alj

Hi Guys,
I'm setting up a stereo in my 85 F402. I have some technical knowledge since I had worked for a large consumer electronics manufacturer for about 19 years. However that knowledge is definetly limited. Here's what I started. Starboard engine has it's own 140 amp alternator feeding two Optima deep cycle marine batteries through a Arco Marine isolator. Those batteries go to a separate diesel battery switch which feeds power to the cabinet above the refrigerator. Cables from the battery switch and the ground from the battery bank are Ancor marine 2/0 cables. Nothing else but stereo equipment is on this system. I will be running #2 power cable from the terminal blocks to the respective amps. 12 guage speaker wire for the 4 component speakers from their passive crossovers back in the amp locker, 10 guage speaker wire to the subs.
The head unit is a JVC KDSH9750 with three 4 volt outs. This is their Digifine unit and has some frequency adjustment on it. I will be running 2 MTX thunder 6304 four channel amps 37.5 watts RMS advertised. MTX test sheet - 69 watts RMS into 4 ohms X 4; 112 watts RMS into 2 ohms X 4 all @ 12.5 volts. It's my understanding that these older MTX amps are much better than the current models. One amp will drive 4 speakers in the cabin. The other amp will drive 4 component speakers in the cockpit.
Heres where I need some advise. I haven't purchased the cockpit component sets yet, and I haven't selected the sub amp and subs yet. First the cockpit components. Option one: Alpine components... SPXF17T flagship 3 way components for the front, and SPX177A flagship 2 way components for rear fill. The 3 way has a wild passive crossover that adjusts the soundstage for different speaker placements. It has a 6 1/2 midbass, 5 1/4 midrange and a 1'' tweeter. Crossover shows 4 ohms to the amplifier. The 2 way has the 6 1/2 driver and the 1" tweeter and the crossover shows 4 ohms to the amp. One concern was the cone material that Alpine uses here. It is a wood fiber cone treated with carbon.I can get the 3 way set for about $500. and the 2 way set is about $200.Seems to me these speakers have been around for a couple years and are nearing closeout. Anyone know anything about Alpine?
Option 2 is using MB Quart components. In order to make a three way system MBQ uses an add on 6 1/2 midbass kit. So for the fronts.....Premium series PCE213 2 way kit (5 1/4 mid driver with 1" metal tweeter) crossover shows 4 ohms to the amp, with the PCE164 6 1/2" add a woofer system which shows 4 ohms to amp. The three way system together shows 2 ohms to the amp on the front channels. In the rear, for fill, I would use the MBQ Reference series RCE269 2 way component set. It is a 6x9 woofer (fits into existing opening) with a 3/4" metal tweeter. The crossover shows 4 ohms to the amplifier in the rear channel positions. I spoke with MTX regarding 2 ohm loads in the front channels vs. 4 ohm loads in the rear channels. They assured me the amp will be fine but I will notice that the fronts don't play as loud??!! The MBQ front set with the add a woofer is about $470. to $500. The 6x9 rear set is about $240 or so.
So what does anyone know about the Alpine flagship X series speakers? They seem impressive. I put PSD216 MBQ's in my truck last year and I'm pretty happy with them. However, when you close the windows, those metal tweeters really stand out. Annoying sometimes. I think the openness of a boat will drown that out a little. I'm a bit concerned about running a MBQ 3 way system that shows 2 ohms to the amp in the front channels. How much of that can I tweeq out with the gain controls?

alj

Couldn't get every thing into one post........
Now the sub system. Looking for suggestions on an amp. I'll be running two subs. Amps....JL 500/1???? Good to 1.5 ohms so I can't parallel 2 dual voice coil 4 ohm subs down to 1 ohm. Or can I?? Any other suggestions on a sub amp around $400. to $500.? Sub Speakers...Lets talk about the boxes first. In a Formula F402 they didn't have the fancy ass Mcleod electric footrests. Formula didn't forget about the pilot and co-pilot altogether though. There are two footrests built up under each bolster. Basically a box 21" wide, 18" deep, and 9" high with a slope cut into it irregularly for your feet to rest on. Inside each box is about 1 cubic foot of INSIDE space. My idea is to rebuild the box in 1" MDF, fiberglass it, and use it as a sealed sub box. The tricky part is I would build it for a downfiring sub and then raise the box about 2" off the floor sothere is a 2" space all the way around for the sound to get out. (obviously I need to cushion the box from the floor with some rubber feet and anchor the box to prevent it from bouncing around) One sub box under each bolster. Is a downfiring sub going to work? I've seen similar installs where the box is put under a rear bench along the transom and there wasn't enough room to stand a sub driver up facing the cockpit. I'm going for sound quality here so I'm not sure what subs to choose....JL w3's, Kicker L5's, Infinity Kappa, Adire Brahma?????? These boxes will take 10's easily and possibly 12's. OK, sorry for the novel. Just trying to get the facts maam. Any help here will be greatly appreciated and any direction to a source is also appreciated.

Audiofn

Man there are a lot of questions up there so I will try and adress design issues. Your downward firing sub idea.. Great idea, I like it, however it will not likely sound good. When you fire a sub down into the floor you are basically creating a port and unless you get lucky with it you will not get great sound. The other issue is that you need a LOT of power to get a sub like that to play at any volume.

Why not under the back seat? That is were most people put them and you can make a box in there. I would also recommend not using MDF in a boat. Even if just a little water gets in there it will expand at an alarming rate. One of the good thing about different using fiberglass to seal up your sub box is that having different types of material does kill the resinent frequency of the sub box. So you can get away with some slightly less dens material.

Your issue with the MB is not really a issue as I see it. You stated that with the windows down they sound great. Well your boat is the same thing, in fact it actually needs more highs due to the ussually crappy location that you are able to put them in. I have never heared a 3 way system that I like more then a same price 2 way system. If you are willing to spend 500 bucks on a pair of 3 ways you would be in some very high end fronts. Check out Focal, AVI, and some others for sure.

Andy Buzz

I agree with Jon about the downfiring enclosure that it will only sound good if you get lucky. The downfiring not requires tuning, you may have resonant sounds from rattling fiberglass. The down firing creates a mechanical load on the driver which is a good thing on an outdoor speaker, but things may not be as predictable in results.

I suggets the MBQuart 6x9 2 way marine speakers. I would not suggest any car speaker in a boat. You will get a more appreciable advantage with more speakers in a boat than better speakers. My theory is that you are better off purchasing two $250 pairs than one $500 pair of speakers for a boat. In a forty Formula, I would run at least six 6x9 and two subwoofers.

Feel free to call me at 813-882-8477 to help narrow which products will work best for your needs.

Andy Buzz
Buzz Off Alarms
Maximum Audio

alj

Hey guys... thanks for the advice. I guess I thought that going with the 3 ways was going to give me a great SQ system in the boat. So losing a 5-1/4" speaker isn't going to compromise my midrange? Would going to 6-1/2" 2 way components be better than 6x9? Andy, I like your idea on three pairs of speaker rather than two. Maybe I should run both MTX 6304 amps into the cockpit and find a different amp for the cabin. I could run four pairs of speakers at that point. Thanks ....Al