What's to chat about?

[Seth]

The best rational I can come up with is adding a second driver essentially creates 2 narrower (by half) cabs, which lack the higher sensitivity attributes that inherently occur with wider cabs.

Is that it?

[Bill Fitzmaurice]

That's it. You'll get 6dB, but only in the region where the cab isn't part of the equation, which is above 200Hz, give or take.

[Seth]

Calculations note:

The 1.122 constant used in the Voltage/dB equation also works with comparing Vd and/or Xmax as well.

In another thread we were comparing drivers

Vd... based on stated xmax.
3012LF - 496cc
12XL1200 - 584cc
LAB12 - 659cc

If we want to know how much Vd we'd need to make a certain gain, or how much of an increase/decrease to expect from one driver to another, just adjust the dB value...

(1.122^dB) x initial Xmax or Vd value = final value

(1.122^1.42dB)*496cc=584cc
(1.122^2.47dB)*496cc=659cc

3012LF - 496cc - Baseline 0dB
12XL1200 - 584cc - +1.42dB
LAB12 - 659cc - +2.47dB

Or say we want to see what the loss would be going to a Delta 12LFA...

(1.122^-6.19dB)*496= 243cc

Delta 12LFA - 243cc - -6.19dB compared to a 3012LF

[Seth]

Here's a full quick reference cheat sheet for anyone interested

Interesting Stats

Prices are either Amazon or Parts Express, whichever was less... except for the 18Sound drivers. I could only find them for sale on ebay (new).
Looks like the 3015LF in a T48 is about the best output for your money.
Maybe I'll get around to factoring in the lumber cost sometime too.

[Tom Smit]

Here's a full quick reference cheat sheet for anyone interested.....

Scanning the chart, I happened to notice that the Vd/$ is the same as Vd/pd for the 18sound15. Thanks, though, for your effort.

[Seth]

Here's a full quick reference cheat sheet for anyone interested.....

Scanning the chart, I happened to notice that the Vd/$ is the same as Vd/pd for the 18sound15. Thanks, though, for your effort.

You're right Tom. Fixed and re-uploaded the pic. Thanks for pointing that out. I 10-keyed all the stats in there like a pre computer era credit card accounting agent. There could be some fat finger mistakes. If you guys see anymore, please point them out.

A note about the 18Sound drivers Xmax and Vd specs... they obviously measure or calculate their Xmax spec differently than Eminence does. IIRC, Bill mentioned that they in fact have more Xmax and Vd than the LAB12/15 and would reflect that in the specs if they were determined with the same methods... or something to that effect.

In the link that I put in the other thread there was an unverified list of a handful of manufacturers and the different methods they use to determine Xmax. Honestly, it's something I wasn't aware of. Seems it's a spec that means about as much as a power rating.

Snippet from that thread on AVSforum

...Traditionally xmax was defined as (Hvc - Hg) / 2.

More recently manufacturers have been adding a "fudge factor" to make for a larger xmax rating out of thin air. For example:

- Eminence measures to 10%THD, but offers insufficient data (no Hvc) to relate their quoted spec to anybody else.
- Faital Pro quotes based on (Hvc - Hg) / 2 + Hg / 3
- JBL, RCF and 18sound quote based on (Hvc - Hg) / 2 + Hg / 4
- BMS quote most conservatively on the original (Hvc - Hg) / 2
- Beyma and B&C state both Hvc and Hg in their specs, but the quoted xmax spec don't seem to follow any clear methodology and vary also from driver to driver. (Beyma and B&C might be using (Hvc - Hg) / 2 + Hg / 3.5
- Fane's Sovereign series, which is based on Eminence components states both Hvc and Hg, but their quoted specs vary between (Hvc - Hg) / 2 for their older designs and the "better looking" (Hvc - Hg) / 2 + Hg / 3 for their newer Nd drivers....
- IIRC Dayton's old product manager stated they were using the original traditional formula

Some of these might not be 100 percent correct, I haven't had a chance to review spec sheets from all these manufacturers yet...

Not sure what to take away from that other than I really dislike what marketing has done to seemingly skew what should be a simple report of facts.

[Bill Fitzmaurice]

Eminence use 10% THD as that's the standard for XMax. They measure it with Klippel Analysis. That's not insufficient data, it's the benchmark for data. Not all manufacturers have spent the big bucks for a Klippel rig, so they have to use a different standard. The original 80 year old method was coil depth minus top plate thickness divided by two, but that is almost always shorter than what you get with a Klippel measurement. To compensate for that many have decided to add something to that result, like top plate thickness divided by three, but it's an arbitrary and inaccurate method.

[Seth]

Eminence use 10% THD as that's the standard for XMax. They measure it with Klippel Analysis. That's not insufficient data, it's the benchmark for data. Not all manufacturers have spent the big bucks for a Klippel rig, so they have to use a different standard. The original 80 year old method was coil depth minus top plate thickness divided by two, but that is almost always shorter than what you get with a Klippel measurement. To compensate for that many have decided to add something to that result, like top plate thickness divided by three, but it's an arbitrary and inaccurate method.

That's good to know.

But, I get his point that they don't include enough information in their specs to be able to compare to other drivers made by companies that haven't invested in a Klippel rig. On the same point... I don't read driver specs all too often. But, I haven't seen any other company disclose, on their spec sheet, the method or calculation they use to derive their Xmax rating either. So, no easy way to convert any of them to an apples:apples(ish) comparison.

Would be great if all of them listed the result of the (Hvc - Hg) / 2 calculation as Xmax. Then, in a second spec, list what they consider to be the "usable Xmax" with a footnote explaining how and why they calculate or measure that way. Or, the other way around. List the measured/calculated usable Xmax as Xmax with a footnote of how is was determined and a second spec indicating the (Hvc - Hg) / 2 result... or at least include the information in the specs to be able to calculate it.

When you model the 18Sound drivers in Hornresp and spec voltage limits, how do you designate what point to call it at, given they're conservatively rated and don't have the Klippel derived specs?

[Bill Fitzmaurice]

They don't have to include any other information, Klippel is the benchmark. It's up to those other companies to join Eminence in the 21st Century. I generally add 10% to 20% to the mechanical measured result, depending on the formula they used.

[Seth]

Something is wonky about the 18Sound 15's xmax spec. You'd have to add 47.5% to their 8mm spec just to get up to the 11.8mm of the LAB15, then another 15% on top of that figure to account for the extra excursion (13.6mm calculated total Xmax) that would come with the additional 200watts.

Oh well. Not like I'm in the market. It's just a curious observation.

[Seth]

By show of hands , how many of you guys actually have an Excel spreadsheet with audio formulas too?
37602

[Tom Smit]

Handsdown.

[Grant Bunter]

By show of hands , how many of you guys actually have an Excel spreadsheet with audio formulas too?
37602

No Seth,
It's all in my head...

[himhimself]

[Bill Fitzmaurice]

You can't consider any one spec for maximum voltage. You have to consider all of them, and then model the driver in HornResp to see their combined result. Sometimes the overall limiting factor is Pe, sometimes it's xmax, sometimes it's xlim, and sometimes it's none of them.