A sensitive question

[SEAWOLF97]

was discussing L26's with another forum member....
he asked about sensitivity being low ...the tech sheet shows 76dB

they have always seemed easy to drive and needing not much power, so I questioned whether the sheet was correct...

then looked up others

L36=76dB
L88=76dB
L100=78dB
L166=76dB

L7=91dB

have measurements changed OR are these older speakers really that inefficient ?

it gets stranger when I lookup my "hard to drive" , inefficient Walsh F's ...the factory page shows 87dB

[timc]

Measuring distance has changed.

The L26 is measured at 15 feet. The standard today is 1m.

Thats a HUGE difference.

In a normal speaker the SPL reduces with 6dB when the distance doubles.

So in that case you would get about 90dB/1m for the L26. Still not very sensitive in JBL terms, but about normal.

-Tim

[scott fitlin]

The measuring techniques have indeed changed. I look at the old drivers from the 50,s and 60,s, JBL rated their high efficiency woofers at 52db, or whatever number, and this shows they were measuring different distances.

[Mr. Widget]

The measuring techniques have indeed changed. I look at the old drivers from the 50,s and 60,s, JBL rated their high efficiency woofers at 52db, or whatever number, and this shows they were measuring different distances.They were also using milliwatts of input power instead of watts... even today people throw around 1 watt at 1 meter and 2.83V at 1 meter as though they were interchangeable.

Then there is the question of dB sensitivity at which frequency? Are we talking a 1KHz measurement or a limited band that is averaged...

You have to read the fine print.


Widget

[jcrobso]

They were also using milliwatts of input power instead of watts... even today people throw around 1 watt at 1 meter and 2.83V at 1 meter as though they were interchangeable.

Then there is the question of dB sensitivity at which frequency? Are we talking a 1KHz measurement or a limited band that is averaged...

You have to read the fine print.


Widget
If the load impedance is different the voltage will be different. If you use 2.83 volts for a 4 ohm speaker you will get 2 watts.

[Mr. Widget]

If the load impedance is different the voltage will be different. If you use 2.83 volts for a 4 ohm speaker you will get 2 watts.That was my point... the impedance is always different. There is no "8 ohm" speaker... and if measuring at Altec's usual 4' or the current industry standard of 1 meter, or the old JBL 15' measurement... none of these are as precise as they seem without knowing more about the drive level and frequency(s) etc.


Widget

[SEAWOLF97]

You have to read the fine print.
Widget

many times there is no fine print...they just toss out a number.

when were the measurement techniques changed ?
and by everyone at one time or
unorganized , as a producer felt like it. ?

[Mr. Widget]

L36=76dB
L88=76dB
L100=78dB
L166=76dB

L7=91dB
my "hard to drive" , inefficient Walsh F's ...the factory page shows 87dBHere is a conversion for those curious about new vs. old JBLs... at least in terms of rated sensitivity.

L36=89dB
L88=89dB
L100=91dB
L166=89dB

Now, the L88 vs. the L100 is an example of the point I was trying to make about sensitivity at what frequency. These two speakers should be the same... the only difference is the added midrange driver and it's Altec mimicking rising midrange...


Widget

[4313B]

You have to read the fine print.


many times there is no fine print...they just toss out a number.

when were the measurement techniques changed ?
and by everyone at one time or
unorganized , as a producer felt like it. ?Here is some fine print to read:

http://www.lansingheritage.org/images/jbl/catalogs/1976-comp/page9.jpg (http://www.lansingheritage.org/images/jbl/catalogs/1976-comp/page9.jpg)