System Flexibility

[colterphoto1]

I've been experimenting with my Klipsch Kp682 (dual 18) subs and KP362 (full range 15" three way) cabinets. I thought I'd open a thread here to discuss some of my findings and thoughts so that you all could join in.

What I'm trying to do is to allow some system flexibility and experimentation with the least possible cost and messing around. Currently I have an amp rack with three Crown MicroTech 1200's, a Rane AC23 stereo tri-amp unit, and patch bay.

The original thought was to bi amp the stacks using one 1200 for subs, one for mains, and another my Klipsch monitors.

One problem though- the Rane in bi-amp mode wants you to use the MF and HF sections, which means the lowest crossover point is 190 Hz- too high for the 18's and it limits the bandwidth of the 15" in the 362's too much.

One way out would be to build a little summing box per Rane's instructions which would electrically sum together the MF and HF for my 362 cabinets, allowing the sub channel to power the 682 bins at a nice 80-120 Hz crossover point. These boxes would use a bunch of XLR connectors and cost a bit of money and time to build.

An ebay seller has several Rane AC22B stereo two way crossovers, which would immediately solve the problem for about $115. This also has a summed mono sub output so in some instances when I wanted to take only one truckload of gear I could carry two mains and one sub and make do.

Another thought has crossed my mind. The KP362's have a jumper on the input cup that can be cut and make that cabinet bi-ampable, therefore creating a tri-amp stack. I could use a smaller amp like BGW150 for the HF section and use this setup for bigger gigs. Also I have two pairs of the mains so it would be possible to use one 362 15" only for my 'sub' and biamp the other 362 cabinet. This would be easy to load in the truck (the big 682's are beasts), and I could carry all four mains, amp and processing racks in the truck and load/unload pretty easily. In the case where I wanted to use both sets of 362's for mains, I could just jumper the MF/HF sections of the input cup together with a neutrik cable.

Or if I wanted, I could just take the bi-ampable set of 362's out for clearer sound than running the full range pair.

Does any of this rambling make any sense? I'm trying to balance cost, complexity, and flexibility.

Thoughts?

[jacksonbart]

First thing I am giong to do when I get home tonight is try to touch my toes. That and drink a beer.

[bhendrix]

Hi Michael,

We took a little different approach with our KP-682's and KP-3002's with Crown XTi 1000's. One XTi for sub, one for KP-3002 full range, and one for monitors.

The 3002's (or KP-362's) lose a lot of low end when pole mounted. Need the subs (either KP-682 or KP-4000) coupled with the floor.

Advantage of XTi over Micro Tech 1200:

Weight - XTi is 18.5 pounds, 1200 is 41 pounds. With three amps, that's a 67 pound savings, 56 pounds of amps instead of 123 pounds. Remember, we're over 50 now. []

On-board DSP -

With XTi, I can preset hi-pass filter at 35Hz with 48db slope to protect 682 woofers. For subs, low-pass at 90-100 Hz for "crossover".

Full range cabs can hi-pass at 90-100 Hz to reduce distortion.

XTi have built-in user selected clip limiter too. No more blown tweeties.

Multiple presets on DSP so you can have amps pre-configured for multiple different speaker setups. Select preset for each gig requirement.

With DSP on board, other equipment can stay home. Lighter rack. Remember, we're over 50. []

[colterphoto1]

18 pounds = no balls

I know, I'll have to try it out for myself some day.

Anyone got a spare $400?

M

[michael hurd]

The on-board DSP is nice, but the Crown XTI did not like driving a 4 ohm load very much at all, plus the power output down @ 20hz is pretty dismal, although NOT an issue with pro 'subs'. For 8 ohm nominal loading mains and pro 'subs' the XTI does great.

When you are moving gear all the time, lighter weight equipment is sure nice. Even for me, I will pay more for a lightweight switching ps amp than a linear power supply amp.

[bhendrix]

but the Crown XTI did not like driving a 4 ohm load very much at all, plus the power output down @ 20hz is pretty dismal

Hi Michael,

Remind me where this came from. I remember reading it somewhere, but don't remember its source. I've been driving 4 ohms loads with absolutely no problems at all. I don't understand what the problem (real or perceived) may be.

Thanks!!

[michael hurd]

18 pounds = no balls?! !? \

Hmm... how about some tests. http://www.avsforum.com/avs-vb/showthread.php?p=13869426#post13869426

Keep in mind these were tests with sinewaves and a variac to hold input voltage constant. Actual 'music' will result in higher scores. In 8 ohm per channel the XTI fared decent, with 252 wpc at 1000hz. At 4 ohms, power at 20 hz took a huge nosedive, as this amp has aggressive protection built in. Power at 1khz is 388 wpc.

Compare this amp with a 21 pound QSC PLX 3402.

http://www.avsforum.com/avs-vb/showthread.php?p=12937520#post12937520

PLX does well at 1 khz into 8 ohms, with 661 wpc. 4 ohms at 1khz, 1095wpc. 2 ohms 2073 wpc.

[michael hurd]

but the Crown XTI did not like driving a 4 ohm load very much at all, plus the power output down @ 20hz is pretty dismal

Hi Michael,

Remind me where this came from. I remember reading it somewhere, but don't remember its source. I've been driving 4 ohms loads with absolutely no problems at all. I don't understand what the problem (real or perceived) may be.

Thanks!!

Bill: the XTI did not like driving a resistive load that is 4 ohms, keep in mind there is only very few times a speaker or sub will approach it's impedance minima. I can think of a few instances where this would result in a change in effective FR of the cabinet.

For instance, a pro sub that is vented, will have a high impedance above and below tuning, with a minimum at tuning. Most "pro" subs are tuned high, commonly 35 hz or above. This means that if you have spectral ( source ) content with a high level of 35 hz bass, and the effective impedance at this frequency is low, it will cause a shift in FR, the amp cutting back in power output.

This is an interaction between source, amp and cabinet. Some cabinets may be affected more than others, particularly those that dip below 6 ohms in the bass region.

When you don't have a lot of content that is in the region of the impedance minima, it should not come close to kicking in the protection circuitry. You could almost liken the effect to a compressor, but one that only works when power demands are high, and impedance is low.

[bhendrix]

the XTI did not like driving a resistive load that is 4 ohms

Oh, that's right, Michael. I remember now. I talked with the Crown engineers about this and they said the amp should never see a pure resistive load when driving a speaker, so the protection circuit kicks in. A properly operating speaker will present a reactive load to the amp in addition to the resistance. If resistance only, the amp says there's a problem with the speaker. The Crown engineer said that the person doing the test apparently didn't understand the amp design.

I've been driving the heck out of these little XTi 1000's in a PA setting outdoors at camp with KP-682's and two pair of Ki-362's and the little Crowns have performed flawlessly with both live sound and pre-recorded tunes.

Here's the response from Crown:

All,

We appreciate your patience while we got some data together to appropriately answer the question posed. In response to the question regarding 20Hz power on the XTi1000:

The XTi series of amplifiers was completely designed, tested, and is manufactured in Elkhart at our factory. When the XTi (also CDI and DSI which share a common platform) was designed and released for production we absolutely tested each model thoroughly and documented all of the results. The reason it took a few days for us to respond with power numbers is because we wanted to retest the amplifiers and have fresh data to compare with your numbers as sometimes things “drift” after production starts. We have shipped over 100,000 units since this product launched so it was imperative that we test a unit that was representative of your amplifier.

With that said, our engineers tested a new XTi1000 production unit two different ways:
1. 120V regulated power source
2. An unregulated power source at the end of a 50ft extension cord – our engineers read 115V

All of the power numbers were measured at 0.5% THD.

The amplifier put out 400W @ 4ohms at 20Hz with the 120V regulated power source and put out 220W @ 4ohms at 20Hz with the unregulated power source. Can you please tell us what your mains power voltage was? Based on our findings we feel your mains might have been well below 115V which would also explain what you thought was an oscillation. This was actually the DC/Under-Voltage protection activating at 20Hz due to sagging mains.

We also tested the amplifier at 30Hz with the same two conditions. The amplifier put out 425W @ 4ohms with the 120V regulated power source and put out 380W @ 4ohms with the unregulated power source.

It's worth noting the 220W number at 20Hz. We expect the 20Hz power to be decreased when compared to 1kHz, but not by this much. What we found is that our DC/Under-Voltage protection is a little bit too aggressive at 20Hz. We will add this to our ongoing improvements list for the product. It hasn't been a problem in the real world because the circuit doesn't activate with a loudspeaker connected, only with a resistive load.

Again thank you for your patience while we have gathered the above information. Please let us know if you have further questions regarding this subject and we look forward to hearing what your mains voltage was.

Thanks,

Andy Flint

[michael hurd]

They shoud work fine for most applications, but they won't like your typical HT sub with low impedance, heavy magnet, and high EMF. BTW, the fellow doing the tests is a factory trained Crown technician. The XS series from Crown tested MUCH better, although it is a different architecture than the XTI.

The test is linked above, page 1 has a master list and links to all the amplifiers tested.

Reference mdeneen's tests on the XTI as well, he had the power supply squealing like a pig trying to test it.

[SWL]

Michael,

I have been powering the bass on my RF-7's with XTI-2000's with what sounds to me like it is doing it very effectively. What is your opinion on this?

Note: Power hungry, low impedance dippin' RF-7's......[]

[michael hurd]

Bhendrix, I read the same song and dance before, it was linked on the AVS forum.

"With that said, our engineers tested a new XTi1000 production unit two different ways:
1. 120V regulated power source
2. An unregulated power source at the end of a 50ft extension cord – our engineers read 115V

All of the power numbers were measured at 0.5% THD.

The
amplifier put out 400W @ 4ohms at 20Hz with the 120V regulated power
source and put out 220W @ 4ohms at 20Hz with the unregulated power
source. Can you please tell us what your mains power voltage was? Based
on our findings we feel your mains might have been well below 115V
which would also explain what you thought was an oscillation. This was
actually the DC/Under-Voltage protection activating at 20Hz due to
sagging mains.

We also tested the amplifier at 30Hz with the
same two conditions. The amplifier put out 425W @ 4ohms with the 120V
regulated power source and put out 380W @ 4ohms with the unregulated
power source.

It's worth noting the 220W number at 20Hz. We
expect the 20Hz power to be decreased when compared to 1kHz, but not by
this much. What we found is that our DC/Under-Voltage protection is a
little bit too aggressive at 20Hz. We will add this to our ongoing
improvements list for the product. It hasn't been a problem in the real
world because the circuit doesn't activate with a loudspeaker
connected, only with a resistive load.

Again thank you for your
patience while we have gathered the above information. Please let us
know if you have further questions regarding this subject and we look
forward to hearing what your mains voltage was.

Thanks,

Andy Flint"

The amplifier was in fact tested while connected to a 30 ampere variac on it's own dedicated 30 amp line, with heavy gauge wire. Amplifier input voltage was held constant to 120 volts, throughout the test. Chasw98 who did the tests is a Crown factory trained technician, used the same test methodology with all the amplifiers he tested. The load bank was cooled with a water and ice mix with the actual DCR measured before and immediately after test.

Maximum voltage before the amp started to collapse the waveform and add distortion was noted, and acutal power was derived from the voltage^2/RE.

Crown didn't say much on thier own forums after the test at all. The XS amplifiers tested much better.

[DrWho]

I've got an Xti in my arsenal now...gonna have to run some power numbers of my own...maybe see how easy it is to mod the protection circuit too. It sounds like a time constant thing to me.

Back to the original topic...it sounds like your Rane is the thorn in the side. I might suggest looking at other alternatives...don't you already have a driverack?

[colterphoto1]

Yes Doc, I think getting the Rane AC22B would solve a lot of problems. At $115 on eBay it's a good purchase, and I could sell this un-needed AC23 for about the same amount.

The DriveRack is definitely an option, I should take it in the shop and do some setups with various speaker combinations just for the practice. I've wanted to stay old school with the knobs, but really once a system is dialed in there's very little need to tweak based on the venue. Getting used to the DriveRack's optimizer function with PEQ and the limiter/feedback functions would also be helpful in a PA situation. Only the Driverack is usually at the amp position by the stage and not possible to tweak during a show.

[michael hurd]

Colter: Is your DBX Driverack the 260? If so, why not put the driverack out in the rack, hook up a cable, and you can tweak with a computer via cables and software, same as the Behringer DCX 2496.

[DrWho]

I think he's got the DriveRack PA:
http://www.dbxpro.com/PA/PA.htm

It's got the worst interface in the world...very hard to navigate and not something you want to be dealing with when in a rush before a show.

But like Colter says, it's a set and leave kind of thing...and most all the settings can be set ahead of time for various speaker combinations. The only thing I could see tweaking at a show is relative volume levels (probably easier to do on the amp) and time delays (like if the subs gotta be positioned way different than the mains, etc...). But that's getting tweaky...you could totally get by without making any changes.

Btw, I've been to dozens of outdoor concerts where the system was dialed in with the Auto-EQ utitlity...When I'm in charge of the setup I avoid that feature at all costs - there's just so many bad things it can do to the sound. [:@] (It's an awesome concept though...they just don't pull through on the actual performance part of it).

[bhendrix]

Hey, Doc, have you figured out the "truth" about the XTi's yet. I'm having a real hard time believing that the folks at Crown would intentionally produce a comprimised product. I've been driving the little XTi 1000 into the KP-682's and Ki-362's outdoors with CDs with plenty of deep bass and these little guy sound great. They sound great on my Jubilees, too. I can't figure it out. [*-)]

[DrWho]

Well thus far I can definitely hear the hiss...and it very certainly
sounds like the digital noise floor of the DSP (which is good news
because that's easy to mod).

I haven't had a chance to do any
power testing yet...I really need to use an oscilliscope for that (and
not a multimeter). I've also got to put together a load cell for eating
that kind of power and maintaining a reliable resistance, etc etc...
It's actually going to be quite a bit of work.

However, I can say
that they can totally rock the house with my Chorus II's. I haven't
gotten full throttle yet because I'm worried about the neighbors (even
though I'm in my own house) [A] They sound fine at lower listening
levels except for the loss in resolution.

To be honest, I think there might be some merit to the
fact that it limits its power at 20Hz. Based on Crown's comments, I can
see how they didn't see it as a design flaw, but I can also see how
it's bad that it can't drive a resistive load. They probably have a
circuit that compares the expected voltage at the output against the
actual voltage (which would indicate a short circuit condition)...that
circuit probably has a time constant built-in for making it more
stable, but in the process they probably didn't make that time constant
long enough to allow 20Hz without the back EMF from the speaker its
driving. There's gonna be a crap load of back EMF from a subwoofer
driver at 20Hz (lots of cone movement), so I can see how it wouldn't
trip. In fact, it's gonna be rare that you've only got a 20Hz sinewave
playing too....so anything with lots of frequencies should be able to
provide that circuit with enough information that it knows it's not
driving a short.

So in a way, I would expect that both worlds are
true. It can't drive a resistor to full power, but it should be able to
drive a speaker to full power no problem. Some of my tests were going
to involve multiple sine waves and even speaker loads (another reason I
need a scope). Also, even
a "measley" 220W at 20Hz is gonna be sufficient for efficient speakers.
You won't be coming anywhere close to 200W continuous (or at least you shouldn't be). You might see 200W on a short peak depending on the efficiency of your mains (and how dynamic your music is).

[bhendrix]

They sound fine at lower listening levels except for the loss in resolution.

Is the loss in resolution a function of the higher noise floor?

[DrWho]

Yeppers