The Steel Guitar Forum

I've read about locating single speakers off-center in open-back combo cabinets to reduce standing waves, resonances, etc. Any merit to doing this? I'm about to make a single 15" baffle board to mount my Altec 418 in my '68 Twin Reverb.

The Fender Twin Custom w/ 15" is off-center - by quite a bit. Don't know if there is anything to it or not.

I would not think it would matter for an open-back cabinet.

http://www.fender.com/guitar-amplifiers ... ml#start=1

Ken posted dimensions once to center a 15" in a Fender cab. I rotated my 15" SRO slightly to center in a Twin Build.

I always thought the Fender 15" speaker location was to avoid the transformer.

Ken is the man. I hope he sees this and weighs in.

jon is right. no way to center it. the output tformer is right there in the middle. i would favor the side away from the power tubes if you can.

Jon, that is correct. I had one put in mine and it had to be set off center because of the transformer

G. Robertson wrote:I've read about locating single speakers off-center in open-back combo cabinets to reduce standing waves, resonances, etc. Any merit to doing this?

In a practical sense? And in a Twin Reverb amp? No, none whatsoever.

It's done both to avoid the output transformer and to counterbalance the power transformer.

It is, of course possible to center it.

Does it carry level, Bob?

You may be able to center it depending on the speaker but Lane is right, it carries better offset. I had to offset mine so that the transformer could reside between two of the spokes in the speaker.

As an FYI - www.mojotone.com quoted me $90 plus shipping to build a 15" Twin Reverb baffle, complete with grille cloth of your choice. You might want to contact them. I like to DIY but I could hardly build one myself for cheaper than that, if I include my time in the cost.

I had an AB768 chassis Twin Reverb (I think a 70 model). It came with two JBL D-120F's. I replaced the speakers with one JBL K-130 4 Ohm. It had to be off centered because of the transformer.

G. Robertson wrote:I've read about locating single speakers off-center in open-back combo cabinets to reduce standing waves, resonances, etc. Any merit to doing this? I'm about to make a single 15" baffle board to mount my Altec 418 in my '68 Twin Reverb.

My experience is the opposite. I just redid an amp so the single speaker was centered and it was an improvement. It can be tricky to center a speaker in a combo but it can be done.

Lane, I had never thought about the weight offset, any Twin should be the same, so I did an (un?)scientific experiment last night involving a mic stand through the handle, and a couple of stools. Measuring sides to the floor is almost 3" difference, so approx. 1.5" off center drop.

I don't see how I could have centered the speaker in my '73. Hard to see in this picture, but the transformer comes really close to sticking into one of the openings in the speaker's frame.

It's not particularly balanced in this configuration, although not badly out-of-balance.

My hat's off to anyone with good enough ears to hear a significant tone difference from moving a speaker a few inches in a shallow, open-backed cabinet.

IIRC Vibrosonic Reverb amps had their single 15 offset too.BTW the Fender Amp Field Guide says the Vibrosonic Reverb and Twin Reverb cabinets are the same size.The Custom 15 cab is 2" taller.

I always thought the offset speakers looked awkward.
Centered sounds OK to me. Had to align the transformer with the space inbetween the spokes

The same idea was used in Vibroclones I built. Rotated the speaker to miss the Twin Reverb transformer I used in 6 of these amps I built years ago.