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Any budget subwoofer with in-line high pass filter?

tifune

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#1
Thinking about options like Dayton, Monoprice, etc. that are doing 12-15" subs for <$200. Has anyone found one that offers in-line high pass filtering? The cheapest I've found so far with that option is SVS' 1000 series. This is for a garage system so I'm really just trying to squeeze a few dB out of the bookshelves I have lying around in storage, I have no illusions about fidelity.

I'm not opposed to buying a separate crossover but I don't really know where to start with something like that - just like cables, it seems the sky is the limit price-wise and also just like cables I'm highly skeptical that the quality scales with the cost.
 

pjug

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#3
https://www.amazon.com/FMOD-Crossover-Pair-High-Pass/dp/B0006N41KG

These cost under $30 are 12db/octave, passive, and go inline between your DAC and power amp. Note that Crown XLS amplifiers have (among other features) a built in crossover. That's what I use.
The idea above seems better if you can do that, but another option is a pair of these between power amp and main speakers:

https://www.parts-express.com/80-Hz...MIodfAn6-y7gIVi4nICh0FPwYyEAQYASABEgIScvD_BwE

https://www.parts-express.com/80-Hz...MIt4C93q-y7gIVEVNyCh3USgS6EAQYASABEgLag_D_BwE

1611416041048.png
 
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tifune

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Thread Starter #7
Is there any genius around here who knows if it is better to put the filter before or after the power amplifier?
Because they come in 4/8 ohm ratings, I'm guessing between the amp and speaker/driver.
 
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#8
I think the Dayton 10 and 12" have this.

Edit: Sorry, just looked. It's a low pass filter only. Never mind.
 

andreasmaaan

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#9
Is there any genius around here who knows if it is better to put the filter before or after the power amplifier?
Putting the filter after the power amplifier is far less likely to result in the desired outcome, because the frequency and slope of the filter is highly dependent on the impedence presented by the loudspeaker, which tends to be far from linear around the point at which it will typically cross over to a subwoofer.

@tifune, which speakers do you have? Whether such a passive high-pass filter will give anything like the correct result will depend on this.
 
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pjug

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#10
Is there any genius around here who knows if it is better to put the filter before or after the power amplifier?
Before the power amplifier allows smaller, less expensive parts. But you can't do this with an integrated amplifier and multiple sources. Well, not unless the integrated has external connections between the pre and power sections.

Also, miniDSP 2x4 is only $85 without the case. It is really great if you can make do with the 0.9V output limit.
 

andreasmaaan

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#12
Very old Paradigm Titan v1's
Thanks. I can't find any measurements of this speaker's impedance response but, given it's a ported design that appears to have its port tuned to around 55Hz or 60Hz, my view is that the chances of success of a passive high-pass filter between amp and speakers would be extremely slim.

To illustrate why this is, understand that the functioning of such a filter is dependent on the impedance of the loudspeaker. Any off-the-shelf filter you buy will be based on the (almost always false) assumption that the speaker will present a flat impedance to the filter.

For example, here is the frequency response of a textbook 80Hz Butterworth 2nd-order high-pass filter (the kind you would expect to find in an off-the-shelf passive filter) when used with an "ideal" loudspeaker, i.e. one that has a flat impedance response.

The filter:

1611493263712.png


And the frequency response:

1611493437979.png


And here is the response of the same filter used on a typical ported loudspeaker with its port tuned to around 50Hz:

1611493536515.png


The second result is more like what you can expect with a real loudspeaker.

The only way to know what the result will be in your case is to measure the speaker's impedance and to then model the behaviour of the port using software. Or, of course, to take acoustic measurements with and without the filter in place.

If you're not willing/able to measure, however, I would avoid any amp-to-speaker passive filter on the basis that it's overwhelmingly unlikely to work anything like the way it's intended to.
 
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tifune

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Thread Starter #13
Thanks. I can't find any measurements of this speaker's impedance response but, given it's a ported design that appears to have its port tuned to around 55Hz or 60Hz, my view is that a passive high-pass filter's chances of success would be extremely slim.
Thank you so much, this kind of unexpected response is the reason this forum is the only one I spend time on. I definitely understand your point re: a passive filter between amp and speaker/driver, but if I use the RCA option between the pre and amp wouldn't I get the smooth slope I'm hoping for?
 

andreasmaaan

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#14
Thank you so much, this kind of unexpected response is the reason this forum is the only one I spend time on. I definitely understand your point re: a passive filter between amp and speaker/driver, but if I use the RCA option between the pre and amp wouldn't I get the smooth slope I'm hoping for?
No worries :) And in general, yes, everything I discussed above applies only to passive filters placed between the amp and the loudspeakers.

Which RCA option did you have in mind?
 
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tifune

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Thread Starter #15
No worries :) And in general, yes, everything I discussed above applies only to passive filters placed between the amp and the loudspeakers.

Which RCA option did you have in mind?
This one looks cheap and easy, as recommended by Ron Texas

https://www.amazon.com/FMOD-Crossover-Pair-High-Pass/dp/B0006N41KG

I have, however, read complaints that these aren't so much filters as they are frequency-speciifc attenuators. Even if true, to me that seems academic at best but I'm certainly interested in more experienced opinions. I wish I could find the specific comment, but I'm guessing it was just a typical cranky internet guy
 

pjug

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#16
If you're not willing/able to measure, however, I would avoid any passive filter on the basis that it's overwhelmingly unlikely to work anything like the way it's intended to.
You mean passive between amp and speakers, right? A passive filter like in post #2 does not have the same issue.

I tried the big passive filters in line with my speakers and measured voltage and current at some points where it would be peaking as in your curves, and it was not nearly as bad as what you show in your example. I would say the passive filter was a reasonable option in my case, although I ended up using a miniDSP. As you say, the results will be different for every speaker design.
 

andreasmaaan

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#18
This one looks cheap and easy, as recommended by Ron Texas

https://www.amazon.com/FMOD-Crossover-Pair-High-Pass/dp/B0006N41KG

I have, however, read complaints that these aren't so much filters as they are frequency-speciifc attenuators. Even if true, to me that seems academic at best but I'm certainly interested in more experienced opinions. I wish I could find the specific comment, but I'm guessing it was just a typical cranky internet guy
I actually don't know what's inside the case, which makes it impossible to answer the question I'm afraid...
 

pjug

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#19
FWIW here is the predicted response of the filter in line with my speakers (Salk WOW1). When I measured, that peak near 80Hz was a couple dB higher than predicted (sorry, I lost the actual measurements).
1611496021352.png
 

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andreasmaaan

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#20
This one looks cheap and easy, as recommended by Ron Texas

https://www.amazon.com/FMOD-Crossover-Pair-High-Pass/dp/B0006N41KG

I have, however, read complaints that these aren't so much filters as they are frequency-speciifc attenuators. Even if true, to me that seems academic at best but I'm certainly interested in more experienced opinions. I wish I could find the specific comment, but I'm guessing it was just a typical cranky internet guy
I actually don't know what's inside the case, which makes it impossible to answer the question I'm afraid...
Actually @tifune, just thinking this through from first principles: the same principles apply as to a passive speaker-level filter. The difference here is that the amplifier's impedance is (a) likely to much flatter than a speaker's (which is good) but that (b) its magnitude is unknown.

In practice, this will mean that, assuming this filter is what I think it is (a series capactitor and parallel inductor), the shape of the filter is likely to be more linear than in the case of a speaker-level filter, but the frequency and Q of the filter will depend on the load presented by the amp (i.e. its impedance).

In other words, it's still going to be hit-and-miss, but the chances of getting it closer to right are arguably going to be a bit higher than with a speaker-level filter.
 
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