I'm not sure which JohnBlue speakers you're looking at, or how large a space you would be using them in, but I have a pair of JB3's and drive them with a 10 watt EL84 amp. Mine are in an office setting and the 10 watts drives them easily. The sound is exceptional from such a small rig, as well. I'm very happy with the combination.
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?
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?
11 responses Add your response
For quiet listening it will be fine. Going to 90db won't get much of an increase. 87db to 90db will double the power but it takes 10db to double the perceived volume. I'd look at 93db or better if you want to "rock". Currently I have a 7 watt amp that drives 88db speakers fine. However, it really sings with my 94db speakers. |
So, you have apprx. 3 wpc of clean power.Alas apprx. 4 db = 91db (87+4db's) of clean output from the driver/s. Can you get by on peaks of 92=92.5db of peak output. Personally I can almost get by with that but, I have found that most, NOT all, audiophiles ears are no longer sensitive enough for this to be adequate. As always YMMV. |
I'm not following Harley52's math, but I found that a 300b was fine w 89 dB speakers in a medium sized room (14 x 23 x 8.5 = 2735 cu. ft.) if I wasn't pushing them to high spls. If your room is truly small (12 x 12 x 7.5 = 1080 cu. ft, which means my room is 2.5X bigger)), I would imagine that the combination would be adequate, unless you wanted to try to play back large scale classical or hard rock at high spls. One advantage of tubes is that they generally clip much more gracefully than ss. |
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>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. |
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? |
> 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. |
How I look at wattage. Continuous power, not peak. I always considered peak to be bull anyway. The really good amps with great transformers could produce 3db extra on peaks and the lesser amps got 1.5 or so db gain. However, crap amps kept boasting much higher peaks because they didn't care about distortion levels of 10% or more. 1 watt = 87db 2 watts = 90db 4 watts = 93db 8 watts = 96db At about 10db gain you will get a 16 watts = 99db perceived doubling of volume. 32 watts = 102db There you go, 15 db of gain at 32 watts 64 watts = 105db This is getting fairly loud 110 db is THX, 112db is ultra thx |