Rerurn to Romy the Cat's Site


In the Forum: Audio Discussions
In the Thread: Lowther Driver
Post Subject: Living With DX4s (or, trying to...)Posted by Paul S on: 11/13/2010
fiogf49gjkf0d
IMO, any sonic benefits from running Lowthers stock are totally swamped by excessive, ragged response that is generally (but not steadily...) rising - a lot - toward HF.  There have been many ideas for "taming the Lowther", and here is another one, based on my long-term use of DX4s in my own version of Dick Olsher's original (and proprietary) Diamond Edition BassZillas.  It is "given" in the DEBZ plans that one has to do something with the stock Lowther response.

After years of messing with the stock DEBZ filters, and after scrutinizing Martin King's response and impedance plots (Thanks, Martin!), I have finally decided to trade the mallet for a scalpel.  Of course I still use a high-pass cap and a HF roll-off coil; but, whereas the stock notch filter and coil attempt to knock down two sharp humps and a rising top end with a quick 1-2 combination, I finally decided to address the individual response humps individually, with two notch filters before the coil, this in order to avoid dropping stock response dips even farther.

YMMV, but I used 130 uF "1st order" for the high pass, to offset baffle step and in recognition of the fact that the BR Audax PR380M2 does not do well over ~125 Hz.  I figured rising LF impedance at resonance would combine with the cap to effectively stuff LF.  I put the first LCR/notch TIGHT on 2,050 Hz with 60 uF, .09 mH and 5.1 R; I put the second LCR/notch TIGHT on 4,600 Hz with 30 uF, .04 mH and 5.1 R; I rolled it off @ 6dB/octave with -3 dB @ 6,800 Hz using .187 mH.  I left the stock Zobel.  I brought the ribbon in over a 2nd order filter, 6 dB down at 13.5k Hz.  The DEBZs gained weight and overall balance improved for the real.  They lost unwanted HF peaks without suffering adjacent suck-outs.   Clarity is fine now, but I expect the new caps will soon clamp down and then stay clamped for the next couple of months.

Of course, YMMV, naturally, but in any case I think the "double-notch" approach is "viable", given stock ("new" type, with rolled whizzer edge) DX4s, anyway.  At some point I may try wads of cotten instead of the end coil to shape the HF.

Paul S

Rerurn to Romy the Cat's Site