I assembled my new Marchand Bassis kit this afternoon -- scavenging an old analog Fosgate Dolby Surround decoder for the case and regulated +/- 15V power supply. I had ordered the completed circuit board from Marchand and everything in the kit was very nicely made. Pots and switches were meticulously soldered and shrink tubed on twisted jumper cables with molex connectors, so it was just a matter of figuring out a bracket arrangement to mount the board, install four pots, two switches, and a couple of RCA jacks. Got it all wired up and plugged into the system tonight.
This is a very cool piece of gear. Basically a fully adjustable 4-pole Linkwitz Transform Function bass EQ for sealed box subwoofers. You use two of the pots to enter the "Q" and "Fs" resonance (more or less the -3dB point) of the actual driver box combination. Then, you use the other two pots to dial in your target "Q" and target "Fs" (expressed as boost). The EQ changes the subwoofer output from your actual curve to the target curve -- whatever you want. The switches are for "bypass" and an 18 dB per octave subsonic filter at 20 Hz.
What makes it doubly handy is a spreadsheet I found that lets you enter all four parameters and graph the before and after response curves.
My subwoofer by itself had a calculated "Q" of .76 and an Fs of 43 Hz. I replaced that with a Q of .5 and an Fs of about 20 Hz. The response curve is now about -6 db at 20 Hz and about -3 dB at 25 Hz. This requires fairly substantial boost at 20 Hz, but it seems to be within the excursion limits of the rather robust driver, even on the tank scene of Private Ryan. On paper, the boost should be hammering the driver, but the saving grace is that DVDs don't record digital full scale signals at frequencies that low.
I tried a target Q of .7, but at first blush, the lower Q seemed tigher. The theory says that a Q of .5 or lower has zero ringing and nearly perfect transient response.
I haven't had time to do any precise measurements, but I did plop the Radio Shack meter down and looked at a couple of before and after low-frequency sweeps. The EQ works as advertised.
The combination of a sealed box sub and the Linkwitz Transform Function seems like a great way to design a subwoofer. Several companies seem to be taking this route: starting with a smallish high-Q driver/box combo and equalizing for extended low-Q response. But, being able to have full control over it to make you own choice about the bass extension/power handling tradeoff is a good thing.
This is a very cool piece of gear. Basically a fully adjustable 4-pole Linkwitz Transform Function bass EQ for sealed box subwoofers. You use two of the pots to enter the "Q" and "Fs" resonance (more or less the -3dB point) of the actual driver box combination. Then, you use the other two pots to dial in your target "Q" and target "Fs" (expressed as boost). The EQ changes the subwoofer output from your actual curve to the target curve -- whatever you want. The switches are for "bypass" and an 18 dB per octave subsonic filter at 20 Hz.
What makes it doubly handy is a spreadsheet I found that lets you enter all four parameters and graph the before and after response curves.
My subwoofer by itself had a calculated "Q" of .76 and an Fs of 43 Hz. I replaced that with a Q of .5 and an Fs of about 20 Hz. The response curve is now about -6 db at 20 Hz and about -3 dB at 25 Hz. This requires fairly substantial boost at 20 Hz, but it seems to be within the excursion limits of the rather robust driver, even on the tank scene of Private Ryan. On paper, the boost should be hammering the driver, but the saving grace is that DVDs don't record digital full scale signals at frequencies that low.
I tried a target Q of .7, but at first blush, the lower Q seemed tigher. The theory says that a Q of .5 or lower has zero ringing and nearly perfect transient response.
I haven't had time to do any precise measurements, but I did plop the Radio Shack meter down and looked at a couple of before and after low-frequency sweeps. The EQ works as advertised.
The combination of a sealed box sub and the Linkwitz Transform Function seems like a great way to design a subwoofer. Several companies seem to be taking this route: starting with a smallish high-Q driver/box combo and equalizing for extended low-Q response. But, being able to have full control over it to make you own choice about the bass extension/power handling tradeoff is a good thing.