QRD and other diffusers - how close is too close?

[BigFry]

I'm looking for some perspective and your personal experience, so please enlighten me if you can!

In my limited practical experience, I haven't noticed any issues with being too close to QRD's and I'm curious. I have read that weird lobing issues can occur at close proximity to QRDs, but I have spent plenty of time sitting at the back of a control room in front (inside a meter) of a QRD, I've recorded drum kits directly in front also and never noticed anything at all, no frequencies sticking out.
Have others noticed weird frequency response in close proximity to a diffusor? Do poly diffusors theoretically have the same issues?
I know theoretically it's a no-go in a smaller room, but in practicality I haven't perceived a problem.

Thanks!

[BigFry]

This is an example of something we've done quite regularly in the past.

drooms.jpg

[Paulus87]

Well the rule of thumb is you should be away from the diffuser at a distance of at least 3x the wavelength of the design frequency of the diffuser.

But, that's really only for a critical listening environment. In a live room or theatre or hi fi room diffusers can be used to add some desirable enhancement to the sound source.

Also, in highly damped rooms sound travels slower in fibres, so you can theoretically get away with being closer than the above rule.

That's my understanding,
Paul

[ACBRON]

I've been researching QRD's lately too, like everything else with acoustics its a rabbit hole of information that easily overwhelms a mere muso like myself. There's a calculator via this page https://www.subwoofer-builder.com/qrdude.htm

You'll find one of its outputs is a "minimum distance to seating position" if it is accurate then you can make some reasonably decent ranged (broadband) diffusers and not have to be 5m away.
if anyone else can shed light on the accuracy of this calculator's seating distance and what else you need to consider, would be very helpful to everyone (total room volume? physical size and placement?).

[BigFry]

Thanks for the replies guys. I do appreciate the research, but do hope to hear from those with practical experience of spending time close to them. I know there is a theoretical issue, but I am not convinced of how much it actually causes problems in a real world scenario.