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
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
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.
MJK said:
While you are their read as much as you can...
Is this the calculator linked from Madiosound? http://www.mh-audio.nl/Transmission Line Loudspeakers.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
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.
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.
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.
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.
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.
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. 🙄
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. 🙄
Re: Tables
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?
jmillerdoc said:
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?
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
😎
I plan on using the W0838R-8".
Thanks
😎
Response to email
Paul, I just got your Email at 2:50 pm CST today and just sent you an email. Yes definitely want your help!!! Hope the offer still stands.
Thanks,
Jeff M.
Paul, I just got your Email at 2:50 pm CST today and just sent you an email. Yes definitely want your help!!! Hope the offer still stands.
Thanks,
Jeff M.
Re: Response to email
I sent you another email with some sample response graphs resulting from some modeling.
jmillerdoc said:
I sent you another email with some sample response graphs resulting from some modeling.
tadaa
first note: turn on macros, or it won't work (it uses a VBA formula to do the interpolation in the tables).
other points: I have protected the worksheets, but no password (to prevent accidental overwriting of the formulas); there are 2 sheets: one for the calcs from the tables and another that gives an example cabinet (single fold); fields shaded yellow are input, all other are calculated (and thus protected); field names have been used for the formulas to make things easy to understand;
so, here it is.
first note: turn on macros, or it won't work (it uses a VBA formula to do the interpolation in the tables).
other points: I have protected the worksheets, but no password (to prevent accidental overwriting of the formulas); there are 2 sheets: one for the calcs from the tables and another that gives an example cabinet (single fold); fields shaded yellow are input, all other are calculated (and thus protected); field names have been used for the formulas to make things easy to understand;
Thanks Henkjan,
I attempted this some time ago, but your spreadsheet is much more elegant than mine.
cheers,
Pete McK
I attempted this some time ago, but your spreadsheet is much more elegant than mine.
cheers,
Pete McK
I sent you yet another email, Jeff, to show modeling results for an ML-TL for an MTM. If using that email address isn't working out, do you have a different email address to use?
Delays
Paul,
Email is working fine, My real life (job) is getting in the way of my hobby. Please don't feel the delay in writing back represents a lack of appreciation. I have crazy hours these days.
Again, Thanks for all you have done, I'm going with the last design. I will post pics as the build progresses.
Jeff M.
Paul,
Email is working fine, My real life (job) is getting in the way of my hobby. Please don't feel the delay in writing back represents a lack of appreciation. I have crazy hours these days.
Again, Thanks for all you have done, I'm going with the last design. I will post pics as the build progresses.
Jeff M.
Henkjan,
I think it's great.
can you explain/comment on the use of the 'Correction on the line cross section' number?
Thanks,
Pete McK
I think it's great.
can you explain/comment on the use of the 'Correction on the line cross section' number?
Thanks,
Pete McK
Henkjan, dankjewel.
(/me switches back to english)
I am also currently in the proces of designing my own TL cabinet and am awaiting the arrival of the AJHorn product.
Ofcourse, any input on calculating the TL is welcome since Martin shut down access to his mathcad worksheets. Your spreadsheet is really really welcome at this very moment. So THANKS!
(/me switches back to english)
I am also currently in the proces of designing my own TL cabinet and am awaiting the arrival of the AJHorn product.
Ofcourse, any input on calculating the TL is welcome since Martin shut down access to his mathcad worksheets. Your spreadsheet is really really welcome at this very moment. So THANKS!
Martin has now also uploaded an Excel sheet based on his alignment tables on his site -it's in the TL theory section.
Suggestion: don't assume you have to tune to Fs. It's not automatically a good idea.
Suggestion: don't assume you have to tune to Fs. It's not automatically a good idea.
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