Guitar amp isolation

JoeyBones

We're trying to silence our stage, so we've been looking at the easiest/cost effective way to isolate our amps. I've seen a few guys who have just built a four sided MDF cabinet lined it with sound absorbing material on the inside. I've also seen guys who use perspex for the front.

My question is, are there specific angles, size and shape that these containers have to be ? Doesn't the perspex cause the sound to bounce around and would that bleed back into the mic ? We want to make it big enough to contain/silence a 4x12 marshall cab.

Any advice will be appreciated.

JoeyBones

I found these two designs that look promising.

majestikc

Is your main goal to have the sound come primarily through the p.a system rather than the amp?
If it is then it would make more sense to just use smaller amps that don't make as much noise, otherwise if your after the full sound of a stack going full blast, then why would you need it to go through the p.a?

Otherwise just do what they did in the picture but I'd suggest using the covered boards all the way around, never tried anything like it (or heard of anyone trying to silence a stage) but it should help a bit, maybe even more if there was a top cover as well.

Manfred-Klose

the perspex will most probably reflect, not shure about its absorbtion coeffecient.
The 3rd pics looks most promising.

But i would give it just a little more space at the front.

otherwise if your after the full sound of a stack going full blast, then why would you need it to go through the p.a?

get a valve amp attenuator to solve this problem.

Garth-S

We have an enclosure made by the same people for our drums at church, It works like magic. Very effective for the drums, but I dunno how effective they'll be for an amp. For the electric guitars we use a system made by Radial called studio guitar interface, and the amps are in the back room, now THAT works great -> http://pro-audio.musiciansfriend.com/product/Radial-SGI-TXRX-Studio-Guitar-Interface?sku=153923

TomCat

I must say that these things give me the same heeby geeby's as drum screens.

Their main problem is that the only work at higher frequencies and then only to a relatively small degree. Using a reflective material such as perspex causes the sound to reflect off and enter the microphone with a slight delay, causing the output signal of the microphone to be "Comb Filtered" which completely wrecks the tonal balance of the amplifier/mic combination. Once the comb filtering has occurred, there is no way to fix it except remove the screen causing the comb filtering in the first place.

What we do at church where we need to keep stage levels down is to use smaller amps and tilt them back in a "Kickback" fashion in front to the guitarists ALA stage monitor style and mic it up from there. Works really well, the guitarists hear themselves clearly and levels are under control.

If you want to mask a large stack (4 x 12) then use absorbent type screens placed around the amp to reduce the chance of reflections back into the mic. For me having perspex would be a big NoNo......

AlanRatcliffe

Meh. I don't like iso boxes. First prize is to bring the amps volume down, which means either smaller amps or amp attenuators. If you want to silence your stage, then you have to look at amp modellers.

You get iso screens, iso cabs and iso boxes - all are different:

Iso screens - look like office partitioners. Ideally made from MDF with rigid fibreglass on one side. Made with sheets of acrylic plastic (perspex) if you want to see the amp, but are less effective as the perspex is both more reflective and retransmits sound from its own vibration. Don't absorb much sound, but help redirect it, but also don't change the tone of the amp much. Useful for getting separation between mics and redirecting sound away from areas where you want to keep the volume lower.

Iso cabs - are complete speaker cabs with built in box and absorption. Have their own tone - obviously more of the closed back speaker cab tone than open cab. Sound absorbing material only operates on the mids and upper frequency ranges, but leave the bass untouched, do you get a bit of bass buildup.

Iso boxes - are little "rooms" for housing the complete amp with power, cooling, audio connections for mics. Have to be very heavily built (usually from MDF), so done properly, weigh a ton and rarely look good. Cooling is essential if you don't want to shorten the life of your valves. Amps sound different in smaller rooms (basically what an iso box is) because of reflections. Also prone to bass buildup.

You also get screens which are not transparent, but are made rigid fibreglass and cloth. These absorb some of the sound but are not transparent. Spacing away from the amp a bit at the back and also from the wall makes them more effective - the sound travels through them twice and they get lower frequencies with a bit of air.

What you have in the pics is basically an iso screen in front and an absorptive one behind. Both help cut volume, but wont make your stage silent. What I would probably do is use the screens as in your pics and add attenuators on the amps (speak to Graeme).

[EDIT] Must learn to type faster, some of the others have already said much of the above ?

JoeyBones

We're trying to be as flexable with this design as our guitarists use everything from an AC-15 to a marshall 4x12 stack to get the tone they like.

Moving the amps off stage might be the best option for our setup.

Thanks for the feedback guys.

TomCat

Does the stage have a basement under it. If so then you can put the amps under the stage and mic them up. I've seen this done many times in churches and works well. You will still need some degree of isolation between amps so they do not bleed across microphones.

As Alan has mentioned, absorbent screens will probably work best to provide the isolation between amps.

JoeyBones

TomCat wrote: Does the stage have a basement under it. If so then you can put the amps under the stage and mic them up. I've seen this done many times in churches and works well. You will still need some degree of isolation between amps so they do not bleed across microphones.

As Alan has mentioned, absorbent screens will probably work best to provide the isolation between amps.

Yip, we have more than enough space below our stage. Just need to get the other guitarists to buy into the idea and accept that they will have to rely on in ear monitoring only.

TomCat

Give it a bash and see how it goes......

guitarboy2828

Or just turn the cab backwards so its facing the poor drummer behind him. ? I've seen many guys do that, not sure if it works.. But it must do something! ?