Question about sensitivity (SPL) of a driver

[CauYem]

I'm unclear about the result of the sensitivity of a system when a driver is:
1) Loaded in a box (folded horn...) with higher (or lower) sensitivity
2) Loaded in a horn with different sensitivity
3) Connect in parallel with the same driver (same sensitivity)
4) Connect in parallel with different driver (different sensitivity)

Any help is much appreciated!

[boputnam]

First, sensitivity is not SPL - SPL is Sound Pressure Level. Sensitivity is measured in dB (SPL), but SPL is used to describe loudness.

Sensitivity is a metric of a transducer's output at a set standard distance (1m) with a set standard voltage drive (1 W) over a specific frequency range. The dB output reported is the SPL under those conditions. Sensitivity is used as a method to compare different drivers.

Therefore, I think wrt most of your questions, those are configurations in-which you will need to balance each transducer's output (based upon their sensitivity) for an overall even response.

[ratitifb]

Sensitivity is a metric of a transducer's output at a set standard distance (1m) with a set standard voltage drive (1 W) over a specific frequency range.could i suggest to add "in a specified environment" ;)

[toddalin]

Sensitivity is a metric of a transducer's output at a set standard distance (1m) with a set standard voltage drive (1 W) over a specific frequency range. The dB output reported is the SPL under those conditions. Sensitivity is used as a method to compare different drivers.



No, as I stated before, it is at 2.83 volts, not 1 watt.

As you said a set standard voltage drive, not watts as these vary with the impedience.

[CauYem]

First, sensitivity is not SPL - SPL is Sound Pressure Level. Sensitivity is measured in dB (SPL), but SPL is used to describe loudness.

Sensitivity is a metric of a transducer's output at a set standard distance (1m) with a set standard voltage drive (1 W) over a specific frequency range. The dB output reported is the SPL under those conditions. Sensitivity is used as a method to compare different drivers.

Therefore, I think wrt most of your questions, those are configurations in-which you will need to balance each transducer's output (based upon their sensitivity) for an overall even response.


Thanks Bo, so I need to measure the response of each case in order to know what exactly the SPL of each config. This would be lot of work!

Let make it simpler: If I connect (2) JBL 2226H (97dB SPL) in parallel, would the SPL increase or decrease under the same power (1W/1m) compared to one driver in the same box?

[boputnam]

No, as I stated before, it is at 2.83 volts, not 1 watt.I guess I don't follow you around enough - I can't see where you said that.

Regardless, I was quoting 1W as per the JBL specifications sheet's I double-checked just before posting. Checked again - yup, they still say 1W.

Ah, I found it - on a completely different thread! How silly of me... :p


Nope. The sensitivity is actually taken using only 1 watt!
Allan.

Maybe at one time, but I don't think so anymore. I think that sensitivity is taken at 2.83 volts input to the speaker.

The amount of wattage is a function of the impedience and this varies with each speaker so the actual wattage also varies.

So, you're not so sure there either.

Well, I did some more checking and the "1W/1m" metric looks to have been changed in more recent instances - but not in every one I checked - to specify 2.83v. So, as usual, with standards, YMMV...

[boputnam]

Let make it simpler: If I connect (2) JBL 2226H (97dB SPL) in parallel, would the SPL increase or decrease under the same power (1W/1m) compared to one driver in the same box?The sensitivity of the drivers will not change.

By using two drivers of identical sensitivity, they will each be (ideally... ;) ) putting out the same SPL under the same voltage drive, or watts, or whatever. They will be balanced (equal) in their outputs.

[toddalin]

So, you're not so sure there either.


Sure I'm sure.

[boputnam]

Sure I'm sure.I know.

[Allanvh5150]

but regardless of the measurement system, if you compare apples to apples the outcome will always be the same.

Allan.

[toddalin]

Let make it simpler: If I connect (2) JBL 2226H (97dB SPL) in parallel, would the SPL increase or decrease under the same power (1W/1m) compared to one driver in the same box?

Depends on the amp. Could be louder or could even remain the same.

If the amp is capable of doubling its power into half the impedience, it could be 3 dB louder as each speaker is now receiving what one speaker received and you are now moving twice the air volume.

If the speakers are arranged so that they "acousticaly couple" the increase could be as much as 6 dB; 3 dB for the increase in air movement and 3 dB if the peaks and troughs line up and reinforce each other.

However, if the amp can't handle the decreased impedience and only drives each speaker at half the voltage, there my by no increase as eac hof the two speakers is now moving half the air volume. But the speakers could still acoustically couple for an increase of 3 dB.

[boputnam]

but regardless of the measurement system, if you compare apples to apples the outcome will always be the same.
2.83v into an 8 ohm load = 1W. So, if we're talking 8 ohms all the time, everything would be fine. But impedance varies not only by driver, it also varies with frequency.

Ballou, sums it up:

[boputnam]

CauYem, maybe we need to understand your question better.

As Todd sez, if your amp can handle a 4 ohm load (what it will see by you running those two 2226H's in parallel), you will get a +3dB increase in output.
If the amp is capable of doubling its power into half the impedience, it could be 3 dB louder as each speaker is now receiving what one speaker received and you are now moving twice the air volume.

What is the plan? Are you worried about matching the output of these to the other elements of the cabinet?

[Hoerninger]

Ballou, sums it up:
Ja.




From the efficiency, we may calculate sensitivity, which is the sound pressure level a speaker produces for a given input:
A speaker with an efficiency of 100% (1.0) would output a watt of energy for every watt input. Considering the driver as a point source in an infinite baffle, at one meter this would be distributed over a hemisphere with area 2π m² for an intensity of (1/(2π))=0.159154 W/m², which gives an SPL of 112.02 dB.

SPL at 1 meter for an input of 1 watt is then: dB(1 watt) = 112.02 + 10*log(η0)

SPL at 1 meter for an input of 2.83 volts is then: dB(2.83 V) = dB(1 watt) + 10*log(8/Re) = 112.02 + 10*log(η0) + 10*log(8/Re)

http://en.wikipedia.org/wiki/Thiele/Small

This corresponds with my German books includung "in a specified environment"
____________
Peter

[CauYem]

CauYem, maybe we need to understand your question better.

As Todd sez, if your amp can handle a 4 ohm load (what it will see by you running those two 2226H's in parallel), you will get a +3dB increase in output.

What is the plan? Are you worried about matching the output of these to the other elements of the cabinet?

Bo,

The current set up I have:
JBL 4250 loaded with (2) JBL 2226H
JBL 2482 driver w/ 2350 horn
Fostex supper tweeter T90 (this super tweeter can go down to 3KHz)

Crossover at 550Hz & 5.3KHz with Mid Freq BP-8dB, and HF HP-5dB. 8dB & 5dB attenuators were put in place of the 2 L-pads after I adjusted to the sound level I like.

Since the Fostex & 2482/2350 are 8 Ohms, I want to use only (1) 2226H so the amp would see only 8 Ohms load across the freq band. If I connect (2) 2226H in parallel (4 Ohms) then power output from the amp would drop 3dB (from 8 Ohms), then the SPL would see no gain as if the amp drive only one 2226H.

Assume that the amp is capable of pumping out more power to drive the lower impedance then the system would gain 3dB. But how do I know if the amp can do that, or would there be any distortion if the output level of the amp changes (like a step down) to drive 4 Ohms at low freq & 8 Ohms at higher freq?

This system sounds wonderful (better than my L200 +077 now moved to storage) but it looks a bit ugly & takes too much room.

[toddalin]

But how do I know if the amp can do that, or would there be any distortion if the output level of the amp changes (like a step down) to drive 4 Ohms at low freq & 8 Ohms at higher freq?



Should be specified in your owners manual or look for info on your amp on-line.

[boputnam]

The current set up I have:
JBL 4250 loaded with (2) JBL 2226H
JBL 2482 driver w/ 2350 horn
Fostex supper tweeter T90 (this super tweeter can go down to 3KHz)

Crossover at 550Hz & 5.3KHz with Mid Freq BP-8dB, and HF HP-5dB. 8dB & 5dB attenuators were put in place of the 2 L-pads after I adjusted to the sound level I like.

Since the Fostex & 2482/2350 are 8 Ohms, I want to use only (1) 2226H so the amp would see only 8 Ohms load across the freq band. If I connect (2) 2226H in parallel (4 Ohms) then power output from the amp would drop 3dB (from 8 Ohms), then the SPL would see no gain as if the amp drive only one 2226H.

Assume that the amp is capable of pumping out more power to drive the lower impedance then the system would gain 3dB. But how do I know if the amp can do that, or would there be any distortion if the output level of the amp changes (like a step down) to drive 4 Ohms at low freq & 8 Ohms at higher freq?

This system sounds wonderful (better than my L200 +077 now moved to storage) but it looks a bit ugly & takes too much room.This is a little confusing to me.

Are you running the "system" now, with the amp in question, with (2) 2226H? If so, I guess it's working! :) Seriously, most amps can handle a 4 ohm load, but it is best to check as Todd suggests.

If I understand the above, and you want to run only (1) 2226H you might have to fiddle with the attenuation of the MF and HF once you go to one 2226H. But, I may have gotten confused of your goal.