Son hounding me to install sub...any advice/precautions? - PeachParts Mercedes-Benz Forum

shertex · #1 03-03-2012, 01:23 PM

Son just got his driver's license, will be driving Milo, my 92 300D with 233,000 miles. His current obsession (he moves from one to the other....his mother wonders where he got that from

) is installing a subwoofer. He got the sub and amp, now trying to get a hold of the cables. He's done a bunch of research, claims it's an easy install, and that he and I can do it together. I don't doubt that he's correct, but thought I'd check with some of you guys who've done this on a 124 to see if there's anything in particular I need to be aware of. FYI the head unit is not the original Becker but a replacement Pioneer.

Thanks.

cmbdiesel · #2 03-03-2012, 01:29 PM

If it were me, the car would not have a stereo capable of anything over 95db until he has had his license for at least a year. New drivers (all drivers really) need to be able to hear as well as see what is around them.

As to installation, it really depends on what you want the finished product to look like. Removing interior trim from an aging vehicle is always a little dicey. Other than that it is pretty straight forward.

Might want to check the draw of the sub amp, and make sure the alternator can handle it. More than one has bitten the dust as a result of increased draw.

shertex · #3 03-03-2012, 01:34 PM

Quote:

Originally Posted by cmbdiesel

If it were me, the car would not have a stereo capable of anything over 95db until he has had his license for at least a year. New drivers (all drivers really) need to be able to hear as well as see what is around them.

As to installation, it really depends on what you want the finished product to look like. Removing interior trim from an aging vehicle is always a little dicey. Other than that it is pretty straight forward.

Might want to check the draw of the sub amp, and make sure the alternator can handle it. More than one has bitten the dust as a result of increased draw.

That's helpful. The existing can go pretty loud (all four speakers have been replaced), so he CLAIMS he's not after increased volume but better base extension. I had wondered about the danger of removing trim but had not even considered the draw on the alternator.

ChiefRider · #4 03-03-2012, 01:34 PM

I'm probably not the guy you want responding to this question!

I'm not a fan of ANY wiring changes, including installing a power amp. Do you really want your teenager driving while paying more attnetion to the tunes than the traffic?

That said, my son and I sent an afternoon installing the amp, speakers etc. in his car, and as long as you are comfortable removing and replacing interior panels and carpet, it's doable.

My 126 came with a trunk mounted amp installed, and a "portable" subwoofer that just sits on the trunk floor. It is weighted and carpeted, and doesn't seem to move at all. Sound quality is actually quite good. I'd have been ok with the stock system, fwiw.

mespe · #5 03-03-2012, 01:37 PM

My advice is NO! Unless you want to hear the rumble as he pulls up the driveway. I think all subwoofers should be outlawed, as I shouldn't have to be subject to the relentless boom boom boom as someone drives down my street.

shertex · #6 03-03-2012, 01:38 PM

Actually, you're EXACTLY the guy I want responding to this question! I want to know all the risks and uncertainties....they may add up to my not allowing it.

Quote:

Originally Posted by ChiefRider

I'm probably not the guy you want responding to this question!

I'm not a fan of ANY wiring changes, including installing a power amp. Do you really want your teenager driving while paying more attnetion to the tunes than the traffic?

That said, my son and I sent an afternoon installing the amp, speakers etc. in his car, and as long as you are comfortable removing and replacing interior panels and carpet, it's doable.

My 126 came with a trunk mounted amp installed, and a "portable" subwoofer that just sits on the trunk floor. It is weighted and carpeted, and doesn't seem to move at all. Sound quality is actually quite good. I'd have been ok with the stock system, fwiw.

ChiefRider · #7 03-03-2012, 01:42 PM

Quote:

Originally Posted by shertex

That's helpful. The existing can go pretty loud (all four speakers have been replaced), so he CLAIMS he's not after increased volume but better base extension.

Uh, yeah. And he likes Playboy for the articles. LMAO!

shertex · #8 03-03-2012, 01:43 PM

Quote:

Originally Posted by ChiefRider

Uh, yeah. And he likes Playboy for the articles. LMAO!

Yes....I didn't mean to suggest that I believed him!

shertex · #9 03-03-2012, 01:56 PM

Re current draw, the amp is a Dual XPA4640. I can pull up the manual online, but there don't seem to be an specs for how much current it would draw.

shertex · #10 03-03-2012, 01:57 PM

Quote:

Originally Posted by shertex

Re current draw, the amp is a Dual XPA4640. I can pull up the manual online, but there don't seem to be an specs for how much current it would draw.

But there are two 25-amp fuses, so I guess that's an indication.

shertex · #11 03-03-2012, 02:08 PM

Son claims that he checked on Amazon (that oh-so-authoritative source on all things Mercedes) and that the amp he got is compatible with a 92 300D. How would I go about confirming this?

Crazy_Nate · #12 03-03-2012, 02:09 PM

Quote:

Originally Posted by shertex

Re current draw, the amp is a Dual XPA4640. I can pull up the manual online, but there don't seem to be an specs for how much current it would draw.

P = I*V

shertex · #13 03-03-2012, 02:27 PM

Quote:

Originally Posted by Crazy_Nate

P = I*V

That much I know.

So I've got a 70 amp alternator. From what I've read, reserve capacity is 40% of that, or 28 amps. Correct so far?

"To calculate the current draw of an amplifier, multiply the number of channels by the RMS watts per channel (a 2 channel amp rated at 300 watts RMS per channel would be 600 watts). Double it to account for amplifier inefficiency (600 watts X 2 = 1200 watts), then divide by the average output Voltage of an alternator, 13.8 volts (1200 divided by 13.8 = 87 amps). Since the average music signal requires about 1/3rd of the average power in a test tone, divide by 3 (87 amps divided by 3 = 29 amps). The result is the amplifier's approximate average current draw."

In my situation, that would be 14.5 amps average current draw.

JamesDean · #14 03-03-2012, 02:36 PM

That amplifier is pretty lower power compared to most subwoofer amplifiers out there.

It looks like it'll draw 300 watts RMS (always look at RMS, peak values are useless), which will be about 20 amps. If you use an 8-gauge wiring kit you should be fine. Ideally a 4-gauge would be best. See below. I've not installed a sub on a 124 yet but the 201 and 126 were easy as cake.

Mercedes has a grommet right behind the battery area and you can use that to feed the power line to the trunk. You're "supposed" to feed signal RCA lines down the opposite side of the vehicle as power however I've never had any noise issues. So my power, remote turn-on and signal all went down the passenger side.

Take off the door sill, B pillar, and remove the bottom of the back seat. Run the three cables against the wall and then up underneath the backseat and finally into the trunk. Find a ground in there somewhere and you're set to go.

With only 300-watts to work with I think he actually might be going for better bass response rather than BOOM BOOM BOOM.

I have 1000-watts in my 190, but its only BOOM BOOM BOOM when I make it so. Also my trunk is covered in sound deadening as well. I also have two JBL amps running Boston Acoustics all around.

With only a 300-watt load I think the factory alternator would be OK with that. Looks like its a 70-amp unit. The subwoofer wont be running at 300-watts continuously so I dont think it'll be a problem.

satyr · #15 03-03-2012, 03:21 PM

Hi,
As an electro-geek who has installed dozens of after market systems in autos, and has built dozens of closed, vented, bandpass and hybrid loudspeakers for home and auto use, AND who has also worked with teens in mental health and social services settings, I think I might have some info to offer here.

I think you might consider a bigger picture here, rather than just how much current draw some "amplifier" made in china might draw. First, while ANY sub application in an auto will add fill for the lower octaves, (You can basically count on at least 12 dB of cabin gain from ANY sub installed), is your son looking to construct a 6" driver-based folded horn or passive radiator speaker driven by 50- 75 watts? No, your son's choice is 150 watts RMS per channel bridged. What will he drive with the 300+ watts RMS he has on tap? Whatever it is, it certainly will provide considerably more musical "material" for him to enjoy!...

Having said that, the bigger question is, do you really want that much more distraction in the vehicle for his hormone-driven, adrenaline-fueled, adolescent mind? Especially if you consider the other inherent distractions, AND passengers (including-potential candidates for meaningful, but short term relationships), some redbull, 4 Lokos, or starbucks espresso (pick your flavor), some swisher sweets, and a bangin' 105dB stereo blaring in (WHOA) a mercedes benz!... I think you get the picture....

At 16, maybe you should consider encouraging him to save his funds to "trick" his own vehicle, that he can purchase when he gets a little older..