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Quest for Real Bass Traps

FrantzM

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Try re-reading this part of my earlier post:

Thus harmonically complex musical notes are overwhelmed by modes, which are harmonically bereft plain sine waves. EQing drops the harmonically complex notes into inaudibility, leaving only quieter harmonically bereft sines in the audible realm. Thus:

My point is that note, hoot, note, hoot might look smooth on REW, but is musically ridiculous. Is that clearer?
No. No Data. Seriously what does those terms mean: "Musically ridiculous"?

Any musical signal is reproduced well or not. If it music it can be approximated by a series of sines. Making sure that series of sines are well reproduced is a scientific endeavor. measurable at that and in a room this is a done with a microphone and software of hwich REW represents one of the best at any price. THat is free is a feat. so powerful and useful it is. Now a nice graph doesn't guarantee great results, again Science can explain why. It is one thing to measure, it is another to know what, how to measure and how to interpret the measurements.
Thus your points are not clear to me, before because no data is presented. Just subjective opinions...

Let's leave it at that

Peace.
 

abdo123

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My point is that note, hoot, note, hoot might look smooth on REW, but is musically ridiculous. Is that clearer?

This doesn't has to be the case, if EQ is limited to the region where the system has minimum phase behavior, EQ will fix both the amplitude and the phase response and eliminate the audible effect of ringing.

I wrote a post about it in this thread:

 

FrantzM

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IMO (in suitable room) DBA (double bass array) is good solution. Persuasive reasoned objections are very well appreciated!))
Multiple subwoofers results have been studied. By the ex-Harman people, mainly Olive, Duvantier, Toole , etc, and by Earl Geddes. Double array, do fall in the multiple subwoofer category. Olive et Duvantier preconize 4 subwoofers placed at mid-wall in a rectangular room. Geddes prefers a quasi-random distribution of 3 subwoofers... The results speak for themselves. In the low bass, below 100 Hz you are in a quasi-steady state region. EQ works well there...
Multiple subwoofers do not address well the so-called sub bass, that is the region between 150 to 300 Hz, there, room treatments are more practical and of more mangeable size...

Peace.
 

FrantzM

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This doesn't has to be the case, if EQ is limited to the region where the system has minimum phase behavior, EQ will fix both the amplitude and the phase response and eliminate the audible effect of ringing.

I wrote a post about it in this thread:

Perhaps we should move this discussion to that thread...
 

Kal Rubinson

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I have been using a pair of MSR Spring Traps for years but I do not know if they are still available.
MSR Spring Trap.JPG
 

Inner Space

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No. No Data. Seriously what does those terms mean: "Musically ridiculous"?

Any musical signal is reproduced well or not. If it music it can be approximated by a series of sines. Making sure that series of sines are well reproduced is a scientific endeavor. measurable at that and in a room this is a done with a microphone and software of hwich REW represents one of the best at any price. THat is free is a feat. so powerful and useful it is. Now a nice graph doesn't guarantee great results, again Science can explain why. It is one thing to measure, it is another to know what, how to measure and how to interpret the measurements.
Thus your points are not clear to me, before because no data is presented. Just subjective opinions...

Let's leave it at that
No, let's not leave it at that. A room mode is not a series of sines. It's a single sine. That is not a subjective opinion. It's a physical fact. REW will show the absence of higher harmonics. Look and see. The data will be there.

If replacing a series of sines (i.e. the unique timbre of a musical instrument's note) with a single sine (like blowing across an empty beer bottle) is musically OK with you, I'm not at all sure why you're in this hobby.
 

Bjorn

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Highly effective treatment isn't neceassarily expensive but it can take up space. Below is measurement of a small room I was hired for consultance. Treatment here was cheap.

Frequency response before (red graph) and after 80% of treatment was in place:
before an after freq response at 4m distance.jpg


Waterfall before:
waterfall before at 4m distance_higher resolution.jpg


Waterfall after with 80% of the treatment:
waterfall after at 4m distance_higher resolution.jpg


Unfortunately I don't have a measurement after all treatment was placed at the moment.
 

Morla

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Way more uptake than I would have thought. I'll update the main post later.

As I see it the problem is this. In the modal region there is no hope unless the room is constructed to control the issues from the outset. In the transitional region SBIR is king but few acoustical products are appropriate. Overwhelmingly the majority of offerings are biased towards effectiveness in the statistical region, where they are least needed because the speakers dominate.

Most of people I know aren't able to use extensive or thick treatment. Multiple life reasons intrude usually. So these restrictions breed the need for practicality and the following approach.

Modal: Sub or subs. Use the approach that most floats your boat. Welti, Geddes, Griesinger, source/sink. Supplement with PEQ. I would imagine for most this would be limited by budget or real estate or both.

Statistical: PEQ broadly the first arrival according to JJ's advice, or a spatial average according to MMM results. Use diffusers if you have space. Buy good speakers to minimize the amount of work here.

Transitional: This is the area of concern for this thread. This region has nonminimal phase problems which do not respond well to EQ, unless you are running FIR filters. Enough treatment should be used to make the variations PEQable. And the treatment is the hard part, given that it can't be bulky or overly broadband towards the HF.

And that's the genesis and purpose for me.
 

Bjorn

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As I see it the problem is this. In the modal region there is no hope unless the room is constructed to control the issues from the outset.
That's not true at all. But it does require treatment that are highly effective.

In the transitional region SBIR is king but few acoustical products are appropriate. Overwhelmingly the majority of offerings are biased towards effectiveness in the statistical region, where they are least needed because the speakers dominate.
I showed on the last page an of a product that works really well for SBIR. They can be made to be reflective in mids and highs too.

Overlay where can you see the 120 Hz related SBIR dip has been almost diminished by only a few panels on side walls. The small remaining part would require some more treatment at other surfaces. The change below 35 Hz was related to some diffusers being moved by the way.
Overlay frekvensrespons før og etter.jpg
 

Hipper

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Perhaps .. I should open a thread on the subject of DRC/EQ vs Room Treatments .... ;)
What do you all think?




Peace.
I would be interested in such a comparison. I'd add a comparison with subs would also be interesting.

Subs, DSP/EQ and room treatment seem the three main options for solving sonic problems in a room (as well as careful positioning of course).

In particular I would like to see how EQ/DSP on its own alters the decay times compared to room treatment on its own. I found one of the benefits, if indeed not the most important one, was the smoothing and reduction of decay times from using room treatment (21 bass traps!). It still didn't completely solve the Frequency Response issues but use of some EQ helped with that. I don't use subs.
 

JPA

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The problem is that effective acoustic treatment is fantastically huge and very expensive. I just did a room for a (fortunately rich) person, involving nearly 100 24" tube traps. It sounds absolutely wonderful (and looks surprisingly good) but is obviously a niche solution for an extreme minority.
Tube traps are interesting. On one hand, they're not effective below about 100-200Hz (depending on the diameter of the trap). On the other hand, they are cheap and easy to DIY.
 

Inner Space

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Tube traps are interesting. On one hand, they're not effective below about 100-200Hz (depending on the diameter of the trap).
Individually, maybe, or when used few in number. These 24" examples were stacked two high and two deep all around the perimeter of the room, and proved effective below 40Hz. Nuts, I know, but they worked fine for what I needed them to do. I would have chosen an equivalent mass of bulk material (sheep's wool household insulation is my new favorite - really exceptional) but the client wanted more of an "art installation" look.
 

Bjorn

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Individually, maybe, or when used few in number. These 24" examples were stacked two high and two deep all around the perimeter of the room, and proved effective below 40Hz. Nuts, I know, but they worked fine for what I needed them to do. I would have chosen an equivalent mass of bulk material (sheep's wool household insulation is my new favorite - really exceptional) but the client wanted more of an "art installation" look.
Appreciate if you can share before and after measurements. Waterfall graphs would be sufficient.
 

ernestcarl

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I would be interested in such a comparison. I'd add a comparison with subs would also be interesting.

Subs, DSP/EQ and room treatment seem the three main options for solving sonic problems in a room (as well as careful positioning of course).

In particular I would like to see how EQ/DSP on its own alters the decay times compared to room treatment on its own. I found one of the benefits, if indeed not the most important one, was the smoothing and reduction of decay times from using room treatment (21 bass traps!). It still didn't completely solve the Frequency Response issues but use of some EQ helped with that. I don't use subs.

I know it's somewhat off-topic on this thread so I'll post just a few decay graphs comparing two levels of equalization in my already acoustically treated small room:

1662743841253.png 1662743847704.png 1662743853902.png
*time-domain correction via FIR convolution is merely icing on the cake

The couch is close to the rear wall of the basement (directly behind the drywall is the concrete foundation), hence the pressure is also at its maximum in the lowest frequencies.
 
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