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Old 07-30-2006, 04:36 PM   #1
geolemon

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"What matters" with regard to speaker specs, T/S specs, for the layman

If you are looking to "get your feet wet", with understanding what the heck all these specs, figures, and numbers mean - my best advice is to NOT worry about the textbook definition of "what they mean" literally - there's really not much practical value in that for most enthusiasts.

Let's take a look instead at "what can I use these specs for, to understand this subwoofer better?"
...and you may be surprised that with many of these specs, comparing them from one manufacturer to another is like compariing apples to oranges.
So it pays to understand what questions to ask when you are looking at them, also.

Qms -
A mechanical / pneumatic "quality" number that truthfully doesn't lend a great deal of insight to helping you choose a subwoofer for most applications.
It is affected by physical properties that you can look at more accurately (IMO) through other specs, such as moving mass (look at Mms), suspension compliance (look at Vas, or a Cms curve), etc.

Qes -
An electrical "quality" number... think of it instead as a good indicator of motor strength. Do you need a subwoofer with a strong motor? You might be surprised to learn that high strength isn't always a good thing. (hint: Look at EBP... or check out Qts. )
The smaller the number, the stronger the motor.
(also, the smaller the number, the smaller the enclosure, quite often - but it is just one factor in that equation )

Qts -
A calculated number, using Qes and Qms - for a "total quality" number. I sort of downplayed Qms's importance earlier... and even in this calculation, Qes so far outweighs Qms in this calculation, that Qts actually ends up quite close in value to Qes - and small adjustments to Qes affect Qts much more than even large adjustments to Qms would have.
Anyway - this is an important one. One of the "main 3" you need to calculate enclosure size/type/performance. (along with Fs and Vas).
Qts mainly can tell you what sort of application your subwoofer is compatible in:
High Qts value? Very compatible in a sealed enclosure.
Low Qts value? Very compatible in a vented enclosure.
Qts around 0.45 (middle of the road)? Design compromise to work OK in either, rather than outstanding in one and bad in the other.
It's very helpful that way.

Fs -
Resonant frequency. This is the frequency the subwoofer most easily resonates at - and in free air, has the highest impedence (actual resistance with a subwoofer varies both with frequency and enclosure - it's not just "4 ohms" or whatever - it may rise up over 40 ohms, in fact, at points!) at that frequency.
What it's useful for looking at is in judging how low a subwoofer can play.
A low Fs means the subwoofer will be able to play lower...
...but means it won't be as efficient in the higher frequencies either.
So maybe not always a good thing - or rather, something you need to compromise with realistically, to target your own personal tastes... loud? Or low? Or a little of both?

EBP -
EBP stands for "efficiency bandwidth product", and it's just a helpful calculation, to expand on what Qts tells you with regard to the "what box is it good with?" question.
EBP = Fs / Qes. Simple calculation.
It includes Fs in the equation, because in a sealed box, the subwoofer needs a low Fs in order to play low frequencies.
In a vented box however, you can design the enclosure so that it helps extend the low frequencies farther than a sealed box, so Fs isn't as important for that.
Qes is important because in a vented enclosure, you have higher pressure forces at work - so you need a stronger motor to contend with them. In a sealed box, that stronger motor will drive up the system resonance (a box/sub combination version of Fs), making for bad sealed performance.
The actual EBP number tells you whether it's good in sealed or vented...
EBP at 50 or below, sub is best suited to sealed.
EBP higher than about 80, sub is best suited to vented boxes.
EBP in between, sub is OK in either sealed or vented.

Vas -
Suspension compliance. This number represents the "volume of air" that provides the same "spring" force as the suspension system on the subwoofer.
What it means to you, is that a smaller Vas makes for smaller enclosures.
What it also means, is that a smaller Vas makes for lower efficiency, and a higher system resonance as well.

Mms -
Moving mass. The cone and coil, and surround and spider even have a mass associated with them. The higher the moving mass, the lower the efficiency of the speaker - but the lower the Fs as well. A designer adjusts these when deciding how thick of a cone (of course a thick cone may be rigid too, which is a good thing), or what cone material to use.
This is one reason why "high output" SPL subs are actually much less efficient than cheapo subs. Cheapo subs can be louder than SPL subs? Yes, unless you have the wattage to make that SPL sub scream, and that cheapo sub melt.

Xmax -
Here's a good one... represents the linear excursion of the subwoofer, from the "at rest" position, moving in one direction, until the measurement limit is met.
AT least that's how SOME manufacturers list Xmax.
Others list it as "peak to peak" - which obviously doubles the value.
Others list Xmax when they really mean Xmech (like Polk, for example).
Some perform a calculation of voice coil winding length compared to the thickness of the top plate - that's the traditional method, and it's not horrible, it's just also not "apples to apples".
So you have to know what you are looking at, when comparing.

(and by "linear" - that means that the motor strength spec doesn't change, and suspension compliance spec doesn't change, as excursion changes. When it does begin to change, that marks the end of "linear" excursion)

Xmech -
This is essentially excursion without regard to how "linear" excursion is. This is how far the cone assembly can physically move, before it crashes into something and something breaks - coil smacks the back plate, cone crashes on the spider mount ring, tinsel leads rip out of the cone - needless to say, it's a limit you don't want to find the hard way!

Xsus -
This is the suspension component of "Xmax". Subwoofers may be "suspension limited", having a suspension that has a smaller range of linear excursion capability than the motor has. Xmax is always the smaller of the two values.

Xmag -
This is the motor strength component of "Xmax". Subwoofers may be "motor limited", having a motor that has a smaller range of linear excursion capability than the suspension has. Xmax is always the smaller of the two values.

BL curve -
This is an actual plot of motor strength with respect to excursion - simple plot really - motor strength on the Y-axis, excursion shown on the X-axis (and generally shows both positive and negative excursion - so traditional subwoofers with traditional architectures can look quite a bit like parabolas on these plots).
Very helpful for understanding visually exactly HOW LINEAR a motor can be - and even how gradually it rolls off after that limit.

Cms curve -
The same thing as the BL curve, but shows suspension compliance with respect to excursion... so you can see exactly how linear the suspension is, and what it's limits are, where they are reached, and even how graduallly it rolls off after that limit.

Re -
This is just the DC resistance measurement of the coil. It's always a bit less than the "nominal impedence", and really doesn't tell you too much, other than "this is the lowest the impedence will ever dip to, on the impedence curve". (at some frequencies, impedence may rise up very high - a 4 ohm speaker might hit 50 ohms at Fs!)

Le -
Inductance is potentially an important thing to look at.
a voice coil is a coil of wire - and so resembles an inductor.
What does an inductor do? It resists changes in current direction and flow.
What does a speaker do? It changes direction and frequency as quickly as the music throws those changes at it.
So - basically you want your inductance to be as low as possible.
Also... an inductor is a 6dB/octave low pass crossover - so at some point, inductance could be high enough that it prevents the speaker from playing frequencies higher than a certain point - the speaker itself prevents it - the lower the inductance, the higher the speaker is capable of playing.

Hopefully that helps someone - happy reading!

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Old 07-30-2006, 06:43 PM   #2
dolbsss

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its about time this thread got made..... i honestly can't believe you didn't make one like this already.....
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Old 07-30-2006, 06:50 PM   #3
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nice..................

Last edited by nauc; 07-30-2006 at 07:00 PM.
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Old 07-30-2006, 07:21 PM   #4
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sweet

10 char
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Old 07-31-2006, 01:37 AM   #5
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mmm.....tasty


EDIT

But I have also read that the cut-off point with EBP for ported enclosures is 100, not 80. Why the discrepancy?

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Old 07-31-2006, 05:35 PM   #6
geolemon

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{EDIT}

xxPunkORamaxx:
I actuallyy split your comment off into a separate thread, because it's a very good technical topic...
..where this thread here is largely intentionally trying to AVOID the technical aspect (and/or background behind the specs, technical definitions, measurements, etc), instead providing a resource for "the layman", that is clear and as concise and informative as possible, to the end of "practical, directly applicable" aspects of these specs.
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Old 07-31-2006, 05:46 PM   #7
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Quote:
Originally Posted by PuffDaddy_d
mmm.....tasty


EDIT

But I have also read that the cut-off point with EBP for ported enclosures is 100, not 80. Why the discrepancy?
Good eye.

The question specifically is with regard to EBP showing you what sort of enclosure your sub is suitable in:
0 - 50 = sealed
50 - 80 (or 100) = neutral (sealed OR vented)
80 (or 100) and higher = vented

It's one of those things I've seen discussed across a range of values - sometimes 100, sometimes 80, sometimes 75, etc... it depends on what you read.

Personally, my impression has always been that the "stuffy SQ types" are more likely to recommend that you shouldn't rule out using a sealed box until EBP reaches 100 - but by nature, those guys cling to their sealed boxes (and I'm often one of them! ). On the other hand, most car audio guys are tempted to get the most loudness out of their subs as possible.

The bottom line is, if you run the EBP calculation on a few FS and Qes combinations, you'll likely conclude (as I have) that the 100 limit is pretty much "way up there", particularly for a car audio crowd - and I'd personally argue (based on my own experience), even "way up there" for car audio SQ guys.

Remember, it's only a guideline - the same with Qts - and Qts is even MORE often discussed across more differing range of values. I actually simply picked the most neutral definition that I've settled on in my own head, with THAT one. But that one too - it's just a guideline, and different people sometimes skew the 'ranges' one way or another.
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Old 09-09-2006, 06:03 AM   #8
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Good stuff, as usual Geo

Although this thread seems to focus on certain t/s specs that are most often discussed on forums, you did mention qts and ebp methods for determining what type of enclosure to go with (or at least which one is ideal given the speakers design). Warbleed, however, brought up a good point a year or so ago...

Here

The qts vs. ebp "debate" used to have me pulling my hair until I realized quite often they match up and it's mostly a 'non-issue'. War, however, pretty much thinks ebp is useless. Your thoughts on War's comments would be appreciated.


Also, the Q values have formulas associated with them. Ex. qts = 1 / (1/qms + 1/qes) .....a little algebra will allow you to "solve" the others, too ). Knowing the meaning of the Q values only helps if they're accurate/consistent. Another reason not to put too much weight in them is that quite often the formulas don't work out (ie: inaccurate specs...or worse, the manufacturer is just lying or making them up). I still wish there was an industry standard (dumax, klippel, BUCKLE [adire tech], or JL's fancy program) so that we could, more or less, do an apples vs. apples comparison. Can you imagine shopping for a vehicle based on power while there were countless different ways the Big 3 calculated HP and Torque in engines Instead, we often buy a number of different speakers because listening to them might be the only way to tell if the do what their specs "say" they will do.

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Old 09-09-2006, 07:11 PM   #9
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Quote:
Originally Posted by luvdeftonz
Although this thread seems to focus on certain t/s specs that are most often discussed on forums,
It does, because like MPG and 0-60 and HP with cars, they represent the measurable specs that directly indicate or allow the modelling [simulations] of either performance or limitations (and sometimes a performance benefit in one context might be a limitation in another).

And only very infrequently, when someone asks "what the heck does this spec mean"?, does someone actually give a meaningful, "this is how you can use this spec in everyday life" explanation, as I'm trying to do here.
MORE often, there's a technical definition of the spec, how it's measured, differences between Klippel Xmax, DUMAX, and traditional winding vs. top plate calculations, etc.

As I said before:
Quote:
Originally Posted by geolemon
This thread here is largely intentionally trying to AVOID the technical aspect (and/or background behind the specs, technical definitions, measurements, etc), instead providing a resource for "the layman", that is clear and as concise and informative as possible, to the end of "practical, directly applicable" aspects of these specs.


Quote:
you did mention qts and ebp methods for determining what type of enclosure to go with (or at least which one is ideal given the speakers design). Warbleed, however, brought up a good point a year or so ago...

Here

The qts vs. ebp "debate" used to have me pulling my hair until I realized quite often they match up and it's mostly a 'non-issue'. War, however, pretty much thinks ebp is useless. Your thoughts on War's comments would be appreciated.
Qts is an easier "quick glance" spec, because its usually right there for you, where EBP often has to be calculated (not that THAT is hard).
But I always look at Fs also.
So in a way, I AM using EBP - if not the formula directly, it's the spirit of the formula - Qts and Fs helping tell me what type of enclosure, and even getting me closer to what I need to tune to to get the sort of response I'd be looking for.
...I consider that a "more advanced" way of looking at it, and it's not because I'm disregarding Fs from the equation - and I'm sure Warbleed would never say he'd disregard Fs either. More a question of whether you want to look at it separately, or combined in a convenient little formula.

Maybe EBP hides Fs, but Fs can sometimes explain why you might have this one subwoofer that has an EBP indicating "sealed box", when Qts would seem to indicate "vented" on it's own... Oh wait, Fs on that sub is 15 Hz. (or vice versa).

Generally, when EBP and Qts disagree in this respect, it's nearly always indicated a scenario where the sub would be a candidate for either - so it's difficult to say either spec was misleading - really, it would have been fine in that application, right?
Quote:
Also, the Q values have formulas associated with them. Ex. qts = 1 / (1/qms + 1/qes) .....a little algebra will allow you to "solve" the others, too ). Knowing the meaning of the Q values only helps if they're accurate/consistent.
Reference the comment from me above, where I REMOVED a whole set of comments that were related to formulas, technical definitions, "technically, this is...", and other information that's great fun for geeks like you and I to argue detail and formulae on, but doesn't help anyone understand "how I can take this to the store and buy a loaf of bread with it" (and arguably at the end of such detail, definition, and formulaic depth of understanding - neither you nor I would have a better stereo, either ).

That discussion is for another thread.

Quote:
Another reason not to put too much weight in them is that quite often the formulas don't work out (ie: inaccurate specs...or worse, the manufacturer is just lying or making them up).
That's what this thread is entirely about:
Not defining.
Not discussing chalkboards of calculations that lead to a particular spec.

But rather, "don't worry about what they technically are, let me instead show you how to use them, as guidelines to help you determine ______ about a particular subwoofer."

And that's all they are - guidelines.

Inaccurate specs - what are you going to do about that? That doesn't make the interpretation effort incorrect.

It's on YOU to first determine or learn the reputability of the manufacturer - another great thing forums are great for, and another reason a thread like this is more powerful in a forum environment than it would be say, in a magazine.
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Old 09-09-2006, 09:59 PM   #10
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stop looking at FS and Q. take my advice. look at MMS, CMS, QES, and QMS, they will describe to you what boxes AND tunes as well as APROX port area are ideal for years people thought a high Q wouldn't work ported or in small boxes when its not the whole truth at all. if you wnat more spicifics it getins into and big damping issue and basically which damping you perfer as the final result

NOTE that all specs are taken @ resonance so anything above and below everything changes. a woofer can easily play well below FS its just up to the damping mechinal powerhanlding and linear throw. for instance. take the new XXX 15 model it up port 6 cubes tuned to 20 then LISTEN and measure how low that ****er will actually drop measure with an RTA.

Last edited by bassfreak; 09-09-2006 at 10:07 PM.
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Old 09-10-2006, 01:21 AM   #11
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Quote:
Originally Posted by bassfreak
stop looking at FS and Q. take my advice. look at MMS, CMS, QES, and QMS, they will describe to you what boxes AND tunes as well as APROX port area are ideal for years people thought a high Q wouldn't work ported or in small boxes when its not the whole truth at all. if you wnat more spicifics it getins into and big damping issue and basically which damping you perfer as the final result
Okay, seriously...ported boxes are not the only thing people use (I know you know this). MMS, CMS, QMS, etc...none of that is crucial when comparing the performance of subs that will be used in a sealed box. Please do not whore your preferences out on everyone else as if it should be law.

Oh, and we kinda need Fs and Qts to help us determine if the sub should be sealed in the first place.
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Old 09-10-2006, 12:34 PM   #12
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Fs comes from Mms, Cms
Qts comes from Qms, Qes

so Mms,Cms,Qms,Qes will provide at least the same information as Fs and Qts.
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Old 09-10-2006, 07:17 PM   #13
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Quote:
Originally Posted by bassfreak
stop looking at FS and Q. take my advice. look at MMS, CMS, QES, and QMS,.
Thanks for the effort... BUT

Once again - we're looking for nice, easy information that the layman can use, to help them shop and select subs (and plan their system in general), using the specs that are generally common across spec sheets.

And the red flag here - you simply aren't going to find Mms and Cms on many spec sheets to begin with.

(For that matter - sometimes, all you have are Qts, Fs, and Vas.
THOSE really represent the "big 3" of the spec world anyway - you can even model a sub in an enclosure fairly accurately with JUST those three. )


But specifically in response to your post - in a way in the spirit of the goals of this thread, Mms and Cms simply determine Fs, for our purposes here.
So if we were to translate the "techie" suggestion of using "Cms and Mms" into our "layman level helpful tips and guidelines", what we'd translate your suggestion into there, is simply "go look at Fs".

And, since Qts is so directly tied to Qes (where Qms hardly shifts Qts), we could translate this into "go look at Qes" (or "Qts" for that matter. ...hell, you could perform the EBP calculation using Qts rather than Qes and end up with the correct answer 90% of the time ).

So, to translate what you are saying into something appropriate for this thread:
You support looking at EBP (which uses Qes and Fs) over just looking at Qts.


Thanks.
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Old 09-10-2006, 07:19 PM   #14
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Quote:
Originally Posted by thechris
Fs comes from Mms, Cms
Qts comes from Qms, Qes

so Mms,Cms,Qms,Qes will provide at least the same information as Fs and Qts.
I should have just read down to this post, and quoted you.
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Old 09-11-2006, 12:40 AM   #15
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CMS and MMS point to FS but its NOT nessicarlly the same as the spec can be derived in different ways. CMS isn't as important sealed? i disagree, just put a 9515 sealed, and then find andother woofer with the same FS but a higher CMS(less MMS) and see the differences. as for Qes it is very impotant when determining the final Q you desire as well as the F3 you desire.
all you need to find MMS is SD and VAS pretty simple don't you think? if you cna use winisd you can find it. QMS and CMS are different. QMS is useful in any type of box. CMS and Q are important. the more CMS you have the lower the Q for the same efficiency. as for QES becaseu QTS doesn't vary much and it play a larger role in your final Q. i can have an MMS of 500 grams and get a Qts of .25 but i need so low a CMS that QES is much much higher. sleep time.
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