Ford JBL frequency response tests

[gadget73]

Did some testing on one of my half-dead JBL units. I believe this one came from a Towncar. 3 of the channels operate, so I only did left front and left rear measurements.

To explain what you see here on the chart, this is the frequency response plot of the amplifier using 1 watt of output power at 1khz on the rear channel as the 0db point. There are three lines on here. The blue one is the rear channel. The red one is the front channel using the 0db point of the rear channel. As you can see, its not as loud as the rear, which makes perfect sense due to seating positions. The yellow one is the front channel using a 0db point from the front channel. Not sure if the yellow band is particularly useful, but it was easy enough to put it in.

If anyone wants to know, the audio generator is a Sound Technologies ST1700A distortion analyzer and the meter used for volt measurements is an HP 3456A. Input voltage was 13.8 volts DC from a BK Precision 1692 40 amp bench power supply. Tests were across a 5 ohm dummy load. Not the proper load for this, but at these low power levels it won't affect anything.

[sly]

interesting.

[lincolnlarry]

Good freq. response. I still haven't gotten the urge to change anything in the 89 TC. It really sounds good enough for me. Thanks for sharing the specs.

[Whosondephone]

So this is measuring the amp output not the speakers?

I listened to a sweeping sign wave generator on the ford premium sound. Keep in mind I have replaced the rear drivers and am using a tape adapter. Sitting in the front I notice that there is a Peak at 80Hz then roles off then a slightly bumps back at 40Hz. Interesting that they role the bass off on the JBL amp. Most likely wouldn't hear anything the drivers put out below 80Hz. The car/trunk is to big.

I always wanted to seal the trunk from the cab and mount the driver from the top. Perhaps one should get a better amp before trying this.

Thanks for sharing!

[gadget73]

yes, this is just output of the amplifier. I've got no means to measure the effective response of the speakers. Would be interesting to assemble a complete system using the proper matched drivers and electronics and see what it actually comes out like at the driver's seat with a microphone rig.

I suspect the response of the amplifier is tailored to compliment the speaker + car characteristics to hopefully come out closer to flat. They may also have things tweaked so it sounds better to the ear, even if its not actually accurate reproduction. I have to admit that the setup in my Mark VII sounds quite nice to listen to, but it probably measures horribly. I knew these didn't measure flat, but I honestly had not realized how non-flat it was until I actually collected the data.

Dropping the lows off makes sense though. A 6x9 in the trunk just isn't going to make 20 hz. They do seem rather bass-strong when you listen to one, but that huge bump around the 40hz mark would explain that. Keeping the lows out of the front speakers makes sense for the same reason.

[DerekTheGreat]

Interesting. Thanks for the work Thain!
The blue line is much like how I set up my own equalizer. Would be a good amp to use for my Firebird I think. Could put it in that rear compartment or in the dash. Probably in the dash if it fits. The JBL 6x9's respond very well to 60hz bass, the power series stuff I bought responds just a tad better. Bottom line is, if you have fully functional Ford-JBL 6x9's it would be a waste of money to replace them IMO.

[tjc78]

In my 89 LTC with factory JBL I put the factory 6x9s back in when i realized they actually performed better with the system than the aftermarket Pioneers I had put in. The fronts were replaced with something that did sound way better than the OEM. It made for a nice sounding system with a good Pioneer CD player.

[DerekTheGreat]

I don't talk about the fronts much because I haven't been able to test side by side. Riding around with the door panels off just isn't my thing. Ashley has the two ways from a Mk. VII in her car and they sound good enough. Finally pulled Townie JBL door speakers but they're still sitting on the shelf as I told Ash she needed to start doing some of her own work. It's not that she can't either, I've seen her pull door panels and dashpads it just must not be a priority for her like it is me. Same story with her driver door westherstripping..

[gadget73]

I don't think the door speakers are any different from premium to JBL. The Mark VII stuff is not at any rate, the ones in JBL cars have stickers that say Premium Sound. The dash speakers are specific in the Towncar, but they're basically all bad by now so it doesn't matter much.