Hi Art,
If I may, I'd like to separate my box and how it sims,
.....from how a reduced plenum width sims, all other things being equal.
I think it will help me see better....
OK first, my box...
The sim I posted in #779 is not what I think most reflects my build.
It was what Brian helped me with (although TS parameters are a little different), and was meant to be no more than a point of discussion vs a narrower plenum. I never adjusted that sim for box changes...
My box is even less than 333L.
333L was before I added 40 inch^2 to the port, and put the 2nd driver into the rear chamber, or deducted for braces.
My best net calculation gives right at 300L.
It's outside dimensions are 48H x 21.75W x 31.5 D.
Oh, and it sits on recessed corner caster wheels, and front bumpers that raise it 1.5". We get lots of sudden rainstorms...no more need for 2x4's underneath.
Looking at the attached pict, which one would you call larger?
Now I need to ask you a question about port length....
The 8" high shelf port is 24" deep, at the bottom of the box as you can see.
The interior box depth past the shelf is about 7".
Is the back bottom corner, past the port shelf, rear chamber ? Or is it a port extension turned upwards?
If it's more port, that would make port length closer to 31" and net volume closer to 280 L ?????
Oh, one more modeling question.... with the drivers vertical as they are...
is rear chamber length, Lrc, the distance between the driver baffle and top of box, 13.5" (or down to shelf port for bottom driver, same distance" ) ??
Ok, on to reducing plenum width.
What I've been finding, is that I can make a sim of a 2 driver OD bass reflex, with nice looking response, using a plenum that's wide enough to allow push-pull mounting. (11" again)
When I explore narrowing the plenum to 3" , I get a dip in response at 100Hz.
I really think it's more than just an apparent dip vs a 40Hz peak....
it really seems to be a 5 dB or more relative drop against 100Hz using the wider plenum.
And no amount of readjusting chamber volume, port size or length, seems to be able to get the dip at 100Hz out.
So sim against sim, ignoring my box, can you show me how to get response leveled out ?
Whew, sorry for the never ending need for schooling ...
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Mark,
1) Easiest way to see the result of the plenum resonance is to eliminate the BR resonant system, use a large sealed box with no LF peak for the sim.
2) In post #769 you wrote "The OS is a little smaller, which is always better." Can't tell wich is larger without knowing the depth, but now that you have given dimensions, and redacted, we know the answer ;^).
3) Since your box response has a much lower Fb, it's obvious that the port shape and placement has altered it from the sim. Slotted ports tune lower than a circular (simmed) port. You'd have to play around with Hornresp port size and volume until it matches your measurement.
4)Look at the Hornresp schematic and determine which dimension you are looking at.
5) See # 1, the dip is relative to a peaked bottom.
6) Easy to confirm if you are not dealing with a rising response around Fb.
Cheers,
Art
In terms of cone sag, the lower plenum depicting vertically mounted drivers would be better.
In terms of reduced plenum volume vs overall cabinet volume, the arrangements would be driver shape dependent.
Hi Art,
I've been simming narrow plenum designs....
Started simple, comparing a narrow plenum dual 18" sealed, vs 2 simple single 18" sealed.
The narrow plenum, simmed, dual box needs more internal volume to smooth out, as you would expect...
but it's 3 db down from just using 2 single 18"s.
I cant see it's a 'power thing' either...as voltage is parallel to the drivers....
And moving to a dual BR design, narrow plenum appears to be a disaster.....
I mean, any good BR design is about matching port to main output, right?
....and narrow plenum appears to kill main output so much (in similar fashion to sealed) , that port output looks exaggerated .....when it's not...
Please advise, give sims, point me to the truth lol.... cause so far all I can see is narrow plenums don't work for ****, for anything !
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1) A picture is worth 1000 words. Assuming the sealed plenum back dual 18" chamber volume is equal to the 2 single 18" sealed, LF output should be equal, and plenum output (an upper band peak) increased.
2)A more narrow plenum will result in a higher frequency, more narrow upper band peak than a wider plenum, which will have less output in the 100 Hz region in your simulations. "Main output" is an ambiguous term- the plenum increases upper band output, which may or may not be in the desired pass band, and the trade off of plenum volume to cabinet volume should also be considered.
That said, the narrow plenum idea was in response to your desire to have vertical cone mounting to avoid cone sag in a narrow, tall enclosure-the plenum volume does not have to be reduced in such an arrangement if the upper gain is more important than the lower gain lost from a smaller Vb.
3)In your sim, the BR port "pipe resonance" has more output level than the LF output. The port resonance is likely not as predominant when measured as the simulation would indicate. When speaker "Output1" and port "Output 2" are combined with a smaller plenum, the upper peak is likely to appear larger than what it actually would be "as built".
A few sims below, forgot how to do "screen saves" on the PC, so crap quality, but they prove I did something ;^).
Art
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Oh no, you didn't just take photos of your computer's screen, LOL!
ALT-PRINTSCREEN will capture a copy of whatever window you've selected with your mouse. If you've got Onedrive installed and enabled, it can automatically save a PNG image of the capture as well.
I'm still confused.
Unless you want some extension above 120 Hz, I STILL don't understand the reason to build a PPSL, as opposed to a simple push-pull, especially if the box is going to be simple vented.
(I also don't understand why anyone would want to run a sub over 120Hz, but that's a different issue.)
Having read this entire thread seventeen thousand times, and every other thread I could Google on PPSL, (there aren't many) it still sounds like maybe the slot minimizes some "even higher" frequencies & so MAYBE lessens some higher odd-order harmonics, but Art is adamant that this is not the case.
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So can someone explain this in a simple way?
Forget the choices of sealed, BR, or Horn. In fact, just assume the box will be vented, as the bulk of this thread shows / talks about.
I can't upload an image, but I've done a simple test with my dual 12", BR subs, simply reverse-mount / reverse polarity on one driver, and it CLEARLY sounds better.
For someone like me, running the boxes at maybe 40 - 100 Hz, does PPSL have some advantage over my NON-slot loaded push-pull experiment?
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ALSO:
With my 2X12" experiment, the sound becomes cleaner, but it still doesn't have the punch I currently associate with a horn. (especially at higher volumes) Does the slot somehow help with that? I don't see how, since that "horn loaded" punch & clarity (AFAIK) comes from having less cone excursion.
With so many folks raving about how good the PPSL sounds, but referring to a BR design, and yet so many folks ADAMANT that a horn sounds much better, I find this very puzzling.
So?
Unless you want some extension above 120 Hz, I STILL don't understand the reason to build a PPSL, as opposed to a simple push-pull, especially if the box is going to be simple vented.
(I also don't understand why anyone would want to run a sub over 120Hz, but that's a different issue.)
Having read this entire thread seventeen thousand times, and every other thread I could Google on PPSL, (there aren't many) it still sounds like maybe the slot minimizes some "even higher" frequencies & so MAYBE lessens some higher odd-order harmonics, but Art is adamant that this is not the case.
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So can someone explain this in a simple way?
Forget the choices of sealed, BR, or Horn. In fact, just assume the box will be vented, as the bulk of this thread shows / talks about.
I can't upload an image, but I've done a simple test with my dual 12", BR subs, simply reverse-mount / reverse polarity on one driver, and it CLEARLY sounds better.
For someone like me, running the boxes at maybe 40 - 100 Hz, does PPSL have some advantage over my NON-slot loaded push-pull experiment?
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ALSO:
With my 2X12" experiment, the sound becomes cleaner, but it still doesn't have the punch I currently associate with a horn. (especially at higher volumes) Does the slot somehow help with that? I don't see how, since that "horn loaded" punch & clarity (AFAIK) comes from having less cone excursion.
With so many folks raving about how good the PPSL sounds, but referring to a BR design, and yet so many folks ADAMANT that a horn sounds much better, I find this very puzzling.
So?
You can also just use the Microsoft "Snipping" tool, which is built into Windows.
Hmm. Maybe it's the same thing as "ALT-PRINTSCREEN?" Anyway, I just keep the snipping tool icon on my dock, and click it when needed.
Very simple.
Yes, probably as simple as using Hornresp, go ahead with your designs and post up the results of your definitive PPSL's that fit in your particular pickup truck when you get a chance ;^).
By the way, you may consider the plenum to be a "horn" after you work with various plenum sizes for a while..
1)Notice that the rather large plenum needed for push pull 18" results in almost +4dB gain at 100 Hz as opposed to a simple push-pullas can be seen in the first screen shot in post #786.
2)Lifting lightweight small top boxes that are not capable of LF output that would keep up with the bass speakers is one reason anybody that has lifted heavy cabinets understands.
3) Push-pull will cancel even order harmonics due to suspension and magnetic differences in the driver's forward and backward stroke, the large series of "suck-outs" the plenum causes will reduce upper harmonics in those frequency ranges.
Perhaps you'll get the second part of the above on the 17,001 reading, but I won't hold my breath ;^).
4)Deep nulls=less harmonics.
5) The bulk of this thread refers to cabinets with a plenum, the plenum is a peaky upper bass horn, don't forget that choice. The bulk of the thread deals with 12" and 15" cabinets, resulting in upper peaks that are higher and more narrow than the 10" x 18" plenum Mark 100 introduced recently.
7)See item 1. Re-read post #786. Look at the crap screen prints again, the fuzzy pictures contains the information that you seem to overlook.
Note that a standard BR upper response in the 100 Hz region is the same as sealed, but the addition of a plenum changes the upper response.
And once again, why would I care about response above 100Hz?
Do you not understand my question?
If I'm crossing to my tops at 100Hz, I want my subs to be 3dB DOWN at 100Hz. Why the heck would I choose a design that boost this are, then just have to sculpt it back out with EQ? (Possibly screwing up the sound of my tops in the process?)
As for HARMONIC distortion, a "simple P-P design already minimizes a lot, so is the plenum even "betterer," somehow?
My questions still have not been answered, and no, not in those other posts, either.
And again, (Do I really have to repeat this?) How is a PPSL bass reflex design "The best sub I've ever heard" according to some very knowledgable guys, if horns are so much better in so many ways? (except LF extension.)
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1)Response does not "end" at the crossover point, so care should not either.
2) Look at the response of the vast majority of pop music produced over the last 5 decades and you will see a great rise in average and peak demands of kick, snare and bass in the 80-160 Hz region. Having the upper potential, and equalizing it down by 3dB (or more) allows that much more headroom for most music, without power compression.
I prefer to EQ any sub "flat" to it's F3, but have found a rising upper response fits the dynamics of most of the music I work with.
It is best if the raw response of the sub fits the average envelope of the music, so what works "best" for rock may not for some forms of EDM that require most energy a few octaves lower.
3)Yes, as explained before- the series of deep "suck-outs" AKA acoustic band pass filters the plenum causes above 100 Hz also reduces upper harmonics (and harmonic distortion) in those frequency ranges by the same amount as the dip.
4)They have been answered, but not understood- I understand that I'm not the best communicator, but you get what you pay for :^).
5)The last sub one builds is usually "The best sub I've ever heard" ;^).
For most home systems, PPSL certainly would be better in regards to LF extension than a vastly undersized FLH. In small rooms, the upper "punch" of an undersized FLH seldom is appreciated, as there is often too much low mid to begin with with 8 foot ceilings.
There are a large variety of PA cabinets that have found the upper gain of various plenum mountings useful, that subset is less than "standard" BR, but exceeds FLH by a good margin in recent decades.
Is that a serious answer? It was a serious question.
and yet, when I have stated, for verification (based on all my reading here and elsewhere) that one apparent advantage of the PPSL design is a reduction in harmonic distortion, you have practically jumped all over me, saying this isn't so. This has happened TWICE, after which I decided you must be right and I'd forget about slot loading since it thus has no apparent benefit to me.
I am once again befuddled.
With respect, Art, they have not. Your a great guy, but a typical response from you goes like this: First, you tell me what I already know, (Making me feel even more clueless than I already am) then you answer a question I didn't actually ask. Then you stop, and no one else answers my question because they see a long response from you & figure it's over & done with.
For an obvious example, see below:
I am not asking about PPSL vs horns. I don't know how to possibly be more clear. I'm asking about PPSL versus a non- slot loaded P-P design.
If the slot DOES further reduce some distortion artifacts (I no longer have any idea, since if I say it does, you'll say it doesn't, and it I say it doesn't, you'll say it does...) but if it DOES, then:
It begs the question, how much reduction is enough, given other trade-offs?
A simple P-P already can reduce harmonic distortion by rather incredible amounts, and given that some folks actually PREFER the sound of that distortion, one would think this is then enough.
If, on the other hand, the slot reduces ALL distortions because it's a filter (something others have claimed, I have repeated for verification, & then you have adamantly told me is not the case) then the slot loading would of course be preferable to a simple P-P, even when the sub is used from 40 - 100 Hz.
But getting a simple, clear answer seems impossible. I'm right at the point where I don't care any longer and will just live with the garbage I already own.....
Art, Let's try it this way:
you wrote:
"Push-pull will cancel even order harmonics due to suspension and magnetic differences in the driver's forward and backward stroke."
Which of course I already know.
then you continued with:
".... the large series of "suck-outs" the plenum causes will reduce upper harmonics in those frequency ranges."
And I have no idea what that means. In WHAT frequency ranges? Reduced upper harmonics in the upper harmonics? Huh?
If you just mean that the plenum reduces various groups of upper frequencies, well then YEAH, that's what I've been saying all along, and why I thought it made sense when other folks wrote that the slot reduces some odd-order harmonics, whereas regular p-p only reduces even order. But again, you have twice, very clearly told me this is not so.
PLEASE clarify.
Surely you're not suggesting that only even order harmonics (from the 40-100Hz fundamentals) fall into those "suck-outs?' Or are you?
I would find that very hard to believe.
you wrote:
"Push-pull will cancel even order harmonics due to suspension and magnetic differences in the driver's forward and backward stroke."
Which of course I already know.
then you continued with:
".... the large series of "suck-outs" the plenum causes will reduce upper harmonics in those frequency ranges."
And I have no idea what that means. In WHAT frequency ranges? Reduced upper harmonics in the upper harmonics? Huh?
If you just mean that the plenum reduces various groups of upper frequencies, well then YEAH, that's what I've been saying all along, and why I thought it made sense when other folks wrote that the slot reduces some odd-order harmonics, whereas regular p-p only reduces even order. But again, you have twice, very clearly told me this is not so.
PLEASE clarify.
Surely you're not suggesting that only even order harmonics (from the 40-100Hz fundamentals) fall into those "suck-outs?' Or are you?
I would find that very hard to believe.
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No, not suggesting an acoustic band pass would apply to only even order harmonics.
An acoustic band pass will equally reduce even or odd order harmonics that happen to "fall in the hole".
That said, sorry if I gave the impression that the acoustic band pass "suck outs" from the plenum slot would greatly reduce distortion generated in the usual <100 Hz "sub" range.
From the limited distortion testing of PPSL I have seen, can't say the slot is a big deal, at least not with decent drivers, other than the increased upper sensitivity it provides.
In the simulation example below, the acoustic band pass dip extends from around 300 to 600 Hz.
Maximum excursion occurs around 50 Hz, and maximum distortion will also be generated from around that 1/3 octave range.
The plenum dip would only reduce 6th order and up from that range. Decent drivers don't have much distortion past third order, though there are plenty of PPSL using less than decent drivers being used much higher than 100 Hz..
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?? for someone VERY familair with this thread ??
I'm asking for help here. Somewhere (I believe) in this thread is shown a comparison of conventional mounting vs, ppsl with respect to 2nd order harmonics.
I am planing a push-push "V" slot and I was wondering about the measurements that were posted a while back. Thanks in advance for anyone who might find this info !
I'm asking for help here. Somewhere (I believe) in this thread is shown a comparison of conventional mounting vs, ppsl with respect to 2nd order harmonics.
I am planing a push-push "V" slot and I was wondering about the measurements that were posted a while back. Thanks in advance for anyone who might find this info !
The only actual comparison of harmonic distortion measurements between push push and push pull was done by Mark100 in post #758.
Art, thanks for the clarification.
I'm still lost, but I suppose that's mostly on me. I still can't figure if, for a Band / small DJ system like mine, PPSL has any benefits over a "simple" P-P. Again, I'm referring to something like this:
EAW FR250z Dedicated Subwoofer System, New | Planet DJ
If I am going to LPF the subs at, say 120 Hz, would changing that EAW sub to PPSL, and keeping the internal volume the same , have any sonic benefit? That's the "simple" question. (And probably not a "simple" answer, I know.)
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But now I have new knowledge, and am wondering if 100 - 120 Hz really is the optimum crossover point for me. As I described in my thread about "12" vs 15" tops", Dennis at Radian suggests I might solve me "anemic sound in the low ids" problem not by using more tops' cone area, but by raising my subs' LPF an octave or two. This goes against EVERYTHING I've ever believed or read, but I have to consider it.
And if that turns out to be a good suggestion, then suddenly I'm seeing your explanation of the plenum in a whole new light.
Also, FWIW, it seems to me that using a plenum, instead of a simple P-P, is almost a no-brainer, anyway:
1: You don't lose any volume, because you no longer have to have a grill that sticks out a few inches from the baffle.
2: You also get "built in" cabinet stiffness, so 5/8" or even thinner plywood should work OK. (with other careful bracing.)
3: In the somewhat unlikely case that "Doppler" distortion actually matters in a sub, having the drivers sideways might help. (Or not. But it certainly won't HURT.)
4: For my personal needs, it's a bit easier to design a wide / shallow sub if doing PPSL.
But if I go PPSL / BR, instead of someTH variant, (& I'm still not sure) then I really DO need to understand if the slot is going to be a benefit, so as to then properly size that slot.
Yes, I've read this entire thread many times, but I'm still not clear on the "how it relates to MY setup" part. Working on it.....
I'm still lost, but I suppose that's mostly on me. I still can't figure if, for a Band / small DJ system like mine, PPSL has any benefits over a "simple" P-P. Again, I'm referring to something like this:
EAW FR250z Dedicated Subwoofer System, New | Planet DJ
If I am going to LPF the subs at, say 120 Hz, would changing that EAW sub to PPSL, and keeping the internal volume the same , have any sonic benefit? That's the "simple" question. (And probably not a "simple" answer, I know.)
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But now I have new knowledge, and am wondering if 100 - 120 Hz really is the optimum crossover point for me. As I described in my thread about "12" vs 15" tops", Dennis at Radian suggests I might solve me "anemic sound in the low ids" problem not by using more tops' cone area, but by raising my subs' LPF an octave or two. This goes against EVERYTHING I've ever believed or read, but I have to consider it.
And if that turns out to be a good suggestion, then suddenly I'm seeing your explanation of the plenum in a whole new light.
Also, FWIW, it seems to me that using a plenum, instead of a simple P-P, is almost a no-brainer, anyway:
1: You don't lose any volume, because you no longer have to have a grill that sticks out a few inches from the baffle.
2: You also get "built in" cabinet stiffness, so 5/8" or even thinner plywood should work OK. (with other careful bracing.)
3: In the somewhat unlikely case that "Doppler" distortion actually matters in a sub, having the drivers sideways might help. (Or not. But it certainly won't HURT.)
4: For my personal needs, it's a bit easier to design a wide / shallow sub if doing PPSL.
But if I go PPSL / BR, instead of someTH variant, (& I'm still not sure) then I really DO need to understand if the slot is going to be a benefit, so as to then properly size that slot.
Yes, I've read this entire thread many times, but I'm still not clear on the "how it relates to MY setup" part. Working on it.....
I think it's safe to add three important points, on top of that very impressive measurement he did.
1: While that test showed a surprisingly large change, it might be less significant with certain high-end drivers, which have been designed to minimize such non linearities. Of course, it will still help.
2: Evidently, some folks actually LIKE the sound of even order harmonic distortion. I don't get it, at all, but it's a fact. It certainly does sound "louder," so, well, there's that, I guess.
3: As I've been "discussing" earlier in this thread, you can get "about" the same reduction of even order distortion with a simple P-P design. Art has implied that PPSL might be slightly better, but it's a mind-numbing thing to understand. The main point is that there are other possible benefits, to using an actual slot-loading. Which brings us back to all of my recent questions.
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