Basic Passive Sub Question (Wiring)

[Inductor]

Originally Posted by head_unit

By the way, speaking as someone who had to design them, passive sub crossovers DON'T WORK.
Not really.
The impedance peaks at the resonances of the sub and satellites interfere to much for any simple passive design to function as designed. Yeah, you can kind cut out some low bass from the satellites and some highs out of the sub, but it will be a very crude approximation.

I agree and disagree, doesn't mean it can't be done...
Mission 73pi - passive sub | AVForums.com - UK Online

[head_unit]

Originally Posted by Xoc1

Yes agreed that a passive system won't work very well but there are ways to get a system functioning with 3 speakers.
In car audio amplifiers, often one channel has the signal inverted and the outputs labelled according to the phase. This allows for easy bridging of the amplifier outputs. The speaker connection is just moved from one connection to the other one to bridge the amplifier.
So it stands to reason that if the stereo amp has one input signal inverted by use of a opamp (or transformer!) then the amplifier can be bridged in the same manner.
It is then possble to run a pair of stereo speakers in normal mode but with one speaker connected in reverse to re-correct the phase, and a single speaker in bridged mode.
There are issues with the overal impedance loads that the amp must tolerate, and the sub especially must be not to low an impedance, but it does work (crudely)

Yeah, that's one of the applications I had to design passive crossovers for, which can't really work properly. Of course, you will hear sound, but that does not mean it is accurate. In that kind of configuration, you might accidentally load the amplifier down really hard at certain frequencies.

[head_unit]

Originally Posted by guangui

Thanks for the advise, any recommendations on an active XO that will not break the bank.

The cheapest active would actually be passive filters feeding the power amplifiers. For example, a capacitor in-line with the satellite amp, and an inductor in-line with the sub amp.

If you don't want to make homemade, Google "Harrison FMOD" or look at Amazon or Parts Express.

[guangui]

Originally Posted by head_unit

The cheapest active would actually be passive filters feeding the power amplifiers. For example, a capacitor in-line with the satellite amp, and an inductor in-line with the sub amp.

If you don't want to make homemade, Google "Harrison FMOD" or look at Amazon or Parts Express.

Thanks for your advice. I don't mind going the DIY route, just a learning curve as far as designing XO goes, but as far as soldering, brand/model selection, etc. I got it pretty much under control. Will check H-FMOD anyways.

But, I already went the "easy route", and maybe what would have been the most logical. Took the good 'ol 1998 8" 50W Audio Source SA-50 that I had in the family room (very good with music and movies, but lacked the extra "oomph" to rattle windows and feel explosions in your bones), and moved to my home office, as it was compact enough to fit under a PC workstation. It's plate amp already has the "by-pass" needed for satellite speakers. Then I ordered a Bravox PXW12D-2, and Dayton SPA-250 Plate Amp to build a sub for the family room. With a 200L enclosure it will produce an Fb of 22 Hz, and an F3 of 20 Hz, and an all concrete home like mine can make it go even lower.

[Inductor]

You got two Basic Active Subs then...

[guangui]

Originally Posted by Inductor

You got two Basic Active Subs then...

Yep, the passive was becoming to much of a hassle for what I wanted to do...

[Inductor]

The main problem with the passive is that, besides what was already said, you have to match sensitivities very wisely, in this case for production models they came as a complement of the satellites already tested by the manufacturer.