subterranean tibia

I've read the books and can do the calculations if need be and all that but to my limited understanding they are just numbers in an equation... what do they actually MEAN? I see people talking about OB, Dipoles etc. and saying whatever driver is suited or not suited for it because of whichever Qxx, or talking about infinite baffle subs and lots of other things that aren't springing to memory. I'm just wondering what you guys are reading into them that you can make these deductions of the drivers capabilities off of a single number and further more WHY that is the case. This came about because I want to replace the drivers in my car, I'm not really to sold on what is traditionally available for cars. It all seems so gimicky and flashy, and component sets come with passive XO's. I'm not an XO guru or anything but I've waded in those waters enough to ask how can they presume to design an XO with no regard to any diffraction effects that would probably be fairly nasty being mounted in a car and probably different in every case. Plus who knows what axis the listeners ears will be when installed. Then there's phase alignment, and on and on. I'm not keen on paying a premium for a XO that might not be much better than a text book version. I'll measure and do my own thanks.

Sorry for the off topic rant. Point is I trust the drivers we deal with here much more because they have been used and tested to death and there is lots of info on them and what they sound like, not just "they rattle my mirrors" or "I can hear then down the block" as the typical mentality goes in the mobile audio forums. I need to know how to usefully interpret the TS params to know what will work. For example the 6.5" in my doors obviously use the door cavity as an enclosure but it'll be a non-ideal and leaky enclosure to be sure and a rather large one too. Also I have a RSS210 which seems like a good fit to replace the 8" sub in my back deck but how do I know it will work well being sort of infinite baffle using the trunk (leaky too I'm sure) as a way too large sealed enclosure.

Concerning t/s parameters, see if this helps: http://www.diysubwoofers.org/definitions.htm#tsparam

Concerning car audio crossovers, they tend to be fairly generic in nature, and I always felt they were more about power management (i.e. keep damaging low frequencies away from the tweeter, and perhaps keep high frequencies that fall within the breakup zone away from the woofer) than FR adjustment - that's what you've got EQ for .

For door woofers, IMO it's the combination of Fs and Qts that counts, e.g. if the driver has low Qts, it should also have low Fs.

Concerning infinite baffle mounting, IMO it's more about how the driver behaves under large signals, which t/s parameters aren't going to accurately describe. If the cone seems to go "out of control" when the volume's turned up (or worse, the suspension actually allows the former to hit the back plate) , then it's probably not a good match for infinite baffle mounting in a car audio environment.

Q's?

Well, there's mechanical Q (Qms) which is said to be a driver's mechanical propensity to resonate. To relate it to cars (suspensions, actually, and not really all that different), if you had 2 cars of the same weight (mass), and one had soft springs and the other VERY stiff springs; if you "bounce" each of them, the stiff springs won't oscillate too many times compared to the softer springs. For a driver, this number changes with changes in cone mass (dia. and material, and really includes the mass of ALL moving components, like the voice coil and its "former") and the stiffness of the suspension (typically the spider and the surround).

Electrical Q (Qes), the driver's electrical "resonance factor", is related to the electrical "motor" strength (magnet size and configuration, and its relationship to the VC) and how well it can control (or "damp") the moving cone. Small motor systems can't control a massive cone with a soft suspension very well. It's like having worn out shock absorbers on your car. A strong motor has a low Qes (and subsequently, a lower "Q", or Qts) and can be a highly damped system. With VERY low Q drivers, you sometimes lose the ability to provide deep bass. Little (cheap) magnets are common on high "Q" (typically cheap) drivers. Goldwood comes to mind.

"Qts" is the "Q" of the "system" (a mathematical relationship between Qms and Qes). A number we can use in box design that takes both the mechanical AND electrical resonance factors into consideration.

Putting a driver in a closed box raises its Q, and yet this is another Q, Qtc. The Q (a.k.a. "Quality factor") is NOW describing a given driver placed into a box of a given volume. Since (for mathematical reasons) a closed box "Q" (Qtc) of 0.707 (half the sq.rt. of 2) is most often considered a nominal "aim point", only drivers with Qts values BELOW 0.70 will be able to achieve 0.707 "in box". Drivers with higher Qs (like many Goldwoods) can work better NOT in a box, since the box only raises their Q even higher. These are typically the kinds of drivers that get used in auto sound, because they've got the right "Q".

Drivers for a vented box work best with a Q (Qts) in the range of 0.30 up into the 0.40's (SOMEtimes, even into the 0.50's), but higher Qs in a vented box most often can not avoid a "roller coaster" rolloff response.

In a car, you want a Low Fs if possible, and ideally a Qts of about 1.0 for in-door drivers. The RSS210 will not like an IB setup, as its suspension is awfully compliant. Qts = 1.0 is best for this as well.

If you have a higher Qts, then you get one-notey bass, or bass that peaks and is really muddy without anything in terms of low extension.

FWIW- many people love the Silver Flute drivers in car doors. They apparently have the best compromise of in-door speakers.

My 2c,
Wolf

Q is defined as the amount of 'damping' that the mechanical, electrical, and total contain. For instance- a higher Qms is a tighter suspension. Qes works the other way, More Qes is a lossier electrical damping.

I find that Qts of up to 0.6 can be used in a vented box- in most cases. (Most people prefer mid 0.4X to be optimal.) And you can vent Qts of 1.0 if you can make the driver work in that alignment. There are so many factors to play with.

Later,
Wolf

Q is defined as the amount of 'damping' that the mechanical, electrical, and total contain. For instance- a higher Qms is a tighter suspension. Qes works the other way, More Qes is a lossier electrical damping.

I find that Qts of up to 0.6 can be used in a vented box- in most cases. (Most people prefer mid 0.4X to be optimal.) And you can vent Qts of 1.0 if you can make the driver work in that alignment. There are so many factors to play with.

Later,
Wolf

To be a little more precise, Qms is the measure of mechanical loss associated with a driver suspension. Qes is a measure of electrical loss. Whether or not a suspension is "tight" refers to its compliance - not the degree of mechanical energy loss. Reading posts here and at other DIY sites, there are a lot of generalizations about whether a driver is good for a particular loading type or not as if a clear line were drawn in the sand. A more wise approach is to focus more on the impedance plot of a driver under test. One should think of it as an energy storage curve and decide whether or not the intended loading mechanism will be efficient in converting that stored energy to acoustical energy.

One should also keep in mind that the behavior of mechanical and electrical losses changes significantly with applied signal level and that T/S parameters are derived from a standard that is set at essentially 1V applied signal. For example, at low signal voltage, low frequencies a low compliance woofer is likely to have higher electrical losses than a high compliance one since very little of the applied energy results in deflection of the driver diaphragm and hence there's very little mechanical energy storage. The voice coil becomes essentially a transformer. On the flip end, at very high excursions and high signal levels, the high compliance driver's suspension loses its ability to store more energy and the voice coil winds up (pun intended) acting once again like a transformer.

As I see it, new designers are better served by focusing on Vas (driver compliance volume) and building enclosures that are reasonably close to that parameter as the primary or fundamental consideration. Whether or not a sealed, vented, or infinite baffle type loading is used should be a secondary consideration that affects ultimate response. To me, if the enclosure's volume is not reasonably close to the driver's compliance volume, you're not likely to get an "optimal" result.

YMMV, of course

Q as a term, equals damping. It's damping in xover filters, it's damping in notches. All are using Q as a term.
Higher losses would be less damping, plain and simple.

Later,
Wolf

As I see it, new designers are better served by focusing on Vas (driver compliance volume) and building enclosures that are reasonably close to that parameter as the primary or fundamental consideration. Whether or not a sealed, vented, or infinite baffle type loading is used should be a secondary consideration that affects ultimate response. To me, if the enclosure's volume is not reasonably close to the driver's compliance volume, you're not likely to get an "optimal" result.

Maybe I misunderstand your meaning, but you appear to be saying the box should add the same amount of 'spring' to the cone as the suspension does. Seems to me for drivers with a Qts of over .7, this would not be a good thing.

Ryan,

Much of the sense of what the T/S parameters mean in terms of the possibilities or limitations of a particular driver simply come from a lot of experience building boxes and/or modeling designs. You might try using a modeling program and altering the various T/S parameters of the driver in increments to see what effect they have on different cabinet designs.

Maybe I misunderstand your meaning, but you appear to be saying the box should add the same amount of 'spring' to the cone as the suspension does. Seems to me for drivers with a Qts of over .7, this would not be a good thing.

Air within the enclosure effectively has a mass and spring associated with it. If the spring constant of the suspension is vastly different from that of the enclosure's air, obtaining a more perfect "counterbalance" or anti resonance to cancel the fundamental resonance of the driver will be more difficult. You can use the spring aspect of the air volume to increase effective damping but that is not the only way to reduce stored energy associated with resonance to get a more ideal response. Adding stuffing to a sealed or vented box also increases mechanical loss that can flatten out or reduce the Q.

If you compared the second harmonic distortion for a driver in a sealed box with volume much lower than Vas to a setup with internal volume closer to Vas that uses stuffing, you'll find the larger internal volume version has less distortion in the output FWIW. The differential equations that define the motion of a damped oscillator also back this up.

I'm only talking about what is "optimal" or for me, the optimal approach. Anyone can modify the approach as they see fit. For me, I use the Vas as a baseline parameter and work out from there.

http://en.wikibooks.org/wiki/Enginee...ical_Analogies
with no regard to any diffraction effects T/S parameters are not involved with aspects such as diffraction ( as you probably know )

Higher losses would be less damping, plain and simple.

Now that is funny

subterranean tibia

Monday, December 17, 2012

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