Flabby GK 200MB

[Axtman]

I am working on an old "lunch box" style Gallien Krueger 200MB combo bass amp. It has a flabby/buzzy sound coming from the internal speaker.

The speaker is a new GK replacement speaker and is not blown nor have coil rub. The amp sounds nice when run directly into a 15" extension cabinet with the internal speaker off.

It almost sounds like I am overpowering the speaker, but again, this is a new high-wattage replacement speaker with an intact foam surround.

Any help would be appreciated.

[Axtman]

How important is the post/tube that goes from the back of the speaker to the inside back of the cabinet? My amp has that part missing. The amp came to me without a speaker and the replacement speaker in a box.

[The Dude]

Are you referring to the port? If so, yes it will make a difference. Without that, speaker excursion may exceed it's design parameters.

[Axtman]

It is not so much a port as it is a support....I think....if my memory serves me correctly. I have been trying to locate pictures.

[The Dude]

Well, if it's a support, maybe what you hear is cabinet rattle?

[g1]

Is there a vent in the magnet assy. where that tube would go?
Those all metal enclosures were troublesome so agree with The Dudes assessment.

[Axtman]

Yes, there is a vent in the back of the speaker magnet.

This must be a later version of the amp because it has the power switch on the primaries. A previous amp I worked on had the power switch on the secondaries....so the amp was always "on".

[g1]

So with the tube on the vent and the other end of the tube flush against the rear panel, there would be some restriction on the venting. Not sure if it is relevant but it's a possibility.

[Axtman]

Yeah it is weird. I would think covering the vent would cause the speaker to overheat.

[Chuck H]

Here's an interesting read from Juan Fahey on a thread related to the GK MB speaker support arrangement. No functioning image links unfortunately. But maybe this can help anyway.

https://www.diyaudio.com/community/t...-style.327519/

[Axtman]

Here is where the missing support post should have gone.

[g1]

You could probably jam a piece of fairly rigid styrofoam in there to do a rudimentary test. Or rubber ball or similar.

[Chuck H]

I thought the same. Juan seemed to be under the impression that it was just a cusioned brace between the speaker and the rear baffle. I think something creative could be done.

[Axtman]

I just got an email back from GK Technical Service. They said. "From a previous email regarding the speaker support, it does play a significant role in making the cabinet more firm when the speaker gets bolted onto it."

So it looks like I will be fabricating or trying different supports.