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Thread: Small but perfectly formed JBL home cinema

  1. #61
    JBL 4645
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    Done a few tests Good or Bad?

    Hello all, just bloody fine weather we’re having here in England at the moment, hope the pissing raining keeps to the night time to make the dry air smell fresh in the morning.

    Anyway I’ve downloaded a free software package from (Home Theater Shack) site dedicated or one part, of it to the (Behringer FBQ2496) and I’ve managed to get a few issues sorted out on the JBL 4645.

    One is this took a few hours to get the whole thing, well almost I need (MIDI) lead connection between the pc and (Behringer FBQ2496) to make this fully user-friendly.

    So far these are test results.

    Test done at 10 feet to the present listening area where the sofa is, ECM8000 was positioned behind and slightly over the back of the sofa, at ear height.

    What I have done here is taken three frequency sweeps with (REW) Room EQ Wizard, the first one is with all three ports on JBL4645 18” sub as is.



    Second frequency sweep is with one port hole plugged up, and as you can see there is mild difference between the, first frequency sweep.



    Third frequency sweep is with two port holes plugged up, and as you can see again there is difference.




    I’ve done a few more tests as well as a few guess works on the signal level calibration on the (FBQ2496). I took a reading with RTA my standard basic RTA and placed the ECM8000 1m away from the JBL sub and played some wideband pink noise from the dts calibration disc track 14 and slotted in a few filters where I saw the peak.

    Filters used are
    25.1Hz
    +2db
    0.75

    40.3Hz
    -23db
    0.75

    Now is this right is it wrong, it all seems to be trail and error and it kinder looks right to me, so far.

    The first sweep wasn’t showing up to well, according to REW (Room EQ Wizard) and I forgot to add a little amplifier power, so I did a second frequency sweep test.

    Final frequency sweep was with ECM8000 placed back at seating position.

    First frequency sweep test



    Second frequency sweep test



    Cheers.

  2. #62
    Senior Señor boputnam's Avatar
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    Ashley, I have no idea what you are trying to do.

    Questions:

    - what is your crossover frequency (HPF) for the sub? Why is there all that higher frequency stuff there, the stuff above 90Hz...?

    - start with no filters. Run the sub alone, with the HPF at something like 90Hz.

    - make sure no other speakers are running.

  3. #63
    JBL 4645
    Guest
    Morning bop

    I almost forgot about? The JBL 4645 doesn’t run with crossover as its direct link between the LFE.1 and the LFE.1 has crossover drop off at 120Hz. Or more rather it’s (restricted to 120Hz max!) The lowest it starts off from is, 10Hz to 120Hz.

    I know that is nether here or there and it should have crossover fixed to regardless, but I’m fresh out of crossovers and I haven’t had any issues with it in the 10 years now.

    When I first had it up and running it was running with basic 100Hz crossover via my Yamaha DSR-70Pro back around 1998. and when I went digital with dts around the same year it would have only been getting signals as low as they go to has high as they can go.

    I always turn off or (mute) other channels when doing independent frequency sweep or wideband pink noise to prevent overlapping from other channels.

    I think I ran the frequency sweep yesterday from 20Hz to 120Hz for the JBL 4645 I could run the sweep test again. And moving the microphone around all the time is bothering me. I’d sooner have a few of the same ECM8000 microphone and patch several into mixer.

    Also you mentioned 90Hz what crossover slope should be used 6db 12db 18db 24db 48db?

    As for the high frequency stuff! Bugger I can hear pigeons above me, sounds like they’re in the loft “rats with wings!”

    Yes the high end of the sub lows,... [Getting up into investigate sound?] bugger they where coming from the bathroom near to the open window and yet it sounded like they where above!! Psychoacoustics, hay, sure fooled me.

    Yes the high end I haven’t the slightest clue but I would guess that was as far as I was letting the frequency sweep run to from 20Hz to 120Hz.

  4. #64
    Senior Señor boputnam's Avatar
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    Hey...

    Well, I'd try treating the 4645 as a true subwoofer - restrict the 4645 from doing anything above 90Hz - that's just a guess, but I think a reasonable start. JBL recommends HPF of 80 - 150Hz. In the case where this is mated with your "mains" - Control 5's - o it's likely you may need to move it higher, but I did not like the curves you posted. They were not good. Something is wrong.

    Quote Originally Posted by JBL 4645 View Post
    I think I ran the frequency sweep yesterday from 20Hz to 120Hz for the JBL 4645 I could run the sweep test again. And moving the microphone around all the time is bothering me.
    I don't understand what you are doing. Try this:

    - use only the 4645
    - use some full-range Pink Noise.
    - do not use any filters, no HPF, no nothing.
    - do not move the measurement mic.
    - post the curve

    This is the curve JBL has in their brochure - controlled conditions, surely - but yours was SO different there is something wrong.

    So, back to the beginning - try NO FILTERS, and run the subs raw. No HPF. No nothing. Just run them and post the curve. Let's see where you are at.
    Attached Images Attached Images  

  5. #65
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    WOW

    This thread makes me wonder why I havent seen this particular theater design in one of the popular magazines yet.

  6. #66
    Senior Member pos's Avatar
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    Quote Originally Posted by boputnam View Post
    Hey...

    Well, I'd try treating the 4645 as a true subwoofer - restrict the 4645 from doing anything above 90Hz - that's just a guess, but I think a reasonable start. JBL recommends HPF of 80 - 150Hz. In the case where this is mated with your "mains" - Control 5's - o it's likely you may need to move it higher, but I did not like the curves you posted. They were not good. Something is wrong.

    I don't understand what you are doing. Try this:

    - use only the 4645
    - use some full-range Pink Noise.
    - do not use any filters, no HPF, no nothing.
    - do not move the measurement mic.
    - post the curve

    This is the curve JBL has in their brochure - controlled conditions, surely - but yours was SO different there is something wrong.

    So, back to the beginning - try NO FILTERS, and run the subs raw. No HPF. No nothing. Just run them and post the curve. Let's see where you are at.
    Also, there is no 2245H in Ashley's 4645 clone if I remember well, but a 2240H, and the box is custom made (tuning?)

  7. #67
    Senior Señor boputnam's Avatar
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    Quote Originally Posted by 234STI View Post
    This thread makes me wonder why I havent seen this particular theater design in one of the popular magazines yet.
    It a top secret configuration. You're lucky to have seen it early...

  8. #68
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    Quote Originally Posted by 234STI View Post
    This thread makes me wonder why I havent seen this particular theater design in one of the popular magazines yet.
    Would sir like a saucer of milk?
    MEEEOOWWWWWWWWWWWW!

  9. #69
    JBL 4645
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    Quote Originally Posted by pos View Post
    Also, there is no 2245H in Ashley's 4645 clone if I remember well, but a 2240H, and the box is custom made (tuning?)
    What pos said is right its mimic and there’s no shame in it, most of the members hare and making DIY JBL products for home entertainment.

    Anyway I’ve taken a direct link test with single lead going directly into Alesis RA 300 for the sub bass LFE.1 channel, without any filtering other than the frequency sweep from 20Hz to 120Hz.

    ECM8000 microphone was placed behind the sofa at distance away from the DIY JBL 4645 clone, LOL with JBL 2240 at 9 feet 8”.


  10. #70
    Senior Señor boputnam's Avatar
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    Well, Ashley, it seems that with that post, you do know what you are doing, but that response curve is severly not good. You have some serious -20dB down points that to me suggest acoustic cancellations, but I don't know.

    Can you reverse the phase on that sub, and re-run the tests for grins?

  11. #71
    Senior Member grumpy's Avatar
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    Have a look here regarding what might look reasonable, even including room nodes:

    http://bobhodas.com/pub3.html

    1st & 2nd order room modes, based on raw room dimensions match some of the nulls,
    but it does seem as though a comparison of nearfield response curves might help
    (one at port, one at 2240). I don't claim to have a cure, but that's likely what I'd do.

  12. #72
    JBL 4645
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    Quote Originally Posted by boputnam View Post
    Well, Ashley, it seems that with that post, you do know what you are doing, but that response curve is severly not good. You have some serious -20dB down points that to me suggest acoustic cancellations, but I don't know.

    Can you reverse the phase on that sub, and re-run the tests for grins?
    bop

    I would say 100% on the room mode issues there are few in the, in fact we all them in our rooms or even in the real world with real word sounds I’ve heard room modes.

    I could place the microphone up close, how close and at what angle do you recommend I should position the microphone at?

    Thanks.

    Oh, there is just one other thing. I’ve moved the sofa back I mean moved it back a few feet, where I noticed a bit more of the depth in the lower end.

    I could test it again and in the new position. I also had to space the left and right out a bit wider due to stereo front filed narrowing and half pans were a bit hard to follow.

    Anyway you give tell me where I should place the mike and I’ll tackle it again. I would prefer a and full range RTA one that only monitors.
    Quote Originally Posted by grumpy View Post
    Have a look here regarding what might look reasonable, even including room nodes:

    http://bobhodas.com/pub3.html

    1st & 2nd order room modes, based on raw room dimensions match some of the nulls,
    but it does seem as though a comparison of nearfield response curves might help
    (one at port, one at 2240). I don't claim to have a cure, but that's likely what I'd do.
    grumpy

    I’ve heard of Bag End when reading about some of there 18” subs during around (2000) response down to 8Hz though its electronic active crossover, and the baffle wall.

    Bag End 18" sub
    http://www.hometheaterhifi.com/volume_4_4/bagend18.html

  13. #73
    Senior Member grumpy's Avatar
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    I was thinking you could get an idea of what your sub is capable of
    by getting the mic close... say 1-2cm, so the room will influence the
    measurement less. One measurement at the port, one at the woofer...
    I put the mic off center, ~ 1/3 way from the center.

    Omni mic? measurement angle shouldn't be critical, just be consistent.
    Next is sorting out what is room, what isn't, and how sub placement,
    room treatments (if in the plan), or EQ might help.

    That's quite an impressive/dedicated system you've built up -grumpy

  14. #74
    JBL 4645
    Guest
    Just finished fitting the remaining other JBL control 1 to the ceiling for matrix height surround as well as working with monaural surround. How that works is with the Pioneer VSP-200 other matrix functions called (Simulated and Studio) modes that work with sidewall surrounds when in this mode.

    Simulated provides a bit involvement with the opening of “InnerSpace” (1987) as the liqueur is pored into glass and rather having it on left and right sidewall surrounds I can place a little bend overheard that works quite will.

    Studio mode presents a lesser watery liqueur sound as that is mostly on left and right sidewall arrays.

    Dolby stereo Pro-Logic even lesser in this mode as the sound is directed to the centre back surrounds as it would appear the surrounds are monaural.

    Drilled into the ceiling with small pilot-holes to make the task easier and then mounted the brackets and attached the JBL control 1 up and tightened up the screw. Anyway I tidy up the dangling cables from the ceiling with cable trunking and need to get a few more lengths of it to finish it up as I ran out, its only £1.98p for 2.4m length, so what the heck.



















  15. #75
    JBL 4645
    Guest
    Quote Originally Posted by grumpy View Post
    I was thinking you could get an idea of what your sub is capable of
    by getting the mic close... say 1-2cm, so the room will influence the
    measurement less. One measurement at the port, one at the woofer...
    I put the mic off center, ~ 1/3 way from the center.

    Omni mic? measurement angle shouldn't be critical, just be consistent.
    Next is sorting out what is room, what isn't, and how sub placement,
    room treatments (if in the plan), or EQ might help.

    That's quite an impressive/dedicated system you've built up -grumpy
    Okay I’ll give that go, cheers.

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