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  1. #1
    Join Date
    Dec 2006
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    Tigard, Oregon
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    3,016

    Default Bass Boost & Remote Bass Control on Kicker Amp

    Okay, time for another one of my dumb questions. My Kicker ZX700.5 has a bass boost control knob on the amp and a remote bass level control knob for the sub channel (channel 5). The manual says that the bass boost control knob gives increased output (o-18db) at 40 Hz. So increasing this knob increases the volume of sound just at 40Hz? Or 40 Hz and below? So why would I want to turn up just this part of the frequency/frequency range?

    I also have a remote bass level control knob. Is this a separate volume control knob for channel 5 and is different than either the bass boost control knob and the input level (gain) knob on the amp?

    Finally, how do I set the gain on channel 5 - should I have both the bass boost control knob and the remote bass level control knob at zero when I set the gain? If not, where should I have them set when I set the gain?

    Thanks,

    Al
    Al

    2006 Mobius LSV

  2. #2
    Join Date
    May 2009
    Location
    Carlton Oregon
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    6,008

    Default

    The separate boost knob, the one with the phone line looking cord is really just a Volume control. It has no effect on the bass frequency.

    Its used so that if you have your Gains cranked up for the high volume bass hit, then at low volume you will have way to much bass, or say if you get a heavy bass song playing and its just too much bass, you can turn only the sub down.

    When you visited thats the knob i have on my dash and can turn down the sub but still keep the rest of the amp cranked up.

    As for the dials on the sub, you will have 3 seperate sets.

    Channel 1,2 channel 3,4 and lastly channel 5.

    Channel 5 is at the top by its self and has the boost dial, frequency dial and Gain dial.

    Set the frequency as you normally would, you want it set so when the bass if kicking out you cant tell its under the dash. You want your bass set so its very non directional to your ears.

    Setting the boost is more like that extra umph to the amp, i keep mine right around 3/4 its the same as a bass dial on your stereo boosting your overal bass frequencies by + what ever.

    The gain is just that, a gain and thats the one you have to tune so when your at 80% max volume you arnt over driving your sub. I had mine set to like 75% i think. My system still needs to be dialed in now with that new sub i got.

    Hope it helps and makes sense for you AL

    On another note im going to work on that stereo Tech tune with Brian at Exile for Feb i think. Portland Boat show is coming up in a couple weeks, then the Seattle show so i figure he will be busy. < Plus gives me more time to get all my new gear installed proper. >
    Malo <--- Means--Evil or Mean One. This explains a lot.
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  3. #3
    Join Date
    Nov 2009
    Location
    Stillwater, Oklahoma
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    311

    Default

    Good morning, and Happy New Yrear!

    mmandley is right, and his description is good. The remote knob you can mount at the helm provides control over the volume level of the subwoofer and nothing more. His example of how it can be used is spot on too!

    The bass boost control at the amp adjusts the amount of boost, (centered at 40 Hz) that the amp adds to the subwoofer. this is like a graphic equalizer, only it has just one slider, right at 40 Hz. When you turn it up, you add a "hump" to the sub-amp's frequency response, right at 40 Hz.

    Be careful with the bass boost knob; the 40 Hz boosting one at the amp. When properly used, the bass boost knob is only there to correct for shortcomings of the total stereo system's low-end response. A well designed system will sound best with bass boost barely turned on, or even off.

    Here is a classic example:
    Say a guy, (we'll call him Newby Norm) has a woofer mounted free-air in the footwell wall area of the driver's helm seat, (yeah, I know, driver's seat and helm are redundant! ). The wall provides a barrier between the storage area in the bow rider section and the feet of the driver. The wall the woofer is mounted to is thick, solid, and rigid; that would be a good panel to mount a woofer to. BUT... this wall does not totally seal off the forward storage area... The wall does not go all the way up to the underside of the dash, but stops short. In this situation, the sound pressure coming off the back of the woofer can, (and will) go over the top of the footwell wall mix with the sound coming off the face of the woofer. The sounds have same or similar amplitude, but are largely out-of-phase and therefore cancel each other out. The result is little or no bass.

    In this instance, Newby Norm wants more bass, so he turns up the bass boost. Problem is, he is turning up the 40 Hz frequency for both sides of the woofer, and even though the amp is working harder, and the woofer is moving A LOT more, there is no more bass output; the sounds from both sides of the woofer are still mixing and cancelling out. At the same time, the woofer is moving at or near its mechanical limit and is prone to failure due to excessive excursion, and the amp is working way harder than it should have to, moving the woofer so far in and out... the amp will get pretty darned warm in this situation, and if it is at or beyond its ragged edge, could fail for its own reasons...

    The thing Newby Norm needs to do first is examine his stereo system for problems. Had he identified the problem with the big air gap at the top of the footwell wall he could have fixed it first. Sealing off that wall would provide a huge increase in low frequency performance... The bass would have been louder and better without touching the bass boost knob...

    This is but one very simple example and there are many other examples that Brian, David, myself and/or others could go into. The point I am trying to make is this: turning up the bass boost to make up for poor low-frequency performance should be done AFTER you consider all the possible acoustical and mechanical reasons for the lack of bass. Is your free-air installation correct? Is the free-air mounting wall completely sealed between both sides? Is your woofer enclosure the proper size? Is it leaking? If you are using a ported box is it tuned too high? Too low? Did ytou accidentally wire your dual voice coil woofer so that the coils are out-of-phase?

    Sorry for going off on a tangent of sorts, but this seemed a good time to go into a little discussion on the bass boost knob. Use your bass boost with care, and if you have it turned way up, consider looking into the reasons why you have it turned up so much. Your system will last longer and run cooler with as little bass boost as possible.

    good luck!

    Phil
    Kicker

  4. #4
    Join Date
    May 2009
    Location
    Dallas, TX
    Posts
    880

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    cab,

    If you're looking for more sub output, I'm not sure that the Bass Boost, as a form of equalization, is the best answer.

    Unlike an enclosed vehicle cabin, an open boat environment makes it very difficult to produce 40 Hz at any real amplitude. Your sub is already rolling off at a significant rate at this low frequency which is to say that its certainly functioning with far less efficiency as compared to a higher octave. So at 40 Hz, 3 dB of amplifier output will produce much less than 3 dB of acoustic output. So we're pushing the train uphill.

    As compared to one octave higher there's not a high percentage of music fundamentals at 40 Hz. However, pressing your amplifier over a narrow bandwidth, particularly at the bottom octave is extremely taxing. Its easy to premature exhaust your amplifier this way with very little output gain.

    If you're looking for more output while maintaining good tonal construction and without exposing signs of strain, then you might try abandoning the bass EQ feature in favor of other tuning techniques.

    Try raising the crossover frequency to slightly above 100 Hz which has an immediate and positive impact on output. The idea is to increase gain over several octaves versus a narrow spike and to increase gain over a bandwidth which more efficient to produce in a boat.

    Less gain at 40 Hz usually translates to more than that in offsetting positive gain in the one to two higher octaves, once correctly tuned.

    In vehicles we have the benefit of 'cabin gain' and in vehicles we try and avoid the vehicle's natural extra midbass response and we try and keep the woofer separated from lower male vocals. But different priorities apply in a boat.

    So after a little experimentation with a broader bandwidth and gain, return to your woofer/enclosure relationship and make sure that doesn't require some additional attention.

    While I'm being a little more direct than Phil and Phil is using a different example, I believe we're on the same page relating to concerns over a bass boost in a boat and especially when the woofer/enclosure relationship may be less than optimum.

    David
    Earmark Marine

  5. #5
    Join Date
    Dec 2006
    Location
    Tigard, Oregon
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    3,016

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    Phil, David,

    Thanks for taking the time to reply - your comments are very helpful. I already have the crossover set at around 120 Hz - should I try lowering it to 100?. I think the problem is with my enclosure as the footbox is not completely sealed - it is open to the ski locker on the port side and is open to the under floor cable chase on the aft end. Plus there's a hole on top where all the cables running thru the foot box exit. This footbox is very difficult to seal and I don't want to go thru the trouble of cutting out the footbox and building a custom enclosure. Is there a sub that would work better for this application than the 10" Polk/Momo MM2104 that I am currently using? Do u think I need more power than the 210w that the zx700.5 is putting out?

    What about the subwoofer level control on the head unit? It goes from -15 to +15. I currently have this set to 0. Can I turn this up to get more volume? Is this just another volume control like the remote bass knob?

    Thx.

    Al
    Al

    2006 Mobius LSV

  6. #6
    Join Date
    Nov 2009
    Location
    Stillwater, Oklahoma
    Posts
    311

    Default

    I think you may have largely identified your primary issues in your description above... You have a lot of "leaks" as you well know. You may be limited in the amount of bass you can get in your current configuration. I think you may have a woofer that is less than ideal for the application as well...

    I think the head unit bass control, (+and -15) will put you in the same place as I described above... You make the woofer move more, you make the amp work harder, and all you do is increase the sound pressure on both sides of the woofer. Without isolating the two sides of the woofer, the opposite pressures will mix and cancel.

    Think of it mathematically: If the woofer is moving a tiny amount, you might make +1 pressure units on the front of the woofer and at the same time make -1 units of pressure on the back. When you allow the front wave to mix with the back wave you in effect add them together, and you get the following equation: 1+(-1)=0. Now turn the bass boost in the head unit all the way up. The woofer moves more, a lot more, so much in fact that is is producing +10 units of pressure on the front of the woofer! But is is also making -10 units of pressure on the back side. With an imperfect free-air baffle, or with lots of "leaks" tha allow mixing between the front and back of the woofer, the mathematical result is the same, 10+(-10) still equals zero. Does that make it clearer?

    There is no way to equalize an out-of-phase condition

    There are a few tricks you can try. While they are not purist and not totally correct, not correct the way David or I would do it if it were our boats, ( I suspect we both would be building enclosures) they can help nonetheless...

    * Get some closed cell foam, stiff stuff like really firm upholstery foam and try stuffing it into the holes and leaks you identified. While this is a poor fix, it is an easy fix and it is cheap. It will not eliminate the problem of the leaks/holes but it can reduce it.

    * Try swapping the positive and negative wires on the back of the woofer. At the 120 Hz crossover frequency you are currently set at, you may be acoustically out-of-phase with your full-range coax speakers. You might find that one way or the other gives you more bass, or the psycho-acoustic illusion of more bass.

    * If the back of the subwoofer shares space with a full-range coax, consider using some sort of cup, bowl, bucket, or other rigid "enclosure" behind the coaxial speaker. This will prevent to coax speaker's mid from being modulated by the pressure waves coming from the back of the subwoofer. this can clean up the sound, and can reduce the chance of out-of-phase energy being mixed.

    I am not super-familiar with that Polk sub but quick research tells me it is a sub designed for small sealed enclosures. Typically, this type of sub has a fairly low resonance, a low "Q" and a pretty large Vas... I know, blah blah blah... Engineering talk...
    What this tells me, ( I still have not found the Thiele-Small paramters to say for sure) is that you will be happier with that woofer if you put it in an enclosure, and if I am guessing, probably a sealed with a volume of between .65 and .85 cubic feet... that is pretty small as sub enclousures go, so you can likely do it without taking up a lot of space.

    Beyond that, if you don't want to mess with a box, you might want to look into a true free-air sub; one that is designed for the task... Polk has them, so does Kicker, Wetsounds, and others. David will be real good at describing the relative strengths and differences of the multiple brand's offerings; I am slightly biased, so I prefer to keep my comments with regard to brand preference out of the discussion...

    Finally, and I know it sounds "hokey" but even if you end up building a box, think about the points I made above, particularly regarding the sub's phase. Depending on the woofer's location, even though it is elecrtrically in-phase, it might not be acoustically. Flipping the wires for polarity is an easy thing to try, and it will be interesting to hear the difference!

    Good Luck!

    Phil
    Kicker

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