A Thread for those interested in PPSL enclosures

Status
This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.
"They will hit 500Hz easily but are big."

How big for 27hz?

Really?

Using Art's graph, his design was 6dB down at about 280hz. Divide by .8 for a 12 (vs a 15)and it comes out to................350hz.

A LR24 is 6dB down at its crossover frequency, so you will need a low-pass with a Q~1.0 and probably 12dB/oct to achieve an acoustic LR24 transfer function.

It also looks like you may want to throw in about a 3dB dip, frequency TBD after build. Art's would be around 175hz, for a similar proportioned 12 it may be around 220hz or so.

If you keep the plenum sized down to a minumim (especially the depth), it will maximize the bandwidth.
 
I think so.

A three-way makes more sense to me.

Two-way has too many limitations.

I think a Unity style horn on top of a PPSL woofer section is about right. Some of the Unity style two-way tops will go down to 100hz, allowing for a low crossover point to a PPSL design.

unity28.jpg


This is only 24" wide, and would mate well with a dual 12 PPSL that could be about a 24" cube. Cross around 200hz or so. A pair of Dayton 12's that will tune to 27hz (6th order vented) in that box will be about 100.5dB/2.83V/1M.
 
EV MTL-2, 2-DL18's, 14 CF

"i tried to avoid that ", So do I.

EV made a dual 15 PPSL that crossed at 800hz. I never had a chance to hear it though, could it have been that horrible (they wouldn't have offered it if so)?

https://www.yumpu.com/en/document/view/994212/pa-anlage-ev-mts-1-mtl-2

Hi there d: The reference for EV MTL-2 is for 2 DL18 drivers, which I have available boxed-up in the basement. I assume the front plate in the reference is off to show the manifold and would contain two vents in opposite corners (vents estimated at about 9" x 9"). Provided external dimensions are 36"h x 30"w x 22.5"d =14cf. ...regards, Michael
 
Using 24db/octave LR active crossover, crossed at 150hz (-6db there), I replaced 2 x 15" (ported tuned to F9=27hz, bump around 40hz) with my quad 8mm 12's (ppsl, ported F9=27hz unequalized). Some slam/impact went away, but it went deep, smooth, it's not loud at all but the couch is shaking.



The sub is basically un-localizable, crossed at 150hz, wouldn't have figured that.

I'm thinking some impact/slam is actually harmonic distortion.............................

Got to keep playing to figure this out.

Norman
 
Last edited:
"I'm thinking some impact/slam is actually harmonic distortion............................."

Definitely.

At one point I built some dual 12 speakers crossed at 800hz, they had very short coils and cheap magnet structures. This speaker had a lot more 'slam' factor than a dual 15 speaker with much better long excursion drivers with thicker top plates.

The 'Wood Effect' (absolute polarity) is much more noticeable on speakers with high 2nd harmonic distortion.

cjwoodeffect
 
Are the benefits of placing the woofers in the plenum "cone to magnet" lost when the box is crossed over 100hz or lower to be used in a HiFi setting?

If not, would there be any merit in using some sort of diffraction lens between the drivers when they are mounted "cone to cone" to accomplish the same effect the driver basket would have?

DJK, you mentioned that in one of your earlier builds you felt you had made the plenum opening too small and that the subsequent pressure from the drivers was too great. Were you worried about driver failure, loss of efficiency or sound quality(chuffing?)?

Now that you have built so many boxes with this driver arrangement, have you come to a preferred Sd to Plenum opening ratio that you can apply without too much deliberation every time? I've read through this entire thread and would really like to put a pin in this ratio.

Has any one tried applying Vent Velocity calculations to the plenum? Just curious if we could use a similar methodology to pick the best plenum size for a given set of drivers.
 
The first dual 15 prototype had a 5" x 16.5" plenum, 82.5 in^2.

The opening on a Klipschorn, Belle, or LaScala is 40 in^2 per 15" driver. I've run a Carver M1.5T (750W/8Ω) on program material on Klipschorns without an issue.

The pressure from the 82.5 in^2 plenum seemed quite intense , but I doubt it was any real kind of issue, I was just surprised. I think the main thing I did not like was the removable front panels for mounting the drivers. I made the plenum width 7" and skipped the removeable panels.

"Now that you have built so many boxes with this driver arrangement, have you come to a preferred Sd to Plenum opening ratio that you can apply without too much deliberation every time? I've read through this entire thread and would really like to put a pin in this ratio."

Not really, I just try and keep it as compact as practical. If I needed to have a removeable panel for driver loading I think I would cut the access holes in the top (or bottom) and have panel over the holes (as done in the Klipschorn, Belle, or LaScala).
 
I treat it as a normal box, sealed, vented, OB, whatever.

The top of the range is determined by the depth of the plenum. If you use too large of a plenum you will get a small peak at the top end of it's range. If you need the top end of it's range you may have to attenuate the peak (usually less than 3dB).

Art Welter has some good measurements on a double 15 design showing this peak.
 
I treat it as a normal box, sealed, vented, OB, whatever.

The top of the range is determined by the depth of the plenum. If you use too large of a plenum you will get a small peak at the top end of it's range. If you need the top end of it's range you may have to attenuate the peak (usually less than 3dB).

Art Welter has some good measurements on a double 15 design showing this peak.

Why then give that Plenum advantage? I now qts is important for low bass, so I presume that the plenum is used to load the cones rising qts but not Fs or even lower it like in a dipole? normal closed box has qts 0.6 a 7, but rises the speaker FS with it, here is the problem making a good sub.

I have done a time ago a open baffle with this idea, only for bass very small but go low and not so sensitive for room modes.

So far I see now, the visatons has high vas, good for closed but not vented.
regards
 
Last edited:
No, it's not about the magnet structure but about cancelling the asymmetry in the woofer itself.

Wouldn't this be achieved regardless of magnet in or magnet out? Are the asymmetries not being reduced by the coupling of the cones in the plenum?
Similar to what is achieved by an isobarik alignment but greater on account of the cones forcing each other to behave?

It would be very interesting to see some Klippel data on this arrangement.
The close quarters would likely complicate the measurement.
 
Wouldn't this be achieved regardless of magnet in or magnet out? Are the asymmetries not being reduced by the coupling of the cones in the plenum?
Similar to what is achieved by an isobarik alignment but greater on account of the cones forcing each other to behave?

It would be very interesting to see some Klippel data on this arrangement.
The close quarters would likely complicate the measurement.

In an isobaric alignment, only one cone can 'see' the outside world and the second, 'inside' cone is, effectively, being used to change the T/S parameters of the 'outside' cone and enable a smaller box to be used (as I understand it).

In the PPSL alignment, both cones can 'see' the outside world and the 'reverse' driver


I think the key thing is that if you have two cones facing each other, both moving in and out identically, if the behaviour of the cone of one of the drivers, from one end of its excursion to the other end of its excursion, is not linear, both cones will have that behaviour and double the effect of the non-linearity.

Whereas if the second driver is mechanically reversed and its magnet and basket is now facing the cone of the first driver, as the 'normal' cone exhibits the non-linearity at a given point in its excursion, the 'reverse' cone's non-linearity will be doing the exact opposite of the 'normal' cone, meaning the non-linearity will cancel out.


Does that make any sense? I am struggling to explain it today :eek: lol
 
Status
This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.