question about ohms laws

[EdgarG0721]

And since I alrdy had 2 subs and they were 15s I want to do bigger. So I guess the cool factor kick in lol. I'm going to get a truck sooner or later this year And I know when that time comes I want 4 15s ported and will be hopefully satisfied ...... But every one that likes bass knows u always want to eventually upgrade lol

[matt402]

And since I alrdy had 2 subs and they were 15s I want to do bigger. So I guess the cool factor kick in lol. I'm going to get a truck sooner or later this year And I know when that time comes I want 4 15s ported and will be hopefully satisfied ...... But every one that likes bass knows u always want to eventually upgrade lol

^ we can all agree to that im sure

bigger isnt always better...

pretty sure thats a tline box ^. setup looks familiar...

[MrSkippyJ]

as I was in the process of making a small sealed box for a 10inch sub, that just so happened to be dual 4 ohm, I did just that.

SoundStorm 10inch subwoofer, 8 litre sealed box, DD Z1 running the sub.

I even made a video...

excuse the fact that I wired the coils up out of phase at first on the second test, and the fact that I forgot to connect the multimeter on the second test

damn, wish you wouldn't have done that already. i kept thinking to myself after snafu posted of why I was wrong and I couldn't put my finger on it. I kept thinking, if I have a 4ohm sub, I set my voltage to X amount, if I have a 2ohm sub I set my voltage to Y amount. I just kept thinking that is different voltages so he is wrong. Then it hit me that I'm a dumbfuck and of course it is 2 different voltages, the gain was set differently. Changing the impedance won't change the voltage, that's why you set the gain at a certain level. So my apologies, I had a blond moment (or hour). Sorry you went through the trouble to make a video, my bad!

ps also, why didn't the sub make a sound when you gave it voltage? and LOLS at the thumbs up when you forgot to hook the leads up.

[TheyDontWantMusic]

ps also, why didn't the sub make a sound when you gave it voltage? and LOLS at the thumbs up when you forgot to hook the leads up.

it did, from 24 - 30seconds you can hear the 50Hz tone, and again from 1:45 - 1:48 and 2:09 - 2:14.

and the reason for the 0.5volt difference, is there was 4 times the voltage drop along the cable, as it was inadequate for the 2 ohm wiring! I measured 0.9volt drop along the cable wired at 2 ohm.

strangely, I don't make statements unless I know what I'm talking about, so chances are if you're disagreeing with me, you're probably wrong

[MrSkippyJ]

ps also, why didn't the sub make a sound when you gave it voltage? and LOLS at the thumbs up when you forgot to hook the leads up.

it did, from 24 - 30seconds you can hear the 50Hz tone, and again from 1:45 - 1:48 and 2:09 - 2:14.

and the reason for the 0.5volt difference, is there was 4 times the voltage drop along the cable, as it was inadequate for the 2 ohm wiring! I measured 0.9volt drop along the cable wired at 2 ohm.

strangely, I don't make statements unless I know what I'm talking about, so chances are if you're disagreeing with me, you're probably wrong

I probably had my volume down, I JUST woke up and watched it. I also don't make statements unless I know what I am talking about, however, I do have moments where I am thinking one thing and applying it wrong for some reason. So I was right about the voltage changing with impedance...when it comes to setting your gain! haha. I am also not afraid to be wrong and man up to it.

[TeamHT]

If only others could do the same...

[Sammitch0]

I think you basically shut them up man , Kudos! and gl btw man to your 4 15's.

[snafu]

Guys - well done. Yes, I knew the outcome. I'll explain why in a minute.

The reason that I asked someone to try this (and video it) is because sometimes it's just too easy to get caught up in the this is how it "should be" mentality. First and foremost, car audio is a FUN hobby but secondly it is a science. Sometimes, what looks good on paper doesn't happen in reality. They call it Ohm's Law for a reason - it's not just a really good idea.

At SMD, we are on the cusp of being not only the biggest but also the best. I for one would love to see more posts like this and less of the "hey dumb ass, you're wrong." If you don't know, then LEARN. If someone asks a question and you don't know the answer, don't guess. Refuse to guess or speculate. Find out. For those of you on SMD that are in the know, then sharing what you know with those that don't is an excellent way to build your brand. This is exactly what Steve did many years ago and look where it has gotten him!

Now . . . if the following is true:

Power = Voltage^2 / Impedance

[And it is.] So, how did the voltage measure the same (TDWM is correct about voltage drop being a factor so we'll ignore that) at both 2 ohms and 8 ohms in this example? Simple. Because a power amplifier is a source of voltage. Since the amplifier in this video was only producing 20 volts (20 x 20 / 8 = 50 watts & 20 x 20 / 2 = 200 watts), it never broke a sweat. At some level of voltage at 8 ohms, the amplifier would be unable to deliver that same voltage into a lower impedance.

"High Current" amplifiers are those that are able to resist drops in voltage that are a result of the load. Keep in mind, a subwoofer presents a widely varying load to an amplifier - that load is resistive, capacitive, and inductive and two of these components vary with frequency.

Given that all of the above is true, the maximum voltage available from a power amplifier will be reduced as impedance is reduced. The perfect amplifier would be able to maintain voltage as impedance is reduced.

TDWM - thanks for the video. [i also chuckled at your thumbs up btw.] My challenge to you is to do MORE of that kind of stuff in the future. Some good narration is never a bad idea as well so that everyone watching it can benefit.

As far as the OP's original question, I'm going to agree with the camp that says err on the side of conservatism for a daily driver. This means, follow the manufacturer's guidelines in your system design process.

[TheyDontWantMusic]

TDWM - thanks for the video. [i also chuckled at your thumbs up btw.] My challenge to you is to do MORE of that kind of stuff in the future. Some good narration is never a bad idea as well so that everyone watching it can benefit.

yeah, see, there's an argument going on that someone thinks 80amps worth of blade fuses will blow in an amplifier before an 80amp ANL fuse at the battery... because:

when your amp blows, exspecialy if it is a slow burn. That means the amp will blow and the heat will be comming from the amp and will be building up the most heat from the amp and now that heat has to build up over a 17 foot distance of power wire to get to the fuse that has a 5 second burn up threshold that is all the way up front.

I'm not even sure if this is meant to be a serious argument, or if someones just having a laugh... but testing when 80amp fuses blow isn't the easiest thing to do

[snafu]

In a series circuit (battery to connector, connector to wire, wire to fuse holder, fuse holder to fuse, fuse to fuse holder, fuse holder to wire, wire to amplifier B+ input, amplifier B+ input to fuse, fuse to power supply, power supply to amplifier B- input, amplifier B- input to ground) the current is the same across all components. Having said that, one would have to look at the actual characteristics of the ATC fuse versus the ANL fuse to make that determination. Or, one could easily do it and determine the results in about two minutes.