Stereo Upgrade Help

1985 Checkmate 18' bow rider - the custom stereo system it came with sounded pretty awful and drained the battery fast... I don't know all too much about stereos but it looked sweet when I bought the boat Pulled some stuff apart and I think the speakers are cheapo and amp seems a bit funky.

I started reading as much as possible before replacing the system - I'd like to have a decent setup that I can hear over my old Merc inline plus wind noise, somewhere in the $600 range. Only room for 1 battery, so I don't want a huge power-hungry system and I will keep an eye on the voltmeter.

Head unit:
I like the Sony DSX-MS60, I can just toss a digital device safely inside the unit.
52 watts x 4 at 4 ohms $150

Amp:
I'm leaning toward a Class-D amp to squeeze efficiency out of my single battery.
Rockford Fosgate R400-4D Amp $150
4 channels,
400W RMS:
75 Watts x 4 @ 4-Ohm
100 Watts x 4 @ 2-Ohm
200 Watts x 2 @ 4-Ohm Bridged

Bow speakers:
I'd like to reuse the Roadmaster box since it fits nicely in the space in the bow, so it seems like I can just replace the craptastic speakers with matching sizes.

Heard nothing but good things about Polk...
polk db351 3.5" for highs, 35W RMS $40/pair
polk db651 6.5" for mids, 60W RMS $55/pair

Running the Polks (two pairs in parallel), I think would take care of Channels 1&2 100W at 2 ohms nicely.
Cost is at about $400 so far.

Rear Speakers
Thinking I should slap two decent marine 6x9s in these pockets


Is there a way I could add a subwoofer in the mix? Not sure where to put it space-wise, but I feel like I'd be missing lots of low end without it

Power the 6x9s from head unit and channels 3&4 for sub? I'm kind of lost as to what would work....

Re: Stereo Upgrade Help

and add around 150.00 for a group 31 deep cycle battery into the mix. and yes you will need one and a battery selector switch for another 50 to 70. O and dont forget a battery charger at home after every trip out or a dedicated one if its slip kept.

Re: Stereo Upgrade Help

First I'll point out that the amp is not a marine amp. However, I have a non-marine amp on my boat that has been there for many years and still works great.
Ideally you would have a crossover in the front box to split the frequencies between your 3.5" speakers and your 6.5" speakers. This would essentially present a 4 ohm load to the amp so you would only get 75w RMS. However, since this is above the rating of both speakers it is still plenty of power. You could use a 3 way crossover and send the lowest frequencies to your subs, eliminating the need for an additional amp.
I would power the 6x9s off the deck and use the amp channels for a sub if you want one. There are some crazy wiring schemes that will allow you to hook lots of speakers to the amps 4 outputs but I don't recommend it.
How big is your alternator? You will want at least a grp. 31 battery.

Re: Stereo Upgrade Help

MH Hawker said:

and add around 150.00 for a group 31 deep cycle battery into the mix. and yes you will need one and a battery selector switch for another 50 to 70. O and dont forget a battery charger at home after every trip out or a dedicated one if its slip kept.

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I agree that this is an optimal setup, but space is pretty tight on this little boat... I'd like to try a 1-battery setup. I'm hoping to get a fair amount of play time and I don't really hang around anchored for hours listening to tunes. From what I understand, the power draw from the amp is relative to how much power you sent to the speakers (volume), so not blasting it should help conserve a bit?

KD4UPL said:

First I'll point out that the amp is not a marine amp. However, I have a non-marine amp on my boat that has been there for many years and still works great.

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Yup it will be mounted in an enclosure under the passenger foot well, nice and dry. The old amp (an old school California 600W) still worked and it was in that spot.

Ideally you would have a crossover in the front box to split the frequencies between your 3.5" speakers and your 6.5" speakers. This would essentially present a 4 ohm load to the amp so you would only get 75w RMS. However, since this is above the rating of both speakers it is still plenty of power. You could use a 3 way crossover and send the lowest frequencies to your subs, eliminating the need for an additional amp.

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Yeah, I was wondering if a crossover would be called for. Both the 3.5" and 6.5" have a tweeter and midrange
3.5" response: 90Hz-22kHz
6.5" response: 35Hz-22kHz
but it seems to make sense to push the highs toward the smaller speakers.

I'm guessing something like this type of crossover would work fine?

Once that crossover in place, I'm at a 4 ohm load to the amp?

I would power the 6x9s off the deck and use the amp channels for a sub if you want one. There are some crazy wiring schemes that will allow you to hook lots of speakers to the amps 4 outputs but I don't recommend it.

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Cool yeah that makes sense! Hopefully the 52W from the head will do ok with these

Rear Speakers
Kicker DS693
70W RMS
4 ohms
response: 30-20k Hz

How big is your alternator? You will want at least a grp. 31 battery.

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I know the output on the inline mercs is unregulated, and won't put much of a charge out under 3K. I will definitely look into upgrading my battery to a group 31.

Thanks so much for the help

Re: Stereo Upgrade Help

I use a head unit with the amp built in a 75 watt x 4 way into 4, 6 inch 200 watt speakers and it dose fine.