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Old 4th January 2003, 07:08 PM   #11
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I took the liberty of adding another port arm to the Smallís equivalent circuit diagram of a BR type speaker. It becomes clear (I miss it the first time, and 2nd, andÖ) that Up1 and Up2 are separate until they add acoustically to Up(total) at the upper-right node. Also since Map1 and Map2 are not mutually coupled, they are free to resonate at their own frequencies with their own losses, amplitudes, and phases. This make both Charlesí and Alís cases logical. From there itís a matter of manipulating the individual losses and port dimensions to arrive at a suitable combination for the total output required (Qptotal). This is also without adding other reactive components like extra enclosures, which would be a entirely different ballgame, as Sy points out.

I think this also answers Rolfy72ís questions as well.

Rodd Yamashita
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Old 4th January 2003, 07:22 PM   #12
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Originally posted by roddyama
I took the liberty of adding another port arm to the Smallís equivalent circuit diagram of a BR type speaker. It becomes clear... that Up1 and Up2 are separate until they add acoustically to Up(total) at the upper-right node. Also since Map1 and Map2 are not mutually coupled, they are free to resonate at their own frequencies with their own losses, amplitudes, and phases. This make both Charlesí and Alís cases logical. From there itís a matter of manipulating the individual losses and port dimensions to arrive at a suitable combination for the total output required (Qptotal)..... I think this also answers Rolfy72ís questions as well.
Err, could you break that down just a teeny bit more for us non-engineers? Are you saying that when have two ports of different lengths, we end up with one tuning frequency, but the port output might have a peak that is broader than with a single port?

And could this be used to extend output lower than with a single port?
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Old 4th January 2003, 11:02 PM   #13
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Originally posted by kelticwizard


Err, could you break that down just a teeny bit more for us non-engineers? Are you saying that when have two ports of different lengths, we end up with one tuning frequency, but the port output might have a peak that is broader than with a single port?

And could this be used to extend output lower than with a single port?
Hi Kelticwizard,

Not quite. Each port has its own tuning frequency so will resonate at that frequency. So now you end up with two ports that resonate at different frequencies. When we talk about frequency response, weíre talking about the entire bandwidth of the speaker. Therefore, the contributions of both ports are included to provide output over a broader band. This is only when we are talking about response vs frequency or the frequency related effects.

In service, each port is going operate as a single port, and their outputs will add only when the resonances of both ports are being excited at the same time.

Rodd Yamashita
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Old 4th January 2003, 11:28 PM   #14
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Thanks for clearing this up Rodd, it's always nice to have someone who knows the math and theory around

I really must start learning more of the hard theory side, rather than just relying on my experience and ears, but for someone with a degree in psychology it gets difficult
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Old 5th January 2003, 12:29 AM   #15
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Does stuffing the port with drinking straws relate to this?

How about many straws, of differing lengths?

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Old 5th January 2003, 02:06 AM   #16
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Rolfy72,

Of course there is the double chamber reflex box - which is a known way of tuning a reflex to 2 different frequencies.... don't ask me how though!

Taking that to the next level - no doubt you can have a triple, quadruple etc.... box (sort of like a constricted TL )

Dave.
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Old 5th January 2003, 03:06 AM   #17
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Originally posted by Dave Bullet


Of course there is the double chamber reflex box - which is a known way of tuning a reflex to 2 different frequencies.... don't ask me how though!
For a thread on double chamber reflex boxes, complete with formulas and illustrations, see the following thread:
article about double chamber speaker enclosure
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Old 5th January 2003, 04:46 AM   #18
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Thanks Al. Certainly itís theory, although you have experimented with it and seemed to get some supporting results.

Math, Theory, Humm, un lezt zee, Zsychology? Is that like a story about Pabloís dogs?

Lawriebuck, All,

This is certainly not the last word in port design. Iím still thinking on this one as some things just donít set quite right yet.

Rodd Yamashita
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Old 5th January 2003, 07:55 PM   #19
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Thanks fella's, I thought that someone would've tried dual/varied lenght ports before!
So its not really not worth trying then?(plus I have no method of measurement or understanding...yet!)
And yup I've heard of the dual chamber with a port inbetween(sorta like a dual bandpass eh?) I've never heard any yet
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Old 6th January 2003, 01:42 AM   #20
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Rodd, NB that in most systems, Rap is assumed to be close to zero so that the port masses are in parallel. It's a good assumption if you don't put stuffing in the ports.
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