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Tackling room resonances

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Re: Tackling room resonances

Postby Hugh Robjohns » Tue Jul 30, 2019 11:05 pm

Superbly useful and informative post. Thanks Max. :clap: :thumbup:
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Re: Tackling room resonances

Postby blinddrew » Wed Jul 31, 2019 7:34 am

Ditto! Really useful stuff (again) Max, thank you. :thumbup:
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Re: Tackling room resonances

Postby Studio Support Gnome » Wed Jul 31, 2019 10:55 pm

Hugh Robjohns wrote:Superbly useful and informative post. Thanks Max. :clap: :thumbup:
Don;t think I'm much good at any other kind of post Hugh ;)

Unless you count the acerbic but informative as different type of post.... ;)
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Re: Tackling room resonances

Postby Zukan » Thu Aug 01, 2019 12:58 pm

Studio Support Gnome wrote:Just a note on density and absorption coeffiecents and which to use why.


the absorption curve of 60 and 45 is very similar, although slightly different.... , 60 on edge gives something closer to 45 flat fronted. Edge performance is higher as the gas entry impedance is lower.

I recommend 60 not necessarily because it is the best all round absorber, at the ultimate edge of theoretical performance , because it's not, but it's close enough to 45 to make bugger all practical difference in terms of real world performance, but I generally recommend it for DIY use as well as paid labour use, because it is by far the most practical , easiest material to actually build with.

As well as being easier to handle, easier to cut accurately, and least messy, generating far less fluff and dust , , and on top of that 60Kg is dense enough to be structurally self supporting when laid flat , with edge facing the room, up a 2.5-3 metre high stack.... no great problem, Higher if you're careful and precise with the edge bracing... so framing it is just a matter of a braced edge frame, and fabric finish over it... and building the thing only requires two uprights one at each face corner... placed so you :"just" have to tuck the corners of the slabs in to the upright. and you can use these uprights as the edge of the fabric mount as well

45 will "spring out in the middle when you try and stack it that high, so requires far more bracing and framing to make it stay still.... especially if you build a "super duper chunk" 4 feet across the front....

this then also makes getting a flat finish on the fabric harder , unless you also eat up more space by spacing it further away from the absorption material


When faced with building a number of these devices.... especially if paying for the labour, speed and ease of construction is a matter of some concern. The minimal trade off of absorption at some frequencies is more than made up for in the saving on costs. (labour being far more expensive than the materials of any density )

even bigger ones are built using a front section of 60, but the infill behind it is lower density... at that point using 30kg stuff is fine.... indeed layering different densities can give additional loss effects as the impedance change point between densities is a transmission medium interface .

and Studio tips did NOT invent the "large absorption mass " design. to give it a more PROPER name... ... this technique was around a LONG time before the internet even existed ...

thus I have always treated their appropriation of it as their territory with the contempt it deserved.

60Kg also has the benefit of maintaining a more consistent density once you start building properly large devices..... I've built traps 4 metres high with it with no discernible change in density , you try that with 45kg and you can SEE the lower section compress into denser material... just before the entire stack springs out of the corner , from the middle ,spraying itself all over the room. . (bitter experience in early days , before forums were a thing... )

45kg works equally well , and provides higher absorption performance at higher frequencies , but since we are primarily concerned with the lo end it's of little practical import, and it's a lot harder to build large devices with, but it works fine for smaller ones and flat framed panels.

similarly 30Kg is a viable absorption media , but an absolute twat to build with..... more so than 45 by a long stretch.

buit as infill behind a layer of denser material, it works well.

I have endless designs for such devices....

there's some I use more often than others, because they're practical to implement , and easy to adjust for odd specific elements of individual rooms .... and they can be delivered in a predictable time , at a fixed cost....

It is all to easy for the DIY evangelists to dismiss the time and ease of build concerns.... but before being swayed by these , you should ask yourself, quite seriously, what your time is worth to you, and your family.... and your clientele , if you're of the semi-pro persuasion....

is it better to spend a year building a studio that is 1% "better" than one you could have built and been ready to work in in 3-4 months ?

My rather pragmatic view is that it is not.... not even if you're trying to build a mini abbey road... 10 or 20% , then you'd have a valid argument, but 1% ?? I think not.

The difference in monitor speaker quality and set up in the room will make more odds than the 1% on that corner trap .

Where i DO like to go bananas on detail is in isolation design.... room geometry , ergonomics, and wiring .

Making the place a nice environment to be in , as well as and accurate monitoring environment, is key to productivity in actual use.

This ^^^^^^ Jedi!!
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Re: Tackling room resonances

Postby Martin Walker » Fri Aug 02, 2019 11:38 am

Yes indeedy - those reams of PRACTICAL advice on why choosing 60Kg/m3 rather than 45Kg/m3 sum things up perfectly for me, and Max must have built and installed more bass traps than anyone else I know.

I've bought 45Kg/m3 in the past as that was all I could find locally available, and yes, it does its job, but in a saggy and sloppy way. Any more rockwool I buy in the future will most definitely be 60Kg/m3.

Thanks Max!


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Re: Tackling room resonances

Postby TNGator » Sat Aug 03, 2019 10:43 pm

Mike Stranks wrote:I don't where you're based TNG, but I've treated my small room with these fibreglass panels:

https://www.studiospares.com/Studio-Gear/Acoustic-Panels/Acoustic-Panel-1200-x-600mm-Grey_465220.htm#rtabs3

set 25mm off the wall - ie total depth is 50mm. I have consciously chosen to use small (10mm woofer) speakers so as to keep bass excitement to a minimum, but it's still an issue in my small room. For mixes with significant bass then I switch to headphones. A good compromise in my small room otherwise the treatment would preclude me from getting in here!

Blue Frog also have a good range of treatments: http://www.bluefrogaudio.co.uk/

and they're well thought of.

and there's one very simple guideline for acoustic treatment... never use foam! :lol:
Hi Mike. Im next door in Dublin and my small terraced house room is about 11ft by 11 and about 8ft high. My desk faces a window but at least its about in the halfway position. I want to go look at those links you included so thank you so much for sending those. My recording is on hold for the moment becasue I dont have any suitable DIY materials to do a decent job. I might just buy the real thing tobe honest . I just got my test mic and am starting to play around with REW. Ive really no idea what Im doing but i got it configured and did a sweep. I chose a range of 40Hz to 300Hz to begin with as Im sure its the bass will be my problem in the small cube room. Im just not sure how to read the graph. Its pretty much a mountain range going up and down. REW has an option to do a screen shot...Im not sure if its possible to attach a pic with posts here.
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Re: Tackling room resonances

Postby Mike Stranks » Sat Aug 03, 2019 11:06 pm

TNGator wrote:..Im not sure if its possible to attach a pic with posts here.

You have to use a third-party site... I use IMGUR. You then get various options for sharing your uploaded pic... just copy the one that begins and ends 'img' and paste that link straight into your post here.
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Re: Tackling room resonances

Postby TNGator » Sat Aug 03, 2019 11:29 pm

Mike Stranks wrote:
TNGator wrote:..Im not sure if its possible to attach a pic with posts here.

You have to use a third-party site... I use IMGUR. You then get various options for sharing your uploaded pic... just copy the one that begins and ends 'img' and paste that link straight into your post here.
Dropbox anyone? https://www.dropbox.com/home/Public The pic is called First sweep. This is done in my room with no treatment. I tried some DIY stuff just for a laugh but the graph didnt change. I'll buy some proper treatment.
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Re: Tackling room resonances

Postby TNGator » Sun Aug 04, 2019 1:07 am

Studio Support Gnome wrote:Just a note on density and absorption coeffiecents and which to use why.


the absorption curve of 60 and 45 is very similar, although slightly different.... , 60 on edge gives something closer to 45 flat fronted. Edge performance is higher as the gas entry impedance is lower.

I recommend 60 not necessarily because it is the best all round absorber, at the ultimate edge of theoretical performance , because it's not, but it's close enough to 45 to make bugger all practical difference in terms of real world performance, but I generally recommend it for DIY use as well as paid labour use, because it is by far the most practical , easiest material to actually build with.

As well as being easier to handle, easier to cut accurately, and least messy, generating far less fluff and dust , , and on top of that 60Kg is dense enough to be structurally self supporting when laid flat , with edge facing the room, up a 2.5-3 metre high stack.... no great problem, Higher if you're careful and precise with the edge bracing... so framing it is just a matter of a braced edge frame, and fabric finish over it... and building the thing only requires two uprights one at each face corner... placed so you :"just" have to tuck the corners of the slabs in to the upright. and you can use these uprights as the edge of the fabric mount as well

45 will "spring out in the middle when you try and stack it that high, so requires far more bracing and framing to make it stay still.... especially if you build a "super duper chunk" 4 feet across the front....

this then also makes getting a flat finish on the fabric harder , unless you also eat up more space by spacing it further away from the absorption material


When faced with building a number of these devices.... especially if paying for the labour, speed and ease of construction is a matter of some concern. The minimal trade off of absorption at some frequencies is more than made up for in the saving on costs. (labour being far more expensive than the materials of any density )

even bigger ones are built using a front section of 60, but the infill behind it is lower density... at that point using 30kg stuff is fine.... indeed layering different densities can give additional loss effects as the impedance change point between densities is a transmission medium interface .

and Studio tips did NOT invent the "large absorption mass " design. to give it a more PROPER name... ... this technique was around a LONG time before the internet even existed ...

thus I have always treated their appropriation of it as their territory with the contempt it deserved.

60Kg also has the benefit of maintaining a more consistent density once you start building properly large devices..... I've built traps 4 metres high with it with no discernible change in density , you try that with 45kg and you can SEE the lower section compress into denser material... just before the entire stack springs out of the corner , from the middle ,spraying itself all over the room. . (bitter experience in early days , before forums were a thing... )

45kg works equally well , and provides higher absorption performance at higher frequencies , but since we are primarily concerned with the lo end it's of little practical import, and it's a lot harder to build large devices with, but it works fine for smaller ones and flat framed panels.

similarly 30Kg is a viable absorption media , but an absolute twat to build with..... more so than 45 by a long stretch.

buit as infill behind a layer of denser material, it works well.

I have endless designs for such devices....

there's some I use more often than others, because they're practical to implement , and easy to adjust for odd specific elements of individual rooms .... and they can be delivered in a predictable time , at a fixed cost....

It is all to easy for the DIY evangelists to dismiss the time and ease of build concerns.... but before being swayed by these , you should ask yourself, quite seriously, what your time is worth to you, and your family.... and your clientele , if you're of the semi-pro persuasion....

is it better to spend a year building a studio that is 1% "better" than one you could have built and been ready to work in in 3-4 months ?

My rather pragmatic view is that it is not.... not even if you're trying to build a mini abbey road... 10 or 20% , then you'd have a valid argument, but 1% ?? I think not.

The difference in monitor speaker quality and set up in the room will make more odds than the 1% on that corner trap .

Where i DO like to go bananas on detail is in isolation design.... room geometry , ergonomics, and wiring .

Making the place a nice environment to be in , as well as and accurate monitoring environment, is key to productivity in actual use.

Well sadly I made a mess of things here. The absorbers i made a way too shallow and dont seem to be doing anything. Im testing an insulating material i have left over from some attic work i was doing. Its a dark dense wool like material (not the bright yellow fiberglass stuff). Well that was a waste of money buying wood etc. Time to stop the nonsense and buy some traps. Thomann do quite a good range and one of the guys posted a link to Bluefrogaudio who do a nice free standing panel style bass trap. Either way, time to get the real thing and get back to recording. Im just being held up at this stage.
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Re: Tackling room resonances

Postby Sam Spoons » Sun Aug 04, 2019 11:40 am

Given that a couple of duvets can make a significant difference can you post some pics of your DIY traps in the room? It seems a shame to righty them of after the money and effort and there may be other reasons why they don't see to be working as you expected.
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Re: Tackling room resonances

Postby TNGator » Sun Aug 04, 2019 11:57 am

Sam Spoons wrote:Given that a couple of duvets can make a significant difference can you post some pics of your DIY traps in the room? It seems a shame to righty them of after the money and effort and there may be other reasons why they don't see to be working as you expected.

Hi Sam. I didn't test the duvet just yet. But yes that is on the menu. You see my plan is to try out this REW software I downloaded starting with a naked room then bring in the DIY stuff and re-test. Im hoping to see what DIY stuff works, doesnt work, kinda works etc. My home made absorbers might work if i select a higher range of frequencies in the REW sweep. At present Im testing from about 40Hz to 300Hz. I just picked that range arbitrarily.
Now my panels may not need to be ditched but I might have to put deeper sides on them. I really made them too shallow which was a silly goof on my part. Im concerned about the weight of the panels and wood can be very heavy. That guy on YT who tested bathroom towels? Tried it. Didnt make a blind bit of difference to the graph. I'll keep you updated Sam. Bank holiday weekend here. So...pub :)
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Re: Tackling room resonances

Postby blinddrew » Sun Aug 04, 2019 12:21 pm

You're going to need something chunky and fairly heavyweight to make an effective difference below 300Hz. It'd be worth running again to look higher up the spectrum. What you've got so far might still be of use as part of a combination of treatments.
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Re: Tackling room resonances

Postby TNGator » Sun Aug 04, 2019 1:02 pm

blinddrew wrote:You're going to need something chunky and fairly heavyweight to make an effective difference below 300Hz. It'd be worth running again to look higher up the spectrum. What you've got so far might still be of use as part of a combination of treatments.
I think so my friend. My mam Lord rest her used to sew and i have her machine here. Im making a large deep sort of cushion (about 20 in by 20in by 15in) and will pack it tight and test. As you say, the lighter panels might work as a combination treatment.
Im finding it hard to read the graph in REW as you test higher frequencies. The low graph is easy to view. Its almost like you zoomed in on a waveform. The higher sweep looks like what they call the Waterfall view.
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Re: Tackling room resonances

Postby room66 » Wed Aug 07, 2019 9:48 pm

Not sure if this has been suggested already ... Helmholtz resonators work very well for low frequencies.
We built one ourselves for a 50Hz peak in our room.
There's some threads on gearslutz forum how to.
You may try this
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Re: Tackling room resonances

Postby TNGator » Wed Aug 07, 2019 10:08 pm

room66 wrote:Not sure if this has been suggested already ... Helmholtz resonators work very well for low frequencies.
We built one ourselves for a 50Hz peak in our room.
There's some threads on gearslutz forum how to.
You may try this
Hey thanks guy. No hadnt heard of this. As it happens, i only joined the gearslutz forum yesterday so I'll bounce over and do a search. Thanks again.
ps... I got my REW configured and my test mic arrived. Have been able to do a sweep of the room but...... I havent the foggiest on how to read the graph. I may as well be looking at a chest x ray.
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Re: Tackling room resonances

Postby Sam Spoons » Wed Aug 07, 2019 10:56 pm

TNGator wrote:
Sam Spoons wrote:Given that a couple of duvets can make a significant difference can you post some pics of your DIY traps in the room? It seems a shame to righty them of after the money and effort and there may be other reasons why they don't see to be working as you expected.

Hi Sam. I didn't test the duvet just yet. But yes that is on the menu. You see my plan is to try out this REW software I downloaded starting with a naked room then bring in the DIY stuff and re-test. Im hoping to see what DIY stuff works, doesnt work, kinda works etc. My home made absorbers might work if i select a higher range of frequencies in the REW sweep. At present Im testing from about 40Hz to 300Hz. I just picked that range arbitrarily.
Now my panels may not need to be ditched but I might have to put deeper sides on them. I really made them too shallow which was a silly goof on my part. Im concerned about the weight of the panels and wood can be very heavy. That guy on YT who tested bathroom towels? Tried it. Didnt make a blind bit of difference to the graph. I'll keep you updated Sam. Bank holiday weekend here. So...pub :)

I think measuring in a small room is a bit of a red herring unless you have pro kit and extensive knowledge.

To achieve any effect below 300Hz you'll need a panel at least ¼ wavelength or 25cm deep so its not surprising your 50mm panels are not tickling your graph. Just listen to the room and ask yourself "does the room sound better than before the treatment?"

Don't worry about deep sides BTW, just spacing the panels off the wall will be almost as effective in improving the response at lower frequencies.
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Re: Tackling room resonances

Postby TNGator » Thu Aug 08, 2019 7:35 am

Sam Spoons wrote:
TNGator wrote:
Sam Spoons wrote:Given that a couple of duvets can make a significant difference can you post some pics of your DIY traps in the room? It seems a shame to righty them of after the money and effort and there may be other reasons why they don't see to be working as you expected.

Hi Sam. I didn't test the duvet just yet. But yes that is on the menu. You see my plan is to try out this REW software I downloaded starting with a naked room then bring in the DIY stuff and re-test. Im hoping to see what DIY stuff works, doesnt work, kinda works etc. My home made absorbers might work if i select a higher range of frequencies in the REW sweep. At present Im testing from about 40Hz to 300Hz. I just picked that range arbitrarily.
Now my panels may not need to be ditched but I might have to put deeper sides on them. I really made them too shallow which was a silly goof on my part. Im concerned about the weight of the panels and wood can be very heavy. That guy on YT who tested bathroom towels? Tried it. Didnt make a blind bit of difference to the graph. I'll keep you updated Sam. Bank holiday weekend here. So...pub :)

I think measuring in a small room is a bit of a red herring unless you have pro kit and extensive knowledge.

To achieve any effect below 300Hz you'll need a panel at least ¼ wavelength or 25cm deep so its not surprising your 50mm panels are not tickling your graph. Just listen to the room and ask yourself "does the room sound better than before the treatment?"

Don't worry about deep sides BTW, just spacing the panels off the wall will be almost as effective in improving the response at lower frequencies.

Hi Sam. Well to be honest I wouldn't spend hundreds on that test gear. I knew it existed but I always thought it was expensive gear just for the pro studio. But when I found REW was free and the test mic was only 30 euro I thought..hey why not. Ive been advised on this forum that in a small room, wall panels wont do much and bass traps would be a much better idea. So Im slowly getting educated on this stuff. With that, Im going to concentrate on the corners i.e. traps. Yes I'll experiment with some home made "deep" devices and test. I had also heard as you mentioned, about keeping a space behind them. Im not sure of the science how this works but the tip seems to be...keep them away from the wall. And anyway Sam, like the rest of us here, there's only so much i can do. Im in my small living room which is a perfect shape, has a fireplace jutting out, a window facing me and a door on either side of me which are not opposite each other. So yeah...its not Abbey rd. I'll do what I can but if I turn down Nerd avenue I'll never get back on the freeway.
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Re: Tackling room resonances

Postby Hugh Robjohns » Thu Aug 08, 2019 9:15 am

There are basically two separate issues to deal with at a project studio level. The first is mid-band and HF reflections from the mirror points that mess up the stereo imaging and colour the midrange room your monitor speakers, and the second are the standing waves that give a lumpy bass.

Standard broadband panels of 2 - 4 inches deep will deal with the first issue pretty effectively.

Dealing with LF standing waves is much, much harder. As Sam says, if you go down the lossy absorber route -- using mineral wool or foam etc -- then you need a lot of it in very deep panels, which is rarely practical in a small room -- although you can often make use of corners quite effectively to gain more depth than would otherwise be possible.

But there are other, less invasive solutions... It's just that they are far more complicated and expensive to build. Limp mass membranes are one option, and resonant cavity absorbers are another...
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Re: Tackling room resonances

Postby Sam Spoons » Thu Aug 08, 2019 10:32 am

REW is great, I have it but you are measuring the bass region and wondering why your mid/high frequency absorber panels are not making any difference. No surprise that they make little or no difference ;) . If you set the frequency limits to 300-3000Hz you'd see a difference and, hopefully, you'll hear a difference too.

Don't worry about an imperfect room, as Hugh says the mid/high absorbers help to improve stereo image and tonal balance in the mid and high frequency ranges, in an ideal word they would be symmetrical around the mixing position but if you can't do that just do your best* with the room you have you should still hear an improvement.

*good headphones are the standard means for checking mixes in an imperfect mix environment.
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Re: Tackling room resonances

Postby blinddrew » Thu Aug 08, 2019 12:56 pm

Sam Spoons wrote:*good headphones are the standard means for checking mixes in an imperfect mix environment.
And pretty much essential for checking your low end in even a fairly well treated project room.
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