Aren't you worried that the fumes or vapor from the rubber roofing will eat on the glue or surrounding of the woofer?
I like the idea though but I would try to put a layer of thin plastic over it.
Maybe you can do the same with the ports.
On the other hand, I doubt that the rubber will have much effect. Good bracing should be enough.
I like the idea though but I would try to put a layer of thin plastic over it.
Maybe you can do the same with the ports.
On the other hand, I doubt that the rubber will have much effect. Good bracing should be enough.
Have not priced those amps but if you want the ultimate in Kick S** for weight, go with the Speaker Power SP 4000, rated at 4000W/2 ohm, 2400W/4, 1300W/8, it weighs only 7 lbs.
I was amazed that a featherweight amp could kill old school heavy metal transformer with beer can size capacitor amps did.
Brian Oppegaard, President of SpeakerPower sent me one of his Torpedo SP1-4000 amps for evaluation.
Brian spent 11 years as Director of Engineering at QSC Audio Products, Inc. and seven years in the same capacity at Renkus-Heinz before starting Speaker Power in 2002.
When comparing a QSC PL 3600 to the SP 4000 at full tilt boogie, the 3600 was like a hair dryer for heat output while the Torpedo was cool.
I have used it for driving four Lab 12s in ported configuration, which drops to well below 1.5 ohms, and it still kicks!
Art Welter
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Have to let the mastic dry fully and cure, should take about a week or so. Any other sound absorbing coating would do though, at extra cost.
Got the tops today, peavey impulse 100's. Tested them them out with a very solid mid 90's 70w yamaha stereo receiver, hits 100db in room barely getting warm, so I think they should be fine with the car amp, and will get plenty loud with the adcom big iron. Sounds pretty good but definitely need eq. Just the right package for portability.
The plastic boxes leak in the corners where the baffle attaches and the sides vibrate a good amount, I'll definitely be taking them apart to brace and damp them where appropriate, might even plug the ports and heavily stuff. Good speaker overall for what I spent, but really needs a subwoofer.
The plastic boxes leak in the corners where the baffle attaches and the sides vibrate a good amount, I'll definitely be taking them apart to brace and damp them where appropriate, might even plug the ports and heavily stuff. Good speaker overall for what I spent, but really needs a subwoofer.
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I've gone ahead and ordered a single 15" HO plus some speakon connectors and other parts. Will build something up and see what it sounds like. Need to pick up the car amp and batteries. Once I have the portable setup going, I'll add another sub, a behringer nu6000dsp, usb interface and amp rack, etc for a full setup.
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So I got the 15" HO yesterday, looks like a very well designed and built woofer, especially for $172 shipped. Beefy cone, basket, large magnet. It actually weighs just under 24 lb, compared to 30 lb listed on the PE website.
I've been kicking around various design ideas since I figured out that 5" pipe is not at all common. I've considered 3x 4" ports, one large square port, slot ports, 90 bends, various flare ideas, and port velocity limits vs. onset of compression. I read the very enlightening JBL study on port shaping. I'm currently considering a 20"x16" front face by 22" deep box, with a 15x2.5x19" straight slot port, tuned to the high 30's, some small flaring. Volume around 2.75 cubes. I'm trying to figure out how the slot port will be impacted by compression as port speed increases, any thoughts?
I've been kicking around various design ideas since I figured out that 5" pipe is not at all common. I've considered 3x 4" ports, one large square port, slot ports, 90 bends, various flare ideas, and port velocity limits vs. onset of compression. I read the very enlightening JBL study on port shaping. I'm currently considering a 20"x16" front face by 22" deep box, with a 15x2.5x19" straight slot port, tuned to the high 30's, some small flaring. Volume around 2.75 cubes. I'm trying to figure out how the slot port will be impacted by compression as port speed increases, any thoughts?
My thoughts mirror what I see in most current high Xmax, small cabinet BR subs.
Use triangular corner ports in two or four corners, round the ends, and add a 90 degree "L" on the inside port end for more symmetrical port action.
Fb will be lower than predicted for the port area/length, a good thing as less cabinet area is used up by the port, but requires some tuning. Go with the predicted length for desired tuning, but be prepared to cut off an inch or three after doing a sine wave sweep and watching cone movement to determine if the Fb is correct.
Art
Art, interest stuff, thanks. I am mostly worried about port compression at full power, I'm looking to hit this with a 1000+ wrms amp running them pretty hard. Everything indicates that I should experience pretty noticeable port compression at the tuning frequency, but is 38 hz so high as to minimise this vs. a 20hz tuned HT sub...?
I tried calculating "hydraulic diameter" of the 15x2.5 (4.28") vs. two equivalent triangular ports (3.58"), so, you would think that single slot port would have less flow losses and higher threshold for compression? I also tried "equivalent diameter", and got 6.12" for the 15x2.5 port, but no real way to calc for triangle ports?
Equivalent Diameter
Hydraulic Diameter
Everything I've seen indicates that a large single round port has a higher velocity limit and less compression, than multiple ports or sloted ports....?
So I started pulling JBL spec sheets, scaling the pdf and measuring port dims. They seem to use a wide variety of ports - 15's with 2x 3" round, 2x18's with 2.5x20 2x, triangle ports, etc. The way they are sized, I have to imagine they suffer from a bit of port compression.
I found this 18" ASB series that uses 2 triangle ports about 36 sq-in total area, with pretty reasonable extension, could work for me. Thanks Art!
JBL :: Product
I found this 18" ASB series that uses 2 triangle ports about 36 sq-in total area, with pretty reasonable extension, could work for me. Thanks Art!
JBL :: Product
I sketched out some plans last night, and just wasn't able to come up with a compelling design with two triangle ports. It seemed like adding complexity for very marginal gains. If I was going to go with a harder to build port setup, I'd go 3x 4" with bends or one large square port with a rounded bend.
I can do the slot port box much more quickly and easily, and will nicely flare the in and out of the slot per some designs I've seen. I haven't built a box in several years and my woodworking skills are pretty basic. We'll see how this works out, and maybe I'll do a box with a large square flared vent at some point if the slot port box falls short at high output.
I can do the slot port box much more quickly and easily, and will nicely flare the in and out of the slot per some designs I've seen. I haven't built a box in several years and my woodworking skills are pretty basic. We'll see how this works out, and maybe I'll do a box with a large square flared vent at some point if the slot port box falls short at high output.
Hi,
They don’t tune lower it seems you’ve only used the wrong end correction factor(s) as the triangular ports are not 'one end open and one end 'IB' terminating at the baffle .
b
Hi,
They don’t tune lower it seems you’ve only used the wrong end correction factor(s) as the triangular ports are not 'one end open and one end 'IB' terminating at the baffle .
b
Everything thing that I've seen says that as you move away from a round port, you end up with a lower tune than the equivalent round port. Regardless of end correction. Probably because the sound propagation isn't quite as linear. This also explains why if you model a folded horn in hornresp, with round sections, if you then build it with rectangular sections, you get a lower response than modeled.
Youre partly right on your observation but the valid end correction factor depends on Port diam. to lenght, wavelenght to diam., sound pressure and air velocity... baffle placement..speaker placement to room boundaries...and so on.
Dont know if this picture(my notes) can be of any help:
b
PS: For PA I use the notes under 'End corrections' for a conventional simple port with aspect ratio <= 3:1 L/Diam. placed away from the corners and the sides.
Attachments
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Bjorno, regarding end correction factors, I'm hoping your notes and expertise might be of some help to me regarding a slot port for an enclosure not flat on the floor, but placed on a stand.
In the interest of getting some clarification from you without distracting from the topic of this thread, I have sent you a PM. Please check your PMs, and thanks in advance for any help.
David
Perhaps the old Fane sub plan is the way to go to keep it KISS. It would give good venting without "touching the sides" making the tuning difficult to predict?
http://www.fane-acoustics.com/downloads/Cabinets18inch200Lres.pdf
col.
http://www.fane-acoustics.com/downloads/Cabinets18inch200Lres.pdf
col.
So I did get to work on this a bit over the weekend...
Got some 1/2" birch ply. This has 3 main plys and inner and outer veneer. It's just shy of 1/2" thick, more like 7/16-15/32. In a big sheet it seems pretty flexy, but it's plenty stiff in small panels. I will brace it pretty well.
I managed to get 4 sides of the box done. Cutting with a small 5-1/2" circular saw, battery powered. I've got a larger saw too, but the small one cuts well enough and is easier to handle. With a guide and carefull measuring the cuts are accurate to about 1/32". Using 90 clamps and 3 or 4 small sheetrock screws per side, pre drilled holes, titebond 3 woodglue. Next step is getting the port mounted, then the bracing, then last side, then the baffle. Will post some pics when there is something interesting to show.
Outer dims are 20x16x22, with the sub and slot port on the 20x16 side. Port should be about 15x2.5x21 actual, 23" effective length, for a tune in the mid-high 30's. Will put a 1" radius flare on one side of the exit, and there will be a proper bend on the inside.
Checked the fit in the car, with some creative moving around, I can actually fit 2 of these in the trunk. So I could run them as a car sub......lol.
Got some 1/2" birch ply. This has 3 main plys and inner and outer veneer. It's just shy of 1/2" thick, more like 7/16-15/32. In a big sheet it seems pretty flexy, but it's plenty stiff in small panels. I will brace it pretty well.
I managed to get 4 sides of the box done. Cutting with a small 5-1/2" circular saw, battery powered. I've got a larger saw too, but the small one cuts well enough and is easier to handle. With a guide and carefull measuring the cuts are accurate to about 1/32". Using 90 clamps and 3 or 4 small sheetrock screws per side, pre drilled holes, titebond 3 woodglue. Next step is getting the port mounted, then the bracing, then last side, then the baffle. Will post some pics when there is something interesting to show.
Outer dims are 20x16x22, with the sub and slot port on the 20x16 side. Port should be about 15x2.5x21 actual, 23" effective length, for a tune in the mid-high 30's. Will put a 1" radius flare on one side of the exit, and there will be a proper bend on the inside.
Checked the fit in the car, with some creative moving around, I can actually fit 2 of these in the trunk. So I could run them as a car sub......lol.
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