I used to know the answer to this waaay back in the day, but it's been quite a while since I built a system. Currently I have a JL Audio JX250.1 Monoblock amp pushing a JL Audio 12WXv2-4 12" Sub. Link for those who are curious... http://www.sonicelectronix.com/item_...12-JXWXv2.html

The amp will put out 175RMS @ 4ohms and 250rms @ 2ohms. So right now it's at 175rms. If I add a 2nd sub @ 4 ohms and drop it to 2ohms, will the 2 subs out play the single sub? I know it seems like a no brainer, 2 is better than one and 250 is better than 175, but here is where Im overthinking this...

does one sub @175 play louder than 2 subs @125 each? Naturally the 250rms gets divided equally between the 2 speakers. I cant remember exactly how many db are added when you add a second speaker. I know you need to double the power to get a 3db increase for a single speaker and you need 6db for it to sound "twice as loud" to a human ear, but how many db does a 2nd speaker add? Like I said, 10 years ago, I knew the answer, but now... not so much.

 

I think I found my answer...

http://www.caraudiohelp.com/car_audi...subwoofers.htm

Adding a 2nd sub adds 6db. If Im doing my math correctly... 87.17db is the sensitivity of my sub. 175 watts adds about 22 db to that = 109.17db. Cutting power down to 125 cuts it by about 1 db roughly, then add in the 6db for a 2nd sub and its up to 114.17db, so a 5db gain, nearly a "double" in volume as far as a human ear can tell.

Just nice to know that in theory, it will increase the volume, not decrease it.

Now I just have to convince the wife to let me build a box and buy a 2nd sub.

 

More surface area = more air movement = more noises

 

I remember that to "double" the loudness of a speaker, power requirements go up exponentially...
So from 1 watt to 10 to 100 to 1000....
The few watt's you're losing, 1db as you said, is not noticeable.... supposedly the "average person" only notices a 3db drop or raise, not 1... But adding the other speaker with 6 db, plus the added speaker area, for sure noticeable...

Rafael

 

From what I recall, two 10" = 12". Two 12" = 15". Two 15" = 18".

Dont fool your self on lowering the resistance, your not increasing the output of the amp. Its just ohms law! lower the resistance, the more current its gonna pull.

It's nice that an amp will go down to .5 ohm, or 2 ohm load. < hope you have some good batteries and and altenator to support it.....

 

????

Some old school amps, you could lower the ohm load (by adding another speaker) and it would double it's rated power... so 1 4 ohm speaker, 100 watts, or 2 4 ohm speakers wired in parallel, you got 200 watts.

Some of the newer digital amps do that too, but not quite double... I have an Alpine amp that is 90 watts @ 4 ohms and 120 watts @ 2 ohms...

Rafael

 

My current amp puts out 175 watts @ 4 ohms. I measured it with my multimeter to verify the gain setting and the manual says to aim for 26.2v AC using a 50hz test signal. Well, thats roughly right where my amp is. 26.2 x 26.2 / 4 = 171.6 watts of power. The manual states that this amp will put out 250 watts into a 2 ohm load. It also says to set the gains for around 22.3v AC. 22.3 x 22.3 / 2 = 248.6 watts. Seems right on the money to me.

Ive also decided to switch gears altogether and just swap out equipment. This amp/sub combo will go into the wifes car while my car gets a huge upgrade, sticking with a single 12" sub.

 

And the old school cheater amps, rated @ 20 Watts @ 4 ohms, could play @ .5 ohms and 500 watts (or some outrageous amount)... Lowering Ohm load raised the output....

Rafael

 

OK, the old Orion & Rockford Fosagte amps are awesome. Great output sections and power supply's. rated at 4 ohms, drop to 2 and the wattage doubles.....HCCA's even better. Just what a real amp should do (not getting into the Class A, B, AB, D and such lol). Should you be pushing right at the limits of your power supply? Not really..

So, 100w to 200w.. More power, just an illusion.

Say you have your amp, 100w driving a 4 ohm speaker. How are you going drive that speaker harder? More power!
Bigger amp, Bridging an amp......
Taking it to 2 ohms??? NO!

How are you taking it to 2 ohms, adding another 4 ohm speaker. So now you have your awesome amp feeding Two 4 ohm speakers, each getting 100w, for your More Power of 200w.. ?

Just an illusion

 

Now we are back to my original statement, each speaker getting equal power and for every speaker you add at that equal power you add 6 decibels to the sound level. Yes the output PER speaker is the same, but added together, it is still double. The formula isnt going to change... (V^2)/R If I measure 22.6VAC at my amps output, square it, and divide by 2ohms, it's 250, which is the recommended safe level of my amplifier. If I measure 26.5, square it, and divide by 4, its only 175, also set to the safe level recommended by the manufacturer. How is that an illusion? The power output of the amp is higher at a lower impedence. It doesnt matter how the power is divided up after it leaves the amp, the amount of wattage at the point of exit on the amp is still higher.

Or lets use Ohms Law, where I is amps, V is Voltage, R is resistance... I = V / R... we will also use the exact same output voltage for arguments sake...
I = 26.5 / 2... I = 13.25
vs
I = 26.5 / 4... I = 6.62
Hmmm at 4 ohms I am getting 6.62 Amps of current but at 2 ohms I am getting 13.25 amps of current. Where is the illusion? The amplifier is putting out more power using either formula. Of course using Ohms law, we can now use Watts law... P=VI
P=26.5*13.25 = 351.1 watts
P=26.5*6.62 = 175.4 watts

So mathmatically proven that dropping resistance increases power output at the point of exit at the amplifier.

 

It does matter,, So your amp does 175w @ 4 ohms, drive one speaker it see's 175w. But at 2 ohms it can only do 250w. (that's not double)...
Two speakers now(each one still 4 ohms) paralleled for 2 ohms, your amp is doing its 250w.. Bummer, each speaker is now only seeing 125w each.
Looks like you just lost 50w across your speaker.
But wait! I have 250w, that's more power...... come on?

 

Yes I lost 50 watts to one speaker, but added a whole 2nd speaker. Thats what matters most here. In the link I provided in post #2, there is a chart... here it is cut and pasted.

Now then if 100watts gives me +20db over my rated efficiency, and my rating is at 87db, then 175watt puts me right around 109db. Right? 87+22 (23db is 200 watts, so a little lower than that) So now then, if we drop power to 125watts per speaker, then the db is closer to a 21db gain, ok call it 20 for arguments sake. so we are at 107db. Now add in the extra 6db for the 2nd speaker and its 113db. So even though we have less wattage per speaker, we actually have more total output.

Heres a totally different way of looking at it. In terms of horsepower, do they rate output by how many wheels are being driven? By your logic, an awd car would suck horribly because its power is being divided by 4 instead of only 2 or 1. The wheels all work together towards a common goal and the same can be said for speakers on the same channel.

 

Uhh what?

What here is an "illusion"?

There IS double the power (or whatever the actual increase is), plus the whole additional cone, so the output does increase. There's no illusion about it. Sure in the theoretical amp you suggest that has 100W @ 4 ohms and 200W @ 2 ohms, and you use two 4 ohm speakers to get that 200W output, you are getting 100W per speaker, but there is still double the power and double the cone area.

You could also choose to change to a different speaker that is 2 ohm, this will increase the output (ignoring any other changes in speaker properties by changing to a different speaker).

You could also increase output by adding cone area, again a change to two speakers that are 8 ohm each, connected to that same 100W amp, would increase the overall output.

Or you could change to a different amp that has double the power at the same load, this would also increase output.

So what exactly is an illusion?

Keep in mind, I've been installing professionally for 20+ years, and have many training certificates.