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Old 7th August 2006, 01:14 AM   #1
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Default Multi driver TLs

I was thinking about a TL sub using two drivers. At first I envisioned what amounts to two seperate TLs in a single box but I figure some space could be saved by mounting the two drivers in the same line. The question is how to simulate it.

-Would you design a line for a single driver and then just double the area of the pipe?

-Or would you design a single pipe for an imaginary driver with twice the Sd and Vas?

-My next thought concerned placement. I know that drivers are often placed part way down the line to smooth out the high frequency irregularities (not completely clear on the theory behind that yet) so the immediate question that comes to mind is what would happen if we placed one driver toward the beginning of the line and the other part way down the line as shown below? Anyone ever try that?

-Another possible variation is to place two drivers with different parameters in the same pipe. If drivers were chosen carefully might they possibly compliment each other making a system with a wider passband than is possible with either driver alone (in a non-stuffed line)? Thoughts?

mike
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Old 7th August 2006, 01:22 AM   #2
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I would think you'd want to mount them as symmetrically as you could, IE have a wider face so you could mount them side-by-side in the line so they were at the same position relative to the beginning and end of the line.
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Old 7th August 2006, 02:03 AM   #3
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What I was wondering is if the minima and maxima of each position might be arranged to cancel the other.

mike
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Old 7th August 2006, 09:41 AM   #4
sreten is offline sreten  United Kingdom
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Hi,

There are a number of TL designs using two drivers to smooth response.

THe simplest is the Thor : http://seas.no/thor.htm

more complex the Ariel : http://www.nutshellhifi.com/Ariel.html

Exact cancellation of modes is difficult, smoothing easier.

/sreten.
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Old 7th August 2006, 01:08 PM   #5
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take a look at Martin King's website -- he has written several white papers on the topic. http://www.quarter-wave.com/
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Old 7th August 2006, 11:05 PM   #6
Ap is offline Ap
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I would get the drivers as close together as possible - this way they will couple more effectively. Placement 1/3rd the way down the line is best for hf response. As for size just double Sd. If your calculations require Vas then double that as well.
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Old 7th August 2006, 11:18 PM   #7
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Quote:
Originally posted by Ap
I would get the drivers as close together as possible - this way they will couple more effectively. Placement 1/3rd the way down the line is best for hf response. As for size just double Sd. If your calculations require Vas then double that as well.
and don't forget to manipulate Re as well.
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Old 7th August 2006, 11:36 PM   #8
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Very good. Thanks for all the good tips. I was thinking allong the lines of a more extremem version of what the Thor does (but for sub only so sans tweeter and stuffing).

I will probably have to find a way to get Martin's stuff to work on my computer (or just learn the mathematical theory so that I can calculate this myself) since the software I have can not model driver location. If I could determine the locations that would attenuate the first and second irregularities I could then try placing a driver at each location and see what happens.

mike
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Old 8th August 2006, 12:51 AM   #9
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I have heard that MJK's spreadsheets can do this task. I have seen and heard of people using this method (on the internet, not in person), but most of the time you see the drivers mounted close together at the end of the line. Supposedly they work magic on the harmonics and work good for low response as well, because they are located at the end of the line. Unfortunately, most of the info I have happened upon on this subject are on non-english webpages, so I don't know much.
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Old 8th August 2006, 01:21 AM   #10
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As I reviewed Mr. King's web pages it appears that I may have misunderstood the effect of offset drivers. It appears that the 1/3 length placement affects all of the harmonics not just the first. If so then different locations for multiple drivers probably does little if any good.

What was not clear is how one adjusts the location in a tapered line so that the impedences of the closed and open lines work together for proper cancellation. I would guess that the driver would need to be less than a third of the way down in a tapered line.

mike
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