[ortho transplant] "Orthosex": SFI into AKG K240 Sextett LP (in progress) - Page 2

I wired up one side temporarily so I could put the rear cup on. Response up to 1kHz is surprisingly smooth when playing a frequency sweep, with a very slight and narrow dip somewhere around 400-500Hz which might be a reverb dead zone. Very similar to my T40v1 transplant actually, but better low end extension and flatter response overall in this range.

After 1kHz... wow so there's a reason these things are tweeters right? It's clean and doesn't come off shrill... but you know those adjustable flashlights that let you narrow the beam? It's like that. I can actually hold this a few feet away from my face and point the sound; the directionality is very strong. It starts climbing at 1k, then 2k it ramps up a bit, there's a big dip later on (around 8kHz?) before it comes back up, which in my experience is fairly common in a headphone response but it's just very strong. Compared to my T40v1 transplant, the treble is much stronger and far better extended, though admittedly my other one rolls off a little sooner than I'd like. 

Any recommendations on damping to reduce/diffuse treble?

Quote:

Originally Posted by JamesMcProgger 

can anyone tell me how can I meassure if my SFI are 120 ohm or X ohms?

 

Do you have a multimeter?

My set is actually a little imbalanced... 122 on one, 128 on the other. 

That's what I do. Mind you, this is measuring resistance and not impedance.

Anyone know what the sensitivity of these SFI drivers are? I'm not really getting much volume out of these things (besides the treble that is).

Quote:

Originally Posted by dBel84 

The sensitivity is directly affected by the damping. These little SFI's can be extremely insensitive when highly damped. I more or less gave up trying to use them without amplification.

 

On a somewhat related note : I had an SFI - K140 transplant ( not sure of the exact model but silver like the 142 ) , which suffered similar troubles initially. The pivot assembly for attaching the headband acts like a huge reflector disc and essentially turns them into tweeters. I drilled much of the plastic away leaving just enough for structural integrity. I then damped the driver very lightly - this is a compromise as the bass then tends to be a little more "loose" ( it is still good bass and not flabby by any means but you can hear the difference when comparing other orthos ) . The damping I used was a thin , dense donut behind the driver - center of driver completely undamped while outer portion reasonably damped. The space is very tight and I used a dense cashmere material , a synthetic chamois would give similar results. The earpads of the sextet and larger airspace will affect the response , probably for the better compared to the smaller AKG but it also means more air for a smaller driver to move. Your experience will guide this theory. 

 

great work thus far ..dB

What is the sensitiity undamped?

Should there be any damping that goes in front of the driver? Right now there's nothing there except the nylon dust shield. I'm thinking at minimum I'll just put a piece of micropore tape over the driver. Not sure if I'll be able to fit anyting else inside the cup, but I can probably squeeze something beneath the pads.

A lot of motivation for putting tape over the drivers is just to keep dust out. Seriously, getting dirt in the drivers is like the bane of my existence. Ok so maybe that's a bit melodramatic, but argh it's the most frustrating thing when you start hearing the buzz of debris. The paper micropore breathes fairly well. There's a plastic micropore that breathes better, and the drivers that I got came with some of it on them, but I took those off because they were fairly dirty... I still have them stuck on a piece of paper somewhere though. I suppose I could put them if they've still got any stickiness left in them.

I found some foam scraps today. Hopefully tomorrow I'll find some time to stuff them into the cups and see how that turns out. So far I'm really liking the response across the midrange, so I'd like to keep that intact while tuning down the treble. That or bring everthing down a notch while retaining the bass at the same level, to effectively bring up the bass.

There were originally paper filters on the back side of my T40v1 drivers. Taking them off immediately opened up the sound and cleared up the midrange. Then a half hour later some fuzz got in and I had to disassemble the entire blasted magnet assembly to get the dirt out. Ugh, not worth it.