Acoustic Shield

[sirrus]

Yes, I know I screwed up the title ;) Moderation: Fixed now!

 

 

From the artistic director himself: \"I\'d like to create an acoustic shield to control band sound, a sort of penned in area with good monitoring - any good ideas?\" ... So, any good ideas? :P

 

I should also add, this is for a school (but with not an overly tight budget, if you know what I mean) and not permanent e.t.c. and also that the space is roughly 4 to 5 meters by about 1 to 2 meters.

 

 

Also, If I wanted to suspend mic\'s from lighting truss / scaff to prove ambient amplification to a general area, what mic\'s are good? I have done it before but cannot remember for the life of me which mics I used :** laughs out loud **:

 

 

Cheers BR :blink:

[Chris Adam]

You can buy acoustic baffle panels from a million and one places. I've used the ones from studiospares before as they were pretty cheap and did the trick.

If it's a one off, I'd just rent them from your local hire company. Theatre set people often have them too, but broadcast guys are your way to go on this one.

As for the mics, we'd need to know what you were miking up. There's loads of ways to mic a general area, but it all depends on the source.

[Simon Lewis]

"I'd like to create an acoustic shield to control band sound, a sort of penned in area with good monitoring - any good ideas?"

 

The acoustic treatment that you can buy for studios will go some way towards meeting your needs, but bear in mind that foam panels wilnot generally give good low frequency absorption.

However, if money is tight, why not make your own? An upright box or frame(s) to suit the area to be enclosed can be made from 3/4" x 6" wood plank can have both a limp membrane in the centre and suitable thickness glassfibre roll fixed either side of it. Cover the front and back with hessian (to stop the fibres annoying everyone) and then put castors on metal bars at 90 degrees to the frame to make it movable.

 

'Perspex' shields are often used to help shield noisy instruments, but these do not absorb sound to any extent!

 

Simon

[soundgeek]

Im at Worth School, and made them. We made some boxes (about 1m by .75) that sloped at the front. Fill with rockwool, and put felt over the front. Then added strips of wood along the front (getting closer together as you go along). We ahve some mounted on the walls and some that can be moved for each different recording! Work perfectly!

Here are some rough recordings I have done recently: http://discosussex.co.uk/wiggins/

USERNAME: rwiggins

PASSWORD: rwiggins098

 

You will have to enter twice to get in. Let me know what you think. It is a live recording (apart form vocals) but the room doesn't sound nearly as bad as it did!

[mostlyharmless]

There are two ways to approach this; absorbing the sound and "breaking up" the sound (for want of a better term).

 

So something like a soft covering (felt), a layer of rockwool (house insulation) then a thin membrane (plastic?) then rockwool and felt again will be the aborbsion part.

To reflect the sound randomally, you could cut up lots of small cubes/cuboids of wood in random sizes in all directions and stick these to the front - this is where the idea of sticking egg boxes to the walls come from, except egg boxes arn't that effective due to the repeated pattern.

[Hugh]

Have you thought about putting the band in another room altogether, its been done many times, though the musical director/conductor will need a video feed of the stage.

[sirrus]

Mmm very interesting and useful information. Thank you BR, myself and the head carpenter should be able to sort something out :)

 

and I will be doing general amplification of actors talking / singing. The show is Iolanthe (A Musical) and the space is relatively medium sized and the target is to just amplify. I was thinking suspending shotguns / plausible omnidirectionals... from LX bars and then maybe some at floor level.

 

The space, is roughly 10m by 10m with the band at the far back, with the back cyc behind that and then two large folding flats left and right (but further down stage) of the band, and has a large pond / water feature (splashing water around) just off centre, far downstage for act one (act two set mostly in a grave yard e.t.c.) if that helps :(

 

And not sure to the moving the band, our theatre has very nice acoustics and as its a school the only other space the band could fit into close by would be the sports hall (horrible acoustics). It's not a problem to have them there, it’s just with the setup being mostly acoustic and miced up, and I don't want the band overpowering the actors. I would have imagined that the key characters will be radio miced anyway.

 

It's early in the production process, but it all heats up after we return (on half term at the moment)

 

Cheers BR,

[soundgeek]

Im happy to send some photos of ours if you wuld like.

[Simon Lewis]

There are two ways to approach this; absorbing the sound and "breaking up" the sound (for want of a better term).

 

In "absorbing the sound", sound pressure waves are converted to heat, therefore reducing the acoustic energy to some extent. ' "breaking up" ' the sound is known as diffusion, and instead of the usual specular reflection, a diffusing surface will scatter sound (usually in one or two dimensions - depending upon the diffuser).

This will broaden the spatial response and will tend to lengthen the temporal response.

Although diffusion will occur with irregular surfaces, to get good results (I.e for it to work properly) the diffusion surface is carefully calculated. One popular approach is the quadratic residue diffuser based on:

 

well depth proportionality factor = n² modulo p

 

where

n = integer

p = prime number

 

So, some random wooden blocks might look the part, but it really is far more complex than that! Furthermore, diffusion does not absorb sound to any great extent (unless you are using a specific absorbing diffuser product).

 

So something like a soft covering (felt), a layer of rockwool (house insulation) then a thin membrane (plastic?) then rockwool and felt again will be the absorption part.

To reflect the sound randomally, you could cut up lots of small cubes/cuboids of wood in random sizes in all directions and stick these to the front - this is where the idea of sticking egg boxes to the walls come from, except egg boxes arn't that effective due to the repeated pattern.

 

The soft covering is there primarily to keep the rockwool from shedding bits and inquisitive fingers (and to make it look good). It doesn't have a brilliant absorption co-efficient. Mid to high frequencies are absorbed by the rockwool (but denser grades than building grade may be better). The thin membrane is there to take out the low frequencies, so that the device is a broadband absorber.

 

Egg boxes were used because they seemed to mirror the shaped foam blocks seem in studios in the 60s and 70s. The profiles were used because it provided varying depths (i.e. effective for absorbing different wavelengths) and it presented a larger surface area. Egg boxes looked to be similar and cost very little. In fact, they provide some absorption over a small range of frequencies, and therefore cause more problems than they supposedly solve. Schroeder's work on "Diffuse Sound Reflections by Maximum Length Sequences" wasn't published until 1975, so I don't think people used eggboxes to mimic diffusers...

 

Sorry for the long post ;-)

 

Sirrus - before you get too stuck in with the woodwork, have a look on DIY Studio sites for more details on making these devices!

 

 

 

Simon

[sirrus]

Cheers for the info Simon, I have the advantage that the head carpenter is a retired (very successful) professional .. well there isnt much he hasnt done in the sound industry (I can direct your attention to a few products he built and papers he wrote e.t.c.), lets put it like that :) - He is basically my sound guru, I will go to him with the BR responces and we will work something out I'm sure :(

 

soundgeek - Yes Please! (wanna PM them to me?)

 

 

Cheers BR,

 

sirrus

[mostlyharmless]

Thankyou Simon, you explained what I was trying to get at in a lot more useful detail!

[aidso]

Drum Sheilds??? 2M X 4.5m high panels of perspex and split into 3 roughly 1.5m panels. A few of these should do the job rightly. It will still allow people to see the band and will reflect the sound back at the band. http://www.pennzonidisplay.com/index.asp?P...D&ProdID=66

[Simon Lewis]

Drum Sheilds???

 

Perspex drum shields hardly absorb sound. You have to buy the absorbing panels as an extra. (OK there's some LF energy removed as a panel absorber). Unless you need the clear plastic, you will get better noise isolation with the panels described in this thread.

[J Pearce]

Indeed they don't.

 

They normally succeed only in deafening the drummer, making it impossible to hear any wedge and preventing the drummer from hearing and communicating with bandmates. The sound normally still gets to FOH, unless you have the screen with lid, and by the time its got there it has bounced off 14 surfaces and sounds mushy and non percussive, thus adding to the general mush that precludes a good clear mix.

 

Can you tell I'm not a fan?