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guangui 21st February 2013 06:18 PM

Basic Passive Sub Question (Wiring)
 
I am in the process of building a small passive sub for a PC system. It will be powered by a DTA-1 T-Amp. I can design the box, I can build it, etc. But, when it comes to electronics I need some guidance.

I want to go from the L/R speaker output on the amp, to the sub, then the signal continues from the sub to the speakers. I know I need a High Pass filter, so only signals under 120 Hz go to the sub. The speakers is no problem, because they are full range (2-1/2" Dayton Audio ND-65-8 FR drivers).

How do I do the internal wiring for the sub? For connection I will be using spring terminals. Have not calculated the HPF, but there are plenty of calcs for that. Basically, how do I wire from the spring input terminal to the HPF, then to the sub driver, and how do I go from there, or from the input terminal, to the output spring terminal, while keeping everything 8 Ohms?

Inductor 21st February 2013 06:56 PM

Quote:

in the process of building a small passive sub for a PC system
Quote:

how do I go from there, or from the input terminal, to the output spring terminal, while keeping everything 8 Ohms?
It is a 8 Ohm, just having the subs in parallel doesn't change a thing, they work in different frequencies. Small changes in overall impedance if working with the right design.
Many times the "old" type subs you mention where 4th Order Bandpass Systems with two subs drivers.

guangui 21st February 2013 07:07 PM

Quote:

Originally Posted by Inductor (Post 3380021)
It is a 8 Ohm, just having the subs in parallel doesn't change a thing, they work in different frequencies. Small changes in overall impedance if working with the right design.
Many times the "old" type subs you mention where 4th Order Bandpass Systems with two subs drivers.

I think you got it wrong. All I want is to power the sub (one 8 Ohm) woofer using the 2-Channels from the amp, then going on to power the speakers. Obviously, I need to filter the signal to the woofer, so it only carries 120 Hz and below.

weltersys 21st February 2013 07:41 PM

Quote:

Originally Posted by guangui (Post 3380038)
I think you got it wrong. All I want is to power the sub (one 8 Ohm) woofer using the 2-Channels from the amp, then going on to power the speakers. Obviously, I need to filter the signal to the woofer, so it only carries 120 Hz and below.

You can't use both sides of the amp to power one single voice coil sub.

Fortunately, most bass is mixed mono, so operating the sub from only one side of the amp is not a problem.

If your sub had dual voice coils, you could use both sides of the amp.

You also need to filter the lows out of the 2.5" high speakers or they will distort.

At minimum you will need an inductor in series with the sub, and a capacitor in series with each of the high speakers.

There is a sticky on making passive crossovers on the multi way forum.

Inductor 22nd February 2013 11:57 AM

Quote:

Originally Posted by guangui (Post 3380038)
I think you got it wrong.

No I didn't. You have to learn on how to operate the 4th Order Bandpass Speaker system from the point of view of the natural/acoustic filter roll off. :D
Using dual woofers (or dvc) and matching then the satellites it's easy... (this is if that's what you're looking for).

guangui 23rd February 2013 06:32 PM

Quote:

Originally Posted by weltersys (Post 3380089)
You can't use both sides of the amp to power one single voice coil sub.

Fortunately, most bass is mixed mono, so operating the sub from only one side of the amp is not a problem.

If your sub had dual voice coils, you could use both sides of the amp.

You also need to filter the lows out of the 2.5" high speakers or they will distort.

At minimum you will need an inductor in series with the sub, and a capacitor in series with each of the high speakers.

There is a sticky on making passive crossovers on the multi way forum.

I can do the crossover, that is no problem. It is just that I'm being told that I cannot do it using a single amp, that I need a 2.1 amp, or an amp for the sub, and an amp for the speakers. I'm aware about DVC. My intention was to take advantage of the mono low signal of one channel to power the sub, then continue to the speaker.

Quote:

Originally Posted by Inductor (Post 3381095)
No I didn't. You have to learn on how to operate the 4th Order Bandpass Speaker system from the point of view of the natural/acoustic filter roll off. :D
Using dual woofers (or dvc) and matching then the satellites it's easy... (this is if that's what you're looking for).

Understood...Looking for the later. Thanks, using the speakers as satellites of the sub is the correct term.

head_unit 2nd March 2013 11:51 PM

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.

guangui 4th March 2013 02:38 AM

Quote:

Originally Posted by head_unit (Post 3393234)
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.

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

Xoc1 4th March 2013 12:57 PM

1 Attachment(s)
Quote:

Originally Posted by head_unit (Post 3393234)
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.

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):o

Inductor 5th March 2013 02:32 PM

4 Attachment(s)
Quote:

Originally Posted by Inductor (Post 3381095)
...the 4th Order Bandpass Speaker system

Examples:
Mission 73PI Passive Sub
Canon S-B20 Passive Sub
JBL Control SB-2 Passive Sub (Dual Coil)


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