JBL 804 vs TangBand 740P

[N.Webber]

Hi,

I am currently building two ATs and thought it would be a good opportunity to try and see if there is any substantial difference in performance,
output or any other noticeable aspect between the JBL GTO804 and the Tang Band W8 740P.

The T.B. is the recommended driver for the AT but the JBL is also within specs and is obtainable here (Israel) allot cheaper then the T.B.,
so If there is no apparent loss in performance, the JBL will be (my) preferred option.

One issue that literally jumps out of the specs pages is the sensitivity figure difference. The T.B. specs 84 dB (1w/1m)
while the JBL specs 91 dB (same 1w/1m). Theoretically this is a major difference in favor of the JBL.
With supposedly 7dB difference the JBL should walk all over the T.B… But being skeptical of (too…) nice numbers on spec sheets
(especially when they are meant for the car audio market…) I decided to actually check the sensitivity of both drivers for real.

I arranged this setup, nothing scientific by any means; I simply run a sweep and measured the response of each driver.



Both drivers are 4 Ohm nominal and were driven with the same signal/level. As seen both drivers are at the same distance from the measurement mic,
and all the settings are the same. The switching of the drivers is done by Banana jumpers at a connection box.

Here is the response result, the green plot is of the JBLs and the purple is of the T.B. By the way, further up the spectrum,
the T.B. tops the JBL by a great margin (this is of coarse not relevant as it's well out of the driver's working range)



So, to my humble eyes (and ears), at the intended working range of the AT (40 - 100 Hz), it looks as if these tow drivers are actually very similar.
Certainly no 7dB difference there…

Of coarse this is 'open air' test and the results may vary once the drivers are loaded into a cab.
I plan to load one AT with the JBL and the other with the T.B. and measure again.
I'll keep you updated.

[Bill Fitzmaurice]

There are lies, there are damnable lies, and there are specifications.
However, SPL is measured in a standard baffle configuration, not free-air, and the results would be quite different, for both drivers. In-box is what matters, and that will be interesting to see.

[Gregory East]

Very interesting indeed. I wish BAT could be measured like that.

[bassmonster]

Thank you for doing this. I've looked for a direct comparison between the two for some time now and this seems to be the one I was looking for. The JBL is $15 cheaper in my area than the Tang Band, so it really will be interesting to see which one wins in the box.

[Ryan A]

Yes it does seem like the JBL's sensitivity numbers are inflated a bit. However, even if they are the same sensitivity, I would prefer the JBL due to higher power handling of up to 800 watts. I have driven an JBL804 with 600 watts (1 channel of QSC PLX1804) without much problem, as long as its high passed properly.

One thing I would like to know though is how the spec differences affect the drivers once installed, since the TB is more "in-spec" than the JBL (Look at QT and VAS difference). I can't wait to see your numbers once installed in box.

[Bill Fitzmaurice]

Yes it does seem like the JBL's sensitivity numbers are inflated a bit. However, even if they are the same sensitivity, I would prefer the JBL due to higher power handling of up to 800 watts.

You have not driven one with 600 watts, you've driven one with a 600w amp. It's not the same thing. The 800w rating is peak, which is the adspeak way of saying 'piffel'. The only ratings that matter are RMS, and that for the JBL is 200w.

[Ryan A]

The rms rating is very useful if you plan on playing sine waves for extended periods. Both RMS and peak ratings are important, though, for music. The ability to take peaks (like high impact kick drum) is just as important as continuous power handling. Peak ratings show that when the juice really gets flowing, the driver will be up to the task, both thermally and mechanically.

Whether the JBL's power numbers are inflated compared to the TB are another matter. Maybe the test will shed some light.

[Bill Fitzmaurice]

Peak ratings show that when the juice really gets flowing, the driver will be up to the task, both thermally and mechanically.

Not really. Peak ratings are advertising crap. At one point the FTC banned the use of anything but RMS. Then the Reagan administration came in and put the foxes in charge of the hen houses and that was the end of that. Peak ratings are meaningless and should be ignored. And mechanical limits tend to be lower than RMS.

[bassmonster]

And mechanical limits tend to be lower than RMS.

Is this partly why my drivers seem to be "excursioning" quite a lot even though I'm not putting in more than 10 volts each? Or is this due to many more factors?

[Ryan A]

And mechanical limits tend to be lower than RMS.

Very true at low frequencies and when the driver is not loaded....which is why the higher the high pass is set, the greater the mechanically-limited power handling. With the high-pass set to 40hz or higher I can really take the leash off my amplifier

Thanks Bill for the history on peak power ratings politics...I did not know about the ban before.

[Bill Fitzmaurice]

Is this partly why my drivers seem to be "excursioning" quite a lot even though I'm not putting in more than 10 volts each? Or is this due to many more factors?

You'll get a lot more excursion when the driver is out of the cab, as there's no air load to overcome.

[bassmonster]

You'll get a lot more excursion when the driver is out of the cab, as there's no air load to overcome.

Thank you Bill. My drivers are loaded in the cab and when I have the cab turned around to see the inside of the driver chamber, still show a lot of excursion at 10 volts though obviously not as much as outside the cab. At around 20v it's a little bit more but not as much. IOW, the increase in excursion from 1 to 10v is much greater than the increase in excursion from 10 to 20v. Is this due to power compression or something else? I remember reading about how after a certain point most of the power is being turned into heat anyway.

[Tom Smit]

IOW, the increase in excursion from 1 to 10v is much greater than the increase in excursion from 10 to 20v. Is this due to power compression or something else?

1-10v is ten times the voltage, 10-20v is twice times the voltage.

I remember reading about how after a certain point most of the power is being turned into heat anyway.

With most drivers, the first half of the rated power is always an upwards climb in db,ie, every doubling of voltage results in 3db more. But going from 50% to 100% of the voltage only gains 3db (theoritically) and power compression sets in. The exception being the 3012 and 3015 which will keep on giving up to rated power.

[Gregory East]

You'll get a lot more excursion when the driver is out of the cab, as there's no air load to overcome.

Thank you Bill. My drivers are loaded in the cab and when I have the cab turned around to see the inside of the driver chamber, still show a lot of excursion at 10 volts though obviously not as much as outside the cab. At around 20v it's a little bit more but not as much. IOW, the increase in excursion from 1 to 10v is much greater than the increase in excursion from 10 to 20v. Is this due to power compression or something else? I remember reading about how after a certain point most of the power is being turned into heat anyway.

I think Bill already said as much with fewer words, it's not properly loaded without a boundary close to the opening, I don't know how close but enough room to get your head in and light in to observe is probably not close enough. Considering you like a LOT of bass a highpass might be a good thing.

[N.Webber]

Finished assembling the ATs and did a preliminary 'in room' comparison between the two.

Overview of the test setup:



As you can see, the ATs are coupled and facing the corner. I run the test twice with the cabs alternated, so that each cab was tested on the right and left hand side of the setup.

The corner loaded, coupled ATs:



And these are the measured results:



This is a small room, so the peaks at 50Hz and at 100 – 125Hz are probably due to room modes.
Interestingly, both ATs appear to be almost identical.

Next step/test: real world comparison = in the car.