Amp Power Questions

[PsychoBeano]

I have two JLAudio W0 12" Subs in an enclosure and all I need now to drop them in is an amp. After looking around a bit, I think I know what I want. The Owners manual gives me this:

The amp that Im thinking of getting is the Kenwood KAC-7203.

This amp is rated at 170 W *2 ch RMS at 4 ohms and 250 W at 2 ohms. My question are as follows:

What is the difference between the two Watts ratings?

Which will sound better and which will be better for the subs?

Also, should I get a capacitor (I would imagine 1 farad, correct me If Im wrong)?

BTW, the enclosure is a dual bandpass quad-ported enclosure if that makes a difference. Ive also been looking around for a while before deciding to post this topic seeing if I could figure it out on my own. A couple of really helpful resources are:

Club Knowledge Car Audio FAQ

Car Audio Help Basics

[CAPT_BLOTTO]

the W0 are SVC subs iirc which means the amp will put 170 W to each sub which is right about the perfect power for those subs. (with the gain not up all the way)

I doubt you'd need a cap for a small amp like that.

Dualbandpassquadportedenclosure? That sounds like a mouthful and maybe overkill or too big.

[paulr]

I think the W0's were all SVC, with 4/8/12 ohm versions. Chances are yours is a 4 ohm, but you'll have to check the actual speaker. I don't think there's any chance of it being multi-coil.

Amp seems decent, I doubt it will be the limiting factor in this system. If you can get a good deal on it, probably not a bad choice.

If your "dual bandpass quad ported" enclosure was purchased off eBay / not made exactly for a W0 be careful. Not only are bandpass enclosures some of the hardest to tune to a specific driver / vehicle, but poor construction can make problems even worse. I've had several experiences with friends purchasing similar enclosures off eBay and having rather poor results... They were much happier with basic sealed or ported designs.

The "difference between the wattages" is how much power the amp can put out depending on the load it has to "push". This is determined by what speaker you have connected, and how you connect it. That amp has a maximum voltage it can provide based on it's design, and a maximum current it can handle, based on how it's constructed + other factors like line voltage, temperature, etc.

Here's a general example (I don't know if these specs are actually true for this amp, but the theory is there).

P (Watts) = V (volts) X I (amps); Volts = I (amps) X R (Ohms)

170W = 26V * 6.5

26V = 6.519 * 4 or 26V / 4 ohms = 6.159 amps

Now, connect a 2 ohm speaker, 26V / 2 = 13 amps, which at 26V is 338W - however, 13 amps makes the amp burn up, so kenwood says that only 9.5 amps is a good idea, and (9.5 * 26 = 250W). If you connect a higher ohm speaker, the opposite happens, and the power level goes down. Were 26V the maximum voltage of the amp (determined by it's design), it would only be able to supply 3.25 amps or 85 watts to an 8-ohm speaker, no matter what you did.

Also note turning down the volume and/or gain lowers the maximum voltage which reduces the current. This is why the amp won't explode the instant you connect a 2-ohm speaker, but might have issues when you crank the volume. Of course this is all hypothetical, I have no idea what the actual specs for that amp are.

Less ohms = more power moves through the speaker = amp does more work, but if amp does too much work, it goes into "protect" mode, or burns up. With SVC speakers (Single Voice Coil), you're fairly limited with your options, but with DVC (Dual Voice Coil) or QVC (Quad) you have a more options based on series and parallel configurations, to take advantage of what specific amps can offer. This is what I assume blotto thought you were referring to; there is no "power switch" or "turbo mode" on the side of the amp. With you having SVC subs and using a 2-channel amp, you have only 1 possible configuration.

Now with a a capacitor, there is no "rule". They can't really "hurt" a system (they can make existing problems less apparent, but they don't cause any new ones). When an amp/sub "hits", the battery / alternator may not be able to react fast enough, causing a dip in the input voltage to the amp. The capacitor can release it's power much more quickly than an alternator or battery, helping to counteract this. They don't magically "add" overall power to the system, they have to be recharged. This "dip" can cause all sorts of minor annoyances depending on the situation, but assuming your alternator is in good shape, you have a decent battery, and wire correctly, it's unlikely to be an issue on a system this small. However, if you have the lights dim or can confirm in some other way the voltage is dropping (ideally with an oscilloscope), you can add one - like I said, it won't really hurt anything, but could be a waste of $$.

Hope that helped, and sorry if I rambled.

[PsychoBeano]

If your "dual bandpass quad ported" enclosure was purchased off eBay / not made exactly for a W0 be careful. Not only are bandpass enclosures some of the hardest to tune to a specific driver / vehicle, but poor construction can make problems even worse. I've had several experiences with friends purchasing similar enclosures off eBay and having rather poor results... They were much happier with basic sealed or ported designs.

Well the Enclosure looks pretty much exactly like this:

I actually didnt buy any of this, I sort of "came up" on them. (My dad was selling a house and It looks like the previous owners did car audio and/or boosted cars/car parts). It was just lying around so my dad took an opportunity .

The "difference between the wattages" is how much power the amp can put out depending on the load it has to "push". This is determined by what speaker you have connected, and how you connect it. That amp has a maximum voltage it can provide based on it's design, and a maximum current it can handle, based on how it's constructed + other factors like line voltage, temperature, etc.

Less ohms = more power moves through the speaker = amp does more work, but if amp does too much work, it goes into "protect" mode, or burns up. With SVC speakers (Single Voice Coil), you're fairly limited with your options, but with DVC (Dual Voice Coil) or QVC (Quad) you have a more options based on series and parallel configurations, to take advantage of what specific amps can offer. This is what I assume blotto thought you were referring to; there is no "power switch" or "turbo mode" on the side of the amp. With you having SVC subs and using a 2-channel amp, you have only 1 possible configuration.

Yeah, the ohms part was confusing me. I thought there was some way to be able to choose between the 2 "modes" but if Im understanding correctly it depends on the speakers, right? How would I know if my speakers were 2 ohm or 4 ohm? On the JL Audio site it says Nominal Impedence is 12 ohms. What is the 1 possible configuration? Series @ 4 ohms?

Now with a a capacitor, there is no "rule". They can't really "hurt" a system (they can make existing problems less apparent, but they don't cause any new ones). When an amp/sub "hits", the battery / alternator may not be able to react fast enough, causing a dip in the input voltage to the amp. The capacitor can release it's power much more quickly than an alternator or battery, helping to counteract this. They don't magically "add" overall power to the system, they have to be recharged. This "dip" can cause all sorts of minor annoyances depending on the situation, but assuming your alternator is in good shape, you have a decent battery, and wire correctly, it's unlikely to be an issue on a system this small. However, if you have the lights dim or can confirm in some other way the voltage is dropping (ideally with an oscilloscope), you can add one - like I said, it won't really hurt anything, but could be a waste of $.

Hope that helped, and sorry if I rambled.

As for the cap, I just didnt want my headlights to be dimming as that doesnt sound too safe.

Thanks for your guys' help, I feel like I understand a bit better now.

[paulr]

I plead the fifth on commenting on that enclosure. While there's a chance you got lucky and it happened to be designed exactly right for the speakers you have, it also could have came with the ultra-crap pyramid speakers, the previous owner blew them, and threw some W0's he found at a pawn shop in. They didn't sound any better, perhaps even worse, and he abandoned the project. Exactly what happened to a friend of mine, but the design was slightly different, and he used Infinity Kappa Perfects. Damn thing actually sounded worse, because the speakers were so different from what the enclosure was designed for. Regardless, it's what you have now, so there's not much you can do. Either you like the way it sounds and you're happy with it, or you don't, and you consider a new enclosure / new system. Only way to see / tell is to go ahead and hook it up, and listen. Then you can make up your mind from there.

Here's some info on sub enclosures, it appears yours is simply a variation of a 4th order bandpass, not really uncommon, but they're much more picky with driver selection. A sealed enclosure is by far the easiest to deal with, and ported ones can be done with minimal construction difficulty / math, but I rarely think they're worth it.

The JL W0 manual is here (pdf), and it appears they came in 4/8/12 ohm variants just like I thought, except the 15s, which were only 4 and 8 ohm. The only way to know for certain is to put an ohmmeter to the speakers (a function on most multi-meters)and measure (it will say a number that's close, like 3.48 or 4.2 ohms for a 4 ohm, 7.5 or 8.3 for an 8-ohm, etc), or look at the actual driver and see how it's labeled. If your speakers are in fact 12 ohms, all hope is not lost; you can still get decent performance by wiring them in parallel (positive to positive, negative to negative), which will create a 6-ohm load. Connecting this to a mono amp (one channel) will still produce somewhat decent performance. However, I'm still betting you have 4 ohm speakers, in which case you just plug them in to your 2-ch and be done with it (alternatively, you could get a 2-ohm stable 1-CH amp, again wire them in parallel, and connect them up, but the benefits to doing this are small).

Basically, when you have 2 coils of equal load (keeping it simple here) series doubles the ohm rating, while parallel cuts it in half. A case of how this is useful is a setup with three JL W6's, which were 6 ohms with 2 coils per speaker. You could set the speakers up for 3 ohms a piece (parallel) and then wire them in parallel again, getting 1 ohm, for competition setups, or you could wire them 12 ohms (series), then wire them in parallel, netting 4 ohms, for a more "normal" setup. However, you have 2 coils total, not 6, so your options are as I described above.

Regarding the headlights dimming, install your system and see if it happens at all, they don't get radically dim or anything, you'll just see them "flicker" when your system hits. It's not really a safety issue for driving, it's just a sign your electrical system isn't running the way it should, and means you're over-stressing things. When I had a 1500W system (and stock electrical) I could make it happen just by cranking the volume, now with 650W (and possible electrical problems) it only happens when I'm idling and have it cranked for a while. Again, it's not a safety issue, it just means the alternator can't keep up, the battery is discharging as opposed to charging, the amp is probably working harder than it needs to be, or several other things. However, with your system being ~350W, I doubt you'll have it happen at all, unless you leave your system cranked all the time, and sit idle in parking lots for long periods. However if safety is how you're convincing your parents to buy you a $70 cap then sure it's unsafe as hell .

Good Luck

[PsychoBeano]

Yeah, about the enclosure if it doesnt sound that great Ill probably just get another one. Its just hard to not use something thats free . As far as money goes, I usually pay for everything myself, lol. My car is all I work for. On a $300 two week check, $250 goes to the car and $50 goes to gas and movies. This week: An amp, wiring, and maybe a 16t. I usually spend my check before the weekend is over. Thanks for your help

[CAPT_BLOTTO]

Well if its all free stuff give it shot. Most likley though you'll be replacing the box

I like how the box is "rated" for 800W :lol:

[PsychoBeano]

Yeah, lol. Thats not the box I have though, however it does look very similar