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Old 11th August 2012, 02:45 AM   #1
Bare is offline Bare  Canada
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Default PAWO

went and retrieved my Madisound shipment from USA Package depot service I typically use.
A pair of CHP 70-2 70mm paper cones and a pair of Aurasound NS525-255-8A 102mm Paper Cone 8 Ohm.
CHP's @ $28, the Aura's @ $4
First impressions: CHPs are curious things. Cheap plastic Frame, Dinky 20mm voice coil. Nice, albeit 70mm 'cone'. Ferrite motor. Surround is quite nicely done too. Aura's have Stamped Metal chassis, a strong Neo motor, significantly larger voice coil w vented dustcap & pole.
A foamy surround tho.. eww. Hey ! it was $3.60 :-)
BOTH mag materials have longevity issues, But ferrite historically exhibits measurable Flux loss by it's 10th B'day, while Neo has a nasty habit of oxidising into powder .. eventually.
Much higher Flux with Neo though, often being above the Cobalt range. However Neither is as remotely viable as Alnico.
Buy Cheap.. buy twice :-) no news there.

One could conceivably co-ax the Aura with a Tang Band teeny weeny 20mm tweet, IF one was willing to deal with the time issues..imo it would be a looong struggle though.
No notion if either driver will meet expectations.. yet.
Faith assumes/hopes the CHP will.

Decided on a PAWO box, because it's dead simple to assemble and has 'pleasing to me' aesthetics.
Appears that it can be quickly cobbled out of lumber yard 1 x 4 stock and not very large pieces of 3/4" B Birch for fronts and backs, materials happily on hand.
I'm guessing a short cutting/assembly time, each box.
Bit of travel scheduled for the next few days.
But on return, I will build these rascals and hopefully discover firsthand the Magic of a 'full range' teeny tiny driver.
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Old 11th August 2012, 08:50 AM   #2
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Hmm.

On the subject of magnet materials, I've never had any issue with ferrite losing charge (unlike AlNiCo, which is extremely vulnerable to this). I don't recall anyone I know encountering this problem either. Ditto for what was mentioned regarding neodymium, so YMMV on that score.

Regarding frame cost, according to the figures I saw a couple of years back, the MA polymer frame actually costs substantially more than an equivalent stamped or cast equivalent, both of which are very cheap for manufacturers to buy in bulk. They're custom to MA, & were done to be lossier than can be achieved with metal. How much of a difference? Don't know, since there aren't any with metal frames to back-to-back test against with accelerometers, but they're certainly well damped.

Since the PAWO (assuming you mean this one Tom Zurowski PAWO Rear Loaded, Wide Baffle, Side Venting FR125S Horn ) wasn't designed for either of these two units, and I haven't heard of anybody using them in it before, you're taking something of a risk. They may work fine. Equally, they might not. YMMV on that too. Note that neither of the drivers you have got there are the most neutral widebanders; the Aura is decent given the extremely low price, but it does have some midband issues, while the 2nd. gen CHP was designed with a shelved down HF.

Last edited by Scottmoose; 11th August 2012 at 09:10 AM.
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Old 13th August 2012, 08:08 PM   #3
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The MA plastic baskets are far from cheap. They are very elegant and do their job very well.

Voice coil size has a direct effect on the high frequency extention potential. The VC size is a compromize between a range of conflicting requirements and one has to consider it in the context of the result. All 3 of my favorite FRs have 19mm coils. Due to a the goal of a "vintage" sound the CHP isn't the best example of small FR HF extention, adhesives and a few other things were manipulated to create a HF shelf above 5k.

I would not recommend the PAWO. It did not work well for the driver they were originally designed for and they did not work with the myriad of drivers we tried in them until the FE127 (and we only looked because we didn't want to burn our 1st sheet half-sheet of bamboo ply). In the end our patience was rewarded, and inspired us to do a clean sheet design in the same form factor (Mileva) which got the intended bass out of the FE127.

Click the image to open in full size.

Note that we feel the circular supraBaffle is not optional on this box.

Build a box that is known to work with the CHP. It would be a shame to have your 1st FR impressions tarnished by bad choice in box. If you want something in the the same form factor, i'll see if i can help.... one folds an ML-Voigt (with driver at 50% offset), into a thin slab (not too thin or early reflections off the inside back screw things up)... Scott would it be possible to get some numbers for an ML-V? Should pretty much be applicable to CHR as well.

You will note that PAWO plans have not been included in recent site revisions.

Bare, pick a nice russian girl's name, you can have the privilege of naming it if we go ahead.

Or mutate a known reflex box (ie CGR Mar-Ken70.2p) into an appropriate shape and create a false bottom (maybe room toput helper woofer?)

You should take the opportunity to get your butt over here on the 25th and get a large sampling of FR projects to explore the possibilities.

dave
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Old 14th August 2012, 05:09 PM   #4
Bare is offline Bare  Canada
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Well Thank you for that.. It's an impressive offer.. NATASHA .. who else But from Boris and Natasha she was hot f
I was finding the PAWO box an 'attractive' shape, a choice influenced in part by the very simple construction.
Albeit building to even remotely Furniture grade would quickly reduce the assumed simplicity advantages.
Shame... But clearly, You are the master .
Natasha.. from Boris & Natasha she was hot
Pensils? Metronomes.. perhaps?
Maybe an FH3? Can I straighten the back of it? :-)

As aside: Ferrite does lose Flux.. long proven. ie: Motors lose torque and Rpm.. over time, even unused, easily verifiable.
Does it matter on our drivers? Perhaps? will we notice? unlikely.
Neo is attractive except for it's habit of oxidising Very rapidly when
it's protective/encapsulating plating fails. It also has genuine intolerance to heating.. an issue with motors and actuators of long term importance.
Cobalt has close to Neo flux density and it's Currie point (temp where Flux changes) is in the 600C area.
also that it has a projected 2000 YEAR! life to.. measurable.. Flux degradation. Tough Stuff indeed.
Not surprising that it's classified a 'strategic' material.
Alnico is a loose naming of a reduced Cobalt content alloy... quality reputedly varies significantly with alloy mix age of mfg, and even by whom, unfortunately.
Prized for it's neat trick of Flux deformation under heavy loadings yet springing back to full flux, when those have eased. THE basis of the 'alnico ' sound apparently. Guitar world has all this arcane stuff 'down pat'.
I've seen / heard of the Remag process/service.
That's.. Not.. a cash grab from the naive ?
Many swear at it, while some swear by it. Dunno never tried it.

Was only amazed that the Cheapy driver had a Neo mag, as it's multiples more costly than Ferrite.

Last edited by Bare; 14th August 2012 at 05:19 PM.
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Old 14th August 2012, 05:57 PM   #5
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Quote:
Originally Posted by Bare View Post
Well Thank you for that.. It's an impressive offer.. NATASHA .. who else But from Boris and Natasha she was hot f
Intersting that that is the first name i thot of, un-americanifying it, Natalia might be better. (i have an eastern european sister-in-law that sports this name)


Quote:
Pensils? Metronomes.. perhaps?
Pensil (if you leave out (or simplify) the brace has got to be one of the easiest boxes in the world to build. You could even turn it 90 degrees and make the side the baffle to give it more of a PAWO aspect.

Met & Natalia (Natasha) share the same DNA, one comes with the other.

Quote:
Maybe an FH3? Can I straighten the back of it? :-)
No.

Quote:
I've seen / heard of the Remag process/service.
It is a real service. A magger for neo or alnico/samariaum colbalt exotics needs to be much more powerful than those that just do ferrite.

Quote:
Was only amazed that the Cheapy driver had a Neo mag, as it's multiples more costly than Ferrite
Price driven way down because they are old surplus, neo was cheap then and drivers were bought up for (guess) 10 cents on the dollar.

dave
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Old 14th August 2012, 08:43 PM   #6
chrisb is offline chrisb  Canada
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If I may - Dave's reply of "no" to the question on FH3 is not that it's an inappropriate enclosure design for CHP70, but that the curve in side panels shouldn't be eliminated for aesthetics or ease of build.

I think it's fair to say that the Pensil design has been proven with a range of drivers (including non Mark Audio ) , and is certainly a simple build.

The original drawings from which, if IIRC I built a total of 3pr of the PAWO, shows net internal dimensions of 89mm deep by 267mm wide, so simply turning the Pensil P70.3 sideways would result in close to identical width, and 2 /12" deeper - I'd be inclined not to fiddle with those at all, and retain the port dimensions / location, which would place in on one of the sides. It probably wouldn't hurt to mount the driver off center at a GR location ( i.e. at approx 4 5/8" from one edge) and mirror image them.

Dave, Scott, any thoughts?


and as for Ms Fatale, I shouldn't admit this, but I'm of the age where more than a few of my pre-pubescent fantasies certainly included the better distaff side of such partnerships ( same applied to young Barb Feldon as "Get Smart's" Agent 99 ) - even the voice talent behind the cartoon could be considered fetching in her own mid fifties drop earrings & bullet bra aesthetic
Click the image to open in full size.


Click the image to open in full size.

remember, this was years before "gentleman's" entertainment was readily available at your corner newstand, and a kid has to start somewhere.
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Last edited by chrisb; 14th August 2012 at 09:00 PM.
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Old 14th August 2012, 10:46 PM   #7
Bare is offline Bare  Canada
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Hey! Agent 99 is back.. in recyled reruns, still looking as good as in memory :-)
No shame there..at least you weren't amongst those addled ones lusting after Betty Rubble.

Will look up the Pensil dwgs Thanx for the heads up.
Meeces and Men ...yet again.

Ted Weber... Years ago, despite having an Alnico mag machine, necessary to the manufacture of his bespoke drivers. Made public statement that he could not/would not, in conscience Remag Alnico drivers as a for profit 'revitalisation' service. Claiming this, in his limited experiences, was completely unnecessary.
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Old 15th August 2012, 01:47 AM   #8
Bare is offline Bare  Canada
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