Can you expressed Speaker efficiency comparing it to increase in power?

Discussion in 'Archived Threads 2001-2004' started by Chris PC, Sep 7, 2001.

  1. Chris PC

    Chris PC Producer

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    For instance, if I compare a speaker rated at 90 dB anechoic (92 dB room) with a speaker rated at 91 dB anechoic (93 dB room) , with reference to a amplifier of 100 watts per channel. If you power the 90 dB speaker with a 100 watt per channel amplifier, and you power the 91 dB speaker with same amplifier, how does it compare with the 90 dB speaker in terms of watts, for instance, I'm asking for an expression like this:
    Powering a 91 dB speaker with a 100 watt amplifier is like powering a 90 dB speaker with a ??? watt amplifier. "is like" meaning sound output volume, as in a 91 dB speaker powered by a 100 watt amp sounds as loud as a 90 dB speaker powered by a ??? watt amp.
    Get my gist?
    Using a with the same SR 5200 receiver, I compared speakers that only had a difference in efficiency rating of 1 dB and the difference in output at the same volume setting on the SR 5200 seemed quite significant. It took noticably less volume setting to get equal sound out of the more efficient speaker.
    [Edited last by Chris PC on September 07, 2001 at 12:21 PM]
     
  2. Len Cheong

    Len Cheong Second Unit

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    All I remember from reading ht mags is that for every 3db decrease in sensitivity, you need double the amplifier power. So a speaker with a 93 needs half the amp power to drive it as compared to a speaker with a 90 sensitivity.
     
  3. AjayM

    AjayM Screenwriter

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    The difference between those two speakers isn't very big, and barely audible in the real world.
    If you were to compare an 82db speaker to a 92db speaker then the difference's become very clear.
    82db 1watt 92db
    85db 2watts 95db
    88db 4watts 98db
    91db 8watts 101db
    94db 16watts 104db
    97db 32watts 107db
    100db 64watts 110db
    103db 128watts 113db
    106db 256watts 116db
    109db 512watts 119db
    There will always be a 10db difference (I belive that is percieved to be a little more than twice as loud). Of course the above doesn't take into account the physical limits of the speaker or room effects.
    In my room I have a set of 95db effecient speakers with a 400w amp, and not to stir up the pot but I love the sound of a high effeciency speaker with a lot of power behind it, I'm never driving them very loud, so the amps are hardly working and I have just gobs of headroom available. It makes the whole presentation sound "effortless"...
    Andrew
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  4. Randy G

    Randy G Second Unit

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    If you could notice a significant difference between the two speakers, then one of the manufacturers was likely fudging the specs.
     
  5. Ryan Schnacke

    Ryan Schnacke Supporting Actor

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    Powering a 91dB speaker with 100 watts is like powering a 90dB speaker with 126 watts.
    I tend to suspect speaker sensitivity ratings about as much as I suspect receiver power ratings. And it seems strange that so many people get outraged when a receiver doesn't meet its power output spec, but they don't seem care at all about the accuracy of the speakers sensitivity rating.
    If the sensitivity rating is 1dB off that's the equivalent of a receiver with 79% of its rated power.
    If its 2dB off that's like a receiver with 63% of its rated power.
    These are rather sobering numbers that show how important it is to balance our priorities.
     
  6. Chris PC

    Chris PC Producer

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    Both speakers come from the same manufacturer and are in the same line. The PSB Image 5T and 6T. They are very similar, appart from the larger, more efficient speaker having one more woofer operating from 500 hz on down and the enclosure (ported) being about 40% larger.
    Like I said, I noticed a fairly large difference in real world sensitivity. I'd have to compare again, which I hope to do this weekend, but I had to decrease the volume by quite a bit when trying to compare one speaker to another. I noticed it quite well. It was obvious.
    In the real world, at moderate listening levels using my subwoofer, I think the efficiency would afford me more headroom, lower power usage etc when listening to the 91 dB anechoic 93 dB room 6T's compared to the 90 dB anechoic 92 dB room 5T's.
    However, playing the speakers without a subwoofer at high volume I would not see much gains, because the receiver power would be gobbled up by the bass. The 6T's go 3 hz lower, and although its not much, its going to gobble up power.
    5T's 35hz-21,000hz +/- 3dB
    6T's 32hz-21,000hz +/- 3dB
    As you can see, its more the efficiency that I'm concerned obout, as the extra bass is not really significant, in my opinion. I'll take it for sure, but whether I will notice it all that much is another thing. I was considering 4T's at first and they are -3dB at 38hz, so to compare the 4T's and 6T's there would be a difference.
    I'm really undecided. The 6T's are quite large. If they weren't alot larger and didn't cost too much more, then I would not even think about it. I'm demoing 6T's with my SR 6200 this weekend.
    Anyways, thanks for the info.
     
  7. Robert Fellows

    Robert Fellows Stunt Coordinator

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    Chris:
    For the money, I'd get the 5T's
     
  8. Chris PC

    Chris PC Producer

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    How come? The 5T's sound better? Or the 6T's aren't worth the extra?
     
  9. Chuck C

    Chuck C Cinematographer

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  10. ThucN

    ThucN Agent

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    Another possible reason for the large perceived difference in volume level is that one pair of speakers has more bass/midrange than the other pair.
    I've found that, even with two speakers that measure the same sensitivity, if one has more bass/midrange, and the other has more treble, the speaker with more bass/midrange will appear to be louder.
    Interestingly (and contradictory), if a speaker has way too much treble, it'll sound overly bright, and even at a low volume level, I want to turn down the volume because of the harsh sound.
     
  11. AjayM

    AjayM Screenwriter

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  12. Kevin C Brown

    Kevin C Brown Producer

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    Plus, even though they are rated "90" and "91" dB's, it may simply be 90.42357 vs 90.62398 dB as well. And they just round off!
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  13. Kevin C Brown

    Kevin C Brown Producer

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    Chuck- That is a great article. Short and to the point.
    You could also add the effect of speaker impedance and efficiency on a "bridged" amp.
    (There's another thread floating in this forum asking about the sound quality thereof. I missed the THD issue with lower impedance.)
    (My donation just paid off again. I didn't know how drastic the effect of efficiency of a speaker could have either.)
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  14. Kevin C Brown

    Kevin C Brown Producer

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    You could also add the effects of an amp's dynamic headroom on the speakers hooked up to it.
    An "amplifier/speaker interaction FAQ" ...
    [​IMG]
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  15. Chris PC

    Chris PC Producer

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    OK. Points well taken. I had been listening to PSB 5T's connected to a Marantz SR5200 and I had listened to quite a few CD tracks, popping in like 8-10 different CD's. After a while I got used to the different sound levels that corresponded to volume control. We then hooked up a pair of 6T's to the 5200 and playing the same track, I had to decrease the volume noticabley. Playing subsequent tracks with the 6T's, I could always tell that the volume control did not have to be advanced as much in order for sound to be as loud as when playing the 5T's.
    Here are the deciding factors between the 2 speakers, the 5T and the 6T:
    1) Speaker specs:
    5T's 35hz-21,000hz +/- 3dB 90 dB anechoic (92 dB room)
    6T's 32hz-21,000hz +/- 3dB 91 dB anechoic (93 dB room)
    2) Speaker sound. Of course that is the most important, but I can't listen to all my CD's before buying. I have gotten a sense for the sound of each speaker. Not a huge difference, but I believe the 6T has more low end.
    3) Driver complement, and what it means to the sound. More or less distorted? Both have a 1 inch tweeter. The 5T has 2 6.5" midwoofers. One woofer operates from 2500 to the lower limit and the other operates from 500 hz to the lower limit, so a 2 and 1/2 way design. The 6T has 3 woofers, one 2 1/2 way and 2 500hz to the lower limit woofers.
    4) Cost 6T $1169.00 CAD 5T $929.00 CAD
    5) Size, the 6T is 5 inches deeper! 5T=14" deep and 6T=20" deep Its quite large. Not prohibitively so. Any stereo stand
    or TV stand will be 20 " from the wall anyways, but its still a consideration.
    I will be demoing the 6T's at home this weekend. Not sure about demoing or comparing directly to the 5T's. I guess ideally I should, but not sure if thats too much hassle to bring home.
    [Edited last by Chris PC on September 08, 2001 at 08:45 AM]
    [Edited last by Chris PC on September 08, 2001 at 08:53 AM]
     

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