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Old 9th April 2013, 08:45 PM   #1
Join Date: Aug 2007
Default adjust bass boost frequency

first of all, if this is the wrong section of the forum.. feel free to move it.

we all know car amplifiers usually come with a bass boost centered at 40hz - 50hz

well i (and i figure most others) don't need the boost at 40hz - 50hz
but could use something low like 20hz

for my situation,
i've got an amp that is at its limits, if i turn it up any more.. the upper bass gets louder, but the lower bass starts to distort.
i can turn the bass boost on and get a significant boost in output, almost as if the amplifier power doubles.

i wonder if the capacitors simply can't keep up with the requested output at the lower frequencies, because it doesn't make much sense how the lower notes distort and the higher notes dont distort .. unless it is because the lower notes require more power to move the cone and the power simply isn't there.

i don't know what would stop the amplifier from 'refreshing' or recharging it's power.
it's got a 2.2 farad capacitor in line with the amplifier, and it made the amp sound a little bit more cleaner.. but the amplifier obviously doesn't want the power from the capacitor, only the voltage stability.

so i wonder if it would be easy like swapping out some pieces with new values to get the bass boost pointed at a different frequency, or if i need to swap out the capacitors for some larger capacity, or maybe higher voltage?

i'm really stuck here..
because for one, the amplifier sounds amazing compared to some of the other amplifiers i've heard.
i don't know if it is the subwoofers improved, or if the amplifier is simply using higher quality pieces inside.. but i'm a bit nervous about taking the old capacitors out and putting in some new ones, only to get worse sound quality, and then try to put the old ones back in and the sound quality is again missing.

the amplifier is rated at 150 watts RMS .. and i've got another older amp laying around that is 240 watts RMS
i don't want to use the bigger amplifier because then i would need to adjust the equalizer settings on the radio.
those equalizer settings also control the 3-way 6x8 speakers in the front doors.
if i turn down the equalizer, those front door speakers won't get enough bass to blend the soundstage with the subwoofer .. and that is why i am avoiding the larger power amplifier.

i just need to get the low extension boosted.. and i was thinking the bass boost focused at 20hz would do it.
it's got a switch for +6dB and +12dB .. even the +6dB was a big boost of output power.

i mean, i kinda wonder if there are some additional capacitors inside the amplifier that simply aren't being used unless the bass boost is turned on.
maybe i can use those very caps with the other caps together as a team and leave the bass boost turned off?

i kinda also wonder if maybe the damping factor from the amplifier has something to do with it.
because the speakers are rated for 600 watts RMS in a sealed bandpass box.
i took the plexiglass off that was sealing the speakers and ran 'em to see if they sounded any better, and to my surprise they do.

it sounds like my phase curve from the lowest of 5hz all the way up to the midbass range has a linear movement (except maybe i found a gap in the 10hz - 15hz area)

it's like i am only looking for one or two more bumps in the 20hz graphic equalizer slider.
i can't do it with the radio because it distorts.
i tried turning the amp gain up a little bit with the other graphic equalizer knobs down a bump, but the amp still distorts.

i thought about getting a line driver with variable phase knob, but as i said.. i think the phase is already awfully smooth from sub to front door speakers.
i mean, the phase might not be a total match for the car's interior.. but for the $50 i paid for subs and amp, and the $25 for the front door speakers.. it is beyond surprising at how smooth it is.
at least to say, it is smooth.

some songs on the bass cd will literally thump the inside of the interior, making me think it is a match (or close to a match).
but the whole system at full volume is hardly audible from outside, and i'm not looking to raise the level of everything.. i just want some more spl (or decibels) in the lowest octaves without needing to reduce the amplitude going to the front speakers.

the amplifier is a dual xpe2700
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Old 10th April 2013, 06:06 AM   #2
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east electronics's Avatar
Join Date: Jan 2006
Location: Athens GREECE
you need to do a lot of reading ( and you been told before ) your conclusions about the nature of the problem are 99% wrong

Your approaching the problem from a wrong aspect ...amplifiers is not only capacitors and transistors there are other things that might effect performance Car Audio ? twice as many ...

Obviously there is going to be plenty of members willing to make suggestions but probably it will be in a ""language "' that you don't understand anyway .

here is the DIY audio !!! lots of friendly people encourage the diy spirit only you have to do some reading to be able to implement the help !!

Kind regards
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