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Using diffusers in my home mixing / recording studio
Johannesburg, South Africa
Posts: 5
May 30, 2017 - 11:39 am


Hi all

A friend of mine and I recently built a pair of QRD-23 diffusers based on plans I bought off Acoustic Fields.

I have been experimenting with placing them in my room. I am a musician with a home studio so I need them for two purposes – mixing and recording. I have put them on wheels which means I can move them around. So far I have placed them behind my speakers, and have also used them to try improve the sound of my acoustic guitar recordings. I must say placing them behind my speakers has been a real revelation in terms of the positive impact on the sound coming from the speakers – a really big improvement in openness and phase coherence. They really help to bring out the best from my speakers.

However, I have three questions.

1: Sweet spot (a)

How far behind my speakers should I place the diffusers to get the best response from them? So far I have them quite close, about 5 – 8 inches from the back of the speakers. I have a pair of Genelec 5031’s which have a very nice overall frequency curve.

2: Sweet spot (b)

When in recording mode, how far in front of the diffusers should I place the microphone? My logic is one doesn’t want to place the mic too close because one wants it to “hear” an even response from each of the “channels” in the QRD-23, and not just from the one or two that are right behind it (if too close). Also, what arrangement of the two diffusers would work best? I have experimented with them being in a flat line, and also in a V-formation. So far the V-formation seems to work a little better.

3: Harshness

I have noticed a very subtle harshness from my speakers (and I mean real subtle, but I am nit picking) when I placed the diffusers behind them. I was trying to figure out why. But when I reread the info associated with the QRD 23 I noticed the following: “A fully built QRD – 23 diffuses energy starting at 185 Hz. and goes all the way through 3,450 Hz”. This makes sense to me because I am noticing the harshness above the normally problematic 2k range. So my question, does it make sense that I might be getting problems in the 4k range that the diffusers are not dealing with? And can I do anything with the QRD-23’s themselves to deal with this problem?

Thanks in advance for help with the above.

Nietzsche: without music life would be a mistake

Posts: 563
June 2, 2017 - 3:57 pm

Hi Owl, You should place them between your speakers on the front wall. When recording, start at 4′ distance from mic to diffuser and adjust backwards from that point. You are hearing more of your speaker sound. Most are weak in the 4 K area.

Johannesburg, South Africa
Posts: 5
June 5, 2017 - 12:39 pm


Hi Dennis

Thanks for the advice. I will be trying out the placements for recording in the next few days so am glad for the assistance.

In terms of placing the diffusers behind the speakers. Is there an ideal distance?

I am intrigued that you said BETWEEN the speakers and not directly BEHIND them. I had them behind the speakers but will try your suggest there as well.

Thanks again

Nietzsche: without music life would be a mistake

Posts: 563
June 12, 2017 - 10:17 am

Hi O, Place them against the front wall between the speakers.

Posts: 4
June 15, 2017 - 8:56 am


I agree with Dennis’ assessment about your speakers. I’ve built and deployed serveral dozen diffusers in the past 20 years, and one thing that everyone has noticed once the diffusers are deployed, is that you can finally start *hearing* your speakers. Without so many *direct* reflections and comb filtering messing with your ability to hear the source sound produced by the speakers…well, you start to hear what your speakers really are doing…for better or worse. LOL

In dedicated listening rooms, just a few diffusers makes the music so much more engaging. I imagine that will come across in your recordings as well.

Johannesburg, South Africa
Posts: 5
June 30, 2017 - 5:35 am


Yeah, thanks. When I initially deployed the diffusers I really noticed the difference (now I am used to it). When my sound engineer friend came by and I played him music without and with the diffusers in place his jaw dropped. The diffusers are phenomenal in how they help to deal with resonances and create more balanced frequencies.

In terms of the upper mid buzz I heard… I have pretty high-end genelecs (8351’s) so I am surprised that they would have a problem in the upper mids. I would say, though, that I don’t notice it as much any more, either cos I am used to it or because I was just hyper-sensitive at the time.

One more question. I now want to build more diffusers to go behind me as my back is against a glass sliding door. Even though I have acoustic curtain in front of the glass it still does horrible things to the sound. Is it ok to have 2 banks of diffusers facing each other?

Nietzsche: without music life would be a mistake

Posts: 563
June 30, 2017 - 8:37 am

Hi Owl, Diffusion is an amazing technology. You have just shown that to be true once again. You can use opposing walls with diffusion. just watch your distances.

Johannesburg, South Africa
Posts: 5
June 30, 2017 - 1:56 pm


Thanks Dennis. Yes, you are right, this is really amazing technology! And thanks for sharing with us.

Distances? Is there a minimum distance?

Nietzsche: without music life would be a mistake

Posts: 563
June 30, 2017 - 2:17 pm

Hi Owl, Yes, you should have 8′ between diffuser and listening position for P-17 and P-23. You can get away with 6′ for P-11 and P-13.

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