My subs should be here this week,
Creative Sound Solutions | High End Speakers and Speaker Kits
Parameters.
Fs 21.3 hz
Senstitivity 87.2 @ 2.83V/1M
Mms 275.9 g
BL 18.4 N/A
Cms 0.276 mm/N
Vas 67.5 L
Qms 3.962
Qes 0.414
Qts 0.374
Nom Imp 4 ohm
Re 3.7 ohm
Le 1.38 mH
Xmax 28 MM
Sd 491 cm^2
Dimensions,
Outside Diameter 312 mm
Cutout Diameter 277 mm
Depth 225 mm
Sealed box looks like it should be 1.84'^3 before drivers and slot.
Slot opening looks like it should be ~6"x12" wide (1/2 total SD, 76"^2) and I guess about 12" deep. How do you install a 9" deep sub in a 6" opening?I was going to leave the plenum square as I am not looking for higher extension.
The plate amp I have is 800 watts at 8 ohms (plan was to wire drivers out of phase in series) and use a 6db gain at 30hz (amp has 5 point variable PEQ) to get an F3 of around 27 hz (my hope was the PPSL design would lower the F3). I have an Omnimic and REW to hopefully EQ it correctly.
Thoughts on this plan? Do I have the basics correct for a PPSL sub? Or am I out to lunch?
My goal was the most sub in the smallest space.
Plan B is to build a M&K clone...
Thank you,
David, London, Canada
To be quite honest, I am NOT a real big fan of this type (subwoofer) driver. However, if your application is strictly for Home Theatre, then you are fine. These type of drivers take HUGE amounts of power to get them going. It's the price you pay for deep bass in a small box (Hoffman's Iron Law). My next question: Why, a sealed enclosure ? .... What I would do, if this was my project, would be to build up at least one of the plenums, and then make a quick-and-easy test box, to be able to measure the parameters, once they are installed into a plenum. The specs WILL change. And speaking of specs, at least one of them looks suspect {Le only 1.38?} The test box construction will also give you some experience as to which way would be the most convenient way to actually do the plenum. With this type of driver, with it's massive magnet structure, you are going to have to require a plenum size that will limit your ability to space these drivers very close together, which, if this is for sub-woofer duty, is not of much consequence. Remember to allow for maximum wooer excursion~~ 9 inches might be okay, I can't tell without actuality looking at them. SD ratio of .74 is okay for a sub. Hope this helps !
p.s. Also, if it were me, I would build a vented enclosure for the final install, but the test box MUST be sealed, in order to obtain your Vas value.
I am kind of wishing I had bought a pair of Dayton 12" subs for the price of one of these to try this box now. I had ordered them wanting to do an M&K clone, they I read the entire PPSL thread and I thought I would try PPSL.
I was thinking closed for space. I really want the smallest sub I can make.
How did you measure VAS and Fs in the box?
David.
You'd need a pair of the Daytons to equal the output of a single SDX12. Distortion will also be much lower with the CSS subs. You should be able to increase your plenum height to 9" or so, but then continue the front baffle down to leave a 6" x 12.75" opening. This will change the parameters from your original design, but maybe for the better. You could model it in HornResp or build the test box and measure the parameters.
I was already thinking of a 6"x12" plenum. Did you mean make it 9"x12"?
If only I had a clue how to use HornResp..
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based on the latest info you gave me, I have an alternate design for you.
I'll post it as time permits....I gotta run now....
IIRC (which I may not...) PPSL lowers anticipated Fs of the drivers - would that be because of an air spring effect??
There is discussion in the long PPSL thread about compression ratios created by the slot opening area vs driver swept volume, so I am pretty sure it does act as an air spring.
If your drivers are 12" diameter and 9" deep, and assuming vertical mounting, you'd need ~9.75" width x ~12.75" depth x ~12.75" height if you want to fit them once the box is complete.
If you want a narrower slot opening (so the aforementioned 6"x12") you'd have to screw them into the box and wire them up before sealing the box up by screwing the front sheet on.
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I was already thinking of a 6"x12" plenum. Did you mean make it 9"x12"?
If only I had a clue how to use HornResp..
The plenum would still be 9 x 12, but if you extended the front baffle down, you could make the slot opening whatever you wanted - 6 x 12, for example. This extension could be a separate piece so you could try different lengths to make different slot heights and would still be able to get the driver in and out without disassembling the rest of the cabinet. I don't use Hornresp either, otherwise I'd model it for you, but don't get discouraged - I think this idea could yield great results.
Hey guys, if I were to try building a double 18" PPSL where the slot (plenum) runs vertically.......
.....for the driver pushing into the plenum, with its coil out in the cabinet...
what is the minimum distance you would keep between the coil and the cabinet side wall?
....for the pull driver fully inside the plenum, what is the minimum distance you would keep between it and the other cabinet side? (Actually, between the plenum's outer wall and the cabinet)
I'm trying to minimize box width....
Thx in advance, Mark
.....for the driver pushing into the plenum, with its coil out in the cabinet...
what is the minimum distance you would keep between the coil and the cabinet side wall?
....for the pull driver fully inside the plenum, what is the minimum distance you would keep between it and the other cabinet side? (Actually, between the plenum's outer wall and the cabinet)
I'm trying to minimize box width....
Thx in advance, Mark
Mark,
1) Exposed coils ;^) ? If your driver has rear venting, the distance should be such that the overall area surrounding the circumference of the vent is at least equal to the vent area. The vent distance from the cabinet wall should be at least 1/4 the vent width, or half the vent radius. Even without a rear vent, best to leave an air cooling gap around the magnet structure.
2) More shades of post 685... The plenum baffle, having three sides open to the cabinet interior could be placed within 10-20mm of the cabinet side with no problems. At some very small distance less than that, turbulence noise could be a problem, though being inside the cabinet would be hard to detect.
As a reality check, I've used a plenum exterior exit in a push-push design with a 14/1 Sd/exit ratio, and that ratio is exceeded in many Synergy/Unity type designs with no cone problems.
Cheers,
Art
Thx Art, sorry to be dense, but I'm having a hard picturing what you mean by a "plenum baffle, having three sides open to the cabinet interior".
A "plenum" is the PP "slot".
A "baffle" in speaker cabinet construction language is a piece with a speaker hole.
Graphic: "|"= cabinet wall, "I"=plenum baffle, >= speaker cone.
| I>I>|
Perhaps the photo below will help explain- the push-push plenum exit dimension is only 3/4" x 10.25". This dimension caused no audible "chuffing" or cone problems. This arrangement allowed replacement of a single 12" driver with 2x10" with no cabinet modifications.
If one of the speaker baffles was 3/4 inch (.75") from a cabinet interior side wall, three times the area would be open and the output of one driver rather than two would go through that area.
The distance from the baffle to the cabinet side could be reduced to 1/6th of .75", just .125" and have the same air velocity.
Art
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Speakers showed up today, holy crap are they big!
I am really reconsidering this PPSL box and going back to plan A, which was make an M&K clone with a PWR-ICE250 DSP 500 watt @8 ohm amp I can do a Linkwitz Transform with.
These things are going to pound whatever I do with them.
I am really reconsidering this PPSL box and going back to plan A, which was make an M&K clone with a PWR-ICE250 DSP 500 watt @8 ohm amp I can do a Linkwitz Transform with.
These things are going to pound whatever I do with them.
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Hi CRESCENDO,
Aren't you forgetting something?.... a Push-pull loaded TH
Cheers,
Djim
Doesn't the nature of a TH sort of negate the need for a slot, since it also minimize odd-order harmonics? (Or do I have that wrong?)
If that's correct, then it would be much simpler to simply make two TH subs, with one reverse-mounted and out of phase, then just group them.
You might have to make them slightly larger internally, so that the external dimensions were the same, but it would still be much easier than a true PPSL with horn loading, no?
Mr Ed,
I'm considering this myself, but need to know how portable they are. (I'll probably have to use 12's)
PLEASE let me know!
What is the total weight of each sub?
Did you use DJK's exact dimensions, or modify them a bit? What was the final shape?
What is your frequency response?
- Thanks!
1) TH don't "minimize odd-order harmonics".
2) You are mistakenly using "phase" for "polarity" (they are not interchangeable terms), but a "reverse-mounted" TH is not as easy to build as a standard TH, which has the driver's magnet in the mouth of the horn. The throat normally would be too shallow to fit a magnet assembly, so standoffs would be required to make the area of the throat chamber (ATC) equal to a driver mounted with the cone side to the throat.
Push-pull TH are generally built as in the photo below, with the magnet facing left in the upper "stub", the magnet facing right in the lower horn throat entrance.
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That's not what I've been reading. Several builders with similar high-end knowledge as yourself have specifically written this. One even emailed me, and explained this in detail, ending with his opinion that this is why horns make the ultimate design for PP, since both even & odd harmonics are negated. Sadly, I rarely save names or urls with the info I gather, so I can't remember who wrote what.
But perhaps you are correct. Perhaps these guys are confusing harmonic distortion with intermodular distortion?
Or perhaps I used the wrong term, (misquoted) i.e. intermodular distortion is mostly odd-order, and so you are right, I used the wrong term, but the basic point is still valid?
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Oh c'mon now. With all due respect (tons of it) you are nitpicking. Revering polarity reverses the phase. But fine, I'm all for clarity in terminology. (Like most "flared" ports actually being "radiused," not flared.)
Wow. Clever design that.
Hard to build? It makes me wonder why "everybody" isn't already doing this. (Unless, again, P-P isn't nearly as helpful with a horn as it is with other cabinet types.)
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Still learning.... I think I've almost reach "noob" level.
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Bass horns can band pass HF, which reduce (not negate) harmonics, though the band pass is usually above 2nd and 3rd order. Since a horn also increases gain relative to excursion, and distortion is related to excursion, you could say a bass horn reduces distortion, but it certainly does not negate distortion.
Intermodulation distortion (IMD) results when two or more signals of different frequencies are mixed together, which forms additional signals at frequencies that are not, in general, at harmonic frequencies (integer multiples) of either source signal.
A bass horn could reduce IMD through the same mechanisms as HD.
^ Thanks.
So an important question seems to be:
Which is more effective as a LPF, for the distortions we want to minimize, a horn or a PPSL plenum
You seem to be saying the plenum, which makes sense based on some glowing PPSL opinions (And once again why I'm not looking at a horn, at the moment.)
So then the really big question is, how to determine the ideal plenum size, in terms of filtering the odd order harmonics?
I've read this entire thread, 3-4 times now, and this information seems elusive.
One consideration of plenum size is HF extension, but I'm looking for a "standard" subwoofer, crossing over at about 100 Hz.
Another consideration is compression, though the general thought seems to be "it looks small, but probably isn't a problem."
But what about those harmonics? (And high frequency modulation noise, while we're at it.) Should I not be trying to make the plenum limit as close to 100 Hz as possible?
- And if so, how does one calculate that?
I'm obviously still mostly clueless on this.
So an important question seems to be:
Which is more effective as a LPF, for the distortions we want to minimize, a horn or a PPSL plenum
You seem to be saying the plenum, which makes sense based on some glowing PPSL opinions (And once again why I'm not looking at a horn, at the moment.)
So then the really big question is, how to determine the ideal plenum size, in terms of filtering the odd order harmonics?
I've read this entire thread, 3-4 times now, and this information seems elusive.
One consideration of plenum size is HF extension, but I'm looking for a "standard" subwoofer, crossing over at about 100 Hz.
Another consideration is compression, though the general thought seems to be "it looks small, but probably isn't a problem."
But what about those harmonics? (And high frequency modulation noise, while we're at it.) Should I not be trying to make the plenum limit as close to 100 Hz as possible?
- And if so, how does one calculate that?
I'm obviously still mostly clueless on this.
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