From: Terry Pinnell
Subject: Re: Problem with Spice simulation of Linkwitz-Riley filter
Date: Tue, 24 Sep 2002 11:06:20 +0100
NNTP-Posting-Date: Tue, 24 Sep 2002 10:06:21 +0000 (UTC)
X-Newsreader: Forte Agent 1.92/32.572
email@example.com (Carlos) wrote:
>Sorry I haven't been involved in this thread which I started, it seems
>by the time my "I found it!" message reached the ng (I use Deja which
>is very slow) there had been a lot of discussion already.
>Just to clarify a couple of things, yes what I was worried about was
>the -6 dB point. This thing, whatever it is called (John L. Murphy of
>Trueaudio does call it a 2nd order Linkwitz-Riley in his papers on the
>subject, that's where I took it from), will be used as a low-pass
>filter for a subwoofer, where the main speakers are closed with Q=0.5,
>the whole thing having theoretical flat frequency response when the -6
>dB points match.
>The schematic is exactly like the one you published, except that I
>didn't have the 100 K resistor between the first R/C section and the
>first opamp. The -6 dB point was measured as the frequency where the
>output voltage halved (with respect to its value down at 1 Hz). The
>input voltage was 150 mV and the gain of the first stage was 6.666667
>(feedback R from out to In- = 6.8K, R from In- to Gnd = 1.2K).
Thanks, Carlos. All now clear. BTW, that 100k was accidentally added
(although it makes no difference to the relevant analysis).
Hobbyist, West Sussex, UK