Anyone have specs for 075? Fs, Qms, Qes, Le

[Eric M.]

I'm using Crossover 3 Pro to design crossovers for a system using an 075 for the high end. Unfortunately, this driver is not in their database. Would anyone know these parameters for the JBL 075:

Fs
Qms
Qes
Le


Thanks,
Eric M.

[Horn Fanatic]

I'm using Crossover 3 Pro to design crossovers for a system using an 075 for the high end. Unfortunately, this driver is not in their database. Would anyone know these parameters for the JBL 075:

Fs
Qms
Qes
Le


Thanks,
Eric M.

Greetings, Eric -

What you're asking for are a few Thiele-Small parameters for a tweeter. Very few manufacturers ever publish that data, and as far as I know, JBL only published the nominal impedance, frequency range, and recommended crossover frequency. T-S parameters are typically used for designing enclosures for cone loud speakers. If you're that concerned about the parameters of an 075, then the only parameters that should be considered are Le, and DCR. Knowing the DCR and Le will allow you to determine the magnitude of the impedance at the crossover frequency.

fs would be simple to determine if you have a sine wave signal generator and a VOM in conjunction with a test resistor of a certain value, typically 100 ohms. There is another simple method to determine fs that doesn't require electronic testing, but you would have to know the mechanical mass and the mechanical compliance of the diaphragm. Good luck getting that from a company the got out of the ring radiator business five years ago.

The reactive element in the network circuit of course, will be the relationship between the the inductors and capacitors. From there the impedance of the network can be determined by including the value of the resistors into the equation.

H.F.

[Eric M.]

Thank you. Unfortunately, the only tool I have a present is a digital VOM. I'm not sure if X-Over 3 Pro needs all the parameters I listed, but it certainly needs more than what I have entered so far, Z, Re and SPL. Is there anyway to test for Le? If you're correct, that should be the last figure I'd need for crossover construction.

I'm just getting back into the hobby after about 25 years. Learning lots of new things and having fun do it.


Thanks,
Eric M.





Greetings, Eric -

What you're asking for are a few Thiele-Small parameters for a tweeter. Very few manufacturers ever publish that data, and as far as I know, JBL only published the nominal impedance, frequency range, and recommended crossover frequency. T-S parameters are typically used for designing enclosures for cone loud speakers. If you're that concerned about the parameters of an 075, then the only parameters that should be considered are Le, and DCR. Knowing the DCR and Le will allow you to determine the magnitude of the impedance at the crossover frequency.

fs would be simple to determine if you have a sine wave signal generator and a VOM in conjunction with a test resistor of a certain value, typically 100 ohms. There is another simple method to determine fs that doesn't require electronic testing, but you would have to know the mechanical mass and the mechanical compliance of the diaphragm. Good luck getting that from a company the got out of the ring radiator business five years ago.

The reactive element in the network circuit of course, will be the relationship between the the inductors and capacitors. From there the impedance of the network can be determined by including the value of the resistors into the equation.

H.F.

[Horn Fanatic]

Thank you. Unfortunately, the only tool I have a present is a digital VOM. I'm not sure if X-Over 3 Pro needs all the parameters I listed, but it certainly needs more than what I have entered so far, Z, Re and SPL. Is there anyway to test for Le? If you're correct, that should be the last figure I'd need for crossover construction.

I'm just getting back into the hobby after about 25 years. Learning lots of new things and having fun do it.


Thanks,
Eric M.

Yes, there is a way to test for the value of inductance, and the price on those units can range up to and over $300. I'm not sure, but I think the inductance may be affected when the voice coil is in the magnetic gap. Someone on the forum with more electrical expertise than I may know the answer to that question. Perhaps you may find a kind person at JBL in the tech department for pro components who can give you that information.

Years ago I tried to get some technical data for the 2206 that wasn't published. Weeks went buy before a kind sole who happened to be passing through the depertment where that information was stored spent a whole minute and a half to locate the data I wanted. Once I called about another bit of data I needed on another component, and the chap on the other end of the line asked me, 'why do you want to know that?', not that he would have understood why I did. There are people at JBL who just plain don't care about helping customers, and then there are the few who do.

Good luck,

H.F.

[Eric M.]

I got this response from X-Over 3 Pro tech support, I thought I would post it in case others ran into the same situation:


"The JBL 075, 077, 2402 and LE85 all have compression drivers. Compression drivers do not fit the Thiele-Small (T-S) model which is why you can't find T-S parameters for them. X-over 3 Pro cannot display the response of these kinds of drivers in its graphs. The program will still help you design crossover networks with compression drivers, but you will need to rely on the response graphs provided by the driver manufacturer (in this case, JBL).

It's relatively easy to measure the T-S parameters of a driver with a measurement device made for that purpose. A digital VOM, by itself, is not adequate. We recommend the DATS from Parts Express or the Woofer Tester 2 from Smith & Larson. Either measurement device will measure high-frequency drivers as well as woofers.

But this won't help with compression drivers like you've cited from JBL. It would be like trying to measure the magnetism of aluminum. It's doesn't exist because aluminum isn't magnetic.

The T-S model is based on a conventional direct-radiating piston attached to a moving coil in a magnetic field. A compression driver is more complicated than that (it isn't a "direct radiator") and doesn't fit the T-S model. What the DATS and Woofer Tester 2 do is measure the complex impedance (ohms and phase) of a driver at many different frequencies and use that data to determine its resonance frequency (Fs), mechanical Q (Qms) and electrical Q (Qes). If a test box is used or a known mass is added to the piston, you can also calculate its compliance (Cms and Vas).

You can sometimes obtain pseudo T-S parameters for a driver that doesn't actually fit the T-S model if its impedance response is smooth and has either no resonance or has a single symmetrical resonance peak like a regular woofer or dome tweeter. You'll find a few ribbon tweeters in X-over Pro's driver database whose pseudo T-S parameters were estimated like this. But this seldom works for compression drivers because their impedance response is usually very messy with numerous asymmetrical peaks that cannot be approximated by the T-S model."






Yes, there is a way to test for the value of inductance, and the price on those units can range up to and over $300. I'm not sure, but I think the inductance may be affected when the voice coil is in the magnetic gap. Someone on the forum with more electrical expertise than I may know the answer to that question. Perhaps you may find a kind person at JBL in the tech department for pro components who can give you that information.

Years ago I tried to get some technical data for the 2206 that wasn't published. Weeks went buy before a kind sole who happened to be passing through the depertment where that information was stored spent a whole minute and a half to locate the data I wanted. Once I called about another bit of data I needed on another component, and the chap on the other end of the line asked me, 'why do you want to know that?', not that he would have understood why I did. There are people at JBL who just plain don't care about helping customers, and then there are the few who do.

Good luck,

H.F.

[ratitifb]

and never forget that TS linear lumped parameters describe the vibration and transfer behavior of a transducer in the small signal domain and at frequencies where the size of the transducer is small compared to the wavelength.


@ 8000Hz wavelength = 4cm (approx.) ;)

[ivica]

I got this response from X-Over 3 Pro tech support, I thought I would post it in case others ran into the same situation:


"The JBL 075, 077, 2402 and LE85 all have compression drivers. Compression drivers do not fit the Thiele-Small (T-S) model which is why you can't find T-S parameters for them. X-over 3 Pro cannot display the response of these kinds of drivers in its graphs. The program will still help you design crossover networks with compression drivers, but you will need to rely on the response graphs provided by the driver manufacturer (in this case, JBL).

It's relatively easy to measure the T-S parameters of a driver with a measurement device made for that purpose. A digital VOM, by itself, is not adequate. We recommend the DATS from Parts Express or the Woofer Tester 2 from Smith & Larson. Either measurement device will measure high-frequency drivers as well as woofers.

But this won't help with compression drivers like you've cited from JBL. It would be like trying to measure the magnetism of aluminum. It's doesn't exist because aluminum isn't magnetic.

The T-S model is based on a conventional direct-radiating piston attached to a moving coil in a magnetic field. A compression driver is more complicated than that (it isn't a "direct radiator") and doesn't fit the T-S model. What the DATS and Woofer Tester 2 do is measure the complex impedance (ohms and phase) of a driver at many different frequencies and use that data to determine its resonance frequency (Fs), mechanical Q (Qms) and electrical Q (Qes). If a test box is used or a known mass is added to the piston, you can also calculate its compliance (Cms and Vas).

You can sometimes obtain pseudo T-S parameters for a driver that doesn't actually fit the T-S model if its impedance response is smooth and has either no resonance or has a single symmetrical resonance peak like a regular woofer or dome tweeter. You'll find a few ribbon tweeters in X-over Pro's driver database whose pseudo T-S parameters were estimated like this. But this seldom works for compression drivers because their impedance response is usually very messy with numerous asymmetrical peaks that cannot be approximated by the T-S model."


Hi ,
I will suggest you put pure resistor about 10 Ohms instead of the driver in the network model.
some amount of compensations has to be done after measurements the driver response with the driver connected to the network.

regards
ivica

[Ian Mackenzie]

Hi ,
I will suggest you put pure resistor about 10 Ohms instead of the driver in the network model.
some amount of compensations has to be done after measurements the driver response with the driver connected to the network.

regards
ivica


If you like I cam measure a similar driver the 077 in LMS.

But what I would do is obtain the schematic for the JBL crossover used for the 075 and go from there.

Ian