Active Crossovers

[Rudy81]

DrWho,

Excellent synopsis on how to measure the delay. I will have to wait for that graphic from the other forum to come up. I am currently using an audio card calibration file, but will go back to loopback for these tests. I guess I can only run them using the active filter, where I can set low and high pass individually as well as mute the MF and HF. You did not mention the woofer delay. I suppose the same applies, no lowpass filter and just let it naturally rolloff.

Thanks again. I'm waiting for FedEX to pull up with the DC-ONE. I will have to take a time out to watch the Dallas vs. Philly playoff game though. Priorities, priorities.

[Rudy81]

Posting the grahpic DrWho mentions in the above post that is not showing up.

[DrWho]

How bout this...I even circled it.

[Rudy81]

How bout this...I even circled it.

You have now officially figured out my knowledge level! []

[Rudy81]

Well, the test is underway. Setup was rather simple, it just took a long time in order to make darn sure I din't mis-wire something.

First impression upon firing it up is that the EV is 'noisy', it creates a high frequency 'hiss' that I normally cannot hear from my sitting postition with the passive network. I know some of it comes from using the balanced section of the amps and the pre/pro. I beleive they have a 6dB gain. The other issue is probably from the EV DC-ONE, which I'm sure has gain.

So, first question, is how do I get rid of the 'hiss'.

Ran frequency sweeps as per DrWho's recommedation to get driver delay information and here it is:
Woofer delay is: 19.6 ms, 22.09 feet, or 6.73 meters.
Mid delay is: 16.0 ms, 17.96 feet, or 5.48 meters.
Tweet delay is: 15.1 ms, 16.98 feet or 5.18 meters.

So far I haven't blown anything up. []

[Rudy81]

WOW! I love the flexibility the crossover is giving me. After hooking everything up I sat down to start setting the system up. As I said in the previous post, I was MOST careful to hook everything up correctly. I figured out the time delay and set it for the mid and tweeter drivers. I then sat to have a preliminary listening session.

My first musical impression: This sucks, no imaging. Great enveloping sound stage, but not imaging. I was very concerned since my system has awesome imaging with the passive crossovers. I just could not figure out how it could loose the imgaing just by chaning the crossover. I decided to mess with the settings on the crossover and messed with the mid and tweeter drivers' polarity. No dice, it still sounded 'odd'. I then decided to change the polarity on the right woofer. It immediately sounded better, but sitll had something missing. I realized the problem may lie in a polarity issue. Shut the system down and re-checked my ever so carefully hook-ups. Guess what, my left woofer was MIS-WIRED!!!! I had reversed the polarity. What a dumbass!

I am now listening to pristine imaging!!!! I love the flexibility of the system.

I can't comment on the time alignment changes since I have not had time to A/B the time differences. However, now that I took care of the imaging problem I am SO MUCH happier.

If I can figure out how to reduce the 'hiss' when nothing is playing I'll be thrilled.

[mikebse2a3]

If I can figure out how to reduce the 'hiss' when nothing is playing I'll be thrilled.

You should be able to solve this and just need to identify how your gain levels need to be balanced in your system.

Are you getting plenty of input drive to the EV? You want to see the levels reaching +3db on the loudest peaks when playing the system around the loudest levels you desire.

If you engage the (-6db) input pad located on the back of the EV is there a reduction in the hiss level?

Does adjusting the output levels(or engaging the output mute function) of the EV reduce the hiss level?

Do you have the ability to adjust the input levels of the amplifiers your using?

mike tn

[dtel]

Guess what, my left woofer was MIS-WIRED!!!! I had reversed the polarity. What a dumbass!

I had done the exact same thing with this sub I built, the bad part is both drivers were in the same cabinet and it was a horn sub, which meant they were fighting against each other and doing almost nothing.

I did feel lika a dumbass but was glad to find a problem for the VERY low output.

From the way you sound your going to find real improvment when your done. [Y]

[Rudy81]

You should be able to solve this and just need to identify how your gain levels need to be balanced in your system.

Are you getting plenty of input drive to the EV? You want to see the levels reaching +3db on the loudest peaks when playing the system around the loudest levels you desire.

If you engage the (-6db) input pad located on the back of the EV is there a reduction in the hiss level?

Does adjusting the output levels(or engaging the output mute function) of the EV reduce the hiss level?

Do you have the ability to adjust the input levels of the amplifiers your using?

mike tn

mike tn: If I engage the -6dB pad on the back, the his greatly reduces to a reasonable level....still slightly louder than my passives, but I am now using the balanced section which boosts everything 6dB.

Adjusting the output levels the hiss level does decrease, but when engaging 'mute', there is still a hiss present, small, but present.

No, I cannot adjust the input level of the amps as they are set right now. I can set things up a little differently and I would be able to adjust the gain. Do you think that would help.

BTW, speaking of the LCD lights, here is the deal. The Input lights barely twinkle off the bottom stop. I might get to -6 at the loudest. The ouptut lights, I have never seen lit up. I'm sure they work, I just can't get them to light up.

I am really liking the flexibility this system offers. For example, after setting the driver delays, I can do a fast A/B comparrison from my listening position. There most certainly is a noticeable difference. The time aligned signal seems to present a more coherent sound, more robust if you will. Same goes for the steeper slopes, you can definately tell.

Once I get this gain thing down I'll be well on my way. At this rate, the ALK universals will be for sale soon.

[Rudy81]

I had done the exact same thing with this sub I built, the bad part is both drivers were in the same cabinet and it was a horn sub, which meant they were fighting against each other and doing almost nothing.

I did feel lika a dumbass but was glad to find a problem for the VERY low output.

From the way you sound your going to find real improvment when your done.

I am so glad I was quickly able to track the problem down. I was stunned to see that the problem was a woofer, not a mid as I had anticipated.

The nice thing is that I can compare any change I make immediately. This thing rocks! Just some gain tweaking and I think I'll install it permanently.

[Rudy81]

Here is how the crossover is set up right now. Perhaps you eagle eyed experts can spot some problem....

[Rudy81]

Spent most of the afternoon working on the setup. The only intital thing I have to figure out is the 'gain' issue which is causing the high frequency 'hiss'. I did some troubleshooting and found that if I just have the amps on, it is totally silent, so I don't think it is an amp problem. BTW, I am using 6 channels from two Parasound HALO amps. 125wpc.

As soon as I turn on the DC-ONE and the protection circuit quits, the hiss comes on. It is equally noticeable from both mid drivers and both tweeters. So, I am guessing it is a gain issue from the EV DC-One. I just need to figure out how to balance the gain for such an efficient system.

You guys have been a tremendous help and I am grateful for the hand holding throughout all this. After just one afternoon playing around with the active filter in my room with my Khorns, I am convinced this is the way to go. The active crossover provides a much more coherent and cleaner sound with the time alignment and steeper crossovers. The nice thing is I don't have to wonder how it sounded one way or the other, I can just compare on the fly.

The only issue I MUST resolve before I go permanent is this 'hiss' thing. I'm anally retentive that way. Any ideas on the gain issue with pro gear?

[Rudy81]

Over a glass of wine, I have started to think I have approached this hiss problem incorrectly. I hit the -6dB pad on the back of the unit which reduced the hiss just a very little bit. That of course, caused me to have to boost the output gain. Well, that may not be what I want to do. After dinner I will try to put the -6dB input gain in normal, and just reduce the output gain to compensate. I think that may be the way to go. Yes???

[Rudy81]

Here's a crash course in how I personally go about doing it...

When you pick a xover point (based on polars/distortion numbers), what you want to do is put in the filter and then measure the MF and HF separately, but plot them on the same graph (use the "all measured" tab in REW). The frequency where the two lines overlap is the acoustic xover point, which can be different from the electrical xover point since your speakers won't be perfectly flat. Then take a measurement of both drivers combined...what you want to have happen is for the combined response to be 6dB louder than each driver is individually at the acoustic xover point. Usually what happens (especially with horns) is that you'll measure a dip instead of +6dB.

To fix the phase, what you want to do is add delay to the tweeter to time-align the two signals. You can actually measure the time delay using REW, which would be a good starting point, since that compensates for the propogation delay. Using a LR xover type ensures that the xover is phase aligned (since it is by definition). So all that is left is to compensate for the individual driver phase. The easiest way to do this is to adjust the delay on the HF.... Start by playing a test tone at the acoustic xover point and measure the SPL. You'll notice that you'll be able to make the SPL at the acoustic xover point go up and down as you change the delay...so stop when you hit +6dB. Also make sure you limit yourself to within +- 1/2 cycle so that you don't mess up the time alignment (every 360 degrees of phase the on-axis magnitude will be +6dB).

Now measure again and you should see that your dip got filled in real nicely and your passband is flat.

Keep in mind that this is just the basics...there's a lot more involved with voicing a speaker than just setting the xover frequency and getting proper summation through the passband. There's a few other nuances that show up with the xover settings too that are hard to describe without having measurements handy.

DrWho: I was able to find the crossover points based on your description. The mid and tweeter are no problem because I can pick many points that are strong for both drivers. The problem seems to be the mid and woofer. The plots cross right at 470 Hz. As you predicted, during a full sweep, I get a dip right at that frequency. I have two options with this crossover. I can change the 'crossover' delay time, which is set to align the drivers. Or I can change a parameter in the 'Output Delay', which sums or subracts from the crossover delay. I can raise the dB level about 4 dB, but no more. Funny thing is that when I run the sweep, I still get a dip right at the crossover. Either I'm doing something wrong, or the drivers just are not able to reach the proper cutoff. The bass bin is just not strong above 400 Hz. and the mid seems to have difficulty below 600 Hz. I may have to go back to the K55's to make this work. Any suggestions?

[DrWho]

Measure the Khorn LF by itself without a xover...is it flat to 500Hz? The raw measurements I've seen from Klipsch show it rolling off by around 300Hz or so if my memory is correct.

Any chance you can show plots of what you're measuring? Ideally I'd like to see one like the xover graph you just showed with the xovers enabled for each driver inpedendantly, but then also include the total system measurement. So 4 graphs total: the LF with its filters, the MF with its filters, the HF with its filters, and the total system with all the filters in place.

If the khorn can't reach high enough for your target xover frequency, then this leaves you with two options, either add EQ to bring up the top end of the khorn LF (use a highshelf), or lower your xover frequency. You might also consider adding EQ to bring the midrange of the khorn down too. This is where the real power of the active comes into play... (way more freedom to tailor the frequency response).

The cool thing about EQ is that if the khorn frequency abberations are minimum phase (which they probably are), then adding EQ will flatten the phase response of the total system too...so it's a double benefit in that regard.

As far as the hiss, you want to drive the input of the EV as hard as you can and then attenuate after the EV (and/or use the EV's output gain). What you should do is play no music and turn down the EV output until the hiss goes away....assuming you can't turn down your amplifiers. You'll probably find that you need to drive your preamp to near its maximum level.

Just keep in mind that volume knobs aren't very reliable for volume matching...even though they might visually look like they're in the same position (unless there's detents). Even small 0.1dB offsets can wreak havoc on your imaging....so if you end up putting volume knobs somewhere that isn't a detent, then you should fine a way to measure that you've volume matched all the outputs. Or you can do like I've done to the Dx38 and lower the output gain in the circuitry. I wouldn't worry too much about this right now, but it's something to keep in mind later on if you think something sounds off.

[Rudy81]

DrWho,

The graphic I posted is a picture of the EV DC-ONE pc software setup for the crossovers. So, it shows a totally flat response. That is not what i am measuring with REW. I will post what the bass bin is putting out. No, it does not reach 500 Hz at all, at least not until it rolls way off. That, is the problem. The JBL 2470 doesn't really kick in until 600 Hz, so I have a hole right around 470 Hz which I cannot fill without boosting something. Now, Audyssey apparently saw that, and boosted the frequencies necessary to fill the void, because a room response plot of that shows a mostly flat response, although there is a dip in that area. I am beginning to suspect that the JBL is just not a good match for the Khorn....something Al K had told me to begin with. He had indicated that the K55 is almost impossible to beat for the Khorn due to the low frequency demands on the mid range. I will post some REW graphs tomorrow. Its been a long day of tweaking and learning.

As far as the hiss, I was able to greatly reduce it by taking out the -6dB attenuation on the input I incorrectly set. However, there is still a noticeable hiss when nothing is playing. It bugs me only because my system used to be dead silent. The hiss is caused by the gain in the DC-ONE. If I mute all the channels in the DC-ONE, I still have the hiss, so I am guessing this is going to be an output gain issue. Is lowering the output gain difficult? If not, might as well post the directions 'Sensei'. [] The only way I can turn down my amplifiers is if I put some XLR to RCA adapters on my gear and use the RCA inputs. I have amps that can attenuate the gain but I can only do that with RCA connections.

As I mentioned in a previous post, I am thrilled with the gazillion things I can do with the DC-One. The driver alignment and steeper crossovers DO make a noticeable difference. I definately will work hard to keep this setup. I love the flexibility. If I could only get rid of that hiss.

Again, thank you for all your help!!!!

[DrWho]

Hey Rudy, my apologies that I'm not more familiar with the
DC-ONE...it doesn't appear to have any analog output controls. On page
52 of the manual they show a diagram of the signal path (it's also the
label on the lid I believe):

http://www.electrovoice.com/documents/ev/EV_DC_one103b_web_CDROM.pdf

You
can see that the Mute and Output level are both before the DAC (they're
probably functions built into the DAC), so the hiss you're probably
hearing is related to the digital noise floor of the DAC's.

It
should be noted that the DC-ONE has a 111dB unweighted dynamic range,
which should be more than enough to have hiss free listening. The
problem is getting that dynamic range such that you can actually use
all of it. If you're not lighting any LEDs on the output, then there's
at least a 15dB reduction in hiss possible (if not more). The problem
(as I see it), is that you'd have to dig into the circuit and make some
modifications.

Another option would be to put a multichannel
attenuator between the DC-ONE and your amplifier. Maybe I can whip
something up that would also take care of any unbalanced/balance
interfacing just to make it easier on everyone. I don't know of
anything that exists like that on the market, but maybe someone else
knows of something...the trick is maintaing the volume matching across multiple channels. I was also thinking of making something that had continuously adjustable gain, but then that opens another huge can of worms trying to keep it matched.

[Rudy81]

Hey Rudy, my apologies that I'm not more familiar with the DC-ONE...it doesn't appear to have any analog output controls. On page 52 of the manual they show a diagram of the signal path (it's also the label on the lid I believe):

http://www.electrovoice.com/documents/ev/EV_DC_one103b_web_CDROM.pdf

You can see that the Mute and Output level are both before the DAC (they're probably functions built into the DAC), so the hiss you're probably hearing is related to the digital noise floor of the DAC's.

It should be noted that the DC-ONE has a 111dB unweighted dynamic range, which should be more than enough to have hiss free listening. The problem is getting that dynamic range such that you can actually use all of it. If you're not lighting any LEDs on the output, then there's at least a 15dB reduction in hiss possible (if not more). The problem (as I see it), is that you'd have to dig into the circuit and make some modifications.

Another option would be to put a multichannel attenuator between the DC-ONE and your amplifier. Maybe I can whip something up that would also take care of any unbalanced/balance interfacing just to make it easier on everyone. I don't know of anything that exists like that on the market, but maybe someone else knows of something...the trick is maintaing the volume matching across multiple channels. I was also thinking of making something that had continuously adjustable gain, but then that opens another huge can of worms trying to keep it matched.

This is beginning to sound complicated, if not expensive. I know what you mean about the volume controls. I have already dealt with the issue and it is a pain. My gain knobs do not have any detents, so it is a wild guessing game. What I did was to have a fellow in England make me a 'Goldenjack' attenuator, which is a custom made attenuator that plugs into the RCA connector on the amp. You can custom order the attenuation. I think he also makes them in XLR variety. Is that the kind of thing you have in mind? If so, what attenuation level do you think I would need? I would prefer to use the balanced connections just for noise reduction. The only reason to go to XLR-RCA would be to be able to use the gain knobs on the amps.

I like the active capabiltiy so much, I'm willing to pursue this issue.

[Rudy81]

DrWho: BTW, I ran into this hiss issue once before. When I first got all my Parasound HALO gear I used the balanced section between my preamp and my amps. I hated the hiss and it was very similar, if not identical. I eventually got help from the President of Parasound who personally handled the issue. It turns out that the balanced section of that preamp is not a 'true' balanced section, but is added to the system somehow. In doing that, it has a 6dB boost. When sent to the amps and the highly efficient Khorns, you get noise floor hiss. Same problem it seems. Due to that issue, I have always used RCA unbalanced connections.

I sent an inquiry in to the guy that makes the 'Goldenjacks' about making some for XLR connections. Here is his website. http://www.goldenjacks.com/

Obviously I woul rather not have to go skulking around inside the DC-ONE. As I mentioned previously, I cannot get even one LCD on the output side to light up even playing fairly loud. I'm guessing this all has to do with the issue of balancing the gain etc.

[Rudy81]

I also found these:

http://www.amazon.com/Dayton-XATT20-Line-Attenuator-15dB/dp/B0024TFHRG