George (on Topic Only)

Let's see if I can help with this.

Well you must look at how the progressive spider is designed. Near the former the "rolls" are small, and they get "progressively" larger as you move out from the center. This means that it is more stiff on the inside, and less stiff on the outside. When the cone moves in or out, a linear spider (where the rolls are all the same size) get's stiffer as it moves farther from rest. Well a progressive spider moves into the larger waves as it moves farther from rest. This means that while it would naturally get stiffer, the spider is moving in it's progressively less stiff area.

I hope that made sense. :huh:

 

The "male" end goes into the "female" end and a spring loaded clip slips into the hole in the center of the male end. This locks it into place, keeping the seatbelt around the driver or passenger. Pushing a button releases the spring loaded clip from the male end, allowing it to be released from the female end. But I'm not sure if this is quite on topic.

 

I hope I'm not misunderstanding you again and commenting on the wrong thing.

So you are asking how they can measure the two in the DUMAX report when as an example the suspension will stiffen, effecting BL measurements? Well the answer to this is that one is a mechanical issue, while the other is more of an electrical one (or magnetic one?).

For Kms measurements, I would expect them to see how much pressure it takes to move the cone a certain difference, which will show you how stiff the suspension is.

I'm not sure how they would measure BL. I would have to think about it for a little bit. But I think it is more electrical in nature, eliminating the stiffness issue.

 

Stephen...
I posted this on my DUMAX description post:

"As I recall, the Kms measurement is taken as the amount of pressure required to move the cone to a certain position.
And the BL measurement is taken by manipulating the cone to a certain position, applying a small DC voltage to the voice coil, and monitoring the resultant movement, with respect to (ie. factoring out) the Kms measured previously."

In this respect, BL is subject to Kms.
But, I believe Kms is factored out, as BL is (as I recall) a subsequent test. If you know Kms already, you know the rate of increasing stiffness... and therefore, know how much motion a given DC voltage would create at a given excursion.
I don't know this as a fact, but it seems logical in arriving at a BL curve that is independent of the effects of the Kms curve.

 

As of late, I have been wondering a lot about how individual parameters effect the necessary box size for any alignment.

When looking for a small box woofer what are the best parameters to look at?

How does each parameter change the box size needed?

Example if X is raised necessary box size is increased
if X is lowerd necessary box size is decreased

Something real simple like above for each parameter and maybe an explanation of why.

Also if you have a sub that should ideally be ported, but you like sealed subs what is a good sealed alignment.

I hope this counts as relating even though it deals a lot with speakers in their enviroment rather than the speaker itself.

 

Scroll back for Dan's post on this exact topic actually.

One thing I'd like to add to that however, is the consideration of Hoffman's Iron Law.
The Iron Law states that the following three design items are mutually exclusive:
1) small enclosure size
2) low frequency extension
3) high efficiency

These rules apply not only for loudspeaker design, but enclosure design....
Really, this is the law that explains how a particular subwoofer/enclosure alignment can be manipulated.

So...
While there are certainly specs that will show you if a particular woofer is designed for small enclosure use, what also needs to be considered is 'what am I trading off, to get this small enclosure performance?"

In fact, in Dan's post, he illustrated one of those trade-offs nicely... illustrating how if a woofer were particularly manipulated for small enclosure application, how Fs would rise... in essence, trading off "low frequency extension" for "small enclosure size".

If the woofer design / enclosure design alignment instead were one that favored low frequency extension along with small enclosure size, the trade off would be efficiency. This would be akin to taking the woofer that Dan was talking about, and adding mass to the cone unit, to bring the Fs back down to where you want it. In doing that, you make the woofer less efficient.

Just something to mull over...
Yes, you can have micro-box woofers, but there is ALWAYS a cost. It's inherent, it's not free. You won't be winning SPL competitions with a tiny enclosure (efficiency trade off). :detective:

 

I thought of a perfect example for Geo's post above. Let's look at the10A, 12A, and 15A (ED's numbers, not the review). Both the 12 and 15 require roughly the same size enclosure and have the same efficiency. But when you model them up, the 15 looks to have less low frequency extention than the 12. Now look at the 10A and it has a very similar efficiency as the others, has better low frequency extention, but get's that by having an extremely high Vas.

 

i didnt read the whole thread
kinda lazy

steven, you can use irons law on the A situation
IIRC, its been awhile.... the 10 12 and 15 have different motors and suspensions.

when comparing the 15a to 12a
the 15 has more bl(higher eff)
using a small enclosure and high efficiency, it cannot extend as low as the 12a, which given the same enclosure has lower BL which should dictate greater extension

the 10 on the other hand, has a larger vas(larger box) higher eff, and IIRC, a lower FS than even the 15?) all that dictates decent extension

i wouldnt put the 15 and 12 in the same box.... id go at least 1.5 cubes for the 15 for decent extension
but it can all be ironed out with enough EQ and power
hell i have my 12s in .85 cubes and i get claims that people didnt think it was possible to extend that low

done rambling, probably incoherent, im watchign star trek

 

I do doubt the w7 is a ported indicative woofer.

 

Seems to me that the 10 and 12w7 are closer to border line than the 13w7, but i'd say they all should be sealed. The 13w7 has the lower EBP out of the 3. But im sure you're using another means of gathering than i am. Judging by the performance of the 10w7 i definately dont think it needs to be ported.

 

I think it's interesting to note this phenomenon... either technique used.
EBP or Qts...
Just the very fact that one woofer might be more "ideal sealed" or "ideal ported".

I'd like to just spit out a side note that I believe XBL^2 results in a woofer actually being more "ported capable" than it's Qts or EBP might lead you to believe... the reasons why might be fun to discuss later (particularly since it does perform well in sealed also, as Qts or EBP both DO lead you to believe, as Seth mentioned)...

But first, maybe we should discuss this interesting phenomenon...
Just simply that a woofer might be "ideal" in a ported box, implying that it's performance might be compromised when sealed -
Or vice-versa, that the woofer might be "ideal" in a sealed box, implying compromised performance if ported.

After all, this touches on so many of the things that we groan over on the forums...
People purchasing pre-fab enclosures for their woofers... putting woofers that don't really belong (if you will) in one type of enclosure in another, giving sealed boxes a "bad rap", or even more so... ported boxes a "bad rap"... and very similarly - bandpass boxes their bad rap - because 'sealed box' woofers fit in 4th order BP's while 'ported box' woofers fit in 6th order BP's, primarily!

What do you think of this phenomenon...
And the factors that contribute to it?

 

Hey Seth, with QTS being your TS param of choice, would you say that EBP is a wrong, or should i say inaccurate way of determining ported vs sealed? I am under the impression that EBP is the accepted method of determining yet its contradictory of what QTS is telling you. Just tryin to get my stuff straight here.

 

They generally DO agree...
I'd consider BOTH, rather than choose one or the other.
If one spec shows one way, and the other shows the other way... it's probably a "middle of the road" type of sub.
On the other hand, if they both agree... you know what to do. B)

Consider what is similar about them, and what is different:
EBP:
What is it?
A simple calculation:
EBP = Fs / Qes
This means that as the motor gets stronger (lower Qes indicates a stronger motor.. ie. a higher BL), the sub moves towards being more ideal in a ported enclosure.
This makes sense, as the subwoofer has higher forces to contend with inside a ported enclosure, particularly playing frequencies near the tuning frequency of the port.
This also means that as resonant frequency goes up, the sub moves to being less ideal in sealed boxes.
This makes sense in that ported boxes can be used to extend the low frequency response of a subwoofer... ones that are naturally low don't need this boost down low.

Qts:
What is it?
A simple calculation:
Qts = (Qes x Qms) / (Qes + Qms)
This again means that as the motor gets stronger, the sub moves towards being more ideal in a ported enclosure.
...Which again sense, as the subwoofer has higher forces to contend with inside a ported enclosure.
This also means that as the suspension itself becomes more capable of restoring the driver to it's "at rest" position after a signal stops, the sub moves towards being more ideal in a ported enclosure.
This makes sense not specifically with respect to the higher forces happening inside the enclosure, but more so with respect to the fact that the counter-forces from the port aren't going to be exactly in-phase with the subwoofer, so that energy could theoretically knock the woofer into an odd resonance as the port energy will inherently push at the cone mere milliseconds after the signal stops.

So...
Which is better? h34r:
EBP takes into account Fs, where Qts doesn't.
Qts takes into account Qms, where EBP doesn't.
Your call...
I'll use both. B)

 

I also wanted to provide this link:
http://momentum.soundillusions.net/februar...02FebTech1.html

I'm no fan of SoundIllusions, but this magazine has some great, well-worded articles.

This particular article explains Qms and Qts in laymans terms.

In particular, towards the bottom, is an interesting comment:
"If you haven't already noticed, Qes is closer to Qts than Qms ever thought of being. Back EMF plays such an important role that Qes (or the electrical damping) outweighs Qms by a significant amount. However, this is not to say that Qms does not affect how the driver reacts."
This is quite true, if you look at the T/S specs for any woofer. B)

 

I must add that even by EBP numbers, the 10 and 12w7 are close to borderline, so i guess by that i can agree that they could go both ways. But, the 13w7 seems to fall further into the sealed range by the EBP method, but closer to ported by your QTS method. Seems they go in oposite directions. I don't quite understand this. Higher the EBP, the more indicative of ported/6th order BP, the higher the QTS, the more indicative of sealed. Is there some sort of exception to be considered?

 

No exception.. just read what I posted above.

Each calculation/guideline considers something the other one doesn't.

In reality, you are looking at 3 individual specs, all of which give you a clue about it's performance in ported vs. sealed...
But either one of them only considers 2 of them... neither of them consider all three.
Make sense? B)

Maybe we could make up our own calculation to take all 3 into account...
Fs / ( (Qes x Qms) / (Qes + Qms) )
We'll call it the "geolemon" :lol: