that unit uses a mic and I use the signal, I did/do concede that your unit is a better and also easier and more complete solution, it is actually what I designed in my head, I just don't/didn't have the money to make it. Trust me on this, I more than fully understand the physics and what I did was/is based purely on physics and acoustics.
 

A J Womack

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I have treated 40+ rooms with tube traps and they work a treat.
Look up absolutekarl on YouTube for his very thorough explanation of room acoustics.
Karl, is the inventor/developer of the RaTs system has obviously treated many more rooms than me.
He speaks and preaches no nonsense acoustics.
 
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mors

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There's a limit to what you can do for resonance below 100Hz. I have many resistive bass traps 4" and 6", all four corners floor to ceiling, and others spaced a couple feet from the wall where I can. My 40Hz resonance persists. The problem is resistive traps are most efficient at 1/4 wavelength from the wall which in your case is nearly 6ft. I wondered about membrane and Helmholtz, but there's no way to know how many of these expensive devices will be needed. At this point your best bet is probably Parametric EQ with a miniDSP or something similar. Or Dirac room correction.
Yes, same case for me too, I installed quite a lot of 6" foam (the black one), and the resonance still here. I have also tried the the mini dsp EQ and the result was awful, cannot handle the power though. And then I tried digital EQ, but whole bass had been pull down and the peak and dip still there. I wonder how EQ can treat the room mode efficiently without losing other bass.
 

mors

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Peq would be your best option but you need to be willing to experiment and keep tweaking. The peaks at 52 and 60 should be handled but it could also reduce your gain but will involve trial and error
Hi, thx for the suggestion, I also tried the PEQ, but the results were not very good, I lost the whole bass. But having a PEQ dip with high Q factor won't distort the signal?
 

mors

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I've had very good results with my two PSI Audio AVAA Active traps on the floor in the left ands right front corners. My mix room is 2.9-meters wide, 2.45 m high and 3.6-m long. I'm due to do some new measurements having replace my main monitors recently and I'll post those soon. With the AVAAs, I have, in the past gotten the room flat down to 30Hz, leaving only the floor-ceiling- 1st room mode node at 71Hz. So my next acoustic treatment will probably be a pair of tuned membrane traps mounted on the ceiling over the listening position (I havre a hardwood floor). I already have two very thick absorbers hanging as a cloud overhead so adding these two more panels will be it--no more space on the walls or ceiling as I have many absorption panels--to the point of over doing it.

So it possible to flatten out at some cost. I am trying to avoid using DIRAC or any electronic room correction if I can. I mix Pop music in this space and so far it has worked well!
Hi, Barry, thx for introducing me the AVAA Active traps, but its really really expensive! I am waiting for your measurement. Why avoiding using DIRAC or electronic EQ? I think PEQ should be goof your are tuning in 1/3 octave or higher, right?
 

mors

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Well I would disagree about you assessment of passive absorbers but that's another discussion really. You are incorrect it equating the PSI Audio AVAA units--to a phase-inverted subwoofers--in fact they emit no sound at all because they work on the build up of pressure at the boundaries--notably in the corners where I have them. I, along with Bob Katz and a few others, have these devices and I love mine!

Please read my review--the link is included in the the txt file.

Thanks
Thx Barry, I will read through your page tmr.
 

mors

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I have treated 40+ rooms with tube traps and they work a treat.
Look up absolutekarl on YouTube for his very thorough explanation of room acoustics.
Karl, is the inventor/developer of the RaTs system has obviously treated many more rooms than me.
He speaks and preaches no nonsense acoustics.
Hi, tube traps you mean this one?

 

DanDan

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The legendary Boggy achieved EBU Critical Listening Room specs in small rooms using 60cm fibrous absorption.
While Quarter Wavelength absorbers will theoretically absorb 100%, Fibre traps of 1/10 Lambda easily do over 80%.
It is often forgotten that Area of treatment is very significant.
 

A J Womack

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Hi Mors, have you watched absolutekarl to the end? I cannot tell you too much about them as they are his invention. blacksea.coolroche.com is his website, tell him I referred you to him.
We used Linear x to measure, Rt30 was usually best, using pink noise, to excite the room, at numerous locations around the room. There are many out there who will say that it cannot be done, because they have not found the right product. Believe me they really do work, good luck.
 

DanDan

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Active trapping works by cancellation. This requires power input equal and opposite to the problem.
Given the reviews, tests, and testimonials, company reputation, and a proven principle of operation, lets take it as read that the PSI traps are helpful.
Large amounts of passive treatment will work too, particularly the higher end products like Modex. When the space and money run out, Dirac Live, or Accourate or Sonarworks can tie up the loose ends nicely.
 

kanef

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Active trapping works by cancellation. This requires power input equal and opposite to the problem.
Given the reviews, tests, and testimonials, company reputation, and a proven principle of operation, lets take it as read that the PSI traps are helpful.
Large amounts of passive treatment will work too, particularly the higher end products like Modex. When the space and money run out, Dirac Live, or Accourate or Sonarworks can tie up the loose ends nicely.
I agree.
Something I’m noticing (being new to this forum) is the lack of hard measurements. Measurements are vital. If we know the nature of the problems, and there are always multiple problems in an untreated room, then we can make a start on resolving them. And it’s often not that difficult to do.
if you’re not sure where to start I’m happy to send a sound file to you and you can record the results from several positions in the room, send the recordings to me and I’ll take a look and we can discuss the findings.
I see many people reaching for a product, hoping it will solve their problem only to find that they’ve got little to show for it.
 

Bpape

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Sorry. Late to the party.

Passive treatment can certainly work IF it is the correct type and in the correct locations for the problem to be addressed. Corner traps won't do much if the problem is from the rear wall or a length mode for example. Active can work (EQ) as long as you are EQing DOWN a peak (not EQing up a null). Seat location, speaker location, sub locations, etc. are your best friend along with treating the knowns (decay time, decay time, decay time, reflections, etc.)
 

DanDan

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Alway welcome Bpape. Yes active treatment has been and can be tricky. The Bag End and AVAA both use mics to detect a few modes, not just the lowest. But they are capable of oscillation I gather. I have found similar instability in a DIY version here. For the length mode only I would guess a simple phase reversed, eq'ed and delayed sub or two at the back should work? kanef. that is a kind offer. This is the world Home of REW. I generally keep fairly up to date with the Beta versions. To be honest I am finding it so feature and control rich that I am about to look for an older simpler version as my goto working tool.
 

Bpape

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That sub arrangement can certainly work though many times I have seen it cause issues at other frequencies. You know, by getting rid of one thing another pops up that was being cancelled before. As always, just have to play with it.
 

DanDan

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Yup, I think many people omit to Eq everything except the lowest mode out of the rear subs.
 
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