Why do people place boards under their cabs?

[namuxtree]

I've seen a ton of pics uploaded by TBers with a solid board under their cabs. Does it have something to do with the resonance of having a solid foundation as opposed to (let's say for example) a hollow stage? Any insight to this? Does it help THAT much?

[will33]

They're probably Gramma Pads. A thick foam pad to try to isolate the rig from vibrating stages. Without a page full of arguing mechanicsl vs. acoustic coupling.....some say it seems to work.

[oinkbanana]

some people don't like coupling.
the frequency response (of the stage vibrating) from one stage to another can never be the same.
the foam helps cut that down some. i'm not sure how effective that is.

[billfitzmaurice]

A hollow stage will vibrate, sympathetically resonating in response to the acoustical output of the speaker. A pad will help keep that vibration from rattling the cab and amp. But a parametric EQ notch filter works better, eliminating the resonant frequency at the source.

[Vandy]

With all due respect to a loudspeaker designer / audio expert, I'm not adept enough to "isolate" a specific sympathetic frequency. Then be able to afford a parametric EQ notch filter to soothe the stage?
Yikes!
If a placebo pad is available, I'll use it, but I'm usually just happy to be there . . .

[DBCrocky]

Yeah, I pretty much saw those pads as something to keep guitar player's spring reverbs in their amps from rattling when the bass player drops the floor-rattling bombs.

[will33]

Originally Posted by Vandy

With all due respect to a loudspeaker designer / audio expert, I'm not adept enough to "isolate" a specific sympathetic frequency. Then be able to afford a parametric EQ notch filter to soothe the stage?
Yikes!
If a placebo pad is available, I'll use it, but I'm usually just happy to be there . . .

The pad is a solution because a fully parametric eq is not a feature found on most bass amps. The knowledge required to properly use one isn't a feature found in a lot of bass players either, but it can be learned, isn't too dificult. Technically though, the pad is a mechanical band-aid for an acoustic problem.

[DWBass]

Originally Posted by billfitzmaurice

A hollow stage will vibrate, sympathetically resonating in response to the acoustical output of the speaker. A pad will help keep that vibration from rattling the cab and amp. But a parametric EQ notch filter works better, eliminating the resonant frequency at the source.

Had a gig once at the Windows Of The World Restaurant (top floor of the no longer standing World Trade Center) and no amount of eq worked! That resonance would not go away. I ended up turning the amp off! Had to utilize my DI box & the monitors to hear myself.....barely! NOT a fun gig that night!

[billfitzmaurice]

Originally Posted by Vandy

With all due respect to a loudspeaker designer / audio expert, I'm not adept enough to "isolate" a specific sympathetic frequency.

All you do is turn a knob. And a parametric works just as well at notching out a boom frequency that can be present even when the stage is not the cause.

Had a gig once at the Windows Of The World Restaurant (top floor of the no longer standing World Trade Center) and no amount of eq worked! That resonance would not go away.

The cause was said windows. What's best for the eyes is usually the worst for the ears.

[4-stringB]

Originally Posted by will33

The pad is a solution because a fully parametric eq is not a feature found on most bass amps. The knowledge required to properly use one isn't a feature found in a lot of bass players either.

Will33, thanks for the insight...LMFAO...

[Biggbass]

wow...40+ years of playing and I've yet to either see or use such a device.
hmmm...wonder if that's part of the concept behind putting little rubber feet on the bottom of an amp cab?

[moles]

As an example of a low cost parametric eq, the Presonus EQ3B can often be had for under 70 bucks used.

As far as not knowing how to use one...The learning curve really isn't that hard if one actually puts forth the effort to learn...

[NWB]

I put a solid board underneath my cabs to keep them from falling into the gates of hell.

[darius8]

Originally Posted by billfitzmaurice

A hollow stage will vibrate, sympathetically resonating in response to the acoustical output of the speaker. A pad will help keep that vibration from rattling the cab and amp. But a parametric EQ notch filter works better, eliminating the resonant frequency at the source.

Originally Posted by will33

The pad is a solution because a fully parametric eq is not a feature found on most bass amps. The knowledge required to properly use one isn't a feature found in a lot of bass players either, but it can be learned, isn't too dificult. Technically though, the pad is a mechanical band-aid for an acoustic problem.

The only amp, that I know of, that has a feature that remotely comes close to this "parametric EQ notch filter", as Bill said, is Acoustics "B" series stuff. Theirs is called a "Sweepable Frequency Notch Filter". Same thing?

[will33]

Originally Posted by darius8

The only amp I know that has a feature remotely comes close to this "parametric EQ notch filter" as Bill said is Acoustics "B" series stuff. Theirs is called a "Sweepable Frequency Notch Filter". Same thing?

Not sure. A parametric has three adjustments, one for boost and cut, one to select the center frequency and one for the Q width. It may be a "semi-parametric", those have the first 2 adjustments but not the Q width, sometimes called a "sweep". The only bass amps I've seen with a true parametric are some older Peavey's, there might be others.

[GrowlerBox]

Originally Posted by darius8

The only amp, that I know of, that has a feature that remotely comes close to this "parametric EQ notch filter", as Bill said, is Acoustics "B" series stuff. Theirs is called a "Sweepable Frequency Notch Filter". Same thing?

That's almost certainly a centre-frequency adjuster with a fixed deep cut and a very narrow Q, most often used for cutting a feedback-causing frequency when amplifying acoustic instruments. Or, in this case, an amp-chassis rattle-causing frequency.

[JimmyM]

Originally Posted by NWB

I put a solid board underneath my cabs to keep them from falling into the gates of hell.

Makes as much sense as any reason.

[billfitzmaurice]

Originally Posted by darius8

Theirs is called a "Sweepable Frequency Notch Filter". Same thing?

Almost. A full parametric will boost or cut, and has a variable bandwidth (Q).
Signal Processing Fundamentals

[ack]

My Peavey Pro500 has a "Q" section within the Parametric EQ's.
I always wondered what those knobs did...

[billfitzmaurice]

Originally Posted by ack

My Peavey Pro500 has a "Q" section within the Parametric EQ's.
I always wondered what those knobs did...

You could have read the manual, but then you'd have had to turn in your Man Card.