Can someone explain to me, in simple terms, how some of these designs are considered sealed, when there is obviously a slot port of center opening?
Do they still have the tight phase response, and lack of 2nd order harmonics, that a true sealed cabinet gives?
- And what does this mean in terms of efficiency?
Do they still have the tight phase response, and lack of 2nd order harmonics, that a true sealed cabinet gives?
- And what does this mean in terms of efficiency?
A traditional sealed enclosure has the rear chamber sealed and the opposing side facing the listener (or ground, if downfiring - but, you get the picture). Same is going on here - the rear chamber is sealed. The opposite side isn’t ported, though there is a plenum the drivers reside in to take effect of the P-P arrangement.
Fascinating thread.
Really thinking about trying this.
For PA use.
100Hz to maybe 135Hz at most, low pass crossover range.
Especially if PPSL also mitigates cabinet vibration???
I've built some 160L single 18" reflex, f3 31Hz, using the bms 18n862, and am very happy with them....other than the amount of vibration.
They are only 90lb boxes made from 15mm BB and well braced, but I'm guessing 90lbs is simply too light not to dance when cranked.
If PPSL's opposed motion knocks down vibration, that would go along way to make me willing to build some heavier boxes....
I'd probably just stick with the BR volume and ports sizes that I like on the single 18", and extend it to the PPSL double 18", ...unless directed to a more optimal design through further conversation.
Biggest question: is the 18n862 a good driver for this? ....Thiele-Small
I read djk saying ideal Qts is 0.312.....the bms is 0.34, 25 Fs.............
So I'm hoping
One concern beyond parameters (which I admittedly know very little about)
is Josh Ricci says he would have concern using it under horn loading...
with its relatively light , high compliancy cone. Data-Bass
I know the PPSL is not a horn loaded design by any means, but does slot mouth area matter here? Is there a recommended slot opening area?
About all I could find definitely is to minimize distance between drivers and keep plenum as small as possible....
Many thanks, Mark
Really thinking about trying this.
For PA use.
100Hz to maybe 135Hz at most, low pass crossover range.
Especially if PPSL also mitigates cabinet vibration???
I've built some 160L single 18" reflex, f3 31Hz, using the bms 18n862, and am very happy with them....other than the amount of vibration.
They are only 90lb boxes made from 15mm BB and well braced, but I'm guessing 90lbs is simply too light not to dance when cranked.
If PPSL's opposed motion knocks down vibration, that would go along way to make me willing to build some heavier boxes....
I'd probably just stick with the BR volume and ports sizes that I like on the single 18", and extend it to the PPSL double 18", ...unless directed to a more optimal design through further conversation.
Biggest question: is the 18n862 a good driver for this? ....Thiele-Small
I read djk saying ideal Qts is 0.312.....the bms is 0.34, 25 Fs.............
So I'm hoping
One concern beyond parameters (which I admittedly know very little about)
is Josh Ricci says he would have concern using it under horn loading...
with its relatively light , high compliancy cone. Data-Bass
I know the PPSL is not a horn loaded design by any means, but does slot mouth area matter here? Is there a recommended slot opening area?
About all I could find definitely is to minimize distance between drivers and keep plenum as small as possible....
Many thanks, Mark
Mark,
1) Any dual-opposed design, or single down or up firing design will eliminate "dancing" of the cabinet. You could simply add a small "lip" on three sides of the front of your existing cabinets, lay them with the cone down, and they won't walk any more. That said, long term, down or up firing cones will sag, not a problem if the cabinet is stored with cones upright when not in use.
2) Yes it is. Your drivers will work the same in a PPSL as a BR of the same volume, other than a reduction of even order harmonic distortion and the slot resonance. The slot resonance should be well above the bandpass you are using.
3)The PPSL's small plenum (slot) will not subject the cones to the stress of a horn, as evidenced that the sensitivity is the same a BR cabinet.
4)I have used a plenum with a over a 14/1 ratio, an exit of only 6.9 square inches for a pair of 10" (49.1 Sd each) with no cone problems. The minimum opening area for a PPSL would be a fraction of that ratio.
As the slot volume reduces the effective cabinet volume, minimizing it's volume maximizes output for overall volume.
Art
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To be clear, the 14/1 ratio using a 3/4" exit for 10" drivers were facing each other, not "PP".
Probably not possible to get the ratio under 5/1 in a PPSL unless the magnet of one driver is nearly touching the dust cap of the other, which requires mounting the drivers from inside the cabinet, rather than from inside the plenum.
Good luck with that
!
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Right. More like the way we used to check polarity on our speakers by placing them face to face. Besides, the magnet structure is going to interfere with my concept. I have three or four pairs to play with, and whatever I can do that shows off their handsome old bones is what I'll do. Again, for laffs. No high spl aspirations with this
Thank you Art, it's looking like a go !
If you'll remember, I asked about using the 18n862 in a Keystone not long ago, and you very straightforwardly told me it's not optimal for the same reasons Ricci gives. I appreciated that...
I really like the bms driver...it has such a smooth response... the fact it fits a PPSL has me ginned up !
My understanding is the benefit to a reflex PPSL is reduced distortion (and cabinet vibration
And that there is no gain compared to a dual 18 BR....correct?
Less gain compared to a dual 18 BR of the same physical size, reduced even order (musically benign) distortion, no reduction of odd order distortion.My understanding is the benefit to a reflex PPSL is reduced distortion (and cabinet vibration
And that there is no gain compared to a dual 18 BR....correct?
Good to know. Thanks!
In my strong opinion, 2nd order harmonics are FAR from "musically benign."
I'm a pro recording engineer. When mixing a record, we have plugins today that can add various harmonics in a controlled way. 2nd order are not harsh, but they make things muddy & thick. We use them "warm up" or "fatten thin sounding tracks, but you'd never add them to a finished mix which already sounds good.
So, why would you want them coming out of your sub? (Maybe for HT, but definitely not for music.)
Granted, odd-order harmonics are harsher, but they are also not nearly as loud. Additionally, they can actually make things sound exciting and more defined. (This is exactly how the original Aphex Aural Exciter worked.) - Something that might actually sound GOOD on your lowest frequencies.
It all comes down to the ears, in the end.
HaHa, now that's funny ! Don't think I've ever heard of a gain reduction being due to a distortion reduction
HaHa, now that's funny ! Don't think I've ever heard of a gain reduction being due to a distortion reduction
I have.
I recently read thread (on this forum, I think) where someone compared a pair of horn-loaded 18's to a pair of good BR's, while doing some rock gig. He said that the BR's sounded louder, even though they measured softer. He surmised is was all that distortion, adding volume. Muddy volume, but volume nonetheless.
He also said they everyone including the staff thought this as well, but that the horns sounded cleaner & ore musical.
HaHa, now that's funny ! Don't think I've ever heard of a gain reduction being due to a distortion reduction
I don't think Art was referring to a gain reduction due to a distortion reduction. The PPSL has a plenum, a BR does not, so the net volume behind the drivers is less. Less net volume = less gain at low frequencies.
Ideally, I'd like a sub that was the size of pack of cigarettes that could play 10 Hz to 100 Hz at 150 dB SPL at one meter with no distortion, but that ain't going to happen
.I don't want even order harmonic distortion in a reproduction system, but I certainly don't want odd order harmonic distortion louder than even order, which it becomes once even order is reduced.
Ideally, I'd like a sub that was the size of pack of cigarettes that could play 10 Hz to 100 Hz at 150 dB SPL at one meter with no distortion, but that ain't going to happen
I don't want even order harmonic distortion in a reproduction system, but I certainly don't want odd order harmonic distortion louder than even order, which it becomes once even order is reduced.
Has it been established beyond the shadow of a doubt, that ppsl reduces 2nd order harmonics *only* ? I am thinking the more beneficial benefits of a ppsl scheme is vibration canceling with respect to the cabinet, and the acoustic coupling of the two drivers, since they are so close to each other.
In my own tests and all those I have seen by others, even order (not just second) harmonics are reduced using PP, but odd order harmonics are not.
Adjacent woofers are acoustically close without sharing a plenum.
Vibration cancelling is equal in a push-pull or push-push plenum, though a push push plenum can be made smaller.
Ideally, I'd like a sub that was the size of pack of cigarettes that could play 10 Hz to 100 Hz at 150 dB SPL at one meter with no distortion, but that ain't going to happen
I don't want even order harmonic distortion in a reproduction system, but I certainly don't want odd order harmonic distortion louder than even order, which it becomes once even order is reduced.
So you want lots of second order in order to make things muddy enough that your don't notice the odd order harmonics as much?
Hey, to each his own, I guess.
Personally, when I take a really smelly poop, I don't spray perfume into the air, I open a window.
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Also, I'll say it again:
It is completely possible that at least CERTAIN odd order harmonics could actually make a subwoofer sound better. - Not accurate, but very possibly more defined and alive. It would obviously depend on the specific design, and only listening "with & without" would tell you, but it really is a possibility.
(To be clear, I am only referring to audio below 100 Hz.)
Even order, on the other hand, will ALWAYS sound thick and muddy, and I can't see how that could ever be considered beneficial in a playback system, unless your source audio is deficient to start with.
- And no, I'm not a fan of the "tube" sound (typically meaning a poorly designed tube circuit) nor the "vinyl" sound, though I do like the LF compression vinyl gives.
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As I have stated, not a fan of harmonic distortion in reproduction systems. In fact, years ago I shifted from using small horn loaded subs to ported long-excursion subs specifically to reduce LF distortion- you can't EQ additional harmonics out of the mix, whether even or odd!
To be clear, I have both listened to and measured distortion in PP vs standard loading in a controlled outdoor situation, using the same drivers and cabinets, which I based my observations on.
You have not yet heard a PP sub, yet seem to argue that a reduction of even order leaving primarily odd order harmonics will sound better.
Have fun, good luck!
Art
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