This Old Headphone: Reconstructing the Pioneer SE-700 (56k=slow)

[ericj]

By the way, my SE-500 showed up last night. Wualta is right, they sound midrangey, seventiesish, and even disappointing and lackluster.

The driver modules are interesting, they have an integral cage that holds the damping sandwich together.

I think the SE-500 are more deserving of a two-way rebuild, but it may actually be harder to accomplish on the 500 than on the 700.

I'm thinking, cut out some of the damping foam (or make a whole new damping sandwich with a hole in it), cut a circle out of the interior plastic back-grille (but not the exterior mesh back-grille), and squeeze in a KSC75. Maybe add some series resistance to it to even out some of the efficiency difference.

Certainly easier to picture myself doing it to the SE-500, since the one working side of my SE-700 sounds better than both working sides of the SE-500 combined.

Plus the SE-500 is dead sexy. I love the curve of the earcups.

 

[wualta]

Hmm! The question is, what did they do to the 700 that made it sound so much better than the 500?

 

[Inkmo]

Quote:

Originally Posted by wualta /img/forum/go_quote.gif Hmm! The question is, what did they do to the 700 that made it sound so much better than the 500?

my money is on voodoo. ;P

 

[ericj]

Well, the SE-500 driver is encapsulated in a metal frame. There appears to be roughly the same amount of film, but the SE-500 driver is vertically oriented, and there's a shield covering all but a 2" circle of it, toward the bottom of the capsule.

The SE-700 driver is completely open-faced on both sides, and while there is the same 2" opening in the grille, perhaps it is better acoustically?

The SE-500 film seems to be a rectangle, where the SE-700 is barrel shaped - perhaps this is just better geometry.

The SE-700 may also have a better connection to the film. I'll take some pictures that may illustrate this.

 

[wualta]

Eric, is there an efficiency/sensitivity difference between them? I was thinking that the 700 might make use of the lamination technique (adding extra layers of PVDF) to increase the bending/volt.

 

[ericj]

That's an excellent question.

I'll see if i can figure out how to tell. For starters the impedance can't be read in DC ohms - none of my DVMs have any clue.

I could hook up a capacitance meter . . . .

Edit: 87nf per side for the SE-500, 58nf for the good side of my SE-700, 28nf for the damaged side.

My meter (Wavetek LCR55 in this case) generates a tone to measure capacitance. These tests were done in the 200nf range.

The SE-500 seems a little louder in this test.

 

[ericj]

Doh!

I'd connected common to the ring, and right to the sleeve.

Having rewired the plug, they're behaving better.

And i already blew $10 on some quick-grid and opened the package. *sigh*.

The SE-700's are behaving now, and both sides read within 1nf of 57nf (including cable). I'll listen to them for a while and try to get a feel for their sound.

 

[wualta]

Save that Quick-Grid for when you get your first ESS Heil-tweeter speakers. It may come in verrrry handy.

Extra glad to hear both halves of the SE-700 are up and doing. See if you can pinpoint the changes they made to make them sound different/better compared to the 500s. I'm particularly interested to know how they managed to get more bass out of the 700s, as you can imagine.

.

 

[ericj]

Well, the SE-700 has "more" bass than the SE-500 - which is to say that it has a little bit vs. none.

It also has a more evenly balanced sound overall.

I really think it's the barrel shape of the membrane that improved things. The SE-500 driver module seems to have a perfectly rectangular membrane. With the angle of the corners so tight, this would restrict the motion, wouldn't it?

 

[ericj]

By the way, if we want to start talking about stuffing a dynamic driver behind the piezo film, we get to start worrying about impedances.

The piezo film is a fully capacitative load. Even in the 20mohms range, the pioneer drivers read infinite ohms on my meter. But they do have capacitance.

The equation I've been handed for calculating the impedance of the film is Z = 1 / ( 2*pi*F*C ) where F is in hertz and C is in whole farads.

 

[wualta]

If the film is the same in both cases, you might be right, although that would mean that the ideal shape would be a circle or maybe something easier to cut out on a production line, like a hexagon, so why didn't they do that? The film expands on one surface and contracts on the other when signal's applied, so the film domes up and down. Interesting problem. Is the 500's film supported/damped in the same way?

 

[ericj]

Well, i don't dare open up the SE-500 driver module, because the electrical connection to the film is on the outside of it, but it appears to be a fully-encapsulated right-angled version of the same thing, oddly covering all but about half the surface, and that on the bottom half of the driver.

From what I'm hearing through other channels, the impedance of piezo film decreases with frequency - basically infinite at DC, but almost a dead short at very high frequencies - requiring a source with a very high output impedance for good response - another consideration in understanding the TakeT transformer box?

The SE-700 may have the best bass response anyone was ever going to get out of a flat piezo film.

 

[wualta]

Quote:

Originally Posted by ericj From what I'm hearing through other channels, the impedance of piezo film decreases with frequency - basically infinite at DC, but almost a dead short at very high frequencies - requiring a source with a very high output impedance for good response - another consideration in understanding the TakeT transformer box?

Yes, just like any transformer for any capacitive load, including electrostatic 'phones and loudspeakers. Capacitive reactance decreases as the frequency goes up in an ideal capacitor, so what you're hearing makes sense. The flat film probably has no other components (like parasitic inductance or series resistance).

Quote:

Originally Posted by ericj The SE-700 may have the best bass response anyone was ever going to get out of a flat piezo film.

Which, I take it, isn't saying much. Is there any point in boosting the bass? And have you considered connecting them up directly to a speaker output, as Nights85 did with his SE-700? Apparently this is something Pioneer recommended.

.

 

[ericj]

Quote:

Originally Posted by wualta /img/forum/go_quote.gif Which, I take it, isn't saying much. Is there any point in boosting the bass?

Dunno yet. I've been listening to them plugged into a home theater receiver that won't let me eq anything if headphones are plugged in, for some reason.

Quote:

And have you considered connecting them up directly to a speaker output, as Nights85 did with his SE-700? Apparently this is something Pioneer recommended.

Sure, I've thought of it. Haven't tried it yet.

Directly to the speaker outputs? not even a dropping resistor?

Edit: The only power handling spec that Pine Ear gave for these things is a maximum of 30 volts. I know that my Akai power amp can swing 80 volts, who knows what my home theater receivers swing. Perhaps i should build a simple hookup cable with protection zeners like you see in old beyerdynamic headphones

Edit: better yet, i could do just like beyer and install the protection zeners right in the earcup. Of course, for my se-700, it turns out to be far more difficult to pull the decorative rings off when they're stuck on with silicone RTV. So, perhaps I'll try and do up the SE-500 that way - it's dead easy to open.

 

[wualta]

I was doing some mind-numbing testing and refining of YH-100s tonight on my Panasonic SA-XR25 digital receiver and once that was done I spotted my Pioneer SE-500 on a nearby shelf. Plugging it into the XR25's headphone amp was disappointing-- I couldn't play them very loudly before I heard gross clipping. Bass boost was out of the question. They were also much less efficient than the YH-100, so I brought my source and the 500 into the MOSFET Room and placed them before Duh Beastie:

[size=xx-small]RADIO SHACK'S REALISTIC STA-2200 RECEIVER WITH MOSFET POWER AMP, CA. 1980[/size]

This old receiver's modest 60w/ch MOSFET amp will shrug off even the most difficult-to-drive headphones. The preamp section can supply hellacious amounts of bass (and treble) boost and can usually put it where it'll do the most good. One thing's for sure: if it doesn't have bass on the ol' STA-2200, it don't got none. This is the amp I tested my first [bass-free] K501 on. I smiled when the n00bs claimed I wasn't driving them with a strong enough amp.

Anyway, sure enough, with a big boost in the lows below 200 Hz, out of the headphone jack the SE-500 was putting out real bass and doing it at healthy levels. Had to crank the treble up quite a bit too to straighten out the 500's giant "frowny", but it could be done, more or less. They're still not my favorite 'phone soundwise, but I did prove to myself that strong piezo bass was possible-- yeah, I was surprised too. The real problem with the 500 is a horrible peak in the nasal honk region which remains even with heavy EQ.

.