School sound upgrade

[Johnno]

I'm required to upgrade the sound system in our school hall (50ft wide x 60ft in front of stage x 18ft ceiling, all reflective surfaces, around 200 seats, no balcony). Objective is better speech/vocals. We don't need to amplify acoustic instruments. Use is ordinary school stuff and lightweight musical theatre. Budget low £K.

 

Using simple geometry I've calculated that a single speaker centrally mounted on a roof truss 16ft up and 10ft in front of the stage would give coverage desired if it had 110Hx55V dispersion. Alternatively, two speakers with 110x45 disp. one in the same position and t'other 30ft in front of the stage would do similar. I've found possible speakers in EAW's MKxx26 range and TOA's HX-5 (that articulated one). If any side/front-fills are needed this would be determined in use. A sub-woofer is an option.

 

Does this sound reasonable to you? If so, what electronics would you be looking at to drive it all?

 

Oh, and a Merry Christmas to you all :biggrin:

[stillgoingstrong]

Hi,

I've recently seen a pair of HX-5s flown in a school hall about the same width and height as yours, with the subs flown above them.

 

The tops were flown standard left and right configuration. The tops were fantastic but the subs were pitiful due to the lack of surfaces around it and they didn't seem to push much air.

They've ended up hiring extra subs for their noisy charity events with bands.

We also have 2 HX-5s in our hire stock and are fantastic for speech based applications. We don't tend to use them much for full bands as we have other speakers to do that job.

If you want a sub as well, I would avoid using the HX-5s and getting a matching top and subs system. (It may be that floor mounted subs (or even a pair a side) perform much better than being flown)

 

Regarding the other bits. If you're looking for 16 channels or smaller, then I would go for the Allen and Heath Mixwizard. Built in FX and 6 auxes with 2 mid swept EQ bands its brilliant bang for your buck. I saw the new Soundcraft FX16 at Plasa and wasn't impressed at all. We have 3 original FX16's in our hire fleet and they are good, but we wouldn't replace with the new model.

If you're looking for more than 16 channels then the GB4 is a fantastic 24 channel board. Once over 24 channels the desk will depend on what you are wanting all the channels for and the extra functions you require.

 

I would recommend having a graphic EQ for the main speakers, and try and avoid the cheaper digital graphics unless they have a lock-out feature to stop the kids messing with it.

 

As you are in a school, then I'd have to recommend Shure SM58s and 57s for mics, and JTS radio mics are good for the budget range you are talking about. Sennheiser e845 are pretty durable as well.

 

I have tended to find that durability (and cost to replace stolen, 'missing', or broken equipment) ends up being the main deciding factor as they can see the prices before they go ahead. Unfortunately they can't hear the difference in end result.

 

Whoever I choose to install I would recommend you ask for other 'local' installs they have done to see their install quality, and talk to the technicians who use it as they'll know if they did a good job/cut corners etc. As usual, the cheaper quotes tend to also come with lower install quality which doens't appear until after the job I complete.

 

I know it sounds like a rant rather than advice but I've come across too many bodged up school installs just so the school could save some money.

 

I hope that helps, and happy christmas to you to ;)

 

P.S. Is the roof truss already in place or is that to be installed as part of the install?

[Bobbsy]

I won't get into specific brands and recommendations (all my catalogues and spec sheets are in packing cases right now waiting for me to build some shelves!) but one initial comment would be: if you use two speakers for coverage, do NOT put them in two different places. There will be an effective 20 millisecond delay between the two speakers which will result in making your sound hollow and muddy rather than improving intelligibility. Remember that published coverage angles do not mean there is no sound outside the lines. The coverage varies quite a lot with frequency plus there are plenty of reflections.

 

If you need to use two speakers (and looking at your angles I think it likely) instead consider a centre cluster, i.e. both speakers in the same position (near the stage) angled to each cover half the room.

 

As for electronics, to a large extent this depends on what you have already. However, ideally I wouldn't be placing the speakers 10 feet in front of the stage; I'd rather have them nearer the tab line. However, I suspect you reason for this position is the location of an existing truss and, if so, something you might want to consider is a delay on the speakers so the direct sound from performers arrives a few milliseconds before the sound from the speaker cluster. As you dial in the delay (start at around 10 milliseconds and work up from there), you'll be amazed how the sound seems to suddenly become "right" when the Haas/Precedence effect kicks in.

 

Bob

[Johnno]

Thanks for the suggestions, I think I need to be clearer about the hall's layout.

 

When I said "truss" I meant the thing which holds up the roof, not a lighting truss. If you look up at our ceiling you see five "things" spanning the hall's width to hold up the roof. These are masonry constructs rather than steel girders, but I call them trusses. There may be a proper architectural term for them but I don't know it. To me they are simply five small walls that slope to a maximum of six feet deep in the centre. They are spaced about 10ft apart lengthwise down the hall. Which is probably bad news for acoustics as their parallel surfaces probably resonate at about 50Hz (half wavelength about 10ft).

 

I can't put anything above the proscenium as there is a dirty great bit of wood sticking out at an angle above the opening, presumably to help reflect sound down to the audience.

 

I doubt if management will let me attach anything to the ceiling itself for fear of it containing asbestos: it shows up everywhere in schools built in the 60s and we try not to disturb it. So I can only use either the proscenium walls, the auditorium walls, or these roof "trusses", and if I use anything other than the prosc. wall then 10ft is the closest I can get to the stage due to full height windows down one side of the auditorium, and the prosc. walls are recessed for most of their height with what were once the loudspeaker enclosures. All this makes the roof trusses look attractive!

 

I thought if I used two loudspeakers angled steeply downwards - 53 degrees calculated - down the centre line I would be ok if I added appropriate delay to them both. Is that wrong? Surely there would be less mutual interference than from speakers mounted on the walls which will almost certainly spray onto the opposite walls, and the undamped rear wall. I'll look into an angled centre cluster.

[Bobbsy]

I thought if I used two loudspeakers angled steeply downwards - 53 degrees calculated - down the centre line I would be ok if I added appropriate delay to them both. Is that wrong? Surely there would be less mutual interference than from speakers mounted on the walls which will almost certainly spray onto the opposite walls, and the undamped rear wall. I'll look into an angled centre cluster.

 

In a perfect world this might be the case, but in reality the dispersion specs on speakers are only very roughly accurate. As I mentioned, the true coverage varies greatly with the frequency, HF being much more directional than the low end. Add to this the inevitable reflections (inevitable because the coverage isn't perfectly accurate) and, even with delays, your scheme will result in a "muddier", less intelligible sound than two speakers at the same time origin.

 

Bob

[Trunker]

I won't get into specific brands and recommendations (all my catalogues and spec sheets are in packing cases right now waiting for me to build some shelves!) but one initial comment would be: if you use two speakers for coverage, do NOT put them in two different places. There will be an effective 20 millisecond delay between the two speakers which will result in making your sound hollow and muddy rather than improving intelligibility. Remember that published coverage angles do not mean there is no sound outside the lines. The coverage varies quite a lot with frequency plus there are plenty of reflections.

 

If you need to use two speakers (and looking at your angles I think it likely) instead consider a centre cluster, i.e. both speakers in the same position (near the stage) angled to each cover half the room.

 

As for electronics, to a large extent this depends on what you have already. However, ideally I wouldn't be placing the speakers 10 feet in front of the stage; I'd rather have them nearer the tab line. However, I suspect you reason for this position is the location of an existing truss and, if so, something you might want to consider is a delay on the speakers so the direct sound from performers arrives a few milliseconds before the sound from the speaker cluster. As you dial in the delay (start at around 10 milliseconds and work up from there), you'll be amazed how the sound seems to suddenly become "right" when the Haas/Precedence effect kicks in.

 

Bob

 

 

In this case if the hall is wide ( 50ft seems wide to me) would it help to have smaller (in-fill) speakers to cover the problems you mentioned? And regain some of the stereo image lost? Just my 2p

[Johnno]

It isn't stereo, Trunker. Would you like a refund of your 2p? :biggrin:

[Trunker]

It isn't stereo, Trunker. Would you like a refund of your 2p? :biggrin:

 

Sorry, what I meant to say was that if the hall is wide, which it is, and the pa was to run in stereo and run the speakers from either side of the stage i.e. left and right, most of the audience would not get the stereo image and also get the delay talked about earlier. I and many other people have used 'in-fill' speakers to help reduce the problem for the listener, delay wise and stereo wise.

 

Anyone agree or not!?

[Ben Langfeld]

But Johnno doesn't want stereo, nor does he want L&R clusters!

[benscrawford]

another thing you could consider, seeing as you are "upgrading": To "improve", or to use a better word - remove, some of the reflections of all the reflective surfaces, could you maybe consider dampening/blocking these surfaces with something, could be something as basic (but does the job very nicely) as curtains/drapes on the walls, or padded seating? this will help to improve the overall sound of your PA in my opinion

[Johnno]

Ben (I) is right in saying that I don't want stereo. L&R clusters? I'm not well-up on audio: is a 50x60ft school hall with 15 rows of seats big enough to need them?

 

Ben (II): an interesting suggestion that I hadn't considered. We're up for some seriously expensive rebuilding in two years time and I will put forward your idea as a possiblility. Thanks for that.

[Bobbsy]

I would normally frown on "me too" posts but, knowing a bit about the original query, I would say that if improving the room acoustics is an option, that would probably be a better way to go than any sort of rushed changes to the number or configuration of speakers.

 

Bob

[Johnno]

The changes I want to make to our speakers do need making. We have a pair of 110W Carlsbro floor/pole-mounting cabs screwed flat to the proscenium wall 8ft up, pointing at the rear wall not the audience and giving us some gain-before-feedback problems. I don't know how much the school was charged for this masterpiece of installation- 'though I gather it was quite a bit -but my predecessor wasn't happy with it either, so rushed it ain't! All I'm proposing to do now is spend some donated money to fit one or two speakers that would be better for speech (our main use) and point them at the audience, and propose to the Head that we get a proper consultant to do a proper job in a couple of years time when we're scheduled for a rebuild of up to 50% of the whole school.

[benscrawford]

we're scheduled for a rebuild of up to 50% of the whole school.

 

do consider how long the rebuild will take, will the hall take priority? etc. is it worth proposing to your head that seeing as you are revamping your hall, soundwise, in the very near future, a larger project could be undertaken say now, rather than 2 years down the line? thus saving time to focus on other areas of the build at a later date