dba, active absorber instead of porous material?

[yentz]

Hi,
does anyone of you have any experience using a dba or active absorber to tame roommodes?

I just moved to a new flat with a dedicated room for music. Unfortunately the room has a nasty mode around 47 Hz and very long decay times (which are that bad that setting decay of a kick isn't possible not using headphones). The second mode should be not that difficult to treat as for 150 Hz material thickness needed is way less.

So far I did 2 diy Basstraps soffit style 41 x 41 cm sonorock acoustic floor to ceiling in the left and right corners of the front wall with about 5 cm air-gap which are having positive effects on the sound (didnt have time to measure again). The rockwool was covered with 0,05 mm thick foil to reflect mids and highs and will be covered with molton soon.

As there isn't any treatment at the rear wall (yet?) the modes still exist and are causing nulls at the listening positiion at around 80-90 Hz or so.
The room geometry isn't ideal with a door at the rear wall set back around 80 cm. Besides doing the standard treatment (first reflection points + front wall) there will be substantial further treatment necessary.

Huge traps using porous material at the rear wall are not possible due to room geometry (door at the rear wall and door at the left wall), passive Elements like Helmholtz resonators seem to be not that effective and very small within their bandwidth and tuned traps with membranes probably too difficult to do diy.

My options are, as far as I can see, buying tuned traps or trying a dba or active absorber.
Does anyone of you have experience using those? I just ordered a Behringer DCX 2496 to try both if necessary.
1. using a mic (for now Behringer test mic) a bit above a subwoofer (for now Adam Audio Sub 7 which hasn't been used for ages) with the subwoofer placed at the place with maximum spl (which seems to be a bit befor the rear door around 150 cm high) with the mic feeding the signal into the DCX 2496 , phase shift or taking the dry signal from the audiointerface ohase shifting, delaying according to room position and feeding into the sub
2. using a dba with 2 subwoofers at the front and 2 at the back. If so I would build them myself. So far I see mostly threads in Hifi forums which is why I am not sure if this is the route to go as I can't tell if the materials recommended match criteria for production.

If any of those experiments would work I would use a dsp instead of the Behringer for longterm use. Checked Sigma Studio and programming the DSP is comparable to using a virtual modular synth. Using a mic without phantom power a preamp should be easily be done diy, even without etching the pcb.

Does anyone of you have any experience with this kind of treatment? I know that the room is never going to have mastering qualities but it would be nice if it could be used for audio production on a semi professional level.
Attached waterfall diagram is before adding the soffits. I am on vacation at the moment ad will measure again when I am back.
Thanks for helping

[Lost to the Void]

I'm not fully convinced by active solutions.
At least not as a DIY solution. I think, like decent monitors, if that's what you want then you need to pay for professionally made units or you are just wasting time and money.
I still think the time delay of active units will never resolve (as it is impossible for an active unit to be look-ahead, it will always be straggling behind transients and microdynamics).
PSI audio do active units, which I looked into for my room, but I would have needed 4 to be truly effective, and they sit at 2000 jib a unit, so you might as well hire an acoustician and go conventional for that money.

There are many more alternatives available now, such as vicoustic vari bass traps etc.

If you really want to get it done properly then DIY isn't the way to go.

[yentz]

I saw the psi things, i think there is also another product e trap or so but as you said already they are quite expensive.
I think I will try the diy solution (gonna post measurements if worth posting) but will definitely have a look into the vari basstraps you mentioned. 2k for all is kind of affordable but 2k just to kill one mode (not sure one of the commercial products can do 2 frequencies apparently) is just too much for me
I read they work completely analogue. Maybe someone will undo one and discover how they do it at one point
Ohh I forgot... as there are many different tips online - does anyone recommend something else than 0.05 mm foil + 160g / m2 molton above the soffits to limit absorption to low frequencies? At vacation now. Molton is ordered but not attached yet.

[Lost to the Void]

As far as I am aware, the PSI solution covers everything under the 150hz threshold, like any speaker it can reproduce more than one frequency at a time.

[yentz]

Maybe I should have a look on ebay to see what tehy are going for

[Lost to the Void]

Best price I have seen is about 1800 quid.

There are many other solutions that aren`t active.

[yentz]

Still quite a lot of money
What other alternatives are there apart from Helmholz resonators, tuned traps with membranes and classic basstraps using porous material?

[Lost to the Void]

There was a multi multi page discussion about it on the forum.

[Mattias]

The PSI AVAA's are great but expensive. No free lunch in the world of acoustics.

[Mattias]

I still think the time delay of active units will never resolve (as it is impossible for an active unit to be look-ahead, it will always be straggling behind transients and microdynamics).

AVAA's have no latency.

[ekwipt]

If you were going to do a room properly would you start with someone like this and start with the actual plaster, or is this way over the top?

https://www.australianplasteracoustics. ... index.html

I’m in Sydney, Australia FYI

Found this one online as well

https://www.acoustica.com.au/product-range/

[Lost to the Void]

I still think the time delay of active units will never resolve (as it is impossible for an active unit to be look-ahead, it will always be straggling behind transients and microdynamics).

AVAA's have no latency.

That is scientifically impossible.

[Lost to the Void]

If you were going to do a room properly would you start with someone like this and start with the actual plaster, or is this way over the top?

https://www.australianplasteracoustics. ... index.html

I’m in Sydney, Australia FYI

Found this one online as well

https://www.acoustica.com.au/product-range/

Well.
When I built my new place we actually used acoustic plaster and plasterboard. It allowed the guy to fit all non absorber parts of the walls with acoustic plasterboard and then skim for uniformity with acoustic plaster.
If you are doing room within a room then it's worth doing this as well, you end up with a nice clean finish.
I'm not sure if it is over the top, but if you are building from scratch you don't have to do it to this level.
There are plenty of nice looking wall tiles and such that will do broadband absorption/diffusion and be asthetically pleasing.

[Lost to the Void]

About the best low end absorption you can get for an "off the shelf" low end treatment product are RPG Modex plates.

Type 2's cover 35-150 and are about £1100
Type 1's cover 50-500 and are about £950

Cheaper than active solutions, take up less space, and are passive. Couple of 1's and a 2 will deal with a project studio nicely.

[ekwipt]

About the best low end absorption you can get for an "off the shelf" low end treatment product are RPG Modex plates.

Type 2's cover 35-150 and are about £1100
Type 1's cover 50-500 and are about £950

Cheaper than active solutions, take up less space, and are passive. Couple of 1's and a 2 will deal with a project studio nicely.

Nice one thanks mate

[Mattias]

I still think the time delay of active units will never resolve (as it is impossible for an active unit to be look-ahead, it will always be straggling behind transients and microdynamics).

AVAA's have no latency.

That is scientifically impossible.

There is little difference between an active monitor and an AVAA. There is no DSP. Analog unit.

[Lost to the Void]

AVAA's have no latency.

That is scientifically impossible.

There is little difference between an active monitor and an AVAA. There is no DSP. Analog unit.

An active monitor receives the signal directly, it is not reactive.

Analog does not mean zero latency.
The unit is reactive, not only that, reactive to it`s own microphones, microphones themselves are not zero latency in terms of converting physical motion to electrical impulse.
So the things is, I tested some of the AVAA`s, and I swore I was hearing something odd going on when doing short, high transient pops when doing timing tests.
Looking at waterfall charts it shows early transients peaking, and then the action of attenuation.
I thought maybe it was a unit issue, but various other plots put online also show this.
So I figured it was a latency issue.
Now if you read the technical/scientific papers on active absorption they all mention latency problems, and PSI must have used those papers to base their tech from.

They are amazing once they capture the audio, the reduction of decay times is impressive, but you`d still need other shit in the room to deal with time domain problems with microdynamics and transients.

I think as a combination solution they are great, but the price they cost and the amount you need to be effective, they just don`t compare to the alternatives. The most expensive physical solutions, that truly are zero latency, being purely physical and working by removing energy through dispersion/conversion, not opposing it, are still cheaper.... and superior, taking the Whole in to account (maybe with the exception of space and setup).
I think they are a relative space saving solution though... well...kinda.

[Mattias]

Well yes, microphone latency is a thing but it's a non issue in these types of measurements. No one is accounting for microphone latency when they read reverberation times, impulses and ETC for example.

[Lost to the Void]

Well if you are recording to generate an FFIR or whatever the time it takes for the microphone to respond and "translate" doesn't matter as long as it is recorded.

Anyway, I am talking in very small number microseconds here, how much of an issue is it really? We all loved life and worked before this tech, so it's still a leap forwards/upwards.

However, let me register this prediction here... Because I think this is gonna happen, and I'm normally good at spotting future trends in monitoring.

PSI or, I think more likely, a more widespread brand, let's say Adams, are already looking at jumping on this tech to bring to market a complete monitoring and active absorption system.

I used to use the JBL LSR (linear spacial reference) system for my production room. A good few years back now.
The LSR monitors came with a calibration mic and on board DSP to calibrate the monitors for your room. Moreover the monitors were networked via a Hi-Q network (ethernet cables) So you calibrate one monitor and it does the whole system (including an LSR.sub if you added one) and also synced all the on face controls, stereo image etc
They worked amazingly.... I passed them on, after a few years being in shortage, recently to a friend.

Anyway.
Someone is going to basically do that but add add active absorbers to the range (matched to the subs for perfect mirroring). The whole thing could be networked (wireless these days), the original signal could be fed to the active absorbers so that it could compare it to the signal it gets from its own mic, which would give a more accurate read and prevent any timing issues as the latency would apply to the whole system.

You can bet your ass this is going to happen.
Pretty sweet too if you ask me.

My money is on Genelec.