Sealed cabs more prone to feedback?

[bassbuddy]

I've got two cabs - an Aggie GS112 (ported) and an Ampeg Portabass 1x12 (sealed). The Ampeg sounds great for slab and I love its portability, but it seems I get a lot more feedback with it than I do the Aggie - even at the same amp settings. I play a lot of blues and swing and go for a pretty old school bottom heavy sound, so I'm wondering if the sealed nature of the cab is emphasing low-mids that the Aggie doesn't. Any thoughts? Common experiences?

[fdeck]

Is there any possibility that the speakers are wired out of phase with one another? I realize that would require a "mistake" with one or the other, but anything is possible.

At the same time, the low-mid emphasis might be doing exactly what you say.

If you want to go off on a geeky adventure, download my real time analyzer program, get a cheap microphone, and measure the relative curves. I might steer you in the direction of how to EQ your system to get similar performance with the two speakers.

[Uncletoad]

I can't imagine a sealed cab has higher feedback potential than a vented cab.

There has to be more going on there, drivers, box size etc. that emphasize frequencies that your bass doesn't like.

[Marc Piane]

Originally Posted by Uncletoad

I can't imagine a sealed cab has higher feedback potential than a vented cab.

There has to be more going on there, drivers, box size etc. that emphasize frequencies that your bass doesn't like.

I agree. I have a GK 150MB which is sealed and I've cranked that thing to the point of explosion and never had any problems.

I've found that there are usually two culprits.

The first is a 'ringer' frequency. Some note that sustains forever and gets louder and louder. This can usually be fixed with eq. If not you can do things like shoving a towel behind your tailpiece.

Second is the orientation of the amp to the bass. DBs are made to resonate. Feedback often comes from the amp causing excess vibrations in the body. Somebody more technical than me can explain it better but my understanding is it creates a feedback loop - the bass picking up the amp picking up the bass etc. This can be fixed by having the amp off axis from the bass. I carry a little folding amp stand that puts the amp at a 45 degree angle to the floor.

Good luck.

[bassbuddy]

Well, all of that makes sense as I also have an older MB200 that I use without issue. And I did have the amp facing off axis from the bass, so that didn't help. maybe just a bad match between bass & cab. Wierd.

[drurb]

Originally Posted by Uncletoad

I can't imagine a sealed cab has higher feedback potential than a vented cab.

There has to be more going on there, drivers, box size etc. that emphasize frequencies that your bass doesn't like.

IMO, this is precisely correct.

[joelb79]

Feedback is caused by microphonic pickups or loosely mounted pickups. You should pull your pups out and make sure that they have enough behind them (foam/ect) to keep them from vibrating.

Edit: Didnt realize i clicked into an upright thread. Microphonic Pizo's are not my thing but usually its because of how they are mounted which i know nothing about.

[bassbuddy]

Odd you should mention that - I squeezed the cable coming from my Bass Max and it stopped the feedback. However, it seems to me that EVERY piezo PU I've tried (Bass Max, Rev Solo, D. Gage) has a cable that is "microphonic"; at least you can hear it fairly loudly if you tap the cable. So either I've gotten a solid run of all bad PU's, or this problem is simply part of the package when you choose a wing PU.

BTW, on a related topic, does anyone know if the Schroeder Mini 12 is ported, and if so where? I can't find on the net.

[mstclairmiller]

LowNote has two versions - see this link:
Acoustic Image Issues?

Also, Jorg is renowned for being super helpful, so just ask him!