Sensitivity Calculation and Speaker Measurement

[Buck455]

First of all, I love this forum and I've learned a ton from all you guys.

I have three questions for a build I'm working on.

1. I bought a Pyle Audio Mid Bass driver because I liked the published specs, but I'm questioning the manufacturer's sensitivity rating. The factory specs are:

Fs - 122 Hz
Qms - 11.52
Qes - 1.21
Qts - 1.09
Vas - .1707 ft^3
SPL - 97 dB

Using those nubers, I get a sensitivity of about 90.4. Any ideas on where the 97 dB they claim is coming from?

2. I have 2 woofers I'm going to wire in parallel. I've generated seperate impedance curves and Q numbers for both of them. One of the driver's is darn close to the manufacture's specs. The other driver is about 6 Hz too high on Fs, and about .06 too high on Qts and Qes. The question is, how do you design a vented cab for this driver mis-match? Take the average of the specs? Remeasure the specs with the driver's wired in parallel (as they will be in the cab)? Or is is close enough not to worry about?

3. When designing a zobel correction for the woofers, should I use two seperate ones, one for each woofer, or can I get away with one for the parallel woofers? This is my first internal crossover.

Thanks in advance!

 

[billfitzmaurice]

Using those nubers, I get a sensitivity of about 90.4. Any ideas on where the 97 dB they claim is coming from?

Probably a break-up mode spike. Which, BTW, is where more than a few cab manufacturers get their numbers as well, Kosher or not. :scowl:

The question is, how do you design a vented cab for this driver mis-match? Take the average of the specs?

+1. OTOH with a Qts that high these drivers aren't well suited for a VB. For that matter not well suited for anything in pro-sound IMO.

3. When designing a zobel correction for the woofers, should I use two seperate ones, one for each woofer, or can I get away with one for the parallel woofers? This is my first internal crossover.

Unless you're running separate filters for each driver you should run one zobel, though professional crossover designers don't use zobels at all, but use the actual measured impedance at the crossover frequency to calculate the component values.

 

[DukeLeJeune]

1. Maybe the 97 dB rating is based on a midrange or treble breakup peak. Maybe they are assuming 1/2-space loading. If it's a 4-ohm driver, then the 2.83 volt sensitivity will be 3 dB higher than the calculated 1-watt efficiency because 2.83 volts into 4 ohms is 2 watts. Maybe they are using an "in-room" figure, which includes the reverberant field's contribution. Maybe some combination of the above.

2. Using the average Fs and Qts values will work fine, but personally I think this driver's Qts is too high for use in a vented cab. Even in a stuffed sealed cab, you're going to get a large, wide 2 dB bump centered somewhere between 150 and 200 Hz.

3. Just use one Zobel for both drivers.

edit: Hello Bill, ya beat me to it.

 

[Buck455]

Thanks for the quick reply guys.

1. I figured they were playing games with the sensitivity issues. It's a Pyle PMW6A, 8 ohm driver. I couldn't get ahold of the Q values before I bought the driver. I should have know it was too good to be true. I figured the sensitivity was a good value because all of the other Pyle mids had much lower (around 88-90dB) sensitivities.

2, 3. I confused the issue of my second and third questions by not specifying that wasn't planning on using the driver with the specs I listed for the woofers. I am using Eminence BP102s for the woofers and the other for the mid range because of the 97dB sensitvity and power handling looked good, with about a 500-600 Hz crossover. Back to the drawing board for the mid range, I guess.

Thanks again gents!

 

[DukeLeJeune]

Thanks for the clarification, Buck455.

The hump in response down below 200 Hz on the Pyle won't matter if you're using it from 500-600 Hz on up. So it might work just fine.

Your plan to use a pair of BP102's crossed to a midrange at 500-600 Hz sounds like a darn good idea to me. I like the parameters and excursion of the BP102, but don't like the broad dip at 500 Hz. If you do a decent job of overlapping with the Pyle in the crossover region, you may be able to fill in that dip almost like it was never there and wind up with the best of both worlds.

Very best of luck with your project.

 

[Buck455]

Thank you very kindly sir.

Hopefully it'll work out like I plan. The only thing I don't care for is the 90 dB actual sensitivity of the Pyle, so I'm going to persue another midrange, I think. I'm leaning towards a pair of the Alpha 6s at this time.