The Ergo AMT Review. (56k, Dont Even Try)

[m8o]

Originally Posted by Duggeh

Continuing to listen to these, there is a complete inability to handle anythgin that soars, or any reverb or echo, .... Sound is just a bit sucked out. Plucked strings die on the note instead of fading as gently as they should. ... I tried them from my iPod, it takes 90-95% volume to get them driving and they sound thin, lacking all of the bass they have from a desktop amp.

the downside of providing such candid and helpfull commintary is what head-fi'er is going to buy them from you now?

edit: I stand corrected. All that's because you were being fed a mono signal I see now?

[facelvega]

Originally Posted by Duggeh

Haha! I've been trying to get to the bottom of this damn suckout with certain songs and why theres this flatness to all the sound.

The headphones are terminated with a MONO plug Time to break out the soldering iron I think!

That was the last thing I was expecting you to say. Wow. A later refit, I assume? OH, wait, I should tell you, my pair had some shorting problems inside the plug that caused some funky issues early on. I simply unscrewed the plastic cover and inserted tiny pieces of paper between the solder points to repair this. If it's the original plug and has the usual three-zone stereo format but is just acting like a mono, give this a try before warming up the soldering iron.

[Duggeh]

No its an actual mono jack, with 1 ring. It also doesnt unscrew, I had to cut it off. So until I do this recable, these headphones are out of action.

[wualta]

Wow, quite a Yamaha adventure! Facel, yours is stereo but Mr. Duggeh's is mono? I gotta go siddown.

It's worth pointing out the similarity in construction of the Yamaha's isodynamic driver and the Ergo's AMT: they're both "printed" aluminum voice coils stuck to polymer film, driven magnetically in what are hoped to be uniformly distributed magnetic fields, as opposed to the focused, concentrated field of a dynamic driver.

Oh, and great photos, Mr. Duggeh. Interesting construction on the HP-50A, too-- no screws! it snaps together! Nice and simple and cheap to assemble.

.

[wualta]

Originally Posted by facelvega

...essentially they radiate a sound wave off the back which is identical to the front wave but precisely opposite in terms of vibrations.

Right. Just like Mr. Duggeh's AMT or Heil driver, iso drivers are inherently dipoles. Same thing out the front and the back but opposite polarity. If you could combine them, you'd hear nothing at all. You have to keep the bass component of the backwave from finding a shortcut into the earcup, and all the Yamaha Orthodynamics except the wacky YHD series did this just fine. Dynamic drivers generate backwaves too; they're usually not as strong as with a classic dipole, but manufacturers know they have to control them. If they don't, you get crazy variations in bass in production, as with the AKG K501. With the AMT you need all the bass you can get.

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[facelvega]

Originally Posted by wualta

underdamping creates a big smooth very broad lower-midrange hump in the response curve that makes the treble seem weak. By adding an acoustic resistance, we suck most of the energy out of this hump and let the treble do its thing (we even add a bit to the treble by moving the frequency of the hump upward, which happens because we're effectively making the diaphragm more stiff by adding an additional air "spring").

In a classic dipole, treble doesn't have a backwave cancellation problem because the wavelengths are short enough that they just beam straight out the back. Treble doesn't bend and wriggle around things to come back to bite you the way bass does. Bass is tricky but stupid.

Alright, I think I'm getting a clearer idea of how all this works: that there are two problems, lack of damping and backwave. Damping seems to explain what I'm hearing with the HP-50a, where the upper end of the bass, though pleasing in itself, seems to be swallowing up the full body and texture of the treble. And backwave seems to explain why my other orthos are bass-light. So what can I do about the bass backwave?

ps, I have a theory about why some HP-50a's are mono: I read somewhere that these were mostly sold as a practice accessory with Yamaha keyboards. You wouldn't really need stereo to monitor a single instrument, and what's more, by giving only a mono out, nobody could switch to another headphone. It's possible that my stereo plug with its iffy soldering work is actually a very old replacement.

[Duggeh]

BWAHAHAHA! Fear my soldering skills. You may think you've seen that cable before, that's because it came off those NAD 16 headphones I got several weeks back. Now that these have a stereo jack all those awful self destructive mono sound artefacts are gone. haven't got any felt yet, although it might be a little tricky fitting it, my rewiring inside the earcup takes up a little bit of space.

Regarding damping and the backwave and such, wouldnt the best solution be to have a completely open backed design so that the backwave isnt an issue? Or is the damping actually nessessary in order to obtain low frequency response?

[facelvega]

Originally Posted by Duggeh

Regarding damping and the backwave and such, wouldnt the best solution be to have a completely open backed design so that the backwave isnt an issue? Or is the damping actually nessessary in order to obtain low frequency response?

Nice work on that recable. To answer the question: damping to adjust frequency response as opposed to backwave, which I suspect would help these headphones, by definition is using a kind of closed-ness to open up the treble and make the bass tighter, i.e., by keeping the driver from over-vibrating, and thus would be ruined by a completely open arrangement. At least this is what I've understood from Wualta's explanation above.

Interestingly, trying to get rid of the backwave by going fully open-backed has a weird effect. Remember my PMB100 latter-day Jecklins? This is their approach, with a huge open space behind the driver and a screen at the back. Result: mids to make any AKG weep, but a slight rolling-off of the treble (probably due to the lack of any damping) and annoyingly, a load of bass cancellation that sneaks around to the front and cuts down percussion alarmingly. The bass is all there, but is just made weak.

I accept it as a compromise because the combination of the extremely fast planar driver and the Jecklin-designed earspeaker housing does something magical for a lot of mids-based music; they're actually the most intimate-sounding headphones I've ever heard, especially with anything acoustic or vocal.

And here's a little note on that subject: I've just picked up an MB Quart Phone 85, the later dynamic version of this Jecklin frame. (to remind you, it came in four versions I know of, two electrostats, the PMB500 and 1000, one ortho, the PMB100, and finally the dynamics. I'll report back on the sound when it arrives. (sorry for always cluttering your threads with this stuff, Duggeh)

[Carl]

Originally Posted by Duggeh

Regarding damping and the backwave and such, wouldnt the best solution be to have a completely open backed design so that the backwave isnt an issue? Or is the damping actually nessessary in order to obtain low frequency response?

Planars lose control at lower frequencies as its hard for them to retain rigidity and move enough air when slowly cycling. Giving something for them to "push against" can help mitigate that.

Open or closed doesn't really matter, either can sound good, but if you can achieve proper venting of the backwave then the more closed the design the better things will tend to be in practice. Of course, if you can't then closed designs will sound like bollocks...


To put it in simple terms - and this is true for conventional headphones too to a lesser extent - closed vs open is a matter of trading off damping for reduction in the backwave.

[Duggeh]

Originally Posted by facelvega

And here's a little note on that subject: I've just picked up an MB Quart Phone 85, the later dynamic version of this Jecklin frame. (to remind you, it came in four versions I know of, two electrostats, the PMB500 and 1000, one ortho, the PMB100, and finally the dynamics. I'll report back on the sound when it arrives. (sorry for always cluttering your threads with this stuff, Duggeh)

Not at all, I like to have so much conversation on the headphoen stuff im interested in consolidated like this. So you got yoruself another Peerless wonder eh? Well hopefully Ill have an unusual headphone won on ebay later tonight myself.

On the AMT front, the AMT driver only just doesn't fit inside a Stax Lambda housing, jerry rigging it up in that configuration though, with the Stax pads turns it into a whole new headphone. Oodles of bass with only minimal expense to the airy sound signature. Sennheiser and AKG really do need to set their research engineers on the AMT driver and see what they can come up with.