I'm planning to add two diy subs to my HT setup, replacing my one commercial sub. These new subs will be passive speakers which I will power through an old power amp I have lying around.
I always assumed a subwoofer doesn't need a filter. After all it's one driver in a box, why wouldn't you send the entire potential signal to it, seeing as most of us tell our processor / receiver to cut off at 80 hz anyway.
Then I googled it and a lot of people seem to think (insist even) that a sub does need a filter. It would be easy and cheap enough to add a simple first order filter, but I'd rather not if it's unnecessary. Most of all: I cannot see why.
Your thoughts?
I always assumed a subwoofer doesn't need a filter. After all it's one driver in a box, why wouldn't you send the entire potential signal to it, seeing as most of us tell our processor / receiver to cut off at 80 hz anyway.
Then I googled it and a lot of people seem to think (insist even) that a sub does need a filter. It would be easy and cheap enough to add a simple first order filter, but I'd rather not if it's unnecessary. Most of all: I cannot see why.
Your thoughts?
If you are planning to use the cut off at 80 Hz you are filtering it, I don't understand your question.
If you just want to know why it should be filtered, ideally there should be a crossover between it and your other speakers, it's because if it wasn't the sound would interfere with your main speakers
If you just want to know why it should be filtered, ideally there should be a crossover between it and your other speakers, it's because if it wasn't the sound would interfere with your main speakers
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Vented/horn/pr subs (heck even sealed) often benefit from a very low frequency high pass filter as to avoid ejecting voice coils though.
What exactly are you trying to accomplish is the better question.
What exactly are you trying to accomplish is the better question.
Passive low frequency cross over filters aren't cheap as they need quite big heavy inductors, obviously depending on wattage of driver.
I have never bothered with filters for subs.
I do though for tweeters but they are often just a simple cheap 2u2 polyester capacitor.
That's what I thought, until I googled it anyway and got confused.
Thanks all for your input.
Which leaves the matter of a "very low frequency high pass filter" to prevent the driver from self-destructing. How would I determine whether a high pass would be necessary? Doesn't the box prevent it from going too low? Or is this only true for sealed enclosures? I will be building vented.
If it's vented, you would definitely benefit from a subsonic filter(a filter that cuts off sound below the tuning frequency of the box). It might NOT be necessary if the drivers have very good power handling ability, long cone travel and you aren't feeding them that much power. For example a 1kw driver with 20mm travel in each direction in a low tuned enclosure only being fed 100w will likely not have excursion problems.
A 100w driver being fed 100w in a box tuned to 35hz may have issues with low frequencies from a newer movie with lots of very low frequencies in the LFE track for example.
A 100w driver being fed 100w in a box tuned to 35hz may have issues with low frequencies from a newer movie with lots of very low frequencies in the LFE track for example.
That's a clear and useful reply. Thanks. I shall consider a subsonic filter.
I'm thinking of a 300w rated driver, with 9.3 mm xmax in a vented enclosure tuned to 22 Hz. And i'll be feeding the subs with an amp that produces 200w rms per channel at 4 ohms. So between 100 - 150w in real life, give or take.
Instinctively i'd say there's enough leeway there, to be able to forget about the filter. I need to keep cost down on this build.
I'm thinking of a 300w rated driver, with 9.3 mm xmax in a vented enclosure tuned to 22 Hz. And i'll be feeding the subs with an amp that produces 200w rms per channel at 4 ohms. So between 100 - 150w in real life, give or take.
Instinctively i'd say there's enough leeway there, to be able to forget about the filter. I need to keep cost down on this build.
I have never felt the need for subsonic filters in my subs. Especially not when tuning low like 22Hz. That will give you low cone excursion down to 18-20Hz somewhere.
Specify the driver and/or T/S parameters and it is easy enough to check how it will behave.
Specify the driver and/or T/S parameters and it is easy enough to check how it will behave.
Had my eye on two of these:
http://www.daytonaudio.com/specs/specsheet.php?prod=295-206
(in seperate enclosures to be clear, i'm building two subs)
When I simulate the box, the 'cone excursion' graph (I suppose that's the one I want to look at) shows cone movement exceeding 10 mm at about 15 Hz. But this presumes a power input of 300w and i'll be feeding it only 200w. Even less in real life. Besides, at 15 Hz the 'amplitude response' graph shows it's down 9db already. Or is this beside the point?
Anyway, based on my meagre knowledge I conclude a subsonic filter isn't strictly necessary. Feel free to correct me.
http://www.daytonaudio.com/specs/specsheet.php?prod=295-206
(in seperate enclosures to be clear, i'm building two subs)
When I simulate the box, the 'cone excursion' graph (I suppose that's the one I want to look at) shows cone movement exceeding 10 mm at about 15 Hz. But this presumes a power input of 300w and i'll be feeding it only 200w. Even less in real life. Besides, at 15 Hz the 'amplitude response' graph shows it's down 9db already. Or is this beside the point?
Anyway, based on my meagre knowledge I conclude a subsonic filter isn't strictly necessary. Feel free to correct me.
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