Old Speaker Efficiency Rating in the 40s db???

[kvk]

I've seen specs for all speakers that have the efficiency rating with values like 45db, 47db, etc. That can't be the same rating as used today.

Anyone know what the conversion is?

[Corax]

Well, I've seen many (vintage) SPL diagrams scaled from i.e. 0...50dB (or even less). But the scale is and was always relative to a known (or even unknown) reference level just made for displaying purposes and they aren't intended to show you any absolute value.

However, very seldom, I've seen the absolute SPL level (in a diagram) measured at different distances from the speaker, i.e. 10 meters (or approx. 33') away - this was, for instance, the case with some PA-speakers. But then an SPL of just 45...47dB at a distance of 10 meters is below anything I would buy or built .

A copy/scan/screenshot of the datasheet posted here might help us/me to identify it.

Basically, you should remember that dB (decibel) is always and forever a (logarithmic) ratio. In some cases the reference is either stated seperately (i.e SPL at 1 watt and 1 meter distance for that specific speaker) or by a postfix like dBm, dBA, ... but these latter do not refer to SPLs of loadspeakers .

[kvk]

Originally posted by Corax

A copy/scan/screenshot of the datasheet posted here might help us/me to identify it.

http://archives.telex.com/archives/E...LS15%20EDS.pdf

[Ouroboros]

This may refer to the old and bizarre sensitivity rating of 1mW at 30 feet. If this is the case, it would give the sensitivity for these in the mid 90dBs for the conventional 1W at 1 metre.

[Ouroboros]

Actually it will be +30dB to correct for 1 Watt, and then +19.2dB to correct for 1 metre. So 45dB sensitivity will be (45 + 30 +19.2)
= 94.2 dB when corrected for the modern way of specifying things.

[EspenE]

Today, speaker manufacturers generally quotes speaker sensitivity at 1W/1m.

Back in the 60's JBL quoted sensitivity ratings at 1 mW/30 ft.

For instance, the 4311 studio monitor was quoted as having 91dB at 1W/1m, and 42dB at 1mW/30 ft.

I don't know if Electrovoice followed the same convention.


EDIT: You beat me to it, Ourobouros

[Corax]

OK, I already had the feeling you ment Electro Voice and my dream/nightmare became true - now, the so called "EIA sensitivity rating" is based on the following formula:

0 dB = 1 mw/10 dynes/cm²

For "dynes" have a quick look at "http://en.wikipedia.org/wiki/Dyne" and you'll find out that

... the dyne (symbol "dyn") is a unit of force specified in the centimetre-gram-second (CGS) system of units, a predecessor of the modern SI

In addition you may read "http://en.wikipedia.org/wiki/Sound_pressure_level" and figure out yourself.

This comes out very close to what Ouroboros just mentioned.

[Pano]

Wow! You guys are smart!

Thanks for the info.