High pass filter graph calculation?

[ripmixburn]

For a basement system, I bought a little subwoofer with a built-in high pass filter that would allow me to fill in the bass where my bookshelf speakers struggle.

My bookshelf speakers are specified at:
Frequency response 80Hz to 20KHz ± 3dB.
Input impedance 4Ω.

The subwoofer’s speaker-level high pass filter is specified at:
6 dB/octave speaker level at 100Hz (fixed)

Is there an online calculator that will help me understand what this filter is doing?

It seems like quite a subtle roll off and the speakers still struggle with bass.

 

[abdo123]

I hope this helps?

 

[DonH56]

6 dB/octave is first-order and a very slow roll-off indeed. An octave away, at 200 Hz, the signal is down by 6 dB and that is only half in voltage (though 75% in power). That is still a lot of signal. 10 dB is about half-loudness in the midrange. Typical crossovers are from 12 dB/oct to 24 dB/oct so suppress the bass much more effectively.

Is is a relative comparison from Wikipedia (https://en.wikipedia.org/wiki/Roll-off) -- there are also numerous on-line calculators available:

HTH - Don

 

[abdo123]

6 dB/octave is first-order and a very slow roll-off indeed. An octave away, at 200 Hz, the signal is down by 6 dB and that is only half in voltage (though 75% in power). That is still a lot of signal. 10 dB is about half-loudness in the midrange. Typical crossovers are from 12 dB/oct to 24 dB/oct so suppress the bass much more effectively.

Is is a relative comparison from Wikipedia (https://en.wikipedia.org/wiki/Roll-off) -- there are also numerous on-line calculators available:

View attachment 146563

HTH - Don

we're discussing a high pass filter though so the roll-off would be in the opposite direction

 

[DonH56]

we're discussing a high pass filter though so the roll-off would be in the opposite direction

Yeah, well, it was the first picture I grabbed, not at my home PC where I have examples coded into Mathcad or Matlab to run. So look at the slopes to get an idea of what happens for various orders, but remember for a high-pass filter they go the other way. There is probably a Wiki on high-pass filters with pictures, and I know there are gobs of online resources, but I am a bit buried at the moment.

 

[DVDdoug]

I bought a little subwoofer

How "little" and how does the subwoofer size compare to your regular woofer size?

Is that an active woofer? How much power does it have compared to the bookshelf speakers?

Do you get enough bass from the subwoofer alone with the bookshelf speakers disconnected?

It seems like quite a subtle roll off and the speakers still struggle with bass.

I don't think that's your problem... If the speakers are in-phase you would expect a boost between 80 & 100Hz where both speakers are operating together. And actually, beyond that range because of the slow roll-off and no intentional filtering of the bookshelf speakers.

If they are out-of-phase you'll get a dip where they overlap. But it gets a little more complicated because the filter introduces it's own phase shift. It won't be "perfect" unless you get a proper crossover with "matched" (complementary) high & low pass filters. The easiest & cheapest solution is to get an AVR.

 

[abdo123]

It won't be "perfect" unless you get a proper crossover with "matched" (complementary) high & low pass filters.

Isn't this already the case? there is both a HP and an LP on the subwoofer.

 

[ripmixburn]

How "little" and how does the subwoofer size compare to your regular woofer size?Is that an active woofer?

I think they are well matched as the sub, by Definitive Technology, is small and reaches higher frequencies than a large sub.

How much power does it have compared to the bookshelf speakers?

Speakers, by Linn, are passive.

Do you get enough bass from the subwoofer alone with the bookshelf speakers disconnected?

Yes definitely.

I don't think that's your problem... If the speakers are in-phase you would expect a boost between 80 & 100Hz where both speakers are operating together. And actually, beyond that range because of the slow roll-off and no intentional filtering of the bookshelf speakers. If they are out-of-phase you'll get a dip where they overlap. But it gets a little more complicated because the filter introduces it's own phase shift. It won't be "perfect" unless you get a proper crossover with "matched" (complementary) high & low pass filters. The easiest & cheapest solution is to get an AVR.

Well as luck would have it I have a spare Panasonic AVR, the one reviewed here, which has excellent subwoofer integration. The 100Hz filter seems to integrate them the best (no bookshelf chuffing, sub disappears).