Restoring signal from JBL Amp: LC6, Cleansweep

The prius JBL amp heavily EQs the signals in such a rather nasty way, as shown in graph 1 of:

http://www.tom-morrow-land.com/tests/priusaudio/

There are two products that address some of the issues that complicate adding aftermarket audio systems to the Prius JBL factory system:

AudioControl LC6: (list $149)

http://mobileaudiocontrol.com/product.asp?...249&l1=5249&l2=

and the JL Audio Cleansweep: (list $400?)

http://www.jlaudio.com/press/CleanSweep05.html


The LC6 will sum the front woofer and tweeter channels to produce a single channel that can drive an amp with a speaker system that has it's own crossovers. This gives the end user the ability to keep the factory fader control operational with aftermarket front and rear speakers/amps. It does not do any equalization to compensate for the equalization in the JBL amp.

The Cleansweep does not do that kind of summing, so you would drive it exclusively off the rear channel output from the JBL. But it has a way cool feature where it digitally compensates for the equalization that the JBL performs. You could keep the Prius volume control, or use the volume control included with the Cleansweep to reduce possible hiss at low volumes.

Both these products could be used together to yield fadable, flat frequency response signals to drive an amp and aftermarket speakers.

The cleansweep is apparently just now starting to be introduced, so there aren't many reports about sound quality, and it seems to me that it's not ideal in that the amp does a Analog-> Digital -> Analog conversion, and then the Cleansweep does another Analog -> Digital -> Analog conversion, and both likely introduce some equalization artifacts into the sound. And if you use the factory prius volume control there may be issues with low level hiss, since the rated 24 bit per channel is likely in reality less than 24 bits in actual resolution, and having to cover the 16-bit CD dynamic range plus the range of volume levels the system accomodates means there will likely be some digitization artifacts at lower volumes... whether they will be audible remains to be seen.

But this does give a relatively straightforward solution to the problem of getting clean signals to aftermarket amps for an upgrade of the audio system.

Another approach would be to simply tap into the signals before the JBL amplifier, with something like this soundgate LOCB.2 (list $92) :

https://www.soundgate.com//index.php?reques...1&usereferrer=1

(Note that for some reason this site seems to not list this as being compatible with the 2005 Prius, so maybe this one won't work for some reason)

And use a remote volume dial mounted near the dash instead of the steering wheel controls like the SNAVM2 (list $44):

https://www.soundgate.com//index.php?reques...9&usereferrer=1

And perhaps add a very small super cheap speaker connected to the JBL amp for beeps and such.

 

Wow, that is really clever! Great idea to put the cleansweep before the JBL amp if possible. Solves the volume issue and removes the need to have more amps.

The possible issues I see are:

- The Cleansweep outputs an 8V signal, which is likely too much for the JBL amp to handle. There doesn't seem to be any adjustment on the cleansweep to lower the level of the signal. But aftermarket adapter boxes might be able to solve that.

- In order to compensate for the lack of bass that the jbl amp has, the cleansweep would boost the bass that it sends to the jbl amp, which might overload the input section of the jbl sending it into clipping. Or else if somehow levels were adjusted to avoid that clipping the input to the amp might be so low that it can't use it's full power range. Actually as I think about it, this issue would occur with aftermarket amps with cleansweep mounted after the jbl as well. But aftermarket amps might deal better than the jbl since they are designed for a wide variety of inputs.

- Logistically it would be necessary to connect it after the amp for programming, and then again reconnect before the amp, a bit of a pain.

- Perhaps most significantly, you would only be able to use the rear channel of amplification in the JBL to get a full range signal, which means you couldn't use aftermarket full range speaker systems in both front and back.

 

Hey, does anyone know what the voltage of the analog left/right signals that drive the amp is? I'm really starting to think that tapping that is the way to go for aftermarket sound, so it would be nice to know what the characteristics of that input are.

 

Hi NuShrike. Thanks for doing the graphs to figure out the front channel response when you calibrate off the rear channels with the CleanSweep. It should probably be okay if you want to continue driving the factory front JBL speakers. Although it's possible that some of the EQ the JBL amp inserts may be to compensate for weaknesses in the factory speakers, and by reversing that you may actually be throwing more power at those weak spots.

I didn't understand the first graph... the labels say Panasonic Head Unit... is that something you are adding for MP3 and such?

Wilco thanks for the points... Wish I could buy amps and speakers with them


Does anyone know whether the music muting for voice commands and telephone conversations happens in the signal to the JBL amp, or does the JBL amp itself do the muting on an unmuted signal from the head unit?

I'm zeroing in on the solution of just bypassing the jbl amp altogether at this point, and using aftermarket volume controls and maybe an aftermarket fader control hidden away somewhere. I'd keep the jbl amp hooked up to the factory center channel speaker for beeps.

 

FireEngineer, the sales note off the link above says:

"Another unique feature of the LC6 is sumable outputs. This means you can take multiple inputs from a factory amplifier that have been crossed over and sum them back together to get a full range input for your aftermarket amplifiers. How cool is that!"

I think the way you would use this is to feed the JBL front tweeter signal into the Front input on the LC6 and the JBL front woofer signal into the Subwoofer input on the LC6. As you say, the instruction manual doesn't really cover how to use the summing feature.

 

The navigation and the bluetooth phone both use the same mini amplifier inside the nav unit, if you used the center for one you would also have to use it for the other.

I'm planning on just leaving the nav amplifier connected to the left front woofer. Or maybe to the left full range system when I go aftermarket with the speakers. I just ordered a pair of Focals 165KP speakers.

 

There are apparently two issues with beeps and aftermarket audio:

1. If you bypass the JBL amp completely, you won't get beeps at all since they are generated by the JBL amp. Using the cleansweep or other products on the signal out of the JBL amp passes those beeps thru.

2. Some folks who added amps after the JBL amp found the beeps got louder, because the aftermarket amps were amplifying more.


I would guess the source of issue #2 is something like this: The aftermarket amp speaker level input section probably is not capable of dissipating the equivalent of the 45 Watts that the JBL would be putting out at full volume. So the installer cranks up the input gain on the aftermarket amp so it reaches input saturation (full output level) with a much lower volume setting on the head unit. Say the aftermarket amp is adjusted to saturate at .5 Watts of JBL output (my made up number). That means that the gain factor is 45W/.5=90. So beeps are 90 times as loud (I think that's around 18db higher).

Note that I was oversimplifying in the above discussion by assuming the amplifier would be putting out 45 watts at full volume... actually the impedance of the speaker level inputs on an amp would be much higher than the under 8 Ohm speaker resistance, so it would have to dissipate much less power. But the principle is the same.

One solution to that issue would be to use a line output converter (LOC) that can accept the full power of the JBL amp, or something close. Such as the Soundgate LOCHVA (85 Watts, $58 list):

https://www.soundgate.com//index.php?reques...3&usereferrer=1

The downside of that approach is that you end up using up to 45 Watts peak per channel of power driving that LOC which is a waste of power (and therefore gas). At least with that kind of LOC you have the flexibility to strike a balance between beeps being loud versus wasting gas. There is probably a happy middle ground where beeps are a little louder but you aren't wasting that much power in the LOC, especially if you don't usually listen to music at top volume.

 

Cool to have a rep from JL available like that!

Another issue to consider is that the signal to the amp might be balanced (opposite signal on + and - wires relative to ground rather than - being ground and signal on +). That kind of signal might not be directly compatible with the CS, but there are boxes that can convert. I'm planning on investigating it this weekend to see whether it is a balanced signal or not.

 

Newsflash: the JBL system does change the equalization based on volume setting. I added lots of measurements to my document at:

http://www.tom-morrow-land.com/tests/priusaudio/

The higher the volume, the flatter the response, and at the higher volume levels the equalization curve is not so horrible.

 

Wow, that's a cool hack NuShrike. Very futuristic to replace hardware (EQ) with data!

What volume level were you listening at?