j-curve
100+ Head-Fier
- Joined
- Apr 15, 2002
- Posts
- 489
- Likes
- 11
Here's a different way to drive any of the 4-series transducers by Etymotic.
The idea is to reduce the driving impedance without sacrificing the treble/bass balance.
This will improve the damping factor at the transducer's resonant frequency, to produce a more natural sound.
Unfortunately, there is a catch. Unless you have access to the rare (unobtainable?) machined pins Etymotic uses to connect their cables to the earphones, you'll be required to perform a "podectomy"
, i.e. removal of the series resistors and injection-moulded pod from the cable. However, this is nowhere near as scary as I anticipated. See below for some tips.
Nonetheless, you probably need a good reason to go hacking into the cable of your $200 earphones. My reasoning was as follows:-
i) Impression of the ER-4P: rolled-off in the top-end, but with a rich mid/treble which makes oboes and violins particularly sweet. That same effect tends towards treble colouration as the music becomes agitated.
ii) Adding series resistance to emulate the ER-4S, highs are better supported but the treble peak also becomes accentuated and annoying at times.
iii) Headroom's impedance graphs point to a driver resonance at 2.5kHz. This resonance cannot be controlled by the amplifier when a high series resistance is present. The ER-4P could be electronically equalised, or better still...
iv) Remove the pod resistor. Find a way to achieve the necessary upward treble tilt in a low impedance circuit.
Crucial Quantities
Input impedance: 36 Ohms, almost constant across the range, due to R6/C6 impedance compensation.
Sensitivity: Around 101 dB/V, i.e. a notch below the HD580, and no apologies! [See the hissbuster link for justification.]
Construction
For portability, I wanted to rig this into a cable, but a small box would have made things infinitely easier.
Sub-assemblies, front
and back. These had to fit into a length of 8mm heatshrink tubing.
Wired, front
and back.
Luckily I realised it was going to be a squeeze, and had the sticky heatshrink primed with chalk dust before wiring the cable.
Not quite as attractive or robust as hoped. [Do you like the DIY strain relievers in 6mm half-shrunk heatshrink? Classy, I thought.
]
PS: I just saw setmenu's Ety filter build. Very neat, wish I'd seen it before I put this thing together.
The idea is to reduce the driving impedance without sacrificing the treble/bass balance.
This will improve the damping factor at the transducer's resonant frequency, to produce a more natural sound.
Unfortunately, there is a catch. Unless you have access to the rare (unobtainable?) machined pins Etymotic uses to connect their cables to the earphones, you'll be required to perform a "podectomy"
Nonetheless, you probably need a good reason to go hacking into the cable of your $200 earphones. My reasoning was as follows:-
i) Impression of the ER-4P: rolled-off in the top-end, but with a rich mid/treble which makes oboes and violins particularly sweet. That same effect tends towards treble colouration as the music becomes agitated.
ii) Adding series resistance to emulate the ER-4S, highs are better supported but the treble peak also becomes accentuated and annoying at times.
iii) Headroom's impedance graphs point to a driver resonance at 2.5kHz. This resonance cannot be controlled by the amplifier when a high series resistance is present. The ER-4P could be electronically equalised, or better still...
iv) Remove the pod resistor. Find a way to achieve the necessary upward treble tilt in a low impedance circuit.
Crucial Quantities
Input impedance: 36 Ohms, almost constant across the range, due to R6/C6 impedance compensation.
Sensitivity: Around 101 dB/V, i.e. a notch below the HD580, and no apologies! [See the hissbuster link for justification.]
Construction
For portability, I wanted to rig this into a cable, but a small box would have made things infinitely easier.
Sub-assemblies, front
and back. These had to fit into a length of 8mm heatshrink tubing.
Wired, front
and back.
Luckily I realised it was going to be a squeeze, and had the sticky heatshrink primed with chalk dust before wiring the cable.
Not quite as attractive or robust as hoped. [Do you like the DIY strain relievers in 6mm half-shrunk heatshrink? Classy, I thought.
PS: I just saw setmenu's Ety filter build. Very neat, wish I'd seen it before I put this thing together.