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Old 7th October 2004, 08:39 PM   #1
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Smile TL and JBL could it work

Hi

Is there anybody out ther who have ever built TL speakers for JBL drivers.
If so what is your experiences ?

I plan to start a TL project to build a TL subwoofer where the
speaker shall be a 15 inch JBL bass driver (probably the 2215H former "LE15")
I could allso choose the JBL 2245H (18 inch) but in the beginning I will
try the 15 inch model.

I have installed the MathCad 8 Explorer (freeware) and have done a lot
of simulation plots for the 15 inch driver (Martin J King´s worksheet TL Sections), on a Mac with installed Virtual PC 5.0.4-Windows 98.

But I´m not so experienced with the plots and I don´t know what to look
for in the plots. Any sugestions ?

The box / cabinet could not be bigger than w=23, H=45 D=18 (outer dimensions, inches).

Regards
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Old 7th October 2004, 11:26 PM   #2
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Transmission lines are wonderful things. They are quite forgiving. In this case, I think a JBL would be a very interesting experiment, indeed.
Go for it.

Grey
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Old 8th October 2004, 12:00 AM   #3
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Can you give us the driver parameters?
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Old 8th October 2004, 12:59 AM   #4
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Default Parameters for the JBL 2215H

Hi Timn8ter

Thank´s for asking.
These are the parameters of the driver (JBL 2215H):
fs=20Hz, Qts=0.21, Qms=5.5, Qes=0.22, Vas=736.2, Re=5.7 ohms
Le= 1.0mH, BL=22N/Amp Mass=97g, Xmax=4.06, P=100W, Eff=2.6%
Flux=0.9T (9000 Gauss)

If you would like to do some simulations you could start with a TL dimension
like this: Sd=880cm2. So=2.0 x Sd, SL=0.3 x Sd, total length L=100 in
Driver offset= 7 in from closed end. SL (small / opened end) must be at the same side as the woofer

Hope this is a beginning

Ragards
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Old 8th October 2004, 03:13 AM   #5
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http://www.jblpro.com/pub/technote/thiele.pdf

GM
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Loud is Beautiful if it's Clean! As always though, the usual disclaimers apply to this post's contents.
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Old 8th October 2004, 04:40 AM   #6
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TL's tend to need a fairly large cross sectional area relative to the SD of the driver so a big driver usually means a massive TL ...

I suspect with sub drivers you might be able to get away with some eq as when the cross section gets close to SD with something like a sonotube TL you tend to get early rolloff.

There's an interesting article on Pass Labs about some massive sonotube TLs you might like to see ...

As far as those drivers go, how about posting some of your results in MathCAD? That would be a good start ...
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Old 8th October 2004, 07:30 AM   #7
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My thinking seems to be going the same direction as paulspencer's. Consider making your line shorter and your cross-sectional area larger. Skip the tapered line. Something like a 84" line and a cross section of 360"^2. I'm just tossing numbers out but something like that would probably work better.
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Old 8th October 2004, 12:03 PM   #8
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Default Model in WinISD first

This driver is not suited to a sub in general or a TL in particular. The Qts is much too low.

A TL mimics a sealed box, a MLTL mimics a vented box, and in both cases you can model them in WinISD first to see how a driver works in those alignments to judge its suitability in a TL or MLTL. The 2215 in a vented box has an f3 of 50Hz, in a sealed box an f3 of 70 Hz. That makes a TL completely out of the question, and a MLTL marginal at best, and certainly not worth the large cabinet that would be required or high cost of the driver.

The only alignments that can get to even 30 Hz with this driver are 4th or 6th order bandpass; a horn could take it to perhaps 25 Hz. In short this is not a driver for a sub.
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Old 8th October 2004, 05:35 PM   #9
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Hello

BillFitzmaurice has expressed this opinion on low Qts drivers in TL's in another thread on the latter. I and many others, including M J King, disagree. If you look at the TL's that have been built in the past most have used low Qts drivers. Even the Kef 139B which was used in many famous models over the years IMF - Rogers, etc, had a low Qts according Bills's criteria, of 0.36. I have built a number of TL's using Seas units with Qts's of between 0.25 and 0.28, and all have worked superbly. The most recent Line I built for a friend uses a Scanspeak 8554, which has a spec Qts of " 0.22 ". As with the above Seas, the bass end is superb, tight and deep. So if I were you I would try it in a line, you can model it on MJK's worksheet, you may well like the result. I do not know why Mr Fitzmaurice insists that there is only one way to build TL's.

Roy
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Old 8th October 2004, 10:35 PM   #10
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I do not know why Mr Fitzmaurice insists that there is only one way to build TL's.
I only offer advise either based upon what I have personal experience with or when I have read published results by recogized experts in the field of loudspeaker design. If you'd care to tell me what publication I could see your measured results in I'd certainly give them due consideration.
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