El-Pipo using Jensen 15" - diyAudio
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Old 30th October 2009, 06:02 PM   #1
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Default El-Pipo using Jensen 15"

I was looking through the NHT surplus drivers and the Jensen 15" caught my eye.

How would it do in a simple el-pipo style straight sonotube transmission line, about 8.5 feet tall for the 33 Hz Fs? The Qts seems to be in the ballpark, but Qms is rather high.

Xmax is rather low, but with the high sensitivity, it should be pretty decent.

Cheers!

Part # Jensen 15"
Cone material Paper
Re 4.73
Fs 33.2
Qms 8.049
Qes 0.356
Qts 0.341
Vas 266.80
Cms 0.000263
Mms 87.7
diameter 329
BL 15.57
SPL 96.20
Zmax 111.5
Sd 0.08501
Xmax 6.0
Hg 8.0
Wire material Copper
# of coil layers 2?
Coil diameter 64
Frame OD 389
Through hole diameter 357
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Old 31st October 2009, 08:50 AM   #2
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Come on guys!

Any last words before I send 10 bucks to Jack?
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Old 31st October 2009, 09:17 AM   #3
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Run the numbers thru MJK's TL tables and see what you get. With end correction it will likely be closer to 8' long.

Curiosity got the better of me... 331 in^2 xSection, 95" long. That gives a pipe diameter of 20.5". It also suggests an driver offset of 32" but given an El Pipo that is moot

dave
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Old 1st November 2009, 04:47 PM   #4
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Thanks Dave!

I'm curious as to the effect of using a smaller than recommended pipe diameter (The pipe i have is 12"). Many have built El Pipo with one driver, then added another driver (NP himself did this) without noticing any significant deterioration of SQ or other nasty effects.

Is there a more scientific way to quantify the effect of a certain pipe cross section, either too large or too small?
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Old 1st November 2009, 08:44 PM   #5
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Too small a pipe means a significant reduction in bass (you end up with a long skinny aperiodic box) -- you will note that Nelson used a filter that threw away gobs of efficiency because his pipe was too small.

I did do a sim for an isobarik pair which came out to about 14" IIRC but figuring it would be tricky to fit a 15" driver into a 14" tube discarded it.

dave
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Old 2nd November 2009, 11:58 PM   #6
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Thanks. Is that conclusion from simulating different cross sectional areas, and comparing the results?

Is there a more 'physics' explanation for the reduced efficiency?
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Old 3rd November 2009, 01:37 AM   #7
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Yes.

Vb is too small. You can look at it as less efficiency ifyou EQ it like Nelson did, or as not as extended if you don't.

dave
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Old 3rd November 2009, 02:56 AM   #8
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Quote:
Originally Posted by rhapsodee View Post
Come on guys!

Any last words before I send 10 bucks to Jack?
$10? You had me excited there for a sec. Spreadsheet still says $40 - web site $60. $10 puts those in the range of potentially disposable toys for experimenting with dipoles.
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Old 3rd November 2009, 06:24 PM   #9
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10 bucks to place the order. The AR 12" is only $30, still pretty good deal.

Dave: You mean Vb is too small relative to VAS? I've come across this comment several times for TL designs. Although Vb is not really an accurate description of the line, it usually works to build a line that has total volume near to the driver VAS.

Is there an optimum cross section or Vb? I have seen 1.5-2 x Sd as a good starting point. What happens if the TL cross section or Vb is too large compared to the driver?
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Old 3rd November 2009, 08:40 PM   #10
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Quote:
Originally Posted by rhapsodee View Post
Dave: You mean Vb is too small relative to VAS? I've come across this comment several times for TL designs. Although Vb is not really an accurate description of the line, it usually works to build a line that has total volume near to the driver VAS.
Vb in a TL is length x cross-section. Length is determines by Fs and the pipe geometry (with a straight pipe wl(Fs)/4 less end correction).

Quote:
Is there an optimum cross section or Vb? I have seen 1.5-2 x Sd as a good starting point.
Yes. Sd has no impact on the size of a TL (other than that there is a VERY loose correlation between driver size & Vas -- it is unfortunate that Martin choose Sd as a unit of area in his model, it confuses things). Just like any other box it is Vas (in combination with Qt and Fs)

The 1.5-2x Sd is classic design and you are as likely to get a good TL as you would be by getting spun around blind folded and trowing a dart. King's (and Auspurger's parallel, but not as well developed) model & software have revolutionized TL design. For a TL with a linear taper and no mass loading of the terminus, the spreadsheet based on Martin's table gets you really close to an optimum line just by plugging a few numbers in (note that as Martin uses them, Vas is buried in some of the other input numbers, and the formulas could be reworked to have that as an input)

Quote:
What happens if the TL cross section or Vb is too large compared to the driver?
It gets closer to an IB.

dave
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