sm

I'm looking at the KLA subs and was wondering which one I should get. What's the difference, pros/cons, etc. of the 4-ohm vs. the 8-ohm sub?

Thanks!

Simpson

slevy951

It has to do with how you wire it and the capabilities of your amp. Here we go...

1) If you are using just one sub, go 4 ohm.
2) If you are using 2 subs and your amp is 4 ohm stable, go 8 ohm and wire them in parallel.
3) If you are using 2 subs and your amp is 2 ohm stable, go 4 ohm and wire them in parallel.

That about covers it.......

RSflared72e

Resistance isn't so much a performance issue - it's a wiring parameter. To expand on the above posting, you need to give each channel the appropriate resistance from the subwoofer. Too low, and you blow the amp. Too high, and you reduce your amp's effective power output. If your amp is rated to a given minimum resistance, let's say 2 ohms per channel, that's the lowest total sub resistance rating you can use per channel.

Mathematically, to create the appropriate resistance, use the following rules when combining speakers:

1) If wiring the speakers in parallel, the resistance you create to the amp will be the product (result of multiplication) of the resistances divided by their sum.

For example, using two 4-ohm speakers in parallel: 4x4/4+4 = 2 ohms

2) If wiring in series, the resistance will be the simple sum of the speakers:

Two 4 ohms speakers in series: 4+4 = 8 ohms

You can also use a pair of speakers in parallel as a component of a series system. Let's say you have four 4-ohm woofers. You can wire them in two parallel pairs, and then wire the pairs in series with each other to create the same total 4 ohm resistance as each speaker originally had. This is how some of the mega systems are wired that you see in magazines.

SO, how many subwoofer channels are you going to run - just one? Or are you using a stereo amp to potentially run 2 subs? You can also run a 2-channel amp into a single sub if it has dual voice coils - each voice coil "counts" as a separate speaker, just be sure the woofer can handle the output of both channels.

What sort of crossover system are you using?

slevy951

Ahh....thanks for expanding. I was assuming single channel.

sm

Wow, thanks guys for the in depth explanation. It helped a lot.

I was planning to either go with a:

3-channel amp - two channels to front speakers and one channel to sub

or

4-channel amp - two channels to front speakers and two channels bridged
to sub

I've read that the rear speakers aren't really needed, which would only leave me with the:

2 x front speakers
1 x sub in cubby

Is that enough? Should I go with a front component speaker system? I like the music loud and clean, but don't plan on entering competitions EVER [anytime soon] ---EDIT--.

BTW, do I need a crossover?

Thanks!

odie

I'd say however you wire it, keep the resulting load at 4 ohms.

I know lots of amps now claim 2 and even 1 ohm stability. But the reason is marketing. Car stereo competitions class you by total system power, based upon amp manufacture's output claims at 4 ohms. Lots of competitors wires speakers in parallel to drop the ohms and increase the power but remain in a lower class. So amp manufactures play up the 2/1 ohm stability to promote sales.

The 4 ohm rating of a speaker is only and average. At some frequencies the resistance much is lower, at others higher.

RMills944

BASICALLY:

The 8 Ohm will sound cleaner and use a lot more power to push it.

The 4 ohm will sound less-clean (I say this becuase it will still sound good) and use less power to push it.

600 Watts @ 4O hm = 300 Watt @ 8 OHm

theedge

Depends on the amp, some will drop the THD for 4 ohms, some wont.

Rear fill (running speakers in the rear) is up to you, the owner. If you often carry passengers (ie all your friends are midgets ) or you prefer the surround-ish feel of 4 speakers go for it.

Legoland951

I would keep it at 4 ohms and worry about the actual output of the subwoofer and tuning (take into consideration of its efficiency in output with input of 1 Watt at 1 meter) while leaving dynamic headroom to keep the amp from clipping (maxing out). Its not really the resistance more than impedance that matters, which is dynamic resistance across different power output. If you drop it to 2 ohms, you would have to reduce the input to the sub due to the extra power output of the amplifier from the lower impdedance. I personally like accuracy more than bumpy bass and we used to play back pink noise (flat output from 20 hz to 20k hz) and using a 3rd octave RTA (real time analyzer) with a caliberated microphone to tune the system to get a relatively flat frequency response curve (+/- 3db from 20 hz to 20k).

With all that said, its all up to what you like. If you like max bass to impress ghetto superstars, wire it up to 2 ohms and drive the amp hard. If you like accuracy and have enough power in your amp, keep it 4 ohms, tune for a flat frequency response, and keep your amp cool (too much heat damages amps).

sm

I may end up with the 4-Ohm sub under my tree, thanks to my other half

So here's a question that I couldn't find an answer for in the archives:

Can I use the head unit to drive speakers (2 front and 2 rear) and then connect a 1-channel amp to the RCA-pre outs to drive the sub?

Or does using the RCA-pre outs "turn off" the respective speaker level wires from the head unit?

Thanks again...

simpson

slevy951

SM-

You can use the head to drive the fronts and a single channel amp for the sub. I'd recommend a mono sub amp with a crossover built in.

RCAs turning off....depends on the head.

BTW, you've got mail.....

RSflared72e

Component systems on average sound better, and allow for more flexibility in placing the drivers for optimum imaging. Depends on the product.

You definitely need a crossover, which divides up the frequencies between the appropriate drivers. Two types are out there: passive ones, which are the type usually found in component systems, usually these split the sound between a tweeter and mid-range woofer. And active ones, which act on the line-level output of the source unit, in this case to roll off the high freqs to the sub and roll off the low freqs to the full-range speakers.

If you have a 3 or 4 channel amp, these days, you probably have a built-in active crossover that will provide a dedicated subwoofer output and full or high-frequency output to the front drivers. (You will also have a passive crossover as part of your component front speaker setup).

Many ways you can wire things up:

4 channel amp into 2 front full range speaker systems and 2 rear subs, or

4 channel amp into 2 front full range speaker systems and one dual-voice coil rear sub (acts as 2 speakers for hook-up purposes), or

3 channel amp into 2 front systems and one rear sub, or

3 channel amp into 2 front systems and 2 rear subs, such as 2 8 ohm drivers wired in parallel to create 4 ohms, or...etc etc etc

Don't get hung up on the ohm thing. It's a simple electrical parameter of the component. There are no hard and fast rules as to what resistance speaker sounds best, its a matter of what is feasible with the equipment you have.

Power measurement of amp output is a relatively simple thing to mathematically conceptualize - much more complex in the real world, with the variations in resistance you see throughout a speaker's range, and many other variables. It's a given power output over a given frequency range at a rated distortion level. Decrease the resistance, you increase the power and unfortunately the distortion, and vice versa.

So, if you have a high quality amp, it will cleanly run a 2 ohm or even 1 ohm load if that is what it's legitimately rated to do. The deciding factor on that once you wire it up is whether the distortion level becomes unacceptable when the reduced resistance allows the amp to output more power - then you see if their ratings are BS or not....

The technology has come a long way from the 70s and 80s when there were many fewer options. Hell, these days, a lot of factory systems sound better than custom systems of 10 years ago, which is why I don't dabble in this stuff as much as I used to.

YMMV Al

RSflared72e

Crutchfield has a good series of diagrams somewhere on their website that shows the possible RCA vs. speaker-level ouptuts that are possible with various head units. They used to tell you which type each head was, not sure if they still do...

It will work quite well to run the fronts full-range, but keep in mind you may get more distortion at high volume levels, where the fronts will also be trying to put out a lot of bass - that's the sub's job, so using an active crossover for the whole system will work well too. Depends on your budget and needs.

sm

Thanks everyone for the replies. This has been very helpful...



Which account did you write to? Did my gf contact you about the purchase? It's supposed to be a surprise

slevy951

uh oh.....it was a female name, yes......well, there will be a surprise....