Not Enough Power? Or Knowledge?

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stevdart

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Posted: July 04, 2005 at 3:47 PM / IP Logged

Discussions like the above are good in general...educational for us all. Sometimes during a thread, as your intent changes from one subject to another ( remember "Not Enough Power..."? ) it becomes necessary to start another thread. It's not often we can enjoy the heavy-hitters here, so I'm all for a little educational diversion from time to time. I got two new links out of it as well, which I'll get more familiar with and use in the future. Hope some of the other regular members do the same...

Use the preout that is meant for the sub to the sub amp, the other full-range preout to the 4 channel amp. Use splitters on that one to feed the extra two channels. Your head unit will have a control for sub out, I believe, IIRC, and one of the preouts will be designated for sub use.

Build the box so that it performs well in the worst case scenario and, in return, it will reward you at all times.

bpensak

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Location: United States

Posted: July 04, 2005 at 4:10 PM / IP Logged

Well Said.

The back of my head unit (Alpine CDA-D852) only has PreOut Front & PreOut Rear. No Sub Preout. Per the Alpine Manual it allows the following setting:

Non Fading Pre-Out (N.F.P.)

- NFP On - In this position, the front Pre-Out will not be affected by the fader.This is ideal for driving a subwoofer

amplifier.

So what would be the best choice for hookup?

1. Front Pre-Out With "NFP On" To The Sub Amp, Then From The Sub Amp Preout To Front Input On 4 Channel

2. Front Pre-Out To 4 Channel, Y'd Out To Front & Rear, Rear Pre-Out To Sub Amp

As I mentioned, I don't want to purchase a new HU just yet, waiting to save alittle more and get an in-dash DVD. The flip-out I'm looking at does have 3 Pre-Outs (Alpine IVA-D310). Wife would not be happy to spend another $1300 at this point!

kmitchel

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Joined: May 09, 2005

Posted: July 04, 2005 at 5:08 PM / IP Logged

Your going to have to hook it up and try it out, then try something else, until you find what you like. Each configuration is going to have pro's and con's. The NFP-On option would be most useful if you were driving a pair of speakers off the deck. Personally I would drive the 4 channel off the front pre-out's sub separately on the rear. Turn the gain on the rear channel down at the amp. And use the fader to help balance out the subs. The rear channel level will probably be more consistant between different songs than the sub level. I would not tie the rear channel level with the subs if you could help it. My antique Pioneer has the one set of preout's tied to the rear fader. I would have to pop the trunk and adjust the gain on the sub amp too frequently depending on what I was listening to. But like I said you need to hook it up and try it out until you like it.

boulderguy

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Posted: July 04, 2005 at 7:48 PM / IP Logged

I like option #2 for more flexibility - you're more likely to adjust sub volume on the fly than you are the front to rear fader. It's all temporary til the new HU comes in anyhow.

That brings up another question - does your main amp have an x-over, or is it running full range? If it has an x-over, I'd DEFINITELY use that, I like 80-90hz, but it depends on your ears & how the individual speakers do.

The other thought I had was the box size. .6 cu ft for a 10" ain't huge, and it means it won't be super efficient. It's certainly within parameters & will sound very tight, but generally a smaller box requires a bit more power than a larger box to get the same sound from (let's see who attacks that statement). It'll really depend on how efficient the sub is & how much bass you want. Check it out early, if it feels like you need more power, take the amp back & trade for a larger one. Most shops are good about that if the amp is still new. I still believe the 250/1 is a good place to start.

Good luck.

Poormanq45

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Posted: July 04, 2005 at 8:48 PM / IP Logged

I noticed something while readin a few descriptions of lower ohms equal higher wattage.

With a standard AC current, meaning no transformer, the higher the ohms the HIGHER the current. 120v = 120/1, 120v = 240/2, 120v = 480/4. Get the point?

Anyways, the difference is that an audio amplifier is a VOLTAGE source, not a current source. As you half the ohms you double the VOLTAGE. Notice the difference?

Now that I've said that it probably seems obvious to you, but I bet alot of you never knew exactly WHY the current increased when lowering the ohms.

haemphyst

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Posted: July 04, 2005 at 9:50 PM / IP Logged

Poormanq45 wrote:

I noticed something while readin a few descriptions of lower ohms equal higher wattage.

And you feel this is wrong information?

Poormanq45 wrote:

With a standard AC current, meaning no transformer, the higher the ohms the HIGHER the current. 120v = 120/1, 120v = 240/2, 120v = 480/4. Get the point?

I honestly have no idea WHERE you are getting these numbers from. I agree with your math, but I think you are transposing your constants. Whether you are dealing with DC to AC conversion in a switching power supply (like in a car amplifier), or AC to AC, with or without a transformer, Ohms law says that this is so: "watts equals volts times amps" or "volts (squared) divided by impedance"... it does not matter at all... If you double the input voltage from 120 to 240, you will halve the input current for the same output power. Is this what you mean?

Poormanq45 wrote:

Anyways, the difference is that an audio amplifier is a VOLTAGE source, not a current source. As you half the ohms you double the VOLTAGE. Notice the difference?

Nope. This is WRONG. If you have one 4 ohm woofer, you have X voltage across it, if you put another in parallel with that same woofer, your output voltage from the amplifier does not double, does it? No, the amplifier will try to maintain that same voltage by producing more current. You are correct - an amplifier IS a voltage source, as it will try to maintain VOLTAGE by producing more current. A current source will output a fixed current, and adjust the voltage to make sure that current always stays at the preset level.

Poormanq45 wrote:

Now that I've said that it probably seems obvious to you, but I bet alot of you never knew exactly WHY the current increased when lowering the ohms.

...huh? this is exactly the OPPOSITE of what you said above...

boulderguy wrote:

It's certainly within parameters & will sound very tight, but generally a smaller box requires a bit more power than a larger box to get the same sound from (let's see who attacks that statement).

Well, since you seem to think I am attacking you, rather than trying to offer help and a bit of knowledge, I'll take that... except I am actually going to agree with you (weren't expecting THAT, were you? {emoticon SPECIFICALLY left out}). You are correct, in a smaller enclosure, a given driver will require more more power to achieve a given output. Dude, please lighten up a little bit, and recognize when people are offering experience and knowledge, and NOT attacking...

It all reminds me of something that Molière once said to Guy de Maupassant at a café in Vienna: "That's nice. You should write it down."

Poormanq45

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Posted: July 04, 2005 at 9:57 PM / IP Logged

Ok, I'm confused then.

Here we go,

12v = 12a/1ohm, correct?

Then if voltage stays the same(12V) then:

12v = 24a/2ohm, correct?

How is that not a current increase with increased ohms?

haemphyst

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Joined: January 19, 2003

Location: Michigan, Bouvet Island

Posted: July 04, 2005 at 10:06 PM / IP Logged

I see where you are confused. Here's where you want to look... study that, and you'll see where your confusion is happening.

It all reminds me of something that Molière once said to Guy de Maupassant at a café in Vienna: "That's nice. You should write it down."

Poormanq45

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Joined: October 27, 2004

Location: United States

Posted: July 04, 2005 at 10:11 PM / IP Logged

oops, I'm ashamed, and I'm studying to be an electrical engineer. I may have to rethink my career choice Not Enough Power? Or Knowledge? - Page 3 -- posted image.

SO v = I x R . I'm embarrassed Not Enough Power? Or Knowledge? - Page 3 -- posted image.

I don't know where I was getting V = I/r. ANy idea?

Poormanq45

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Joined: October 27, 2004

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Posted: July 04, 2005 at 10:12 PM / IP Logged

I guess I was thinking of I = V/R Not Enough Power? Or Knowledge? - Page 3 -- posted image.

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