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How much bass trap/panel am I expecting to have to tame the bass below 500Hz?

the (gigantic) first mode is actually deep enough not to annoy for 99% of the music out there. So that would make the classic corner straddle good enough IMO (acting in both axes). to really treat this mode a lot of material on the back wall would be necessary
 
I have emailed @storing the excell sheet for the quarter waves tubes.
And he is free to post it here, i do not have the time to give 100% support on it.

Efficiency historically have been a bit better then helmholtz.
Easy to build, does not take much space etc etc
 
This thread is sad and has become greatly misleading. Focusing wrongly on RTx, something that doesn't exist in this type of room. Recommending DSP for something DSP can't address. Plus wrong information about needed thickness of absorption panels to reach a certain frequency. So much for a science based forum I guess.

The spirit of science also requires that any errors are correcting and any misunderstanding or wrong understanding straightened out.

I may or may not have said in this thread that the RT60 does not apply where there are no reverberant fields, i.e. below the transition frequency. If I did not say that, then I apologize.

I did say that DSP can not cure residual bass ringing.

Is there anything else where the record needs to be set straight, in your view?
 
How thick are we talking about here? 12"?
I guess that is super thick bass traps at ALL room corners (vertical and horizontal)? That is a lot of money.
Yes.
it's not really a lot of money, if you try to be creative.

for example, if you have your standard 120x60cm rockwool sheet, you could cut it lengthwise so it becomes two 120x30 sheets. then you stack 3 sheets in a cube 30x30 (or 2 if these are 15 cm sheets), roll em up in some fabric, and place them all round your rooms vertical corners on velcro tape:

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I highlited with red the velcro tape connections. Since you don't use any kind of rigid framing, these traps are somewhat light.
 
So, my understanding is that the colloquial use of RT60 is incorrect because sound bouncing in a small room does not become effectively random before it totally decays. You can still identify individual reflections in the Energy Time Curve for most of the decay time. What you have in small rooms is 'modal decay' and not reverberation. The sound field needs to be totally jumbled into randomness for it to qualify as true reverberation.

RT60 is defined in terms of real reverberation and critical distance so it doesn't technically apply to small rooms where the direct sound is louder than reflected sound everywhere.

I think this is a real and important distinction, but what I'm not sure about is how this changes the recommended approach to treating a small room. I think you still want to control decay time and modes regardless of what you call them.
 
So, my understanding is that the colloquial use of RT60 is incorrect because sound bouncing in a small room does not become effectively random before it totally decays. You can still identify individual reflections in the Energy Time Curve for most of the decay time. What you have in small rooms is 'modal decay' and not reverberation. The sound field needs to be totally jumbled into randomness for it to qualify as true reverberation.

RT60 is defined in terms of real reverberation and critical distance so it doesn't technically apply to small rooms where the direct sound is louder than reflected sound everywhere.

I think this is a real and important distinction, but what I'm not sure about is how this changes the recommended approach to treating a small room. I think you still want to control decay time and modes regardless of what you call them.

Since I was criticised earlier in this thread for using the RT60, and I invited my critic to post his reply with no response, I guess I'll give my explanation on RT60. RT60 has two components - "reverberation" and "time to decay 60dB after EDT". Neither makes sense in a small room.

First, the 60dB decay requirement. EDT is the "Early Decay Time", which is the rapid decay in sound after the speaker's impulse. It is excluded because it is not room reverberation since the sound hasn't had time to travel and reflect. Also, the speaker itself may still be producing sound, e.g. cabinet resonances, driver ringing, etc. It is conventionally defined as 5ms. The 60dB requirement is problematic because the typical noise floor of a listening room is about 40dB, meaning that the speaker has to sweep incredibly loud (> 100dB) if we want to observe a 60dB decay. Fortunately, SPL decays linearly, so we measure the time to decay by 20dB or 30dB and extrapolate it to 60dB by simple multiplication.

"Reverberation" refers to multiple overlapping room modes. ALL wavelengths form room modes, but short wavelengths form thousands of them and they overlap so much that the modes even out and form a reverberant field. We are interested in the decay in the reverberant field. As the wavelengths get longer, the modes start to separate out until we can see them distinctly below the transition frequency. So if you see a huge peak in the RT60 below the transition frequency, you are not looking at decay, you are looking at a room mode.

For this reason, in small rooms, we drop the "reverberation" and "60dB decay" requirements and use the T20 and T30. Both T20 and T30 are acceptable substitutes for the RT60, but only down to a certain frequency defined by the transition zone. I calculated the Schroder frequency to help the OP determine his transitional frequency (4x Schroder). It is important to remember that this is an approximation.

It is difficult to look at decay on a waterfall graph if we are looking at low frequencies. This is because peaks create longer decay, and nulls shorten them. This is why I flattened the peaks using my DSP software so that it is easier to look at the decay. Even after doing this, it appeared that bass decay was still prolonged. This is why DSP can help a little with LF ringing, but it can not ameliorate it. What is effective are large pieces of furniture.

Re: critical distance in a small room. It is untrue that the direct sound is louder than the reflected sound "everywhere". In small rooms, reflections are earlier and louder so this shortens the critical distance.

I hope this clears it up, and if I am still wrong about something, please pull me up on it.
 
@Keith_W DSP correction simply works for room modes, actually works better than anything else. With those out of the way decay times improve as it's not ringing in standing wave area. In the small room some things are impossible to achieve as good back to front refractions levels so we go for next best thing putting them close to wall so that direct and refracted are minimal and sum together (partially). You didn't say anything wrong actually you main pretty good effort from the Start. RT60 decay times might not be best or best suited but it's best you have.
My approach is try to minimise potential problems especially if they are hard to correct later by design and placement so that you have to deal with less of them In the future avoid suspicious sails man criticism as it's absurd as such only want your money.
Accustic treatment is efficient in highs and that's for what it needs to be used but such ain't either thick nor expensive. DSP processing it's harder there to a point it's not possible if the focus is shattered too much. Measurements with thick absorbers of popular room correction softwares confirm this and show minimal improvement with them to software only.
 
Hello everyone. I bought 5 packages of Rockwool 40kg/m3 batts for my room. I want to buy Knauf brand as I heard it is more environmentally and human friendly (ECOSE tech?) but my local seller doesn't have the density that I want. Here are the measurements. Kindly comment if I am doing this right. MDAT file attached.
The discussion here previously ended with this measurement being moot because it is a small domestic setting.
Here is the graph of 5 sweeps vector average.
1.jpg
 

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  • run27_Vectoraverage_LRxo80.zip
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Firstly, why do your measurements start at 50Hz?

There is significant ringing at 60Hz, up to 1.8 seconds. This is not accompanied by a peak in your frequency response which suggests it is not a room node.

I just looked back in the thread and I saw a piano. I am kicking myself for not seeing it earlier. Are you sure that your piano is not resonating with your measurement? It does not look as if it is easy to move. I suggest you play a 50-60Hz test tone then touch your piano to see if the strings or chassis is vibrating. Or maybe close the lid and put something heavy on it to damp the resonance. Maybe as many books as you can find, or a luggage filled with clothing, or something similar. Repeat the measurement and report back.
 
Firstly, why do your measurements start at 50Hz?

There is significant ringing at 60Hz, up to 1.8 seconds. This is not accompanied by a peak in your frequency response which suggests it is not a room node.

I just looked back in the thread and I saw a piano. I am kicking myself for not seeing it earlier. Are you sure that your piano is not resonating with your measurement? It does not look as if it is easy to move. I suggest you play a 50-60Hz test tone then touch your piano to see if the strings or chassis is vibrating. Or maybe close the lid and put something heavy on it to damp the resonance. Maybe as many books as you can find, or a luggage filled with clothing, or something similar. Repeat the measurement and report back.
What's wrong with a start at 50Hz? My current target is to improve 100Hz to 500Hz. Besides that, I don't think a typical sized Rockwool can do much for <100Hz.
What do you suspect then?
I don't have a piano. That photo is just a sample to show the type of wall absorber panels that I have.

Anyway, here's the 20hz-20khz sweep MDAT.
 

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  • run27a.zip
    4.8 MB · Views: 22
Firstly, why do your measurements start at 50Hz?

There is significant ringing at 60Hz, up to 1.8 seconds. This is not accompanied by a peak in your frequency response which suggests it is not a room node.

I just looked back in the thread and I saw a piano. I am kicking myself for not seeing it earlier. Are you sure that your piano is not resonating with your measurement? It does not look as if it is easy to move. I suggest you play a 50-60Hz test tone then touch your piano to see if the strings or chassis is vibrating. Or maybe close the lid and put something heavy on it to damp the resonance. Maybe as many books as you can find, or a luggage filled with clothing, or something similar. Repeat the measurement and report back.
If 60 cycles electricity are used it can very well be the reason.
 
Here is my clarity graph for center speaker, crossover at 80Hz to subwoofer. From what I have read, I need to have level beyond 10dB to be considered ok. Is mine considered as terrible? I need to add a lot more thick absorbers?
By the way, is C50 also not relevant in home sized room?

cc.jpg




cf.jpg
 
What's wrong with a start at 50Hz? My current target is to improve 100Hz to 500Hz. Besides that, I don't think a typical sized Rockwool can do much for <100Hz.
What do you suspect then?
I don't have a piano. That photo is just a sample to show the type of wall absorber panels that I have.

Anyway, here's the 20hz-20khz sweep MDAT.
You can get decent results with Rockwool under 100hz. I just has to be thick enough to matter. In that range, 7.25 would probably be best. 2 sheets to make it 14.5 and that would put a decent sized dent in them. That's what I have in my room.

I have a small office and the thick absorption is used in all my panels (7.25") with a 6" airgap between the panel and wall/ceiling (airgap helps increase the panels effective range).

The only initial problem is the room will sound very dead, which was fixed by adding some slats to about a quarter of the panels.

I'd rather the room dead then too lively. For my ears, it sounds best.
 
I have a small office and the thick absorption is used in all my panels (7.25") with a 6" airgap between the panel and wall/ceiling (airgap helps increase the panels effective range).

According to a long Ron Sauro interview I saw on Youtube (posted here some time ago), and agreeing with my own experience, you can vastly improve the low-frequency absorption by enclosing the air gap. For example, if you build wall absorbers, make the frames so that they sit against the wall but hold the absorption material some distance away from it.

One good way of combining optimal room location, air gap and enclosing the air gap is installing floor-to-ceiling corner-straddling absorbers.
 
According to a long Ron Sauro interview I saw on Youtube (posted here some time ago), and agreeing with my own experience, you can vastly improve the low-frequency absorption by enclosing the air gap. For example, if you build wall absorbers, make the frames so that they sit against the wall but hold the absorption material some distance away from it.

One good way of combining optimal room location, air gap and enclosing the air gap is installing floor-to-ceiling corner-straddling absorbers.
I had considered a full encasement, but had difficulty figuring out the logistics of it all. Basically, it would have been the equivalent of building another ceiling with fabric covering instead of drywall.

I wanted the option to move things around and remove it if I didn't like the results.

Next time I may go with it. Would definitely clean it up a lot. I have about 80% of the ceiling covered already.
 
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