[Sir Yacho]

I'm looking for suggestions about how to best hook up a passive sub to my 8BST.

The subwoofer driver is dual voice coil, 6ohm and 250W handling per coil.  Sensitivity of the driver is listed as 90db when wired in series, and 96db in parallel. 

I've got 2 channels on the 8bst available for this, so, two questions I guess... what's possible, and what's my best move?  The way I see it is that I've got 4 options really.

1.  8bst bridged into 12ohm series dvc (what's the math here in watts?)
2.  8bst single channel into 3ohm parallel dvc (is a single channel stable at 3 ohms?)(again, what's the wattage tally here?)
3.  8bst single channel into 6ohm single voice coil (am I leaving too much on the table here?)
4.  split input signal into 2 8bst channels, each into individual 6ohm single voice coils  (this seems like a terrible idea, but it is a physical option so I listed it)

My motivations are tight control for music only, and using what I have.  I'm not shaking the house with movie explosions, just trying to grab an extra octave down low.  The mains are ADS L1290s bi-amped via 8bst with a listed sensitivity of 90db.

Thanks in advance!

-Mike

[Sir Yacho]

Hmmmm.....   no response yet, so let me try to narrow in using specifics.

Can a single channel of 8bst handle a 3ohm load? 

I don't have an impedance graph of the driver, but it has a Fs at 18.2hz.  And, FWIW, the driver's manual states that "the parallel 6 ohm voice coils will present an acceptable load to an amplifier rated for 4 ohm operation when used as a subwoofer below 100Hz."  DC resistance per coil is listed at 5.6 ohms.

[James Tanner]

Hmmmm.....   no response yet, so let me try to narrow in using specifics.

Can a single channel of 8bst handle a 3ohm load? 

I don't have an impedance graph of the driver, but it has a Fs at 18.2hz.  And, FWIW, the driver's manual states that "the parallel 6 ohm voice coils will present an acceptable load to an amplifier rated for 4 ohm operation when used as a subwoofer below 100Hz."  DC resistance per coil is listed at 5.6 ohms.

Hi

Subwoofers have real easy 'duty cycles' given their typical frequency range so 3 ohms is not a problem.

james

[Sir Yacho]

Thanks James, good to know.  At least I can maintain running the voice coils in parallel as an option.  Options are good, as I will likely boil it down to trusting my ears and choosing between the viable options.

Though, I am still interested in the advantages of damping factor and headroom variances as they relate to the the options from the OP, mainly 3ohm parallel single channel vs. 12 ohm series bridged.

[Sir Yacho]

OK,

So, using the conservative Bryston factory specs for the 8bst (120W@8ohm, 400W@8ohm bridged) as a baseline, I've calculated my two likely options to show 265W@3ohm parallel DVC on a single channel, and a very similar 265W@12ohm series DVC bridged.  So if I did that correctly, the headroom argument is nulled. 

That leaves me with damping factor being the only possible difference.  Using the methods described here...

http://www.bryston.com/PDF/newsletters/Bryston_Newsletter_V5_2.pdf

...the difference in damping factor between two impedances is directly related to the ratio of those impedances.  In this case, assuming the variables of speaker cable resistance and voice coil temperature deltas are equal, the 12ohm series DVC would have four times the damping of the 3ohm parallel DVC into the same amp.  But since the 12ohm version would be into a bridged amp, we had to divide the final DF value in half, which ultimately gives the 12ohm option twice the DF of the 3ohm version.

This is my first time diving into these kind of calculations.  Did I do this right?  If it is all correct and there's nothing else I'm missing about bridging amplifiers, my only question left unanswered is whether or not having twice the damping factor is worth using another channel in the amp.

Thanks in advance for any input!