Restoring signal from JBL Amp: LC6, Cleansweep

[tmorrowus]

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.

[NuShrike]

Nice! A self-tuning 30-band equalizer, instead of myself picking up a Behringer, or something. Too bad we can't use this to get the equalization settings, and then burn it into some cheaper device for mass production as a 'harness' to plug in.

I even see a steering-wheel control interface that's supposedly compatible with the 2002-05 Prius that lets you control a new Sony or Pioneer head unit.

Thanks again for the great sleuthing!

[edit]
For the CleanSweep, it seems kinda pointless to put it after the JBL amp because it just attempts to reconstruct a flat signal with volume & fader, but we already have a clean&flat head signal, just not volume controlled. And it looks like it puts out pre-amp outs (not speaker outs) so we would still need another multi-channel amp, and the JBL becomes just dead-weight & space for just two little things.

Instead, I'm wondering if we can calibrate it from the JBL rear-outs and then put the CleanSweep inline in front of the JBL amp, and so the two will sorta cancel, and we get "flat" out of the JBL amp without any more extra equipment. Also, because the HU is constant level, low-volume hiss would be eliminated. All that's left is changing the speakers, and/or adding something like the LC6 before the CleanSweep to get clean sub outs.

Maybe it'll be cheaper to swap to the '#4 AM' HU (loosing the 6cd-changer+cassette changer which could be added back in another way), and then we can dump the JBL amp and properly set things from there.

What a waste and burden this JBL system is.

[tmorrowus]

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.

[tmorrowus]

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.

[NuShrike]

Thanks, I wasn't sure if my idea was just a shot in the dark since I'm not a EE trained as you seem to be (ICS here).

So, I'm going to ask the CleanSweep people about this, but if mounting post-amp for calibration, and then mounting pre-amp for normal usage with not other issues like impedence, voltage, JBL doing even more clipping, etc etc.. Putting in some speaker wire binding posts might make it easier to setup too.

Here are some charts based on your data of what "I imagine" it would look like before/after CleanSweep, and after CS&JBL.

As you can see, although the Front Woofer wouldn't be as flatclean post-JBL as the Rear Woofer would be, it could be clean enough you can shoot it through something that sums (like the LC6), the full-range aftermarket speaker with any necessary amp in between. Or, just use the Rear Woofer outs and shoot it through a multi-channel amp...

Could probably clean up the Front Woofer a little more by dropping the "Bass" adjustment on the HU to -3 or below, and moving the fader 1 or 2 to the rear too.

I want to do as little as possible, and just put in aftermarket component speakers at that point as needed.

[wilco]

Tom, you are the man. I hereby donate all of my points to you.

That Clean Sweep looks intriguing... I like this part:
...OEM head units now incorporate non-defeatable equalization curves aimed at correcting the response of factory speakers, as well as protecting relatively weak factory speaker systems from overload. Examples of these include bass roll-off at increasing volume settings, or severe midrange EQ to tame the response of OEM speakers...

That's it alright

[tmorrowus]

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]

Tom, are you sure the AudioControl LC6 can sum the front woofer/tweeter channels together. From the installation manual there is no summing involved, it will just provide a signal to sub-woofer out if no sub-woofer exists. The CleanSweep would be a perfect solution if the front channels could be summed, the CleanSweep instructions even state to sum together any bi-amped/bi-wired speakers. The problem is to find a device to sum those speakers.

Wayne

[NuShrike]

<div class='quotetop'>QUOTE(tmorrowus\";p=\"107072)</div>

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

Like it says in the VFAQ, the BC or AM headunit in the Prii are by Panasonic, so I'm basically saying the stock BC HU, and showing how the signal is before and 'would be' after shaping by the CS.

You know, some of us have the center-speaker disconnected. Can we just hook it in into the NAV instead of using the driver's woofer to make that center useful? Wouldn't want to do that with the BT phone setup (wherever the sound comes from) though because that would put it too close to the mic and feedback looping woohoo.

You know now that a NAV motion defeat was discovered today which the devs probably used for debugging, makes me wonder if there's a EQ defeat somewhere in the JBL amp also.

[tmorrowus]

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.