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Old 19th July 2012, 07:56 PM   #1
opa1 is offline opa1  United States
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Default Betsy in open back cab

I have a pair of cabs that I'm putting new front baffles in. The front and back panels are both removeable. They measure 13w 21.5h 11.5d.
What I'm wanting to know is the best placement of the 8" betsy on the baffle. Center of box, bottom? I might add a tweeter later if I need to. Any suggestions?
Also has anyone added a tweeter to the betsy? What kind and what crossover did you use?
Thanks
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Old 19th July 2012, 09:23 PM   #2
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OK....Just what is "The Betsy"?......do you have any T/S parameters we can work with?

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Old 20th July 2012, 12:46 AM   #3
Bigun is offline Bigun  Canada
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Originally Posted by Richard Ellis View Post
OK....Just what is "The Betsy"?
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Old 20th July 2012, 01:16 AM   #4
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I've been meaning to try open backed cabs for years. I would love it if somebody could play around and post results. I'd put the Betsy a little off center. Those cabinets aren't very big. You might consider some sort of tuneable aperiodic vent.

Most of the folks using tweeters are using rear, up or side firing to add sparkle. The "phase-y" sound of that isn't for me. I'm fine without tweeters, but if you want to use them, you might consider a whizzer-ectomy.

Paul
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Old 20th July 2012, 01:28 AM   #5
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From what I've seen, usually you get a smoother response but lose some low end when you offset a driver on a baffle.

Norman
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Old 20th July 2012, 01:50 AM   #6
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I have the betsys in ob now. I'm liking what I here. Footprint is a little large for my room. I going to try them in the open cabs and see what they sound like. I have to cut new baffles for the cabs so thats why I asked about placement. In my small room 9x12 I think the cabs might work real well. The backs of the cabs are removeable. So I could make a aperiodic back to the cabs. With the ob's, No tweeter needed. They sound great.
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Old 20th July 2012, 06:38 AM   #7
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I think open back may be to your liking. I've been looking at the auditorium 23 "solovox" design.

6moons audio reviews: Auditorium 23 SoloVox

open backed boxes allow more of the wall bounce that usually is a nice addition. The solovox shoots probably 80% of the sound left and right of the enclosure. With parallel walls, you have to watch your depth or you get resonances (spikes). I believe the stand rule of thumb is the wings shouldn't be more than 1/3 or 1/4 of the width. I had a 2' x 2' x 19" deep with 3" foam across the back. Every now and then the addition of a bit more chest was too much, but not often.

I have a email from someone that said not to cut off the dust cap and add a whizzer, but if you want to add a tweet, that's up to you. If you cut off the whizzer, I bet you'd have even more climb from 1-5khz, lose everything after that, and really lose dispersion past 1.5-2khz.

I'll dip up some more links.

Norman
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Old 20th July 2012, 08:50 AM   #8
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"Years ago I tested a Coral Flat 8A (8" driver with 160mm cone and 80mm horn shaped whizzer) with and without whizzer, and found the whizzer cone starts to have a large effect on the on and off axis response as low as 2.5Khz.

Specifically the presence of the whizzer cone reduced the on axis response from 2.5Khz to about 6Khz by nearly 3dB, but increased the (30 degree) off axis response by several dB, in other words the dispersion between 2.5Khz and 6Khz was greatly improved at the expense of some loss of on axis response.

However the on axis response without the whizzer actually had a +3dB shelf from 2.5Khz to 6Khz, which suggests the main cone of the driver was deliberately designed with an increased output in this range (probably due to decoupling rings) so that the response was balanced once the whizzer was in place.


Above 7Khz the response of the single main cone by itself disappeared rapidly, so above 7Khz the output is almost entirely the whizzer cone.

So technically the whizzer is only acting as a second separate cone above 7Khz, but between 2.5Khz and 7Khz it is still acting as a source of sound as well as a directivity modifier for the main cone, much like a phase plug would.

The improvement in dispersion is so great that at 4Khz without whizzer cone the 30 degree off axis response was 9dB down on the on axis response (severe beaming) while with the whizzer cone in place the 30 degree off axis response at 4Khz was only 1.8dB down from the on axis response... "
whizzer and intelligibility ?

see reply #14 for a pic on open back ratios
Charlie Hall & Friends - Another AC15 project

norman
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Old 20th July 2012, 05:12 PM   #9
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That's such an interesting box Norman.
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Old 20th July 2012, 09:06 PM   #10
opa1 is offline opa1  United States
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Neat box. Looks like the front is about 22x30. Wonder how much difference it would make if the curved panels in back were straight? Would'nt be too hard to make.
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