What is the Sound of Front Wall Diffusion?

sel53

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Dec 22, 2020
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Hi,
New to acoustic treatments ...

I see countless photos of listeners’ setups with (attractive) diffusion panels on the front wall between the speakers.

Can anyone generally characterize the “sound” that changes with the addition of these panels? I assume they affect higher frequencies, but when I put my ears by the front wall, I don’t hear many highs! What malady are those intended to fix, or what change in sound would one expect to hear by adding them?

Thanks
 
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ArnoFenn

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My own experience is that it seems that the front center gets a more mature "center speaker" by including more definition in the mids (and then you experience this as the center seems to have a treble emphasis without the diffusor). Unfortunately I can not keep the diffusor since that is where the TV is :-( . Got some temporary mounting for longer listening events though.
 
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MTB Vince

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I concur with @ArnoFenn's observations about a stronger center image and improved mid band clarity. I would add that for front wall diffusion to be best practice effective, the loudspeakers need to be placed off the front wall and out into the room. When implemented properly soundstage depth increases as does image specificity. If you haven't treated your back wall, treating your front wall with diffusion will eliminate a "slap echo" between the opposing walls. Being rid of that slap echo allows for listening at higher volume levels without the high frequencies taking on a hard splashy edge.
 
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Artnet

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If you haven't treated your back wall, treating your front wall with diffusion will eliminate a "slap echo"
I am building a Quadratic diffuser for the front wall in 3 panels that will give me a little less than 40% coverage. I am doing this to start a process and hope to discover some things a long the way.
Its a 2 channel listening room and without getting into the contentious aesthetic argument of QRD's am interested in the general theories being shared here.

it seems that the front center gets a more mature
Am hoping to achieve this and was curious about what to do next.
May involve some absorption front, side and rear wall's if needed. But will be dependent on what my ears hear.

Wanting to add to the original question
What malady are those intended to fix, or what change in sound would one expect to hear by adding them?
In general terms, what benefits can be heard from treating other surfaces, including the ceiling, what priority was given?
 

benito

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I concur with @ArnoFenn's observations about a stronger center image and improved mid band clarity. I would add that for front wall diffusion to be best practice effective, the loudspeakers need to be placed off the front wall and out into the room. When implemented properly soundstage depth increases as does image specificity. If you haven't treated your back wall, treating your front wall with diffusion will eliminate a "slap echo" between the opposing walls. Being rid of that slap echo allows for listening at higher volume levels without the high frequencies taking on a hard splashy edge.
@MTB: what is happening when the speakers are not placed off the front ? Mine are at 0.5 m to the wall (0.5 m is the distance between wall and speakers rear)
 

MTB Vince

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@MTB: what is happening when the speakers are not placed off the front ? Mine are at 0.5 m to the wall (0.5 m is the distance between wall and speakers rear)
To understand how having either the sound source (loudspeaker) or listening position too close to a phase grating diffuser will impact sound quality, try the following experiment. Start by standing about 5 feet away from your diffuser and facing directly towards it. Begin speaking and listen closely to the sound of your voice. Continue speaking and listening while you slowly walk towards the diffuser. Your voice will gradually take on a "wiry" buzzy tonality as you enter the diffuser's nearfield and the effect will worsen with proximity.

BTW, when measuring the distance from sound source to diffuser, we measure from the front baffle where the drivers are located.
 
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benito

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To understand how having either the sound source (loudspeaker) or listening position too close to a phase grating diffuser will impact sound quality, try the following experiment. Start by standing about 5 feet away from your diffuser and facing directly towards it. Begin speaking and listen closely to the sound of your voice. Continue speaking and listening while you slowly walk towards the diffuser. Your voice will gradually take on a "wiry" buzzy tonality as you enter the diffuser's nearfield and the effect will worsen with proximity.

BTW, when measuring the distance from sound source to diffuser, we measure from the front baffle where the drivers are located.
thanks MTB. then the correct distance is 0.95 m in fact. I can't move far away my speakers except if I accept to have some trouble with my wife. I do not have any diffusor right now and I was wondering in my case if it was worth it (see the picture).
 

Addicted to hifi

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thanks MTB. then the correct distance is 0.95 m in fact. I can't move far away my speakers except if I accept to have some trouble with my wife. I do not have any diffusor right now and I was wondering in my case if it was worth it (see the picture).
Nice system
 

Cellcbern

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thanks MTB. then the correct distance is 0.95 m in fact. I can't move far away my speakers except if I accept to have some trouble with my wife. I do not have any diffusor right now and I was wondering in my case if it was worth it (see the picture).
Alternatively you might consider the ZR Acoustics panels which both reduce reflections and have a mild diffusive effect. They work best with the speakers as close to them/the wall as possible. See:


You can read about my experiences with the ZR panels here:

 

benito

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Alternatively you might consider the ZR Acoustics panels which both reduce reflections and have a mild diffusive effect. They work best with the speakers as close to them/the wall as possible. See:


You can read about my experiences with the ZR panels here:

Thanks for the informations on ZR Acoustics panels. I ve read rapdly all the topic " trying-the-zr-acoustics-panels".
I have one question: how you decide to choose on kind of panels. You started with ZR Sample Rate Tech "sunspot" and "toccante" if I am right:

I love the design and my wife may like them.
I will contact DeltaH Design to see if I get them in Europe.
 
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MTB Vince

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thanks MTB. then the correct distance is 0.95 m in fact. I can't move far away my speakers except if I accept to have some trouble with my wife. I do not have any diffusor right now and I was wondering in my case if it was worth it.
Well a quadratic diffuser with a useful operation bandwidth, lets call that effective diffusion with a low frequency cut off in the vicinity of 900Hz-1kHz with a maximum well depth of 5-6", will have an "acoustic no-fly zone" of about five feet. You need your loudspeakers or your head to be outside of the nearfield of that diffuser, so no closer than 5 feet.

Shallower quadratic diffusers like the 2-3" max depth 2D N7 wooden versions (which look like 3D chess boards) offered cheaply for sale on Ebay and Amazon aren't worth bothering with. They have a narrow scattering bandwidth, typically only an octave, and that is likely located between 4-8kHz. While they look cool, they are a total waste of time.

On the other hand you have the huge 1D slot diffusers which Dennis Foley recommends and often crop up on the rear wall of big mix and mastering studios. These will be properly designed and based upon higher prime numbers which offer wider operating bandwidths. However a quadratic diffuser that offers efficient diffusion down to the bottom of the midrange will exhibit a massive nearfield region. A 400Hz wavelength is 34" long. A quadratic diffuser designed to work down to that frequency should be a minimum of 3 wavelengths distant from both the loudspeaker and listener. So these 400Hz capable diffusers should be located almost 8.5' feet away from the loudspeaker sound source or the MLP to avoid issues. That requires a pretty big and inevitably dedicated room in order to both meet the diffuser's minimum distance requirements and leave yourself with some flexibility in where you will place the loudspeakers and the MLP!
 
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Cellcbern

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Thanks for the informations on ZR Acoustics panels. I ve read rapdly all the topic " trying-the-zr-acoustics-panels".
I have one question: how you decide to choose on kind of panels. You started with ZR Sample Rate Tech "sunspot" and "toccante" if I am right:

I love the design and my wife may like them.
I will contact DeltaH Design to see if I get them in Europe.
I started with the "Sample Rate" panels because they are both cheaper and more attractive. I added the "Hybrid" panels because DHDI recommends using both together. The "Hybrid" panels are the "Sample Rate" panels with a 1/2" thick layer of absorptive material and fabric over them. Frankly both work well and I don't hear a big difference between them. Here is the tradeoff - the "Sample Rate" panels are delicate and I had to put them in floater frames for protection. The "Hybrid" panels come in a wooden frame and therefore aren't as delicate, but of course the wood "sculpture" is covered up.
 

Artnet

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That requires a mighty big room!
Thank you for the responding to this. The QRD's are a bit of a journey of discovery for me. I was originally looking at a design frequency of 600hz with a cabinet of 12", largest well depth 10 1/16". excuse the conversions as I work in metric.
These are to start with and give me a seating position 5'7 11/16.
The limitations on this are definitely the space but I can accommodate them at 600hz. If I move to a design frequency of 400hz it gets big in the room, particularly with working from home currently.
It was were my questioning of treatment for other surface was heading and hoping to fly through with some base traps or adsorption? But one cant ignore the science at this point so will do some more math or I will have to live with the compromise.
Curios about "1D slot diffusers which Dennis Foley recommends" will search on the forum.
Thanks again .
 

MTB Vince

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Thank you for the responding to this. The QRD's are a bit of a journey of discovery for me. I was originally looking at a design frequency of 600hz with a cabinet of 12", largest well depth 10 1/16". excuse the conversions as I work in metric.
These are to start with and give me a seating position 5'7 11/16.
The limitations on this are definitely the space but I can accommodate them at 600hz. If I move to a design frequency of 400hz it gets big in the room, particularly with working from home currently.
It was were my questioning of treatment for other surface was heading and hoping to fly through with some base traps or adsorption? But one cant ignore the science at this point so will do some more math or I will have to live with the compromise.
Curios about "1D slot diffusers which Dennis Foley recommends" will search on the forum.
Thanks again .
A few observations about your math along with a few questions @Artnet ? First your minimum distance calculation has a problem. A 600Hz wavelength is 22.5". The best practice minimum diffuser vs sound source/listener distance is 4x the wavelength of the lower cut-off frequency, so 90" or 7.5 ft with your proposed 600Hz cut off. When you calculate these in-room distances, make certain you are adding the diffuser's mounting depth to the measured distance to the boundary it will be mounted on. In your proposed use case, best practice minimum mounting distance requirements along with the 12" mounting depth require 8.5 ft of clearance between the wall you mount it to and either the loudspeakers or listener.

So how large is the listening room and where in the room will you employ the 1D quadratic diffuser(s)? What is the prime number and slot width you intend to use for the diffuser design? Will you use a single large prime, N31 and 2" well width for example to build a single 60" diffuser? Or a modulation of several identical N13 or N17 diffusers? If the latter, you must account for the additional mounting depth of the diffusers which protrude furthest due to the modulation.
 

Artnet

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A few observations about your math along with a few questions @Artnet ?
Apologies for the slow response. Some time ago I purchased the DIY Acoustic Fields package so should have known of Dennis Foley. I have been re reading or should I say reading more thoroughly now his publication.

I was using my own configuration using QRDude software. But again may be encountering information that I need to drill down on to get my math correct. I was looking at 2 designs, a 43 well and a 31 well unit with 1 1/16" interval.

My room dimensions are approx 13' wide x 26' long x 8.6' high or 4m wide by 8m long x 2.76 high. I have some room to play but the room houses Vinyl and books, Upright piano at far end and currently a work desk, and something to sit on.
Going back to Foley's QD13 and QD17 elements may be simpler with 50mm intervals.

Speakers are currently 4.5' of front wall and 4' of sides. Listening position chosen is predominantly near field at 6' but changes obviously when working.

Appreciate your insight and help and wont be cutting timber just yet!
 

MTB Vince

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Apologies for the slow response. Some time ago I purchased the DIY Acoustic Fields package so should have known of Dennis Foley. I have been re reading or should I say reading more thoroughly now his publication.

I was using my own configuration using QRDude software. But again may be encountering information that I need to drill down on to get my math correct. I was looking at 2 designs, a 43 well and a 31 well unit with 1 1/16" interval.

My room dimensions are approx 13' wide x 26' long x 8.6' high or 4m wide by 8m long x 2.76 high. I have some room to play but the room houses Vinyl and books, Upright piano at far end and currently a work desk, and something to sit on.
Going back to Foley's QD13 and QD17 elements may be simpler with 50mm intervals.

Speakers are currently 4.5' of front wall and 4' of sides. Listening position chosen is predominantly near field at 6' but changes obviously when working.

Appreciate your insight and help and wont be cutting timber just yet!
So If I understand the above description, the loudspeakers and nearfield MLP set-up occupy barely half of the one end of the room? Is the 4.5' off the front wall measured to the loudspeaker front baffles where the drivers (typically) are located? How extensive and tall is the record racking?

If I've understood your description of the space correctly, your big QRD based diffusers would all be placed down at the piano and work desk end of the room. The rearmost QRD would be run across most of the back wall, except space in the corners where you would typically employ floor-to-ceiling bass traps. And you could place another QRD on the final 4-5 feet of both rear sidewalls, again adjacent to the corner bass trapping. The long delayed and thoroughly de-correlated return off the diffusers would create a lovely sense of spaciousness at the MLP.

At the front end of the room, floor-to-ceiling corner base traps again for sure with some sort of band limiting applied like wooden slats or a thick plastic membrane so they absorb below 500 Hz and diffuse/return frequencies above that. 4-6" deep broadband absorptive panels along the sidewalls at primary reflection points. A 6" deep ceiling cloud to intercept the primary reflection there. Perhaps some 6-8" deep broadband panels immediately flanking each loudspeaker and on the wall directly behind each speaker as well to address SBIR. If your room response measures somewhat ragged in the upper bass, S(peaker)B(oundary)I(nterference)R(eflection) is the likely culprit. Again assuming I understood your description correctly, That would be a solid start.
 
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Artnet

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where in the room will you employ the 1D quadratic diffuser(s)? What is the prime number and slot width you intend to use for the diffuser design? Will you use a single large prime, N31 and 2" well width for example to build a single 60" diffuser? Or a modulation of several identical N13 or N17 diffusers? If the latter, you must account for the additional mounting depth of the diffusers which protrude furthest due to the modulation.
Well, initially i was thinking front wall and rear wall. The rear wall is compromised by double doors and the piano so was thinking 2 x N11 and 1 N13 up and absorption panel below mostly behind piano.
place another QRD on the final 4-5 feet of both rear sidewalls, again adjacent to the corner bass trapping. The long delayed and thoroughly de-correlated return off the diffusers would create a lovely sense of spaciousness at the MLP.
Loving this suggestion. It may not work out exactly like that due to a window one side (not floor to ceiling) and shelving unit the other. But a good solution to think on and develop given the compromised nature of the rear wall.

On the front wall in a triangulated pattern, N31 in the center slightly elevated from the floor, allowing for an existing artwork above, that will go eventually to be replaced with another N31. Then left and right N19's with deep base absorbers below them (thinking the Foley type) that will be behind the speakers.

Only amps in the center on plinths and all other equipment is being moved to the side, replacing Vinyl storage shelf with lower equipment rack allowing more treatment area on the wall. Current listening in plywood boxes for easy access the rest to another room.

A 6" deep ceiling cloud to intercept the primary reflection there. Perhaps some 6-8" deep broadband panels immediately flanking each loudspeaker and on the wall directly behind each speaker as well to address SBIR. If your room response measures somewhat ragged in the upper bass, S(peaker)B(oundary)I(nterference)R(eflection) is the likely culprit. Again assuming I understood your description correctly, That would be a solid start.

I am safer starting slowly with the 3 QRD's, for front and 2 deep broadband absorptive panels. Then the side and rear walls.
I need to be conscious of other members of the household but usually if it improves the music its okay.
See how far I can go before the ceiling cloud. I will let you know
Very must appreciate the Reflective and absorbing nature of your input thank you.
Allot to get excited about there!
 

Artnet

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Or a modulation of several identical N13 or N17 diffusers?
Just reading about Homogeneous diffusion, discussing the benefits of using multiple identical periods or diffuses as opposed to one large one. ie using 5 x N7 as opposed to 1 x N19.
Hope the use of 3 covers this but may revisit this.
 

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