On Wed, 17 Nov 2004 14:57:33 +0000, Don Pearce wrote:

snip

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.


Surely a 1/2 wave pipe will have a standing node at both ends so no (or
little) sound will come out of the other end at Fs will it? Shouldn't it
be 1/4 wave at Fs?

--
Mick
(no M$ software on here... :-) )
Web: http://www.nascom.info
Web: http://projectedsound.tk

On Wed, 17 Nov 2004 18:01:59 GMT, mick wrote:

On Wed, 17 Nov 2004 14:57:33 +0000, Don Pearce wrote:

snip

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.


Surely a 1/2 wave pipe will have a standing node at both ends so no (or
little) sound will come out of the other end at Fs will it? Shouldn't it
be 1/4 wave at Fs?

The damping ensures that there is no standing wave. And by making it
half a wave long, and adding the effective half wave shift caused by
using the back wave, the sound emerging from the end of the pipe is in
phase with the front radiation. This is pretty much analogous to what
happens at the port of a reflex speaker and the overall effect is also
pretty much the same.

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

Don - I was thinking of ported. If I use a 5" I can get decent bass from a
ported 21 litre enclosure with one of two drivers like the MW144 for instance.
Decent = reasonable response at 40hz.

=== Andy Evans ===
Visit our Website:- http://www.artsandmedia.com
Audio, music and health pages and interesting links.

On 17 Nov 2004 20:12:45 GMT, ohawker (Andy
Evans) wrote:

Don - I was thinking of ported. If I use a 5" I can get decent bass from a
ported 21 litre enclosure with one of two drivers like the MW144 for instance.
Decent = reasonable response at 40hz.

It is certainly going to be dropping a bit by 40Hz, but it won't be
very loud in the bass. At 5" diameter you need a great deal more than
the 3.5mm displacement of this unit to make any serious amount of bass
noise.

My Adire tempest is 15 inches, and has plus or minus 16mm of movement
- that is more like the sort of thing you should be aiming at. OK, you
can't put that sort of diameter into the tube, but to get the volume
you must compensate by greater excursion. Two drivers help, but you
must then use double the cabinet volume for the same shape response.

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

"Andy Evans" wrote in message


Does anybody know the effects of back radiation on the cone.

It can be very significant.

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.

Some of the sonotube subwoofer enclosures I've seen were 6 to 12 feet long.
There could be a lot of *organ pipe* resonances if the tube was not properly
stuffed.

But I'm thinking that the actual length of enclosure behind the cone
is important.

It definately can be signficant. After all, that's what ported enclosures
work with, as do the unported ones.

Hence my plan was to use a larger diameter sonotube
horizontally, rather than a slim one vertically.

Consider the well-stuffed tube as a very lossy transmission line...

But I'm thinking that the actual length of enclosure behind the cone is
important.

It definately can be signficant. After all, that's what ported enclosures
work with, as do the unported ones.

Hello Arny - thanks for contributing. Yes - I mean what you point out, that a
good distance behids the cone is better than being tight up against a back wall
as it would be in a tall narrow enclosure. e.g. I heard Jordan JX92Ss in a TL
enclosure where the back wall was a bare 6 or 8 inches behind the cone - surely
you'll get reflections back into the cone?

=== Andy Evans ===
Visit our Website:- http://www.artsandmedia.com
Audio, music and health pages and interesting links.

"Andy Evans" wrote in message

But I'm thinking that the actual length of enclosure behind the cone
is important.

It definately can be signficant. After all, that's what ported
enclosures work with, as do the unported ones.

Hello Arny - thanks for contributing. Yes - I mean what you point
out, that a good distance behids the cone is better than being tight
up against a back wall as it would be in a tall narrow enclosure.

Agreed.

e.g. I heard Jordan JX92Ss in a TL enclosure where the back wall was
a bare 6 or 8 inches behind the cone - surely you'll get reflections
back into the cone?

It happens.