[Crowbar]

AKG's solution was half-assed, but at least they tried. There are two ways to obtain the HRTF with any degree of precision. One is to measure it, which involves an anechoic chamber and a spherical array of speakers around the listener, and a more recent one which is a laser scan of the person's head then using finite boundary method simulation to compute the HRTF based on the scanned head geometry. I can imagine the latter method allowing many people to have their HRTFs measured so they can put them in their DSP plugins, analogous to the way people get custom ear molds for canalphones.

 

[Duggeh]

Wont a change in the subjects hairstyle lead to a change in the HRTF? That's one awkward niggle I can see behind HRTF compared with binaural. My hair is anything between nearly bald and shoulder length depending on the time of year. Similarly with custom IEM moulds, those have to be redone every few years as the ear grows. A technology which can be applied to anyone's ears/head without that need for cumbersome and transitory personal accommodation is always going to be the more viable commercial solution.

 

[Crowbar]

Quote:

Originally Posted by Duggeh /img/forum/go_quote.gif Wont a change in the subjects hairstyle lead to a change in the HRTF?

Not perceptually significant. The most critical aspects are the shape and density variation of the head (the density of hair is miniscule as it's mostly air), and the shape of the outer ear and the ear canal.

Quote:

HRTF compared with binaural.

You can't compare the two since one is a property, the other a recording method, LOL. When a binaural recording is made, it is convolved by physics with the HRTF of the dummy head (or real head, if a live person is used as in some of the recordings).

Quote:

Similarly with custom IEM moulds, those have to be redone every few years as the ear grows.

I've been told some high quality (i.e. $800 and up) ear molds are soft and gel-like so I doubt it's really an issue, especially since an adult's ear canal changes minimally.

Quote:

A technology which can be applied to anyone's ears/head without that need for cumbersome and transitory personal accommodation is always going to be the more viable commercial solution.

I thought this was an audiophile forum. Don't forget we're in a thread about plasma headphones. If sound quality is of supreme importance, the rest are irrelevant. There are always many people that get ear molds, and there will be ones that go for custom HRTF measurement if that gets marketed well.

 

[Faust2D]

Quote:

Originally Posted by Crowbar /img/forum/go_quote.gif If you scroll down at http://membres.lycos.fr/plasmapropul...pages_menu.htm you can see photos of the insides. I don't know what QP70 is.

MB Quart Phone 70

Take a look, striking resemblance no?

 

[Crowbar]

One thing that I suspect about the Plasmasonics is the noise level may not be perfect. That's just one of the advantages a glow discharge version would have.

 

[d.phens]

The constructor probably did have some knowledge concerning headphone world - that's why the devices look so familiar

Probably none of you would like to obtain them after finding out more:

Although paying $2000 for headphones ain't that much (you know),
the electrodes' lifetime was pretty low and as there was probably no other
company except PlasmaSonic capableable of their production...

P(lasma)S(onic)? DOOMED

 

[ericj]

Quote:

Originally Posted by d.phens /img/forum/go_quote.gif The constructor probably did have some knowledge concerning headphone world - that's why the devices look so familiar

Familiar? The plasmasonics have cardamatic suspension - I'm pretty sure Peerless/MB/MBQuart/Maxxsonics has a patent covering it.

 

[Carl]

Quote:

Originally Posted by ericj /img/forum/go_quote.gif Familiar? The plasmasonics have cardamatic suspension - I'm pretty sure Peerless/MB/MBQuart/Maxxsonics has a patent covering it.

Of course, they may have gotten the housing built for them by another headphone company and only made the drivers inhouse.

 

[spritzer]

Quote:

Originally Posted by Carl /img/forum/go_quote.gif Of course, they may have gotten the housing built for them by another headphone company and only made the drivers inhouse.

I think that just what they did. Why waste resources on that when there are plenty of headphone company's in Europe willing to OEM for you.

 

[ericj]

Quote:

Originally Posted by Carl /img/forum/go_quote.gif Of course, they may have gotten the housing built for them by another headphone company and only made the drivers inhouse.

Yeah, that's what i was implying. Designing and manufacturing a really good headphone frame from scratch is surprisingly difficult. Just ask the guys at TakeT.

 

[Liver]

Quote:

Originally Posted by Carl /img/forum/go_quote.gif Oh yes, they exist all right. Google for PlasmaSonic headphones. The things swung 3000 volts of corona discharge half an inch from your ears. I love it. Of course, with typical French build quality and a 15 odd years of time having past since they were made, I'm not sure even I would risk listening to a set, at least without some pretty serious refurbishment. The amp they came with sucks badly from what I understand, so part of any DIY project involving them would have to include making a proper amp for them.

I am sure you mis wrote. You meant to say "without some pretty serious refreshments."

 

[Psiga]

Oh, nice. There actually IS a thread on this sort of thing.

I'd been barking up another tree, on the topic of some things devised by Thomas Townsend Brown, wherein he used positive and negative current fields to move the ions in air (great grand-pappy of the Ionic Breeze, yes). One of the older designs (I tell myself to go look up the patent again, then get distracted by shiny things somewhere along the way) put an array of positive and negative electrodes in chambers, to coherently reinforce the effect. It would result in a pistonic force with no diaphragm or backwave.

To my understanding, that specific idea was an aside, never taken to prototype form. He did not learn until the '80s, if I recall correctly, how to reduce the power consumption and ozone/nitrus emissions. That idea has been on my list for a few years now as something that I'd like to work on -- but the cold plasma discharge that Crowbar's mentioning would likely be easier.

So, Crowbar, you are thinking of knocking together a semi-replica of the Plasmasonic1? I am very, very interested in following along with this. Heck, this'll probably be the first thread that I'll subscribe to.

Oh, you were mentioning obviating the need for helium in a speaker design; I haven't a clue what your solution is, but my own tentative solution a few years ago was, "Why not use water electrolysis? Fresh oxygen for the room, fresh hydrogen for the speaker."


Edit: Reading up on older threads, giving this one a second pass...

Thoughts off the top of my head, regarding Plasmasonic1:
- 50 to 100 hour filament life.
If the filaments are cheap, and we can design them to be relatively easy for a DIYer to replace, then that'll just be a thing to get used to doing. I presume the internal mesh would need cleaning by then anyway, since the field will probably attract gunk.

- Old solid-state components.
It looks like the jagged low frequencies and the roll-off of the highs are due to the three small transistors used to step up the voltage to 3kV. I'm hoping that superior transistors are available today.

Overall, I'm really interested in trying out a reproduction project. It's strange that I didn't notice this headphone before. In years past, I spent many google-hours learning about plasma-driven audio.

 

[Crowbar]

Moving an ionized body of air was done large scale in a prototype by Nelson Pass. It was called something like ion cloud or ionic cloud, I forget. There was a photo of it on the diyaudio forums at one time. Think corona wire grid sandwitched between electrode grids. No visible emission. Pass ended up in the emergency department from too much ozone.

I'm more interested in Hill's hot plasma. It simply performs better. More difficult from an engineering point to get right, but come on, we do anything for audio

 

[Carl]

Quote:

Originally Posted by Psiga /img/forum/go_quote.gif 'm hoping that superior transistors are available today.

There are: they're big, made of glass, and glow in the dark.

Quote:

Overall, I'm really interested in trying out a reproduction project. It's strange that I didn't notice this headphone before. In years past, I spent many google-hours learning about plasma-driven audio.

Count me in, too. I'm no great DIYer, but if you'd ever like another set of ears to try out a prototype or another set of hands, I'd be glad to help. The allure of a true zero-mass driver is a strong one.

I'm not worried about a bit of high voltage and nitrous, it'd remind me of my misspent youth.

 

[Psiga]

To the extent of my recall, Brown's device would have kept the air in chambers (almost honeycomb-like) while it was being reinforced. The only open end would be the front, which could've been covered with a doped cloth to reduce the ozone emissions to the outside. I don't recall any mention of corona or glow discharges, but it was mentioned that the agitation did often pull air molecules apart. Again, it never made its way to prototype stage (to my knowledge), so who knows how effective it woulda been.

No working model seems to have gone beyond the most standard form of the invention, which looks kinda like Venetian blinds: Here's Brown himself, demonstrating the device in the '60s, and here's Adire Audio's prototype from 2006. Though they look similar, the Adire Audio prototype's technology should have a fraction of the power consumption and ozone production at any comparable size.

The technology should scale down to headphone sizes, and so should the reinforced cell variant. I'm not sure how they would compare to a single point-source corona, though.

Either way, I would flippin' adore the chance to work on a semi-easy HV project. I wouldn't be able to reconstruct the Plasmasonic1 just by looking at it, but probably would be able to follow instructions. $50~$100 for experience and a proof of concept sounds more than great. If you're still considering putting the instructions together, Crowbar, you definitely have some third party interest.

Quote:

Originally Posted by Carl /img/forum/go_quote.gif There are: they're big, made of glass, and glow in the dark.

Haw haw. ;p

Tubes existed back in the '80s, of course, but the suckerpunch here is that we want something small enough to fit on the headphones themselves. This image shows what we're dealing with.

Admittedly, having two functioning 300B tubes sticking off the head would go down in audiophile history... But yeah, we'll stick with solid state for now. I'm just curious to know if there are any solid state transistors which could do the whole 3kV step without affecting the audible frequency response.

Here's the Plasmasonic1's stated frequency response:

Notice how it rolls off at 15kHz, and is really jagged below 50Hz? That's apparently not the fault of the plasma itself!

Check out the three BUX87 transistors:

Notice how if you sum all three of them together, it would keep the frequency flat up to about 15kHz, and create havoc below 50Hz? Booyah. The bottleneck is there.

So the question is, can we find a small modern transistor more effective for our purposes than the BUX87.