Okay, decided to go with the single pair design. Heading down to the lumber yard today 
An externally hosted image should be here but it was not working when we last tested it.
Okay, now my head's about to explode again
The site says:
"Sm = 2.10804*1728/96.175 = 75.751"^2"
But 2.10804*1728/96.175 does not equal 75.751 in^2. It equals 37.876 in^2. Which is a factor of 2 less than it's supposed to be apparently. So either 75.751 is supposed to be 37.876, or there's a factor of two missing in the formulation.
Correct me if I'm wrong, as I sort of reversed engineered the example from the BiB how-to page since i didn't see any explicit formulas for Vb and Sm and I could have made a mistake.
I thought that for a single isobaric pair of these drivers:
Vas' = Vas/2 = 2.77 cu ft.
Vb = 20*Vas*Qts^1.25 = 20*2.77*0.375^1.25 = ~16.27 ft^3
Sm = 2*Vb(in^3)/L =2*16.27*1728/168 = ~334.7 in^2
Is that not how you arrived at your value?
Then Depth =SQRT(Sm*SQRT(2)) = 21.75 in
and Width = Sm/Depth = 15.38 in
16.27 ft^2, which leads to a Sm of 334.7 in^2 (15.38 x 21.76) ?
I'm totally confused. HELP!!!
GM said:
The site says:
"Sm = 2.10804*1728/96.175 = 75.751"^2"
But 2.10804*1728/96.175 does not equal 75.751 in^2. It equals 37.876 in^2. Which is a factor of 2 less than it's supposed to be apparently. So either 75.751 is supposed to be 37.876, or there's a factor of two missing in the formulation.
Correct me if I'm wrong, as I sort of reversed engineered the example from the BiB how-to page since i didn't see any explicit formulas for Vb and Sm and I could have made a mistake.
I thought that for a single isobaric pair of these drivers:
Vas' = Vas/2 = 2.77 cu ft.
Vb = 20*Vas*Qts^1.25 = 20*2.77*0.375^1.25 = ~16.27 ft^3
Sm = 2*Vb(in^3)/L =2*16.27*1728/168 = ~334.7 in^2
Is that not how you arrived at your value?
Then Depth =SQRT(Sm*SQRT(2)) = 21.75 in
and Width = Sm/Depth = 15.38 in
16.27 ft^2, which leads to a Sm of 334.7 in^2 (15.38 x 21.76) ?
I'm totally confused. HELP!!!
An externally hosted image should be here but it was not working when we last tested it.
getting closer.
judtoff, it's not a tapped horn. It's a BiB horn.
FYI, any off-set driver pipe or horn is technically a tapped one, just not a DSL variant, which I guess should be considered a double tapped one.
Also, isobaric loading assumes pretty much a near vacuum coupling the two drivers, so in theory gluing in some shaped scraps to fill in as much of the driver chamber void as practical is worth the effort, but never having built this version YMMV.
GM
Also, isobaric loading assumes pretty much a near vacuum coupling the two drivers, so in theory gluing in some shaped scraps to fill in as much of the driver chamber void as practical is worth the effort, but never having built this version YMMV.
GM
Thanks for the clarification GM.
Anyhow, i got one built. Still some more listening and breaking in before i give my impressions. But off the bat, there sounds like a strong peak at around 70hz, and then a smaller peak around 35hz, and then response drops off at about 30hz. Don't know how much of all of that is the room versus the sub.
only thing i have to measure with is a rat-shack SPL meter. But it's out of batteries. I'll try to get some crude measurements tonight.
Anyhow, i got one built. Still some more listening and breaking in before i give my impressions. But off the bat, there sounds like a strong peak at around 70hz, and then a smaller peak around 35hz, and then response drops off at about 30hz. Don't know how much of all of that is the room versus the sub.
only thing i have to measure with is a rat-shack SPL meter. But it's out of batteries. I'll try to get some crude measurements tonight.
Attachments
frequency response
okay, here's my super crude radio shack SPL meter measured frequency response:
from 25Hz to 55Hz I think it's pretty nice, little bump, but pretty nice. In fact from 25Hz to 40Hz it's pretty dead flat. Then there's a massive bump at 65Hz. I think this is the room as the room is approximately 18' x 18', so i think that's in the range that I'm getting the big boost. Not sure how to get rid of that peak. It's huge.
Little disappointed to see it drop off so fast after 25Hz though, especially with an enclosure so large, i was hoping to get down to 20Hz.
Is there anything i can do physically to help tame the response? I think i may try a little EQ as well. I imagine there's nothing to do to get more extension other than build a larger box.
I think i may also build a more standard ported enclosure (but also with an isobaric loading), and test the two out side by side to see which one I like better.
thanks for the help thus far
okay, here's my super crude radio shack SPL meter measured frequency response:
An externally hosted image should be here but it was not working when we last tested it.
from 25Hz to 55Hz I think it's pretty nice, little bump, but pretty nice. In fact from 25Hz to 40Hz it's pretty dead flat. Then there's a massive bump at 65Hz. I think this is the room as the room is approximately 18' x 18', so i think that's in the range that I'm getting the big boost. Not sure how to get rid of that peak. It's huge.
Little disappointed to see it drop off so fast after 25Hz though, especially with an enclosure so large, i was hoping to get down to 20Hz.
Is there anything i can do physically to help tame the response? I think i may try a little EQ as well. I imagine there's nothing to do to get more extension other than build a larger box.
I think i may also build a more standard ported enclosure (but also with an isobaric loading), and test the two out side by side to see which one I like better.
thanks for the help thus far
santiu said:
Greets!
Yes, and no in that such a corner yields more gain and flattens a simple truncated horn's response better, but the trade-off is that it will unevenly load it. Overall though it's pretty impressive relative to a half space sim (series wired shown):
GM
Attachments
Re: frequency response
Greets, part deux!
You're welcome!
It's a pipe horn, so in essence just a BR with a huge vent, ergo has a 4th order roll-off. I'm a bit surprised you have no room gain bolstering it up down low though.
Anything simple other than digital EQ to tame the peak will roll off the bottom end response. Some folks have used band stop filters and IIRC Akabak even has TL/horn models that calc them as part of the overall design: http://www.akabak.de/Ak-English.htm http://www.gmi.edu/~drussell/GMI-Acoustics/Filters-Frame.html
Yeah, it needs to have a longer path-length to go lower, though net Vb stays the same, ergo a smaller mouth (Sm).
GM
santiu said:Not sure how to get rid of that peak. It's huge.
Little disappointed to see it drop off so fast after 25Hz though, especially with an enclosure so large, i was hoping to get down to 20Hz.
Is there anything i can do physically to help tame the response? I think i may try a little EQ as well. I imagine there's nothing to do to get more extension other than build a larger box.
thanks for the help thus far
Greets, part deux!
You're welcome!
It's a pipe horn, so in essence just a BR with a huge vent, ergo has a 4th order roll-off. I'm a bit surprised you have no room gain bolstering it up down low though.
Anything simple other than digital EQ to tame the peak will roll off the bottom end response. Some folks have used band stop filters and IIRC Akabak even has TL/horn models that calc them as part of the overall design: http://www.akabak.de/Ak-English.htm http://www.gmi.edu/~drussell/GMI-Acoustics/Filters-Frame.html
Yeah, it needs to have a longer path-length to go lower, though net Vb stays the same, ergo a smaller mouth (Sm).
GM
You could stuff the BIB, which should effectively increase line length and VB. It may reduce the SPL a little, but you should gain extension and it may also help smooth the 65HZ peak.
Poly fibrefill from Walmart will do the trick. Use at least 1 LB per cu.ft. of the enclosure, spread evenly through the length of the line.
It's a cheap experiment, easily reversible , and I think it may just do the trick.
Fibrefill (or similar) works by slowing the speed of the soundwaves, effectively making the driver see a larger box /longer line.
The effect on the box volume should help attenuate the peak at 65HZ , and the effect on the line length should move the peak from 65HZ to a lower frequency at the cost of slight reduction in SPL due to the increased loading.
..........................Blake
Poly fibrefill from Walmart will do the trick. Use at least 1 LB per cu.ft. of the enclosure, spread evenly through the length of the line.
It's a cheap experiment, easily reversible , and I think it may just do the trick.
Fibrefill (or similar) works by slowing the speed of the soundwaves, effectively making the driver see a larger box /longer line.
The effect on the box volume should help attenuate the peak at 65HZ , and the effect on the line length should move the peak from 65HZ to a lower frequency at the cost of slight reduction in SPL due to the increased loading.
..........................Blake
Thanks for the fill suggestion. I'll try it out. Will the stuffing take away some of the responsiveness of these. I've been really digging how responsive these are.
However, i just realized there's a huge length behind the couch that I think i can convince my roommates to fill. Can you lay these types of horns on their sides and have them fire into the corner of the room? If so, how much space should i leave between the mouth of the horn and the opposing wall? Also, the room is carpeted, will that damp out the wall/boundary too much? If so, i guess i could just cut a piece of wood to go from the mouth to the wall.
Can one mess with the Depth to Width ratio as long as you end up with the same Sm?
I think i can make about a 12 foot long horn, so that's an L of 288", slightly below the an octave below Fs of the driver Hopefully that should get me lower!
Is this a worthwhile endeavor, or does there come a point where the extra length doesn't help you? Couple logistics questions:
1) How important are the seals in the box?
2) Can the angled divider in the horn be a series of steps?
I ask as in order to get this up the stairs and into the room, i will likely need to build it in sections that can be reassembled.
However, i just realized there's a huge length behind the couch that I think i can convince my roommates to fill. Can you lay these types of horns on their sides and have them fire into the corner of the room? If so, how much space should i leave between the mouth of the horn and the opposing wall? Also, the room is carpeted, will that damp out the wall/boundary too much? If so, i guess i could just cut a piece of wood to go from the mouth to the wall.
Can one mess with the Depth to Width ratio as long as you end up with the same Sm?
I think i can make about a 12 foot long horn, so that's an L of 288", slightly below the an octave below Fs of the driver
Hopefully that should get me lower!Is this a worthwhile endeavor, or does there come a point where the extra length doesn't help you? Couple logistics questions:
1) How important are the seals in the box?
2) Can the angled divider in the horn be a series of steps?
I ask as in order to get this up the stairs and into the room, i will likely need to build it in sections that can be reassembled.
The seals are always very important in any kind of "boxed" design. I would say even in an OB the driver-to-baffle "seal" is very important. It can seriously affect the tuning/sound of the cabinet.
You might be able to get away with a stepped divider board, but I would think (unlike the popular consensus) that the smoothest transition is the best, even in the "bottom" fold.
Corners cause turbulance in regards to airflow, regardless of what frequency you are talking about. Actually , the lower frequencies should be more affected , as they are moving more air than the middle freq's .
The stuffing will change the sound, whether or not it is percieved as "responsiveness" by you is something I can't say. The stuffing is easily adjusted and/or removed, so it is an inexpensive possibility. It may seem to have less "hit" or bass "whack" to it with the stuffing in place, but that is more likely due to the change in tuning, or the reduction and shifting of the 65HZ resonant peak.
A longer line will tune it lower, but it will probably start to roll off sooner, or IOW have a higher F3. It should have a shallower , more gradual rolloff with possibly a better in-room response.
Try the stuffing, it is cheap, quick and easy. Give yourself some time to adjust to the difference in sound, and see if it doesn't sound more like what you are looking for.
.............................Blake
You might be able to get away with a stepped divider board, but I would think (unlike the popular consensus) that the smoothest transition is the best, even in the "bottom" fold.
Corners cause turbulance in regards to airflow, regardless of what frequency you are talking about. Actually , the lower frequencies should be more affected , as they are moving more air than the middle freq's .
The stuffing will change the sound, whether or not it is percieved as "responsiveness" by you is something I can't say. The stuffing is easily adjusted and/or removed, so it is an inexpensive possibility. It may seem to have less "hit" or bass "whack" to it with the stuffing in place, but that is more likely due to the change in tuning, or the reduction and shifting of the 65HZ resonant peak.
A longer line will tune it lower, but it will probably start to roll off sooner, or IOW have a higher F3. It should have a shallower , more gradual rolloff with possibly a better in-room response.
Try the stuffing, it is cheap, quick and easy. Give yourself some time to adjust to the difference in sound, and see if it doesn't sound more like what you are looking for.
.............................Blake
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