SPL formula?

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Poormanq45

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Posted: December 24, 2004 at 6:32 PM / IP Logged

Is there a formula to calculate what the SPL will be?

I'm thinking tha tit would include:

Frequency, Cone/Swept Volume, Excursion

Is there anything else? To keep it kind of simple, lets assume that the diver is not in an enclosure.

So, is there a formula?

Alpine Guy

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Posted: December 24, 2004 at 10:48 PM / IP Logged

im shure there is a formula, ,but it would take a physics professor/engineer about 500 equations to come close.

2003 Chevy Avalanche,Eclipse CD7000,Morel Elate 5,Adire Extremis,Alpine PDX-4.150, 15" TC-3000, 2 Alpine PDX-1.1000, 470Amp HO Alt.

haemphyst

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Posted: December 24, 2004 at 11:57 PM / IP Logged

a VERY GENERAL rule of thumb is this: A doubling of power will net a 3dB increase in output. This applies ONLY to a true infinite baffle loaded driver, and in an anechoic chamber. Boxed drivers, and automotive volumes all have a dramatic effect on the net efficiency, and maximum output of any driver in any given situation.

While it DOES require frequency, the others do not really come into play as much. You will have more output at resonance. Generally speaking, you simply take the Re (Reference efficiency) of the driver, and add 3 to that number for each doubling of power you will be applying to the driver.

It all reminds me of something that Molière once said to Guy de Maupassant at a café in Vienna: "That's nice. You should write it down."

Poormanq45

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Posted: December 25, 2004 at 8:14 PM / IP Logged

So, there is no corelation between peak-to-peak excursion and SPL? I would think that a driver moving 2inchs peak-to-peak would put out a higher SPL then a driver of the same size/volume moving only 0.5 inch peak-to-peak.

Does anybody else have any info about my question? To me, it would seem feasable to get a really accurate equation for SPL based on a few factors.

Now as haemphyst said, resonance would screw up this calculation, but wouldn't it be semi-accurate else where in the frequency range?

Alpine Guy

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Posted: December 25, 2004 at 8:49 PM / IP Logged

Yup, there is a corelation between excursion and spl, but it also has to do with the VC wireing, cone diameter, power requirements. All those fun factors. But one of the biggest is the actual vehicle your putting the subs into. 1 sub in a suv can hit 130 db, ,while that same sub, same box, , everything the same in a car could hit 120db, , , so its really impossible to get close.

2003 Chevy Avalanche,Eclipse CD7000,Morel Elate 5,Adire Extremis,Alpine PDX-4.150, 15" TC-3000, 2 Alpine PDX-1.1000, 470Amp HO Alt.

kfr01

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Posted: December 26, 2004 at 11:38 AM / IP Logged

I think there are two different discussions going on here. One, what haemphyst was talking about, is SPL for a given driver and amount of power, raw SPL, if you will. Haemphysts formula, minus some unknown variables, as he pointed out, is correct.

Two, is what poormanq started talking about, maximum SPL.

It is simply incorrect to assume that a 2" peak to peak subwoofer will be louder than a lower excursion subwoofer. As Alpine pointed out, there are MANY other variables that enter the calculation for both the lower excursion sub and the higher excursion sub. Also, at this point, it is foolish to consider the raw driver itself, outside of the practical application of an enclosure.

High excursion has an effect on power handling, which ultimately effects maximum SPL. Where one sub may reach its physical limits with 300w, a high excursion subwoofer might be able to handle 1200 watts. While this might sound great, remember that physics doesn't allow free lunches. In general that high excursion subwoofer is much less efficient and has less cone area because of its high excursion capability. So, the puny 300w low excursion subwoofer will probably be LOUDER from 0-300 watts than the high excursion subwoofer in similar qtc enclosures.

We've been having practical discussion about this in another thread. Like Alpine and Haemphyst said, there are a lot of unknown variables to any final in-car SPL determination. However, using some enclosure design software you can at least compare subwoofers against eachother. To my knowledge this sort of software modeling is the only way to obtain the most complete picture, outside of actually trying it.

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auex

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Posted: December 26, 2004 at 11:56 AM / IP Logged

You guys want to know the secret formula for SPL numbers?

YOU-$10.00+GUY WITH RTA=SPL measurement.

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Poormanq45

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Posted: December 26, 2004 at 1:40 PM / IP Logged

Thans for the info kfr01, haemphyst, ans Alpine gy.

Ok, I understand that it is not possible to make a formula that works for different drivers in different enclosures, but is it possible to make a formula to calculate SPL based on excursion for single driver?

kfr01

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Posted: December 26, 2004 at 9:17 PM / IP Logged

Poormanq45 wrote:

Thans for the info kfr01, haemphyst, ans Alpine gy.

No.

Why are you so hung up on excursion? Excursion can HURT maximum SPL just as easily as it can help it. You need to look at the whole picture.

Also, what would be the point of a free-air, no enclosure, maximum SPL rating? Maximum SPL is LARGELY a function of the power fed to the subwoofer and the enclosure used. I see no point at all to your idea.

New Project: 2003 Pathfinder

haemphyst

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Location: Michigan, Bouvet Island

Posted: December 26, 2004 at 11:27 PM / IP Logged

You're right, kfr01... I have NEVER seen even a reasonable efficiency on a high excursion driver. Those damn laws of physics again... Output is a function of RATE OF CHANGE, not how MUCH change (which is what excursion would effect)... Excursion is presently the biggest killer of output there is. BTW, I would consider 91-93dB a reasonable output on a driver with 2 inches of pk-pk. Good luck finding ANYTHING close to that. My 9122 by Eclipse is specified at 87, and that is probably a bit optomistic. The Ti 10 from Eclipse was specified at 84, but when my buddy at Harman spec'd it out on the Klippel machine, it actually settled on 78! 78dB/w/m!!! THAT IS ABYSMAL!!!!

I have a few posts regarding this issue under my belt...

Try this...

Or this...

Read some of those posts, and see if that'll answer any of your questions a little better...

I STILL think, though, that with all the technology we have today, why can't we have a low Fs, decent efficiency, long Xmax driver? With NdFeB getting so cheap, why we can't stack about 10 pounds on a motor, and boost that efficiency... Steven?

It all reminds me of something that Molière once said to Guy de Maupassant at a café in Vienna: "That's nice. You should write it down."

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