Transmission line or TQWT with 2 woofers in 2 way system ? - diyAudio
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Old 5th August 2002, 12:19 AM   #1
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Default Transmission line or TQWT with 2 woofers in 2 way system ?

Hello,

I am trying to design a 2 way speaker that has bass reproduction from a TL or TQWT till 2KHz with efficiency 95dB or more.
Is this possible? and what would be a good idea?
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Old 5th August 2002, 03:30 AM   #2
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Default Re: Transmission line or TQWT with 2 woofers in 2 way system ?

Quote:
Originally posted by promitheus
I am trying to design a 2 way speaker that has bass reproduction from a TL or TQWT till 2KHz with efficiency 95dB or more.
Is this possible? and what would be a good idea?
Certainly possible. 95 dB cuts down on the available driver units. 1st thing that springs to mind is the Fostex FE168 -- although its Vas is a little low to get the most out of a TQWT.

1st off, you want to look for a driver with Qt somewhere between 0.3 and 0.55 and then start playing with Martin King's TL modeling software.

dave
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Old 5th August 2002, 05:35 AM   #3
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Thanks for your reply.

Does this SW support two driver units in one box?
I am thinking of using two woofers to get high in efficiency.
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Old 5th August 2002, 07:17 AM   #4
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Quote:
Originally posted by promitheus
Does this SW support two driver units in one box?
I am thinking of using two woofers to get high in efficiency.
Not directly. You model for one in the average position and then double the line's cross-section. An example are these bipolar pipes.

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Old 5th August 2002, 05:09 PM   #5
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I wanted to be able to model a TL with 2 woofers. 1 at 1/3 and 1 at 1/5 of the line length. I have seen this a few times in different projects, as in the new Thor speaker in audioxpress.
Some people use 2xSd, Re/2, Qts same, 2xVas and so on.
Do you think calculating double cross section everywhee is enough?
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Old 5th August 2002, 06:02 PM   #6
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Quote:
Originally posted by promitheus
I wanted to be able to model a TL with 2 woofers. 1 at 1/3 and 1 at 1/5 of the line length. I have seen this a few times in different projects, as in the new Thor speaker in audioxpress.
The Thor was designed using the sketchy alignment tables provided by Augspurger. Augspurger's & King's SW are both in very close aggreement to one another, and whenever i look at the Thor i think "is it optimum" -- what could have been done if the actual analytical tools had been used to try out many more possibilities...

Quote:
Some people use 2xSd, Re/2, Qts same, 2xVas and so on.
Do you think calculating double cross section everywhee is enough?
These are the same thing. Augspurger showed that TL volume is proportional to Vas. Use 2 drivers, you double the Vas, since line length is fixed by the resonant mode you need to double the cross-section everywhere to double the volume.

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Old 8th August 2002, 03:01 PM   #7
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I would just email martin king directly. he's usually very pleasant and willing to answer thoughtful questions. Get his opinion on dual driver TL configurations.

mark k.
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Old 8th August 2002, 04:40 PM   #8
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Quote:
Originally posted by ucla88
I would just email martin king directly. he's usually very pleasant and willing to answer thoughtful questions. Get his opinion on dual driver TL configurations.
Yes Martin is very approachable, and enjoys the intraction. He is also busy so be patient.

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Old 8th September 2002, 10:37 PM   #9
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I've been looking at the Thor and I had a couple of questions.

1) I'm thinking of switching the top or bottom woofer to face outwards - this makes the two drivers more linear. (not an Isobarik, so I don't think this would change any of the line's parameters or design.

2) If 1), should I move the cone inwards to align the center of acoustic mass?

3) If I'm phase alinging the speakers per 2), how about insetting the tweeter as well?

If I do all of this, my thought is that the top part of the enclosure could be offset by an inch or two. This would reduce the volume though, so I'd probably have to work the math.

Thoughts?
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Old 8th September 2002, 11:30 PM   #10
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Quote:
Originally posted by jgwinner
1) I'm thinking of switching the top or bottom woofer to face outwards - this makes the two drivers more linear. (not an Isobarik, so I don't think this would change any of the line's parameters or design.
By outwards do you mean onto the side of the enclosure? This, or taking it further and moving the other driver (& the T) to the other side and then making this the front (ie a bi-pole), will certainly require tweaking the XO.

And if one assumes the line is optimal (& i'm not convinced it is) you would need to move the drivers vertically so that they are at the average position of the drivers when in the MTM (ie preserve the driver offset from the end of the line).

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