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Old 3rd April 2002, 11:31 PM   #1
JBL is offline JBL  Canada
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Default speaker sensitivity problem

Hi,

I have a woofer in an enclosure that don't seem to have the sensitivity quoted in it'S datasheet.

Is their as possibility that the enclosure is the caus of that problem. It take an enormous power to get it to sound loud enough.

The box is a sealed design for a 15 inchs unit. I d'ont know the dimension of the box i didn't mesure it(it wasn'T mine). It's very huge and stuff with some sort of isolation stuff.

Any idea

tanx all
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Old 4th April 2002, 12:48 AM   #2
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Its possible that the enclosure could be restricting air flow and reducing output. Measure the driver in and outside of the enclosure with an SPL meter, and you should get your answer.
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Old 4th April 2002, 01:08 AM   #3
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First off, you'll need to give us some more information about the problem.

Are you looking at the datasheet for the woofer, or that of a prefinished cabinet that you bought?

Just so you know the efficiency quoted in the woofer's datasheet is only valid for a certain part of the frequency range.

If you're using the 15" as a subwoofer, the efficiency of the system (woofer + enclosure) will be far below the efficiency quoted in the datasheet.

It should be noted that if using it as a subwoofer, the efficiency in the bass region will be inversely proportional to the size of the enclosure (up to a point, of course)

If it's in a small enclosure, then it may indeed require a ton of power to get any significant output from it.
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Old 4th April 2002, 02:20 AM   #4
JBL is offline JBL  Canada
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It's a large box (it's 12 square feet!!)
But...
The response from the driver is weird also. I just taked the box size and putted it into a speaker design soft. and it gave me a good respons down to 25hz with no peak and dip and it sound not boomy but kind of out of control like if it was playing outside of is capabilities. But the driver can take more than that i'm sure caus i tried it with a high pas filter to filter subsonic frequency and it still not right.

I have already designed speaker before and this design is ok(altought a littl bit overkill on the size).
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Old 4th April 2002, 08:09 AM   #5
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Can you tell us which woofer it is and the Thiele-Small parameters, including Qes?

There are formulas and programs that can figure the SPL @ 1W/1M from the Thiele-Small data and they do not always agree with the published SPL.
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Old 4th April 2002, 10:09 PM   #6
JBL is offline JBL  Canada
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it's a pyle pro ppa 15

8 ohm
fs 26.7
qms 2.69
qes 0.89
qts 0.67
spl 90.2
vas 11.357
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Old 5th April 2002, 06:36 AM   #7
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All I need now is the "Re", (sometimes called the DC Resistance) specification, and I shall calculate the sensitivity of the speaker. If you have a multimeter handy you can measure the resistance of the voice coil yourself. That is what it is-the resistance of the voice coil.

Just another suggestion. Does this speaker have a passive crossover? If someone threw a really big inductor on there, that might affect the output.

If there is a crossover on there, disconnect it-or short around it-and see how it sounds.
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Old 6th April 2002, 02:28 AM   #8
JBL is offline JBL  Canada
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The dc res. is 7.5(I found this value to be a little high)

No their is no passive xover.
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Old 6th April 2002, 05:05 AM   #9
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Well, the sensitivity ratings are not exagerrated. With the specs you gave me, BoxModel gives the sensitivity as 90.2 dB @ 1W/1M.

The high DC resistance means it is actually closer to a 10 ohm speaker. Theoretically that means that it requires a greater voltage drive level to deliver it's power, but the difference should be negligible.

Just a few possibilites off the top of my head.

A) You said there was no passive crossover. Are you running this off a subwoofer amplifier with built in crossover that is maximized to deliver full power into a 4 ohm load? The Parts Express 250 watt subwoofer amp, for instance, delivers 250 watts into 4 ohms and only 150 watts into 8 ohms. That's a 3 dB difference. Plus this is actually a 10 ohm speaker, making things worse, (assuming it is a 4 ohm amplifier).

B) Do not forget that a single driver subwoofer has to play 6 dB louder than either of the satellite speakers to make the same volume level in the bass that the satellites produce in the midbass and up. A single driver subwoofer that plays at the same volume level as the satellites will seem to have a thin bass.

C) As Super mentioned, filling an enclosure with stuffing may lower it's F3 point, but it also lowers it's efficiency. By lowering the midbass efficency, you seem to be extending the bass extension. How tightly packed in there is this stuff? Try taking some or most of it out and see if things improve.

D) The Xmax of the Pyle is only a quarter of an inch. That means it moves about 35 cu inches of air, enough to generate 101 dB at 25 Hz. That might not be enough to fulfill your idea of big bass, so you think there you have a problem in sensitivity. I'm just guessing here.

I hope these suggestions are of help to you . Good luck!!
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Old 6th April 2002, 03:09 PM   #10
JBL is offline JBL  Canada
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Well I think that i'm going to take out the stuffing. I was aware of the low xmax of this driver. I wasn't wanting big bass out of those driver.
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