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Diffusion distances
Posts: 2
December 6, 2017 - 12:20 pm


Hi everyone,
i plan to use some diffusion on the rear wall but have limited space between my listening position and the rear wall,probably about 3 feet.
Which prime number QD would be most suitable,are the QD7 and QD11 considered near field diffusers or is that something entirely different?
Once decided which prime is best could i ask would two of these on the rear wall be adequate for good diffusion?
Any tips or advice appreciated.

Posts: 559
December 7, 2017 - 7:20 am

K, You can use the QD – 11. Start the diffuser at 24″ from the floor and extend across the total rear wall surface.

Posts: 3
June 18, 2018 - 6:49 am


Dennis Foley said
K, You can use the QD – 11. Start the diffuser at 24″ from the floor and extend across the total rear wall surface.Β Β 

HI Dennis, if K only has 3 feet from back wall to listening position, the QD-11 required calculations are 1132/375 = 3ft, but you mentioned to add another 50% (+1.5) totaling 4.5 ft to develop correctly… has your calculations changed? could it be actually possible to have a QD-11 with only 3 feet apart from listening position and do we need to compensate another 9.5″ for the depth of the actual diffuse box? Thank you in advance!

Posts: 559
June 18, 2018 - 7:53 am

C, Yes, it also depends on room width and length.

Posts: 3
June 18, 2018 - 7:56 am


Thank you for the response Dennis, I also have 3 feet from listening position to wall in a small room… I was debating wether to build a QD-7 but after reading this I think I will build a QD-11, and hope it works! :) any further insight or recommendation will be greatly appreciated !

Posts: 559
June 18, 2018 - 8:08 am

C, It will work. Follow up and let us know what you are hearing.

Posts: 3
June 18, 2018 - 8:13 am


Yes sir will do! Thank you!

Posts: 5
November 16, 2018 - 12:42 pm


I have maybe 18 inches behind me in a 140 inches long by 128 inches wide room, listening to Magnapans that are 53 inches out from the front wall….which prime # for diffusion on the front and which prime # for the back wall.

Posts: 559
November 16, 2018 - 1:00 pm

B, Use two dimensional QD-7 for rear wall and QD-13 for front wall. The QD-7 is 4″ deep and the QD-13 is 12″

Posts: 5
November 16, 2018 - 3:23 pm


Hey Dennis when you said 2 dimensional are you meaning running both vertical and horizontal say in a 14.5 by 24 inch rectangles

Posts: 559
November 16, 2018 - 3:42 pm

B, yes. build them 24″ x 24′

Posts: 5
November 18, 2018 - 3:39 pm


Hi Dennis,

I got about 2M listening position to the rear wall can I use the Prime 23 QD diffuser ?

Posts: 5
November 19, 2018 - 7:21 am


got it now Dennis after watching almost all your videos on acoustic diffuser placement, i have finally understood what prime qd difffuser to use… the quarter wavelength rule.. thanks a lot dennis. looking forward in building my first ever p23 diffuser which the plans i bought from your website.

Posts: 5
January 26, 2019 - 5:22 pm


I’m planning to add diffusion also in my room. But I have question.
I’m thinking, what is happening to the frequencies above diffusor frequency range? For example QD-7 diffusion frequency response is 850 Hz. – 3,400 Hz. As I understand frequencies below 850Hz passes through the diffusor. But what is happening with frequencies above 3400Hz? Are there any diffusors that diffuse above 3400HZ?

Posts: 559
January 26, 2019 - 6:23 pm

T, Yes, our mini wood diffusers go to 8 K. Here is link:…..usor-wood/

Posts: 4
February 24, 2020 - 3:27 pm


Hi my back wall is about 2 meters behind my listening position and i would like to ask if i should go with foam or diffusers.

Posts: 559
February 24, 2020 - 6:02 pm

G, What is the room size and usage?

Posts: 4
February 26, 2020 - 6:53 am


Hi Dennis, my room dimensions are length 3.30m , width 2.88m and height 2.68m. My listening position is toughly at 2 meters in front of the back wall. Usage of the room is mostly dialogue editing and mixing for films and sometimes foley recording. I have treated the front wall (much foam in the center, bass traps(2+2 bass traps1m each in the 2 front corners) and the side wall ( mirror trick, foam in refllection points) and i would like to know if now i should go for the ceiling or for the back wall and what material to use. Thanks!

Posts: 559
February 27, 2020 - 10:04 am

G, You do not have enough low-frequency management for your room size and volume. Treating the corners is just a partial solution when the whole wall surface is producing the unwanted pressure issues. You will need the entire front and rear walls along with both sidewalls.

Posts: 4
February 27, 2020 - 11:26 am


the back wall with diffusors or foam ? in the front wall i have placed 8 foams 30x30cm. Behind speakers i have basstraps. Can i send you an picture?

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