I bought an Alpine MRP-M350 sub amp on ebay last week to start the parts hoarding for my stereo install project this winter. I already have an Alpine CDA-7875 head unit in the donor i need to remove. I'm looking to get a JL 12" W3v2 sub to make some boom, but not too much.
The JL's come with three voice coil options - dual 2, dual 4, and dual 6 ohm. The Alpine amp is 2 ohm stable so I figured the dual 4 ohm vc wired in parallel should work excellent. The amp's max output at that load is 350 watts ( RMS, of course) at 14.4 (which probably won't happen with the stock alternator) and the W3's optimum range is just below 350 watts. Figuring I'll probably never need to crank up the gain to max on the amp, this should work out so I don't cook the amp or voice coils. JL's are built extremely well and could handle more, but I'm looking for optimum sound performance, quality, reliability, and longevity. I hate replacing blown stuff, especially because I'm a broke bastard.
I asked my friend Rodney who's been in the car installation business a while for his opinion. He said he's tested dual voice coils with his Fluke meter and he's noticed that they're not trually 2 ohm. He says that I'd see a 1.5 to 1.7 ohm load and my amp should be 1 ohm stable. Which it is not. He says to go with the dual 6 to be safe, but then I won't be drawing as much from the amp. In comparison, the amp puts out 200 watts with a 4 ohm load. I'd like to use the power I paid for.
I guess I'm asking for a second (and probably third, fourth and fifth) opinion on this from the many geniuses here. Rodney is usually on top of these things, but he's no genius when it comes to helping me with my projects. He's actually a bit of a hack, overlooks small details, and has given me bad advise in the past. I can't afford to make a mistake, and his advise has both helped and hurt my wallet. For example - I ended up with a new alternator, battery, and starter in the foxbox before we figured out I had a bad ground. He's also the reason I have blown head gaskets in my 93 SS.
I'm looking to buy stuff once and for it to work within safe parameters. I'm also looking at getting an Alpine MRP-F240 4 channel amp, Infinity Kappa 63.7i three-ways up front, Kappa 62.7i two-ways in the rear, and a 1+ farad cap. The Kappas are 2 ohm, rated at 75 watts and the amp is 75X4 at 2 ohm (14.4v again). Please give me your opinion on this setup. It will be much appreciated.
Amplifier/speaker impedance questions
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Amplifier/speaker impedance questions
-2004 Liquid Silver WRX "Pretty Hate Machine"
I'm not familiar with Alpine specifically, but I work with Eclipse and Kicker where I work. Your friend is right that the voice coils will meter out a little lower than specs. If your amp does not specify it is 1 ohm stable, then don't hook it up into 1 ohm. Getting dual fours wired to two will be fine. The only problem I see is that your selected amp may be too small. The number one reason that subs blow is becuase the gain on the amp is turned up too far and is feeding distortion to the sub. Distortion is what kills, not excessive power. It is always recommended to go to a larger amp (to an extent!) and be able to keep the gain lower. The power rating means very little in the real world, but it looks good on paper. I'm sorry, I can't give any opinions on the Infinity's specifically, either, since I haven't worked with those myself. I hope I helped anyway.
'91 5MT SS-TD04, WRX TMIC, Bosal twin dump, Spec LW flywheel/pressure plate, FCD, Walbro fuel pump-RIP
'93 5MT N/A wagon, over 400,000 miles!-Gone, parts lived on
'94 Auto SS-vf24, WRX TMIC, Bosal twin dump, Meth kit coming soon!-Now RWD!
'93 5MT N/A wagon, over 400,000 miles!-Gone, parts lived on
'94 Auto SS-vf24, WRX TMIC, Bosal twin dump, Meth kit coming soon!-Now RWD!
I understand that overdriving an amp is what kills the sub in most cases, but I'm just looking for moderate bass - 200 to 250 watts. I don't crank up the volume and gain to max, and I know what square wave sounds like. I'd most likely find that threshold and throttle it back to a safe level. I'm not looking to run everything at peak level I'm looking for modest fill bass with crisp response. I have one of a pair of MTX thunder 5000 12" and I'm sure it will blow. Rodney got the other one and smoked it in a month with about the same power. But you'd think I'd be ok with a dual 4 ohm vc?
-2004 Liquid Silver WRX "Pretty Hate Machine"
I just did some quick reading on these componets, and you probably have a good match, although I don't realy like the idea of JL Audio's "Power Chart". That is a VERY rough guide to go by becuase there are so many other variables than to rely on wattage ratings. Are you planning on building a sealed box? The box design will change the dynamics of how it sounds, as well as the power handling. I would recomend a sealed box, since that'll give you tighter, punchier bass. A ported or vented box will be more effiecient(sp?) giving louder bass, but may sacrifice sound quality. However, if this box is in the trunk, you won't hear the difference in sound quality, but may not be as punchy. Personally, I'm a fan of vented enclosures. I hope I'm not contradicting myself too much here. 
Seriously, I'd build a sealed box and see how it sounds. You can then decide if you want something different. Either way you'll want the dual four.
Seriously, I'd build a sealed box and see how it sounds. You can then decide if you want something different. Either way you'll want the dual four.'91 5MT SS-TD04, WRX TMIC, Bosal twin dump, Spec LW flywheel/pressure plate, FCD, Walbro fuel pump-RIP
'93 5MT N/A wagon, over 400,000 miles!-Gone, parts lived on
'94 Auto SS-vf24, WRX TMIC, Bosal twin dump, Meth kit coming soon!-Now RWD!
'93 5MT N/A wagon, over 400,000 miles!-Gone, parts lived on
'94 Auto SS-vf24, WRX TMIC, Bosal twin dump, Meth kit coming soon!-Now RWD!
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vrg3
- Vikash
- Posts: 12517
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How did Rodney measure the impedance with the Fluke DMM? If he was just measuring DC resistance, that's not the same thing as the AC impedance, which would be higher with a coil of wire like the coil in the speaker. You should be fine.
"Just reading vrg3's convoluted, information-packed posts made me feel better all over again." -- subyluvr2212
Yes, Binford, I plan on using a sealed box. Ported boxes are usually louder, but they sound sloppy to me. I like clean punch myself. Not that I'm totally against ported, I've heard a few setups before that sounded great.
vrg3 - I don't actually have the JL yet, I'm shopping for the best match I can find. My money situation won't let me get all this at once. That's why I plan on doing it this winter. Rodney is just going with what he's seen, but he hasn't worked with JL subs before. I guess I'm going with the JL because of the name and reputation. Reading a voice coil in dc resistance would show a dead short, wouldn't it? I'm somewhat schooled in electronic principals and a voice coil is just a coil of copper wire with both ends loose, kinda like a choke or one side of a transformer. Correct me if I'm wrong.
vrg3 - I don't actually have the JL yet, I'm shopping for the best match I can find. My money situation won't let me get all this at once. That's why I plan on doing it this winter. Rodney is just going with what he's seen, but he hasn't worked with JL subs before. I guess I'm going with the JL because of the name and reputation. Reading a voice coil in dc resistance would show a dead short, wouldn't it? I'm somewhat schooled in electronic principals and a voice coil is just a coil of copper wire with both ends loose, kinda like a choke or one side of a transformer. Correct me if I'm wrong.
-2004 Liquid Silver WRX "Pretty Hate Machine"
-
vrg3
- Vikash
- Posts: 12517
- Joined: Sun Nov 03, 2002 2:13 am
- Location: USA, OH, Cleveland (sometimes visiting DC though)
- Contact:
Ah, okay, so he was just going by what he'd measured on other speakers.
It's not a dead short because there really is a lot of very thin wire. Any wire has resistance, and the thinner and longer it is, the greater that resistance. So while ten feet of 18 AWG wire has no measurable resistance, the huge length of tiny wire coiled up in the speaker's coil does measure an ohm or two.
It's not a dead short because there really is a lot of very thin wire. Any wire has resistance, and the thinner and longer it is, the greater that resistance. So while ten feet of 18 AWG wire has no measurable resistance, the huge length of tiny wire coiled up in the speaker's coil does measure an ohm or two.
"Just reading vrg3's convoluted, information-packed posts made me feel better all over again." -- subyluvr2212
I guess that's probably right. Sounds so. My dad (RIP) had a killer wavetech meter ($600) somewhere in the basement. I should dig that up and see if that's the case. I always understood that it would represent a near-if not totally-dead short, but I haven't tried it in person. Maybe its another case of Rodney blowing smoke just to impress me. As I said, he's overlooked small details before. The signs for ac and dc might look similar when baked. But I'd still like to know for sure before I make my purchase. I don't trust him much anymore. That, and he won't answer his phone. He was supposed to pay back last Friday money I borrowed him last week.
-2004 Liquid Silver WRX "Pretty Hate Machine"
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rightandtight
- First Gear
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- Joined: Mon Jul 25, 2005 6:42 pm
- Location: Los Angeles
As for the sub, here's my two cents. This comes from the experience of putting WAY too much money into car stereos when I was younger.
If all you want is some nice, clean fill bass, get something smaller than a 12. Go with a 10" or 8". That will save you substantial space when building an encloser as well. Get the most efficient sub you are comfortable with. I used to have a 10W6, but it was too much speaker for my application. It was awesome sounding when properly powered, but I could have easily gotten away with something more efficient that required much less power to provide the same levels of sound.
Save the money on a lower rated speaker and make yourself a nice 3/4" MDF enclosure. Rock solid enclosure=tight bass. Don't even consider those pre-fab Circuit City chip board style boxes--they're dog sh*t. That chip board resonates a lot. Sealed enclosures also require MUCH less space than ported--and as covered in previous posts sealed are a little tighter sounding, ported give a bit more 'feeling'.
And the speakers...
Same advice as above. Get the most efficient speakers you can live with. They'll save money and won't require tons of power. For instance, I used to have Kicker 4" two ways and they required so much power that whatever mids that I matched them up with would always be way louder. The Kickers sounded smooth, but had I done some research and listened in the Car Audio shop, I could have found something as sweet sounding that didn't require all that power. So maybe see what the Kappas sound like next to something that requires less power to run--you might find something that sounds better and is cheaper. Car stereo expense, just like car mods, gets out of control real quick.
So, assuming that this system is for your ears and not the car next to you, be frugal. And you shouldn't need a capacitor with the above advise due to less power drain. More money saved, less space and install.
And if you don't gain out your setup, I can't see it blowing out with quality products. I usually make the loudest setting on my head unit the loudest I would ever listen to my music, that way using the least amount of gain on my amp.
*Note, the above assumes that you only run signal through pre-amp outputs. It's probably not applicable if you use your head unit to power some of the speakers.
Hope this helps,
Willie
If all you want is some nice, clean fill bass, get something smaller than a 12. Go with a 10" or 8". That will save you substantial space when building an encloser as well. Get the most efficient sub you are comfortable with. I used to have a 10W6, but it was too much speaker for my application. It was awesome sounding when properly powered, but I could have easily gotten away with something more efficient that required much less power to provide the same levels of sound.
Save the money on a lower rated speaker and make yourself a nice 3/4" MDF enclosure. Rock solid enclosure=tight bass. Don't even consider those pre-fab Circuit City chip board style boxes--they're dog sh*t. That chip board resonates a lot. Sealed enclosures also require MUCH less space than ported--and as covered in previous posts sealed are a little tighter sounding, ported give a bit more 'feeling'.
And the speakers...
Same advice as above. Get the most efficient speakers you can live with. They'll save money and won't require tons of power. For instance, I used to have Kicker 4" two ways and they required so much power that whatever mids that I matched them up with would always be way louder. The Kickers sounded smooth, but had I done some research and listened in the Car Audio shop, I could have found something as sweet sounding that didn't require all that power. So maybe see what the Kappas sound like next to something that requires less power to run--you might find something that sounds better and is cheaper. Car stereo expense, just like car mods, gets out of control real quick.
So, assuming that this system is for your ears and not the car next to you, be frugal. And you shouldn't need a capacitor with the above advise due to less power drain. More money saved, less space and install.
And if you don't gain out your setup, I can't see it blowing out with quality products. I usually make the loudest setting on my head unit the loudest I would ever listen to my music, that way using the least amount of gain on my amp.
*Note, the above assumes that you only run signal through pre-amp outputs. It's probably not applicable if you use your head unit to power some of the speakers.
Hope this helps,
Willie
hmmm, maybe a 10W3v2 would work just as nice. The power handling is the same. Less box too. I'm looking to run one quality sub with moderate power. I'm not looking for a "oh my god, an earthquake is coming" system. I'm looking for an enjoyable listening environment inside my car, not outside.
Another friend of mine had 2 8" MTX road Thunder Pro's in a hack job ported box (no regard to any specs whatsoever) in his 92 Celica that would throw the smoke from my cigarette well over an inch. Two 15's couldn't hold a stick to them. The problem is it was sloppy and it smoked 8 months later. I need a quality and reliable sound system that will not smoke parts or my wallet. I like to invest my time into doing something well only once.
I'm looking to custom build it behind the passenger side fold down seat in a fashion that won't make both folding seats and my trunk useless. I'll definitely be using MDF for that. The multi box over the spare tire will probably get modded if not replaced to store my amps. I have some 4X4 sheets of plexiglass and cooling fans for that.
I won't be using the head unit's internal amps, the unit's lights tend to dim when its cranked. That's what the Alpine MRP-F240 4 channel amp will be for. I probably could go with some polks or something for my main speakers. But I'm really partial to infinity's 3 ways. My 93 has Cerwin Vega components that sounded great, but I never found a good place for the tweeters to go, lost the mounting cups, and they ended up between my door/dash too many times when i closed my door. They're squished flat and the main's are crackling now. I'm not a fan of cutting holes in my dash either.
Only the sub amp is ordered as of now. I'm looking to get the sub next. But it's all up in the air as of right now. That's why I'm concerned with the dual voice coil impedance issue right now. I'd like to have it match my amp. Keep the suggestions flowing.
Another friend of mine had 2 8" MTX road Thunder Pro's in a hack job ported box (no regard to any specs whatsoever) in his 92 Celica that would throw the smoke from my cigarette well over an inch. Two 15's couldn't hold a stick to them. The problem is it was sloppy and it smoked 8 months later. I need a quality and reliable sound system that will not smoke parts or my wallet. I like to invest my time into doing something well only once.
I'm looking to custom build it behind the passenger side fold down seat in a fashion that won't make both folding seats and my trunk useless. I'll definitely be using MDF for that. The multi box over the spare tire will probably get modded if not replaced to store my amps. I have some 4X4 sheets of plexiglass and cooling fans for that.
I won't be using the head unit's internal amps, the unit's lights tend to dim when its cranked. That's what the Alpine MRP-F240 4 channel amp will be for. I probably could go with some polks or something for my main speakers. But I'm really partial to infinity's 3 ways. My 93 has Cerwin Vega components that sounded great, but I never found a good place for the tweeters to go, lost the mounting cups, and they ended up between my door/dash too many times when i closed my door. They're squished flat and the main's are crackling now. I'm not a fan of cutting holes in my dash either.
Only the sub amp is ordered as of now. I'm looking to get the sub next. But it's all up in the air as of right now. That's why I'm concerned with the dual voice coil impedance issue right now. I'd like to have it match my amp. Keep the suggestions flowing.
-2004 Liquid Silver WRX "Pretty Hate Machine"
-
rightandtight
- First Gear
- Posts: 87
- Joined: Mon Jul 25, 2005 6:42 pm
- Location: Los Angeles
as long as your amp has enough power, don't even sweat it. power to spare is never a bad thing. and you can always return it or sell it on ebay if it isn't the right match 
just get the cheapest and most efficient sub you can live with. JL stuff is excellent, so anything of theirs will sound good. and a good box will add a lot.
i'd check the JL site and build something with similar dimensions to what they recommend. their formulas are set up so that the panels of the enclosure do not resonate at similar frequency sets. that should allow you to keep one folding seat. and if you stuff your box with polyester stuffing, you can build it even a little smaller than what they recommend.
and don't be partial to the Infinities, it's worth it to entertain other options. even if you come back to the Infinities. best thing is to go the audio shop and give a listen.
and i don't know about you, but i'm mostly broke...well not really, but an extra couple hundred serves me much better in my 401k than it does in my stereo.
just get the cheapest and most efficient sub you can live with. JL stuff is excellent, so anything of theirs will sound good. and a good box will add a lot.i'd check the JL site and build something with similar dimensions to what they recommend. their formulas are set up so that the panels of the enclosure do not resonate at similar frequency sets. that should allow you to keep one folding seat. and if you stuff your box with polyester stuffing, you can build it even a little smaller than what they recommend.
and don't be partial to the Infinities, it's worth it to entertain other options. even if you come back to the Infinities. best thing is to go the audio shop and give a listen.
and i don't know about you, but i'm mostly broke...well not really, but an extra couple hundred serves me much better in my 401k than it does in my stereo.