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Thread: How to increase the bass signal on JBL 4671OK

  1. #1
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    How to increase the bass signal on JBL 4671OK

    I have just got a pair of JBL Pro 4671OK with bass/mid 2225H. When i first connected it to the amp, I immediately noticed the total lack of bass. I then drug an old amplifier out from the garage that had tone and bass controll, and a loudness button. I turned the bass on at full and in with the loudness button. Now the bass appared, but a bit under what I would call a normal level.

    http://www.axentia.no/hifi/4671ok.pdf

    I then connected a 1.5V battery to check if the woofer turned out or in. The woofer turned in when connecting the + at the battery at the red terminal. So I twisted the speaker cable so that the + went on the black terminal and the minus on the red. Now the bass level went normal, but still with the bass level at full and the loudness turned on at the amplifier.

    So my question are: are there someting I can do at the crossover to increase the bass level on the speakers?? Are the some kind of resistor there that I can remoce or change?

    Regards
    Jan

  2. #2
    RIP 2011 Zilch's Avatar
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    The cone movement spec on the data sheet refers to the terminal on the back of the cabinet. Is that where you're connecting the battery, or on the driver itself?

    There is no "Polarity" in the sense of DC, rather, we're merely talking about phase convention here, as the signal normally driving the speaker is AC, and the phase of the connection wouldn't alter the bass response unless you were playing it with other speakers in the same room. I'd say put it back the way it was, so it is correct with respect to the mid/high driver, and confirm that the drivers in the second speaker cabinet are connected the same way.

    JBL phase convention is that the cone moves inward when DC+ connects to the driver red terminal. You'll find the internal wiring reverses this in connecting to the cabinet terminals (though the schematic below doesn't reflect that).

    As to the response, 2225H is not gonna deliver much extended bass. The spec for that box is +/- 4 dB 40 Hz to 16 kHz. It's a sound reinforcement (PA) speaker. You'll need a sub with it for booming bass, and, assuming the drivers are working properly, you're not gonna tweak it into behaving otherwise.

    Look at the response curve below 50 Hz in that data sheet. You're not going to be able to pump up the bass with external EQ, either.

    http://www.jblpro.com/pub/obsolete/2225hj.pdf

    http://www.jblproservice.com/pdf/The...es/4671OKA.pdf

    Welcome aboard, and please enable location display in your profile. Click "User CP," above, to do it....

  3. #3
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    Yes, I was connecting the battery at the terminal the back of speaker. And if I understand you correct Zilch, it is correct that the woofer shall move inward when connecting the + from the battery to the red terminal? OK, I will put it back so that the pluss from the amplifier goes to the red at the terminal and the minus to the black. Sorry, but I believed I was doing something smart

    I'm aware that the 2225H never will deliver a booming bass, but I realy could wish that the bass volume where louder. Now I have to turn the volume realy loud to get some bass volume. But when I do, the horn plays so loud that I have to leave the room

  4. #4
    RIP 2011 Zilch's Avatar
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    The most important thing is that both cabinets are playing in the same phase, so that the bass from both do not cancel each other out, but rather, reinforce each other. If both are wired the same, they should be in phase. You can reverse the connection to the rear of one of them, and listen for the difference in bass volume, which, if they are close together, will be immediately apparent.

    With respect to phase, your cabinets seem to be behaving according to the schematic. Check the wire color codes given there. I don't know why the data sheet says the opposite. There's nothing in that crossover limiting the bass response. You may want to have the 2225H's checked to be sure they are performing to specification.

    If you want to attenuate the compression drivers, put a 16-Ohm L-Pad between them and the crossover to turn them down. Parts Express #260-261 or equivalent. Follow the wiring directions included with them....

    [Note to self: There's that HF boost bypass again, same's on the 4660. ]

  5. #5
    jbl
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    There may be something wrong with your woofers. I have the same system and the low bass is fine. I use mine with a DC amplifier and leave the preamp in it's flat position. Never considered using the Loudness control. I bought the components separately and assembled the set. My cabinet is the 4507. The system is the 4671. I cut out the necessary space for the 2370 horn and both sides sound the same. You may have a phasing issue. BTW. The crossover is the 3110A. IIRC, the "Ok" version used a different CO.

    Ron

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    Yes, that's what I belived also - that the speaker can play "normal" bass. I don't think there is a phasing problem, I have checked it again and again. So this is a mystery for me. I have tried various of amps on them but without solwing the problem. I just have to keep looking..... I maybe trying the tips from Zilch and put a L-Pad on them even though I'm not sure it will solve the problem...

  7. #7
    Senior Member edgewound's Avatar
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    Hi Janly...


    Other than the phasing issue there's really only two other area's that need to be addressed. In your 4671, are all 4 port tubes in place? If not, the tuning of the cabinet will be off on the high side...make sure all 4 cardboard port tubes are present. Secondly, check to make sure the 2225H is not overly fatigued in the suspensions...spider and compliance. If the spider is sunken or otherwise stretched beyond neutral, level, static starting point, the linearity of the voice coil motion will be off, and the bass will suffer. If the speaker has seen lots of pounding duty, it should be reconed with a new factory kit. Is the speaker all original JBL parts and to the right DC resistance specs? Maybe the impedance is wrong...that's all I can think of.

    Hope this helps,

    Edgewound

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    Hi edgewound and thank you for your tips
    All 4 ports are in place and the 2225H elements are according to what I can see 100 procent ok. The speakers have never been hard driven since they have been used in a small local council cinema, and are in original shape.

  9. #9
    jbl
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    The transition from the 2225 to the 2425/6 should be seamless. Is the 2225 lower in output through out it's range or just the lowest frequencies? Also, it would be helpful to know the history (environment, etc.) of those cabinets since the problem is on both drivers.

  10. #10
    Senior Member edgewound's Avatar
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    Possibly the problem is that the 4671 just doesn't have the amount of low end you're looking for...and no amount of brainstorming or magic dust thrown at it is going to solve the problem...short of changing drivers and box tuning. Does that make sense?

    Respectfully,

    Edgewound

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