Electronics > Projects, Designs, and Technical Stuff

Speaker cabinet (guitar) - Air tightness & other stuff

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TinkeringSteve:
Hey,

I'm experimenting with DIY guitar speaker cabinet stuff.
Right now I'm building a closed-back one, and for that to work properly as I understand it, it needs to be air tight, so that there is some resistance by the limited air volume behind the speaker being compressed or expanded.

So I was wondering how to make the front & back plate / frame joint air tight.
The cab has an inner wood frame around the inner circumference of the whole thing, at the back, against which I intend to press the e.g. back plate with some M6 screws. Between the back plate and that frame, I wanted to put some of that black adhesive foam rubber tape, like 1..2mm, which would seal, hopefully, imperfections in the frame/plate joint, which is, by itself, probably not air tight, due to several "hobbyist in the garage corner & minimal tool set, doing this for the 1st time" construction challenges ;)

Now I wonder... would this actually be "correct", I mean - such a film of foam tape vs. wood-on-wood means that the whole thing is less like "one piece" acoustically, the foam dampens higher frequencies I would guess.
(And the front, as planned so far, gets coarse speaker protection cloth wrapped-around the plate, not sure how air tight that can be made, maybe I'll manage to staple it just to the sides of the plate, instead of going fully around and staple it on the inside...)

But I do not understand enough of speaker cabinets' detailed physical workings to know whether that matters or not. If the wood is not supposed to contribute anything by "oscillating" itself, and it's just about making the thing air tight, then it probably won't matter.

But is that so?

themadhippy:
i tend to run a thickish bead of silicon sealer around the frame then screw the panels to the frame,excess silicon gets squeezed out,but still maintains a good air tight join.
 Also a fair amount of guitar cabs are open backed,even those like marshal that are sealed,aint air tight

Benta:
"Air tight" might be relevant for frequencies below 1 Hz.
Don't believe everything you read on the Interwebs.

TinkeringSteve:

--- Quote from: Benta on September 19, 2019, 07:26:38 pm ---"Air tight" might be relevant for frequencies below 1 Hz.
Don't believe everything you read on the Interwebs.

--- End quote ---

Should I believe you? :D
(yeah I know, the likelihood of woo here is different than on audiophooles-R-us.com ;))

I also noticed there are some in-between cabs which have like, both, the upper and lower third of the back "closed" by a plank of wood, and the center third is open.
I wonder at which point it could be considered "closed" with regards to the frequencies of interest (say 60..70Hz).

As for putting in some sealant which will harden - I want the thing to remain open-able.

SiliconWizard:
Completely closed? That's weird for your application.
Even closed speaker cabinets for HiFi usually have vents (sometimes cleverly designed), or they are simply gigantic (and never completely airtight anyway).
I guess a completely airtight cabinet could give you a number of problems to solve, with only marginally better frequency response (provided the internal volume is sufficient for your speaker(s)...)

For a guitar amp... really? I don't think so.

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