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1981 Mercedes-Benz 300TD
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Discussion Starter #1
I'm planing to replace my non-functioning radio with a nice powerful sound system in my 81 300TD. :D I plan to devote at least 500W RMS to the subwoofer(s). At this point, I plan to run my own wiring because the current radio equipment it truly a mess. I've never heard what a w123 radio setup sounds like, especially with sound bouncing off the windshield and don't know what to plan for. I'm also concerned that the rear speakers won't be large enough to fill such a large area in the wagon. I REALLY rather not cut away any interior trim that covers the speakers to increase volume. I still need a nice looking interior you know.

What modifications will I need to consider and which ones will be absolutely necessary? All additional info is welcome! :D
 

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1771 Cugnot Steam Wagen
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You won't have to drill. I've found 4x6 speakers 500 WATT just googling it. If you wanna take a look at what I found, here's the link:
500 WATT Speakers
Hope it works out with that sick sound system. Post a video with a lot of BASS with a HD camera when it's done. :)
 

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77 240D
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that's peak not RMS. he needs speakers much bigger than that. however, I think 500w RMS is way overkill. make sure you do good sound insulation.
 

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1981 Mercedes-Benz 300TD
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Discussion Starter #4 (Edited)
I will definitely look into sound insulation. I'll also be sure to post a video when its all done! I love the fact they are made by "Diesel audio" however they seem to be discontinued outside of Amazon. In addition, I've read they are 500w peak per pair and as stated, thats not continuous, RMS, power. So we are at 250w peak per speaker so I'd estimate RMS would be 80-110w, not too bad but lets see if we can do a little better; like 130w RMS. How about the alternator? For such an old vehicle it would seem a alternator would be an easy swap but I have a feeling its not. Is a swap even necessary?
 

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i am mass loading steel panels using "grace ultra" butyl and getting closed-cell foam for absorption. let me know if you want to buy some of the former from me, i bought way too much.
 

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1981 Mercedes-Benz 300TD
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Discussion Starter #6
I know about isolating rattling noises but I'm not familiar with this whole insulation thing. What will it do for me?
 

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1981 Mercedes-Benz 300TD
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Discussion Starter #7
After a year do knocking out other countless projects this install has begun! And its better than I had planed. Just a few specs. 900w RMS Kenwood amp powering two 10" Alpine Type-R subwoofers in a professionally made dual ported box. In addition I have a nice Alpine deck, coaxial 4" front speakers, and a JL 4/360 amp.
 

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1981 Mercedes-Benz 300TD
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Discussion Starter #9
I haven't decided yet. I'm still in the testing and tuning phase but today I didn't even notice the fog and headlights dimming. I'll soon check voltage drop during high current draw using my DVOM. Simple load calcs would show that 55A is less than half of what I need however, I want to see where I stand before deciding to upgrade.
 

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85 Audi Coupe Quattro, 85 Audi Coupe GT, 71 BMW turbo 2002, 73 BMW 2002tii, 85 BMW 635csi
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I have 2400RMS on stock alternator and zero issues with the charging system.
 

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1981 Mercedes-Benz 300TD
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Discussion Starter #12
Wow! I suppose our abnormally large battery and lack of other electronics allows us to get away with such a small alternator. But here's a question. Why do others and I run 4, 2, & 0 gauge wire to the amp(s) if there's only a small 12 guage wire coming off the alternator?
 

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85 Audi Coupe Quattro, 85 Audi Coupe GT, 71 BMW turbo 2002, 73 BMW 2002tii, 85 BMW 635csi
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It's about the distance, aka voltage drop. If you ran a 12 gauge wire to your sub from your battery, the amp will be inadequately powered. Larger gauge minimizes voltage drop by optimizing the current carried. A capacitor also helps tremendously at the end of the run, especially with high powered amps. A full farad will do fine with what you're installing.
 

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I deleted the spare tire in my TD and used the cover as a box for my single 12", looks OEM plus, and I can still use my third row. The 1000watt amp is hanging out in the bottom of the spare wheel well. I also have 4 4" alpine components and a alpine bluetooth headunit all powered on the factory alternator.
 

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1981 Mercedes-Benz 300TD
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Discussion Starter #15
That sounds good. I actually ran two 4 gauge power wires, one to the sub amp and one to the 4 channel amp; perhaps I can use one capacitor for both lines???

I did more tuning of the amps today and BOY do the subwoofers hit. I have them against the second row seats and can see my rear window flexing at 70% volume. In addition, the voltage dips to a low of 12.6 volts at idle with heavy sustained bass(I was expecting lower) however it quickly recovers back to 13.6 volts. I just hope I don't break any of my windows because those 10's hit hard in and outside of the car!

Don't worry, I'll make a YouTube video soon.
 

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1999 CL500
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677 Posts
It's about the distance, aka voltage drop. If you ran a 12 gauge wire to your sub from your battery, the amp will be inadequately powered. Larger gauge minimizes voltage drop by optimizing the current carried. A capacitor also helps tremendously at the end of the run, especially with high powered amps. A full farad will do fine with what you're installing.
i'd go with 3 farad at the bare minimum.........

for a 500 watt system i'd do 4 gauge from battery to amp...anything more than that i think it makes sense to go 2 gauge..or if youre in the 1500-2000 watt RMS range go with 1/0

a good ground is very important


alternative to having a cap is putting another battery in the trunk...me personally ive never done that before.

I run a Kinetik HC1800 battery to my amp and i never have voltage drops.


But the chain is only as strong as its weakest link. I'm still trying to figure out how to do the Big-3 in these cars. If i can run 1 or even 2 gauge wire to the alternator that would be amazing.

Mine is the after-market Bosch 120 amp one; same three pin connector design as the stock 55 amp ones
 

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1999 CL500
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That sounds good. I actually ran two 4 gauge power wires, one to the sub amp and one to the 4 channel amp; perhaps I can use one capacitor for both lines???[
Yes sir. The 4 gauge you have running from your battery in the front can go to a distribution block (preferably one with 150amp fuses) which can then go to the cap...have a good ground connection in the trunk somewhere

the cap will accommodate both power wires, the wires will connect to the cap via ring terminals which you can get online for cheap.


I did more tuning of the amps today and BOY do the subwoofers hit. I have them against the second row seats and can see my rear window flexing at 70% volume. In addition, the voltage dips to a low of 12.6 volts at idle with heavy sustained bass(I was expecting lower) however it quickly recovers back to 13.6 volts.
with a stock alternator? thats actually pretty impressive!

In such a case, a cap may not be necessary. Perhaps just a high current power cell battery (like the Kinetiks, which im a fan of).


I just hope I don't break any of my windows because those 10's hit hard in and outside of the car!

Don't worry, I'll make a YouTube video soon.
your TD most certainly will have better acoustics than in my car since the sub is actually in the cabin....

i had to use rolls of dynamat to sound-proof my trunk.....it used to rattle and wave like no other. Especially on those really low 29-35 hz beats :D


i will wait impatiently for the video!
 

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1999 CL500
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Wow! I suppose our abnormally large battery and lack of other electronics allows us to get away with such a small alternator. But here's a question. Why do others and I run 4, 2, & 0 gauge wire to the amp(s) if there's only a small 12 guage wire coming off the alternator?
you'll still be getting a healthy 12 volts it's just a question of the alternator being able to catch up with the high demand of current and being able to keep your battery charged fully while also having to assume the roll as a starter battery (and these cars take a lot of juice when they start)

as long as you arent beating away with the engine off it shouldnt be too abusive....I think having a battery tender does help relieve some stress off the alternator too, but quite frankly --as far as the system is concerned -- if you're getting a good 12.6 + voltage even on bass notes then you're just fine!
 

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1999 CL500
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Yeh keep an eye on it....maybe fine but I have heard adding anything with a woofer and a amp can kill the voltage regulator, alternator or cause not enough juice to hit the battery....
low voltage drops wont in all cases mean dimming headlights (though in a lot of cases it can at least affect the instrument cluster) --but over time if the alternator is struggling to keep up then if you're hitting bass notes and the amp is getting less than 12 volts then its a sure way to overheat and cook an amp, which is struggling to produce more power

thats recipe for a clipped signal which is extremely bad.....
 

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1981 Mercedes-Benz 300TD
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Discussion Starter #20 (Edited)
The subwoofers definitely have the loud rumble but seem to lack any punch; you know, the rhythmic boom, boom, boom. Could this be due to the fairly long power cable and/or the need for a capacitor?

I need to keep tuning because they don't hit low notes nearly as hard as they hit mids. I'm powering these older style Type-R 10"s with a Kenwood KAC-9103D amp wired to 2 ohms. I'm not too clear on the effects of some of its switches and adjustments but I'm currently reading up on them.


EDIT: HHMMM!! Now that I think about it.....I may have wired them to 8 ohms instead of 2... I'll have to check tomorrow...

EDIT 2: I had actually wired for 8 ohms and resolved this problem rewiring to 2 ohms.
 
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