SPL formula?

2 reasons for excursion: 1) You hit the nail on the head. Excursion is sexy. 2) Maximum SPL can be much higher, because the driver has the potential to displace more air, and driver box size can be smaller. This makes high excursion ideal for car audio. Remember that displacement = cone area * xmax. If xmax is low you must have a much larger cone area to displace the same amount of air. Take the Brahma, it can operate in a TINY! box. Which is awesome for car audio use. It's max SPL is LARGE. Like I said, however, there are no free lunches. In exchange for these positives you lose efficiency. Thus, there is no "perfect driver," high excursion is right for some people/applications and wrong for others. What do you think of WinISD, have you played with it, comparing different drivers? New Project: 2003 Pathfinder

Yeah, WinISD is a neat program. I have been comparing a few of the "big name" subs. Well, I still am wondering. Why don't the companies focus on increasing efficiency instead of increase excursion? I mean, why not try to develope a sub with an efficieny of over 100Db 1w/1m @2.83v, and can handle 300~500w RMS? That would be a loud sub. And if the excursion was kept low, let's say less then 0.75in peak-to-peak, it would be extremely easy to prevent side to side motion from occuring.

Poormanq45 wrote: Yeah, WinISD is a neat program. I have been comparing a few of the "big name" subs. Well, I still am wondering. Why don't the companies focus on increasing efficiency instead of increase excursion? I mean, why not try to develope a sub with an efficieny of over 100Db 1w/1m @2.83v, and can handle 300~500w RMS? That would be a loud sub. And if the excursion was kept low, let's say less then 0.75in peak-to-peak, it would be extremely easy to prevent side to side motion from occuring.

Well, because of the same reasons I stated earlier.  Massive excursion allows the woofer to produce greater displacement with smaller drivers in smaller enclosures.  This is very valuable in cars, as space is at a premium.  But you're right... Pro audio generally uses higher efficiency lower excursion woofers.  Stevdart and I actually had a conversation about this recently.  I think we were comparing 2 generic but very efficienct 12" pro sound woofers to one Brahma.  Basically for SPL above 40hz or so the 2 12" pro sound woofers kick the snot out of a single Brahma.  However, they require a 5ft^3 ++ box to operate like this.  The Brahma would work great in a 0.5ft^3 box.  Also, the Brahma had better low frequency extension even though it had smaller cone area, because of its excursion capability. 

There is a high efficiency following in home audio.  Basically most tube amplifiers you see are very low wattage and are meant to drive high efficiency speakers.  Adire makes a bookshelf speaker that is high efficiency, works well with as little as 3 watts and is 95db sensitive. 

With amplifier power being cheap and true home audiophile grade stuff just being impractical for car audio use, I don't see high efficiency catching on in car audio.  However, that doesn't mean you can't be a smart consumer rather than fall prey to the "MORE IS BETTER EXCURSION RULES!"  trend that seems to be going on.  I see real value to high excursion for SPL people.  For daily drivers, SQ cars, and just about everyone else not willing to spend big amplifier dollars, I think that the smartest strategy is to evaluate the space you need to operate in, your sound quality and level goals for the system, and the amplifier power willing to throw at the subwoofer... I'd take those considerations and use them, together with software modeling and education like we're conducting, now to make the smartest buying decision. 

For me it was a lower excursion more efficient sub that operates within my goal levels at 200w.  For others it will mean a RE XXX with 1500w in a low Q sealed box with a band of +3db of parametric eq around 30hz to really make the bottom end deep.... It'll change along w/ goals :-)

New Project: 2003 Pathfinder

Poormanq45 wrote: [quote]Dood, as I have stated several times, SPL is RATE OF CHANGE!

Isn't the rate of change called the Transient Response? SPL = Sound Pressure Level.[/QUOTE] No, transient response is a drivers bility to react, FROM A STATE OF REST, and be able to accurately follow the electrical curve, accurately reproducing acoustically the original signal. Poor transient response is indicated by smearing or inaccurately following the electrical impulse. SPL, or sound pressure level is determined by a driver's ability to go from out to in (WHILE ALREADY IN MOTION) in the minimum time. Transient response has LITTLE, IF ANYTHING to do with a drivers maximum output capabilities.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."

"sound pressure level is determined by a driver's ability to go from out to in (WHILE ALREADY IN MOTION) in the minimum time." So, does that mean that a tweeter can produce a much higher SPL then a Sub? I mean, tweeters usually go up to, and above 20K Hz. That requires a really fast response time.

Look what I found: http://www.silcom.com/~aludwig/Physics/Exact_piston/Exact_piston.htm

[QUOTE=Poormanq45]Look what I found:

http://www.silcom.com/~aludwig/Physics/Exact_piston/Exact_piston.htm[/QUOTE]

What exactly do you think you've found there?

New Project: 2003 Pathfinder

Poormanq45 wrote: "sound pressure level is determined by a driver's ability to go from out to in (WHILE ALREADY IN MOTION) in the minimum time." So, does that mean that a tweeter can produce a much higher SPL then a Sub? I mean, tweeters usually go up to, and above 20K Hz. That requires a really fast response time.

Well, most tweeters ARE much more efficient than woofers.  Thus, given the same amount of power, tweeters DO produce more SPL than a sub.  This makes perfect sense.  Remember our friends Mms (moving mass) and motor force (BL) that comprise SPL?  Well, if the moving mass is very small the motor force doesn't need to be large to produce large SPL.  The rate of change haemphyst was talking about can be extreme.

Your asking this question actually probes at the usefulness of xmax.  Producing a 10khz tone through 1" tweeters you can hit ear piercing SPL levels if fed enough power.  However, like haemphyst stated earlier, drivers are drivers, xmax limits tweeters too.  The same tweeter probably won't be able to produce a 1khz tone at the same spl level without greatly exceeding xmax.  It'll probably be damaged.  Excursion limits maximum spl differently at different frequencies. 

Again, xmax shouldn't be used to determine SPL, it should be used to determine max spl at a given frequency.

New Project: 2003 Pathfinder

Sound Pressure in the Far-field Using the definition of f o in the wave spectra section, equation (W19), the sound pressure in the far-field can be written So apart from minor changes in notation, this is identical to the exact boundary integral result. A rather remarkable consequence of equation (P6) is that for a constant value of u0, on the z-axis the pressure is a linear function of frequency from DC up. Considering the complex behavior that occurs as a function of frequency, this is extraordinary. Sound Pressure in the Near-field Substituting the solution for D(b ) into equation (P2), the pressure at an arbitrary point in space is This integral is tricky to evaluate numerically. To obtain results at the baffle surface z=0 it is best to divide the integration range into 3 segments. The first segment from 0 to 4k is evaluated using a change of variables b =sing . From 4k to 10k the form above works best. The final infinite segment can be evaluated as a Weber-Schefheitlin type integral [NBS Handbook equations 11.4.33 and 11.4.34] less another numerical integration. A plot of the pressure at the baffle surface z=0 shows the result of this equation as solid lines, for ka=2p [30kb]. The piston velocity profile is in blue. Pressure is normalized by Zo, so it is expected to approach the velocity value of 1.0 for large ka. The result of the boundary integral is shown by the dots. A rather dense set of integration points were used, spaced .01 wavelengths apart. The pressure was evaluated at z=.05 wavelengths, and then a phase shift applied to approximate the surface value. Finally, the results of the numerical solution are shown, as the dashed line. I am quite happy with the agreement between these three results. The boundary integral is off a bit, but the agreement between the other two is pretty darn good. In all of the remaining plots, the exact equation result is shown as a solid line, and the numerical result as dashed. The agreement so good you have to look carefully in some cases to see that there really are two curves.

Right, that's what the page says, but what do you think this means with regards to our discussion? To me it simply tells us that for some generic driver we can obtain numerically _relative_ pressure for a point in space, either in the near or far field. In other words, I think this page helps us little. We're talking about finding either specific or maximum pressure based on physical parameters on a specific driver. Someone correct me if I'm wrong, its been over a handful of years since I've had any reason to look at integral math. New Project: 2003 Pathfinder