2. speakers
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Are these speakers fully compatible?

I have a 10 watt 300B tube SET amp with these specs:

Power output: <= 10W x 2, THD <= 3%, 1Khz
Frequency response: 16—38 Khz, -2dB
Output impedance: 8 ohms
Signal/Noise: >= 90 dB

I was thinking about getting a pair of John Blue bookshelf speakers for my small room and the speakers have these specs:
Efficiency : 87 dB / W / mImpedance : 6 OhmMax power : 30 W

Would I be better off getting a pair of speakers with a 90dB effiency or higher?
spareribs
Post removed 
drew_eckhardt
394 posts
 
>03-18-11: Spareribs
Thanks. I'm in a small bedroom so playing at very load levels is not really a need. Plus I usually listen to jazz and classical music with some classic bluesy rock.

I wouldn't assume that. Good jazz and classical recordings have a lot of dynamic range and I'd worry about clipped peaks.

Out of curiosity I ran _Take Five_ through some Octave (the GNU Matlab clone) functions and found an 18.4dB crest factor on the right channel.

Playing at a pleasant 85dB SPL with incoherent addition from the speakers (it's a classic pan-pot recording) implies 82dB from each. Applying typical draw down rates that suggests about 87dB 1 meter from each speaker.

87dB + 18.4dB = 105.4dB 1 meter from the right side.

With 87dB efficient speakers that would take an amplifier that can produce 35W on sine waves which have a 3dB crest factor.
harley52
79 posts
 
Drew and anyone that wants to read. 18.4db of sound will take 85-95 watts of power,all things being equal.

One hundred watts equals a 20db gain.You can't rewrite the elect. laws at your leisure.
sfar's avatar
sfar
1,760 posts
 
I've never tested sound levels with my JB3's, and I'm sure I never will, but in a 10'x 10' office they provide all the volume I could ever use, whether I'm listening to Jordi Savall or Tom Petty. I know volume control position doesn't have much to do with anything but with my 10 watt EL84 amp I've never had it beyond 11 o'clock playing any kind of music.

I went through several small monitors and the JB3's are the ones that stayed. They're extremely musical, the perfect size for my setup, front ported and they look great. Have you read the 6moons review?
drew_eckhardt
394 posts
 
> Harley52 writes
>Drew and anyone that wants to read. 18.4db of sound will take 85-95 watts of power,all things being equal.

As fall out from the 1970s amplifier power advertising shenanigans the US FTC requires consumer one and two channel amplifier output power to be rated using sine waves which have a 3dB difference between RMS and peak level.

Reproducing the right channel of _Take Five_ takes 18.4dB Peak - 3dB = 15.4dB more power than a sine wave at the same average SPL. With 87dB @ 1W efficiency and 87dB SPL from each speaker you need an amplifier rated for sine waves at 1W * 10 ^ 1.54 = 34.67W which I round to 35W for convenience.

Peak power will be 1W * 10 ^ 1.84 or 69.18W.

Regardless in such a scenario your peaks are going to be compressed with a 10W amp. You might like the effect but it's not accurate.
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