Low sensitivity from 91dB 8Ohm Coda 70, NAD C370 amp

Discussion in 'Hi-Fi and General Audio' started by longlam, Aug 5, 2004.

  1. longlam

    longlam

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    i'v already posted this in the HFC Forum, General Discussion under the title of "Possible Speaker Problem?", but didnt get much response. so if uv read up to here and recognise this thread, press Back...

    i'm changing the title so that it makes some more sense.

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    not sure if this is a problem, it could be the way bi-wiring works, wanted to know if anyone has had this experience:

    recently got a pair of KEF Coda 70s from Superfi. definitely new speakers, so not duff ones...
    8Ohm impedance, 91dB and they r bi-wireable, so i got some single ended leads (QED SAs) from my amp (NAD C370) to 4 connections at the back of the speakers.

    nothing wrong with the sound. just seemed lower in volume than my Dynaudio 40s and they're rated at 87dB, 4Ohm and single wire.

    what's making this noticeable difference in volume?

    does this have anything to do with NAD's commutating power supply?
    ________
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    Last edited by a moderator: Feb 16, 2011
    longlam, Aug 5, 2004
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  2. longlam

    I-S Good Evening.... Infidel

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    I think it's more to do with optimism on KEF's part.

    My old B&W DM602s were nominally 91dB, 8 ohms, but my current Meadowlark Kestrel Hotrods are nominally 89dB, 8ohm and were noticeably louder for a given volume setting.
     
    I-S, Aug 5, 2004
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  3. longlam

    andrew1810

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    Must have missed the HFC post, sorry.

    I tested my repaired Coda 7's against the Rega Ela's last night and the KEF's were louder. Both KEF's are louder as well so it must be the speakers because of the brand new tweeter.

    Andrew
     
    andrew1810, Aug 5, 2004
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  4. longlam

    andrew1810

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    I tested my repaired coda 7's against the Ela's last night and the KEF's were louder by quite a way considering they are smaller speakers!

    Nice sound for the money though so I'm not complaining, don't want quiet speakers for films!!

    Andrew

    p.s. Must have missed the HFC post, sorry!!
     
    andrew1810, Aug 5, 2004
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  5. longlam

    Lt Cdr Data om

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    Dont' believe a word that the makers tell you, I have even seen a 5" woofer claimed to go to 38 hz, small boxes with 5" are around 80 hz, period, don't let anyone tell you otherwise.
    Figures are meaningless, you can twist them any which way you want, depending how you place conditions on them.
    eg, the 38 hz, perhaps 30 dbs down, yes.
    usually mission and b/w are some of the more accurate ones.

    I mean, if a speaker only does 70-80 hz, who is gonna buy it in this age of bass? so its in their interest to make it look low, sound louder.
    Kef lower impedance to boost volume for a 1 to 1 comparison in the shop, as its well known that buyers opt for the louder one. naughty.
    same with cd players, the higher volts ouptut one sounds better

    There is no such thing as an 8 ohm speaker, either, it veers anything from 3 ohms to maybe 40 ohms, only depends where you measure it.
    Kef are usually 4 ohm.
     
    Lt Cdr Data, Aug 6, 2004
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  6. longlam

    alanl

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    I think you will find, the KEF speakers are rated at 91db in room with two speakers. This would = about 86db @ 1w 1m. Many US speaker makers now use the Sensitivity 2 speakers in a typical room measurement. Your Dynaudio 40s must use the single speaker 1w 1m measurements.

    Hope this helps you understand why the KEF is lower in SPL's for the same input level. Bi wiring has nothing to do with it, sorry other than reducing the sound quality.
     
    alanl, Aug 6, 2004
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  7. longlam

    GTM Resistance IS Futile !

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    I suspect it has more to do with "percieved" loudness rather than actual measured output. The Dyns should be much quieter, even if you accept that the keffs have been measured as a pair and in room rather than singularly in an anechoic chamber.

    87db @ 1m @ 1 watt with a 4 ohm load equates to 84db @ 1m @ 1 watt for an 8 ohm load.

    91db as a pair would equate to 88db for a single speaker, even if we assume a room adds a further 3db then that would bring the kefs down to around 85db. Which is an insignificant difference from the Dynaudios.

    So then the "percieved" loudness of the speakers will be down to the response of the speakers. It's perfectly possible that the Dyns are a good 2 db higher in the all important 2-5khz range than their sensitivity spec (which is taken at 1khz usually) would suggest. If the Kefs are on the dull side in the presense region then the difference between the two speakers could be as much as 3-4db over the 2khz-5khz range which is the bit that makes a speaker "sound loud".

    GTM
     
    GTM, Aug 6, 2004
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  8. longlam

    Doctor Jeep

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    Interesting reading guys.
    I've just bought some Kef Q7's and, don't laugh, they're officially rated as 8ohms and - surely a piss-take - any amplifier from 15w up to 175w can run them. Kef's figures are laughable. I'm guessing but I bet the racetrack woofer dips into the 3ohm territory with alarming regularity. I've got a 2x170w amp driving them but I'd shudder to attempt any sort of decent sound with a 15w amp! I bet the mid and high frequencies would sound ok but there would be practically NO bass, the woofer would hardly be moving. :eek:
     
    Doctor Jeep, Aug 6, 2004
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  9. longlam

    Paul Ranson

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    I think usually in speaker sensitivity specs the '1W' is actually a nominal one, what they do is use 2.72v, which gives 1W into 8Ohms, and then if your speaker is actually 4 Ohms you get to measure it with a whole 2W of power.

    Anyway I wouldn't worry about the detail, do they go loud enough? Is your amp powerful enough?

    Paul
     
    Paul Ranson, Aug 6, 2004
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  10. longlam

    longlam

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    cheers for the replies guys (and girls if there are some here, couldnt tell by the logins). u seem to be a more helpful and intelligent lot that the HFC bunch (LOL, i know most of u r from there too...!).

    i'm not really bothered, just curious why it was that way. and my conclusion is that it is misleading for any manufacturer to print such figures, but like u guys said, it doesnt really matter that much at the end of the day.

    LCD: the Codas r rated at 45 - 27KHz +- 3dB. and the Dyns at 53 - 28KHz. the Dyns have smaller internal volume and supposedly lower impedance too. doesnt make any sense, but my ears tell me that the bass out/p on the Dyns r a little lower, with more slam and smoother too. its to do with the driver technology more than anything.

    GTM: thanx for the calculations. but the Dyns still sound a bit louder and it just wasnt what i was expecting thats all.

    Paul R: yes, my amp's (NAD C370 = all 185W, measured that is) powerful enuff, i dont like to play my music that loud all the time, only once in a while, when all the family/neighbours r out...
    my amp's also got a Soft Clipping mode for LOUD volume to protect the speakers, when i've never used it, does anyone know when i should start using it?

    regards,
    Long.
    ________
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    Last edited by a moderator: Feb 16, 2011
    longlam, Aug 7, 2004
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  11. longlam

    Doctor Jeep

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    With the C370 my bet is that the speakers will give out long before the amp drives to clipping. Those amps go LOUD! So unless you're throwing a mamba party and cranking that volume dial to 3 o'clock I'd not bother using the soft clipping circuit. I've heard that it can affect the sound and 'soft clip' when it's not warranted. Of course it shouldn't do that and if you feel more comfortable then leave it on all the time. It'd be of more use in a 15w amp though than a 2 X 120w (minimum) beastie.
     
    Doctor Jeep, Aug 7, 2004
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