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Old 21st March 2008, 10:10 PM   #1
schmeet is offline schmeet  United Kingdom
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Default Transmission Line Question (Yet Another)

Ok then,

i understand the basic principles of transmission lines and how they work. My question is, could you put two or more speakers onto the front baffle of a TL (sharing the same "pipe"). i have never seen this done anywhere so it leads me to believe that it wont work.

My initial thoughts are that it might actually help to reduce the higher resonant peaks, in teh same way as moving the driver down the line, say 1/3 or 1/5 helps to reduce them, having a driver at the beginning AND 1/3 the way AND 1/5 the way may also do the same thing.

However my knowledge of ported and sealed boxes tells me that you can't just use an enclosure that works for one speaker and put another one or two into it. You ned to double the size of the enclosure, or halve the size of the enclosure if they are isobaric.


Any thoughts?

Pete
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Old 22nd March 2008, 12:03 AM   #2
bjorno is offline bjorno  Sweden
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Quote:
...i understand the basic principles of transmission lines and how they work. My question is, could you put two or more speakers onto the front baffle of a TL (sharing the same "pipe"). i have never seen this done anywhere so it leads me to believe that it wont work...
Hi,

If you put your drivers side by side, i.e. both the drivers sees the same CSA and section length will work without flaws but placing at different CSA: s makes a difference.

Quote myself from an earlier posting:

'See the animated system freedom of two degrees coupled oscillators and try imagine what happens when (n) drivers all slightly off specification is put in a long narrow box where also the acoustic load behind each driver is different but box position symmetric, hence the action from the many different ‘stretchy cords’ that must exist in a box with many drivers sharing the same volume:'

http://www.kettering.edu/~drussell/D...d/coupled.html


http://www.kettering.edu/~drussell/D...multi-dof.html


The problem with drivers at different section positions will show up in an impedance plot and in a FR plot too.

Risk exist that the drivers are working counteractive at some frequencies making the FR less smooth than necessary.

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Old 22nd March 2008, 12:07 AM   #3
GM is offline GM  United States
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Yes, just double the pipe's net Vb, i.e. same length, double its CSA.

WRT Having them at two different points, this is in essence what a TH does with just one driver.

GM
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Old 22nd March 2008, 09:54 AM   #4
schmeet is offline schmeet  United Kingdom
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Ok, So if I kept the first "leg" of the line the same, i.e. not tapered where the drivers are then i could have them one on top of the other. (As two 10" drivers side by side would call for a huge box!)

GM: What does TH stand for?

So does the CSA need to be doubled or not ??
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Old 22nd March 2008, 09:57 AM   #5
schmeet is offline schmeet  United Kingdom
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For example. This box below uses 3 woofers in the same transmission line and that line surely isn't 3 x the normal CSA.

http://www.weidinger-online.de/tml/seas.html
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Old 22nd March 2008, 02:51 PM   #6
GM is offline GM  United States
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TH = tapped horn: Collaborative Tapped horn project

If you want it to have the same response as the single driver alignment it must have 2x the net Vb for two, 3x for three, etc., same as for sealed or vented. The physics doesn't change for TLs, horns, etc..

How do you know it's not 3x a single driver alignment? Regardless, obviously you can design based on the composite specs of 'X' number of drivers and not necessarily wind up with the same response as for a single driver, but if you have a specific alignment in mind you will within a very narrow margin of error.

Physics, it's the Law!

GM
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Old 22nd March 2008, 03:49 PM   #7
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Quote:
..For example. This box below uses 3 woofers in the same transmission line and that line surely isn't 3 x the normal CSA…
Agree with that but again, IMO, it’s not a good design either, look at the following simulations: picture 1(3)-3(3).

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1(3)
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File Type: gif 1-temperance_seas.gif (68.4 KB, 415 views)
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Old 22nd March 2008, 03:51 PM   #8
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2(3)
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File Type: gif 2-temperance_seas.gif (56.6 KB, 363 views)
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Old 22nd March 2008, 03:53 PM   #9
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3(3)
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File Type: gif 3-3x seas.gif (45.2 KB, 340 views)
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Old 22nd March 2008, 04:28 PM   #10
bjorno is offline bjorno  Sweden
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FYI:

Note: In the pictures: 1(3() = 1-temperance_seas.gif and 3(3) = 3-3x seas.gif the calculated Qt values are 0.636 respective 0.5 and are based on only one driver sensing the simulated TL volume if the box is closed.
If based on 3 drivers the corresponding Qt values will be: 0.987 respective 0.714.

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