Sound in a large school hall

[sleah]

I'm specc'ing out the AV for our new school build and am currently looking at sound.

 

One of the rooms is a large 'conference' hall, 21m x 31m x 6m(approx)high. Simple box, no fixed stage, alcoves etc. There will be retractable seating along one of the short walls which come out just under half way along the room.

Floor seating will be used for the rest of the space when used for assemblies etc. Total seating capacity approx. 950.

One long wall is windows, hopefully there will be curtains.... The other 3 walls are hard surface, likely painted block work. False ceiling with lighting grid below.

 

I need a sound system that is flexible so it will cater for when all seating is in use, also they occasionally 'turn' the hall sideways (so just floor seating). There will also be occasions when the room will be set with round tables for meals or other more informal functions.

There's also talk of using a central curtain to split the hall and just use the retractable seating (also means an additional projector/screen - that's another story!).

 

The obvious layout for speakers is to use 6 identical speakers, 2 torwards the front, 2 middle, 2 towards the back, that can be configured by a speaker control system.

 

So far so good.... my question now is if mounting the speakers from lighting grid will work - not physically but in terms of sound.

I think it would be fine for assemblies and lectures etc which tends to be YouTube clips and squarks from PowerPoint. There will be a mic on the lecturn and potentially handheld/headset mics for speakers too.

My feeling is that for theatrical type use, having speakers above wouldn't work so well. Even shutting off the one's above the acting space, I wonder if GBF would be impaired compared to more traditional speakers pointing out to the audience at a lower level? Using a portable system (as we currently do and works very well) wouldn't be a big deal if overhead speakers won't sound right.

 

I was thinking the 4 furthest from the retractable seating could be wall mounted, but there are issues of where they could go. Just the front 2 wall mount might be do-able.

 

I'd value any thougths and opinions please :)

 

[Lamplighter]

Simon

 

Speakers flown from the grid work really well. They need to be angled down into the audience to minimize reflections. The front pair need to be a few feet forward of the podium to give a reasonable GBF and ideally the other pairs suitably delayed. It should be relatively easy to achieve even coverage. The spacing side to side, I find 25%--50%--25% works well. It has the advantage that for the majority of the audience, the perceived direction of arrival is correct. It works well for theatrical productions. You would need to be able to rotate the speakers to cater for your alternative seating plan or for theatre in the round

Brian

[Simon Lewis]

The one thing I'd suggest to make the loudspeakers work well is to get around 40% of the painted block walls covered with 2" rockwool slab covered in suitable hessian type material. Even better if it can be placed in a shallow wooden frame and the absorption spaced from the wall by 2".

 

This will increase speech intelligibility and make any loudspeaker used sound much, much better ;-) It's also relatively cheap at this stage of the planning....

[J Pearce]

Though in a school environment consider the placing of these versus the access of those for whom poking things through the hessian and posting things behind the 2" spacing will be far more entertaining than listening to another assembly.

 

A lot of new schools seem to be hanging such frames vertically in the roofspace. This reduces overall RT60 and floor/ceiling flutter reflections, but doesn't affect side wall reflections (which may or may not be desired for early reflections supporting acoustic speech and music).

[Brian]

The one thing I'd suggest to make the loudspeakers work well is to get around 40% of the painted block walls covered with 2" rockwool slab covered in suitable hessian type material.

 

If you don't think the builders are up to a decent finish I can recommend the range of panels from Soundsorba...

 

https://www.nevilllong.co.uk/products/results/taxonomy:259-soundsorba

[sandall]

One venue I work at has a similar arrangement, though with an extra pair of speakers each side of a proscenium arch, which does give GBF problems for conferences & meetings, where the lectern & top table are invariably set on rostra on the floor in front of the stage. The front, back, side or all-round delays & levels are set by an A&H LD9. This is a Victorian hall, with a high hammer-beam roof, so wall-mounting was the only option, but it gave the advantage that speakers can be rotated by stuffing a long broom handle into the bottom pole-mount socket. Unfortunately this tends to mean they don't get re-pointed after a non-standard event.

 

In your case, as Lamplighter says, grid mounting should work fine, but unless access is easy, & re-pointing becomes part of the discipline of the venue, you might be better off with pairs of back-back speakers, at the cost of more cabling & amp channels.

 

Some acoustic treatment on at least the end wall is essential. Even a few 8' x 4' melamine foam panels can make a huge difference - when the new management, fresh from English Heritage, decided that (like the FoH lighting grid) they didn't look Victorian & had them taken down, it also made a huge difference .

[Junior8]

Well its the standard school hall sans stage isn't it? Get them to strike the word 'hopefully' from in front of curtains. If the space wasn't so hopelessly designed as it is I'd have suggested a perimeter drapes track all round forward of the retractable seats but given the number of exits that isn't possible. These box shaped spaces in school are frequently acoustic nightmares and the other responses are absolutely right. You need to get some acoustic damping on the walls and if it was me doing the job I'd get the floor finished with industrial carpet too.

[Bryson]

We get this a lot. My boss calls them the "Multi-Useless Space".

 

What we have had success with in these type of rooms is the steerable array type speakers to try and keep the vertical under control. If your budget can stand it, they can be re-steered on a preset basis by some kind of controller. (We do Crestron a lot, but many other choices are available.)

[kerry davies]

No expert me and use of an acoustic consultant seems sensible but if you are using the hall lengthways AND sideways then surely any fixed speakers are more or less ruled out? Portable PA has very evident disadvantages in a school environment but I reckon using the hall in two or three directions make boxes on sticks just about your only option without significant spending.

 

Oh and from personal school hall experience with one glass wall like this .... no curtains, forget the PA, tell them to shout.

[bruce]

It may be that the initial cost of installing an extra pair of speakers outweighs the ongoing costs of continually re-rigging.

[Simon Lewis]

Though in a school environment consider the placing of these versus the access of those for whom poking things through the hessian and posting things behind the 2" spacing will be far more entertaining than listening to another assembly.

A lot of new schools seem to be hanging such frames vertically in the roofspace. This reduces overall RT60 and floor/ceiling flutter reflections, but doesn't affect side wall reflections (which may or may not be desired for early reflections supporting acoustic speech and music).

 

Pros and cons... using "clouds" etc. can be quite effective, but can get in the way of heating ducts, lighting, cable runs etc. plus the painted walls remain nicely reflective, as "the acoustic treatment has already been applied". I've come across rooms where Soundsorber panels have been put on the ceiling and killed the floor to ceiling issues but simply emphasised the wall to wall stuff. Ideally something of both could be used, but keep the wall panels a little smaller, out of reach and less depth so that they blend in and also breakup up the side wall reflections a little.