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

I think OP should start to focus on the whole area from 100 Hz and upwards

That's what the OP appears to be asking about.

and to solve that he needs as many as possible broadband absorbers that are at least 10 cm thick with air gaps, and even better 15 to 20 cm thick panels.

Yes, better yet, corner-straddling floor-to-ceiling absorbers. This combines a favourable location in the room with air gapping. Sealing off the air gap (i.e. making the panels floor-to-ceiling) has a big impact on performance. Incidentally, 15cm thick DIY absorbers of this kind have helped my room way below 100Hz.
 
The problem with bass traps is, you have to train the low frequency to be obedient and enter the entrance to the trap. You would be the first to master this art, so go on!
Once released from a woofer, these low bastards are very naughty and spill all over the room. The trap can only catch the sound energy that is at the small opening of the resonator and convert a fraction of that into heat, using some fiber inside. So from all the energy the woofer produced, only a small part of a small fraction will get erased. Which is inaudible. This is why we never hear any success stories about bass traps, except for the ones created by people selling them.
Take a bottle and blow over it, you can produce a sound that way. Now take a number of identical bottles and fill them with some dampening material. Place them around your first bottle. Blow over it. Has the tone been erased or even become less loud? No? Fine, you have just proved to your self that bass traps don't work. You saved yourself a lot of work and money.

If you have too much bass, reduce it at the source, not in the room. A DSP is your friend.
(exceptions would be active noise canceling constructions, producing the same frequency, just of inverse polarity. Quite complicated and expensive.)

Higher frequency and it's decay are another story. A good absorber, meeting the rooms demand and placed right, can work well.
 
Some points to make.

1. Typical rooms have a rising noise floor (EDIT: rising noise floor in the bass region) in the low frequency region. Typical room noise is usually about 35-40dB. Yours seems to be below 25dB which is suspiciously low - it indicates to me that your curve has not been adjusted with an SPL meter.

@Skylinestar I am much more concern what a hell is happening in highs there?
I have done a sweep with louder volume (+7dB louder). Louder than that and I will get a clipping error from REW.
Screenshot 2025-01-24 210603.jpg
 
I have done a sweep with louder volume (+7dB louder). Louder than that and I will get a clipping error from REW.
View attachment 423488
Great now do the PEQ for room mood as explained put it in the chain and do measurement again. It doesn't do only the first bump but also it's first two harmonics. And then you have room decay to work on it. Something is definitely happening in highs either it's series problem with room which you will have to correct with accustic treatment or you are siting to close to the wall behind you. If window glas is ringing put thick curtains on.
 
I have done a sweep with louder volume (+7dB louder). Louder than that and I will get a clipping error from REW.

The way to improve the signal to noise ratio is to increase the sound energy to noise ratio. Sound energy can be increased by:

- increasing the height of the impulse (volume)
- increasing the length of the impulse (time)

My recommendation was five averaged 45 second sweeps, I said nothing about increasing the volume. Raising the volume is not a good idea because (1) you might clip REW's measurement, as you have done and (2) you might drive the speaker into nonlinear behaviour, e.g. dynamic compression at high volume, driver clipping, driver overheating, etc. If you don't know how to average five sweeps, simply do them then zip up the .mdat and post it on ASR. I will take a look at it for you.

And before you do anything else, please read the thread I linked to earlier about how to do measurements and ask for help on ASR. It was specifically written to make sure that we get error-free measurements to analyse.
 
For frequencies down to 100 Hz area you don't necessairly need that much. Something like 6 panels with dimension 120x60 cm (or slightly bigger would be better) can do quite a lot if they are efficient. Broadsorbor has a higher effect in the lows than BAD panels BTW.

For frequencies below 100 Hz and especially below 70 Hz, area of treatment need to be larger for a major change. That being said, we did see a decent difference with only two Modex Plate with dimension 150x100x10,5 cm for a resonance at around 68 Hz. You will also notice that it effected two dips, something EQ would not do.

Before:

before ear height.jpg


After installment of two Modex Plates:
after ear height.jpg


But let's say you wanted to treat a resonance at 50 Hz, that would take more units or surface area to treat effectively.

Unless you can treat large areas, it's often better to focus on a frequency area above a certain frequency and simpoly use EQ for the lowest. Sure, EQ isn't going to work as well as treatment but it's compromise many have to live with.

The benefit of treatment is: It will always work in the time domain, it has an effect on harmonics of the modes, it works for everyhwere in the room, and it doesn't steal headroom the same way as EQ.

P.S. FIY I work with acoustics, offer acoustic services and sell RPG and some bespoke products.
 
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Here are a few 2M sweeps of LCR speakers & 5 repeated sweeps. mdat attached. Should I be worried that 2M sweep is too long of a duration and may damage a tweeter?

Screenshot 2025-01-25 223603.jpg
 

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  • run10a.zip
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  • run12_5repeated (2).zip
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Thanks for repeating the measurements. Let me show you the power of taking five 45 second measurements and averaging them.

1737819737494.png

Some things to note about this graph - note how far I have extended the time scale (to 1000ms) and the vertical scale (from +100dB to -60dB). The noise floor is visible as the flat area of the graph and the signal is the mountain range rising above it. This procedure has pushed the noise floor down to -50dB.

Now for fun, we look at a single measurement:

1737819829000.png


This measurement is "not bad" by any means (in terms of noise rejection) but we can see that five averaged measurements pushes the noise floor down by a huge amount. If you look closely, you can even see the high noise floor appearing to make the bass reverb seem longer. So let us use our cleaned up measurement to take a closer look at your bass and choose a more sensible window to view the waterfall.

1737820910407.png


Just looking at the bass alone, the issue is not very clear. It is obvious that you have uncontrolled room modes, but not obvious if the prolonged decay is due to the height of the peak, or whether the bass is simply ringing in your room. Look at that nasty peak at 25Hz. It is almost 20dB louder than reference.

1737820943754.png


The way to tell is to flatten out the peaks and see what happens to the decay.

Using your measurement, I imported it into my room correction program (Acourate) and did a quick and dirty room correction to smooth out the bass. I then convolved the filter with the original measurement (i.e. the same waterfall as previous). I kept the scale exactly the same so that you can see the effect. We can see that the bass decay is still significantly longer but it isn't as bad as before.

I also calculated your Schroder frequency using a T30 of 0.8s. Fs = 11885 * sqrt (T30/V) with V being room volume in feet. Your Schroder frequency is about 200Hz.

1737821563210.png


I can also show you the RT60 with the upper and lower tolerance targets for your room. This is after room correction. We can indeed see that you have a huge reverberation problem below 600Hz, it is way above the target tolerance. And this is after room correction.

I should be also showing the RT60 in REW, spectrogram, and a few others but it is better for you to flick through them yourself to see the difference. I have uploaded an .MDAT that has the same measurements as your five sweeps, but with two new curves. The first is an average of all five measurements, and the second is after room correction.

Opinion and recommendation
The first thing you need to try is DSP. Your RT60 is very high from 600Hz down but it is OK above that. Sad to say, this is going to be very tricky to fix with room treatment. Reason being, foam absorbers typically attenuate all wavelengths shorter than 1/8 the thickness of the foam. Meaning that if you specify a thickness of foam sufficient to treat (say) 100Hz, it will have effects all the way up to 20kHz.

There are some new products on the market that are a combination of diffuser and foam absorber and can selectively attenuate lower frequencies whilst reflecting upper frequencies. You need to talk to an acoustics expert about finding the right product for your needs. In a nutshell, good acoustic products are specified with a coefficient of absorption per frequency band. Take a look at this product :

1737835799985.png


It's not really a good fit for you because it appears you need to attenuate the reverb between 100Hz - 600Hz. But it gives you an idea what to look for. So you need to go shopping.

To be honest, this pattern of "OK RT60 down to 600Hz and then horrible below that" is a bit weird. It makes me think that you already have acoustic treatment that is creating this spectral distortion. Do you?
 

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  • Averaged and Corrected.zip
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A sofa positioned at a spatial bass dip (or peak) is an easy treatment.

E.G., walk around with a measurement mic while playing pink noise to locate them in your listening space.
 
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So you need to go shopping.

To be honest, this pattern of "OK RT60 down to 600Hz and then horrible below that" is a bit weird. It makes me think that you already have acoustic treatment that is creating this spectral distortion. Do you?
A million thanks for your work.

Regarding shopping, it goes back to the original question. How thick of a bass trap am I expecting to have? My local hardware stores sell Rockwool Safe n Silent (60kg/80kg/100kg /m3, 6 pieces per pack). Do I need 12" (6 pieces) as a block of bass trap?
VPR / membrane bass trap not available in my area.

This Modex plate seems to be suitable but it cost a bomb for me. Is this the price to pay for treatment?

I do have a few panels scattered in my room. Each panel is about 60x120x6cm. The panels barely cover 20% of the wall surface. Instead of sticking it to the wall, I just rest them on the floor, standing. I also have curtains at the left and right side of the mlp.

Not my photo but this is how the panel looks like:
bat_fiberakustic__acoustic_pan_1681035078_0a51ab00_progressive.jpg
 
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A million thanks for your work.

Regarding shopping, it goes back to the original question. How thick of a bass trap am I expecting to have? My local hardware stores sell Rockwool Safe n Silent (60kg/80kg/100kg /m3, 6 pieces per pack). Do I need 12" (6 pieces) as a block of bass trap?

This Modex plate seems to be suitable but it cost a bomb for me. Is this the price to pay for treatment?

I do have a few panels scattered in my room. Each panel is about 60x120x6cm. The panels barely cover 20% of the wall surface. Instead of sticking it to the wall, I just rest them on the floor, standing. I also have curtains at the left and right side of the mlp.

Not my photo but this is how the panel looks like:
View attachment 423854
Modex is a commercial VPR trap... A DIY job that replicated one exactly would be fairly expensive but doing an approximation with more affordable materials would probably only be $100-200 max, maybe more for a really big one.

Per @Keith_W s phenomenal post, it looks like your treatments are working but only down to 600hz or so, so whatever you add to the room, try to keep the absorption spectrum below that as much as you can.
 
Just from looking at the RT60 I am guessing that your absorbers are about 70mm (3") thick. As I said in my post, the thickness of the absorber determines the longest wavelength that will be effectively attenuated. You need to go down to 100Hz, which is 3.43m or just over 13" thick.

Most people are able to get the RT60 down to target with normal room furnishing alone. Would you be able to give us a bit more context or maybe a photograph? Is your room empty for a reason?

1737864931525.png


This is my listening room. Normal furniture only. RT60 is about 0.4s.

I am unable to answer your questions about design for acoustic treatment. I will have to defer to someone else. Otherwise, you can try diyaudio.com.
 
Is your room empty for a reason?
It is a hallway that leads to other bedrooms. Currently, the only furniture there is a tv console and an IKEA Poang style chair. I have no intention to buy more furniture or to put more items in that space. I like the minimalistic empty look.
 
Of course, it's your home and your choice. I think my post shows you that DSP can improve matters a bit (without adding any intrusiveness at all) but it won't fix all fundamental issues with acoustics. DSP aside, these are your options:

1. Choose to add more furniture
2. Choose to add physically intrusive room treatment. As I indicated, for it to be effective down to 100Hz, it needs to be pretty thick.
3. Live with a spectrally distorted RT60

Pick one.

I would personally choose option 1 or 3. There is nothing wrong with non-ideal measurements as long as you are happy with it. As Toole says, we become acclimatised to the room and we "hear through" it. Yes, we can see there is a problem. But is it a problem that needs to be fixed? That's up to you. Maybe add some DSP, see if the sound improves to something you are subjectively happy with, and call it a day.

I don't like room treatment, particularly absorbers that need to be so thick to be effective. It is the opposite of minimalism. They add no function to your room whilst eating up a lot of space. This is "ASR" and not "interior design review" so I shouldn't be talking to you about design. But you can consider something like a Le Corbusier LC2/LC3/LC5 for that minimalist look whilst still providing more absorption than an Ikea Poang. Yes, it's expensive - so look for a nice replica.
 
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To generate the average, is it correct to use the "vector average" button in the All SPL tab?

Yes, that would be a better way of doing it than what I did - which was to manually sum all the measurements together. I use Acourate and I am less familiar with REW. Summing all the measurements is what I would do with Acourate.
 
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.

My tip: Contactt someone who actually who understands acoustics. This is simply a mess with incorrect information.
 
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.

My tip: Contactt someone who actually who understands acoustics. This is simply a mess with incorrect information.
Any plans to add content on your website?

 
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