Getting mixed messages on what happens to ohms, watts, when I add speakers.

[scooper77515]

I have a 400X4 amp in the boat, and the previous owner had the rear 2 channels going to a subwoofer, and the front 2 channels going to the waketower speakers. I added a set of 380 w-max Kicker speakers under the dash so we can hear them while driving.

Best Buy installation guy said that adding another set of 4ohm speakers to the existing set on the same channel (right channel is running two speakers on the right, left running two speakers on the left) that they would be receiving the power at 2 ohms each, stressing them out and possibly blowing them if I listen to them at too high a level.

In my thinking, I am just splitting the watts between the two, thereby getting half as much volume out of all 4 as I did out of the original 2.

Am I stressing my speakers out doing this?

Front speakers are rated 195 peak watts, 65 RMS. Rear speakers on tower are called "500 watts" but not sure if they are really that powerful.

 

[JustJason]

Re: Getting mixed messages on what happens to ohms, watts, when I add speakers.

Depends on the quality of the amplifier. There's a big difference between $200 400x4 amps and $1000 400x4 amps.

I did HiFi for 7 years. 5 of that I managed my own high end car stereo shop. There is so much garbage out there, and so many companies, that power numbers that you see on head units, amplifiers, and speakers almost mean nothing.

At the end of the day, if you turn up the volume to the point the speakers are distorting, (even if you can't hear the distortion), and if you constantly push the envelope as far as volume goes, you will pop them.

1 more thing that will twist your noodle. When you hear speakers distorting...
Are you hearing....
1. The speakers distorting because of to much power
2. the amplifier distorting because the gains are improperly set, and the speakers are just playing the distorted signal the amp is sending it.
3. Or is the head unit distorting, sending that distorted signal to the amp to become a distorted amplified signal, and the speakers again just reproducing the distortion they are given.
4. Any part of all of the above?

 

[BaileysBoat]

Re: Getting mixed messages on what happens to ohms, watts, when I add speakers.

As you add speakers you lower the resistance on the circuit, increasing amperage draw. You are going to overload the amp.

 

[Silvertip]

Re: Getting mixed messages on what happens to ohms, watts, when I add speakers.

Resistances added in series are "added": Therefore two resistors of 4 ohms each means the circuit now has 8 ohms total resistance. Resistance added in parallel becomes halved (assuming both are the same). Therefore two 4 ohms speakers in parallel makes the circuit resistance 2 ohms. As you approach "0" ohms in a circuit you approach a "dead short" which does severely load the amp. A high power amp on a low impedance circuit would tend to pop the load (the speakers) if it was not designed for the power. You did not simply "divide" the power -- you halved the circuit impedance and loaded the amp.

 

[Triton II]

Re: Getting mixed messages on what happens to ohms, watts, when I add speakers.

Music is reproduced by stereo systems as sine waves - a bit like a set of rollers on the ocean. The higher the peak or lower the trough, the louder the music. The speaker cones follow the amplifier's output of sine waves... up to and down to a limit. That limit is the peak power limit of the amplifier. If you turn the amplifier gain up too high the peaks and troughs will be cut off at the power limit and cause a squaring of the sine waves. This forces the speaker cones - especially the tweeters - to change direction suddenly and unnaturally. The result is "clipping".

It sounds dreadful and is more commonly referred to as distortion, although there are many different forms of distortion. Letting your amp go into clipping is a sure way to destroy your speakers. By adding extra sets of speakers to an amp, you risk it clipping earlier and, as stated by a previous poster, you lower the resistance which in turn lowers the ability of the amp to control the speaker cones.

Having an amp that is too powerful for the speakers is not a good idea either, but it's actually preferable to having one that isn't powerful enough. Match your amp's power output to the maximum wattage of the speakers (but be careful, some amps specs are quoted in PPMO or peak power music output and some are quoted in continous or root mean squared power output or RMS and also some speakers are specified in PPMO input wattage whereas others are RMS).

Finally, the amps output is normally designed for speaker impedances of 8 ohms. Some are happy driving 4 ohms and some high end units can cope with 2 ohms. Fortunately resistance is measured proportionally, so if you have two 8 ohms speakers in parallel, the total resistance in that circuit will be 4 ohms. Hope this helps.

TII

 

[380voltz]

Re: Getting mixed messages on what happens to ohms, watts, when I add speakers.

awesome

 

[scooper77515]

Re: Getting mixed messages on what happens to ohms, watts, when I add speakers.

Amp is decent. Rockford fosgate 400x4. Speakers on wake tower say 500 watts but i dont trust the brand name. Sound good and loud. Front speakers are the kickers mentioned above. Not sure what is in that sub box.

Overall it sounds really good and quite loud. Just wondering if something will blow. So far only listening to it around 25-50% volume. Gets loud fast.

 

[380voltz]

Re: Getting mixed messages on what happens to ohms, watts, when I add speakers.

shld suffice for the thump

 

[Lyle29464]

Re: Getting mixed messages on what happens to ohms, watts, when I add speakers.

I know they make heat seeking missiles. Maybe their is hope for a good commercial sound seeking missile

 

[380voltz]

Re: Getting mixed messages on what happens to ohms, watts, when I add speakers.

I know they make heat seeking missiles. Maybe their is hope for a good commercial sound seeking missile

actually ... if im not mistaken torpedos work like this

 

[JustJason]

Re: Getting mixed messages on what happens to ohms, watts, when I add speakers.

Having an amp that is too powerful for the speakers is not a good idea either

I'm going to disagree with that. Usually, in a perfect system, you want to stick the biggest/best amp you can afford. I'm my experience, 90% of the time speakers pop because the amp is distorting, and the speakers are just trying to reproduce that sound. It's not the speakers fault, if you use a cheap amp you give the driver crappy power.

As to ohm load, it all depends on what the amp can handle and that is specified by the manufactorer. For instance, I still run some old school Xtant 202 series amps. Back in the day (10 years ago) they were 300-350 bucks an amp and they are a 50x2 (2 channel) at 4 ohms per channel.
If you drop the load to 2 ohms per channel, the amp becomes 100x2.
If you drop the load to 1 ohm per channel, the amp becomes 200x2 (hence the 202 model ##)
You can bridge this amp, by combineing the left and right channels, and bridge it into as low as a 1 ohm load. Each channel now see's .5 ohm, and the amp is now 400x1.
These amps can do it, and do it all day long as long as i'm not clipping the amp. But you get what you pay for.


What we used to do for fun on slow days is plug subwoofers into the wall Eclipse aluminum 12's will go 4 or 5 minutes before they meltdown.
That's free air, just sitting on the hot top. What ends up happening is the spider eventually starts to tear and the voice coil starts to bottom out and short against the pole plate.

Same sub in a sealed box would go 1-2 hours before they went. The air pressure behind the driver helps control the suspension of the driver. And keeps it from bottoming out. It isn't until heat expands the voice coil enough that it starts shorting inside. We've had a few fires doing this.
We also had a few quick fires when you soak a paper cone subwoofer with starting fluid beforeyou plug it in (make sure you use a looooong extension cord!!)

Just to give you an idea of that kind of power, let's do ohms law and watts law.
Wall power is 120V, the speaker used is 8 Ohms.
OHMS LAW E~I/R
120V/?=8
120V/8OHMS = 15 amps of current to the speaker.

Now we know the current, lets plug it into watts law.

P~I/E
?~15X120
120VX15A = 1800

So thats 1800 real watts that we are dumping into a sub driver at a 60 hertz tone (good bass tone) (wall out power is 60 cycles per second)

Its so loud that if you have neighbors they will call the cops.
If you try it with a 4 ohm driver you will end up doubleing it's wattage (to 3600 watts). But you also double the current, and usually you trip the breaker before the sub goes.

 

[fishrdan]

Re: Getting mixed messages on what happens to ohms, watts, when I add speakers.

Best Buy installation guy said....that they would be receiving the power at 2 ohms each, stressing them out and possibly blowing them if I listen to them at too high a level.

If you have 4 ohm speakers, that statement is wrong. The speakers are 4 ohm, no way to make them 2 ohm speakers. But,,, if you parallel 2- 4 ohm speakers they will present a 2 ohm load to the amp, each speaker is still 4 ohm though.

It all depends on how you wire the speakers and what the amp can handle. With that RF amp I'd suspect that it can handle a 2ohm load, but you need to check the spec sheet. If the amp can handle a 2ohm load, I wouldn't shy away from running 2 paralleled 4 ohm speakers on each channel. Check RF's website, they have manuals for their older amps.

I agree with Jason about distortion, it's usually a problem with the head unit or amp clipping,,, unless you have some really crappy speakers.

 

[rwidman]

Re: Getting mixed messages on what happens to ohms, watts, when I add speakers.

...........Best Buy installation guy said that adding another set of 4ohm speakers to the existing set on the same channel (right channel is running two speakers on the right, left running two speakers on the left) that they would be receiving the power at 2 ohms each, stressing them out and possibly blowing them if I listen to them at too high a level..............

Did he really say that or did he say it would overload the amplifier and possibly damage it? Are you sure what you posted is what he said?

Connecting a 2 ohm load to an amplifier rated for 4 ohms might damage it if it's used at high power for long periods. There will be no damage to the speakers.

 

[John_S]

Re: Getting mixed messages on what happens to ohms, watts, when I add speakers.

I agree with the others that your amp is what is at risk. It may have good protection circuitry, but you may not want to try to prove it works well. You are also driving sub with the same amp. A different channel, but probably a common power supply. Subs hog power and cause dips in voltage, which can cause clipping, which can kill drivers, particularly tweeters.

My suggestion is to remove the subs off the rear channels, and put the tower speakers on them. Add a new sub-amp and you are good to go, assuming your head unit has a sub-out or extra pre-amp out.

 

[John_S]

Re: Getting mixed messages on what happens to ohms, watts, when I add speakers.

What we used to do for fun on slow days is plug subwoofers into the wall Eclipse aluminum 12's will go 4 or 5 minutes before they meltdown.
That's free air, just sitting on the hot top. What ends up happening is the spider eventually starts to tear and the voice coil starts to bottom out and short against the pole plate.

Same sub in a sealed box would go 1-2 hours before they went. The air pressure behind the driver helps control the suspension of the driver. And keeps it from bottoming out. It isn't until heat expands the voice coil enough that it starts shorting inside. We've had a few fires doing this.
We also had a few quick fires when you soak a paper cone subwoofer with starting fluid beforeyou plug it in (make sure you use a looooong extension cord!!)

Just to give you an idea of that kind of power, let's do ohms law and watts law.
Wall power is 120V, the speaker used is 8 Ohms.
OHMS LAW E~I/R
120V/?=8
120V/8OHMS = 15 amps of current to the speaker.

Now we know the current, lets plug it into watts law.

P~I/E
?~15X120
120VX15A = 1800

So thats 1800 real watts that we are dumping into a sub driver at a 60 hertz tone (good bass tone) (wall out power is 60 cycles per second)

Its so loud that if you have neighbors they will call the cops.
If you try it with a 4 ohm driver you will end up doubleing it's wattage (to 3600 watts). But you also double the current, and usually you trip the breaker before the sub goes.

What did you do on the REAL slow days?

Sounds like an experiment I might have done back in the day. Just never thought of it. Then again, sub drivers back then were just large 15" speakers, not the large magnet, long throw, large voice coil, ones they have today.

 

[rwidman]

Re: Getting mixed messages on what happens to ohms, watts, when I add speakers.

I know they make heat seeking missiles. Maybe their is hope for a good commercial sound seeking missile

We should design one!

The guy has a 1200 watt audio amplifier on his boat and he is worrying that he'll damage his speakers at full power. What about damaging his ears?

What about other people on his boat? Nearby land owners?

 

[madgadget]

Re: Getting mixed messages on what happens to ohms, watts, when I add speakers.

I bet this boat is running a 4ohm sub in mono bridged across two of the four channels.
Almost any even half decent amp will take 2ohm load these days.

So on probability ignoring all the probably too complex explanations above (for some) if you connect those extra speakers, I bet it works fine


Oh and off topic kind of, a friend over here has a PA system that will draw easily peaks of over 120A at mains voltage. Oh and don't forget we used 240v, I wouldn't call it a massive system either but its pretty impressive all the same.

 

[scooper77515]

Re: Getting mixed messages on what happens to ohms, watts, when I add speakers.

First off the sub is connected across the two rear channels.

Second, i am not that obnoxious guy who plays hip hop cussing songs full blast across the lake. The wife and i turn it up just enough that we can hear it while floating. And clean music. (She is an elementary librarian, i am a child/adolescent psychfotherapist, so we are typically clean). On the run we go a little louder justso we can hear it over wind and engine.

 

[John_S]

Re: Getting mixed messages on what happens to ohms, watts, when I add speakers.

First off the sub is connected across the two rear channels.

That would be bridged mode, where each channel is driving half the load. Your amp is running fairly hard, especially if a 4 ohm sub.

Given your amp is protected and you haven't tripped it yet, you could probably get by as long as you keep the volume low. Alternatively, you could wire the two sets of speakers in series. Not the best, and you will compensate by turning volume up higher. Or add some sort of switching so you can power the tower speakers or your console ones, but not both. You don't need the tower ones while you are underway (unless pulling a boarder). Overall, the better solution is still another amp.

 

[380voltz]

Re: Getting mixed messages on what happens to ohms, watts, when I add speakers.

... an active xover for the sub driven by a different amp wld be also nice