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Old 17th March 2006, 04:12 AM   #21
jdybnis is offline jdybnis  United States
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Quote:
Originally posted by Corloc
O' I would be intrested in the joint chiefs for the B200. I have a sheet of 3/8" ply that has been sitting in the garage for a year or two. I'm shure that my wife would like it out of the way.
I'm sure she'll be pleased when you cut a hole in it and move it into the living room.
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Old 17th March 2006, 04:30 AM   #22
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Quote:
Originally posted by jdybnis
I'm sure she'll be pleased when you cut a hole in it and move it into the living room.
jdybnis,

You're under the wrong impression. These OB's are smaller than a bookshelf speaker, but larger than a typical computer speaker.
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Old 17th March 2006, 06:00 AM   #23
maxro is offline maxro  Canada
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Is it just my 'puter, or are the pictures not loading? I'm having a little difficulty picturing the design in my mind's eye.

This sounds interesting as I have a pair of old Goodmans, for which I cannot find any information. They have small magnets, so I'm assuming high Q and thus suitable for OB. I just don't have the space for a regular OBs in my apartment.

PS, anyone got any info on Goodmans twinax 220c?

Max
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Old 17th March 2006, 06:53 AM   #24
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I can't see the pictures either, which is a pity; I'd like some small speakers, and these sound rather nifty.
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Old 17th March 2006, 06:56 AM   #25
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A drawing will give you a better idea:

Here's what I've built and is working well, just a bit big since I'm using a 15" driver.

Click the image to open in full size.


I'll have some B200's to try in a couple of weeks. It will be drastically smaller and should have satisfying bass, but not the forget-a-sub bass like I'm getting with the 15" . The small one should compete or beat the extension of any reasonable sized RLH, but retain the natural OB sound.
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Old 17th March 2006, 07:19 AM   #26
jdybnis is offline jdybnis  United States
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Interesting. How much output are you getting out of the lower opening relative to the back of the cone?
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Old 17th March 2006, 08:45 AM   #27
maxro is offline maxro  Canada
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Quote:
Originally posted by jdybnis
Interesting. How much output are you getting out of the lower opening relative to the back of the cone?

Good question. I would think that the driver's backwave would just take the path of least acoustic resistance (straight out the back) and the folded transmission line/horn wouldn't even come into play.

So, just what is going on here to create deep bass response?

Max
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Old 18th March 2006, 03:06 AM   #28
maxro is offline maxro  Canada
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Hmm.. I did a little looking. It seems the TL part is acting as an acoustic high pass filter. although the proportions seem out of whack. Maybe I should try a gesstimate of measurements with the formulae from here:

http://en.wikibooks.org/wiki/Enginee...Implementation

Very interesting, indeed. More research is needed.

Max
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Old 18th March 2006, 05:19 AM   #29
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Quote:
Originally posted by maxro
Hmm.. I did a little looking. It seems the TL part is acting as an acoustic high pass filter. although the proportions seem out of whack. Maybe I should try a gesstimate of measurements with the formulae from here:

http://en.wikibooks.org/wiki/Enginee...Implementation

Very interesting, indeed. More research is needed.

Max
I believe the slot is the low pass filter which combined with the airspace in the horn shape determines what low frequencies go into the horn. I also believe the proximatey to the driver is important because that is where the highest pressure occurs, causing a portion of the low frequency content to see the slot as an acoutical shortcut. I looked to the forumla for Helholtz panel bass absorbers to guestimate an initial slot size.

I got a pair of B200's in today, so we'll see if I can get similar results with a smaller driver. It moves much more than my 15" driver at similar volumes, which tells me I'll have a higher pressure and velocity for loading the slot despite having a shorter open back chamber. I hope that will help make it able to load a wider bandwidth into the expanding pathway.
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Old 18th March 2006, 06:40 AM   #30
jdybnis is offline jdybnis  United States
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Obvious question, can you measure the impedance of the driver in the box? It should be informative.
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