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  1. #1
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    How to determine Amp working hard/Speaker needing more power

    I have B&K 7270 200 X 7 at 8 ohms and 375 X 7 at 4 ohms power amp and Paradigm Signature S-4 Speakers. The preamps min volume is -96 db. I dont hear any sound from the speakers until -60 db.
    My max volume is at -15 db. I am not sure If I am driving my speakers/AMP hard. at -15 db I dont see any clipping. As I dont have a sub right now I feel base is not powerful enough. I am soon going to get a sub anyway.


    One more thing is B&K amp is getting hot. But I see no clipping until this point. Does the life of the amp has any impact because it is getting hot.

    My question for you guys is how do I determine when I am running the system too hard.

    Another thing I am planning to do in next few days is to bi amp my speakers. I am only using three channels right now. L,R and center out of 7 channels available in the amp.
    I intend to use two more to biamp my L R speakers.

    I know power usage in the amp will increase but does the amp sustain the load. Have anybody done this before let me know.

    Thanks

  2. #2
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    Just now I read in Anthem site that power is not wasted.


    Q5: Doesn't passive biamping waste the amp's power because each channel still has to amplify the full range signal and not just the highs or the lows?

    A: No. With the jumpers removed on a biampable speaker, the impedance of each section is not the usual 4 or 8 ohms, but several hundred if not more at the frequencies that the amp is "not supposed to be amplifying". Higher impedance means less current draw. No meaningful amount of current, no wasted power.

    According a recurring audio-myth, only an active crossover should be used for biamping, in order to split the band before the power amp instead of inside the speaker, thereby reducing the amount of work each amp channel has to do. While active crossovers do have their place in PA systems, it should be noted that equalizers are also a part of it.

    A generic active crossover on its own merely divides the audio band into smaller ones. The carefully custom-designed crossover in a high performance home audio speaker does a lot more. It is responsible for correcting frequency response aberrations of the individual drivers, maintaining phase coherence between drivers, optimizing off-axis response, balancing levels between drivers, setting up impedance, at times improving woofer performance by rolling off not just the top, but also frequencies that are too low and cause it to misbehave, and other things that vary according to model.

    Tearing out the speaker's own finely-tuned crossover to replace it with an active crossover with generic controls almost guarantees that, just for starters, frequency response will be altered. Different sound doesn't mean better sound. Using the passive crossover in the speaker is indeed the correct way to biamp.

    (What's biamping? It's using one amp channel for the speaker's mid-high frequency drivers, and another for the low-frequency drivers. The speakers must have separate inputs for this - be sure to remove the jumpers from the speaker inputs first or amp will become instant toast! If one amp starts running out of power, usually the one driving the woofer, then the other side remains clean instead of becoming part of the problem, a double-win. This is the very idea behind bass management and powered subwoofers in home theater systems.)

  3. #3
    Just passing thru topspeed's Avatar
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    Quote Originally Posted by pdhanwada
    I have B&K 7270 200 X 7 at 8 ohms and 375 X 7 at 4 ohms power amp and Paradigm Signature S-4 Speakers. The preamps min volume is -96 db. I dont hear any sound from the speakers until -60 db.
    These numbers are completely arbitrary and vary from manufacturer to manufacturer. Ignore them.
    My max volume is at -15 db. I am not sure If I am driving my speakers/AMP hard. at -15 db I dont see any clipping. As I dont have a sub right now I feel base is not powerful enough. I am soon going to get a sub anyway.
    S4's are rated to 62 hz, is it any wonder why you're not getting enough bass? It is only a standmount after all and therefore inherently limited. If you want more bass, try placing the speakers closer to the corners for some reinforcement until you get the sub.

    As for driving your speakers too hard, use your ears and some common sense. If you hear clipping and/or compression, you are driving the amp too hard and likely risking severe damage to your speakers. Plus, at 91 dB's sensitivity, I'd imagine it would be unbareably LOUD at this point as well unless your listening room is ginormous. Banging your amp against the rails is detrimental to both amp and speakers.

    One more thing is B&K getting hot. But I see no clipping until this point. Does the life of the amp has any impact because it is getting hot.
    As a class A/B amp, it will be somewhat wasteful by nature (heat is simply wasted energy, nothing more). That said, electronics in general abhor heat. Your speaks are pretty efficient so I'm surprised it runs hot. I ran a B&K for 16 years driving 4 ohm speakers and never encountered anything untoward nor do I remember it running hot.

    My question for you guys is how do I determine when I am running the system too hard.
    Use your ears. If you're into clipping, you're running it too hard.

    Another thing I am planning to do in next few days is to bi amp my speakers. I am only using three channels right now. L,R and center out of 7 channels available in the amp. I intend to use two more to biamp my L R speakers. I know power usage in the amp will increase but does the amp sustain the load. Have anybody done this before let me know.

    Thanks
    Plenty. Does it help? You tell us. I've never been a proponent of biamping, particularly with the same amp. SS on the bass and tube up top? OK, I can understand that reasoning. However, unless your B&K has dedicated power supplies for each channel (IOW, it's a true mono design for each channel, which it may be), all you're doing is draining the power supply by hooking up more channels. Even if it is a true mono design, I think you're going to be challenged to hear any improvement. Of course, you'll be able to feel the difference immediately as your wallet will be considerably lighter after buying extra wire. Still, it's your money so do whatever you think is best.

    Hope this helps.
    "If you can leave black marks on a straight from the time you exit a corner till the time you brake for the next turn, then you have enough horsepower." Mark Donohue

  4. #4
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    Thanks for your reply.

    The bass is good. I am able watch the movies without the sub and able to feel the explosiions and the gun shots and the car chases.

    What I meant it is below 40Hz the response is -10db. By adding a sub and crossing over at 60Hz I should get better bass than what I am getting now. That is not at all a worry for me as of now.

    Comming down to Amp getting hot. Hot is a relative term. I would try to measure it in this way. I am able to keep my palm on the amp for about 10 secs. Then I feel like removing it. Does it mean it is hot, warm etc. It is hard to tell when do we say it is hot or warm is a relative term.

    Another thing I observed is whether I run it for half hour or 3 hours, I feel the amp is at the same degree of hotness. In that context I feel comfortable.

    Also another question is should I leave the amp in the running mode or should I switch it off when the preamp is not running.

  5. #5
    Just passing thru topspeed's Avatar
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    Quote Originally Posted by pdhanwada
    What I meant it is below 40Hz the response is -10db. By adding a sub and crossing over at 60Hz I should get better bass than what I am getting now. That is not at all a worry for me as of now.
    You'll want to cross it over higher than 60. My guess is that the S4's roll off pretty steeply so for an optimum blend, you might try a bit higher x-over point.

    Comming down to Amp getting hot. Hot is a relative term. I would try to measure it in this way. I am able to keep my palm on the amp for about 10 secs. Then I feel like removing it. Does it mean it is hot, warm etc. It is hard to tell when do we say it is hot or warm is a relative term.
    That's not hot. That's normal for a Class A/B. Try doing that trick with a pure Class A amp and your palm will look like the Nazi's from Raiders of the Lost Ark!

    Also another question is should I leave the amp in the running mode or should I switch it off when the preamp is not running.
    I've always left my gear on, except for when I leave for a trip. My B&K was pretty much on for 16 years straight and the only thing that happened was the bulb burned out on the power switch. Now, I wouldn't do this with a Class A simply because it consumes so much energy even when idling (they make wonderful space heaters ). There are different schools of thought on this. Some feel the worst thing for electronics is switching them on and off, much like how a car engine suffers it's toughest wear and tear at start-up. Other's disagree.

    I'm just too lazy to turn everything off !
    "If you can leave black marks on a straight from the time you exit a corner till the time you brake for the next turn, then you have enough horsepower." Mark Donohue

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