speaker ratings.... what do they really tell me??

Discussion in 'Speakers & Subwoofers' started by Corey-Reid, Dec 19, 2004.

  1. Corey-Reid

    Corey-Reid Stunt Coordinator

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    KO, ive just spent the better part of 3 hours reading the primer, and now I think im as confused as ever..... well ok, a little more educated, but still confused.

    I have a boston vr10 center and boston cr6s for my rears. I have a pair of Kenwood floor standing speakers for my mains.

    The kenwoods are rated at 92 db, the vr 10 90 db, and the cr6s at 88db, all into 8 ohms.

    I somewhat understand how the efficiency of the speaker works, but are these numbers always acurate??

    what does the rated input power mean? The kenwoods have a rated input power at 90w, and a maximumm input at 180 watts.

    My RXV 2090 mains have 100w into each channel at .015thd , 8ohms, from 20-20khz. So if the volume is turned up 1/4 max power, how many watts does this mean the receiver is putting out?? I listen to my music when Im alone at very high levels, but i never have it 3/4 of the way up. mostlybecause i would be worried id blow a speaker, or blow the receiver. If the speaker can handle 100w, and the receiver can deliver 100w into 8 ohms, could I theoretically blast it at full volume??

    Sorry these may sound like ridiculous questions, but wow, after reading all of that info, myhead is spinning[​IMG]
     
  2. Nick Bum

    Nick Bum Stunt Coordinator

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    It depends. On the part about how high you have your reciver volum up it really does not matter how high the knob is turned up. Some sources have higher a higher out put and you can have max volume at a lower level on your gain. So it just depends.
     
  3. Jerome Grate

    Jerome Grate Cinematographer

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    The numbers really do mean something. Your maximum Decibels levels are the indicator that gives the maximum output before distortion kicks in. The Kenwood speakers says 92dbs the Boston ctr chnl 90dbs and the Boston surrounds 88 dbs. What you should also take into consideration is the type of speaker and it's usage, the numbers can tell you the most effective way to use them. Are they real numbers, it's hard to say and you can only get a close estimate by using a SPL (sound pressure level) meter. 20-20khz is calculation for high to low range. Some full range speakers can obtain low range bass but most of the time it's about 40hz or so which is high in comparison to 20hz for solid deep bass. The numbers tells you a great deal, I think, but someone here will give you a far better answer than I just did.
     
  4. John Garcia

    John Garcia Executive Producer

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    Those ratings tell you how efficiently a speaker converts the signal fed into sound. The higher the sensitivity, the easier it is to drive. The testing method is standard, 1w @ 1m, and should be fairly accurate. Your room has a huge affect on what these numbers mean though.

    Max input power means something in the x-over or the speaker's drivers themselves can take no more than that ammount of peak power before it fries.


    There's no real way to know, and it's almost irrelevant. If you are comfortable with the level you have it at, and the system doesn't sound strained, don't worry about it.

    I wouldn't shoot for 100% on the dial very often, but the numbers you are asking about will not tell you if you can turn it up that loud or not, only turning it up will tell you.
     
  5. FeisalK

    FeisalK Screenwriter

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    John,


    does this mean that a 90db rated speaker will output 90db if powered by 1W, measured by an SPL meter at a distance of 1m from the speaker?
     
  6. John Garcia

    John Garcia Executive Producer

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    Yep, that is exactly what it means.
     
  7. FeisalK

    FeisalK Screenwriter

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    John,

    thanks. ok.. Theoretically, then, all anyone would ever need would be around, uh.. 20W per channel?

    if a doubling of power gives a 3db increase in SPL

    2W - 93db
    4W - 96db
    8W - 99db
    16W - 102db

    isn't that plenty loud? "reference level" is "only" 85db

    how many db's do you lose with distance? say sitting 2m away from the speakers. i'm guessing not much?
     
  8. Corey-Reid

    Corey-Reid Stunt Coordinator

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    I think this is where some of my confusion comes from. I know that if Ihad a 20 watt amp hooked up to my 12 inch pyle subs I had in my car, I wouldnt get much, but not according to the numbers.
     
  9. FeisalK

    FeisalK Screenwriter

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    Corey,

    I know! practically it doesnt work out.

    Probably because the measurement is made with a sine wave of a certain frequency (I dont know) and that doesnt reflect music as a whole over 20Hz - 20kHz. Also, impedance rating (8ohms) is a "nominal" figure that could go down as low as 2 ohms during music playback - since that's part of the original rating, that affects the power as well (needs more to maintain the same level of output).

    I think if your amp isn't powerful enough to supply the power needed to maintain the same output level, this is when the amp clips (and fries your speaker)

    pretty sure there's some formuale - but i'm too lazy to dig out at 6am [​IMG]
     
  10. John Garcia

    John Garcia Executive Producer

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    Yes and no. That's at 1m or ~3 feet. You have to account for the room size (larger room is harder to fill) and distance you actually sit away from the speakers to figure out how much power will give you reference levels at your seating position. I don't have the formula, but I think SPL drops off by 2 or 3 dB for each additional meter you are away from the speaker. The efficiency also does not tell you how much current a given speaker actually draws either, so it's not that simple to figure out.

    There is a page with a calculator somewhere that does a basic calculation based on your distance and some other specs, that will give you a rough idea of how much RMS power you need, but I don't have the link.
     
  11. Eric Ha

    Eric Ha Stunt Coordinator

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    "isn't that plenty loud? "reference level" is "only" 85db"

    Actually, 85db is just the average. 105db peaks are expected at Dolby reference. This is from Ed Mullen's SVS PB12Plus/2 review:

    "Dolby reference level is defined as 105 dB bass peaks from any surround channel, and 115 dB bass peaks from the LFE channel."
     
  12. FeisalK

    FeisalK Screenwriter

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    Eric,

    even then, you'd need no more than 40W per channel (on a 90dbWM rated speaker, 32W = 105db) and those 105db are peaks (we won't worry about the 115db LFE cuz it's going to be the subwoofer amp that drives it)

    I think this is how receiver manufacturers get away with rating their receivers at 100W per channel and delivering only 40-50W all channels driven 80-20KHz (80 or whereever the xover is)
     
  13. Eric Ha

    Eric Ha Stunt Coordinator

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    Yes, there are many ways to shuffle wattage numbers. Impedance, percentage of distortion, amount of channels driven etc. Peak amperes per channel capability is also something to look for. It is easily possible to get a speaker to squawk out a high spl number with low power, but at what cost to our ears. [​IMG] More power keeps your drivers controlled and not flopping about causing distortion.

    I recently upgraded my front soundstage from an HK reciever with 75 wpc-8 ohm-all channels driven to an Anthem amp with 170 wpc-8 ohm-all channels driven. I have more clarity and punch than before, at sound levels far below reference. The same went for when I upgraded from My 45 wpc HK to the 75 wpc HK.
     

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