For those who were at MWAF - Phil Clements' H-PAS

[Jeff B.]

I just opened my new issue of Stereophile (just came today) and found that it contained a fairly lengthy reveiw of the Atlantic Technology AT-1 loudspeaker which uses Phil Clements' H-PAS bass loading design. From the measurements it appears to do exactly as Phil described in his talk at the MWAF. The small speaker does extend to the low 30Hz range, and the port output curve is shaped a bit different than a typical vented or transmission line design. I also see the effect of the internal bass trap in the impedance curve. I just thought I would bring this up in case anyone wanted to check it out.

Jeff B.

[Taterworks]

Re: For those who were at MWAF - Phil Clements' H-PAS

I said this in discussions with other designers at Dayton: The chamber that is intended to work as a 'bass trap' cannot avoid having some type of quarter-wave mode, simply by virtue of its aspect ratio. For Phil to assert that this portion of his H-PAS line has essentially no quarter-wave behavior just doesn't jive with the physics of a traveling sound wave. Even a bass-reflex port will have meaningful quarter-wave behavior, if it is long enough.

What Phil has is essentially a transmission line that bifurcates at a point about 2/3 of the way along its length, with one passage leading to the terminus and the other leading to a stub, which absorbs higher harmonics while reinforcing the fundamental frequency of the transmission line. Imagine placing the terminus of a transmission line some distance up the line rather than at the end of the line and you'll be closer to what I'm thinking of, and I think that PMC Speakers from the UK have incorporated a similar quarter-wave stub near the terminus of their transmission lines (this comprises their 'Advanced Transmission Line') to absorb higher-harmonic output, but I don't think it is relied upon to reinforce terminus output at the line's fundamental frequency.

The difference with H-PAS is that the quarter-wave stub contributes to the effective length of the transmission line because the traveling wave sees an acoustic impedance along either possible path (down the stub or toward the terminus) that is closer to the same (with the terminus path still being the lower-impedance path), and the wave is split almost in half. The part of the wave that enters into the stub is burped back out at the bifurcation point less than 90 degrees out of phase with the next rear wave from the driver at the line's fundamental frequency. This approach absorbs line output (through cancellation) at higher harmonics of the line fundamental but reinforces the fundamental itself. That's the only way I can see H-PAS working, and because there's not a clearly-defined acoustic mass-spring system in the box (like a helmholtz resonator system), the only other type of acoustic resonance that can be harnessed in this system is quarter-wave resonance.

I think Phil probably arrived at this enclosure configuration empirically through experimentation, and later he brought in the Atlantic Technologies engineers to figure out what he had created, but I point to the line in my signature to sum up my attitude toward H-PAS. Just because you discover a configuration that works through trial-and-error doesn't mean you engineered it. I'll bet it sounds great, but during Phil's talk at MWAF, it didn't seem to me like he had a complete grasp of why his invention worked.

[fntn]

Re: For those who were at MWAF - Phil Clements' H-PAS

I said this in discussions with other designers at Dayton: The chamber that is intended to work as a 'bass trap' cannot avoid having some type of quarter-wave mode, simply by virtue of its aspect ratio. For Phil to assert that this portion of his H-PAS line has essentially no quarter-wave behavior just doesn't jive with the physics of a traveling sound wave. Even a bass-reflex port will have meaningful quarter-wave behavior, if it is long enough.

What Phil has is essentially a transmission line that bifurcates at a point about 2/3 of the way along its length, with one passage leading to the terminus and the other leading to a stub, which absorbs higher harmonics while reinforcing the fundamental frequency of the transmission line. Imagine placing the terminus of a transmission line some distance up the line rather than at the end of the line and you'll be closer to what I'm thinking of, and I think that PMC Speakers from the UK have incorporated a similar quarter-wave stub near the terminus of their transmission lines (this comprises their 'Advanced Transmission Line') to absorb higher-harmonic output, but I don't think it is relied upon to reinforce terminus output at the line's fundamental frequency.

The difference with H-PAS is that the quarter-wave stub contributes to the effective length of the transmission line because the part of the wave that enters into the stub is burped back out less than 90 degrees out of phase with the next rear wave from the driver at the line's fundamental frequency. This approach absorbs line output (through cancellation) at higher harmonics of the line fundamental but reinforces the fundamental itself. That's the only way I can see H-PAS working, and because there's not a clearly-defined acoustic mass-spring system in the box (like a helmholtz resonator system), the only other type of acoustic resonance that can be harnessed in this system is quarter-wave resonance.

I think Phil probably arrived at this enclosure configuration empirically through experimentation, and later he brought in the Atlantic Technologies engineers to figure out what he had created, but I point to the line in my signature to sum up my attitude toward H-PAS. Just because you discover a configuration that works through trial-and-error doesn't mean you engineered it. I'll bet it sounds great, but during Phil's talk at MWAF, it didn't seem to me like he had a complete grasp of why his invention worked.

The stub you're referring to is nothing more than an acoustic filter - very similar to what Danley and others before him have created through the millenia. The length of the added cavity or "stub" is set to cancel certain harmonics that are present in the port output as a result of the driver's fundamental resonant motion. The total length of travel in the stub needs to be 1/2 the frequency of interest's wavelength for this to occur. This is nothing new or patent worthy as you seem to suggest. It reduces the need for stuffing to damp upper resonances that are part of every tl - thus raising efficiency by selectively cutting unwanted harmonics and leaving longer wavelengths intact. Just because someone obtains a patent for something doesn't mean it can't be successfully challenged. Given the H-Pas claims and statements by the patent holders, I'm guessing that they're banking on the likelihood that no one will think that the juice for a patent challenge will be worth the squeeze.

Edit: Given the H-Pas design, I'd say it's safe to ignore Atlantic Technologies' "patent" and build any flavor of transmission line speaker you wish incorporating acoustic filters like Von Schweikert or Danley have used.

[Wolf]

Re: For those who were at MWAF - Phil Clements' H-PAS

I look forward to reading my cousin's copy. I just read the Voxativ article from last issue.

Later,
Wolf

[Brewski]

Re: For those who were at MWAF - Phil Clements' H-PAS

I think Phil probably arrived at this enclosure configuration empirically through experimentation, and later he brought in the Atlantic Technologies engineers to figure out what he had created, but I point to the line in my signature to sum up my attitude toward H-PAS. Just because you discover a configuration that works through trial-and-error doesn't mean you engineered it. I'll bet it sounds great, but during Phil's talk at MWAF, it didn't seem to me like he had a complete grasp of why his invention worked.

Tater from over at the quaterwave Yahoo group it sounds like Martin made updates to some of his sheets so that they could be used to model the behavior. I bought my access to his sheets early last year so I've not checked to see if these updates are available to DIY crowd or not.

Take it easy
Jay

[Taterworks]

Re: For those who were at MWAF - Phil Clements' H-PAS

The stub you're referring to is nothing more than an acoustic filter - very similar to what Danley and others before him have created through the millenia. The length of the added cavity or "stub" is set to cancel certain harmonics that are present in the port output as a result of the driver's fundamental resonant motion. The total length of travel in the stub needs to be 1/2 the frequency of interest's wavelength for this to occur. This is nothing new or patent worthy as you seem to suggest. It reduces the need for stuffing to damp upper resonances that are part of every tl - thus raising efficiency by selectively cutting unwanted harmonics and leaving longer wavelengths intact. Just because someone obtains a patent for something doesn't mean it can't be successfully challenged. Given the H-Pas claims and statements by the patent holders, I'm guessing that they're banking on the likelihood that no one will think that the juice for a patent challenge will be worth the squeeze.

Edit: Given the H-Pas design, I'd say it's safe to ignore Atlantic Technologies' "patent" and build any flavor of transmission line speaker you wish incorporating acoustic filters like Von Schweikert or Danley have used.

?

I think we just agreed. Not sure if you meant to do that. :rolleyes: .

A quarter-wave stub absolutely can be used as an acoustic filter if it produces a null at a frequency that you want to filter, and that's how PMC, Hegeman, et al have used it in the past. It would be great for transmission lines, which produce predictable peaking at harmonics of the line's fundamental frequency, because the stub also filters the harmonics of its fundamental by the same mechanism that causes it to filter out its own fundamental frequency.

I'm not sure if H-PAS is patented - I really didn't feel the need to look that far into it. But the stub in this case is also working as part of a longer transmission line. It's a nifty idea, but I decided it was doubtful that Phil necessarily had that in mind while experimenting with H-PAS.

[fntn]

Re: For those who were at MWAF - Phil Clements' H-PAS

?

I think we just agreed. Not sure if you meant to do that. :rolleyes: .

A quarter-wave stub absolutely can be used as an acoustic filter if it produces a null at a frequency that you want to filter, and that's how PMC, Hegeman, et al have used it in the past. It would be great for transmission lines, which produce predictable peaking at harmonics of the line's fundamental frequency.

I'm not sure if H-PAS is patented - I really didn't feel the need to look that far into it. But the stub in this case is also working as part of a longer transmission line. It's a nifty idea, but I decided it was doubtful that Phil necessarily had that in mind while experimenting with H-PAS.

Nope. You're just agreeing with me.:D

I outed these goofballs last year on another forum I think. Their descriptions about wave acceleration and bass traps have as many swiss cheese holes as their cabinets do. Check out Von Schweikert's designs - I think he's been using internal "bass traps" for years now. He probably laughed his **** off when he first saw AT's propaganda blitz. I'm curious though why the guy with the spreadsheets hasn't come to their defense yet. I haven't seen him on this site or DIY Audio since he last compared the action of the back wave in a TL to whipped cream! :eek:

And actually, it's not really "extending the tl". Effectively, with respect to the system fundamental, it's adding phase distortion - the only real drawback to anti resonance chambers or "bass traps" as Mr. Clements et al like to refer to them.

[edlafontaine]

Re: For those who were at MWAF - Phil Clements' H-PAS

The worksheets Martin J. King

the guy with the spreadsheets

prepared for AT are proprietary. It is not likely we will see them soon. I think he will let AT toot their own horn...

Mr Clements said the output levels claimed for the speakers were measured at the port, much less than a 1 meter distance.

H-PAS is patented...but so is toasted bread, and many patents (some say 30%) are duplications of previous work that was already patented.

[Paul K.]

Re: For those who were at MWAF - Phil Clements' H-PAS

If you had taken the time to check into Martin's posts via his personal page, you would have found he has indeed posted here and fairly recently. In fact I'm pretty sure he posted in a thread precisely about this AT product. Additionally, your sarcastic "whipped cream" comment was totally uncalled for.
Paul

Nope. You're just agreeing with me.:D

I outed these goofballs last year on another forum I think. Their descriptions about wave acceleration and bass traps have as many swiss cheese holes as their cabinets do. Check out Von Schweikert's designs - I think he's been using internal "bass traps" for years now. He probably laughed his **** off when he first saw AT's propaganda blitz. I'm curious though why the guy with the spreadsheets hasn't come to their defense yet. I haven't seen him on this site or DIY Audio since he last compared the action of the back wave in a TL to whipped cream! :eek:

And actually, it's not really "extending the tl". Effectively, with respect to the system fundamental, it's adding phase distortion - the only real drawback to anti resonance chambers or "bass traps" as Mr. Clements et al like to refer to them.

[Paul K.]

Re: For those who were at MWAF - Phil Clements' H-PAS

Not only are they proprietary, Martin signed a Non-disclosure Agreement.
Paul

The worksheets Martin J. King prepared for AT are proprietary. It is not likely we will see them soon. I think he will let AT toot their own horn...

Mr Clements said the output levels claimed for the speakers were measured at the port, much less than a 1 meter distance.

H-PAS is patented...but so is toasted bread, and many patents (some say 30%) are duplications of previous work that was already patented.

[fntn]

Re: For those who were at MWAF - Phil Clements' H-PAS

If you had taken the time to check into Martin's posts via his personal page, you would have found he has indeed posted here and fairly recently. In fact I'm pretty sure he posted in a thread precisely about this AT product. Additionally, your sarcastic "whipped cream" comment was totally uncalled for.
Paul

I don't follow or "stalk" any particular person in blogs or forums. I was merely being factual about what I've read and heard. To some, perhaps you, truth may seem stranger than fiction.

http://www.diyaudio.com/forums/multi-way/161961-real-expert-just-self-proclaimed-29.html#post2108522

[edlafontaine]

Re: For those who were at MWAF - Phil Clements' H-PAS

fntn,

An effort was made by thinking "outside the box" in his attempt to assist those who just don't get it.

...So you choose to be dismissive? :rolleyes: You may discredit yourself by doing so...

Have you worked with his worksheets to know what they are capable of?

AT paid to have work done for them. That is not necessarily a measure of the man doing the work.

[fntn]

Re: For those who were at MWAF - Phil Clements' H-PAS

fntn,

An effort was made by thinking "outside the box" in his attempt to assist those who just don't get it.

...So you choose this to dismiss him? :rolleyes: You may discredit yourself by doing so...

Have you worked with his worksheets to know what they are capable of?

I've reviewed the equations his worksheets are based on. The simple wave equation and volume velocity method for solving acoustic output in one dimension is a very rough and flawed approximation for accurately evaluating acoustic resonance in a complex shaped cavity. None of the currently available "software" accurately models upper resonances - including HORNRESP because of this fundamentally flawed assumption and thinking that was conveniently put into layman's terms with the whipped cream analogy by Martin King. For most of the people that use these spreadsheets, the approximation is "good enough". For some of us though, not so much.

[dlr]

Re: For those who were at MWAF - Phil Clements' H-PAS

I've reviewed the equations his worksheets are based on. The simple wave equation and volume velocity method for solving acoustic output in one dimension is a very rough and flawed approximation for accurately evaluating acoustic resonance in a complex shaped cavity. None of the currently available "software" accurately models upper resonances - including HORNRESP because of this fundamentally flawed assumption and thinking that was conveniently put into layman's terms with the whipped cream analogy by Martin King. For most of the people that use these spreadsheets, the approximation is "good enough". For some of us though, not so much.

Show us your software or the software that you use and the results that improve upon it. You have often castigated him, but you provide nothing but words and claims. You claim it is flawed. If you have evidence to provide to support your position, let's see it. Lacking that, it's nothing but empty words.

dlr

[charlielaub]

Re: For those who were at MWAF - Phil Clements' H-PAS

The stub you're referring to is nothing more than an acoustic filter - very similar to what Danley and others before him have created through the millenia. The length of the added cavity or "stub" is set to cancel certain harmonics that are present in the port output as a result of the driver's fundamental resonant motion. The total length of travel in the stub needs to be 1/2 the frequency of interest's wavelength for this to occur. This is nothing new or patent worthy as you seem to suggest. It reduces the need for stuffing to damp upper resonances that are part of every tl - thus raising efficiency by selectively cutting unwanted harmonics and leaving longer wavelengths intact. Just because someone obtains a patent for something doesn't mean it can't be successfully challenged. Given the H-Pas claims and statements by the patent holders, I'm guessing that they're banking on the likelihood that no one will think that the juice for a patent challenge will be worth the squeeze.

Edit: Given the H-Pas design, I'd say it's safe to ignore Atlantic Technologies' "patent" and build any flavor of transmission line speaker you wish incorporating acoustic filters like Von Schweikert or Danley have used.

This is an interesting read. I had a somewhat similar idea as the stub absorber once, that combines a slotted absorber as part of the rear line of an open baffle loudspeaker or U/H frame type speaker. These have interference peaks because rear radiation changes phase as it propagates around to the front and at certain frequencies there is either cancellation or reinforcement. The slotted absorber is an acoustic chamber having a damping material inside and slots to the outside. If a proper one were designed so it was "tuned" to absorb the rear radiation at some frequency or frequencies (e.g. the freq. at which the "first peak" in the dipole response is found) there could be significant smoothing of that peak and it might potentially allow for longer U/H frames to be used, leading to more bass reinforcement.

I'd still like to try out this idea someday! Thanks for bringing it back in to focus.

-Charlie