Active Crossovers

[AltmanEars]

JC:

I would think that in the interest of 'sound purity' one would avoid putting anything in the way of the driver. I am guessing you may give up some of the advantages of going active, such as more direct amplifier control of the driver. But, since I try to anticipate what could go wrong, I looked into it. The trade off now is the cost of various capacitors just to try various frequency points. I'm sure putting a capacitor in line with the driver is not 'free' of problems. That's why I was asking about the process.

I may just wing it and try it without anything until I know if I am going to stay active or go back to passive and until I gather more information on the topic. I figured the EE types around here could shed some light on the practice.

For obvious sound quality reasons you dont want a capacitor in the chain. esp with a really high efficiency speaker. As far as costs are concerned a really good capacitor can be really expensive (more than the xovers this guy is looking at) --- furthermore it can take literally months to test capacitors by ear as we found by a really particular Khorn user who recently wrote about his experiences.

[Rudy81]

For obvious sound quality reasons you dont want a capacitor in the chain. esp with a really high efficiency speaker. As far as costs are concerned a really good capacitor can be really expensive (more than the xovers this guy is looking at) --- furthermore it can take literally months to test capacitors by ear as we found by a really particular Khorn user who recently wrote about his experiences.

I have already ordered some Solen caps, and will use them while I mess around. I will also take some acoustic measurements with and without caps to see if there is any measurable difference. I would rather be safe than risk blowing a $240 diaphragm on a project that may or may not bear fruit.

[DrWho]

For obvious sound quality reasons you dont want a capacitor in the chain.

Can you list these obvious reasons?

Have you ever thought about the number capacitors in series with your signal between the mic cartridge in the recording studio all the way to your speakers at home?

In your opinion, is it worse to be in series with a speaker or an opamp?

[DrWho]

And now, some completely different questions. The project is now underway. I am waiting for the DC-ONE and I'll be able to actively cross my Khorns.

In light of the discussions of driver alignment etc, it seems the best thing to do is to use a single driver as much as possible. I am limited in the woofer to mid crossover by the Khorn design. However, my mid Trachorn with its JBL 2470 and the eminence APT-150 have quite a bit of overlap. That will allow me to set the high crossover point in a variety of places.

According to the JBL data, the 2470 can go up to 12 kHz and the Eminence can go down to 3.5 kHz. Ideally I would set the crossover as high as possible to keep the majority of sound coming from a single driver.

So, what do you guys recommend? I am very optimistic about this experiment and the flexibility I will have with the active crossover.

I usually try to pick a xover frequency where the distortion and polars line up...

[Rudy81]

I usually try to pick a xover frequency where the distortion and polars line up...

Go easy on me here....I'm just learning. I was thinking I should pick as higher frequency to allow most of the sound to eminate from one driver. I also would think you don't want to cross over, say, in the middle of the human vocal range. How would one go about doing what you suggest?

[ClaudeJ1]

For obvious sound quality reasons you dont want a capacitor in the chain. esp with a really high efficiency speaker. As far as costs are concerned a really good capacitor can be really expensive (more than the xovers this guy is looking at) --- furthermore it can take literally months to test capacitors by ear as we found by a really particular Khorn user who recently wrote about his experiences.

I totally disagree with that comment. No "obvious reasons" exist and has not basis for a blanket statement like that. Dayton film capactors sound great and don't cost that much at all, as one example. All you need is low ESR capacitor and the law of diminishing returns sets in quickly with the exotic stuff. I can easily PROVE that, but I won't do it here.

[ClaudeJ1]

Go easy on me here....I'm just learning. I was thinking I should pick as higher frequency to allow most of the sound to eminate from one driver. I also would think you don't want to cross over, say, in the middle of the human vocal range. How would one go about doing what you suggest?

You can't really avoid a crossover in the "middle of the vocal range", since it goes from about 80 Hz. to 1.2 Khz..........bass voice to soprano voice. I simply do not understand this common notion.

[DrWho]

Turn off all the other speakers and set the highpass on the tweeter as low as you feel comfortable going and then measure the on-axis response. Then measure at 15 and 30 degrees in the horizontal and at 15 and 30 degrees in the vertical.

Now turn off the tweeter and turn on the squawker with no low pass and a highpass as low you feel comfortable going. Do the same set of measurements.

Ideally you would measure at more angles, but this should be enough to get a feel for how the polars are behaving. The polars for the tweeter will get wider as you go lower in frequency. Conversely, the polars on your squawker will get narrower as you go higher in frequency. Ideally there will be an overlapping range where the polars from both don't change much and are about the same.

I'm wagering that the polars on your custom tractrix are gonna be around 60x40, which is gonna be hard to transistion into the 100x50 of the APT150.

As far as distortion goes, that's very difficult to measure or hear inside a room....but if you can get outdoors, what you could do is play test tones and switch back and forth between the squawker by itself and the tweeter by itself. It should be rather obvious which has more distortion. You should be able to find a spot where they sound very similar, and hopefully that's near where the polars overlap. It's important to make sure the two test tones are volume matched for the comparison and that you compensate for the speaker frequency response as you move around in frequency.

With different measurement gear, you would just measure the distortion response and see where they come close.

[Rudy81]

DrWho, thank you. Interesting things to test out. I greatly appreciate your time.

[DrWho]

You can't really avoid a crossover in the "middle of the vocal range", since it goes from about 80 Hz. to 1.2 Khz..........bass voice to soprano voice. I simply do not understand this common notion.

The tonal content of the human voice consists of a lot more than just the fundamental frequency. In fact, many of the harmonics are louder than the fundamentals even. A 10kHz high-shelf filter makes a crazy amount of different to the sibilance. A 3kHz PEQ can pull a voice forward or back in the mix. A 600Hz PEQ can be the difference between muddy and super thin sounding. 80Hz (and lower even) is gonna be your chest voice and your deep thick voiced radio announcers usually have this compressed and boosted way crazy style to give them that signature radio voice sound.

[Rudy81]

I simply do not understand this common notion.

I think it's a common notion because to many of us it is not intuitive. Until I looked at a graph of the human voice, on a frequency scale, I had no idea it went that low. In my case, I was mainly concerned with the high crossover point since I have no choice as to the bass crossover. This particular graph showed harmonics up to 8 kHz. Really a well done grahic if it is accurate. http://www.independentrecording.net/irn/resources/freqchart/main_display.htm

Based on that and looking at the majority of instruments, I am thinking to crosso over as high as possible, as long as the JBL will still perform. I supposedly is good to 12 kHz.

[AltmanEars]

I'm just having fun with you guys --- lets leave it at I have a really nice active system at home and one at a business I own. I also have a fairly nice passive Klipschorn system. In fact I've owned an active system continuosly for 30 years.

I think I am trying to acheive something a bit different in sound than you guys so accept my apologies and pile on the capacitors...

[Rudy81]

I'm just having fun with you guys --- lets leave it at I have a really nice active system at home and one at a business I own. I also have a fairly nice passive Klipschorn system. In fact I've owned an active system continuosly for 30 years.

I think I am trying to acheive something a bit different in sound than you guys so accept my apologies and pile on the capacitors...

In your many years of owning an active system, have you ever had a problem with damaged drivers due to the direct amplifier connection? Just trying to figure out which is the way to go. I certainly don't want to do anything that will 'hurt' the sound I can get from going active. After all, improving things a little is the whole object of the exercise.

[Rudy81]

...

[AltmanEars]

I have NEVER EVER BLOWN a tweeter in an active system. This includes using the two highest powered Naim monoblocks amps directly wired to a cheap Linn tweeter. BUT THERE IS A BIG BUT --- All of my systems have electronic crossovers that have been professionally engineered by a top engineer for the exact drive unit I was using... BTW non of these systems even used a fuse...for reference the Naim amps can swing 400VA and the Linn Kan is only rated at a max of 80 watts when run passively...

[DrWho]

I think I am trying to acheive something a bit different in sound than you guys so accept my apologies and pile on the capacitors...

Don't you think that's a bit arrogant? Apparently only the most elite and refined listeners can appreciate the sonic merits of something so "obvious"?

The problem I have with that logic is the focus on the object itself (the cap) instead of the actual behavior related to that object's implementation. I also don't agree with the relative weighting being assigned to that behavior - especially in light of the other many extreme degradations happening to the sound in other parts of the system. If the degradation of a capacitor is obvious, then what about all the other crap generated by the system?

[ClaudeJ1]

You can't really avoid a crossover in the "middle of the vocal range", since it goes from about 80 Hz. to 1.2 Khz..........bass voice to soprano voice. I simply do not understand this common notion.

The tonal content of the human voice consists of a lot more than just the fundamental frequency. In fact, many of the harmonics are louder than the fundamentals even. A 10kHz high-shelf filter makes a crazy amount of different to the sibilance. A 3kHz PEQ can pull a voice forward or back in the mix. A 600Hz PEQ can be the difference between muddy and super thin sounding. 80Hz (and lower even) is gonna be your chest voice and your deep thick voiced radio announcers usually have this compressed and boosted way crazy style to give them that signature radio voice sound.

Of course I know about the harmonics, etc. However my point was STRICLY about the common notion that one can avoid a crossover point to a midbass or midrange horn that doens't include the wide band of the human voice. You comment on hamonics broadens the band and further drives my point.

[stormin]

I think I am trying to acheive something a bit different in sound than you guys so accept my apologies and pile on the capacitors...

That's treading the waters aweful close to one of these little fellows

[Rudy81]

Ok, almost time for the experiment to begin. I'm just waiting for the DC-ONE to arrive tomorrow or Saturday. I have been playing around with the pc based software for the DC-ONE. Very intuitive and relatively simple so setup. Nice graphics too.

I needed some advice on what setups to try. I have been reading on crossover theory and have some questions in that area as well.

Should I use Butterworth or L-R settings?
What slopes should I shoot for? The system can go as far as -24 dB slopes.
As a baseline, I planned on mimicking the ALK universal. Any ideas on what settings might mimic Al's crossover? I had guessed Butterworth -6dB with crossovers at 400 Hz and 6000 Hz. How does that sound?

As I said, I'm really new to all this, so your suggestions and comments are greatly appreciated.

I will be using the DC-ONE with six channels of my Parasound HALO amps, the A23 and A51. I got the Solen capacitors in, so will at least be using them until I am confident I'm not going to blow something up.

Thanks for all your help gents.

[DrWho]

I would start with LR 24dB for the xover...it's one of the easier filters to dial in properly and then is one of the better sounding ones too. Although with your polar response mismatch, you might find that shallower slopes are gonna sound more natural.

Will you be using your measurement rig to help dial things in?