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Restoring signal from JBL Amp: LC6, Cleansweep

Discussion in 'Gen 2 Prius Audio and Electronics' started by tmorrowus, Jul 12, 2005.

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  1. NuShrike

    NuShrike Active Member

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    <div class='quotetop'>QUOTE(NuShrike\";p=\"108163)</div>
    After listening a bit more on my midday commute, I need to multiply by 1.1 to adjust for that extra bass boosting at low volumes. The previous numbers were set for volume of 30, so for the normal mid-20s it would be:
    Hz
    31: +0.44 dB
    44: -0.83
    62: -5.61
    88: -3.63
    125: +0.22
    176: -0.88
    250: +0.44
    350: +0.96
    500: -1.05
    700: -1.65
    1000: +0.33
    1400: +1.51
    2000: +0.72
    2800: +0.19
    4000: -0.39
    5600: +0.22 dB

    So, YMMV, but by-ear tuning I found multiplying by 2 wasn't bad either, although maybe a bit under boosted, but difficult to tell, so it's just looking for that perfect number between 1.0 and 2.0. :)

    So this proves that pre-equalizing the audio to cancel the JBl amp distortion does work.

    tmorrowus: so in discussing your weekend work, the JBL amp takes balanced line-level input with max 'calculated' voltage of 2V? but isn't the level supposed to be constant so 200mV always?

    The CleanSweep takes in balanced 'differential' input, and puts out unbalanced output up to 8V, so if hooking something inline between the HU and the JBL, would need something that should keep the constant-level of 200mVac so either turn the output gain on the CS way down, or drop in a LOC such as the LOCB.2?

    Reading your other links, the JBL amp 'could' take in unbalanced input, but would that drop the gain? Of course the connection distance from EQ to amp should stay very short to avoiding picking up noise.

    I'm looking at this Pyle 5-band pseudo-parametric which seems to take in 200mV and puts the same out, as a pre-amp device, but doesn't describe how it handles signals. Actually, I just having a hard time finding a small sized 31-band EQ or 5-band real parametric (at any price). :)

    Soundgate isn't very descriptive with their product descriptions, btw.

    Also, interesting comment from a Harman Marketing Manager that the JBL amp will drive 2, 4, 10K ohm etc...
     
    #21 NuShrike, Jul 18, 2005
  2. tmorrowus

    tmorrowus Member

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    Hi Nushrike. I was just recently revisiting how I converted voltage to decibels and realized I left out a factor of two; I mistakenly used formulas for power rather than voltage. So the decibel values in my charts and spreadsheet will be multiplied by two after I fix that error (you will know because the revised date on the top of the document will be greater than 7/17/05).

    That would explain why your x2 factor sounds good if you derived your settings from my charts :)

    Also I recently learned that voltmeters have frequency response, and the high frequency rolloff in my graphs may be in the meter I used to measure, not in the actual signal.

    As far as the level of the amp, the level is 2V RMS, not 200mV. Even though the gain (volume) is fixed, the level of the signal measured will of course depend on the level of the audio signal on the CD. Since the test tone I measured was 10x lower in volts than the maximum voltage (100x lower in power), I think 2V RMS is the right number to report because that is the voltage of a full-scale CD signal (0 dbFS).

    It's nice that the Cleansweep takes balanced inputs.. that should allow you to put it before the JBL amp if you want. Since 2V is less than 8V there should be no problem on input to the CleanSweep.

    I'm not sure how kosher it is to connect the non-balanced output of the Cleansweep to the balanced input of the JBL amp. As you say that would definitely reduce the signal level from 8V to 4V max, which is fine because you will want to turn it down to 2V anyway. Ideally I suppose it would be best to use a balanced line driver that converts the unbalanced signal to balanced, but if you mount the cleansweep near the amp that may not be necessary as long as the input stage of the JBL amp can handle a "zero" signal on one side of the balanced input.

    That carsound forum seems full of knowledgeable folks... I'm trying to register over there but haven't gotten the confirmation email back yet. Good to know that the JBL can drive 10k ohms fine; that means most any line output converter should work; I've been trying to figure out whether any others besides the LC6 support summing... will report when I have more info on that.

    I ordered a Rockford Fosgate T8004 amp today... things are coming together slowly!
     
    #22 tmorrowus, Jul 19, 2005
  3. NuShrike

    NuShrike Active Member

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    Cool! So unbalanced 2V should be okay..

    Time for me to order the CS. After doing some time doing equalizer equalization (the adjustment numbers I'm using for Nero don't adjust for the dB effects on close neighboring bands), I find I'm not really into that too much. :)

    The forum takes like a day plus to get you registered when I got on. Be patient.
     
    #23 NuShrike, Jul 19, 2005
  4. wilco

    wilco New Member

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    Tom,
    Thanks for the extra work, you've answered all of my remaining questions...

    ... so the front door woofer can't be shimmed/spaced toward the interior without modifying the door panel :cussing: That mounting depth really limits the choice of replacements. Plus, the ring in the door panel probably make the fronts a little "beamy" too.

    ... and, so it is a "loudness" contour. I suppose that's both good and bad news.

    Your stereo pan test was a good idea. I too was wondering if the center speaker filled a frequency hole (for lack of a better word) or a hole in the stereo image. It's good to see that it doesn't.

    At volume 40 with the center disconnected, I notice some distortion. Your testing would indicate that it is speaker break-up as opposed to amp clipping at that volume. That's good to know.

    I'm curious about how you're planning to mount the TN52 tweeters. Are you going to modify the "sail" panels, or do you have a separate mounting point/method in mind?

    NuShrike,
    Very creative thinking... I like that. For those of us who have a large number of discs, it may not be too practical, but definitely the best bang-for-buck solution to the JBL "premium" sound.
     
    #24 wilco, Jul 20, 2005
  5. tmorrowus

    tmorrowus Member

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    Yep, seems the only way to get more mounting depth is to cut a hole in the interior plastic door panel. But there are enough speakers with mounting depth 2.5" or less that it shouldn't be a problem.

    I'm hoping I will be able to mount the 2" wide tweeters in the factory sailpanels by just cutting away some of the plastic inside there. Won't really know until I try it, but I remember reading that someone else got 2" wide tweeters into there.

    My testing didn't really address whether the audible distortion is from the speakers or amp, because the test signal I used had only one frequency (1kHz) unlike real recordings that have energy in all bands. It could be that the amp has enough power for the simple signal but not for real music. JBL amp power isn't really an issue in my possible application of using the factory amps to simply drive a high impedance line output converter; I was really wanting to test the input stage of the amp more than anything.

    Anyway, I too notice significant distortion when listening to music at high volumes on the factory system, and I suspect it's more from the speakers than the amp because it doesn't have the "clipped" sound.


    One more interesting thing I recently learned: David Navone himself told me that the NE-774V line input converter ($36 each) can be used for summing with a simple Y cable just like the Audiocontrol LC6 can. Buying two of them (one to convert and sum the front channels, and one to convert the rear channels) would give you use of the factory fader for half the price of the $150 Audiocontrol LC6.

    http://www.davidnavone.com/detail.asp?PROD...DUCT_ID=NE-774V

    I suspect that all or most passive LOCs can be used for summing with a simple Y cable, but they just don't advertise it since until recently nobody has really needed to do summing in car audio.
     
    #25 tmorrowus, Jul 20, 2005
  6. NuShrike

    NuShrike Active Member

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    I've been reading you can create your own summing circuit with just a few resistors.

    I'm looking into summing the front channels together and then sum with the back channels to get an 'average' L&R before I feed it to the CleanSweep.

    Also, I've just discovered there's ways to save 'mp3' streams to disc so I can listen to a favorite Shoutcast station on the road for later. Woo, this topic of the month is fun. Thanks! :)
     
    #26 NuShrike, Jul 20, 2005
  7. tmorrowus

    tmorrowus Member

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    Yeah, it seems that most passive line output converters already happen to have the roughly 10kOhm resistors in the right place so that they form a summing network with the addition of a Y cable.
     
    #27 tmorrowus, Jul 22, 2005
  8. NuShrike

    NuShrike Active Member

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    Blah after a week with better than standard JBL sound, I decided to practically spent the day in the car in the high 90Fs with an RTA, a couple of laptops (because signal generator kept leaking into signal capture on one laptop), and a crappy microphone (actually my decent headphones :) hooked over the passenger headrest (facing the driver) to do some real tuning by instrument of what one hears sitting in the car.

    Never liked how any of the sine wave tunings came out, so tried pink noise which is more like normal music, and the way human ears hear sound because each octave is equally loud, instead of each frequency.

    Wow, now it sounds strangely different, open, and more punchy now with nice spacious sound to it even though the EQ I will have to use is all over the place. 'True Grit', 'PHD': by the Crystal Method, '3AM Eternal' by The KLF, 'Andromeda' by Chicane sound the way I thought it should sound now. Gonna check PVD, CoLD SToRAGE, BT, anime, game, and rest of my collection to be sure.

    So this includes my Kenwood tuned to 180⁰ out of phase (to bring out 40-62Hz area), Kenwood volume at 80%, and crossover set at ~75Hz, so bass settings < 125Hz for other people will vary. Prius volume set to 25, laptop volume set to 75%, and laptop output through Prius's cassette port.

    0062Hz -10dB
    0088Hz -5.0
    0125Hz +4.0
    0176Hz -1.0
    0250Hz +7.0
    0350Hz +4.0
    0500Hz +1.0
    1000Hz -8.0
    1400Hz -4.0
    2000Hz -6.5

    Didn't go above 2k because my 'mic' started dropping off in response. I think this is good enough for me for now though, and maybe more when I get a decent calibrated mic sometime.

    Seems to be some huge volume shifts needed just to get a 'flat' response to the ear that only approximates the opposite of JBL's equalization curves.

    Wow, this makes me totally rethink if I really want flat sound with a CleanSweep. Even though the audio signal would be flat, the environment wouldn't be so it would still need a custom EQ to flatten it out depending on the installed speakers. And, every speaker upgrade would change the sound, meaning some recalibration to flatten it again.

    I think this supposedly heresy to tune by what you hear (because it changes depending on where you're sitting) instead of just having a pure signal, but whatever. :pukeright:

    So, just trying to make my daily 3 hr total commute enjoyable. :)

    [addition]: picked up a mic and did some more dialing and got this:

    0044Hz +2dB
    0062Hz -2.0
    0088Hz -5.0
    0125Hz 0.0
    0176Hz +2.0
    0250Hz +3.5
    0350Hz +2.0
    0500Hz +11.0
    0700Hz 0.0
    1000Hz +5.0
    1400Hz 0.0

    Most important are the first three.. Rest are kinda not too reliable because it's so directional. I definitely see now why a parametic eq would be less 'fun'. Okay, enough for now.

    So COOL!, I haven't heard of Focal speakers or them being that good until this forum. Any speaker setup with real crossovers should just sound that much better. Let us know when you got it all pounded in with a mallet and adjusted. :)

    [edit: 7/27/2005]
    Tweaked above settings (rev 14) to match CD playback instead of cassette; DUH. CD is more flat than cassette except for this weird HUGE dip at 500Hz of close to -11dB. If there's like 2 points to tweak to get satisfactory sound, it's 1/2 octave centering @ 70Hz, the dip @ 500Hz, and you're done.

    Also, fader makes the sound graph WORSE by being more uneven. Everything set at default is best to keep JBL amp doing the least.

    Attached picture is RTA'd sound before-purple (with -2 to the back fader) and after-green (centered fader). Don't know what's going on at 50Hz (not crossover) and 600-700Hz (prob JBL). You can see the JBL boost around 2Khz and up too. The extra leftover boost around 70Hz is actually nice to have to get it above road-noise, but does make the car rattle at volume 25. ^_^;
     
    #28 NuShrike, Jul 24, 2005
  9. tmorrowus

    tmorrowus Member

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    Thanks for sharing Nushrike.

    Yesterday I got the first stage of my project done- I got the front speakers replaced with Focal 165KP speakers, currently driven off the rear JBL output. The back is not connected.

    This is a huge improvement. The imaging is much better, the highs are much more crisp, and I'm getting more bass... not a lot more but it's noticeable. I haven't got the frequency response dialed in yet... I will have to experiment with crossover settings a bit more.

    I ended up drilling four new holes in the black plastic for the woofer, at the same places as the old four holes, but closer to the middle of the opening.

    I cut nearly all the plastic structure out of the backside of the tweeter sail panels using a utlitly knife, and enlarged the hole that the tweeter fires through. The Focal TN52 tweeters just barely fit. I used lots of Mortite type claylike weatherstripping material to hold the tweeters in place in the sail panels.

    I found myself turning the volume control up much higher than I did before. I think there are two reasons. These speakers are probably less efficient than the JBL ones. Also, they cause much less distortion when played loud; I didn't start to notice distortion until they are turned up in the high 50's volume.

    Since I was listening at a higher volume level, that gives flatter frequency response due to the "more loudness EQ at lower volume levels" JBL amp EQ.
     
    #29 tmorrowus, Jul 24, 2005
  10. tmorrowus

    tmorrowus Member

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    Alpine PXA-H701

    I did find another option for getting a flat frequency response. The Alpine PXA-H701

    http://iweb.alpine-usa.com/pls/admn/item_i...m_name=PXA-H701

    Here's the owners manual:

    http://iweb.alpine-usa.com/html/asb/owner/...pxa-h701_om.pdf

    It is a DSP processor that has 31 band EQ, and built in crossovers to output as many as 8 channels: Front tweeter L/R, Front Woofer L/R, Rear L/R, Center, and Sub. You would of course have to use aftermarket amps with it.

    It is used with the RUX-C701 controller:

    http://www.alpine-europe.com/content/engli...OR-PXA-H701.htm

    which provides volume control, balance, fade, as well as access to all the fancy EQ/Xover features. I think it could mount in the space under the JBL system head unit.

    By manually entering the opposite values from what's shown on my charts at:

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

    you could likely get a "cleansweep" type flat output tapped in after the JBL amp.

    It would be best to feed this thing a fixed 2V RMS signal because it has a reputation for having the potential to be noisy. So I might feed it directly from the signal from the head unit to the JBL amp, using a transformer like the $32 Navone N-555 at:

    http://www.autosound2000.com/filters.html

    The downside is that I'd lose LCD beeps and would have to manually mute audio for spoken commands. But I could live with that because it would allow me to totally remove the JBL amp if I wanted to. That way I'm starting from a flat frequency response and can add whatever corrections I want.

    This thing is not cheap, at $600 or so ebay price for the box and controller. But it allows amazing possibilities, like changing the crossover points and time aligning the system, as well as complete freedom to EQ as you see fit. You could even add a center channel back into the system if you wanted to with it.

    It's probably only something that a seriously obsessed audio freak like myself might want, but I'm sure I'm not the only one!
     
    #30 tmorrowus, Aug 5, 2005
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