Stock Passive Sub Crossover

Alex2507

Alex2507

Audioholic Slumlord
First of all I found a tres cool link.

I sold/traded the 12" powered AR sub that I had for my 2 channel rig in man town for a passive Infinity bandpass sub that has a couple of 6-1/2" drivers. Of course I took it apart and saw that the crossover merely puts a 1.5 mH inductor coil in line to each sub driver which are in parallel to the regular speakers ... how cheesy. The inductor coils also have a stamp saying 0.7 O with a / through it. Is that Ohms? I don't know how to find or use a character map.

Anyway, I'm seeing that 1.5 mH provides a relatively high low pass filter and nothing is done to act as a high pass filter for the regular speakers. The sub is also only rated to ~ 45Hz. It just seemed like something neat to play with and it motivated me to find that link to sort of give me an idea of how things work. Now I'm motivated to read Speaker Building 201 also.

The numbers on the back of the drivers in the sub are:

902-5347
A9344

I'm thinking about making a real crossover for this thing but don't know anything about the drivers in the sub. The regular speakers are stock Dayton BR-1's with loved up cabinets.









It's strange how just when I get to wanting to get into something whole hog I end up with other stuff to do so that I end up half @ssing everything but this is my latest thing to spend some time on.

My objective with this would be to make high and low pass filters for the sub and high pass filters for the speakers hooked up to the 'outs'. It's just one of the generic spring clip 'in' 'out' deals. Anyway, I'll muddle through this and learn stuff along the way. One thing that strikes me as wrong is being able to hear violin through the sub. :eek:

Go ahead Greg ... I know I have it coming ... :D
 
Alex2507

Alex2507

Audioholic Slumlord
Edit timed out on me.

I slapped it back together and tucked it away underneath the telephone table.



It sounds kinda nice but where's the fun in that? I'll be dragging it back out sooner or later to do something to it. I'm thinking about stuffing insulation into something. Anyway that's the new thing to play with. :)
 
TLS Guy

TLS Guy

Seriously, I have no life.
First of all I found a tres cool link.

I sold/traded the 12" powered AR sub that I had for my 2 channel rig in man town for a passive Infinity bandpass sub that has a couple of 6-1/2" drivers. Of course I took it apart and saw that the crossover merely puts a 1.5 mH inductor coil in line to each sub driver which are in parallel to the regular speakers ... how cheesy. The inductor coils also have a stamp saying 0.7 O with a / through it. Is that Ohms? I don't know how to find or use a character map.

Anyway, I'm seeing that 1.5 mH provides a relatively high low pass filter and nothing is done to act as a high pass filter for the regular speakers. The sub is also only rated to ~ 45Hz. It just seemed like something neat to play with and it motivated me to find that link to sort of give me an idea of how things work. Now I'm motivated to read Speaker Building 201 also.

The numbers on the back of the drivers in the sub are:

902-5347
A9344

I'm thinking about making a real crossover for this thing but don't know anything about the drivers in the sub. The regular speakers are stock Dayton BR-1's with loved up cabinets.









It's strange how just when I get to wanting to get into something whole hog I end up with other stuff to do so that I end up half @ssing everything but this is my latest thing to spend some time on.

My objective with this would be to make high and low pass filters for the sub and high pass filters for the speakers hooked up to the 'outs'. It's just one of the generic spring clip 'in' 'out' deals. Anyway, I'll muddle through this and learn stuff along the way. One thing that strikes me as wrong is being able to hear violin through the sub. :eek:

Go ahead Greg ... I know I have it coming ... :D
Oh dear Monkey! Are your sure you are not morphing into a curious cat?

A band pass sub is just that. It has a lower and an upper F3 point. The band pass is usually about an octave, sometime a little more.

So the crossover of a band pass sub is acoustic. You just have a low pass filter to stop the driver emanating HF which would other wise radiate from the port. So the low pass Fs us usually set above the upper acoustic F3 and the design of that filter is not critical. So you don't need to monkey with it.

Now band pass subs come in orders depending on the number of chambers and ports and their positioning. Do you know the order of your band pass unit?

The come in second, third and fourth order flavors.

The commonest is the second order, which has a sealed cavity on one side of the drivers and a ported cavity the other side.

Third and fourth order band pass subs are very low Fi as distortion is horrendous.

I don't know if you will have to morph to Homo Sapiens at least to understand this, but I have done my best.

Here are a couple of Carter second order bandpass subs.



The band pass is 27 Hz to 90 Hz.

The speakers they are used with have a pretty decent bass response, so the subs are in supplemental role. There is a crossover here below the upper F3 to give the best splice. There is an active crossover 6 db down at 75 Hz, and so the composite electrical and acoustic slope is fifth order.

If you need to use a crossover below the upper F3 it must be active.
 
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Alex2507

Alex2507

Audioholic Slumlord
Oh dear Monkey! Are your sure you are not morphing into a curious cat?
I've said it before and I'll say it again ... I am not a pussy! :D

A band pass sub is just that. It has a lower and an upper F3 point. The band pass is usually about an octave, sometime a little more.
This sub is rated from 45Hz - 150Hz.

So the crossover of a band pass sub is acoustic. You just have a low pass filter to stop the driver emanating HF which would other wise radiate from the port.
That falls in line with what my book says and I'm with you so far. This sub was designed to work with some real entry level satellites so the 1.5 mH inductor coil allows a fair bit of HF to come through. I was just wondering about lowering the upper F3 (Fu) by increasing the value of mH to 2.2mH or 3.3mH ... :confused:

So the low pass Fs us usually set above the upper acoustic F3 and the design of that filter is not critical. So you don't need to monkey with it.
Resonant frequency and Fu ... this isn't so clear but at least it's got me looking in the book and thinking instead of making asinine remarks all over the forum. :eek:

Now band pass subs come in orders depending on the number of chambers and ports and their positioning. Do you know the order of your band pass unit? The commonest is the second order, which has a sealed cavity on one side of the drivers and a ported cavity the other side.
That's what I have and the book says it's a forth-order bandpass subwoofer which drops off at roughly a second order rate (12dB/octave IIRC).

I don't know if you will have to morph to Homo Sapiens at least to understand this, but I have done my best.
That you have and it's thought provoking and educational as usual. Don't give up on me ... I will walk erect one day! :D

If you need to use a crossover below the upper F3 it must be active.
Active crossovers want external amps. :eek:
(more gear/ more money/ more space ... ain't happening right now) :(
I'm just looking to high pass the signal going to the regular speakers since the sub is already taking care of itself (except for the possibility of a bigger coil :rolleyes:) Actually I'm more interested in the discussion as an educational tool and a past time. Somehow reading the book just murders my spirit.

I'm kind of curious about the load seen by the rec'r with the sub hooked up in parallel as opposed to what it would see if I used speaker connections 'A' and 'B'. I think it might be the same thing with a nominal value of ~ 16 Ohms but that's a guess.

Thanks for the response and for helping me kill a whole mess of time typing out this response ... the research ... :rolleyes: :)
 
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TLS Guy

TLS Guy

Seriously, I have no life.
I've said it before and I'll say it again ... I am not a pussy! :D



This sub is rated from 45Hz - 150Hz.



That falls in line with what my book says and I'm with you so far. This sub was designed to work with some real entry level satellites so the 1.5 mH inductor coil allows a fair bit of HF to come through. I was just wondering about lowering the upper F3 (Fu) by increasing the value of mH to 2.2mH or 3.3mH ... :confused:



Resonant frequency and Fu ... this isn't so clear but at least it's got me looking in the book and thinking instead of making asinine remarks all over the forum. :eek:



That's what I have and the book says it's a forth-order bandpass subwoofer which drops off at roughly a second order rate (12dB/octave IIRC).



That you have and it's thought provoking and educational as usual. Don't give up on me ... I will walk erect one day! :D



Active crossovers want external amps. :eek:
(more gear/ more money/ more space ... ain't happening right now) :(
I'm just looking to high pass the signal going to the regular speakers since the sub is already taking care of itself (except for the possibility of a bigger coil :rolleyes:) Actually I'm more interested in the discussion as an educational tool and a past time. Somehow reading the book just murders my spirit.

I'm kind of curious about the load seen by the rec'r with the sub hooked up in parallel as opposed to what it would see if I used speaker connections 'A' and 'B'. I think it might be the same thing with a nominal value of ~ 16 Ohms but that's a guess.

Thanks for the response and for helping me kill a whole mess of time typing out this response ... the research ... :rolleyes: :)
Your sub is definitely second order, and not fourth. It will roll off acoustically above and below upper and lower F3 points second order.

Where you got confused you need to make Fs F3, my typo.

I would really wonder if the range is 45 Hz to 150 Hz, I would bet it is more like 45 Hz to 120 Hz, it is really tough to make the band width greater than 1.5 octaves.

Now making a passive crossover below 350 Hz is a bad idea. You end up with huge inductor and capacitor values. Apart from the expense, they don't work well, and you can't level the sub to make it level match your mains. For a start you can't boost any passive signal, only cut it. You can't L-pad a woofer, like you can a mid or tweeter, as it drastically changes Q.

You are right though having the sub in parallel with the first order filter you have, will drop the impedance a lot. Unless those are 16 ohm drivers, then your sub is four ohm. If your speakers are four ohm in the lower bass then you likely have a two ohm impedance below 250 Hz or so, so you might blow up your receiver. Your sub is almost certainly four ohm or less, because band pass subs are inefficient, and they need to suck as much power from the amp as they can get.

In order to solve without another amp you have a poor option. You have to change the crossover in your speakers, so that the sub receivers a a low pass signal, and the woofer of your main speakers a band pass signal.

This would require a lot of measurements. I would bet at the end of all this your rig would sound significantly worse than it does now, the main reason being a passive crossover below 350 Hz.

You will not solve this dilemma well or elegantly without another amp and active crossover.

So I would leave things alone and not play too loud, so you don't hazard your amp.
 

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