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Old 28th March 2007, 01:38 PM   #1
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Default 40hz seems too much

Hello eveyone,
My first post.

I put a lowpass 24db/octave 40 hz filter on my LT sub, and its way audible, over my mains, which get down to 40. Should I cross lower?

Cheers Kelloggrice
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Old 28th March 2007, 01:47 PM   #2
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Yes.
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Old 28th March 2007, 02:28 PM   #3
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You might want to cross it lower, but I'd check the levels first. Simply turning the sub down might fix things, of course you probably already tried it...
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Old 28th March 2007, 02:37 PM   #4
infinia is offline infinia  United States
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Hi
Not sure I'm following your question or not.
Don't you mean HPF to control freq's delivered to the mains?
You need both. Depending on drivers and alignments used a crossover freq of somewhere around 80-200 Hz should be considered useful.
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Old 28th March 2007, 03:00 PM   #5
AndrewT is online now AndrewT  Scotland
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Hi,
do you want an active crossover to integrate the sub with the mains?
Then you need a Low Pass Filter on the sub and a matching High Pass acoustic Filter on the mains.

If you use the natural rolloff of the mains which are probably 18db/octave but with a Q that is not Butterworth, then you need an additional 6db/octave to match the LPF.

If you do not know the Q engineered into the mains then moving the crossover point to at least an octave and preferably two octaves above the roll off allows an electrical HPF to nearly match the LPF.

So moving crossover to above 160Hz will allow either Butterworth or Linkwitz Reilly to be bulit up with active electrical filters. I think you stand a better chance of getting sensible integration of sub to mains by adopting this strategy.
An advantage of the higher frequency and steeper electrical HPF on the mains is a substantial reduction of cone displacement on almost all music. The effect is better performance from the mains at all usual SPL levels (not just maximum SPL levels).

Has anyone one else got an alternative suggestion?
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Old 28th March 2007, 06:47 PM   #6
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Quote:
Originally posted by AndrewT
[....]
If you use the natural rolloff of the mains which are probably 18db/octave but with a Q that is not Butterworth, then you need an additional 6db/octave to match the LPF.

If you do not know the Q engineered into the mains then moving the crossover point to at least an octave and preferably two octaves above the roll off allows an electrical HPF to nearly match the LPF.

So moving crossover to above 160Hz will allow either Butterworth or Linkwitz Reilly to be bulit up with active electrical filters. I think you stand a better chance of getting sensible integration of sub to mains by adopting this strategy. [...]
18 dB/octave? Sealed boxes roll off at 12 dB/oct, vented at 24 dB/oct. Infinite baffles roll off at 6 dB/oct at the baffle frequency, and another 12 dB/oct below speaker resonance, to make 18 dB/oct. You need to know what the mains are before playing with filters.

And crossing over at 160 Hz will let the listener localize the subwoofers in the room, not what you want.


Francois.
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Old 29th March 2007, 06:46 AM   #7
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Default Thankyou very much

Hello all, thankyou very much for your replies. I think its a combination of a little too much gain, which I'll need to back down and also because its very audible, I think I'll drop to 30 hz and hear if that makes an improvement.

Thankyou
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Old 29th March 2007, 12:30 PM   #8
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You need an SPL meter, some test tones and preferably an RTA program to blend in a sub. What most people are saying here is that mating a sub to a woofer is exactly the same as mating a woofer to a midrange. You need a proper crossover (phase, XO frequency, slopes) to do it successfully. You need to end up with an ideal Butterworth or Linkwitz-Riley transfer function, or it will never be quite right. I'd also suggest you'll need some EQ, because weird things happen to bass in rooms.
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