DIY Modified Aiwa HP-500 from Kabeer

Kabeer - "I am located in UK, and I have some orthos. Im not sure if its very viable for me to get anything measured?"

Tyll - "I really can't spend too much money on this, so I've limited DIY Ortho testing to the U.S. to keep the shipping costs down. Sorry."

Kabeer - "Id really like to send my Aiwa to you to get measured. I think its pretty great :). Wualta wants to see their measurements too and has kindly offered to pay you the postage back to UK for them."

Tyll - "Okie Dokie. If Wualta wants to see the measurements, it must be good."

You see, while Wualta might be a crusty old curmudgeon, he's also one of the the patron saints of Orthodynamic DIYers, and if he thinks something is worthwhile ... well, you just have to have a listen.

By golly, he's right on the mark again!

The Aiwa HP-500 Schallumformersystem Headphones
It seems the fashion in the '70s to come up with a new word for the planar magnetic drivers of the time. A 1977 German advertisement for Aiwa headphones uses the word "Schallumformersystem" and then conveniently gives an English translation, "Omni Dynamic Transduction System." From the dearth of information on the interwebs it's evident this is a very rare and relatively unknown headphone. From brochures, it appears the HP-500 was introduced to the German market in 1977.

Kabeer wrote the Aiwa HP-500 Wikiphonia page, which had this, in part, to say:

... it is safe to say its orthodynamic driver was developed and manufactured by Fostex, or one of its subsidiary companies. The diaphragm is similar to the Sansui SS-100's in that the voice coil has the Fostex T50-style serpentine shape on Mylar, but the traces are only 8 conductors wide to the SS-100's 14. The HP-500's magnet structure is the same as the original Fostex T50's.

Kabeer's notes on modifications to the headphones read:

I have performed many, many damping schemes on it over time trying to refine it. When it was sent to Wualta, around a year or so back, it was damped a little harder.

The current scheme consists of: Driver > thick white sheep wool from Ludo covering the driver, and half sealed to it only (bluetacked around half its circumference) > Half stock damping (ie one mineral wool biscuit) > earcups. I find this configuration gives it ample bass and enough extension into the treble.

The earpads are quite worn out, but the slight leakiness lends the headphone some air. The treble is more than enough for me, but my personal tastes lean toward the warm side so I dunno if its for everyone. It has a bit of what I call 'euphoria' about the sound, which I like personally. I think there is a slight peak somewhere in the treble region but it doesn't bother me, the vocal region is slightly recessed in comparison to Yamaha type drivers.

It is one of my favourite headphones, the sound is quite laid back and euphoric. I think some resonances may appear in the tests, but overall i have even preferred it to a O2mk1+SRM007t setup (the sr-007 had better detail definition, but the damped aiwa just sounded more alive and real to me, whilst having an overall similar signature).

Thanks I hope you enjoy experiencing these rare cans and look forward to see what comes about it.

Well, I sure did enjoy your headphones, Kabeer! Wow! Terrific! I simply can't believe these headphones are over 30 years old. They look and sound really terrific!

Continue for Tyll's notes ...


maverickronin's picture

The FR and square waves are great but what's up with the distortion? Is noticeable much at lower volumes or does it really ramp up with volume?

gurubhai's picture

but yet wow....
these are some fantastic measurements.
Great job, Kabeer.
And a big thanks to the 'big bad W' for arranging to get them measured.I really wanted to see these.

donunus's picture

Looking almost like an lcd2 frequency response except for the speed in rise time which may actually be good since it might compensate for the rolloff in the lower highs. WOW.

Kabeer's picture

Thanks for the measurements and great review Tyll! I do still feel they give a nice 3D bodied feel to insturments though.

As for the cable and plug. The cable is stock (cloth covered cable). The 1/4" plug is an aftermarket one I put on, it kinda matches the curvy style of the headphones.