Spec. sheet.
While watching this older video, it's hard not to develop antipathy towards the founder. Clearly a small undeveloped ego and quite a few of his claims/arguments can be characterized as BS.
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Lets see your impulse, take one up close so you can drown out the room as much as possible. I'll highlight the multiple peaks for you.
Thinking about some of my comments above, I think I should point out that directivity is going to limit the ways a PPSL could be used in a 2way. In saying that; up to 200hz, a PPSL, can't be "beat". Am I just saying that I think that PPSL is the ultimate Subwoofer? Crossing at 200hz is only 80hz from 120hz, the THX sub xo point. PPSL is definitely not the ultimate "midrange" for the reasons above about reflections in the impulse....but factoring in perception I think the flaws are hidden and sub 200hz is a perfect area for a flaw to live, that needs not be perceived as we have lower resolution in the lower bass range. I probably shouldn't have any dog in the fight and just say that for my situation, where I am crossing at 200hz, A PPSL offers all the headroom needed, in a smaller final radiation source size, which is why I wanted to try it.
2 18"s facing outwards, is the practical answer? IF I take these same 2 - 18's and stack them facing outwards....I now increase the height of the radiation source. This reduces the quality of summation. Just like @mark100 pointed out;
This experience is made from some of the things I spoke of above, about reducing the radiation source size while maintaining, high headroom, which is funny for me to appreciate because I spent most of my time being an advocate of larger sources, ie, larger drivers and horn. I guess that part, is in order to achieve the headroom, but after you get the headroom, its time to find all the tricks to squeeze all that headroom into a smaller area. PPSL is definitely a winner, in my book, when done properly... but it may only work for lower bass. On a grander scale, it is the Synergy of Sub bass. That's probably the best way I can put the idea simply.
I've tried to write my dossier on how I felt one could achieve the title goal. I never gave credit to the PPSL as a lower woofer section of a low crossed 2 way. I think anything that I do differently from this point on, would be in redundancy. I'm definitely still aiming to achieve more than average but I honestly feel like a two way comprised of a horn as large as mine, crossed at 200hz to a PPSL using large woofers is to be revered. The slot loaded drivers in the Haigner Alpha horn would be the next configuration I'd endorse if crossing higher than 200hz but the main thing is that the 2 18's gives the desired headroom I want. I think a lot of people would enjoy a 2way of that size.
Now that I look at his webpage I recall seeing these really early in my journey but not understanding as much, what I was looking at. Interestingly enough I've found a similar solution in my own unique way.
I also thought about using the beginning of the slot as a place to situate another driver, in the spirit of synergy style configuration. Probably just playful thinking. As I discussed with someone earlier. I am kinda at a point, where any move that I would take is more of a step sideways rather than forward or backward, and has about equal cons and pros. I personally feel like the double transient impulse is no issue if kept low enough... I'm basically crossing to a subwoofer....I want horn at ear height....fit as much headroom as possible below the horn.
Meyer doesn't seem to want to get too complicated. They also don't seem to mind using a vented midrange. We've discussed in my other favorite thread, how to deal with F in regards to a midrange. In terms of Impulse, keeping away from F is basically keeping away from the spectrum most actively producing the additional transient peaks in the impulse, but no matter what, to a degree the additional transients will come out of the vent, thinking of BR/BLH type enclosures, and the addition of damping material in the line/enclosure simply is damping out these additional transients. This is the IR of a tapered TL @GM shared (minus damping material) I've highlighted what I believe to be the front and rear wave in the impulse.
compared to a sealed IR
Less stuff being added to the mix...as sensitive as we are to midrange, I understand the importance of keeping it as unadulterated as possible. @gedlee Do you think the same is true for low bass? I figured that the acceptance of TH was evidence that slot reflections are acceptable with low bass reproduction. A TH has the initial transient, the backwave transient And the slot reflection transient(s)...... Is TH acceptable for refence monitoring of Sub bass, is the Question..... @Ro808 maybe you have experience with TH subs. Technical speaking Sealed is going to be more correct. I just wonder where the TH sits in the world of reality. I do know that there are pro studios that use TH subs in studio rooms....Mastering Rooms??? Don't know.... The more I think about it, the more I wonder, why not just error on the side of technically correct.
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I can't follow your discussion or the point that you are trying to make, so I am not sure if I am answering your question.
If by "unadulterated as possible" you mean that the impulse response should compact and smooth, then yes that's true.
What this has to do with "low bass", I am not sure. When you look at these impulse responses you are seeing - visually - mostly HFs. The low frequency stuff is spread over much longer time scales and as such is at a much lower signal level at individual time points. I'm not sure if you follow that, but trust me, you can't see the LFs in any impulse - by eye! The FFT will pull them out for you however as long as you have enough signal.
I can follow it, kind sir. Sort of. Let me tell how I think things go, or at least how I thought things went, before I came to the conclusion that it isn't 100% correct. I believed that the shape of every transient event will be like the IR. In my mind the impulse represents the beginning of every transient event. Thinking about it more, it can only be slightly true or maybe more true in at certain frequency....maybe no where close to the truth but I think...theres some truth to it. It cannot be 100% true because the impulse response test signal, lets go of the driver immediately after the signal spikes and we are left to the suspension and magnet force to return to home. When the driver plays a continuous frequency, the electrical signal remains engaged, guiding the diaphragm to where it should be in the Cycle execution, through peak and trough....This should help to mute that transient character of the driver..... every swing from peak to trough is a transient like event of differing severity having more or less character of the IR....I propose
My point about reflections from a line, They are present for all the frequencies unless it is beamed out of the line in a way that the signal never touches the walls or never makes it out of the line. So in the case of a Tapped Horn, Slot loaded woofers, and to a degree all vented designs, the additional reflections are there at omnidirectional frequencies. How far spaced out these additional reflected transients are, in time, are effected by perception vs frequency, in a way, that I would suspect, to be similar to decay or group delay, meaning that in the bass region the additional reflections are more likely to go unnoticed, as the cycle time is so high in the bass region. It is the midrange and treble, that these additional transients from reflections, will become easier to perceive.....
This measurement, limited to 100hz, still contains reflections in the IR;
It does look much cleaner minus the higher frequencies. Hopefully I didnt miss the mark completely on this interpretation but Im here to learn.
Hoping for some details on IR/reflection topic... but the simplified question might be; Whats the flaw of a ppsl sub used below slot resonance???
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Lets not forget that detrimental diffraction on sharp edges 🙂
Camplo, i don't use subs above 100Hz. And i only care about what kind of impulse response I get with a low-pass in place.
I think the multiple peaks you're scrutinizing are immaterial, especially given the dominance of higher frequency content over lower content, in any linear impulse view.
In real world, are you going to filter the resonances out or not? Can you sim with the filters in place?
Anyway, here is an indoor 1ft impulse I just made of a PPSL.
I don't think it reduces the quality of the summation at all.
C-2-c on my stacked pair is less than 2ft, for 1/4 wave up to 140Hz.
Which given the steep 100Hz xovers I use, covers summation staying within 1/4 wave down thru -45dB.
I say, Let subs be subs .....forget running em up high !!!!!!
Again, I have trouble following what you are saying. The IR is like a signature of a system. Al signals through said system will be modified by the IR as a kind of multiplication and summation (convolution actually). If the signal has a sharp transient and so does the IR then this transient will pass pretty much as the same transient. But if the IR does not have a sharp leading edge - like after a LP filter - then the signals sharp edge will be smoothed out.
As to the "flaw" of a PPSL used only below any resonances, no these resonances will not be as big a problem, except that they can still be excited by other signals etc. My point is that in that regime there is also no benefit to PPSL, it does almost nothing. So why bother.
The only benefit in my experience, is a dramatic reduction in cabinet vibration .......(and perhaps reducing necessary bracing and/or box weight).
Vibration reduction can be a pretty big darn benefit at cranking times😀
Push-pull. The good thing you were talking about is push-pull, but making it sound like the slot was the good thing. (I don't think you meant to)
I understand the appeal of push-pull - the cancellation of even orders of nonlinearity. But the reality is that its going to be dominantly 2nd order, which is not all that audible. I really see how the PPSL (or whatever) is necessarily structurally more rigid. Sufficient structural rigidity is always possible.
Vibration reduction is all i see as a good thing. I think the harmonic reduction stuff attributed to push-pull is trivial at best.
Opposed motors cancelling each other's vibration, works ime.
Any topology that puts motors doing that, like in a reciprocating car engine, is a good thing imo....albeit with tradeoffs of course.
Don't two opposing drivers cancel each other regardless of the configuration. i.e. two opposed drivers on the outside of the cabinet and in phase, versus two driver facing into an internal box. Both cancel each others mass vibration, i.e. the center of mass doesn't move (just like in a balanced car engine. It's called the primary shaking force. There are many secondary forces and torques that occur as well.)
Yes sir.. If i ever build another double 18", it will simply be with two drivers pointing out of opposite sides.
A slot takes up precious box volume, and imo serves no purpose other than to keep drivers prtected from potential damage.
Although a slot does make for the easiest to build protective grill ever 🙂
You
also you
You dont seem to agree with yourself, unless you are saying the slot loaded 18's in your synergy were a step backwards 😊 I guess you could reverse the 18's and have them facing outward...
ppsl allows me this feature for the 2nd channel, facing them outwards is an option but I believe sq is lower...you said ctc doesn't affect summation but your very low ctc synergy horn says otherwise
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