Short TL design

Timn8ter · 9th March 2004, 10:52 PM

In another thread that I almost hi-jacked Sreten posted this picture. I'd like to know how the cross-sectional area is determined in a design like this. It seems like a very narrow pipe. In back-loaded horns the top of the pipe starts out similar to this but gets wider as it nears the terminus.

sreten · 9th March 2004, 11:07 PM

I'd suggest the intention is for each vertical section to be
narrower, as you move towards the terminus.

But by introducing a shielded bass driver they had to tweak
the first divider giving a line profile not in any textbook.

You can't see the half depth of the box but I estimate
the CSA of the line to be ~ = to Sd of the bass driver,
in the first section of the line.

sreten.

Timn8ter · 9th March 2004, 11:46 PM

Thanks, I thought that it was about Sd but it's hard to tell from the picture. I'll have to play around with this. Folks seem to like little boxes.

GM · 9th March 2004, 11:58 PM

Hmm, all I can do is lay a scale on the screen, but it sure appears to be a constant cross section from the first fold to the terminus, and once you subtract out the drivers, probably the first section also. The terminal cup/XO causes a constriction in the pipe, though how much of one depends on how dense the foam is.

Anyway, more than likely it was determined by the decades old rule-of-thumb to make the line's effective cross sectional area = Sd, but as MJK's work has shown, this isn't the Hot Ticket to good overall performance for most drivers. As for short, well this just means a relatively high Fb if it's not reverse tapered.

Browse MJK's TL design tables to get some idea where to start.

GM

Timn8ter · 10th March 2004, 01:42 AM

I played around with So and SL equal to Sd and got some unpleasant results. I'll keep trying.

GM · 10th March 2004, 01:59 AM

Try whatever the max flat Vb is for whatever Fb you chose.

GM

9th March 2004, 11:58 PM	#4
GM diyAudio Member Join Date: Jun 2003 Location: Chamblee, Ga.	Hmm, all I can do is lay a scale on the screen, but it sure appears to be a constant cross section from the first fold to the terminus, and once you subtract out the drivers, probably the first section also. The terminal cup/XO causes a constriction in the pipe, though how much of one depends on how dense the foam is. Anyway, more than likely it was determined by the decades old rule-of-thumb to make the line's effective cross sectional area = Sd, but as MJK's work has shown, this isn't the Hot Ticket to good overall performance for most drivers. As for short, well this just means a relatively high Fb if it's not reverse tapered. Browse MJK's TL design tables to get some idea where to start. GM __________________ Loud is Beautiful if it's Clean! As always though, the usual disclaimers apply to this post's contents.

10th March 2004, 01:59 AM	#6
GM diyAudio Member Join Date: Jun 2003 Location: Chamblee, Ga.	Try whatever the max flat Vb is for whatever Fb you chose. GM __________________ Loud is Beautiful if it's Clean! As always though, the usual disclaimers apply to this post's contents.

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9th March 2004, 11:07 PM	#2
sreten diyAudio Member Join Date: Nov 2003 Location: Brighton UK	I'd suggest the intention is for each vertical section to be narrower, as you move towards the terminus. But by introducing a shielded bass driver they had to tweak the first divider giving a line profile not in any textbook. You can't see the half depth of the box but I estimate the CSA of the line to be ~ = to Sd of the bass driver, in the first section of the line. sreten.

9th March 2004, 11:46 PM	#3
Timn8ter diyAudio Member Join Date: Jul 2003 Location: Seattle, WA	Thanks, I thought that it was about Sd but it's hard to tell from the picture. I'll have to play around with this. Folks seem to like little boxes.

10th March 2004, 01:42 AM	#5
Timn8ter diyAudio Member Join Date: Jul 2003 Location: Seattle, WA	I played around with So and SL equal to Sd and got some unpleasant results. I'll keep trying.

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