how to stop rumbling from hollow stage

[bandkindbass]

I hope you understand my english. As you might understand, this is not my native tounge.

I work occationally as a soundman for a trio that uses an upright bass. I use the direct output from his combo-amp, and he gets monitor from this and from the stage-monitor system.

A lot of the venues we have visited uses a hollow stage, and i get a low feedback rumbling literally in every mic on stage. If the player lifts his bass, the rumble stops. I have used some carpet or textiles to stop vibrations from the bass to get down into the stage, but this doesn't work very good. I'm planning to make some equipment to isolate this, my first try is to fill a tennisball with some rubber/silicone/etc and try to attach this to the pin that holds the bass up from the floor. Have anyone any experience with this?

The band is quite loud with a hardhitting drummer and a fuzzguitar, so I have a lot of trouble with bass-feedback. I will be gratefull for every tip or advice.

Thank you
Tore S Bryhni / Norway

[Chris Fitzgerald]

Wow, that's a new one on me. Two questions:

1) what do the bases of your mic stands look like? I've had problems with transmitted vibrations from the stands with heavy (iron?) circular bases. When I switched to the tripod/boom stands, these issues were resolved.

2) Have you identified the frequency of the rumble? Often, a high pass filter can eliminate a lot of bass rumble, which often centers around 60hz. You might also want to think about moving the bassist's monitor to a different location if it's pointing directly at the bass.

Good luck.

[mje]

You're on the right track with the tennis ball idea, although silicone caulk may be a little too hard. You want a softer urethane resin- sculpting supply houses often have this material.

You need to isolate your bass and stands from the floor. How you do this depends on how much equipment you can carry with you. You can build platforms of layers of plywood and urethans materials that will damp vibration, or you can make sand or lead-filled platforms that will add mass to lower the resonant frequency of the system. Probably not practical for touring.

For bass, I'm going to suggest something I think will work, even though I haven't tested it. A number of companies catering to the amateur astornomy community sell small vibration isolating pads that consist of a two-part plastic unit about the size of a hocky puck that has a layer of soft urethane seperating the two parts. Setting the bass on one of these would probably do the trick. Meade sells a set of three for $30-40:

http://www.buytelescopes.com/product.asp?pid=3175

[Bob Branstetter]

It sounds to me like you need to have shock mounts on the mics. Here's a link for one that is reasonably priced.

http://www.sabrasom.com.br/ing/default.htm

[Bob Gollihur]

I saw a positive review on a new item from Auralex called Gramma: http://www.auralex.com/sound_isolati...ion_gramma.asp

Also, I have an old four-legged stand that I used with a single 15" combo amp I owned several years ago, and it was very effective at de-coupling the amp from the floor and hollow stages. Have you tried putting the amp on a chair or stool?