Active Crossovers

[Rudy81]

miketn, I played with many combinations of gain structure between the Samson S-convert, the integra outputs and the various amp sensitivities. I need to keep the K1's sensitivity at about 12 o'clock in order to keep the 'sleep' circuit from kicking in during soft passage in music.

With the Integra at reference level, (approx 75dB SPL), the input on the DCX is ok, but not near -3dB or better. In a home theater application where you have to balance 7 speakers, it gets really tough to find a good balance where the mains don't overpower the center and effects. The other issue is that I need to keep the speaker levels relatively close or Audyssey won't be able to set the mains to match the other speakers. Granted, I'm trying to do a lot more than just set up a 2 channel system. That makes it much more complitated to set up.

But, I'm getting there. I was trying to find a way to keep the same SPL, yet raise the DCX input levels. That can be done via the S-convert's gain knob. I was curious as to what, if any, problems come up when you lower the DCX output levels to compensate for an input increase, thereby keeping the same SPL, but boosting the input level.

[Coytee]

Late last night I ran some LF tests and found that the K1 has some sort of 'idle' circuit that cuts out the amp if it does not sense enough of an iput voltage

I think they call that the sleep circuit. I've been told that it can be adjusted to cut in from "X" seconds to "Y" seconds of low input. I've also been told that they now have a 'fix' for this where it can be bypassed. I don't know the validity of either comment.

I DO know that mine hardly ever goes to sleep now. If this sleep circuit is indeed, based upon input voltage then it might help me that I have my gains turned down and am driving my Peach harder (even up to maximum at times).

When I first put this stuff together, I had the gains on the K2's maxed out and frankly, just barely had the input lights on my Dx showing at all. Out of ignorance, I had no idea what was going on and finally, Dr. Who smacked me upside the head enough that I decided to fake it that I understood.

I couldn't even listen to the evening news without it cutting out on me. As I now sit & type this out, I can't remember the last time it happened.

I DO think that mixing amps that have gains with amps that do not have gains is a slight disadvantage because you are going to be handcuffed a little by the amp that is fixed (unless lowering the gain in the crossover is enough to fix that difference??? Maybe Mike or Mike or heck, even Mike will chime in on that)

[Coytee]

I need to keep the K1's sensitivity at about 12 o'clock in order to keep the 'sleep' circuit from kicking in during soft passage in music.

I'm intrigued by that. I would think the lower the gain on the amp, the more juice you'd have to feed it from your Preamp/active and the easier it would be to get around that situation. Maybe I misunderstand your perspective.

I'll tell you this... this is one reason I bought a second K2. I could have matched amps top/bottom and not have to worry about some of the matching issues you are going through and in addition, have to worry about matching the amps, relative to each other.

I usually just turn the gains all the way down (or up) and then count up about 5 clicks (for daily use) or turn them up and count down a handful of clicks for stronger use with me being downstairs.

2 amps, 4 gains, I just do it 4 times and figure they're close enough to each other as long as the click count matches.

[Rudy81]

Coytee, yes it is a 'sleep' circuit. I contacted Crown and got the story on it. They have had three iterations of the circuit. Initially set at 6 seconds, but everybody complained abou that, so they increased the time to 36 seconds. The last effort moved it to 56 seconds before it goes to sleep. As you indicated, you can bypass the circuit, but I was advised by Crown that the amp will 'idle' at a 100 watt draw, so will have a tempereature like a 100 watt bulb just sitting there with no signal....less than optimum if you ask me.

What I have learned thorugh trial and error is that if I lower the sensitivity below about 12 o'clock, the amp tends not to sense frequencies below 60 or 70 Hz easily, so will cut out below those frequencies. I'm not sure why that is, but that is how mine works. If I set the sensitivity at 12 o'clock or higher, it will sense everything down to 20 Hz just fine.

In my HT application, I don't want to be tweaking the sensitivities on 3 amps everytime I want to do something, that is just not practical in a home theater and listening room environment. This has become one of the drawbacks to going active. Ideally, I will find the sweet spot for the system and leave it there. Then, use a sequenced power strip to turn everything on and off in sequence once the 12v signal is sent from the Integra source. Otherwise, it doesn't matter how good it sounds, it won't be useable for my needs.

I am working hard at getting everything just right for my application. I now know why speaker builders have not gone active in droves, it may sound better and have other advantages, but it is not practical for the average family setting.

[mikebse2a3]

But, I'm getting there. I was trying to find a way to keep the same SPL, yet raise the DCX input levels. That can be done via the S-convert's gain knob. I was curious as to what, if any, problems come up when you lower the DCX output levels to compensate for an input increase, thereby keeping the same SPL, but boosting the input level.

Hey Rudy I gottcha... I was trying to help you find the best compromise.

I say try a modest amount of adjustment with the DCX output levels and see how that sounds/works for you. This does lower the dynamic range of the D/A converter so no large adjustment is advised though.

For convience early on I used about -7db of level adjustment in the digital domain of the EV DX38 for my LF amplifier and really haven't noticed any audible issues. I could do this with the analog output level controls of the EV or my LF Amplifier's Level Control but at this point I haven't felt the need to change to that setup.

mike tn

[Rudy81]

I was wondering about the dynamic range issue. Hence my question. I'll keep tweaking it and see how it goes.

[DrWho]

What I have learned thorugh trial and error is
that if I lower the sensitivity below about 12 o'clock, the amp tends
not to sense frequencies below 60 or 70 Hz easily, so will cut out
below those frequencies. I'm not sure why that is, but that is how
mine works. If I set the sensitivity at 12 o'clock or higher, it will
sense everything down to 20 Hz just fine.

It takes
time for the sleep circuit to turn off....all you're seeing in your
measurement is the fact that the test sweep triggers the circuit, but
then your sweep gets to 60,70Hz before the sleep circuit turns off
completely. If you slow down your sweep, then you'll notice it turning on even sooner. Adjusting the gain on your input just means its more
sensitive to the noise upstream and its probably kicking on sooner...but it's also going to be louder at the same time.

Long story short, the input attenuator on the amplifier is not
going to affect the sleep circuitry for the same SPL out of the speakers.

Also, as discussed previously, you need to adjust your
amplifier gain at the amplifier...not at the output of your xover.

[Rudy81]

DrWho, I pretty much got all that. I was trying to find a way to maximize the input into the crossover and yet keep the same SPL on the speakers so they stay balanced with my effects speakers. Quite a balancing act. Next week I'll take some readings right at the crossover to see how the phase is actually ocurring.

I was under the understanding that one of the benefits of the L-R crossover is that you get a flat level at the actual crossover point. I have read and re-read your earlier comments on playing with the phase or chaning the delay on each driver to compensate for the 'dip' at the crossover point.

I can see where the phase will matter if the drivers are out of phase at that frequency span near the crossover point.

I spent a few hours listening yesterday and watched a movie last night. I was concerned the time delay would mess with the lip sync for movies, but there was no change in movie audio from the passive network. I guess audyssey takes care of all that.

On the music front, I have seen three big improvements. The biggest and most noticeable is that I now have my tweeters as the same level as the mids and woofers. It's like a found the hi's again. The second is the bass response is crisp and more authoritative than before....noticeably so. Last, is an overall cleaner sound that has excellent imaging and the soundstage has not suffered at all. In fact, it may be 'deeper' and more natural, but I hesitate to really make assertions until I have time to live with the setup.

On the down side, I hate the turn on, turn off sequencing and the susceptibility of the speakers to reproduce every pop and ping from any piece of equipment. I know they were all there before because only so much equipemet was changed, but not I can hear it much louder. I wonder where that energy was going before?

I hope I can get the setup to where it is rather automatic and more user friendly. Thus far I like the changes. I wish I knew more about how to properly voice the speaker. I would hate to lose the hi frequencies again. The efficiency of the woofer and JBL 2470 was killing the APT 150 tweeters. The passives only allowed me to attenuate the mids, but not do anything to match the woofers and tweets. This is one huge advantage with the active tri-amp setup.

[Rudy81]

Gents and Ladies:

I have a couple of questions on how to properly take readigns during my active filter changes. For measuring the drivers, do you suggest pointing the mic at the driver? How close to the horn should the readings be made?

When taking some 'polar' readings in order to determing an optimum crossover, should the mic point at the driver when at 15 and 30 degrees off center? If so, how close to the horn?

I figure I'll take a whole bunch of readings this week and try to get to the finer points of setting the crossover. I do have the ability of going to a 48dB/octave L-R filter. Right now it is set at 24dB since DrWho mentioned it would be the simplest to set up.

[Rudy81]

I wanted to keep notes on anything I found that may later help some other poor soul. In that light, I had started to track down a 'buzzing' I could hear in the mid drivers. Source unknown. I first thought I would try and run the DCX directly from the Integra and compare that output level to that of the setup with the S-convert between the Integra and the DCX. The difference was right around 1dB the way the gain structure is set right now....so not much difference. The great news was that the S-convert is somehow adding a slight buzzing to the input signal noticeable when you get close to the drivers. Once I took the S-convert out of the input chain, the buzzing is gone. Now, it could be interference that was being amplified by the S-convert since it uses RCA cables from the integra. Regardless, no more buzzing. One more small victory!

BTW, I have been out of town for a week and started a listening session this afternoon. Man, I REALLY am liking the sound of the Khorns with the active filter. So far two things keep jumping out at me. One is the quality of the bass. I thought I had great bass before. But this is a more precise bass with great authority. The second is the quality of the mid range. Vocals are superb out of the JBL 2470's and certain instruments have gained a clarity I had not noticed before. I use the "Ultimate Demonstration Disk" to compare any changes.

This project has been a major pain in the arse, but well worth it.

Oh, and another note. I have up until now used the previously mentioned capacitors to protect the drivers. I had noticed that Audyssey kept reading my left Khorn as 1.5dB louder than the right. I had never had that come up before, but had blown it off. Today, I also connected the drivers directly to the amps, no protection at all, and the left now reads just like the right. For some reason these identical capacitors are not quite identical.

It's all in the details it seems.

[Rudy81]

I finally got a chance to try and fine tune the crossover on this project. I did as DrWho recommended and took some polars for the mid and tweeter. Based on that, I chose to cross the mid at 10kHz. The JBL 2470 is plenty capable and provides a long span with a single driver, 500Hz - 10,000Hz. I really wish the bass bin could go to about 600Hz. Both mid and woofer are weak around 500Hz but neither can extend well into the others' territory. So 500Hz was about as best as I could do. That's one place the K55 beats the JBL. But darn the JBL sounds smoother.

Anyway, I also worked on fine tuning the actual crossover point and phase per DrWho. I ended up with the tweeter and woofers with a 90 degree of phase change relative to the mid. At 90 degree of phase on the DCX, I got another 2 dB of SPL. I was never able to get the +6dB DrWho mentioned earlier at the crossover point.

This thing is sounding really nice. I have been able to bring the hi's up to the mid range SPL since the tweeter in the system does not have nearly the efficiency of the mid and the bass bin.

If anyone sees any major problems with the plots to follow please speak up. I'm an amateur at this.

[Rudy81]

Here are some mid-horn measurements at 15 and 30 degrees off the horizontal and level with the driver. (I'm just providing links since the forum keeps cutting off the right side of the graphs)

http://www.prontoweb.com/images/active/polar/midhorizontalpolar.jpg

This is the mid graphs at 15 degrees vertical:

http://www.prontoweb.com/images/active/polar/midvertpolar.jpg

Here are some polars for the tweeter at 0, 15, and 30 degree horizontal at 0 degress vertical:

http://www.prontoweb.com/images/active/polar/hihorizontalpolar.jpg

Here is the tweeter measurements at 15 degrees vertical

http://www.prontoweb.com/images/active/polar/hiverticalpolar.jpg

I used this graph to first set the crossover at 10kHz for the mid and tweeter. Turns out doing listening comparrisons between 4kHz, 6kHz and 10kHz, the 6kHz crossover point sounded best.

http://www.prontoweb.com/images/active/polar/10kcrosspolar.jpg

I really hate working with these WYSIWYG editors....

[Rudy81]

.....consolidated above.

[DrWho]

I used this graph to first set the crossover at 10kHz for the mid and tweeter. Turns out doing listening comparrisons between 4kHz, 6kHz and 10kHz, the 6kHz crossover point sounded best.

http://www.prontoweb.com/images/active/polar/10kcrosspolar.jpg

Looking at your plots, I would have guessed somewhere between 4kHz to 6kHz...trading distortion for polars pretty much.

Btw, I don't understand what you're trying to show on the 10kcrosspolar plot. Also, do you have the Behringer mic calibration file loaded? Your HF seems a bit rolled off...

[Rudy81]

Looking at your plots, I would have guessed somewhere between 4kHz to 6kHz...trading distortion for polars pretty much.

Btw, I don't understand what you're trying to show on the 10kcrosspolar plot. Also, do you have the Behringer mic calibration file loaded? Your HF seems a bit rolled off...

DrWho, you guessed correctly because it sounds best around 6kHz. I tried 10kHz first based on the 10k plot since both drivers seemed to respond similarly out to 10kHz. The thought being that I could use just one driver as much as possible and thus keep a broader frequency range before hitting the crossover point. I later tried a comparrison at various frequencies and 6kHz sounded much better than 10kHz. One issue of course is that when seated my head is well below the center point of the mid and tweeters.

I have noticed the hi rolloff and it shows up in all the plots I have ever taken. The Behringer ECM8000 'generic' calibration file is loaded. I do note that when the calibration file was created all the readings rolled off at the higher frequencies. http://www.hometheatershack.com/forums/downloads-area/19-downloads-page.html I might try some readings today without the file and see what the difference is.BTW, all these plots have the IR window shortened as per your direction.

[KdAgain]

On the music front, I have seen three big improvements. The biggest and most noticeable is that I now have my tweeters as the same level as the mids and woofers. It's like a found the hi's again. The second is the bass response is crisp and more authoritative than before....noticeably so. Last, is an overall cleaner sound that has excellent imaging and the soundstage has not suffered at all. In fact, it may be 'deeper' and more natural, but I hesitate to really make assertions until I have time to live with the setup.

Rudy,

I have been following your progress for awhile now and am really happy for you that it is finally coming together.

If I understand your system correctly you are using one channel of a Behringer DCX2496 for each driver (6 total). I have read on several different forums that this device is good for subwoofer crossover/equalization, but is not supposed to be very good for full range use. This is due to the DA/AD converters and general circuitry used.

As an owner of one of these and Khorns I am pleasantly suprised to hear of your high SQ results. Mine is presently being used for subwoofer crossover and equalization as I don't have a modern receiver in the loop. But using it for active crossover duty is very intriguing!

Thanks so much for sharing all your trials and tribulations.

Rod

[Rudy81]

Rod: As you have gathered, I am no expert on this subject and am anxious to learn as much as possible. I am familiar with the issues you cite regarding the DCX2496 but I must say I have also found several opposing opinions citing it's great performance for the price. I am sure there are 'better' quality products out there, but at what cost? I can only compare the results I am getting with the DC-ONE, the DCX2496 and my old setup with ALK passives and Parasound HALO amps.

I am still in the early stages of evaluating performance since I am just now tweaking the crossover. The only time I ever turned the system on and thought "this isn't going to work" was when I used the DC-ONE with the HALO amps because I could not attenuate the sensitivity and had a lot of hiss and when I used the Crown D75 due to popping noises. Otherwise, I have not had any bad reactions to what I have heard on a superficial basis.

I find the DCX very quiet and it's performance very acceptable....as I said, I'm no expert. I will point out this site to you, which has some reviews and opinions on the DCX as well as an intriguing way to set up the delays to enhance imaging and soundstage. I have not tried this yet, but am about to try their technique.

General page: http://freerider.dyndns.org/

Details on improving crossover setup: http://freerider.dyndns.org/anlage/LeCleach.htm

I would venture to say that some of the improvements I hear come not from the DCX, but form individually amping the drivers. The benefits stand out, although it is a pain to turn on 3 amps everytime, but I'm working on a power sequencer to automate the task.

The more I study this subject, the more I begin to think that we worry way too much on such things as interconnects, power cords etc. Even in a simple setup think about how many electronic pieces are in the way of the source signal from laser or hard drive head to speaker driver! That's a lot of chinese parts of which we have no quality control unless you are buying some very expensive gear. The bottom line is becoming 'how does it sound'.

I have endeavored to keep a running 'diary' of my experience for the next poor explorer that wishes to try this. Well, I'm off to try this improved filter design thing mentioned above.

[Coytee]

I would venture to say that some of the improvements I hear come not from the DCX, but form individually amping the drivers. The benefits stand out, although it is a pain to turn on 3 amps everytime, but I'm working on a power sequencer to automate the task.

The more I study this subject, the more I begin to think that we worry way too much on such things as interconnects, power cords etc. Even in a simple setup think about how many electronic pieces are in the way of the source signal from laser or hard drive head to speaker driver! That's a lot of chinese parts of which we have no quality control unless you are buying some very expensive gear. The bottom line is becoming 'how does it sound'.

I think it's great that you're getting the results you are getting (bruises not withstanding [])

Regarding your comment above.... to add another factor into your equation.... I've had a handful of tube amps and although I've ultimately sold them all, the pair that were (to me) the spookiest were the OTL amps. Most of the others sounded more alike than not (from a 2A3 up to the 100 watt McIntosh MC-2102)

This got me wondering if the key difference between the amps that I was noticing was the absence of the transformers on the OTL amp. I still don't really "know" if that's the reality or not but I'm beginning to think so. Put a bit differently.... take 40 tube amps, each with a transformer. As I understand the basic process, the signal goes to the transformer, jumps across the windings and then hooks up with the other side of the transformer and out to the speakers. Although transformers might be very efficient, who's to say that 'something' might be lost during that leap of faith as the signal jumps across that gap?

On the OTL, the drivers are hooked directly up to the output of the tubes without a transformer between them to buffer anything.

Of all the amps I've had, my wife has always thought the system sounded good. When I started to play the A/B game with her (and her not knowing exactly what I was doing other than asking which sound she preferred) she usually ended up choosing the OTL amp. Then, once at dinner, the entire dinner came to a halt as her sister just put her fork down and said "I just have to say that I have never heard anything sound so real in my entire life" (music playing in adjoining room) Yes, I happened to have the OTL playing then too, which isn't to say that she might have said the same statement with a transister radio playing.

I don't know if you are right or not but you are certainly walking down one of the mental paths I've walked. I agree with your sentiment. We (speaking generically) worry about a lot of nuts/bolts when we really should be looking at the larger picture first.

Keep the experiment going!

[Rudy81]

For the first time I am running the DCX auto align to let the DCX set the Khorn driver alignment. Very interesting results. I will say this thing is very accurate. Upon my first reading, the DCX kept saying that the speakers were different distances from the mic??? WTFO? I measured the mic position very carefully for the center of the room. I then decided to use a piece of string to measure from the mic to the speakers....yep, the speakers were at different distances...I guess my walls are not parallel.

Just food for thought, I have set the crossover as per the mentioned paper above and the DCX basic delay measurements gives me the following:

Woofer: 0.00 ms delay normal polarity
JBL 2470: 8.40ms delay, inverted polarity
APT 150 tweeter: 9.38ms delay, normal polarity.

The polarity issue jives with what I know about the JBL drivers, they are non standard polarity. The delays, are much greater than I was giving the system before at 3.99 and 4.9ms, derived from the REW measurements. I spent some time going over the papers and slide show I downloaded from the site. Very interesting, although somewhat above my head at times. It does cover why horns, in particular, sound better the farther you are away from them when NOT driver aligned.

Now to put these derived values into the spreadsheet and see what we get, then listen and see how it sounds.

[Rudy81]

OMG, I don't know where Mr. Le Cleac'h came up with his crossover calculations, but holy cow this sounds good!!! Anyone who has the DCX needs to try this thing (don't take my word for it). Prior to trying this 3D combination, I had the folllowing crossover setup: L-R filter at 24dB slope all the way around, crossed at 499Hz and 6000Hz. The delays were mid 3.99 ms and 4.9 ms. Sounded good, imaging was good, but I kept struggling with a slight offset to the right (because my speakers were not exactly distant from my center point). That is, the center image was slightly righ of my center position.

After running the aforementioned DCX auto setup, making the speakers equidistant from the center (this time for real), and using the dowloaded spreadsheets here is what I came up with for my listening position and my Khorns:

Butterworth 3rd order filter, crossover points at 434Hz for woofer, 569Hz-5223Hz for mid, and 6843Hz for the tweeter. Mid polarity inverted with delay of 8.83ms. Tweeter was normal polarity with delay of 9.86ms.

I did quite a bit of A/B comparrisons with these two crossover settings and with all types of music. The Butterworth solution as indicated above sounds WAY better. The web site is right, it opens the soundstage up and imaging is pinpoint accurate. Mind you, I have no idea what, why or how, I just followed the directions and found that it is worth the effort. This kind of flexiblity makes me sure I will never go back to passives for my mains!

There is no way I would have stumbled upon this setting anytime before winning the powerball lotto. I wonder how this would work for a two way system?

I'm sure somebody is going to throw the BS flag, but before you do, please try this technique. Certainly better than anything I would have come up with no matter how many REW readings I took. I ran the excel spreadsheet that simulates the settings and here are the results for the L-R and the Butterworth settings.

LRcomparison.pdf

LRcomparison.pdf

LRcomparison.pdf