Got a quick question about the JBL MP418S subwoofer

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Richard Stringer

Sophomore
Jan 13, 2011
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Boston, Lincolnshire, UK
Hi ya guys, got a quick question about the JBL MP418S subwoofer, the 2241 driver is rated at 98db sensitivity, but the MP418S is rated at 101db. Does anyone know why? Someone i've been talking to says the MP418S's sensitivity spec is bull crap because the 2241 driver is meausred by JBL in half space in an anechoic chamber so seeing as the 2241 has a sensitivity of 98db then it means the MP418S does too.

What are your thoughts on this guys?
 
Re: Got a quick question about the JBL MP418S subwoofer

Richard Stringer said:
Hi ya guys, got a quick question about the JBL MP418S subwoofer, the 2241 driver is rated at 98db sensitivity, but the MP418S is rated at 101db. Does anyone know why? Someone i've been talking to says the MP418S's sensitivity spec is bull crap because the 2241 driver is meausred by JBL in half space in an anechoic chamber so seeing as the 2241 has a sensitivity of 98db then it means the MP418S does too.

What are your thoughts on this guys?
Click to expand...

I haven't looked at the spec sheets myself, so the following is just random thoughts.
A raw driver mounted on an infinite baffle, measured half space compared to same driver in a tuned bass-reflex enclosure ?
I'd be woried if the specs WERE the same.
 
Re: Got a quick question about the JBL MP418S subwoofer

Chris Hindle said:
I haven't looked at the spec sheets myself, so the following is just random thoughts.
A raw driver mounted on an infinite baffle, measured half space compared to same driver in a tuned bass-reflex enclosure ?
I'd be woried if the specs WERE the same.
Click to expand...

What Chris said: the driver properties don't really matter independently of the box in which they're measured. You can put the same woofer in 100 boxes and get 100 different measurements.

Also note, the MP418S uses the 2241G which is a 4-ohm woofer, which will affect its sensitivity depending on what test signal is applied.
 
Re: Got a quick question about the JBL MP418S subwoofer

Chris Hindle said:
I haven't looked at the spec sheets myself, so the following is just random thoughts.
A raw driver mounted on an infinite baffle, measured half space compared to same driver in a tuned bass-reflex enclosure ?
I'd be woried if the specs WERE the same.
Click to expand...

That's basically what I thought, the driver in a tuned enclosure would yield the highest sensitivity.
 
Re: Got a quick question about the JBL MP418S subwoofer

Richard Stringer said:
That's basically what I thought, the driver in a tuned enclosure would yield the highest sensitivity.
Click to expand...
The tuning really only affects the around around the lower end of the response (where the tuning is) and has little effect on the response above that.

Now that statement is only for ported boxes-not horns-or bandpass etc.

If you take the same driver and cabinet and tune it for 30Hz it will be louder (at 30Hzish than other tuning freq) . If you tune it for 40Hz, it will be louder at 40Hz, but not as loud at 30Hz as a cabinet that is tuned for 30Hz. So each one can be "louder" than the other-depending on what freq you look at.

When you only look at simple single numbers, you get "wrong" answers to the wrong question.

Just because it is "tuned" does not automatically make it louder-only at the particular freq and response that it is intended for.

There is always a "target" in the design process-you give up one thing for another and have to deceide which is better for the intended target market.

I hope that makes some sense.
 
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