So let me get this straight...

[Rdmarsiii]

Ok, the Heresys have sensitivity of 96 db @ 1w 1m, so does that mean with one watt, it would be 96 db? Is this with tube power, or? Im confused.

[chops]

Theoretically, yes. However, that is at 1 meter in front of the speaker, not at your listening position. At your listening postion, it might be down 1-2 dB depending on your room layout and furniture.

[lynnm]

That spec refers to to the acoustic power detected/measured by a Sound Pressure Level measuring instrument when placed 1 meter ( 39.2" ) away from a single speaker under test while the speaker is driven at 1 watt of power and is reproducing a 1000 hz tone.

Obviously the higher the efficiency rating of a speaker the greater the acoustic output for a given input. This does not translate directly as a measure of quality however. In the end one's ears must determine what sounds best regardless of measured specs.

[J M O N]

This sensitivity rating is also just for one speaker. For two speakers, add 3 dB (assuming both speakers are at 1 meter distance). Also, I believe the sensitivity measurements are taken in anechoic chambers, where no reflections are getting to the measurement device. In most rooms, you will have some reflections from the walls, floor, etc., which will provide even more SPL, all depending on the amount of reflections. So now you can see why in a relatively small room, a 104 dB @ 1 Watt-1 meter pair of Klipschorns can produce fairly high volume levels with just 3 Watts per channel.

[Doc Robin]

Would you please explain how you figure it will go up 3 db with 2 speakers at 1 watt/1 meter. Also are they side by side or possibly 180 degrees out with the measuring equipment in the middle.

In Ham radio you have to increase your power out 2-3 times to get a 1 db increase in siginal strength if my memory is correct. Bill

[JohnA]

+3 dB is twice the power. @ speakers are twice the acoustic power. The speakers would have to be close together and playing the same (mono) signal so they are substantially in phase with each other.

"Tube Power" is not part of this equation.

[WMcD]

We have had a few go arounds on this in other threads.

The 96 dB (or whatever) at 1 meter, is set with an input of 2.82 volts RMS. That results in one watt of electrical power consumed IF the input impedance is 8 ohms.

P = V^2/R. So V must be square root of 8 to make P = 1.

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The often mentioned 3 dB increase is when you have two speakers each fed with the reference level. It does assume that two watts of electrical energy is consumed.

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Sometimes you see reference to 6 dB increase with two speakers. This assumes they are closely spaced and fed in phase. The added gain is because of mutual loading. This is to say that each diaphragm creates a higher air pressure in front to the other. So there is a better air load.

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The next issue is how the SPL varies with distance. The answer is that each time the distance doubles, there is a 6 dB drop. This is because the pressure is spread over 4 times the area with every doubling of distance. So that is like two halvings. It is a simple inverse R^2 law, like light.

We discussed that the drop off theory. In real rooms we have to deal with the fact that echos off the wall come into play. And if you get very close to the diaphragm, it is not acting like a point source.

- - - -

I don't know about the ham radio issue. You might be thinking of S-units on a receiver's meter. Those might be another scale. Incidently, I understand that Mr. Collens, creator of the manufacturing company of fine gear, came up with that scale, whatever it is.

Best,

Gil (AB9BE)

[Colin]

As once measured in my 17x21 living room with super-sensitive walnut-oiled Cornwall 1s, with their B2 crossovers, rated at 100 dB per watt, per meter, and a RS SPL meter, about 4.9 watts gives you ear-splitting 101dB average, C weighted, SPL at 1Khz at listening seat some 6 away! So much for ratings.

Full out, my flea-powered tube Bottlehead 2A3 Paramour amplifiers produce only 6-watts (@aprox. 10%THD), this equated to a painful 110db at the listening spot on my Corns in my room.

[WMcD]

Looking around the web I see that one S unit on a receiver meter is 6 dB, double voltage, four times power, relative to anything else.

Now we know.

Gil

[Juba310]

with all those formulas and everything, it would probably be easier to just measure the spl with a meter if you really wanted to know.

[Doc Robin]

Thanks guys. I will have to some research of my own to refresh my memory. I havent played with the raido's much in the last 5 years. Too many stores and parking lot light's making a lot of noise on the air waves around here now. And i didnt want to spend any more money on the hobby since the value of the new equipment was droping to around 35% of it's new value after about 2 years. So i sold almost everything and went back to the audio hobby. 73's Talk to you later Bill.