I would like to make a TL subwoofer for my upcoming HT setup. I live in a small Mobile home so I don't have a lot of room and the neighbors are close by.
I was thinking of making one with two 7" or 8" woofers with an amplifier for madisound (Keiga). I've been doing some reading on the subject of TLs but it's all new to me.
I was thinking of using Peerless 832732 7" woofer. Some specs are as follows:
fs - 34Hz
Qts - 0.36
Sd - 130.0 cm^2
Xmax - 5.5 mm peak
Sens - 87.9
Max P - 150W
Now why would I want to use 7" woofers? Well I don't really want or need 20Hz extension I my current situation. 35Hz would be ok with me (I used to have a Boston Accoustics 10" powered sub, which had an F3 of 32Hz, but fell upon bad times and had to sell it . Hence the trailer).
I also want and kinda need a narrow baffle. Depth isn't such a problem nor is the height. So i figure the line would be folded behind. If anyone has seen the Yamaha sub which uses two 7" drivers you might get an idea of the shape of the box I'm going for.
I've learned that a 1/4wave line tuned to 35Hz would be 8.1 feet undamped, and 2.9 feet damped with long fiber wool (8kg/m^3).
This is because of the change in the speed of air through the wool, which is c = 405 ft/sec (vs c = 1130 ft/sec for air).
I've also learned that the start of the line should be 1.25 ~ 2.5x the Sd of the woofer(s) used. The start of the line is a matter of choice but should be no less than 25% larger than the Sd. The end, or opening of the line should be equal to the Sd.
Does anyone one out there think a novice, like myself can pull this off?
Any comments would be of great help. I haven't alot of money for this future project some where around $300 ~ $350. Also I would like to ask that comments about vented or sealed alternative be kept to a minimum, but if you have to be my guest
Thanks!
MS* I just stated reading Martin King"s very informative site. But would still like comments from all you knowledgable folks.
*message script
I was thinking of making one with two 7" or 8" woofers with an amplifier for madisound (Keiga). I've been doing some reading on the subject of TLs but it's all new to me.
I was thinking of using Peerless 832732 7" woofer. Some specs are as follows:
fs - 34Hz
Qts - 0.36
Sd - 130.0 cm^2
Xmax - 5.5 mm peak
Sens - 87.9
Max P - 150W
Now why would I want to use 7" woofers? Well I don't really want or need 20Hz extension I my current situation. 35Hz would be ok with me (I used to have a Boston Accoustics 10" powered sub, which had an F3 of 32Hz, but fell upon bad times and had to sell it . Hence the trailer).
I also want and kinda need a narrow baffle. Depth isn't such a problem nor is the height. So i figure the line would be folded behind. If anyone has seen the Yamaha sub which uses two 7" drivers you might get an idea of the shape of the box I'm going for.
I've learned that a 1/4wave line tuned to 35Hz would be 8.1 feet undamped, and 2.9 feet damped with long fiber wool (8kg/m^3).
This is because of the change in the speed of air through the wool, which is c = 405 ft/sec (vs c = 1130 ft/sec for air).
I've also learned that the start of the line should be 1.25 ~ 2.5x the Sd of the woofer(s) used. The start of the line is a matter of choice but should be no less than 25% larger than the Sd. The end, or opening of the line should be equal to the Sd.
Does anyone one out there think a novice, like myself can pull this off?
Any comments would be of great help. I haven't alot of money for this future project some where around $300 ~ $350. Also I would like to ask that comments about vented or sealed alternative be kept to a minimum, but if you have to be my guest
Thanks!
MS* I just stated reading Martin King"s very informative site. But would still like comments from all you knowledgable folks.
*message script
That's not true. It would be if the wool was the transmission medium for the low frequencies, but it isn't, they pass through the air around it as if it wasn't there. You may be able to shorten the line by six inches when stuffed. But with a Qts of less than .7 the fp/fs ratio will be less than 1 anyway, so stay at 8 feet. The volume of the line, and thus cross-section, is determined by driver Qts and Vas. With a Qts of .36 the Vas/Vp ratio can be set at 1:1.
I was quoting info from Vance Dickason's Loudspeaker Design Cookbook. Appearently the line was fully stuffed with wool fiber using 8Kg per cubic meter. The info was from a paper by A.T.Bradbury (1976).
Again I'm new to all this.
So if I were to make an 8' line and then use damping material would the effective lenght the woofer "sees" change conciderably?
Again I'm new to all this.
So if I were to make an 8' line and then use damping material would the effective lenght the woofer "sees" change conciderably?
Bradbury was wrong, and the fact that Vance took his notions at face value without independantly testing it himself probably still keeps him awake at night. The damping doesn't make the line appear significantly longer to low frequencies, but it is required to eliminate internal reflections of higher frequencies within the line that otherwise cause response dips and peaks, and also to keep those same frequencies from exiting the line terminus.
Banned
Joined 2002
Thanks!
Ok I should plan on making a line 8" long, stuffed or not.
This may be a dumb question, but where does the line start? I ask because if I were able to make the cabinet the way I would like then the woofers would be mounted one above the other with the line folding behind. Better put, the line would like like my attached image. So would it start after the woofers or at the "top" above the woofers. My quess is at the "top". Now is it overly problematic to have two woofers exciting the line at different places?
Ok I should plan on making a line 8" long, stuffed or not.
This may be a dumb question, but where does the line start? I ask because if I were able to make the cabinet the way I would like then the woofers would be mounted one above the other with the line folding behind. Better put, the line would like like my attached image. So would it start after the woofers or at the "top" above the woofers. My quess is at the "top". Now is it overly problematic to have two woofers exciting the line at different places?
Attachments
The line starts at one end of the box, ends at the other. Exciting with two drivers works fine. You'll get better performance from a tapered line, though, and in a pure subwoofer configuration the way you have it with the driver down low, meaning you're crossing over around 80-100Hz, a TL isn't very space or SPL effective. It is if you're making a floorstander config using the woofers to a higher crossover (see the Thor at the Madisound site). Otherwise a folded horn like my Tuba 18 is far more effective for maximum extension and sensitivity from a minimal (18 inch cube) cabinet size.
BillFitzmaurice said:
I'm not all that concerned about SPL (or should I say maximum SPL) due to my current living situation. Also I plan to drive them with atleast 200W (not a lot, but sufficent). Though size is a concern to me. I've begun doing some simple calculations to figure out the size of the line according to the Sd (260cm^2) and tuning freq. (35Hz) and at present it doesn't appear to be much bigger than I had originally thought it might be. Also I kinda want the baffle (as stated above somewhere) to be narrow. I can't do a side mounted woofer due to placement issues and I also don't wan't a cube style enclosure (no offence to cubes
).Thanks so far for your helpful info Mr. Bill Fitzmaurice !
Oh by the way I was planning on tapering the line. I quickly made the image shown above just to show the woofer placement in the cabinet.
I'm planing to construct the box out of 1" MDF as I has 12 3' x 3' sheets of the stuff. Plywood would probably be better but I'm going to use what I have on hand.
Sorry for being a little off topic but I think it suits the TL design with two woofers...
1. Should someone taper the line according to 2xSd due to double woofers?
2. Also the volume of a TL subwoofer has any affect in the final result? Sould it be bigger than the Vas or 2xVas?
Thanks
Regards Michael
1. Should someone taper the line according to 2xSd due to double woofers?
2. Also the volume of a TL subwoofer has any affect in the final result? Sould it be bigger than the Vas or 2xVas?
Thanks
Regards Michael
BillFitzmaurice said:
Pretend I'm three years old... what does that mean? I thought the cross section was determined by the Sd of the woofer(s) used, not it's Vas.
Funny how the more one looks into something the more you realize how little you really know. Not that I knew anything about designing TLs. It seems to be getting more and more confusing. But I believe by spring with help and lots of research I'll get closer to a better understanding.
I must comment on what appears to be conflicting info... I went to Planet10's site and was reading (not entirely finnished yet) some the info there and at the links provided. one of those links (http://www.audioasylum.com/audio/speakers/messages/11476.html ) makes this comment:
I was told a few posts back that the damped line wouldn't effect the "perceived" lenght of the line (to the woofer) by all that much. Ok no one said it in those words and I might have misunderstood the comments made. I guess my point is who is right? If the above quote is true than that Bradbury guy wasn't compleatly wrong. "Speed of sound can be slowed to about 1/2 nominal" it states and the Bradbury calculations suggest a slowing of about 35% (with long fiber wool, other materials are different). There percentage reduction isn't the same but it suggests the same thing. To the woofer(s) the lines lenght will change, a lot.
At least I have enough MDF to experiment with. Knowing as I do that I'll be building at the very least two cabinets before I'm finished with this project.
But again what are those ratios quoted at the top? I know I haven't read everything about TLs (and probably never will) but I've yet to read anything like what was quoted by BillFitzmaurice.
Water water everywhere, yet not a drop to drink.
ERICSPEEd said:
The quote is not true... it has been pretty convincingly shown that Bradbury is wrong... tapering the line will allow you to build a shorter line since the taper does move the fundemental resomamce up & down depending on the taper amount & dierction.
Keep in mind that on my site i have both modern & classical (ie historical) info... most of the classical stuff is just as meaningful as the recipe noted here:
http://www.t-linespeakers.org/design/cookbook.html
An externally hosted image should be here but it was not working when we last tested it.
Sd has nothing to do with line cross-section. The Vas, Qt, and Fs determine the line volume. the cross-section is what you get when you divide the volume by the length (in a straight pipe -- taper effects the pipe violume)
dave
Yes, you double the line volume for two drivers, and planet 10 is correct about the use of T/S specs to determine not only line volume but also length. The use of Sd goes back to the dark ages of TL design- perhaps five years ago- when TLs were still largely empirical designs (seat of the pants).
Bradbury was correct about the alteration of the speed of sound through a damping medium insofar as those frequencies affected by it are concerned. But as I previously noted damping materials have virtually no effect upon long wavelength low frequencies, those below approximately 200 Hz, and those are the very frequencies being passed by the line.
As for the Qts, with a driver Qts of .7 the fs/f3/fp ratio is 1:1, as discovered by Bailey. His work still remains the basis for most TL theory, though it did not address T/S specs as in 1972 they were not yet mainstream.
Bradbury was correct about the alteration of the speed of sound through a damping medium insofar as those frequencies affected by it are concerned. But as I previously noted damping materials have virtually no effect upon long wavelength low frequencies, those below approximately 200 Hz, and those are the very frequencies being passed by the line.
As for the Qts, with a driver Qts of .7 the fs/f3/fp ratio is 1:1, as discovered by Bailey. His work still remains the basis for most TL theory, though it did not address T/S specs as in 1972 they were not yet mainstream.
Something I Forgot To Ask.
If I'm able to properly design a TL for the above mentioned Peerless woofers I should be able to get extension to 35Hz, yes?
Attached is a plot of the woofers in a BR. If I can't achive 35Hz or there abouts then I guess I... well I don't know what I would do. Scratch all this and make a BR with a larger driver (10")?
If I'm able to properly design a TL for the above mentioned Peerless woofers I should be able to get extension to 35Hz, yes?
Attached is a plot of the woofers in a BR. If I can't achive 35Hz or there abouts then I guess I... well I don't know what I would do. Scratch all this and make a BR with a larger driver (10")?
Attachments
The definitive work to date on TLs was published by George Augsperger in Speaker Builder magazine in issues 2, 3 & 4 of 2000; Joe D'Appolito's Thor project utilizing Augspergers calcs appeared in AudioXPress in May, 2002. You can get Augspergers TL program at the AudioXpress site but it's quite expensive ($139) for the non-pro to invest in. Your drivers have specs similar to those used in Thor, which has an F3 of 44 Hz and works well down into the 20's (with room gain) from an 81 inch line length.
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