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Old 12th February 2013, 09:27 AM   #41
tinitus is offline tinitus  Europe
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may be a daft question
but how much does isobaric change the volume of a TH can't imagine it would be half size

Quote:
Originally Posted by Xoc1 View Post
Looking back over this thread and trying to make the isobaric TH work.
I don't understand what you say
are you trying make your woofer go lower than its Fs
sometimes could look like that with vented BR
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Old 12th February 2013, 01:35 PM   #42
tb46 is offline tb46  United States
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Hi tinitus,

The best way to answer your question is in Hornresp. Take any TH (e.g.: jbell's SS15), and calculate the SPL response, then change the driver to isobaric (Edit/Tools/Driver Arrangement) and also divide all S values by 2. The result should be pretty much the same response only 6dB lower because of the doubled impedance (same volatage, half the current); see attachement (and yes, they are not identical):

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File Type: jpg SS15_short_S1_single_v_isobaric_SPL.jpg (29.4 KB, 286 views)
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Old 12th February 2013, 09:24 PM   #43
tinitus is offline tinitus  Europe
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Quote:
Originally Posted by tb46 View Post
....; see attachement (and yes, they are not identical):
is that correctly calculated ?

looks like the peak stays the same, but useable output is much less, so...not so good
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Old 12th February 2013, 10:02 PM   #44
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Quote:
Originally Posted by tinitus View Post
is that correctly calculated ?

looks like the peak stays the same, but useable output is much less, so...not so good
If the speakers were in parallel rather than series, the output would be about the same, but would use twice the power and drivers, still "...not so good".

Really, the only reason to consider isobaric is when using low Bl (whimpy magnet) drivers that can't push the air column without "teaming up".

Here is an example:

$10 (plus wood) 18Hz ISOT-TQWP Sub

If only one of those cheap drivers were used, the response would look like a "U" instead of "--".

Art
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Old 12th February 2013, 10:09 PM   #45
tinitus is offline tinitus  Europe
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oh in my world a 100 dollar woofer is cheap, or should I say, cheap enough
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Old 12th February 2013, 10:19 PM   #46
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Quote:
Originally Posted by tinitus View Post
oh in my world a 100 dollar woofer is cheap, or should I say, cheap enough
$10, $100, $1000, ten dB increases.
Every DIY er gets to decide on their budget and SPL requirements.
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Old 12th February 2013, 10:28 PM   #47
tinitus is offline tinitus  Europe
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could be, but not sure its that simple
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Old 12th February 2013, 10:29 PM   #48
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Quote:
Originally Posted by weltersys View Post
Really, the only reason to consider isobaric is when using low Bl (whimpy magnet) drivers that can't push the air column without "teaming up".
Hi Art,

Being the thread starter who lost interest a long time ago due to the fact I didn't bother to look at the driver Q before posting, I urge you to look at the first post to see why dual driver isobaric is a viable option for me. There's no need for sensitivity, the watts are there, I have a desire to downsize the cabinet, that's all. I have the 'whimpy' drivers and they aren't suited to a TH, that's the end of story for me. Thanks for adding your thoughts.

Cheers.
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Old 12th February 2013, 11:03 PM   #49
GM is offline GM  United States
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Downsize how much? The BIB concept tuned to ~23 Hz I did is ~78.5 L net and has 5-10 dB more output than same size ported.

GM
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File Type: gif Reckhorn W-130 BIB TH Vs same size BR.gif (17.7 KB, 255 views)
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Old 5th October 2013, 03:26 PM   #50
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Quote:
Originally Posted by Cal Weldon View Post
I have 4 - 6.5" drivers but only room for two rather small cabinets. Any chance of making this work?
Hey Cal. I have 4 peerless 6.5" buyouts from PE; I like your isobaric tapped horn idea . Wondering if you proceeded with the project. Mitchell.
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