I've been getting quite a few questions about BIB dimensions for the BetsyK. As I said in the "enclosures" forum, these are the dims I used:
L = (Line length) 150.5"
Zdriver = Driver 30.1" down from sealed end of cabinet
Sm = 200"^2
They are a good bit smaller than GM's formula would give you, but they had more than enough bass in my room. I wish I could remember what my exact dimensions were, but I think I used something like 11.5x17.4 WxD internal open space, which means my actual enclosures where 13" wide x 20.4" deep or so. (I used a double thickness front baffle. If you don't, you only need to add three thicknesses to get to your exterior depth). I can't remember how tall they were, but I do know that after trying to accurately calculate the height including a changing radius around the bend, it ended up being really darn close to just assuming straight lines.
hopefully that helps!
Paul
Wild Burro Audio Labs - DIY Full Range Speakers
L = (Line length) 150.5"
Zdriver = Driver 30.1" down from sealed end of cabinet
Sm = 200"^2
They are a good bit smaller than GM's formula would give you, but they had more than enough bass in my room. I wish I could remember what my exact dimensions were, but I think I used something like 11.5x17.4 WxD internal open space, which means my actual enclosures where 13" wide x 20.4" deep or so. (I used a double thickness front baffle. If you don't, you only need to add three thicknesses to get to your exterior depth). I can't remember how tall they were, but I do know that after trying to accurately calculate the height including a changing radius around the bend, it ended up being really darn close to just assuming straight lines.
hopefully that helps!
Paul
Wild Burro Audio Labs - DIY Full Range Speakers
Thanks for the thread. Trying to read through 5053 posts on the TC bib thread will give you a headache.lol Somewhere in the posts GM figured out how to sim the bibs. There is a chart for alot of drivers posted. I couldn't find a sim on the Betsy K. It seems that the design is very forgiving. Using your measurements. The height would about 78". So a internal of 12" wide and depth of 18" and 78" tall. Thats with a single 3/4" baffle. Not sure how for from the bottom to terminate the the internal piece. Placement front to back is unknown too. It could start at the top and go down to about 9" from bottom. Then center it at 9" from the back.[guessing] It would vent out the top. Maybe someone will chime in with there build.
Many people seem to have the bottom of the baffle equidistant from the front, bottom, and back. A more constant rate of expansion makes sense to me. Here again, I can't recall what I did. But it would have been something like half-an-inch closer to the front than to the bottom, and half an inch closer to the bottom than to the back.
Notice that with these specs, the speaker ends up pretty high. They'd be a little more difficult to deal with, but you can consider building an inverted BIB to get the driver right at ear height.
Paul
www.wildburroauudio.com
Notice that with these specs, the speaker ends up pretty high. They'd be a little more difficult to deal with, but you can consider building an inverted BIB to get the driver right at ear height.
Paul
www.wildburroauudio.com
I didn't mind the driver height, but I didn't love it either. I mention it now, as if you are going to consider inverting, it would be good to have that in mind from the beginning. There are also potential loading advantages. If you have the vents loaded with the floor, you might be able to get the speakers out from the wall a bit, which could have positive effects on imaging.
Paul
Wild Burro Audio Labs - DIY Full Range Speakers
Paul
Wild Burro Audio Labs - DIY Full Range Speakers
http://www.diyaudio.com/forums/full...se-fostex-craft-handbooks-74.html#post1190733
http://www.diyaudio.com/forums/full...se-fostex-craft-handbooks-78.html#post1220973
http://www.diyaudio.com/forums/full...se-fostex-craft-handbooks-80.html#post1229324
http://www.diyaudio.com/forums/full...e-fostex-craft-handbooks-125.html#post2945457
http://www.diyaudio.com/forums/atta...sures-hemptone-fr8-bib_calculator_v1x.xls.zip
http://www.diyaudio.com/forums/full...se-fostex-craft-handbooks-78.html#post1220973
http://www.diyaudio.com/forums/full...se-fostex-craft-handbooks-80.html#post1229324
http://www.diyaudio.com/forums/full...e-fostex-craft-handbooks-125.html#post2945457
http://www.diyaudio.com/forums/atta...sures-hemptone-fr8-bib_calculator_v1x.xls.zip
Speaker specs.
Re=5.7
Fs=49.95
Sd=22.966
Bl=5.471
Qms=2.798
Qes=.548
Qts=.458
Spl=94.6
Vas=82.914L
So
L=13526.5/2/49.95 L=135.400
H=L/2 H=67.7
Vb=20*Vas*(Qts^1.25) Vb=624.692
Sl=Vb(in ft^3)*(12^3(inches in ft^3))H Sl=109.522
D=(Sl*(2^.5))^.5 D=12.4470
W=Sl/D W=8.801
Zd=l*0.217 Zd=29.381
I think my cal. on the Sl is wrong. A cab of 67.7x12.44x8.801 doesnt seem right. Where did I go wrong?
Re=5.7
Fs=49.95
Sd=22.966
Bl=5.471
Qms=2.798
Qes=.548
Qts=.458
Spl=94.6
Vas=82.914L
So
L=13526.5/2/49.95 L=135.400
H=L/2 H=67.7
Vb=20*Vas*(Qts^1.25) Vb=624.692
Sl=Vb(in ft^3)*(12^3(inches in ft^3))H Sl=109.522
D=(Sl*(2^.5))^.5 D=12.4470
W=Sl/D W=8.801
Zd=l*0.217 Zd=29.381
I think my cal. on the Sl is wrong. A cab of 67.7x12.44x8.801 doesnt seem right. Where did I go wrong?
Hmm, Vb = 624.692 L since you didn’t convert Vas to ~2.92808 ft^3, so 624.692*0.3531467 = ~22.06079 ft^3, making Sm and its related dims wrong.
Away, easiest to use Vas in ft^3, then the other dims will work out in inches. That, or use Vas in liters and change the SoS and Sm calculation values to cm if you want a metric design.
GM
Away, easiest to use Vas in ft^3, then the other dims will work out in inches. That, or use Vas in liters and change the SoS and Sm calculation values to cm if you want a metric design.
GM
How come you didn’t just use the linked BIB spreadsheet?
Ft^3 = 12”^3 = 12”*12”*12” = 1728”^3
Sl = 22.06469 ft^3*1728”^3 = 38127.784”^3/67.7” = 563.187”^2
The speed of sound [SoS] should be a constant for typical speaker design, but for some reason different programs, technical documents will have varying values. 13526.5”_sec/12” = ~1127 ft_sec or ~ in the middle between the two most extremes. FWIW, until I got on-line, all the docs I’d seen listed 1130 ft_sec, which is ~ what I’ve measured using mil spec calibrated equipment during my working career.
Regardless, the minor differences it makes in typical speaker designs are inaudible and don’t take into account any internal heating unless you take measurements and adjust as required such as for some commercial and prosound apps.
The acoustical path-length is what matters and is a ~1/2 WL of whatever value is put in the ‘Fs’ field, which means it’s tuned to a ¼ WL of Fs = Fs*0.707 or ~35.31 Hz.
Low enough for you? If not, input a lower Fs with the understanding it will put the driver higher up off the floor.
Want to make it smaller? Reduce Vas or Qts as required. Of course less is always less in acoustics, so there will be less of an air cushion for the driver to work against, ergo less power handling down low with a higher roll off if the room’s acoustics don’t help enough.
GM
Ft^3 = 12”^3 = 12”*12”*12” = 1728”^3
Sl = 22.06469 ft^3*1728”^3 = 38127.784”^3/67.7” = 563.187”^2
The speed of sound [SoS] should be a constant for typical speaker design, but for some reason different programs, technical documents will have varying values. 13526.5”_sec/12” = ~1127 ft_sec or ~ in the middle between the two most extremes. FWIW, until I got on-line, all the docs I’d seen listed 1130 ft_sec, which is ~ what I’ve measured using mil spec calibrated equipment during my working career.
Regardless, the minor differences it makes in typical speaker designs are inaudible and don’t take into account any internal heating unless you take measurements and adjust as required such as for some commercial and prosound apps.
The acoustical path-length is what matters and is a ~1/2 WL of whatever value is put in the ‘Fs’ field, which means it’s tuned to a ¼ WL of Fs = Fs*0.707 or ~35.31 Hz.
Low enough for you? If not, input a lower Fs with the understanding it will put the driver higher up off the floor.
Want to make it smaller? Reduce Vas or Qts as required. Of course less is always less in acoustics, so there will be less of an air cushion for the driver to work against, ergo less power handling down low with a higher roll off if the room’s acoustics don’t help enough.
GM
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