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Multi-Way Conventional loudspeakers with crossovers

Help needed with TL calculation
Help needed with TL calculation
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Old 21st November 2017, 10:50 AM   #11
hugo stiglitz is offline hugo stiglitz  Germany
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you know there is wilmslow audio providing you with fully calculated and CNC'd TL cabinets?
3 way Transmission-line cabinets

all you have to do is gluing it together and give it a paint of choice
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Old 21st November 2017, 01:56 PM   #12
pkitt is offline pkitt  United States
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Your suggestion on using two drivers spaced apart sounds like it's bit of a "by guess and by gosh" process, meaning you can't model it to know what you're likely to get. I'd much rather use an accurate modeling program, like Martin King's, because if the modeled design looks to have good performance and I build exactly what I modeled, it will have good performance. Using less stuffing, either in density or length, will definitely lower f3, but it's not a lot and the difference is audibly not very much.
Paul

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Originally Posted by Mario Pankov View Post
Reason is his website is down by some reason. There i an offline installer here - Transmission Line Modelling Software

Dual smaller woofers would allow you to reduce the amount of stuffing because they can offset the line ripples caued by each if spaced orrectly. You have ot experiment but usually putting the drivers at 1/3 and 1/5 of the line length does the trick but sometimes they need to be spaced differently. With reduced stuffing, you will get more low end output.
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Old 21st November 2017, 11:05 PM   #13
pkitt is offline pkitt  United States
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Default Modeling graphs

Just wanted to follow up on the modeling I did as described in Post #7. I've attached 3 modeling graphs. The first one shows the predicted anechoic system bass response (red line) without any stuffing in the 15:1 tapered line where you can see that f3 is ~27 Hz (the system tuning is 24 Hz from the line's 1/4-wavelength resonant frequency). The second graph shows the response (red line) after stuffing is added as I described in Post #7, and you can see that f3 has now increased slightly to 30 Hz (the system tuning frequency has decreased to 22 Hz). The last graph shows the air velocity in the terminus as a percentage of the speed of sound, peaking at 1.6% (5.5 m/s) at ~18 Hz. This modeling shows the predicted response for an input of 35w/1m which is the power required to cause an excursion of the woofer to its Xmax rating, which it first reached at ~33 Hz.
Paul
Attached Images
File Type: gif SPH-300KE-1.gif (7.6 KB, 126 views)
File Type: gif SPH-300KE-2.gif (6.8 KB, 126 views)
File Type: gif SPH-300KE-3.gif (7.2 KB, 126 views)
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Old 22nd November 2017, 07:34 AM   #14
Mario Pankov is offline Mario Pankov  Europe
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Help needed with TL calculation
You can model them one by one by changing the location and then comparing the two graphs so the peaks and dips are matched to whatever extent possible. But you are right that there is uncertainty in this approach as I do not know how the woofers would affect each other when operating simultaneously loading the same line, not until I have built it. AFAIK, the program done by Len is based on the same formulas as the sheets you`re using, but it has a nie graphic interface and does not require a MathCAD license.
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Old 22nd November 2017, 08:55 AM   #15
Scottmoose is offline Scottmoose  United Kingdom
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Careful tap location of a driver (or driver pair) into the line at a single given point should eliminate the need for a large physical separation between the two. A closely mounted driver pair effectively behave (as far as the line is concerned) as a single unit and it is not difficult to optimise this to minimise unwanted excititation of harmonic modes without needing to resort to anything more complicated. Separating the drivers out & tapping them into significantly different points in the line can work if properly designed, but it's not necessary from the perspective of the acoustic loading / performance of the line. There may be other factors such as marketing, overall dimensions / shape of the enclosure, external driver position / height that requires alternatives of course.
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Old 22nd November 2017, 01:26 PM   #16
pkitt is offline pkitt  United States
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Keeping in mind what Scottmoose posted after you, if you had a pair of 8" woofers and a line that's 69" long, if the woofers were located at the 1/5 and 1/3 points, one of them would have its center at ~14" from the line's beginning and the other woofer's center would be at 23", for instance. It's likely, then, that the flanges of the woofers would either be touching or almost so. Therefore, if you model as if there's a single woofer at the midpoint of the woofers with twice the Vas and Sd, which works very, very well and the woofers are working in unison, you will have accomplished what you suggest and there will be no guessing or trial and error. BTW, I don't require a MathCad license because I have the free version of MathCad (Explorer 8 I think its called). It doesn't allow saving an electronic copy of any modeling that can be re-opened and worked on again, but that's a small "price" to pay.
Paul

Quote:
Originally Posted by Mario Pankov View Post
You can model them one by one by changing the location and then comparing the two graphs so the peaks and dips are matched to whatever extent possible. But you are right that there is uncertainty in this approach as I do not know how the woofers would affect each other when operating simultaneously loading the same line, not until I have built it. AFAIK, the program done by Len is based on the same formulas as the sheets you`re using, but it has a nie graphic interface and does not require a MathCAD license.
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Old 22nd November 2017, 03:22 PM   #17
Bill poster is offline Bill poster  Thailand
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Doesnt look like the woofer parameters wd suit a TL.
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Old 22nd November 2017, 05:35 PM   #18
pkitt is offline pkitt  United States
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Assuming the woofer's specs posted by the OP are reasonably representative, I used them and the predicted performance of the TL I modeled looks quite good to me.
Paul

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Doesnt look like the woofer parameters wd suit a TL.
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Old 22nd November 2017, 05:41 PM   #19
pkitt is offline pkitt  United States
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I thought I should add that for a pair of woofers closely located to each other, flange to flange essentially, I'd always use their midpoint as the TL's modeling center, locating it at either the 1/5 or 1/3 point along the line's length (or nearly so, at least) and not worry about each woofer's center not being exactly at either of these optimum locations.
Paul

Quote:
Originally Posted by pkitt View Post
Keeping in mind what Scottmoose posted after you, if you had a pair of 8" woofers and a line that's 69" long, if the woofers were located at the 1/5 and 1/3 points, one of them would have its center at ~14" from the line's beginning and the other woofer's center would be at 23", for instance. It's likely, then, that the flanges of the woofers would either be touching or almost so. Therefore, if you model as if there's a single woofer at the midpoint of the woofers with twice the Vas and Sd, which works very, very well and the woofers are working in unison, you will have accomplished what you suggest and there will be no guessing or trial and error. BTW, I don't require a MathCad license because I have the free version of MathCad (Explorer 8 I think its called). It doesn't allow saving an electronic copy of any modeling that can be re-opened and worked on again, but that's a small "price" to pay.
Paul
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Old 22nd November 2017, 06:09 PM   #20
planet10 is online now planet10  Canada
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Help needed with TL calculation
Quote:
Originally Posted by pkitt View Post
if you model as if there's a single woofer at the midpoint of the woofers with twice the Vas and Sd, which works very, very well
An example of this. A woden specified ML-TL. It does work very, very well. F10 near 25 Hz.

Click the image to open in full size.

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