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Old 13th January 2003, 03:57 PM   #1
Raka is offline Raka  Europe
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Default TL Bass reflex tuned

Hi,

Here I go again with my new project. After the success of my Detaché project, I will try to get more bass.

Now I have another beyma product: The 6B30P, a 6,5" poly woofer. Fs=55Hz. Vas=18l. Qts=0.62 Xmax=4mm. 90dB/m.
I liked very, very much the 5MP60/N, so I'll try its big brother.

I'm trying to design a TL, but I'd like to clarify some points:
- The TL target is to get rid of the backwave as long as the wavelenght shorter than Fs is eaten in the tube by the filling.
- The other purpose is to extend the bass response, since the wave that is not eaten exits through the "port", adding low output to the main wave.

Is this correct?
If so, at what frequency should I tune the 1/4 of the wavelenght? to the resonant frequency of the driver on free air? Or maybe to the resonant frequency of the driver on the selected enclosure? Why should it be to the resonant freq. of the driver? Taking the bass reflex as example: I can fine tune the port to my taste, getting plain response, peaked one, or whatever I'd like, not exactly to Fs. Should this be applied to the TL?

Thanks,
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Old 14th January 2003, 02:44 AM   #2
MJK is offline MJK  United States
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Hello Raka,

If you would like to design your TL, and get some idea of the performance before you actually build it, then you might consider trying my MathCad worksheets. Many people have used them and have built TL's that worked as predicted by the math model results.
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Old 20th January 2003, 10:49 AM   #3
Raka is offline Raka  Europe
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Default Worksheets

Thanks for your work!
I've downloaded your worksheets and the Mathcad explorer 8. I opened the closed box file, and no graph is drawn. Do I have to do something? I haven't written any number yet, is the example complete? with the given values of the focal unit, in the Qtd field appears: "This variable or function is not defined above". Only if I write a Qed value >0 then it works. Anyway, in the graphs doesn't appear a graphic, just blank.
Help with mathcad!! I'm an excel boy!!

Thanks.
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Old 20th January 2003, 12:17 PM   #4
MJK is offline MJK  United States
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Hi Raka,

All of the files should run when you open them, graphs should calculate as you scroll down. Does your computer use a comma or a period for a decimal point? It needs to use a period, if it is set to use a comma you need to change the computer set-up. This is the most common problem I have encountered in running the worksheets and it exhibits the behavior you describe.
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Old 20th January 2003, 01:04 PM   #5
Raka is offline Raka  Europe
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Thanks for your interest,

How do I change the pc setup?
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Old 20th January 2003, 02:10 PM   #6
Raka is offline Raka  Europe
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Default I found out

I've already found the way. Just to change the country I live in.
Works fine your software. Now I need to use the files in order to get used to it and develop my design. I'll need your help, so be prepared to answer my boring questions!

Thanks a lot for sharing your knowledge.
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Old 20th January 2003, 05:21 PM   #7
MJK is offline MJK  United States
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Hi Raka,

Sounds like you are on your way, I am glad the fix was easy. Please do not hesitate to ask any questions you might have, I may know the answer to a few of them.
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Old 20th January 2003, 07:04 PM   #8
kneadle is offline kneadle  United States
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I can tell you that there are many people watching this thread as it develops into a project. Keep us posted!

Dave
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Old 22nd January 2003, 07:51 AM   #9
Raka is offline Raka  Europe
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Default Any Hint?

I've been playing with your software, and seems to be so powerful that fears me (I don't know what direction should be followed). Well, as far as I've found out, the problem of the TL is to tune it until it loads acoustically the driver in a proper way. That gets a lower resonance of the driver in the enclosure (or damp it), and make the waves inside to behave, and to add output as desired.
Is this correct?
It looks like if a checkpoint for a good design is a flat impedance curve in the low end, isn't it?
I'm starting with a lenght equal to the 1/4 wavelenght of the free air Fs, 1.25Sd to 1Sd and constant stuffing. Are those good figures to start with?
I'm still reading and understanding your text, so be indulgent with my questions...

What is n_open?
In the "transmission line definition", I don't have to introduce any value, do I?
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Old 22nd January 2003, 08:14 AM   #10
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Default Re: Any Hint?

Quote:
Originally posted by Raka
I'm starting with a lenght equal to the 1/4 wavelenght of the free air Fs, 1.25Sd to 1Sd and constant stuffing. Are those good figures to start with?
If tapering the line better to start with 3 or 4 Sd tapering to Sd (the line volume is actually not related to Sd but to Vas {which does tend to go up with Sd}). A narrowing taper moves the resonant modes of the line such that you will find that a line shorter than 1/4 Fs is more appropriate.

dave
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