My Q701 usually gets a lot more use than my T50rp, but tonight I've been using the T50rp for several hours sampling a good deal of my music library. I use to think that my T50rp didn't really have that much more bass than my Q701, but I've changed my mind. They bass is plentiful and big. There is still one thing that I can't place my finger on though. I can't tell if my T50rp has too much in the lower mid-range and upper bass region or if it's just the smaller soundstage that sometimes makes them sound congested. Either way, sometimes they sound a bit congested to me, not really muddy or slow, just congested. If I cut out about 3-5db from the 250-500hz area with an EQ they sound cleaner to me. Anyway to fix this without resorting to EQ?
I've noticed this routinely with Shure 840 pads. While they improve overall bass, they seem to overdo it between 70-250 Hz by +3 to +5 dB, depending on the rest of the damping scheme used. Try EQ'ing down by 3 dB, then by 5 dB, between 70-250 Hz, leave 250 to 500 Hz alone, and then take a listen. If this solves the congestion (good description, BTW) you hear, an easy tuning method is to make a "modified bass port" using tape on the outside of the cup vents.
A "modified bass port" does not increase bass, it *controls* bass bloat by lowering the FR from about 300 Hz all the way down to 10 Hz. Make sure you completely cover all 4 slots with tape, with no gaps at the corners. I do this by placing/aligning a piece of masking tape over one of the "top" sides of the cup adjacent to the vents (on the cup area where the logo and jack are located), press the tape down onto the cup vent "side wall," and smooth it out all the way across the vent slots, back up the opposite "side wall" and over the back of the cup using the edge of a mini-screwdriver. Next, use an X-Acto Knife to trim off 1/2 of the tape along each "side wall" and peel off those sections of tape. Use the screwdriver to press the tape down along the bottom edge of the "side walls" right next to the edge of the cup vent slots. This method makes a complete seal over the vent slots with no gaps.
Listen/measure with the cup vents completely sealed. You will notice the congestion disappears but you *may* also notice you lost too much bass quantity. If so, use your X-Acto Knife to cut open a 3 mm wide opening in the tape overlaying the middle of one of the vent slots; the height of the "modified bass port" is 1.5 mm because this is the height of the slots. Re-test. Depending on what your hear, try increasing/decreasing the width in 1 mm increments until you dial it in for your particular mod configuration. Believe it or not, 1 mm either way makes significant difference in measured FR. Typically with my mods, I find 4 mm is the sweet spot but this varies from one modded set of 'phones to the next, no matter how careful I am when implementing the same configuration on two sets of headphones.
Once you've determined the size that works best for you, you can transfer the "modified bass port" to the inside of the cup vents for a permanent fix. I described this method, with photos, in the tuning section of Incremental Mods and Measurements, located just before Graph #56. Alternatively, you can keep the modified bass ports on the outside so you can change the Bass FR "on the fly" as may be needed with certain music genres and when using different amps and DACs.
Hope this helps. Please report back with your results if you try this method.
FWIW, I've also noticed that after installing/removing the pads many times, the FR deteriorates. I think this is likely due to the flaps stretching out too much and losing pad-to-cup seal. This is where Aleene's Fabric Fusion double-sided tape comes in handy, but only after the tuning process is complete; it's hard to remove once installed.
Edited by bluemonkeyflyer - 4/3/13 at 5:48am