Non-linearity of air?

placid warrior wrote: Poormanq45 wrote: Ok thanks. Question: What's the recommend enclosure size for an Adire Brahma 15? The Total volume displaced by it = 124.2163in^3 i believe its 4.731 ft^3

Actually that's closer to a large ported enclosure size.  We normally recommend around 2.5 cubic feet sealed for in car use. 

Steven Kephart

Adire Audio

hamfist:     1) My EQX is so *beautiful* ... how do you solder stuff that small anyway? How is that possible? *cheers* 2) Well... one thing here at the bottom just doesn't make sense to me: Output is SPECIFICALLY determined by rate of change - how fast can the woofer change direction Isn't that... uhh.. frequency.. occilations/second? Like the woofer moves back and forth 50 times when playing 50hz? And the *distance* it is moving when doing so determines spl? I mean.. sound volume is really a measure of air distruption right? Like.. everyone knows the louder a woofer a gets the more back-and-forth it moves. I know from reading here the best determination of a clean woofer at significant output is a high excursion, but ultimately, wouldn't that also be the best determination of ultimate output as well? I notice the way you word this sentence: This is to illustrate the fact that shorter throw will almost always equate to more output for a given input power. Isn't that speakers in general? Like.. the smaller a speakers' excusion, the more efficent it is .. louder at a given input power... likewise however, the speaker loses sq(linearity?) at volume, *as well as* ultimate volume? By that stick both the Adires' and the Eclipses' should have significant headroom on a JBL.. they just need to be plied with more power? Am I misinterpreting this? "I'm finished!" - Daniel Plainview

steven wrote: Unless I'm mis-reading what Heamph is saying, I've got to agree with you on this one. There is no replacement for displacement is as true in speakers as it is in vehicles. It was said "An equally powered Eclipse or Adire woofer will NEVER exceed the output of either of these drivers", but I think enclosure size was left out of the equation. Put the pro sound subs in the smaller enclosures required for the Adire/Eclipse subs and you will greatly limit their output, especially down deep. They gain their efficiency from the enclosure, not their low excursion (well partially from less mass maybe, but at what cost?) or inductance. In fact, I wouldn't be surprised if the Brahma's inductance is similar to the pro sound units being that it uses an XBL^2 motor (shorter coil compared to the overhung units for a given excursion). In other words, inefficiency isn't a symptom of the higher excursion, but a symptom of the small enclosure design because of their intended market.

Ah, but you have to remember that those CVs and JBLs start out with a larger Sd due to the fact that they do not need a surround that can handle an extremely large excursion. This gives them the advantage right off the bat by increasing cone area. Steven: What's the output of one of your 15s(anyone) at 25watts RMS? NM, I just graphed the 15in Brahma against the JBL W15GTi. I put them both in the same size enclosure(2.667ft^3) and tuned both to 30.49hz. Set the input power to 25w on both. The JBL shows higher SPL across the graph until above 400hz where it starts to roll off and the Brahma stays flat. Both the Sd and the Bl are higher on the JBL then the Adire.

Poormanq45 wrote: Ah, but you have to remember that those CVs and JBLs start out with a larger Sd due to the fact that they do not need a surround that can handle an extremely large excursion. This gives them the advantage right off the bat by increasing cone area.

Huh. I never even thought of that. I wonder if that would make the difference? Like a 1/4 - 1/2 inch extra sd would, on the outside of a cone like that, translate into greatly increased cone-area... maybe the extra cone area *would* move more air than an extra few mm of xmax? I'm gonna play with numbers for a little while I post back on this later. What does bl have to do with output? I thought bl was a measure of motor force.. like.. it translates into cleaner sound and more woofer control.. not necessarily more output? What is the connection between bl and output?"I'm finished!" - Daniel Plainview

Yep, that extra cone area does indeed make a difference, but the high ecursion drivers quickly make up for that small difference once they go past the excursion limits of the short excursion driver. Hmm, I think there's a connection between Bl and output, but I can't think of it right now BL   Expressed in Tesla meters, this is a measurement of the motor strength of a speaker. Think of this as how good a weightlifter the transducer is. A measured mass is applied to the cone forcing it back while the current required for the motor to force the mass back is measured. The formula is mass in grams divided by the current in amperes. A high BL figure indicates a very strong transducer that moves the cone with authority!     

I'll respond later -- when I am not up to my ass in alligators. My grandpa always told me "Don't make yourself irreplaceable - because you make yourself unpromotable". I have no idea what that has to do with ANYTHING, but I seem really busy at work lately.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."

wow... I reaaally did it... Y'all asked for it!!! Here's a link to a semi-recent thread here on the12volt... Some other good links to other threads and web-pages within it as well. (please excuse the rantings, tho...) (Answers from here on out, appear as the questions did... ) sedate 1: I'm glad you approve; and practice, practice practice... 2: Yes, rate of change could be seen as simple frequency response, as a woofer DOES have to move faster for higher frequencies, but doesn't it have to move faster for low frequencies as well - because of the throw? As Steven states in his answer to this, it has more to do with the "transient response" of the woofer. (I still hate using that phrase - it, IMO, relates to something completely different) How fast can the motor structure make that woofer cone CHANGE DIRECTION from in to out? This rate of change is the AMPLITUDE of an audio signal in air. When a woofer is moving a great distance, and the amplifier says "Move back in" by changing the electrical signal it is feeding to the voice coil(s), this change is supposed to happen as quickly as possible, right? The BIGGER the electrical signal the amp feeds the woofer, the faster it will want to move the other way, right? Well, the bigger the electrical signal the amp feeds the woofer, the faster it "turns around", the louder the woofer's output, right? And, the longer stroke observed... There you go... Yes, generally speaking, a smaller speaker (like a mid or tweeter) will have an EXTREMELY LARGE (strong) MAGNETIC FIELD, relative to the size of the diaphragm it is expecting to move, and/or a relatively large electrical signal from the amp. This is why a smaller driver will generally have more output for a given electrical input. I have noticed that longer throw woofers do seem to have better sound quality at extreme outputs, and this probably relates to the linearity curve... At longer excursions, a short-throw, high(er) efficiency woofer will (or should) sound not quite as good - because they begin to work in a far less linear range. Yes, I think your assumption is safe, BUT, the determination of ultimate output is determined by how much power is fed to said woofer, not it's excursion capabilities. Steven I was assuming EQUIVALENT ALIGNMENTS. All drivers in a sealed, and say Qtc of .707 enclosure. The enclosure size and alignment DOES ABSOLUTELY affect the output, but my statement should have put all of the drivers on a level playing field, even if it does not say it. The Parthenon also uses so much neo magnet in it's motor, that the steel in the motor structure is this close (dave holds his hand up with forefinger and thumb with a vanishingly small gap between) to being saturated. This gives it a HUGE magnetic field to work with. Again, back to the strong magnetic field, and the mandatory control it will have over the diaphragm for a given inout signal. While it is ABSOLUTELY IMPOSSIBLE to saturate the air in the gap, you can eventually saturate the metal structure UP TO THE GAP... This, and your Parthenon has FOUR SQUARE FEET OF DIAPHRAGM... Quite the advantage there, eh? How about if the Parthenon only had 75 square inches of radiating area? Oh sure, the surround would have to be 6 inches across, but I bet with a motor structure like it has, the output would be even BETTER than the big one. No. Inefficiency is NOT a symptom of excursion, but it is completely a by-product of excursion. The trade-offs are manifest! Another thing I just thought of: Longer excursion almost necessarily maens more stress on a diaphragm, this mandates heavier, stiffer cones to minimize distortions... (exotic materials not completely included, but not completely excluded either - this IS a GROSS generalization) I was looking at an Eminence guitar woofer, and it has an Sd of 95 inches square, a Vd of a MERE 125cc, a MMS of 33g, but an efficiency of 96dB! (this is a guestimate, as the efficiency guide for these drivers actually specifies X efficiency at Y frequency - the sign of a GOOD loudspeaker manufacturer. These actually spec as high as 101.8dB at 3K! (Alpha-12)) Check here for the way Eminence specs their drivers. Poormanq45 Yes the CV and JBL drivers DO have a larger Sd, but not enough to equal the kind of efficiency gains one sees between them and an Eclipse or Adire. My SW9122, for example, spec'd on the Klippel Machine at the Harman Labs, acheived an ABYSMAL 84dB! The old-school (1st gen) 10 inch Ti?, 78dB!!! No WONDER I have to beat it with 2700 watts! To HAVE TO HAVE three+ HORSEPOWER to drive a woofer is a sad state! (One horsepower, BTW, is 746 watts, so really I have almost FOUR horsepower!!!) This goes to answer your final question/statement, too, sedate. Yes, the increase in cone area SHOULD give more output, but I still maintain that all of the above statements have FAR more to do with it than the small (25%) increase in cone area. A 100% increase in cone area nets (again - oversimplified dramatically, for the purposes of discussion) a 3dB increase, whereas these drivers are upwards of 6 to 8 dB more efficient - a 400%increase in output... Damn... my fingers are tired, and so is my brain... sleepy-time...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."

ham wrote: When a woofer is moving a great distance, and the amplifier says "Move back in" by changing the electrical signal it is feeding to the voice coil(s), this change is supposed to happen as quickly as possible, right? The BIGGER the electrical signal the amp feeds the woofer, the faster it will want to move the other way, right? Well, the bigger the electrical signal the amp feeds the woofer, the faster it "turns around", the louder the woofer's output, right? And, the longer stroke observed... There you go...

I understand what you're trying to say, but the way you said it sounds like you're talking about the actually frequency changing. That would be the only time the driver would actually move faster. well, lets look at the sine wave. AS you increase the amplitude the excursion MUST increase, correct? This occurs to move a larger volume of air. Were you just trying to say that the driver covers more linear distance, meaning higher excursion, at higher amplitudes? If so then yeah I agree with you and this post can be disregarded. anyways, good post. Me sleepy too. What was that talk of alligators?

Poormanq45 wrote: Ah, but you have to remember that those CVs and JBLs start out with a larger Sd due to the fact that they do not need a surround that can handle an extremely large excursion. This gives them the advantage right off the bat by increasing cone area.

True, but you are talking about minimal cone area differences.  Especially since a lot of pro sound drivers use undersized baskets.  So the cone area is 5-10% larger, but if I'm guessing correctly (as specific models of drivers for the "low excursion" units weren't provided for me to check) we are talking about significant increases in exucrion.  My guess would be about 4 times the excursion.

Poormanq45 wrote: Steven: What's the output of one of your 15s(anyone) at 25watts RMS? NM, I just graphed the 15in Brahma against the JBL W15GTi. I put them both in the same size enclosure(2.667ft^3) and tuned both to 30.49hz. Set the input power to 25w on both. The JBL shows higher SPL across the graph until above 400hz where it starts to roll off and the Brahma stays flat. Both the Sd and the Bl are higher on the JBL then the Adire.

I don't think they were talking about the GTI sub.  It has a pretty high excursion at over 20mm.  Also, I'm going to venture a guess that you are using WinISD for the above graphing.  WinISD sets the curves based on the sensitivity from the parameters.  JBL lists their sensitivity at 91 dB, but they also specify that at 2.83 volts with an Re of 3.2 ohms.  This means that the sensitivity rating is 2 watts instead of our 1 watt rating.

This is where I wish I had LspCad on my computer since it can provide a more realistic prediction of compared output of the drivers in question.

Steven Kephart

Adire Audio