• 11-25-2007, 03:32 PM
    Tetsuro
    Questions about sensitivity and impedance
    I don't get it for now.. (and I think this could interest some people) example:

    For reference we are using a 40W integrated amplifier.. we have a set of speakers nominally '86db at 6 ohm' with suggested power amps of 20-100W, then we have another set with '90db at 8 ohm' with suggested power amps of 30-100W. Now... how could the 90 db at 8 require more power if it is more sensitive and with higher impedance? And.. would the 86 at 6 sound very well with just those 40W or will it require more power than the suggested wattage?
  • 11-25-2007, 05:06 PM
    Mr Peabody
    Good question and I'm not sure I have the answer but here's my opinion. Manufacturer's give an amplifier range as a guide. I can guarantee you it would have to be a very good 20 watts to push an 86dB speaker and I doubt if some one would be happy with the volume they receive. Some of the difference too is the 8 ohm speaker will require a bit more power than one with lesser impedance. Clearly the 90dB speaker will give you more volume than the 86dB speaker with the same amount of signal into both. If you are going to use a 40 watt amp I'd highly recommend the 90dB speaker unless you have a strong sound quality preference. Then if you are using the 86dB speaker I'd suggest a larger amp, unless you have a very small room or always listen at low to moderate volume levels.

    The main thing to remember that manufacturers ratings on some specs are not standard and the ones that are can sometimes still be questionable. In my opinion the manufacturer of the 86dB speaker stretched things a bit.
  • 11-25-2007, 05:49 PM
    Pat D
    Quote:

    Originally Posted by Tetsuro
    I don't get it for now.. (and I think this could interest some people) example:

    For reference we are using a 40W integrated amplifier.. we have a set of speakers nominally '86db at 6 ohm' with suggested power amps of 20-100W, then we have another set with '90db at 8 ohm' with suggested power amps of 30-100W. Now... how could the 90 db at 8 require more power if it is more sensitive and with higher impedance? And.. would the 86 at 6 sound very well with just those 40W or will it require more power than the suggested wattage?

    Well, the first thing is that you are comparing two figures for recommended power ratings supplied by manufacturers. How they were arrived at is anybody's guess without asing the manufacturers in question.

    They really have not much to do with required power, and usually one is safe to use them with amplifiers rated somewhat higher.

    How the rated impedance for the speakers was arrived at is also an unknown. The impedance of most speakers varies quite a lot with frequency. For starters, take a look at the dummy speaker load at Soundstage.com. Take a look at Chart 1, which is fairly typical of the curves for quite a few speakers:

    http://www.soundstagemagazine.com/me...amplifiers.htm

    If it were a real speaker, would it be a 4 ohm speaker, a 6 ohm speaker, or an 8 ohm speaker? Come on, no shilly-shallying around! (Just a mild joke) The impedance drops below 8 ohms in the mid-bass and in the lower treble. The impedance peaks to around 20 ohms are of little importance because the amplifier doesn't have to deliver much current at those frequencies. The impedance in the upper-bass only drops to around 7 ohms, while the dip around 5 kHz is high enough that not much musical energy is up there. So, I think it would be safe to consider that to be an 8 ohm speaker.

    Now lets look at the sensitivity and impedance vs. frequency curves of another speaker, which is pretty good and which measures quite well. This one has a measured sensitivity of 87.0 dB (that's not just a manufacturers claim). The impedance in the mid-bass gets down to about 4 ohms, so I would tend to consider this to be a 4 ohm speaker, though 6 would be safe enough. But probably most amplifiers would drive it OK.

    http://www.soundstagemagazine.com/me...onnoisseur_c3/

    Here are the curves for an older speaker down in our family room, still sounding quite good. It's sensitivity was estimated by Stereophile at 85 dB and it's impedance gets down below 4 ohms in the upper bass/lower midrange area. I would definitely consider this to be a 4 ohm speaker and it has a moderately low sensitivity as well. It is a moderately current hungry little speaker but for us, a 75 watt Yamaha A-V receiver works just fine. But we just like to play movies loud enough to hear the dialogue clearly.

    It's really hard to tell from manufacturer's specs just how hard a speaker is to drive. Some manufacturers provide better information than others. A good review can be helpful, but in the last analysis, you may not really know whether your amp can handle them at the volume levels you like until you try them out together.
  • 11-25-2007, 10:33 PM
    Tetsuro
    Yhanks guys for the clear explanations. It's only about volume levels or does it influence dynamics and the overall quality of the sound?

    So what amplifier does need the Wharfedales? I thought they were fairly common used speakers, but their sensitivity rating is fairly low.
  • 11-26-2007, 05:34 AM
    kexodusc
    Pat D and Mr. Peabody and steering you in the right direction.

    Quote:

    Originally Posted by Tetsuro
    Yhanks guys for the clear explanations. It's only about volume levels or does it influence dynamics and the overall quality of the sound?

    You will get many opinions on this question - some feel high sensitivity speakers sound better, some feel the opposite. For my part, I stick with what I know. Sensitivity and watts are not units of sound quality, they just play a part in how loud a speaker will play. It is possible to have high quality sound from both high and low sensitivity speakers.

    If you were to use the same 40 watt integrated amp, and always play your music at 90 dB listening level, and you had 2 speakers that were perfectly identical in every way except one had 86 dB sensitivity and the other 90 dB, then it is possible that the 86 dB speaker is making your amp work a bit harder, which in turn might introduce distortion and sound quality loss. That's a lot of if's.

    Otherwise, you probably won't notice a thing.

    Dynamics aren't affected by sensitivity, provided your amplifier has enough head room. If your amp runs out of watts, you will start to clip the sound - that's not good.

    All this to say there's more than one way to build the system you want. High power amps with low sensitivity speakers is one approach (why not, power is cheap). High sensitivity speakers is another - these days more speakers probably take that approach to accomodate home theater 5.1 setups.
    Quote:

    Originally Posted by Tetsuro
    So what amplifier does need the Wharfedales? I thought they were fairly common used speakers, but their sensitivity rating is fairly low.

    The size amplifier you need is determined by how large your room is, how loud you listen to music, and the impedance and sensitivity profile of your speakers.

    I wouldn't be surprised at all if the 86 dB @ 6 ohm speakers play loud enough and sound good on a 40 watt amp. Unless you really like to rock at super loud volumes.

    There's a very simple rule that will keep you out of trouble.
    "If things start to sound bad, turn the volume down".

    One last thing - it speaker companies are pretty reluctant to rate speakers lower than 8 ohms. If they're calling it a 6 ohm speaker, it probably should be rated as a 4 ohm speaker. Just be cautious when using lower powered amps with them.

    What brand and model is your integrated amp? Any idea what its power rating is into 4 ohm loads? If it has a healthy 4 ohm power output, you're probably fine.
  • 11-26-2007, 06:51 AM
    Tetsuro
    Thank you very much Kexodusc. Probably I will not go 'big' and will opt for a 40 W NAD plus a pair of MA BR1, hope those small speakers will do it for me. ;)
  • 11-26-2007, 07:46 AM
    bubslewis
    Quote:

    Originally Posted by Tetsuro
    Thank you very much Kexodusc. Probably I will not go 'big' and will opt for a 40 W NAD plus a pair of MA BR1, hope those small speakers will do it for me. ;)


    Good initial question, and excellent responses = a happy ending for all