Active Crossovers

[mikebse2a3]

Hey Rudy you have a PM

[Rudy81]

Hey Rudy you have a PM

PM'd you back. Can't thank you enough for your help. I'm going to take a break from all this so I can go back to actually enjoying my speakers instead of wanting to throw everything out the window. I put everything back the way it was a month ago and presto. No noise, no hum, no nothing. Just silence when the system is in idle.

After all we have done here, I still think this is the way to go. Unfortunately, trying to use pro gear and home amps doesnt' seem to work very well. The gain issue is a huge problem. I'm going to do some research on pro amps and see what you guys recommend, but at least I can do it at a leisurely pace and not trying to do everything at once.

It was just so frustrating to not get past the setup stage after a full month of working on this, not to mention the money I spent on cables, a second 5 channel amp and the EV.

[Rudy81]

One interesting note. Prior to going back to passive yesterday, I ran an Audyssey calibration to see how it would change the seetings in my Integra. I ran it 3 times to make sure of the results and every time it showed my Khorns about 8 feet further away than they are physically located. When running the calibration with passive crossovers, it correctly estimates the distance. It makes sense that with the time delay the reading would put the Khorns farther away.

I don't know how all that will affect what Audyssey does if I ever do go time aligned and active. All very interesting.

[Rudy81]

Mike, I sent you a PM concerning same. Let me know if you got it.

[Rudy81]

When driver aligning a Khorn, does the issue of group delay come into play? I'm just reading up on that little nugget.

[DrWho]

You sure you want to open the flood gates on group delay? []

[Rudy81]

You sure you want to open the flood gates on group delay?

Well, if you put it that way, no! [:|]

I have started reading about that because I asked an Audyssey expert about the effects of delaying the drivers. My Audyssey registers my mains about 8' farther back when driver aligned. Makes sense. Someone mentioned to be careful about Group delay....of which I know next to nothing about.

[DrWho]

Adding delay in this manner does not create a group delay issue - in
fact, it actually improves your group delay. The reason Audyssey says
your speakers are further away is because it's making sure the sound
(after the extra delay) arrives at the listening position at the
intended time....which is important for watching movies (especially if
your center channel is a different type of implementation).

Group
delay at its most simple form is the derivitive (slope) of the phase
response. So the faster the phase changes, the worse the group delay
is. It's basically a way to describe how much later/earlier different
frequencies arrive relative to each other. The dominate factor of group delay in your system is actually the speaker drivers themselves...lower frequencies require more displacement from the diaphragm to be the same volume, which means it takes longer for the soundwave to be generated relative to the higher frequencies.

[Rudy81]

DrWho, thank you for the explanation on group delay. I am currently looking at the Behrigner DCX-2496. I have been going over the manual and it has the ability to modify the input and output gains +/- 15 dB. I might give that unit a try. I'm starting to hunt around for some D-75 amps, but folks are very proud of those for their power rating. Must be something to them []

[DrWho]

I'm gonna post the email I sent you since others could benefit from it too:

The input sensitivity with the volume knob on the D75 cranked up all the way is 0dBU and your
speakers with the full power of the D75 would be about 126dB SPL for the squawker. With
the 106dB dynamic range of the D75, that would put the amplifier noise
floor at 20dB SPL (so inaudible in even the quietest of rooms).








The DC One has 111dB of dynamic range relative to +26dBU, which puts
its noise floor at -85dBU. Amplified by the 27dB of gain inside the D75
(with the volume knobs cranked) would put the system noise floor at
-58dBU, or 41dB SPL...which will be audible standing near the speakers.
Turning down the volume knobs of your D75 amplifers to the -30dB detent
will lower the DC ONE noise floor to -28dBU, or 11dB SPL which is now
masked by the 20dB SPL noise floor of the amplifier. The maximum volume
would reduce from 126dB SPL to 122dB SPL (still able to drive the
speakers to their max).







One thing I didn't notice earlier is that the DC One wants +26dBU on
its inputs to maximize dynamic range. You would need 30dB of gain
between your consumer preamp and the DC One in order to hit that spec.
In other words, if you set the gain on your D75 to the -30dB indent,
then driving the DC One directly with a consumer preamp will result in
92dB maximum SPL. So with your preamp turned up all the way,
the loudest peak will be 92dB...which with 20dB crest factor music is
only going to be a 72dB listening level (as measured by a radio shack
SPL meter). If you raised the amplifier gain on the D75 from the -30dB
detent to the -10dB detent, then your system noise floor will be 33dB
SPL which will likely be inaudible from the listening position, but
would increase your maximum volume to 92dB SPL (112dB SPL peak).







As you can see, changing the gain on your amplifiers allows you to push
the noise floor around a bit, but it also affects the max SPL too. You'll be capped somewhere between 20dB
SPL and 41dB SPL. Btw, all this is assuming that your speakers have a
110dB sensitivity...which I think the squawker might be close to. The
Khorn LF is about 102dB depending on how you look at it (after EQ) and the tweeter
is about 104dB. So the noise from the Khorn LF section will be
somewhere between 12dB and 33dB SPL, and the tweeter will be somewhere
between 16dB and 37dB SPL.

The
Behringer DCX has a dynamic range of 109dB instead of the 111dB from
the DC ONE. Also, the volume controls you refer to are performed
digitally, which means it doesn't improve your dynamic range problem.
You'll end up losing 2dB of dynamic range by swapping the DC ONE for a
DCX.

Another thing that makes me not a huge fan of the DCX is that I've heard they're using FIR filters instead of IIR.
That opens a huge can of worms that in the end probably doesn't have
much audible impact, but it's enough for me to know that I would prefer
the DC ONE.

To sum it up, there are two problems to solve. Attenuation on the
amplifier (which the D75 solves) and voltage drive from the preamp. The
easiest way to get voltage drive from the preamp is to add an in-line
amplifier. 30dB of fixed gain with more than 120dB of dynamic range would be sufficient.

To answer your other question....tri-amping with the 40W D75
would be just as loud as a 120W amplifier on your khorns. If you get
the proper voltage drive from your preamp, you'll be able to do 120dB
peaks (the limit of your speakers) with a noise floor below 20dB.

[Rudy81]

DrWho, good idea to post the e-mail. I can't beleive others have not tried to tri-amp their Khorns and have not solved all these little issues yet. Now I have to look into in-line amplifiers. This is getting complicated.....

[DrWho]

Well if you purchased an active xover like the DEQX HDP-3, then you wouldn't have any of these issues []
http://www.deqx.com/products.php
($4000 USD after the online discount)

Everyone else that has been doing active has taken the dynamic range hit by not having the full preamp drive. Basically, this just means you need to turn up the levels if you want to jam out (at the expense of a little hiss) and then turn the amps down for more critical listening if you want to get rid of the hiss completely.

[Rudy81]

Well if you purchased an active xover like the DEQX HDP-3, then you wouldn't have any of these issues
http://www.deqx.com/products.php
($4000 USD after the online discount)

Everyone else that has been doing active has taken the dynamic range hit by not having the full preamp drive. Basically, this just means you need to turn up the levels if you want to jam out (at the expense of a little hiss) and then turn the amps down for more critical listening if you want to get rid of the hiss completely.

Well, I just ordered one! Nah, just kidding. YGTBSM, $4000.....I don't need to go active that bad!

So the problem is my constant quest for perfection. Darn it, I want it all!

Honestly, I think you should work on that 'gadget' you were talking about. I think you could get at least buyers from the forum....perhaps many from the outside.

I rarely get up past 95dB SPL in my room, and that's just a rough guess. I am more inclined to do lower volume, more critical listening which is why I hate any noise in the system. I'm looking into the D-75 amps as I type this. I'm also researching 'dynamic range' so I can learn to speak your language better and get more from your excellent comments and advise.

[Rudy81]

Look at what I found: http://www.samsontech.com/products/productpage.cfm?prodID=1699

Perhaps if I can boost the input signal to +4dBu rather than the -10dBV, I can take care of all this gain B.S.

[DrWho]

Ya, one of those would be perfect for boosting your preamp output
into the input of the DC ONE. If you wanted to use your existing
consumer amplifiers, then you would need another 3 boxes to convert pro back to consumer (I think you
might be able to do it with just 3 total, but I'm not sure how they're
wired up inside). The box I was going to make would essentially be four
of those boxes combined into a single unit, but with the addition of a
ganged volume control.

Dynamic range is the difference between
maximum output and the noise floor. So 120dB with a 20dB noise floor is
a dynamic range of 100dB.

[Rudy81]

DrWho: Excellent. However, if I just use my consumer amps with the DC-ONE outputs, what would happen? Would I still have the hiss issue? Why the need to step the output back down to -10dBV? Hang in there with me, the gerbils in my head are turning the wheel as fast as they can.

[DrWho]

Don't you already have hiss with your DC ONE feeding into consumer amps? []

The problem is the noise floor of the DC ONE is -90dBU and that's getting multiplied by the gain of your consumer amp which has no volume control.
Most consumer amps have more than 30dB of gain which puts you at -60dBU
or 39dB SPL for a 110dB speaker. Also, a full +4dBU output from the DC
ONE will result in over 12dB of clipping in the amp because it hits
full output by -10dBV.

If
your consumer amp had a volume control, then you could attenuate the
noise floor of the DC ONE. If you wanted to get the full 111dB of
dynamic range out of the DC ONE, then you would need at least 12dB of
attenuation (to convert from +4dBU to -10dBV). That would put your
noise floor at 27dB SPL and the max output to whatever your amplifier
can do. Usually a consumer amp can deliver more than the speakers can
handle, so you could get by with more attenuation on the amplifier (say
19dB) to bring the noise floor down to 20dB SPL. This is of course
assuming the amplifier you chose has a noise floor lower than that.

However,
if you attenuate the amplifier to where +4dBU from the DC ONE gets your speakers to their
max output, then you're gonna need a preamp that can provide +4dBU to
the input of the DC ONE in order to drive those SPL's.

Maybe this article will help a bit:

http://www.prosoundweb.com/article/how_do_you_set_system_gain_structure/

I've actually not read the article, but the pictures illustrate what I'm talking about.

[Rudy81]

The best thing to do then, is to stay 'pro audio' once I get to that level. Seems the best thing to do is to go from my consumer preamp to some transformer like the Samson, then the crossover and then to a pro amp. That should take care of all the issues.

Sure is a lot of 'stuff' in the signal chain. Although, the passive network is no longer there.

This is going to have to be a much longer term project than I anticipated. I think what I need to do is look for a couple of well priced D-75's and something to power the LF section, all in pro amp line.

DrWho, thanks again for all the explanations and help.

[mikebse2a3]

Although, the passive network is no longer there

Hey Rudy

After thinking about this it dawned on me that your passive crossover (I would estimate to match the Khorn LF) is attenuating the JBL 2470 midrange by approx. -12db. That means your systems noise floor will be lowered by this much also in it's audible range and thus you might not have any noise issues when the amplifiers run through the passive crossovers but when you wire the amplifiers directly to the driver(for active operation) the nosie floor of the amplifiers could be causing a real issue.

Again the best way to test for this is to use a shorting plug(to minimize any noise leakage into the amplifier through the input and thus hear only the inherant noise floor of the amplifier's design) on the input of the amplifier and then wire the JBL 2470 directly(or through your safety capacitor) to the amplifier and then turn on the amplifier and listen for the noise level under this condition. If the noise level is objectionable under this condition then the amplifier's inherient noise by design prevents them from being a good match with very high efficiency drivers in an active system. Note: All hookups should be made prior to turning the amplifier on.

mike tn

[Rudy81]

What is the general concensus on the dbx Driverack PA+? I note that it has a -10dBV/+4dBu switch....still reading up on that one. The other contender is the Behringer DCX-2496.