[ejoy]

Hi,
I've being thinking of this question for a while. I know basically a PtoS cable adds 75 ohm of resistance in series to both channels of er4p to turn it into an er4s. But we know the resistors in this kind of setup will only function as a Voltage Divider: you get lower voltage on the driver part of er4s. How can this affect/change the frequency response curve as shown on the Ety's website? Personally I do think the change in voltage (result in a lower volume) will change the curve.
Can anyone help me clarify this a bit?

Thanks,

 

[Heidshade]

Strangely enough, I've been considering this very same subject today.

One thing I'd say, is that I doubt that Etymotic make the ER4S with a 75 ohm series resistance connected in line with the driver coil; in other words, the reason it has a 100ohm nominal impedance is because the coil windings of the driver have a total impedance of 100ohms, due to either thinner wire or more turns, than the 4P.
So it stands to reason that an ER4P plus series resistance adaptor is not quite the same as an ER4S with the same overall impedance.

As far as the voltage divider goes; the impedance of the driver coil (the 'bottom leg' of the voltage divider) is reactive, so it'll change with frequency. If you had a capacitor in there instead of the earphone driver, it's impedance would go down with increasing frequency, and hence the voltage divider effect would reduce the power output (across the cap) at higher Hz. As it's an inductive winding, I guess the opposite will apply and the power applied to the earphone driver will increase with frequency, which if I'm right should result in a louder HF response (and a shaped response curve).

I've seen it said in other posts that the drivers in the 4S and 4P are the exact same, but as I say above, I can't see this being the case.

I can see I'm going to end up having to buy a 4S as well, to test against my 4P plus resistors....

At least I can build them into a 2nd output socket on the PPA

- edit - Looks as if I'm wrong about the resistors, as there is a thread where the designer says there some in the 'pod'! You could spend weeks hunting for information in old Headfi threads. This forum is too big!