Large Woofers!

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noah katz said:
"I'm saying the supravox has a "larger" linear operation at lower freq.s to its fs."

Fs has nothing to do with linearity, at least as regards BL linearity/ distortion.

Other things (i.e. power handling) being equal, EQ'ing below Fs will give more thermal compression.

The free air resonance of the driver is typically where the driver behaves the most non-linear (..at least in free-air). The effect of which is really about excursion.

Essentially the neither moving mass nor compliance "restrict" the driver's excursion.. you then have to rely on back emf and mechancial excursion limits (..and the spider and surround are really about centering the VC for a given excursion, not about restricting excursion). Additionally, things get really bad when the VC starts moving out of the gap.

As to my statement about the supravox having "larger" linear operation at lower freq.s to its fs is based on two things:

1. the supravox has a higher fs. All else equal a driver with a higher fs will have less excursion than a driver with a lower fs. Of course this doesn't bode well if you intend to eq. below fs.

2. the supravox seems to have a good bit more efficiency between its fs and 200 Hz than the emenince. All else equal (IF correct) the supravox will require less power, which in turn reduces thermal compression.
 
Tenson said:
Well then, how about this - http://www.bcspeakers.com/index.php?sez=1&categoria=1&id_descrizione=2&prodotto=36

99dB efficiant, 550wattsRMS power handling and 7.5mm Xmax.


sd is a good bit larger as well..

remember though you have defined your upper limit to be 1.5 kHz. This was another reason I suggest the supravox as sounding superior to the other drivers.

At higher freq.s dispersion is greatly effected by the cone geometry and the surround. For instance the supravox has a much "flater" profile - which often results in not only wider dispersion for a given higher freq. , but also how "linear" that dispersion is. (.."linear" relating to something closer to pistonic operation.) Additionally, the larger the cone typically the worse the dispersion.

Finally, the mms of the supravox (for its sd) is extremely low. I've found that this often subjectivly results in a "cleaner" sound, which seems increasingly important as freq. response rises. On the other hand, (as I've mentioned before), less mass seems to also give less dynamic "punch" in the midbass.

edit: I went looking for graphical display of dispersion on SL's site and found this:

http://www.linkwitzlab.com/rooms.htm

Notice the difference between the open baffle "panel" and the open baffle piston. The panel is jaged, the piston is smoothly spherical. This was what I was trying to describe with regard to being more "linear" in dispersion.. i.e. all-else-equal the supravox at 1.5 kHz should be more "spherical" than the other drivers.
 
Tenson said:
The 15" B&C seemed like a good mixture of the two drivers to me. Higher MAX SPL than the 12" Eminence and better high frequency extension as well. You just wont be happy until I get a Supravox though will you :p

LOL..

IMO it just seems to be the right driver for the given application at average spl's.

IF you extended the lower freq. response to flat at 40 Hz AND limited the higher freq. response to say 400 Hz - then I definitly would pick that B&C over the other drivers you have selected. (..and actually at a similar expense and sd I'd go for the BMS 15S430.)

http://www.bmspro.info/index.php?show=item&usbid=10282&id=54386
 
"The free air resonance of the driver is typically where the driver behaves the most non-linear (..at least in free-air). The effect of which is really about excursion."

Please elaborate. Any driver that isn't underdamped exhibits no peak in output.

"1. the supravox has a higher fs. All else equal a driver with a higher fs will have less excursion than a driver with a lower fs."

If all else is equal than fs will be equal as well.

Sorry, but you seem to make one generalization after another without a technical foundation to stand on.

As far as suitable drivers, see www.eighteensound.com for an impressive array of high efficiency drivers with spec's as comprehensive as JBL's, including power compression for -10 dB, -6 dB, and full rated power.
 
Hello Tenson!
Here is a Ciare woofer with a similar design philosophy as the CH250 fullrange driver, which has a very accurate bass, but a bit small, if you still plan to build a quasi coaxial. There is no info on the
Ciare website because of an error, so here is an other link:
http://oaudio.net/product_info.php?products_id=67

For a real coaxial the Coherence 12 would have a Qts of 0.46 and a HF extension up to 35kHz.
http://www.cantare-as.de

Greets, Oliver
 
noah katz said:
"The free air resonance of the driver is typically where the driver behaves the most non-linear (..at least in free-air). The effect of which is really about excursion."

Please elaborate. Any driver that isn't underdamped exhibits no peak in output.

"1. the supravox has a higher fs. All else equal a driver with a higher fs will have less excursion than a driver with a lower fs."

If all else is equal than fs will be equal as well.

Sorry, but you seem to make one generalization after another without a technical foundation to stand on.

As far as suitable drivers, see www.eighteensound.com for an impressive array of high efficiency drivers with spec's as comprehensive as JBL's, including power compression for -10 dB, -6 dB, and full rated power.


First of all.. try looking at the data of just about any driver with THD relative to freq. response. I haven't found a driver yet that doesn't have more distortion near its fs. THAT was perfectly simply to discover on your own. Moreover, while this information is quite general, that doesn't mean that it isn't usefull. Yes it is empirical.. if you want a scientific reason then do some reserch on what I elaborated on.

2nd.. I did elaborate. Rather than cut'n'pasting what you find fault with - why not try reading it ALL. i.e.:

"Essentially then neither moving mass nor compliance "restrict" the driver's excursion.. you then have to rely on back emf and mechancial excursion limits (..and the spider and surround are really about centering the VC for a given excursion, not about restricting excursion). Additionally, things get really bad when the VC starts moving out of the gap."

If you have a problem with something SPECIFIC here then fine.. ask, but don't expect an answer. (IMO I've given more than enough info. to start researching what I've stated (if you didn't like the answer).. Note: this was the same problem you had with the ribbon thread: i.e. you seem to want the answer, in detail, and exactly the way you can best understand it.. sorry, thats not how I'm going to spend my time, for either this thread or future threads.)

However, I will add to the above quote:

Think about how a driver is controlled and is NOT controlled:

Above resonance: motor converts current to force applied to mass
Below resonance: motor converts current to force applied to compliance.
At resonance:motor converts current to force.. but what's it applied to?
 
Hi Scott and others still willing to learn,
I agree, in part, with your sentiment.

Too many posters expect to be spoon fed rather that research the topic. Read the responses and make decisions. We have all past the first grade, but even there the juniors are expected to give some input into their own learning.
 
"2nd.. I did elaborate. Rather than cut'n'pasting what you find fault with - why not try reading it ALL. i.e.:

"Essentially then neither moving mass nor compliance "restrict" the driver's excursion.. you then have to rely on back emf and mechancial excursion limits."

I did read it, and I saw a flawed understanding of the topic, which I'm trying to prevent being transmitted to others.

You imply that the back EMF isn't doing the job, but in fact it does it very well in every competently designed driver, or everyone would be using notch filters at resonance.

"...At resonance:motor converts current to force.. but what's it applied to?"

Again you imply a problem w/o solution, but the answer is the same: damping, via back EMF, as evidenced by the impedance peak and reduced input current at resonance.
 
noah katz said:
You imply that the back EMF isn't doing the job, but in fact it does it very well in every competently designed driver, or everyone would be using notch filters at resonance.


No, I'm not implying that back EMF isn't doing its job, rather that it doesn't do its job very well even in competently designed drivers. (..again, as clearly evidenced at the rising THD near resonance for most drivers.)

Additionally, what happens when you "push" the driver some and the VC starts to leave the gap? Whats happening to back EMF then?

Notch filters create their own problems, despite this some in fact do use them. (I can think of one "high-end" manufacturer right now - Kharma.)
 
"Additionally, what happens when you "push" the driver some and the VC starts to leave the gap? Whats happening to back EMF then?"

Then you've exceeded the driver's limits and all bets are off.

As to your comment about THD at Fs, I don't recall ever reading a test where a point was made about this.

Distortion is much more of a function of freq, because excursion increases with the square of freq decrease.

Look at any subwoofer test (the best I've seen being Way Down Deep by Keith Yates in SGHT); I've never seen a comment about distortion at Fs, only that the bass is clean down to x freq at y level, and below/above those it increases rapidly.
 
noah katz said:
"Additionally, what happens when you "push" the driver some and the VC starts to leave the gap? Whats happening to back EMF then?"

Then you've exceeded the driver's limits and you're overdriving it.

And distortion is more of a function of freq, because excursion increases inversely with the square of freq; just look at any subwoofer test (the best I've seen being Way Down Deep by Keith Yates in SGHT.

More then simply "exceeding the driver's limits" - which can often happen with real-world use. (particularly with full orchestral material that has strong dynamic "swings".) BL is reduced and therefor back EMF is reduced.

I too like the "Way Down Deep" article..

And excursion (relative to freq.'s "demands") with higher spl's does indeed increse THD..

HOWEVER, even at low power/moderate spl's, where excursion could well be considered low, THD is much higher at resonance - while usually lower well above AND below resonance. This is because back EMF isn't "good enough".
 
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