Frustrated Sound Tech in a school

[cobra427]

Hi..

 

I'm new to posting on here - but have been reading the posts for some time.

 

I'm getting frustrated with our school hall.

 

The school hall is circular - with a domed roof. Empty - the sound echoes around (infact if you whisper at one side of the hall you'll be heard at the other clear as day - stand under the centre dome and the sound wrap-round is the best thing to mess with your head you'll ever get) - hall full - and the echo flattens off, but unless I mic every person up with radio mics I dont seem to get much progress with our productions as far as picking up the characters that only have to say 1/2 lines and therefore dont qualify for a radio mic - or the groups that have to sing and dance.

 

This year I've invested in a number of AT pro 45 mics to hang over the stage. but still I cant get an acceptable level of sound before I get feedback (yes they are roughly the required distance apart and away from the PA kit).

 

My problem seems to be that there are kids tend not to speak or sing up (or cant sing and dance at the same time)- and no-matter how much they are coached, trained, yelled at - in the end I have to ramp up the mic gain just to get them heard in performances or above the band - and.... screeeeeech.....

 

The band have been asked to not play as loud in the past, but the head of music doesn't seem to see what the issue is.

 

Like I've said - this year we bought pro 45's but in some cases I've relied on the use of both a mix of overhead and the close proximity radio mics to pick up the really quiet kids. But I still get moaned at for the quality of sound...

 

Anyone got ideas?

I know I'm opening myself up for a long list of critisism - I feel I do my best though..

[Just Some Bloke]

What do you have on the walls? It sounds to me like they need deadening. Some form of thick curtaining is usually best. If you're currently hiring mics, maybe the money could be spent on buying cheap but thick curtaining to cover the walls. You never know, it may do more good!

[mutley]

As well as looking at sound deadening, which will certainly help, look at the positioning and angles of your speakers.

When I started working at a hotel in Lanzarote, the speakers has been placed aesthetically instead of accoustically! Being a wide dome-shaped marquee-material roof (think Stewie Griffin's head shape!) the speakers were actually projecting half of the sound upwards to the roof, for it to bounce off and cause an echo that was so bad you couldn't even tell what the compere was saying!

 

By simply putting the mid cabs 4ft lower (it wasn't possible to hang them), it cut the echo by a guestimated 30-40%. Originally, they had been mounted on top of the sub cabs, which were orientated vertically on top of a 3ft wall!

 

Look at the speaker dispersion angle to work out where your sound is going, and in that sort of venue try to point it at the audience's chest. (If you point at their head, more sound will go over them to bounce off the walls). [This may not fit in with everybody's idea of a perfect arrangement, but as far as I'm concerned, the audience being able to hear the dialogue is the most important factor!]

 

If your sound cannot bounce off the walls, you can get a lot more volume.

 

I've also found that shy kids tend to talk downwards towards the floor, so maybe try some rifle mics or pressure zone mics mounted on the floor at the front of the stage. (If using PZMs, try to have at least 1ft of clear stage all the way round them, don't mount them right on the edge)

 

You could also try a feedback destroyer to take out the offending frequencies, but this can cause a 'flat' or 'hollow' sound if not set up properly.

[Simon Lewis]

I know I'm opening myself up for a long list of critisism - I feel I do my best though..

 

Not at all.... you have some serious problems, and you need a combination of acoustic, electroacoustic and political solutions.

 

1) Treat the walls and dome, if at all possible, to reduce the strong, late delayed reflections.

2) If you cannot do this (cost, access, aesthetics etc.) then try and stop sound getting to those focusing surfaces. Either use drapes as a barrier around and above the stage, and make sure that speakers are above the listeners pointing down towards them.

3) Decrease the source to mic distance, use radios and headset mics where possible.

4) Reduce the loudspeaker t listener distance

5) Get the talkers to project

6) reduce the level of other noise sources

7) Use your wisdom to get other stakeholders (music teachers etc.) on side. Cite complaints and give a rational explanation as to why they occur.

8) Mix for intelligibility (reduce low frequency, masking frequencies, control music level and increase vocal levels where possible

 

We have a space with a very similar layout, but on a larger scale. The first time it was used for serious drama to a paying audience, the sound element was somewhat neglected and nothing could be understood. When we got involved, we made sure that each section of the audience was close to a loudspeaker, that an induction loop was fitted for those with hearing loss and that all actors had discrete headset mics. The space above the stage was covered over to stop sound reaching the dome, and drapes were used around the edge of the space to reduce reflections and focusing.

 

Good luck!

 

Simon

[lostinvegas]

I work at a live venue with a dome in the roof and several other parabolic reflectors. The only way to solve the acoustic problems for us was to spray the surfaces with a special type of paper paint which absorbs most of the sound and prevents reflections.

 

Its made a massive difference.

 

I worked in Schools for many years so know the restaints of budgets. In my experience most music teachers do not understand the need for acoustic treatments and think "buying more gear" will solve the problem.

 

Anything you can do to absorb some of the sound will help. Treatments are the only things that will make a big difference, speaker positioning etc.. will help but without some treatments your always going to get those nasty reflections.

 

You seem to say it yourself that having bodies in the hall makes the biggest difference? they are preventing some of the reflections between the dome and the floor so the next step is to treat the dome itself and the area around the stage.

 

I hope this helps you.

 

Chris

[cobra427]

The hall... Bain of my life... whatever you wanna call it

 

Circular (as said) with 4 large openings in it - one being the stage - the other three are sliding partitions - one of which is usually open to allow extra room in the main hall (called the hall extension).

 

The walls are "artexed" - the main dome/roof is wood - with a 10ft diameter perspex centre dome in the middle. There are 3 floor to ceiling windows which are covered with drapes.

 

The "production PA" speakers are not fixed - I have to lug them out each time - the fronts are now on top-hat stands, they are usually lined up with the front row of seats and angled to face towards the hall extension. The rear set are on desks (for now) and face into the "hall extension" (those were added a few years ago when we had complaints of not being able to hear properly from those sat right at the back of the extension.)

 

We have a 100v system that is used normally during assemblies - that has 6 speakers mounted around the hall - this year I totally disabled the system to make sure that there could be no possibility of interference from that - short of removing those speakers as well, I'm not too sure what else I can do. All they do at the mo is to break up the wall surface but not enough I fear.

 

Sound deadening - The hall is considered the main focal point of the building (and as is the chapel that's hidden by one of the sets of floor to ceiling sliding doors when school is not "open" normally) So I'm not too sure that the head will go for hanging drapes all the way around.

 

I have been told that it was suggested years ago, something be stretched in the dome, above the lighting rig to kill the echo. But "the lovely wood roof" will be hidden - so that idea was kicked into touch....

 

The main stage was extended into the hall, by about 15ft, a couple of years before I started here.

 

The company that sold us the Pro 45's, came in and was shocked to "experience" the empty hall. They thought it would be a "bog-standard school hall" and had to go away to re-think their options and instead came up with the pro 45's.

 

As far as the Pro45's go, they are good, but may need gating in future to stop them picking up the noise from the wings, or, should we run another set up like this years production (bugsy malone) the band right at the back of the main stage. They just didnt give me enough pick up of the quieter kids - but the ones who'd listened to "advice" they were great.

 

I'd love to go out and buy a ton of radio mics - but I'm wondering about the impending frequency selloff/changes and licensing. Oh the small fact that I've only got 32ch on my desk..... and we had a cast of 50 (which is the norm).

[MarkPAman]

The only way to solve the acoustic problems for us was to spray the surfaces with a special type of paper paint which absorbs most of the sound and prevents reflections.

 

Its made a massive difference.

 

Now that sounds like a very useful product.

 

Do you have any details please?

[Brian]

Not sure if it's the same stuff but take a look at http://oscar-acoustics.co.uk/Sonasprayfc.html

 

I've even got a quote somewhere.

[Simon Lewis]

Now that sounds like a very useful product.

 

Needs to be applied to some depth for best results, and if used on a solid surface will not give as good absorption at lower frequencies (as would be expected). If the substrate can be made a diaphragmatic absorber (thin panelling etc.) then much better results in the 125Hz and 250Hz octave bands can be achieved.

 

Of course, not everyone wants a 20mm thick layer of regurgitated, recycled newspaper applied to "the lovely wood roof"

[lostinvegas]

That is the stuff. They use it at The Robin 2 in Bilston and we use it at the Assembly in Leamington. Its not cheap and we have used acoustic pannels in some areas to save money. I think there are some pictures on our website www.leamingtonassembly.com if not I can try and dig some out as it actually does not look too bad.

 

I cannot take credit for it myself Alan Caves who is a good friend has worked with me on several projects. He is an expert in acoustics, it might be worth you getting him in to have a look as he might have some better ideas. We have done loads of work in schools before, if you PM me I can send you his details. His CV reads like a whos who of the music industry.

 

Chris

[soundgeek]

Hi There

 

I work often in a similar building, Worth Abbey. This is different because no band stuff happens there - just speaking normally. BUT I do have a solution. If you try using lots of different speakers at a lower volume around the room you can reduce the feedback loop and you should be able to get more level. We are about to impliment it, but I have used it elsewhere and it works!

 

Oli

[Just Some Bloke]

Yes, if you can't improve the walls and ceiling then you need to make sure the sound doesn't reach them. As has been said by others, get your speakers above the audience and pointed down at them. This will stop the sound hitting the ceiling (or dome). Of course, if you've got hard floors then you need to avoid getting the same problem from the floor! Carpet would be nice (school hall - unlikely I know!) but play with the angle they're pointing so they're hitting below the hairline but above the legs. Then you need to stop the sound hitting the walls, so you need to get the volume down into each speaker and that's where having more comes in. The more speakers you have, the more directional each one can be. If you have 200 people in the audience and 2 speakers, each one is addressing 100 people, but with 4 speakers each one is only covering 50 people and 8 speakers gets that down to 25 (hence the 100v line system for assemblies). With fewer people to cover, the volume coming from each can be lower meaning the sound is much less likely to reach the walls - just the audience.

 

Ideally you'd give all the cast a radiomic and all the audience in-ear monitors but then if you're going to do that you might as well just video their performance and give everyone a DVD to watch at home! :** laughs out loud **:

[cobra427]

Having more speakers around the hall walls could be a solution - if we could contain the audience just to the hall itself.

 

However a lot of the big functions we run (production, open/awards evenings etc. where we get upwards of 400+) we have to use the two extensions (in which ever combination fits purpose - either pointing towards the chapel or stage) and this would need speakers in those areas as well we've already discovered by the moans and groans of the audience.

 

We are due a BSF refurb shortly - I was hoping that something would get done then, but I've spoken to a number of the potential consultants/contractors that have been into school to look around when they were putting together tenders.... They all seem to be a bit hesitent about wanting to tackle the hall.

 

In the mean time... Thank you all for your input and words of wisdom, advice and understanding.....

 

No-doubt I'll be back having a moan later on this topic

[Gareth Owen]

You didn't mention what make and model your main speakers are?

 

Some brands are renown for good pattern control (the sound goes where you point it, not out the sides or back) where as some are not.

 

You may want to rent a constant direcetivity box in for a couple of shows - I'm thinking something like a d&b C6 here - and give that a try.

 

Less sound bouncing off the walls equals less reflections equals more gain before feedback etc etc

[Stan Hope-Streeter]

<br />The hall is considered the main focal point of the building (and as is the chapel that's hidden by one of the sets of floor to ceiling sliding doors when school is not "open" normally) So I'm not too sure that the head will go for hanging drapes all the way around. <br /><br />I have been told that it was suggested years ago, something be stretched in the dome, above the lighting rig to kill the echo. But "the lovely wood roof" will be hidden - so that idea was kicked into touch....<br />

 

Unfortunately, the people who run this school can't have it both ways. They have a building designed for aesthetic appearance, not sound reproduction.

As things stand, the two requirements are incompatible.

One would have expected people qualified to at least degree level (teachers are) would have enough sense to understand this.

If they want intelligible sound, they need to treat the room's acoustics, which will involve altering its appearance. Alternatively they need to accept the limitations, of the room design, on the type of events that the room can be used for.

In either case, the solution is political rather than technical.