1. ## Re: Active vs. Passive: An attempt by me to explain

Originally Posted by thch
well, its really application specific. when you design generalized filters you assign goals. you can define a filter by an arbitrary cutoff point, but for most things, its assumed to be -3dB. The biggest example is the Linkwitz Riley crossover which has a -6dB cutoff.

@OP -- please add info regarding the dB scale. you have information about octaves, but not dB.

a nice guide, not cumbersome. at this point i like to classify crossovers into categories:
1.) preamplifier, active analog. (like amplifier crossovers)
2.) preamplifier, passive analog. (fmods)
3.) preamplifier, digital (HU filters using DSP)
4.) postamplifier, electrical (passive crossover)
5.) postamplifier, acoustic (using acoustics to give a desired response).

maybe i'll add some generalized filter stuff, because it comes up ALL the time:
most filters are defined by a combination of 1st (-6dB/oct) and 2nd (-12dB/oct) networks. 1st order filters are not resonant and cannot really favor one specific frequency more then other. 2nd order filters can either be two 1st order filters (Q < 0.5) or can be resonant (Q > 0.5). a high Q* filter is highly resonant, favoring one frequency more then others -- possibly even more then other frequencies in the passband.

4th order networks (-24dB/oct) can thusly be made from 2 2nd order filters. typically it will be a filter with a higher Q (maybe 1.6) and a filter with a lower Q (maybe 0.6). this ends up not favoring any specific frequencies, but also gives a sharp cutoff.

--------------- main point ---------------
This is important becuase EVERYONE asks if you can combine filters. YES you can. BUT not with the intended results. The final filter will be the product of all the filters. thus if filter A is -10dB at 80hz, and filter B is -0.1dB at 80hz, the final result will be -10.1dB @ 80hz. if both filters A and B are -3dB at 80hz, the result will be -6dB @ 80hz. if you were defining a cutoff at -3dB, then the resulting filter's cutoff is not 80hz.

further, just because you have maybe a 4th order filters (made from 4 1st order stages) doesn't mean it will be good. the slope WILL eventually make it to -24dB/oct, but it may not change from -0dB/oct to -24dB/oct in a small bandwidth. i assume this is why some concider fmods to be -6dB/oct filters.

New developments in crossovers are there in digital filters as well as combining bandstop filters with normal filters. the bandstop creates a high slope but only in a small band. the argument is that you can get a filter that is -60dB/oct, and always at or below -30dB in the stopband. CDT and NTM use these filters. NTM has a patent on applying the hourglass filter to audio systems. I also had this same idea, but never finished working on it.

* -- Q refers to the "quality" of a resonator. basically how well it favors a single frequency. a high Q filter may not be desired if the filter is to affect a wide bandwith.
Brilliant! Thanks for the info Chris. We need more guys with BSEE's around here

2. ## Re: Active vs. Passive: An attempt by me to explain

Originally Posted by thch
speakers also have an inductance. so a "zobel" network is sometimes added in parallel with the speaker to basically place a lower and lower value resistor in parallel such that the parallel combination of the inductive speaker and capactive zobel ends up with a constant impedance.
Dammit. That is the term I was looking for. Zobel. Resonates opposite the driver to cancel out the impedance rise and smooth the crossover rolloff. I don't deal with this stuff enough and get my terms confused sometimes...

3. ## Re: Active vs. Passive: An attempt by me to explain

****.

Simple. Nice.

nG

4. ## Re: Active vs. Passive: An attempt by me to explain

www.bcae1.com
Might want to fix that

5. ## Re: Active vs. Passive: An attempt by me to explain

great! i jus wanted to explain a very basic defination distinguishing the two. I appreciate the very detailed information and doing all the work for me guys .

6. ## Re: Active vs. Passive: An attempt by me to explain

very very nice kenny.

7. ## Re: Active vs. Passive: An attempt by me to explain

Originally Posted by helotaxi
Dammit. That is the term I was looking for. Zobel. Resonates opposite the driver to cancel out the impedance rise and smooth the crossover rolloff. I don't deal with this stuff enough and get my terms confused sometimes...
Just an off-the-wall observation....but I remember reading a thread back when I first joined where you did the exact same thing You and zobel networks just don't get along very well.

8. ## Re: Active vs. Passive: An attempt by me to explain

Originally Posted by squeak9798
Just an off-the-wall observation....but I remember reading a thread back when I first joined where you did the exact same thing You and zobel networks just don't get along very well.
haha, good memory!

9. ## Re: Active vs. Passive: An attempt by me to explain

We get along fine, we just aren't on a first name basis...

10. ## Re: Active vs. Passive: An attempt by me to explain

Originally Posted by FoxPro5
Brilliant! Thanks for the info Chris. We need more guys with BSEE's around here
Talk to me in a little over 3years ...

nG

11. ## Re: Active vs. Passive: An attempt by me to explain

woot! i made it to sticky status .

12. ## Re: Active vs. Passive: An attempt by me to explain

You might add that there are two types of "Q" Constant and Variable.

If you use Parametric EQ or Graphic you need a Constant Q to control the bandwidth of channels close to it.

Varable Q is just too hard to know what is really going on when you make changes.

It was one reason I got a H701 and a C701 to get the best sound out of those exspensive speakers.

13. ## Re: Active vs. Passive: An attempt by me to explain

Originally Posted by Team Hammer
You might add that there are two types of "Q" Constant and Variable.

If you use Parametric EQ or Graphic you need a Constant Q to control the bandwidth of channels close to it.

Varable Q is just too hard to know what is really going on when you make changes.
That would be great if it wasn't for the fact this thread is about crossovers and not equalizers.

14. ## Re: Active vs. Passive: An attempt by me to explain

* -- Q refers to the "quality" of a resonator. basically how well it favors a single frequency. a high Q filter may not be desired if the filter is to affect a wide bandwith.

I was under the impression that "Q" along with a Parametric EQ was used to bring the DB up where the Crossover has been set. This Negative DB Region.

Given that you do have a -Db in this region and also has a Phase **** to some degree, Which can be corrected. I know some that just change the speaker wiring to correct this. But I would rather use some sort of Time Correction to fix this.

I seen so many missed matched speakers with as much as a 7db differance its a wonder they sound good at all and no crossover in the world is going to overcome this problem.

If you know of any books that cover this let me know. I do have have most of Chinn's along with others that cover this subject.

15. ## Re: Active vs. Passive: An attempt by me to explain

Hi

I have MB Quarts DFD 6" split components for front and rear of G5 gti. Jl audio 13w3v3 and a RF p800.4 sunning entire car. Pushing 400RMS into sub, running mids of remainder on amp. The crossover on the amp is not doing the job for my mids, not sounding good at all, very sharp at high volumes. I have the crossovers that came with my mids, would that help my problem or would i require a 3way for this problem. OR, is it that these mids are just crap coz i know they are entry level.

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