Heybrook HB2 overhaul

[Shane]

The function of the foam stuffing is to absorb some of the standing waves inside the cab, whereas the bituminous pads are to damp down cabinet resonances. I would be inclined to leave the Spectral mat in place (if it's not too thick, I'm not familiar with it) and put the foam back in. I'm scraping the memories off the back of my skull here, but I think there was a piece the same size as the back panel which sat on top of the crossover (with a slit for the port tube to go through), then a long U-shaped bit tat went all the way from one top corner, down one side, across the bottom and up the other side, ans a little rectangle to fill the gap on the top panel. I could be completely wrong though....

Putting it back will involve taking out the bass unit and the port tube. Don't forget when you put the port tube back in that the holey end butts against the bass unit. Tighten the bass unit carefully to avoid chassis distortion as it clamps the port tube against the rear of the cabinet. There's a small bituminous pad on the back of the bass unit which provides a bit of "give" against the port tube. Don't know what that'll be like after 30 years though!.

[VantheMan]

Many thanks,

I´ll try it with and without the foam. How would the presence of standing waves manifest itself ? What should I listen out for ? any ideas ?

[Shane]

Peaks in the response corresponding to 1/4 wavelengths matching the cabinet dimensions, especially height. Aurally, emphasis of frequencies around 200hz or so, giving a bit of an upper bass hump, and around 450hz from the front/back dimension.

[VantheMan]

Thanks Shane,
Not that I understood much - Could that be translated into instrument frequencies - let´s say in a jazz trio of piano, bass and drums ?
In other words replacing the foam should bring out the piano, say, relative to the bass ?

[Shane]

Originally Posted by VantheMan

Thanks Shane,
Not that I understood much - Could that be translated into instrument frequencies - let´s say in a jazz trio of piano, bass and drums ?
In other words replacing the foam should bring out the piano, say, relative to the bass ?

Well, sort of. It's more a question that a piano will just sound more like a piano, and less like a piano in a box, I suppose. It's notoriously difficult to describe these effects realistically. Best advice is suck it and see! You can always take it out again...