Are these modded t50rp's you are referring to that have "the best bottom end extension you've ever heard?"
I bought a custom pair of Fostex recently and I could not get them loud without them farting. So I was puzzled as both my other headphones go loud and one was HFM-400's so my audio chain was working with unmodified Orthos.To remove the bass distortion they had to be so quiet that they were unlistenable.
It could be the amp is clipping by exceeding its current capacity rather than voltage. How high are you turning the volume knob? Is it roughly at the same spot as the HE-400 or much higher?
Hi it was set at about 40% of capability but I did have to turn it a tad higher to get similar volume as the HE-400's. It was such a bummer as I don't want to have to buy another amp just to feed a pair of custom Fostex when my other 2 cans work fine off my audio chain. I had to send them back.
Right, that is why pretty much everyone agrees that Magnepan speakers have weak bottom end and Martin Logan are hybrids for that very reason too.
I was talking about headphones, and with headphones your statement is not true. I don't know anything about the speakers you mentioned.
The reason Maggie's have less low end is that in a planar speaker the front and back of the driver share the acoustic space. As frequency drops, the wavelength not only increases, the wave becomes omni-directional, so the front and back waves become out of phase in the room and increasingly null each other as the frequency drops. Simply put the bass off the back of a panel bends around out of phase and cancels the bass from the front.
The Logan's bass is in a box that is either closed or vented to allow reinforcement of low bass, but the physical box keeps the back-wave from cancelling the front. That's why a subwoofer driver just sitting in a room makes almost no bass without the box, the rear waves bend around the basket and cancel the front waves. Mids and highs are directional, so this effect isn't such an issue.
Circumaural headphones are in a sense more like a closed box phone (open or closed phones), as the back-wave is prevented from nulling the front-wave because it's blocked by the ear pad. This applies to dynamic, electrostatic, and planar magnetic, open or closed, as long as the pad creates a decent seal.
I'm sure uneven damping and the presence of the jack would affect it. There might be a random little gap somewhere in the cup/pad/baffle too. Are you hearing the level difference across the entire FR or just a specific part?
Yes, it's consistent accross FR - I've generated a chirp tone with audacity from 15hz to 16Khz. The only exception is ~13khz-15khz interval - there balance is jumping to left and right... I guess I'm dedicating this evening for this issue. Will disassemble my T50 in a moment.
You can always put an inline resistor in the "+" lead of the channel with more output. To reduce the gain by about 2dB, just buy a few 1/4 watt resistors (make sure they're non inductive). If it's really about a 2dB error across the spectrum, adding an inline resistor between 8.2 and 15 ohm should do the trick. If your driver is exactly 50 ohms a 12 ohm resistor should do as a first test, and adjust and replace as needed. I've found the Fostex drivers can vary, I've seen 48 and 57 ohms, so a few trials may be needed (especially if your 2dBis a swag).
A more accurate way (assuming you have a multimeter) is to get a variable resistor and trim it until it sounds balanced, then measure the resistor and replace it with a quality non inductive network of resistors giving the same value...