thoughts on minimising backwave reflection

[slr 5000]

hi all
im just finnishing up some new speaker cabs and am after some thoughts on minimising the backwave reflection from the driver

the bass cabs are 450 deep 300 wide and
900 tall

the top cabs housing the mangers are 300 wide by 250 by 300 deep

id like to stop the backwave being reflected back through the drivers as much as possible and am looking for some ideas

the cabs are just shells at the moment so i can use things like angled bracing ,lining ,tapered deflectors , stuffing or anything else you guys could suggest

[gainphile]

I heard that natural wool fiber is the best ?

[slr 5000]

hi mate
im thinking of maybe a combination of wool fibre and some sort of deflectors inside using different angles to trap and diffuse the backwave before it gets reflected back out of the driver

[mwmkravchenko]

Here is a drawing of something that worked well for me. I designed some really good stuff in the late eighties that had a cabinet within a cabinet. The black areas are sand. the eliptical shape is made from a concrete tube form. It is set into the front baffle with grooves cut at the appropriate angle. There are corresponding grooves on the top and bottom of the box to hold the eliptical shape.

If you choose the depth and width correctly you end up with a shape that causes the reflection off of the back wall to effectively kill itself just behind the woofer magnet.

Just test it out by observing dropps of water hitting a toilet bowl. Who says there is no inspiration in the john?

Mark

[Brett]

I know nothing about Mangers, so comments are only for the 12". I'd make a sort-of closed end TL inside the box. Mount the 12 up high on the baffle and do the internals like this. I'd probably taper the line though to make it smaller at the terminus. I'd also make the top 'rear' panel reflector at 45* to get as much of the sound reflected down as possible Covering that panel with thick felt is probably a good idea too.



I've had good results with wool, wool felt and I'm going to try cotton in the current speakers.

Absorption Coefficients of lots of stuff

[slr 5000]

i was wondering about a tL design
the cabs are rectangular so this limits me somewhat but i could quite easiley install tL bracing inside the bass cabs

is there any rules that go along with this design like taper versus crossover freq and such

the bass cabs will be housing a scan 25w8565-01

what about some sort of tL for the manger cab as well

the crossover point will be 400hz

[Brett]

Originally posted by slr 5000
i was wondering about a tL design
the cabs are rectangular so this limits me somewhat but i could quite easiley install tL bracing inside the bass cabs

is there any rules that go along with this design like taper versus crossover freq and such

As you're only wanting to control the back wave and not add an reinforcement to the bass, not really.

Originally posted by slr 5000
the bass cabs will be housing a scan 25w8565-01

what about some sort of tL for the manger cab as well

the crossover point will be 400hz

Copy the B*W Nautilus for the mids. Make sure the tube length is longer than 1/2 WL at 400Hz.