On 17 Nov 2004 14:34:27 GMT, ohawker (Andy
Evans) wrote:

Does anybody know the effects of back radiation on the cone. The simple method
of dealing with this is to stuff behind the speaker, or indeed to have cabinets
with odd dimensions to avoid standing waves. But I'm thinking that the actual
length of enclosure behind the cone is important. Hence my plan was to use a
larger diameter sonotube horizontally, rather than a slim one vertically.

=== Andy Evans ===
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Sound really doesn't know much about whether it is going vertically or
horizontally - so no problem there.

If this is for a subwoofer, standing waves inside the cabinet simply
aren't going to happen - the dimensions are far too small. They will
happen in the room, though, which is a vastly bigger problem.

But how do you propose to use the tube? There are really three ways.
The first is to simply use it as a cabinet, that just happens to be
round. The standard calculations apply, and you can make it sealed for
best sound or ported for maximum oomph.

Second, you could use it as a transmission line, with enough padding
to absorb the entire back wave along the length, resulting in an
effectively infinite baffle - a little like the response of designs
used by me (built into a huge unused concrete cupboard) or Stewart
(into a roof void). This is another maximally flat design that yields
true bass extension without all the bloated thud of the typical home
theatre speaker.

Thirdly, you can make it a half wave long at Fs and pad it lightly
enough that some energy emerges from the far end to prop up the bass
response a bit. It will be good for movies, but not so great for
music.

d

Pearce Consulting
http://www.pearce.uk.com