Slapback/echo/reverb etc.

Sean

So I'm still on a mission to minimize the slapback/echo/reverb in our church. So I heard of a place not far from here that can supply some sort of "acoustic non woven material".

I went there this morning and chatted to a chap and he showed me a sound booth that they have where he has some of these panels on the back wall. It's 20mm thick (looks a bit foamy/spongey) and when mounted must have a 20mm gap between the panel and the wall. I asked him for the name of this stuff and he said he'll email me the details. It comes in rolls that I would estimate are 1.2 or 1.3 meters wide and priced at around R60 meter.

Something that I don't quite understand is that he says it would probably be better to put a couple of these strips on the side walls, and not the back. The back wall is pretty large, the roof is slanted, so I'm thinking to really have this done properly would take an engineer to use all sorts of software etc. but I'm looking at trying to get rid of the worst of the slapback without going overboard. I would have thought covering most of the back wall would do the trick? Once I hear exactly what this product is I'll post it, but in the meantime, any thoughts?

Here is a poor quality pic of the back wall

vic

Sean, that back wall is the culprit indeed.....I notice a glass window/s on the sides as well.....these will also contribute to bad acoustics. Remember sound waves reflect in almost similar manner as light waves. You can solve or minimize this by curtaining the windows.....Fortunately the floor is carpeted which is fine and the benches being of wood (with people sitting there) won't be a problem. No doubt the back wall should be acoustically enhanced. Carpeting that back wall (or most of it) may be an (cheaper) option ?....

AlanRatcliffe

Yup, back wall. The guy is referring to flutter echo between walls (he's probably more used to listening position with speakers than acoustics from the performer's perspective).

Personally I'd look more at diffusion than reflection. Especially in a church where the lower wall treatments must be able to handle traffic - foams are just too delicate for that kind of application. And while it's difficult to absorb the lower frequencies, it's easier to scatter them.

So... Curved panels with some rigid fibreglass behind to dampen any panel resonances (cheap, easy to make and robust). With the rear wall presenting curved surfaces, very little of the sound is reflected directly back at the stage. Polycylindrical diffusers, if you want to Google them (and yes, many sites will tell you that QRD's - Quadratic Residue Diffusers are better, but they are incredibly complex to design and very difficult to build).

If you want absorbers too, then a few absorption panels using rigid fibreglass or rockwool, mounted higher up (I'd probably put them across the wall/ceiling boundaries to do more bass trapping). Area for area, fibreglass or rockwool is much better at absorbing a broad band of frequencies than sculpted foams anyway ...and far cheaper if you DIY.

Slat absorbers are great too - absorbing a wide band of frequencies, applying some Heimholz trapping and diffusion at the same time and they can look great if properly made. Downside is once again, truly effective ones are more complex to design and building them is more difficult.

Sean

Thanks Vic and Alan.

I'm checking out those polycylindrical diffusers now Alan, thanks