Bgavin and Techs , a few driver questions.

First, you cannot use Xmech reliably as an indicator. This tells you how much (non-linear=distorting) movement the cone will stand before damage. Xmax is the linear portion of cone movement, so predicting response beyond Xmax is very unreliable. That said, IMO I prefer a cone with more movement, "just in case."

The Delta series has a high Fs, making it suitable for PA but not electric bass. Driver performance falls off very quickly below the resonant point. In my spread sheet I define "mid" use by its tuning frequency and cabinet size. There is a comment at the top of the column that explains the criteria I use. It is strictly arbitrary.

Almost none of the Eminence drivers will operate at full rated power, due to over excursion of the coil beyond Xmax. Brian Steele's spread sheet does an excellent job of showing the power/excursion relationship. All the SPL values in my spread sheet are based on this, and reflect the maximum SPL possible at the Xmax limit.

When choosing a driver, I want to know:
(1) The tuning frequency
(2) Maximum SPL
(3) Delta in dB between low E and middle E

If I were a 5-string player, I'd be more concerned withe the delta between low B and middle E. But, I no longer play 5-bangers, and this makes driver choice much wider and easier.

A small delta means little rolloff from middle E down to low E. Compare the Delta 12a to the Omega Pro 12. Huge difference. The Delta has a 13dB difference, compared to the 4 dB difference of the Omega. Worse, the Delta will only hit 110 SPL before it is excursion limited, compared to 117 SPL for the Omega. The +7 dB difference is a large amount of noticeable loudness. My subs each hit a maximum of 115 SPL, and I have to drive two of them at full powere to be heard in a loud venue, and four subs for a loud outdoor gig. There is a lot to be said for a driver that can hit 120 or higher SPL at full power. I bought a Magnum 18LF for exactly this reason.

Depending on the driver, a QB3 alignment will make better use of the driver (and louder) than the SBB4. The QB3 is almost always tuned higher, and this might put the particular driver minimum excursion right at the frequency where it is most needed. Check the spread sheet, as I've started adding QB3 data also. In some cases, the Optimal Flat alignment offers the most control and loudness, but at the cost of increased group delay.

You have to move air to make noise. The Omega Pro displaces 255 mL compared to the paltry 83 mL of the Delta. Xmax of the Omega is .1889 compared to .0630 of the Delta. The Omega has nearly 3x more linear cone excursion. No contest, here.

The Delta is rated at 400 watts, and the Omega is rated at 600 watts. The Omega Qts is much lower, meaning it has a lesser tendency to ring at the resonant frequency. Also, the Omega resonant frequency is below the 4-string operating range, where the Delta resonance is right in the middle of it.

The Delta is +2.5 dB more sensitive, but the Omega will make +7 dB more noise. If you are so constrained by limited amp power, buy a JBL instead.

 

Delta is the difference between two points. 43 Hz and 89 Hz in this instance.

Brian Steele wrote a very good spread sheet program.

Deltas come in many flavors:

Delta 12a
Delta 12b
Delta 12 Pro
Delta 12LF

I am looking at the Delta 12a, because only "Delta" was specified.

 

Bgavin, what type of cab do you use with your Magnum 18?

 

I'm building a QB3 type. 3.8 cubic feet at 39 Hz. I want something loud and smaller than my current subs.

TS, I misread "Delta 12 lf" as "Delta 12 if". My bad. I'm so used to seeing it as Delta 12LF, that I blew right past it.

Very little difference between these two other than magnet quality, voice coil diameter, high frequency response, and larger cabinet for the Delta. I prefer lower Qts drivers, but that is my taste.

 

You're just saying that because they're better !

(whines the guy with the .45 Qts subs)

 

Bruce, can you elaborate on that. I understand that low QTS drivers are generally higher quality. The part that confuses me a little is that the lower the QTS, the higher the -3dB point.

 

The king of the low Qts drivers are the JBLs. A lower Qts indicates a higher overall quality that reduces the tendency to oscillate. This is a result of more highly engineered magnetic structures that exert tighter control over the cone. Transient performance is better with low Qts drivers. The BL (motor strength) is directly tied to a lower Qts.

As for the higher F3, the more efficient drivers have a higher rolloff.

 

Bruce, whats your opinion on the JBL 2241's? I have used them for a couple years but dont know alot about them.


Mike

 

Pretty loud, JBL quality, high BL (JBL quality), good Xmax and volume displacment, downside is large cabinet of 8 ~ 9 cubic feet. Payoff is 35 Hz tuning, and F3 around 35 Hz also.

I'd own 'em in an instant, except for the cabinet size.

 

Hey Mike,

I also found this website about your speaker.

http://www.maryland-wireless.com/users/soundpro/jbl2241.html

 

Thanks Gabe and Bruce. Good info.


Mike

 

Do these speakers look promising?

www.beyma.com
(click english near the bottom right)

 

Very promising.

They are very JBL-like in construction. 4.0" voice coils, heavy magnets, high BL factor, moderate Qts, edge-wound copper voice coils with sufficient Xmax.

I added the LX60 and a 10" to my spread sheet.