[Doublej]

Generally how does the sound change as the woofer size increase in a two way? I suspect you get more bass but you have to cross over to the tweeter sooner, so the tweeter has to handle more of the low frequency but what does this translate into sonically?

At what size woofer does a two way become impractical? Or does it ever?

[markC]

Just my opinion, but anything over 8" would be too big. Problem is, the larger the driver, the lower the max. freqency it can produce without falling apart. Check the frequency response curves for drivers of 5",6",7" and note what frequency they can produce remaining relatively flat. Compare that to a 10",12",15" driver and you'll see that you would likely need a midrange driver to fill in the frequencies between where the woofer drops off and the tweeter takes over. It's a tall order to ask a tweeter to cross over any lower than around 1800hz. This is all generally speaking of course, and again, my opinion.

[RooX]

too many variable.  cabinent size, type of tweeter, crossover type and slope and whatnot.

My speakers are two ways, 10" bass driver with a heil driver that runs from 700hz up to 24khz.  Love em to pieces, but its not the only way to make a speaker

[_scotty_]

As a woofers diameter increases so does it's mass and it's ability to deliver
detail in the midrange is progressively impaired.  The woofer cannot start and stop quickly enough to do the job. As the mass increases so does the stored
energy in the cone and this can also act to impair the drivers ability to deliver
detail. The waterfall-plot on the driver would show this kind problem very clearly. As the frequency the driver is asked to reproduce becomes equal to or smaller in wavelength than the emissive diameter of the woofer diaphragm
the woofers off axis frequency response suffers from raggedness and the woofer acts like a flashlight beam in it's directional behavior.  
     Where you draw the line at concerning the trade-offs involved with increasingly larger woofers in a two-way is up to you. A common cutoff point
currently used in many products is 8in. and designers frequently try to stay
under 2kHz for their crossover point. 25 years ago the Larger Advent had a
10in. woofer but no one would consider this design commercially competitive
with modern speakers.
Scotty

[kfr01]

As a woofers diameter increases so does it's mass and it's ability to deliver
detail in the midrange is progressively impaired.  The woofer cannot start and stop quickly enough to do the job. As the mass increases so does the stored energy in the cone and this can also act to impair the drivers ability to deliver detail. The waterfall-plot on the driver would show this kind problem very clearly.

But see: http://www.adireaudio.com/Files/TechPapers/WooferSpeed.pdf

"There's a common misconception out there that heavy woofers must be "slow", and light woofers must be "fast". If a woofer A's moving mass is higher than woofer B's, then woofer A is probably going to be sloppy, or slow and inaccurate. Can't keep up with the bass line. Woofer A simply can't respond as fast as woofer B.
There's also this concept that the "acceleration factor" (BL/Mms) is an indicator of woofer speed/transient response. High BL, combined with a low Mms, should give great transient response, right? Well, on surface these might sound like logical assumptions. However, they are in fact incorrect! More to the point, moving mass has precious little to do with woofer speed or signal response! And we'll prove it..."

[_scotty_]

The pdf.doc discusses a 6.5in. woofer.  The magnitude of the negative going overshoot has been substantially increased by the additional mass.
No waterfall plot was shown illustrating the before mass added behavior and the after. Also no comment was made on how the additional mass affected
the drivers distortion specs or how it sounded. While I didn't mention it in my first post, larger diameter drivers frequently have larger voicecoils with more inductance which the Adire pdf.doc talks about as being a factor in transient response behavior.  A  woofer greater than 8in. in diameter is still a poor choice for operating above 2kHz.
Scotty

[kfr01]

Scotty:  I wasn't saying you were wrong, only providing another resource for readers.

Cheers,  

Karl

[jules]

I believe there's some poor physics in the Adire paper though I haven't read through the whole thing.

Maybe somebody else can evaluate this further but on the first couple of pages the Formula F=ma [where F is force, m is mass and a is acceleration] is reasonably enough, converted to BLi=ma [where BL is the motor force factor, i is the current and a is acceleration]. The paper argues that, removing all "time invariant factors" the equation becomes Ci=Ca [where C represents the time invariants]. This in turn is re-described as saying that i is proportional to a [without justification as far as I can see since the correct interpretation is that i = a if C is the same on both sides of the equation]. Summing this up the author suggests that mass is irrelevant and to quote ... "this says that change in acceleration of a driver is strictly a function of current through the driver. If you could make the current change infinitely fast then the driver would accelerate infinitely fast". [As an aside, we don't actually want a driver to accelerate infinitely fast. If it did the sound would be infinitely high and infinitely inaudible].  

The problem is that the same constant is used on both sides of the equation whereas there are actually different values of C.

In some ways the interpretation of Newtons law here is simple. The force needed to accelerate a mass is proportional to the mass and also proportional to the acceleration. So, increase the mass and you increase the force needed to accelerate it at the same rate. Similarly, to increase the rate of acceleration requires either more force or less mass.

There were several other significant errors in just the short section of the pdf that I read and on that basis the rest of the paper should be treated with care.

jules

[Carlman]

To address the 'how does it change' question, what I've noticed is that the smaller drivers 5-6" have less impact and a more neutral sound.  Larger 7-8" drivers have more impact but sound a little warmer to me... I like the bigger driver sound even though it is a little less accurate in the mids because the bass and impact I enjoy in music is more important than the absolute most timbral accuracy in the mids.... And, the bass is missing in the smaller driver designs I've heard.  (Except the SP Tech's)

If I were a big fan of female vocals, I'd go with a 5-6" driver but I like to 'rock out' so I like 8"'ers... I have a 7" in my Usher's now that is a pretty good compromise, I must say... It's still a little colored in the mid-bass/mid-range area but the amount and quality of sound is to my liking.

So, midrange subtely diminishes with every inch in my experience but bass and impact increases at the same time.  This is a sweeping generalization that won't hold true in many cases but this is what I've observed listening over the past couple decades.

-C

[markC]

2.5 way,(tmm), or mtm designs can give you a little xtra in the bass dept. and still maintain a decent mid range. Two 5.25" mid woofers for example, will move almost as much air as a single 8" driver. All things considered of course, such as xmax. I'm a big fan of female vocals, therefore I cannot picture myself pursuing a large mid woofer 2 way design.

[_scotty_]

And now we get to why I like more than one driver in the midrange. I have the detail of the smaller driver with the image scale, midbass impact and freedom from compression that comes from multiple drivers covering the midrange and lower midrange down to 150Hz. For that matter I am a big fan of multiple woofers for the bass region for the same aforementioned reasons.
Scotty

[JLM]

I use single driver speakers, so all this discussion seems a bit odd to me.

If I were designing speakers I'd start by selecting a cabinet type.  My favorite is transmission lines for the lowest, fastest, most musical sound.  Next I'd pick the lowest in room flat frequency I wanted to reach.  For music that'd be 32 Hz (bottom note of a piano, unless you really want to go crazy and try to reach big pipe organ notes).  Then look for the driver (woofer) to match your cabinet/frequency choices.

[JoshK]

Larger 7-8" drivers have more impact but sound a little warmer to me...

That is because most 7-8" midbass drivers have cone modes in the midrange region that results in a masking of some detail.  Scanspeak drivers are good examples of this, which is why many feel they sound warmer IMO.   You can generally see this phenomena by looking for small "blips" in the impedance curve.  With such Scanspeaks, for example, you will see the blip at about 800, which is smack dab in the midrange.

[tom1356]

This is a very amusing thread.

[Mudjock]

I believe there's some poor physics in the Adire paper though I haven't read through the whole thing.

Maybe somebody else can evaluate this further but on the first couple of pages the Formula F=ma [where F is force, m is mass and a is acceleration] is reasonably enough, converted to BLi=ma [where BL is the motor force factor, i is the current and a is acceleration].

Thanks for pointing this out, Jules.  I have, at least once, addressed this in another forum.  The Adire white paper is clearly misleading in its conclusions.  If you don't mask out all of the terms with the generic "C", it becomes clear that acceleration is inversely proportional to mass (larger mass will produce less acceleration with all other things equal).  This is also readily apparent in their plots if you look closely, with their woofer cone being under less control than others, particularly when it comes to stopping and changing direction.