funkdaddysmack

This weekend I decided to brave the cold and go play around in my car. I already had some power wire run from another amp that turned out to not work, so all I had to do was re-run the RCAs back from the deck.

I got a Alpine MRD-M300 or something like that from a friend of mine. Sounded like a good amp, supposedly delivering 300W RMS @ 2ohms. First of all, I'm a car audio-n00b, so all I basically know is what wires I need to run. Luckily, it's a mono amp, so there isn't a really interesting way of hooking up the speaker wires.

My first problem is that the amp isn't getting enough power (v). The 300W RMS @ 2 ohms is at 14.4v, and I'm only getting 12 back to the amp (it has a built in LCD telling how much it's getting). I think part of the issue is that I only have 8 gauge wire running from the battery, could this be part of the problem? If I upgrade to 4 gauge, will I get more power?

I have it hooked up to an older 15" Kicker Solobaric that I've had sitting around for a long time. I believe the sub is 2 ohm stable, do I have to do anything special to make it run at 2 ohm with the amp? Keep in mind I know nothing about car audio. Anyway, since I'm only getting 12v at the amp, the box said I'd only be hitting about 100W RMS. The sub sounds real nice at low-mid volume levels (which is cool, I don't really need to crank it all the time), but when I turn up the volume to higher levels, you can tell the sub isn't getting enough juice. It gets somewhat distorted, and doesn't hit 'cleanly'.

My HU is a Pioneer MP7400, I have the thing set up properly up front, and I have the low-pass filter set in the back, so it's not getting any high frequencies through.

So basically, I just want to know what I can do to maybe make this sound a little better. I also have a nice ground, so that shouldn't be affecting anything too much. Thanks guys!

b_real45

If the sub is 2-ohm or has dual 4-ohm voice coils, you can run the amp at 2 ohms. Since it's a mono amp (and assuming your sub is 4ohm), its probably doing 4ohms now.. which means less than 300watts... plus the 12V feed isn't good. You might want to check your alternator... I believe the alternator is responsible for bringing your voltage up to near 13.x.

funkdaddysmack

Thanks for the reply, unfortunately I think my alternator is on it's last leg. It was making a god-awful squeeling noise last night. I really don't think it was just the belt, but I could (hopefully) be wrong.

mazdaspeedwest

The alt is a definete possiblity, and so is the 8awg power wire. but more importantly, how is the ground wire from the amp?

should be short, same size as the power, bare metal contact(paint scraped away) and used with a locking washer. You may also want to experiment with running 4awg power AND ground directly from the battery back to the amp.

your battery cables should also be nice and tight on the terminals, as with the ground to the chassis.

hihoslva

You've got good advice above. It's okay to be a car audio newbie!

I think your major issue is the sub itself - subs are not "ohm stable" - they are rated at a certain impedance (ohms) based upon how they are made. Amps are rated as "ohm stable" based upon the minimum impedance load they can safely power.

Think of it this way - the power from your amp travels from the amp, through the sub, and back to the amp again (electricity is a "flow", you know, and it must be a completed circuit to work). The sub represents a blockage to the flow, not a dam, but a resistance. If the resistance is too high, the amp can't flow full power through it. If the resistance is too low, too MUCH power flows BACK to the amp, resulting in overheating. This is simplified, but hopefully it helps your understanding a little bit.

I'd bet that your sub is 4 ohms. If that is the case, the amp will only put out half the 2 ohm rated power - or about 150 watts. If the sub is rated to handle lots more than that, you don't have enough power to really get it moving.

In order to get down to 2 ohms, you'd need an additional sub, or a different single sub. Very few subs are 2 ohms by themselves. You can wire two 4 ohm subs in "parallel" to achieve a 2 ohm load. You can also find "dual voice coil" subs - which can then be wired as though you have two subs, even though you only have one. Dual 4 ohm voice coils wired "parallel" is the same as two 4 ohm speakers wired parallel as far as the amp is concerned.

Quick explanation: parallel wiring is where each sub is in essence hooked up to the amp "by itself" - the pos and neg of each sub (or each voice coil in a dual voice coil sub) is hooked up directly to the pos and neg of the amp. "Series" wiring is just like it sounds - the pos of the amp is connected to the pos of the first sub (or coil), then the neg of that first sub is connected to the positive of the second sub. Then the negative of the second sub goes back to the neg of the amp - like a chain, or a loop. In this case, the impedences are added - so two 4 ohm subs (or coils) equals 8 ohms impedance.

You really shouldn't "need" more than 8 gauge wiring for 300 watts. Check all your connections, especially the ground (make it a short as possible, be sure it, too, is 8 gauge wire, and is contacting bare metal). You could have your alt checked, but remember, cars are 12 volt systems, so only seeing 12 volts is not abnormal at all - and squeaking alternators usually mean a loose belt. Which, BTW, can of course reduce the voltage coming from the alt. Alts don't usually make 14 volts at idle anyway - the voltage should rise somewhat with engine revs. See what your voltage is with the car revving a bit.

But my guess is that your sub needs more than 150 watts to get going, and is a 4 ohm. You'll need another sub, a different sub (dual voice coil), or a more powerful amp.

Also - what kind of enclosure do you have the sub in? Any idea of the internal volume?

~HH

funkdaddysmack

Thanks for the awesome replys guys, that definately explained some of the common terms I hear used all the time.

To answer some of the questions: I bought a wiring kit for my old amp that I had, it has a 1' or 1.5' 8 gauge ground wire, it's grounded to a bolt under the back seat.

Yea, I thought that all the cars were based on a 12v system, so I was confused as how I was supposed to get 14.4v out of it.

If I get time tonight, I'm going to check what kind of power I'm getting up front, to see if I'm losing anything going through the wire back to the amp.

Thanks a lot for all your help, I appreciate the great explainations. I'll have to remember this thread for future reference.

funkdaddysmack

I forgot to mention that I'm going to probably sell the amp to my roomate, and put that money towards a more powerful amp. I had my eye on a US Acoustic USX800D. It's 600Wx1 RMS @ 2 ohm. Seeing that I wouldn't be at 2 ohm with the sub, I'd be pushing less, but it would still be a hell of a lot more. Plus the amp is only $230.

http://www.thezeb.com/caraudio/us_acoustics.html

Bad idea?

b_real45

Nice choice... I'm gonna be going with the USX-600D... I'm pushing a smaller 12" sub rated for 350watts RMS.

hihoslva

A more powerful amp would definitely help your situation.

What you really should do is find the specs on the sub. Look for a model number or something, and find out:

-The RMS power rating of the sub (NOT THE MAX!!)
-The impedance (ohms)
-What type/size box is recommended.

The first two are quite important. Once you find out the RMS power handling of the sub and it's impedance, you can buy an amp that will put out the right amount of power.

Get the sub specs BEFORE buying an amp!! Post the specs here (or even just the model number) and then we can talk amps.

~HH

EZ as 123

you've been getting lots of real good advice audio wise. before you go on switiching amps and stuff may I suggest you take care of your electrical system (mainly your alternator).

1st tighten the drive belt (that should take care of the squeeling like a virgin on prom night too) and have it tested. Once this is up to spec you can continue on to your system

funkdaddysmack

Thanks for the reply. I have been pretty busy the past few days so I haven't had a chance to go out and mess around with it. I will try and do it this weekend

Dave Cameron

Wow- a bunch of stuff going on here- you are getting allot of good help, that is what boards like this are about!
OK- an alternator is a type of generator, it's output will depend upon how fast it is moving, it's temperature, how it is regulated. Most car generators are not surgical machines, that is they are not regulated to put out for example 13.8 volts and nothing else. In pratice they produce a range of voltage. In cold weather like we have had of late here, the alternator of the mazdaspeed starts the morning at 14.5 volts, nice high output to recharge the battery for the use of all those cold crank amps. As the car warms up, the alternator becomes warmer, and it becomes less efficient as a unit, and the voltage starts dropping off to 13.2-13.8. Turn on stuff like the blower for defrost, and lights, and the dip will then get 12.3-12.4 volts. Still within the specifications, but on the low end.
No of this is at an idle mind you- it is somewhere between 1000 and 2500 rpm. Most "high output" alternators are the same, they might crank more amps, but still have to be running slightly faster than a pure idle to make it happen. Try running a load like blower, lights and radio at an idle, it will now run the system down to 11.8 volts!
SO- you can get 14.5 out of the alternator, depend on what you are running the temperature, etc.
Next resistence, the longer the cable runs the more resistence to the wire. The more resistence, the less current that will "flow" along the surface of the wire. It can be surprising how much loss there is though. The guage sounds fine actually, I would make sure the wire is a fine strand though. Current runs on the surface area of wire, not down the core, so lots of fine strands are better than ten really thick ones. If you have a volt meter, I would suggest checking the voltage at the amp, seperate of the little digital readout.
Why would you want more voltage than 12 volts? Amps come in two flavors mostly, regulated and non regulated. Regualted amps are built to deliver consistent wattage no matter what voltage is supplied. This is a good thing in the real world, as we have seen how the pesky alternator can be all over the place on what it is actually delivering. Unregulated amps can produce more wattage if more current is fed to them, right up to the point of meltdown.
This is problematic in the real world (to me anyway) but can be really a nice thing in say DB drag racing where you want to bump as loud as you can.
You said that it does not seem to hit as hard as you would prefer,and it is distorted- I am afraid to say that distortion is simply horrible in subwoofers as a general catagory. .1% is audable, many subs are rated at 3% to 5% distortion levels. That will be painfully distorted a block away, much less close up! Many are also not very efficient, like 88db spl, and that means it will take more amp to get the desired sound.
I prefer to overamp a sub, get a lot more wattage than I will need and then use restraint in turning it up. That has always seemed to help with distortion a little. HiHoslva is right, find the sub first, then get amping to go with it.
Also, what are the crossover spots that you are using and their slopes? I think the mentioned Alpine is a "D" class amp, and they run 250 Hertz down, and do not like anything higher in the way of frequencies. Tune the crossover lower and see it that helps it's punch.
Enough ranting, let us all know what you figure out- good luck!!