402a clipping mids & 602b doing same
Posted 06 February 2006 - 08:50 PM
Posted 13 February 2006 - 09:01 AM
More likely it is related to the amplifier being overdriven by the Bose processor. The Bose speakers require some serious boosting a certain frequencies and the processor may be, at those levels, putting out a voltage that is too high for the input of the amplifiers. The input sensitivity of the XLS402 is 31db/1.025 volts and the 602 is 31db/1.26 volts which would be alright in most cases but I can’t say what their processor is doing.
Posted 13 February 2006 - 09:18 PM
Another theory, (this is what I had wanted to find out from the service manual) Is it possible that Bose would use a zener diode and cap as a power limiter? The reason I ask is that they publish in their literature use with amplifiers having a maximum power of 450 watts, but in their service manual they list amplifier power requirements as "unlimited in noncommercial applications" That type of limiter would be somewhat crude, but would certainly get the job done, along with testing amplifier protection circuits. It would appear if that is the case, the crown is functioning properly, exactly as designed.
I should be able to do an unequalized frequency sweep with an ac ammeter connected between the amp and speakers and be able to produce some sort of impedance curve shouldn't I??
I hope this gives you a little more info to go on, it seems that I'm burning off a lot of power somewhere, I just wish I knew where
Posted 16 February 2006 - 04:40 PM
Efficiency, usually rated in percent, refers to how much acoustical output there is in relations to the amount of energy wasted as heat. Basically the lower the efficiency the less acoustical output there is for the amount of power put in.
Manufactures publish this specs as the devices “Sensitivity” with a “db SPL at 1watt/1meter” rating. It is measured using a specific testing procedure sending a 1 watt signal through the device and measuring the acoustical output at 1 meter with a calibrated SPL monitoring system.
So lets take a speaker, Brand X that has a Sensitivity of 97 db SPL (1w/1m) compared to a speaker, Brand Y, that has an efficiency of 94 db SPL (1w/1m). Brand X would be louder, as a matter of fact, it would be twice as loud as the Brand Y speaker as Brand X has 3db more output. If Brand Z were rated for 91 db SPL (1w/1m) it would be 6 db down in output with the same input level as Brand X. This would make the Brand X speaker sound 4 times as loud as Brand Z with the exact same input. Some people would then try to compensate for this mismatch by driving the input to amplifier of Brand Z higher which would only cause the amplifier to go into clipping sooner as the amp is already loaded the same; the Brand Z speaker is just less efficient.
Add to this to any frequency boosting that Brand Z is doing in their Active EQ and all I can say is you would need an amplifier with more headroom (more output power) to keep the amp from clipping.
Posted 19 February 2006 - 10:22 PM
Posted 20 February 2006 - 10:40 AM
The amplifiers are as they are designed.
Posted 19 March 2006 - 09:55 PM
If this is an unavoidable situation with this setup, what is the acceptable limit for allowing the amp to clip? I realize no clipping is ideal, but can the LED flicker occaionally without doing harm to any component? The rate of flicker seems to be less than once or twice per second. Will this do harm over time? Will it shorten the life of the amp?
I got the 901s for free so I'm going to use them in this configuration regardless of this situtation, so I'm just trying to find out how hard I can push this system without doing real damage.
BTW, I'm running this off of a personal computer with the PC hooked to the Bose equalizer, with a Rolls Promatch MB15 between the equalizer and the amp.
Posted 21 March 2006 - 10:24 PM
Posted 23 March 2006 - 03:43 PM
The Bose has a smiley face EQ in that the lows and highs are bosted from the EQ. So it is totaly possible that the Mid/Hi output of the EQ could be boosted to a point of clipping the amp just like the low end has the possiblity of doing. Remember 3db of boost requires a lot more power from an amp.
Posted 24 March 2006 - 12:41 PM
Posted 24 March 2006 - 03:02 PM
Hi Russ, agree with the "crap" comment, but since I had all the components handy, I figured "why not use them". Definitely wouldn't have picked Bose on purpose. Anyway, I did a quick experiment and took the Bose equalizer out of the loop and the amp did not clip. It sounded horrible, but it confirms that the equalizer is the issue. Just going to live with it until I get a chance to swap out the speakers.
Posted 25 March 2006 - 02:42 AM
Mr Glass: sorry to say this, but how long did it take you to figure out the smiley face eq. thing? In my second post on this problem I had listed the eq curve that bose uses with the 901's, you replied with the efficiency topic. I have even went as far as to run a dynamic impedance test to find out what impedance I am driving at various frequencies, You didn't seem interested in the numbers. Between the eq. curve, the impedance curve, and a known efficiency measurement we have a very close estimation of what an amplifier of a given power SHOULD do. I have asked a question that you should be very knowledgable in, and that is in regards to various driver protection strategies, is it that you don't know, or don't realize that it could be a contributing factor? Given your answers to my questions on basic amplifier theory, we can almost be certain that my next amplifier purchase won't be crown. I am a firm believer that a warranty, no matter how long, isn't worth the paper it's written on if the support is worthless. You may indeed manufacture a top notch product, but if you're not up to helping solve a problem that involves your product, then to me your product is worthless. Bose has sent me a complete checkout procedure on their speakers, lets see you send me one on your amp.
To the Bose Bashers: In researching this problem, I have seen more misinformation from individuals looking for instant gratification than I care to talk about. Yes, in a studio setting Bose is the wrong product for the application, the reflected sound principle would be a severe handicap to what is being done, and referring to studio use is a definite cheap shot, and shows an ignorance of the intended use of the 901. The 901 is definitely not the product to have if you are not willing to be patient about putting a lot of thought and some sweat into your setup. Bose feels that placement is important enough to spell out very specifically how, and where to put the 901. (yes for those illiterates there are pictures) I have heard several sets of higher end Bose that were very impressive, and lots of lower end Bose that sound like crap.
A little background on myself: I am vision impaired, and have been so since birth,(no vision in my right eye) and as a result my hearing has become quite acute to time space cues. I am able to walk through pitch darkness and tell where obstacles are by listening to echos of normal room noises, Tall bridges bug me because there is no sound reflection from the floor or ground, making me feel as if nothing is under my feet.
Bose, When set up properly are some of the only speakers that are able to remove the auditory cues, and almost make me feel as if I am really there. To me the walls disappear. in my opinion, standard cabinets are a little too directional, the highs seem to be too "located" almost like mini stages all to themselves. I can tell exactly where in the room the drivers are located. The mids and bass seem to be coming from someplace totally different from the time space cues (highs)
In closing, To me pure sound pressure isn't important, presence, ambience, and tonal balance are. Should the individual who also had the same problem as myself decide to spend a little less time "Bose bashing" and a little more time enjoying his system, and setting it up properly I may be inclined to share some of what I have learned about setting the 901's up to demand a little less power in the range that causes the amp to clip. I enjoy my 901's very much, someone else might not. That's their right. Some circuits don't work well together. The 901, and xls combination might be one of those cases. They worked great with the yamaha, and so-so with the crown, who knows?? might be the fault of the bose, might be the fault of the crown. Sure would be nice to know for sure. It's not worth my time to try to sort a problem out with people whose minds are already made up.
Posted 12 April 2006 - 04:06 PM
There was no intent on my part to bash any product. As for the others if they had gotten into a Bose Bashing Session than I would have cut them off. However they are intitled to their opinions just as you are.
Now for the reputting of my knowledge or the quality of our product.
This forum is not the place nor will I say anthing else on the matter other than if it continues I will cut you off.
Posted 20 October 2006 - 04:48 PM
One very weird thing I found when I was experimenting is that I could plug my iPod into this contraption and it sounded great and did not clip AT ALL. Go figure.
Anyway, thanks for everyone's help and comments.