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Multi-Way Conventional loudspeakers with crossovers

need help with TL calculations
need help with TL calculations
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Old 2nd March 2009, 11:37 PM   #1
jmillerdoc is offline jmillerdoc  United States
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Question need help with TL calculations

Can anybody tell me where to find a TL calculator that will allow for 2 drivers instead of one? For instance, there is a calculator link on Madisounds website... It seems to me the only variable that would need to be changed is the effective area of the driver...can you simply enter in twice the area for 2 drivers and keep all other variables constant? If this is the case where would you start the length measurement for the TL? Somewhere1/2 way between the 2 drivers? ( this is assuming the MTM axis is in line with the long axis of the TL)

Since nobody has been able to give me a proven design I have decided to try a MTM TL with the Vifa P17WJ00 and Morel MDT33 and let Madisound design the crossover for $30. I'll keep y'all informed when it's done!
Thanks to all,
Jeff
millerjeff@ccmhonline.com
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Old 2nd March 2009, 11:44 PM   #2
MJK is offline MJK  United States
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If you go to my site and look under the General Speaker Related Articles link, there is a short write-up about how to model two discrete drivers as a single equivalent driver. The equivalent driver model is different for drivers wired in series and parallel. You would then place the single equivalent driver half way between the two real drivers in the computer simullation model.
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Old 3rd March 2009, 12:45 AM   #3
planet10 is offline planet10  Canada
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need help with TL calculations
Quote:
Originally posted by MJK
General Speaker Related Articles link,
While you are their read as much as you can...

Is this the calculator linked from Madiosound? http://www.mh-audio.nl/Transmission%...udspeakers.asp

It is a classic line calculator and is very unlikely to generate anything near optimal. You'd be better off with Martin's tables.

dave
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Old 3rd March 2009, 08:34 AM   #4
Scottmoose is offline Scottmoose  United Kingdom
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Just to point out Jeff, it's perfectly possible to take an existing, proven BR speaker kit (or just design) & come up with a TL cabinet for it. That's no big deal. Some are more suitable than others, naturally, but the vast majority should be fine. For e.g., I designed a TL cabinet for Zaph's BAMTM a few months back -not sure if anyone's built it, but it should be a great box.

To re-echo Dave's comments, avoid the older design calculators -they're usually way off the money WRT line-length and pipe volume. The more recent tables, such as Martin's, will give you a much greater chance of success.
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Old 3rd March 2009, 10:58 AM   #5
jmillerdoc is offline jmillerdoc  United States
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Default Tables

It's the tables I am having a hard time with now, UUUUGGGHHH. Im not sure I understand exactly how to use them. Study, study, study.
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Old 3rd March 2009, 11:20 AM   #6
Henkjan is offline Henkjan  Netherlands
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I have made an excel sheet that automates Martin's allignment tables. it is not in english at the moment, if you have some patience I'll translate it and post it here.
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Old 3rd March 2009, 11:36 AM   #7
Scottmoose is offline Scottmoose  United Kingdom
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It's not all that difficult. They look harder than in fact they are. Remember, Martin's done the spade-work for you.

1/ Select line length for a given tuning frequency & taper. Pretty self explanatory.
2/ Select the Dz value, again, based upon your selected tuning frequency & taper. Again, not difficult -just read the value off from the table.
3/ Select the appropriate Dr value for the driver Qt. There is some fudge factor here, as naturally, not all possible Qt numbers are given. Use the existing values to approximate for your own unit.
4/ Select the approriate driver offset ratio (not rocket-science; again, just read it off the table).
5/ Square the Bl value of the driver & write it down.
6/ Carefully work out the following:

1.21 x 342 x driver surface area in square metres x Dz x dr x driver Re. Then divide by Bl squared (which is why I said work it out in advance). That gives you the CSA for the throat (sealed end of the line) expressed as a multiple of the driver surface area. The terminus area will be a percentage of that based upon your selected taper, so divide by 2 if a 2:1 is selected & so on & so forth.

What Martin's tables don't really cover are the selection of an appropriate damping density. I believe he sets a general assumption of dacron (the material used does make a difference however) and 0.5lbs ft^3. So you'll have to experiment somewhat.

Remember, if you're using two drivers, if in parallel (which is usually the most common method), double Sd & Vas, & halve Re before entering any data into the equations / formula above. Alternatively, be a luddite, work it out for the single unit, then double the line cross-section.
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Old 3rd March 2009, 04:45 PM   #8
pkitt is offline pkitt  United States
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Default Re: Tables

Quote:
Originally posted by jmillerdoc
It's the tables I am having a hard time with now, UUUUGGGHHH. Im not sure I understand exactly how to use them. Study, study, study.
Jeff, I sent you an email yesterday and offered to model a TL for you using Martin's worksheets and I asked you some questions to guide my efforts. Did you not get that email? Or, do you just prefer to do this yourself?
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Old 3rd March 2009, 05:35 PM   #9
Cambe is offline Cambe
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I could use some help with a TL sub. Could someone model a TL for me using Martins worksheets? Something folded .
I plan on using the W0838R-8".
Thanks

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Old 3rd March 2009, 06:08 PM   #10
Cambe is offline Cambe
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Oops!
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