t/s specs and theoretical comparisons

This post is questioning my understand of some of the basics and T/S specs and how they theoretically apply to the comparison of how loud a sub can get. I'd appreciate thoughtful responses. I've never seen this information clearly discussed before in a manner which the general audiophile could understand, and that's what I'm looking for. Lets ignore any subjective thoughts or comments; Looking for pure theoretical facts right now. These days, there are soooo many subs out there now, it's hard to know what to choose, and how to box them, and basic T/S parameters and what it means in relation to other specs could help a lot. Yes, there are shady companies falsifying their T/S specs, lets ignore that they exist right now. Modeling subs of course is the best way, but there are some subs you can't get _complete_ T/S specs for, and there are so many subs out there that modeling them all properly takes forever. So if I can figure out what are the most important parameters to look at, I could eliminate some subs right away. But I've never seen anyone detail it in a simple relational comparison I'm looking for: Something that doesn't takes months of study to understand, but that gives a general idea of how the sub will perform in a given basic sealed or ported enclosure by simply comparing the most common T/S specs. Here's what I've learned so far, please correct me if I'm wrong or even not quite right: - The SPL rating of a sub tells how efficient at changing electrical power into sound. - Xmax is the max 1-way travel, also called peak travel; peak to peak travel would be Xmax x 2 - Ohm ratings have to do only with how much load is on your amp, and hence how much power the amp puts to the sub, but nothing to do with how loud the sub can play with a specific power level. - Wattage handling simply tells you how much power the sub can handle and has more to do with how long it will last than how loud it can get. - Subs that move more air can produce more intense sound - The farther a sub can throw, the more air it can move - The larger diameter the sub, the more air it can move. My conclusions thus far: 1) Based on what I know so far, if I had 3 subs with the same SPL, same power put to them, and the same size, they should play at pretty much the same sound levels. Right? 2) However if we increase power, each sub will increase until they reach their Xmax, and the one that reaches Xmax last will play loudest. Is this correct? Or am I missing some critical aspect? 3) To have the loudest sub in a specific enclosure, you want the one with the highest SPL, highest Xmax, and largest diameter. Additional Questions: a) How does using a sealed box vs. a ported box impact my conclusions? b) What am I missing that's important? Thanks for those more knowledgeable than me for sharing!

KyferEz wrote: - The SPL rating of a sub tells how efficient at changing electrical power into sound.

1: No. The Eta null is the number you want to see when determining the actual efficiency. It will typically be less than 1%. The SPL rating or specification only tells you how loud that driver will play, when one watt of power is applied to the voice coil. It *can* be used as a basic guideline to determine how loud a woofer COULD play, at it's rated power... Each doubling of power (theoretically) adds 3dB of output. 85dB@1W 88dB@2W 91dB@4W 94dB@8W 97dB@16W et cetera...

KyferEz wrote: - Xmax is the max 1-way travel, also called peak travel; peak to peak travel would be Xmax x 2

2: Yes.

KyferEz wrote: - Ohm ratings have to do only with how much load is on your amp, and hence how much power the amp puts to the sub, but nothing to do with how loud the sub can play with a specific power level.

3: Mostly correct. The impedance of a driver will ffect how much power an amp can make. Amps don't put out power. They have power available for the driver or load to consume. A fine line, to be sure, but let's call it what it really is. If there is no load, the amp makes nothing, but the potential is always there.

KyferEz wrote: - Wattage handling simply tells you how much power the sub can handle and has more to do with how long it will last than how loud it can get.

4: Again. Mostly correct. The wattage CAN give you an indication of about how loud a driver can play. A high efficiency, but "low" power handling driver could get louder than a high power low efficeincy woofer. See point 1.

KyferEz wrote: - Subs that move more air can produce more intense sound

5: Incorrect. Long throw woofers will always trade peak output for extension. If you have a driver that's just a BEAST, and you can throw 1200 watts at it, it'll get loud, of course, but based on #4 and by extension #1, a short-throw woofer can certainly play FAR louder. There was a huge argument on this a few years back... I'll try to dig up the thread.

KyferEz wrote: - The farther a sub can throw, the more air it can move

KyferEz wrote: - The larger diameter the sub, the more air it can move.

6: Those are both true. That's simple mechanics.

KyferEz wrote: My conclusions thus far: 1) Based on what I know so far, if I had 3 subs with the same SPL, same power put to them, and the same size, they should play at pretty much the same sound levels. Right?

Allowing for the three aspects, exactly as you put them, yes. Three different woofers, with equivalent efficiencies, radiating areas, and power applied, (AND IN IDENTICAL ALIGNMENTS!!! - that's important, too...) will all play roughly the same output.

KyferEz wrote: 2) However if we increase power, each sub will increase until they reach their Xmax, and the one that reaches Xmax last will play loudest. Is this correct? Or am I missing some critical aspect?

Not necessarily. The driver with the highest efficiency will probably play loudest, not the driver with the longest throw.

KyferEz wrote: 3) To have the loudest sub in a specific enclosure, you want the one with the highest SPL, highest Xmax, and largest diameter.

Nope. Highest efficiency. Throw the other specs away.

KyferEz wrote: Additional Questions: a) How does using a sealed box vs. a ported box impact my conclusions?

Dramatically. Vented enclosures will improve overall output for a given driver, but not all drivers will be optimally aligned in a vented enclosure.

KyferEz wrote: b) What am I missing that's important?

Oh, so much more than can be addressed in this thread. You do seem to have a decent handle on the matter as of now, though.

KyferEz wrote: Thanks for those more knowledgeable than me for sharing!

I hope I qualify. :) Here's one of the links... The most important paragraph, relating directly to some of my responses above, is this one:

haemphyst wrote: Also, WOOFER EXCURSION HAS LITTLE TO NOTHING TO DO WITH THE ACTUAL OUTPUT OF A SYSTEM. Frequency response, yes, output, no... If this were the case, then Eclipse and Adire woofers (as we all know, two exceptionally long throw, and equally capable woofers) would be capable of WAY more output than, say, a Cerwin-Vega or JBL Pro... An equally powered Eclipse or Adire woofer will NEVER exceed the output of either of these drivers. You'll notice I chose two relatively short throw woofers to compare with. This is to illustrate the fact that shorter throw will almost always equate to more output for a given input power. Output is SPECIFICALLY determined by rate of change - how fast can the woofer change direction? This factor MOSTLY being affected by 1) voice coil inductance, and 2) magnetic field strength in the voice-coil gap.

Not SPECIFICALLY what you asked for... But handy, nonetheless. Still looking for more.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."

T/S parameters (also called small signal parameters) tell you how the woofer is designed and built, but not always how it will perform in actual usage.  There are a lot of other factors to consider besides just the properties of the woofer, such as the properties of the enclosure and the way the system is installed.  These two have as much or even more influence on the final result that the woofer's T/S numbers.  Here's something I wrote a while back that might help:  https://www.the12volt.com/installbay/forum_posts.asp?tid=73962&PN=1Support the12volt.com

I was looking for that thread, too... Couldn't find it! Thanks DYohn! Additionally... Steven links to an Adire paper that is no longer available. I had the foresight to upload it to the12volt... :P Here it is...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."

Very good info, thanks. I'll read over everything in those links a few times.

The statement about the Xmax having little to do with a driver's output is confusing... While I can understand that a woofer that changes direction faster can produce more SPL because it's compressing sound faster, and that a lighter, more compliant woofer is likely more efficient, I still find it difficult to understand how woofer excursion has "LITTLE TO NOTHING TO DO WITH THE ACTUAL OUTPUT OF A SYSTEM". Why is this hard to understand? Because SPL is sound pressure level. Pressure is generated by speakers by moving air. So it would seem that being capable of moving more air would generate more pressure (SPL), right? Seems correct because if you play a 50Hz tone, as you increase volume, the woofer's excursion increases... So how can a woofer reach high spl when it's excursion is limited? Of course if a woofer has an efficiency advantage it will obviously be louder with less power, but how can it contend with long-throw woofers when they can move, and therefore compress, more air? I know I must be missing something critical... Thanks!

Ah, I just re-read the paragraph in question. The statement is being made assuming equal power... So a long excursion woofer can exceed the SPL of one with a shorter throw, but will require more power. But that still doesn't explain how a woofer with a short throw can acheive such high SPL. Is it simply because a woofer with a shorter throw can be lighter and more efficient and can change direction much faster?

KyferEz wrote: Ah, I just re-read the paragraph in question. The statement is being made assuming equal power... So a long excursion woofer can exceed the SPL of one with a shorter throw, but will require more power. But that still doesn't explain how a woofer with a short throw can acheive such high SPL. Is it simply because a woofer with a shorter throw can be lighter and more efficient and can change direction much faster?

Generally it's because shorter Xmax goes hand in hand with higher efficiency.  But it has nothing to do with the weight of the system.  Weight (and woofer size) has nothing whatever to do with woofer speed.  That is a function of voice coil inductance.

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[quote]Weight (and woofer size) has nothing whatever to do with woofer speed. That is a function of voice coil inductance.[/quote]I beg to differ about weight... Just thinking basic physics, objects have inertia, therefore an object with more weight (or I really mean mass) moving in one direction has more inertia than an object with less mass, and therefore the object with more mass cannot change direction as easily as an object with less mass. Therefore, as I see it, it would take more power to reverse the direction of the woofer travel, and thus a woofer with more mass is less efficient...

KyferEz wrote: I beg to differ about weight... Just thinking basic physics, objects have inertia, therefore an object with more weight (or I really mean mass) moving in one direction has more inertia than an object with less mass, and therefore the object with more mass cannot change direction as easily as an object with less mass. Therefore, as I see it, it would take more power to reverse the direction of the woofer travel, and thus a woofer with more mass is less efficient...

That's a common misconception.  Here, rather than try to explain it myself read this paper.

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