Revel F208?

[stunta]

Thanks That alcove does look like hard work to treat.

I agree with @maverickronin - try to do what you can to put as much absorption in it as possible.

I am not sure how much that will help with lower frequencies. I feel the alcove getting pressurized by the subwoofer and when I move myself to the edge of the seat, its almost as if the sub was turned off. As @mitchco pointed out earlier with amroc tool, this area has a severe room mode.

I've been trying to get some measurements using REW (it was easy for my living room. In the basement, my first round of measurements was inconsistent with another one so I started from scratch) but I am struggling with it in the basement to set the target level (the frequency response curve is literally off the chart and I didn't get any clipping warning during the measurement or in the "Check level" tool). I'll have to take measurements in the living room again to make sure I am doing things right and go back to the basement.

 

[andreasmaaan]

I am not sure how much that will help with lower frequencies. I feel the alcove getting pressurized by the subwoofer and when I move myself to the edge of the seat, its almost as if the sub was turned off. As @mitchco pointed out earlier with amroc tool, this area has a severe room mode.

I've been trying to get some measurements using REW (it was easy for my living room) but I am struggling with it in the basement to set the target level (the frequency response curve is literally off the chart and I didn't get any clipping warning during the measurement or in the "Check level" tool). I'll have to take measurements in the living room again to make sure I am doing things right and go back to the basement.

I see. It would take a lot of absorption to fix the bass problem in that alcove. Stuffing the whole thing with rockwool would probably work, or layering a few sheets of rockwool divided by air gaps.

My estimate is that you'd want rockwool with a density in excess of 80kg/m3 and sheet thickness of 100mm, and you'd want to apply at least 2 to 3 layers across the whole surface area of the alcove, beginning with a layer flush with the room walls and including with one layer (or more) inside the alcove. You may achieve more even bass absorption by creating air gaps of differing depths between the layers and the back wall of the alcove.

ProRox WM series products are examples of the type of rockwool that can be effective for this type of low frequency absorption (this is a UK product I believe - not sure if it's available where you are).

This would obviously be a fairly extreme solution But perhaps not completely crazy to use just two layers of a very dense (>100kg/m3) rockwool, one flush with the room walls, covering the entire surface area of the alcove, and another inside the alcove. These very dense rockwools can actually be effective at absorbing very low frequencies when enough is used.

I don't think I can promise results though unfortunately, based on my level of knowledge and experience.

What are the dimensions of the alcove approximately?

 

[stunta]

Stuffing the alcove is not practical. I'll try to max out what I can do with EQ, a rug and some other furnishings around the room for mid/high frequencies. After that I can add panels and see how it goes. Does that sound like a reasonable plan?

I will post the dimensions later.

 

[DonH56]

The alcove acts like (is, actually) a resonator. It probably provides a very big boost at one frequency and its multiples whilst mucking up the rest of the frequency response. I would put bookshelves in the center and move the seating area out into the room.

 

[stunta]

The alcove acts like (is, actually) a resonator. It probably provides a very big boost at one frequency and its multiples whilst mucking up the rest of the frequency response

Maybe I can get rid of my surround speakers. The alcove is doing all kinds of funny things behind my ears anyway.

I would put bookshelves in the center and move the seating area out into the room.

I would too, but the seating area is fixed and we just installed new flooring in front of it. I'll do the best I can with EQ and treatments and as folks suggested get a movable chair for serious listening.

Maybe I should throw in the towel, get some wireless headphones and call it a day

 

[stunta]

The felt rug pad under a rug is definitely helping tone things down in the room. The rug is polypropylene and I remember reading somewhere that it has diffusive properties but I can't find a reliable source right now.

 

[Floyd Toole]

I just discovered this thread, sorry for the absence. Some others have provided wisdom, but I will add my own spin. I discuss walls behind listeners in Section 9.6 of my book. That was a simple wall. Your alcove is an order of magnitude more complex and worse. In the absence of substantial distance to the rear wall, absorption behind the listener is the choice and the thicker the better - like not less than about 6 inches. The density of the fiberglass matters little, and the newish cotton "denim" fibrous material is human friendly and works very well. The fabric covering must be acoustically transparent (easy to blow through, glimmers of light visible through it - you can make a fool of yourself at a fabric store . Or, you can use thin decorous commercial rigid fiberglass panels for the surface and fill the space behind with inexpensive fiberglass pink, or whatever, to gain thickness.

But that still leaves you sitting in a cavity, so do what you can to absorb side-to-side, up and down reflections.

Diffusion simply delivers uncorrelated sound to your ears, thereby screwing up the stereo image - something that happened in some old LEDE control rooms with rear-wall diffusers too close. BTW, 2-inch diffusers are just "tweeter" diffusers (thickness needs to be about 1/7 wavelength to be effective - p. 104 in book). At about 8 inches things get interesting. Rugs are not diffusers; at best with thick felt underlay they can be useful absorbers.

Good luck.

 

[mitchco]

@stunta perhaps one more old school approach are tuned Helmholtz panel resonators, mounted in your alcove. http://www.mh-audio.nl/acalculators.asp#showcalc Click on the Helmholtz panel resonator. Try the calculator to see if you can come up with something that would fit your alcove and still be tuned to the big resonance frequency your are getting in there.

 

[Blumlein 88]

https://www.homedepot.com/p/UltraTo...ll-16-in-x-48-in-6-Pack-60306-16482/202710055

This is some of the human friendly denim insulation. It was pretty cheap at first. But the price looks to have escalated in the last couple years. It doesn't fluff up as well as fiberglass. Doesn't cut all that easy either. I would have suggested it for your purposes though, but I'd have to rethink it at current pricing.

 

[stunta]

Thanks @Floyd Toole for chiming in. I am considering getting a custom frame built, stuff it with the UltraTouch denim and have it upholstered with Gifford of Maine fabric (ATS Acoustics uses this fabric). This will also serve as a head rest on top of the seating backrest. I would rather avoid rockwool because of irritation to skin. The problem is, I don't think I can go deeper than 2".

I've reading this gearslutz thread (and some others) and folks are saying a thickness of > 4" starts making the UT reflective (which is fine, I can't go past 4") and I see measurements for 3.5". At 2", should I even bother with it?

Also, there are two niches on the two sides of the alcove and they measure 16" x 9" (I have about 3 feet clearance under the custom speaker stands). Would it help if I stuff those niches with something - bass traps? I do have to keep aesthetics in mind as we would be entertaining guests in this room.

And for some entertainment value, here is a guy built what he claims is an anechoic chamber with the UT denim bats:
http://www.silentpcreview.com/article876-page8.html

@mitchco, thank you for the suggestion. That is an interesting idea and a quick search found that Vicoustic makes such a product. Would it be a good idea to place these in the 2 niches I mentioned above? At $400 each, I would expect them to keep my beer cold as well

EDIT: To be clear, I am not expecting to have anything remotely close to ideal acoustics in this room. I understand that regardless of how I treat the alcove, the better seating position will be outside of it. I am looking for help with mitigating the issues versus eliminating them and at the same time keep things relatively pleasing aesthetically. I've placed an order for the Vicoustic Flat Panel VMT (8 x 2' x 2' panels) as their lead time is 2 months and my wife really likes the patterns. If not in the alcove, they will go on the side wall and if they do nothing, they will still look good doing nothing.

 

[Floyd Toole]

https://www.homedepot.com/p/UltraTo...ll-16-in-x-48-in-6-Pack-60306-16482/202710055

This is some of the human friendly denim insulation. It was pretty cheap at first. But the price looks to have escalated in the last couple years. It doesn't fluff up as well as fiberglass. Doesn't cut all that easy either. I would have suggested it for your purposes though, but I'd have to rethink it at current pricing.

I used this version from Home Depot, and later discovered thick walls (R19?) insulation at Lowes, which was more convenient for another job.

 

[Floyd Toole]

Thanks @Floyd Toole for chiming in. I am considering getting a custom frame built, stuff it with the UltraTouch denim and have it upholstered with Gifford of Maine fabric (ATS Acoustics uses this fabric). This will also serve as a head rest on top of the seating backrest. I would rather avoid rockwool because of irritation to skin. The problem is, I don't think I can go deeper than 2".

I've reading this gearslutz thread (and some others) and folks are saying a thickness of > 4" starts making the UT reflective (which is fine, I can't go past 4") and I see measurements for 3.5". At 2", should I even bother with it?

Also, there are two niches on the two sides of the alcove and they measure 16" x 9" (I have about 3 feet clearance under the custom speaker stands). Would it help if I stuff those niches with something - bass traps? I do have to keep aesthetics in mind as we would be entertaining guests in this room.

And for some entertainment value, here is a guy built what he claims is an anechoic chamber with the UT denim bats:
http://www.silentpcreview.com/article876-page8.html

@mitchco, thank you for the suggestion. That is an interesting idea and a quick search found that Vicoustic makes such a product. Would it be a good idea to place these in the 2 niches I mentioned above? At $400 each, I would expect them to keep my beer cold as well

EDIT: To be clear, I am not expecting to have anything remotely close to ideal acoustics in this room. I understand that regardless of how I treat the alcove, the better seating position will be outside of it. I am looking for help with mitigating the issues versus eliminating them and at the same time keep things relatively pleasing aesthetically. I've placed an order for the Vicoustic Flat Panel VMT (8 x 2' x 2' panels) as their lead time is 2 months and my wife really likes the patterns. If not in the alcove, they will go on the side wall and if they do nothing, they will still look good doing nothing.

I cannot imagine why the cotton or any other fibrous material would become "reflective" with greater thicknesses. It should simply be increasingly effective at lower frequencies. There is absolutely nothing special about the cotton - the acoustical properties are well documented on their website. It is not better or worse than fiberglass or mineral wool, just not harmful to humans. Guiford of Maine fabrics are good, but are somewhat reflective at high frequencies - they are treated to be fire resistant.

People who talk about fluff being used as bass traps are not talking about 'real' bass, as in below 100 Hz or so. Bass traps that work at very low frequencies are membrane/diaphragmatic absorbers.

You will find useful information in my book "Sound Reproduction" Third Edition, Focal Press 2017, and in the companion website, which is open access: www.routledge.com/cw/toole.

 

[stunta]

I used this version from Home Depot, and later discovered thick walls (R19?) insulation at Lowes, which was more convenient for another job.

It looks like R19 is hard to find in stock. Lowes shows no availability and Home Depot only sells them in very large packs.

ATS makes these cotton batts: https://www.atsacoustics.com/recycled-cotton-batts.html

I wonder why the specs stop at 4Khz?

I cannot imagine why the cotton or any other fibrous material would become "reflective" with greater thicknesses. It should simply be increasingly effective at lower frequencies. There is absolutely nothing special about the cotton - the acoustical properties are well documented on their website. It is not better or worse than fiberglass or mineral wool, just not harmful to humans. Guiford of Maine fabrics are good, but are somewhat reflective at high frequencies - they are treated to be fire resistant.

People who talk about fluff being used as bass traps are not talking about 'real' bass, as in below 100 Hz or so. Bass traps that work at very low frequencies are membrane/diaphragmatic absorbers.

You will find useful information in my book "Sound Reproduction" Third Edition, Focal Press 2017, and in the companion website, which is open access: www.routledge.com/cw/toole.

Happy to buy the book, but what are the pre-requisites? I am a beginner at best.

 

[DonH56]

It looks like R19 is hard to find in stock. Lowes shows no availability and Home Depot only sells them in very large packs.

ATS makes these cotton batts: https://www.atsacoustics.com/recycled-cotton-batts.html

View attachment 16867

I wonder why the specs stop at 4Khz?



Happy to buy the book, but what are the pre-requisites? I am a beginner at best.

You can buy thinner rolls and layer it but need to pull the paper backing off for maximum absorption.

A lot of reported results only cover the vocal'ish range for OSHA. Aside (rant): OSHA guidelines that are so often quoted are not really good for audiophiles and musicians. If you meet OSHA's guidance for SPL that means you will most likely be able to understand conversations like your foreman yelling at you to get back to work after your coffee break. They are NOT intended as guidelines for keeping your hearing intact over full range of dynamics and frequency. Read the OSHA spec; they are meant to provide reasonable assurance you can talk to someone after you retire, not that you'll be able to hear music or anything else well. (/rant)

The main prerequisite for the book is the ability to read. You may have to read things twice but it is at a reasonable layman level, not something like an AES Journal paper (though some of those... ). One of those you'll get more from as you re-read it.

IME/IMO/FWIWFM/etc. - Don

 

[stunta]

but it is at a reasonable layman level

I shudder to think what your definition of layman is. I might need a 4-year degree in something I have not even heard of.

OK, I'll buy the book and if I don't understand anything, I will donate it to the ASR Lending Library.

 

[amirm]

OK, I'll buy the book and if I don't understand anything, I will donate it to the ASR Lending Library.

You need to read it over and over again and it will gradually sink in. At least some of it will.

 

[Floyd Toole]

You need to read it over and over again and it will gradually sink in. At least some of it will.

After which you may be the audio expert in your group of enthusiasts . . .

I'd like to think that an ability to read and the desire to learn are the prime prerequisites. Oh yes, there is one more: an open mind, because some of what you have heard about audio over the years is wrong. I taught this stuff to CEDIA audiences for years: three 3-hour lectures and some kept coming back in subsequent years. They continue to be taught by my Harman colleagues.

 

[Floyd Toole]

I wonder why the specs stop at 4Khz?

Because 4k Hz is the highest octave band that is specified in standards. The highest frequency measured is about 6 kHz (the upper limit of the 4 kHz band), which ironically, is just below the frequency at which Guilford of Maine fabrics start reflecting sound . All the traditional standards and ratings were created at a time when the only real consideration was voice intelligibility and privacy. Most are also random-incidence ratings which are more relevant to concert halls and reverberant auditoriums than small listening rooms (blame Sabine . A major mismatch. HiFi was not a concern, but habits are hard to break and we are burdened with numbers that don't mean much in our small rooms.

 

[amirm]

After which you may be the audio expert in your group of enthusiasts . . .

I'd like to think that an ability to read and the desire to learn are the prime prerequisites. Oh yes, there is one more: an open mind, because some of what you have heard about audio over the years is wrong. I taught this stuff to CEDIA audiences for years: three 3-hour lectures and some kept coming back in subsequent years. They continue to be taught by my Harman colleagues.

I always say taking that CEDIA class would teach people more about audio than everything else. I sent my son to your class and after that, I could no longer pretend to know more than him about sound reproduction.

One absolutely has to do a full reset and ignore everything they think they know about sound and audio reproduction and start over. I know I did.

An unsung hero by the way for me was the incredible references at the end of your book. I think I once counted and it was over 270! I have found probably two thirds of them and reading them was very useful. Unfortunately for the general public, most of them are behind paywalls and subscription services. As such, it is great to have your book in such an accessible manner.

 

[Laserjock]

I see this is an older thread but have you thought about flipping the seating/projector around and using a AT Screen in the alcove?

That might alleviate a lot of issues.