9 replies to this topic

[1001US]

Allright. I run a small sound system, at least in my eyes.  I have four 18" p.audio challenger series drivers, loaded into custom folded horn cabinets for my bass. They run around 650 watts RMS, 1200 peak each. Until about two weeks ago I only had two of the aforementioned drivers, loaded into some regular old reflex cabs that were probablly too small for these big drivers. Anywyas, I drove those all this summer off of a crown XLS 602b at 4 ohms mono bridged with no heat issues. I did however have a slight popping issue when driven at very high volumes, but I'll discuss that more in full below!


Anyways, I loaded these drivers into the new large folded horn cabs, purchased yet another crown XLS 602b, and now have two drivers per amp, creating a 4 ohm load. Yeehaww. I of course first experimented with these in my basement (much to my nieghbors pleasure), and noticed some wierd things going on.


FIRST of all, when I drove a singular cabinet off of the amp (8 ohms, mono bridged), I could drive the speakers all the way out to peak without any popping noises, and thats around 1200 watts or so on the XLS 602b at 8 ohms... so yeah thats peak with no popping. However, when I hooked the two cabinets up in parallel, one cabinet would begin to develope a "pop" when driven close to the amplifiers peak (1680 watts).

This popping would alternate as to which cabinet "popped' based on how I switched my wiring. I at first assumed it was my cables, as the problem occured only in one certain cable. I was piggy backing bannana clips at the time (I run two cables out from the amp to my bins, instead of bin to bin paralleling), so I decided to swap the bannana clips positions, and it was not one of the cables, it was whatever clip was further out. Ok, I figured that maybe it was a contact issue. I took the two cables, put one into the bannana clip, soldered the two lines together immediatly after the clip (and did a good job ). Sure enough, the pop still developed, and it was certaintly not the cables. I even took my ohm meter and tested it, and saw equal resistance accross both cables from the banana clip. Since whomever answers this is going to make sure i'm not an idiot, i was using 12 guage cable, so it should be able to handle that much power.

So, what would cause the popping? I am led to believe it's the amplifier, as I can drive the cabs out to *beep* near their peak at 8ohms, but when paralleled an issue developes.

SECOND I ran two bassbins in parallel last night off of one XLS 602B for a small club gig, and ran into a whole new issue besides the popping. Now I had heating issues. After being run for three to four hours or so, without being run towards clipping (due to pops in the speaker), the amp started to overheat. The fault light would come on, and the speakers stopped making noise. Disconnect the speakers, still faulting, so it was something internal. Give it a few minutes, it would cool down and I could return to driving them. I encountered this issue a few times before I finalyl decided to just not deliver a very desirable level of bass, and sure enough everything was kosher as far as heat goes. The crowd wanted more bass though...

Now I drove two of these same drivers before this at outdoor events all night (slightly under peak due to popping), with no heating issues, however oregon gets *beep*ing cold at night... so I doubt it's a cabinet related issue.



This lead to my final conclusion and question:

So, what it appears to me, without taking in the science of it all, is that the XLS 602B just can't deliver the power I'm trying to pull from it without overheating. It's rated to deliver 1680 watts at 4 ohms mono bridged, but when the speakers impendances dip (probably bringing it down to 3.3 ohms or what have you) the xls 602 just can't handle it probably, causing the popping noise and lots of heating issues. So, here's the good news. I have a CE2000 I use to power my tops, and I just purchased one of the XLS 602's and can still trade it in for another CE2000. The CE2000's power rating is more towards where I want it, and appears to have a vastly superior dampening factor. I can also take the XLS 602 B I am stuck with and power my tops with it. My tops are JBL TR225s, biamped cause the horns don't really suck, JBL just used a *beep*ty crossover network (Don't believe it? It uses the exact same horn compression driver as the MPRO series, 2412H)


...and the question... (besides if I'm 100% wrong in the above)


Would two crown CE2000's at 4 ohms mono bridged perhaps better serve me than the CROWN Xls 602B?




Thank you very much, and I really appreciate your time in reading my novel. I really hope a crown technician can help answer my question, as I really want to get the information straight from the horses mouth.

[buckeyes]

sounds like the problem i'm kinda having running a xls602 into 2ohm stereo this thing is a piece of junk does nothing but overheat and shutdown about every 5 minutes after about a 1 hr of usage the the 5 min shut offs start this is not clipping on either channel but will continue to shutoff the volume dials are set about 1 1\2 on each channel this amp has plenty of power if it could stay running  so i kinda feel your pain i'm lost here also bro maybe a factory problem don;t know wish i had some answers too??   

[1001US]

I'm sure we'll get them all in due time. Your problem is essentialyl identical to mine. 2 ohms stereo = 4 ohms mono bridged essentially... as the two channels of the amp are in series in regards to their ohm rating, hence the wattage of the two channels at two ohms stereo equal that of 4 ohms mono bridged (2 x 2 ohm loads in series = 4).

Makes sense since one channel provides for the positive side of the signal in mono, and other provides for the negative.  Just a guestimate though based on what I've read. I'm wrong at least three times a day, and have only been wrong once today

[DGlass]

There are two points to remember an 8-ohm rated speaker is not always 8-ohms and you need to make sure both input attenuators are set to exactly the same position for Bridge-Mono on an XLS amplifier.

Impedance is frequency dependant on a speaker as it is a reactive load. A speaker will only be it’s nominally rated impedance at one or two frequencies everything else will be either higher or lower. Lower impedances are usually in the lower frequency range of the device. In one speaker (that I know of) the minimum speaker impedance is about 6 to 6.5 ohms. If this is the case the load presented to the amplifier in the lower frequency range is actually about 3-ohms. Two speakers, of the same impedance, in parallel would present about a 1.5 ohm load to the amplifier at the same lower frequencies. Lower impedances allow for more current flow. The larger the current flow the harder the amplifier is working and the harder something works the more heat it produces. Basically the lower, in impedance, the load is the closer the load is to looking like a dead short to the amplifier. If the speakers impedance is low enough the amplifier may not be able to produce enough current to accurately reproduce the audio waveform.

Another thing to note is that since impedance, of a speaker, is based off of the frequency the spectrum of the music would play a major roll in the current load the speaker presents to the amplifier. Hip Hop DJ music would make the speaker present a larger current load (lower impedance) to the amp with it’s synthesized and extended low end than Pop Rock would. Now if you were to boost the lower frequency range so as to get more low end from the system than you would be compounding the problem since the amplifier would be working within the lower impedance range of the speaker a lot more.

The Second point is the XLS amplifiers were never produced with a Bridge-Mono switch and as mentioned in previous postings must be set up the old fashion way with a Custom “Y” cable and the input Level Controls matched. In Bridge-Mono mode one side of the amp is driving half the waveform while the other side of the amp is driving the other half of the waveform. If one side was not matched one half of the waveform could be clipped before the other half. In the case of the XLS it’s best to set the input level controls to full and vary the amp level with the device preceding it. This way you are always sure the amp is set correctly.

A combination of the above could present all kinds of problems. If you need more power I would recommend either getting another XLS amplifier and running it in Bridge-Mono for the other speaker or getting a larger amplifier and running in two channel mode as you are probably overloading the one XLS amp with your two speakers when the amplifiers in Bridge-Mono. The Popping sound is more than likely the amplifier hitting current limiting.

[1001US]

Ok. I'm aware of the bass line issues. I actually mostly work with DNB, and our basslines are ultra thick, sometimes drawn out over an entire bar, and pitch shifting into another note, instead of going silent at all. In essence we put hip hop to shame when it comes to taxing an amplifier.

Anyways, I do run the amp as you suggested. The popping due to current limiting makes sense, however this is noticably before hitting the supposed 1680 watts at 4 ohms mono bridged. I'm also  aware speakers change in impendance over a frequency range, as you folk at crown obviously know.

However, when PRODUCING an amplifier rating at 4 ohms, isn't it normal in this industry to have the amp be able to handle short dips into 3 ohms, with the understanding it's load will infact be doing so? If the amp is rated to handle 2 ohms stereo as well, when 4 speakers drop down to 6 ohms... you get 1.5 ohms accross the amp! I also know all the previous XLS series weren't rated to 4 ohms. Perhaps this amplifier should not be rated that low either? It simply can't take it, and rating it to be able to deliver these power ratings is almost misleading, as it will not deliver these power ratings for longer than an hour at most, and it won't even deliver all the way up to it's full rating at anything other than a PERFECT 4 ohms. That statement however, is debatable in itself, and a perfect 4 ohm load accross the board is such a rare application that I'm inclined to say it almost doesn't exist!


Now I'm aware that we are discussing bass, however, isn't peak power determined using 20hz to 20khz? I'm aware of all the technical side (impendance not bieng perfectly 4 ohms, etc), but so is crown. I see it in all of your other amplifiers, which when rated to 4 ohms, can handle it for extended periods of time, with the power rated, and no popping. THE CE2000 is proof of this.



I've been really proud to use crown in the past. I really like your gear, and I've commited fully to your company. I run only crown amplifiers, and have four of them now, and not a one has cost under $400. The CE2000 and the microtech ran around $600 each! I've invested a fair bit into the company, and upon further expansion will only go with crown amplifiers as well, both for ease of use and the fact I can say "I only use quality crown amplifiers" when competing with companys in my range that use behringer or even QSC. Your name bears weight.

Therefore, I'm just a bit let down by this amp, and it tranishes Crowns image to me. I honestly feel like the numbers were fudged for marketing purposes, so as this amp could compete with other brands budget amps. The competitions amps are not only rated to 4 ohms but handle it without any of the issues I've run into! QSC Remix, Behringer EP... mackie amplifiers...

Luckily, I just purchased one of these XLS 602's very recently, which I will be returning, and upgrading to a CE2000. I already have another CE2000, which delivers the bass I want from my amplifier to these bins perfectly. I'll be moving my one remaining XLS602 over to powering just my mids, at 4 ohms stereo, and if it for some reason experiences overheating here I'm going to be flabergasted. I surely will not be recommending this line of amplifiers to anyone however, because both your answer as the technician, and from the experiences of myself and others I have now read, this amp hoesntly deoesn't seem to live up to 4 ohm bridged rating it supposedly can handle.

I'm sorry if any of this blame is placed directly on you, as I'm sure the cause of it is not a technicians fault but a marketing fault. So, I'm sorry if you personally take offense.



I'm just quite let down.


Jesse Nicola,
djownspdx@yahoo.com

[DGlass]

The XLS amplifiers are entry level amplifiers. If you need the performance of a high end thoroughbred then you should move up "at least" one model line to the Xs series.  Expecting the same performance from a lesser cost amp to that of a higher cost amp is a bit much don't you think?  
I wouldn't buy a Pinto when I really needed a Mustang and expect the same performance.
In all aspects the XLS series is a great amp for the price range it is in. You are just taxing the limit of that amplifier with the speakers "you" have selected.
As far as the other amps are concerned I think you need to reevaluate your subjective statement. We have done the testing.

[1001US]

The XS series is rated to only to 8 ohms mono bridged everywhere I have seen documentation.


While it is an "Entry level amplifier" it is meant to compete with other brands "entry level amplifiers" like the QSC RMX series, which actually delivers at 4 ohms mono bridged. This amp is rated to 4 ohms mono bridged as well, but doesn't deliver what you said it should. If the amplifier overheats and has issues, it shouldn't be rated that low. While I'm aware the speakers dip, almost ALL speakers do that.


In using an amplifier like this I could understand degraded sound quality, however popping and massive overheating, means it just can't handle a "4 ohm nominal load" and shouldn't be rated that low. Your muscle car comparison is a very true one, however if I buy a car that says it can run a 15 second quarter mile... and the industry standard is that when you say that it delivers that... and it infact isn't even close, the consumer has a reason to be let down.

Why would you release an amplifer rated to handle these loads, which it can't handle? I'm aware it's rated to 4 ohms bridged and no lower, and if going below 4 ohms is impossible with this amp, than maybe you should pull the 4 ohm specifications off of it. How many speaker groupings, at a 4 ohm nominal rating, actually sit exactly at 4 ohms and never go below it? In my experience... none... and it is consitently posted accross these forums that when you goto four ohms you'll often drop below as the speakers rating is purely nominal.

I'm moving into the CE series to power my subs but I'm very let down by the XLS series of amplifiers. I was hoping that this product would be able to deliver what it said it could. It shouldn't be rated this low, espescially with a 20hz to 20khz frequency rating. If I overheated it just running 40-100 hz, I could only imagine what two full range cabinets at 4 ohms would do to the cabinet.

[DGlass]

Chapter 2 Book 1
If you are not happy with the performance of the XLS with your speakers then I would suggest you move up to the CE2000 as you have mentioned doing. But be aware you are still running any amp at the minimum rated impedance this way. Although the CE would be a better option I would suggest an amplifier were each channel is rated for the 8-ohm power of the speakers and run it in two channel mode for the headroom. I would recommend this with any manufactures amplifier, so as to have system headroom. Although you can run an I-Tech or MA-5k this way all day should you.

I know of no pro audio or pro touring group that would consider running an amplifier at 2-ohms per channelBridge-Mono 4-ohms as they want the headroom offered by not having the amplifier already fully loaded nominally. Without even seeing the impedance curve for your speaker and with just what you have told me It sound like the speakers you have are overloading the amp, in Bridge-Mono, at their nominally rated 4-ohms causing the XLS to go into Current limiting. The loads are floating between the two channels and the impedance appears to be  effectively being dropped well below 2-ohms per channel by the natural impedance responce of the speakers. Check out the article in this quarters Syn-Aud-Con Newsletter entitled “Which Impedance?”. In it they discuss that speaker impedance “is not easily represented by a single number. To complicate things further, most audio waveforms have a constantly changing spectrum. There is no simple way to characterize the impedance of a load, a fact that doesn’t keep people from trying.” Saying that a 4-ohm load is a 4-ohm load, based off the nominal impedance, and that an amp should handle it because it is “rated for it” doesn’t take into account what the load is actually doing.

The analysis of my muscle car comparison is slightly off. It's not the speed at which the car is rated to be able to get to, as even the Pinto was rated to do 100 mph , but how long and how well it can take it. The engine under the hood of the Mustang is designed to handle the high speed output longer while the Pinto would be working extremely hard getting hotter and hotter until it shut down. If the Pinto had all the same high end performance as the Mustang why would anyone want to buy a Mustang.     The XLS series is aimed at a particular market, that being the Entry Level segment, who want to do sound but have a limited budget. We have produced a good amplifier with good performance, compared to other amplifiers in the same market segment, and kept the price affordable. For the speakers you are using and the situation you are using them for…. moving up the line to another amplifier would be a better option.

The Horses Mouth
David L. Glass
Application Support Engineer
Crown Technical Support
IQ/Engineered Systems/Touring

Note: For those of you monitoring this who don’t’ know about Syn-Aud-Con Synergistic Audio Concepts they are the premier organization that does audio training seminars across the world. I am proud to say that I am a graduate of these seminars as well as Crown is a sponsor of Syn-Aud-Con.  Syn-Aud-Con was started by Don Davis (one of the great gurus of audio), back in audio’s infancy, and he has written what is considered the definitive book on Audio System Engineering.

[1001US]

Your right. I was silly to trust that your company would proceed like the rest of the industry, in the standard that when you give something a 4 ohm rating, that it can handle it. It also can handle fluctuations in ohm rating, as we're all aware a speakers value is trulely nominal.

I honestly feel your company has abused this industry standard. While I'm fully aware it's a lot to ask of a low end amp, when it is rated that low I expect it to be able to deliver, much like every other brand out there.


"There is no simple way to characterize the impedance of a load, a fact that doesn’t keep people from trying.” Saying that a 4-ohm load is a 4-ohm load, based off the nominal impedance, and that an amp should handle it because it is “rated for it” doesn’t take into account what the load is actually doing."

I would like to see a "4 ohm" load that it can actually handle, at full power, for an extended period of time without overheating (at room temperature). I also, out of curiosity, would like to know just how many 4 ohm groupings DON'T drop down below 4 ohm. I honestly don't think they're in the majority, however i may be wrong and I magically have the minority of 4 ohm groupings that does infact dip below 4 ohms.

[DGlass]

Your right. I was silly to trust that your company would proceed like the rest of the industry, in the standard that when you give something a 4 ohm rating, that it can handle it. It also can handle fluctuations in ohm rating, as we're all aware a speakers value is trulely nominal.

I honestly feel your company has abused this industry standard. While I'm fully aware it's a lot to ask of a low end amp, when it is rated that low I expect it to be able to deliver, much like every other brand out there.


"There is no simple way to characterize the impedance of a load, a fact that doesn’t keep people from trying.” Saying that a 4-ohm load is a 4-ohm load, based off the nominal impedance, and that an amp should handle it because it is “rated for it” doesn’t take into account what the load is actually doing."

I would like to see a "4 ohm" load that it can actually handle, at full power, for an extended period of time without overheating (at room temperature). I also, out of curiosity, would like to know just how many 4 ohm groupings DON'T drop down below 4 ohm. I honestly don't think they're in the majority, however i may be wrong and I magically have the minority of 4 ohm groupings that does infact dip below 4 ohms.

Well I guess nothing I am going to say is going to convince you we have done the testing against the competitors in the same market and we have produced a good amplifier with good performanceand kept the price affordable. If you aren't happy with an entry level amplifier than move up.

As for the "how many 4 ohm groupings DON'T drop down below 4 ohm" I believe yours are doing it excessivly from what you have said.