uFonken speaker cabinet: Design question

[underwurlde]

Hello, hopefully someone knows the answer to this question.

I am 1/2 way through building a pair of small desktop speakers using the uFonken design.

Part of the internal design of the cabinate uses a flat piece of wood, 2 corners chopped off with 3x 1 inch holes. This piece of wood appears to be positioned inside the cabinate such that it's nose end is placed directly behind the speaker magnet.

Question: Should this piece of wood actully touch the back of the speaker magnet or should there be a small gap???

Cheers,

Andy

[gaust]

Hello,
Although I'm no expert and I am sure Dave (Planet10) or someone else involved with the fonken designs will be along soon - I understood that the brace made contact with the back of the speaker magnet.

[ZirconiumZephyr]

It should fit tightly with the back of the speaker as it is there to brace it. I believe it is advisable to cut it to size last of all when you can test fit it with the speaker. You don't want it so tight that it deforms the speaker surround but not too loose either, I believe sometimes a bit of foam helps to pad the gap.

[underwurlde]

Thanks so far chaps..

Won't adding foam dampen the effect of bracing?

Andy

[chrisb]

Originally Posted by underwurlde

Thanks so far chaps..

Won't adding foam dampen the effect of bracing?

Andy

Dave tends to incorporate similar bracing when ever possible, in practice it should contact the magnet as tightly as possible without stressing the flange when driver's mounting screws are tightened. If they're slightly loose, a small piece of closed cell foam tape or, blu-tak/duct seal etc on works well to couple the surfaces. Even better would be a piece of real veneer edge-banding tape.

I assemble and glue up the first 5 sides of the box before iterating a few cut and dry fits of the brace. Since I'm able to get the driver baffle routed on CNC (including rebate for flush mounting), and tend to cheat on smaller boxes with an air powered brad nail gun, it frequently takes longer to get the driver braces right that cut and assemble the box up to that point, particularly on the smaller designs.

[planet10]

In some cases a piece of paper (or 2) is all that is needed to fill any gap.

The brace helps spread the driver's motional energy to more wall panels, spreading the energy & reducing the chance of exciting a resonance (instead of putting all the energy into the baffle)

dave

[Bigun]

I have used a felt pad to close the gap, the stuff that they sell for putting on the legs of furniture when you have a hardwood floor. It's good because it doesn't compress very easily and you can get different size/thicknesses.

[underwurlde]

Thanks for the replies guys!

Am I right in thinking that this bracing of the back of the speaker akin to using a tuning fork.... Stike the tuning fork (silent), put base of tuning fork on a stiff surface and you then hear it's resonant tune: i.e. stiff surface becomes the soundboard for the tuning fork...??

Another question:

Should the outside of the speaker driver be sealed to the hole in the speaker cabinate (e.g. using a thin strip of sticky closed-cell foam)? I'm guessing 'yes' to best induce sound pressure differentials inside the speaker cabinate....

Andy

[Pit Hinder]

Andy - #1, the bracing...other way round. Don´t underestimate the driver´s "recoil"...it´s tiny, but it´s there. (Sir Isaac´s actio=reactio). Coupling the driver to the cabinet´s mass helps a lot to slow it down...remember that cone excursion in the highs is incredibly tiny, so Doppler effect raises it´s ugly head.

#2 - yes, by all means. A driver without a gasket of sorts can produce noises you don´t want, plus the gasket helps decoupling the driver from the front panel.

[underwurlde]

^ Ah, gotcha.