IDriveHonda

OK, here is the scenario, I have 3 subs that are single voice coil. 2 of the subs are 12 ohm and the third is 8 ohm. These are going to run parallel to a 2 channel amp mono. I have calculated this out to be a 3.5 ohm load on the amp, but is this OK to do or will the 8 ohm sub get more power than the other 2? Let me know if I am just totally wrong here or give me some guidance. Thanks.

nsxxtreme

You would actually have a 3.43 ohm load to the amplifier. If the amplifier is bridged the amp will see half the the load. So the amplifier will see 1.71 ohms.

The obvious answer to your last question is yes the 8 ohm speaker will get power.

rjr162

the 8 ohm will get a little more since electricity likes to take the path of least resistance.

nOOber

[edit] d-oh wrong thread !

PupaScoopa

May I ask if all three woofers are the same? If not, they won't sound very good together.

acuradriva

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by nsxxtreme &raquo;</TD></TR><TR><TD CLASS="quote">You would actually have a 3.43 ohm load to the amplifier. If the amplifier is bridged the amp will see half the the load. So the amplifier will see 1.71 ohms.

The obvious answer to your last question is yes the 8 ohm speaker will get power.</TD></TR></TABLE>

I didn't do the calculations just using your #'s but, each channel will see 1.71 not the amp. if an amp is 4 ohm mono stable than it is 2 ohm stereo stable so its basically the same thing. it will be a 3.43 mono load.

IDriveHonda

All of the woofers are JL audio and I found a solution to my problem! I picked up a matching 10 off of ebay for cheap so thanks for all of your help.

nsxxtreme

When you bridge an amplifier the amplifier see's half the load. This is why ratings are given in both stereo and mono. They are usually seperated by a factor of two.

There is a big difference between a 4 ohm load and a 3.4 ohm load exspecially at high voltages.

acuradriva

amplifiers only "see" what is there. if you have a 4 ohm load the amp sees a 4 ohm load. if you want to break it down each channel will see 2 ohms but why do that? if you have a dvc with 2 ohm coils you can hook it up in series and bridge the amp. you will get the same amount of power as if you hooked up 1 coil per channel.


Modified by acuradriva at 6:27 PM 10/8/2003

nsxxtreme

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by acuradriva &raquo;</TD></TR><TR><TD CLASS="quote">amplifiers only "see" what is there. if you have a 4 ohm load the amp sees a 4 ohm load. if you want to break it down each channel will see 2 ohms but why do that? if you have a dvc with 2 ohm coils you can hook it up in series and bridge the amp. you will get the same amount of power as if you hooked up 1 coil per channel.


Modified by acuradriva at 6:27 PM 10/8/2003</TD></TR></TABLE>

There is an error in your logic you have half the impedence on each channel to get the same power as the bridged channel. Put 4 ohms on each channel then put a 4 ohm bridged load on the amplifier compare the output.

It is an excepted practice in the "car stereo" and other audio industries to say the the amplifier "sees" half the load. This is done because it does not require the tech or anyone else to care how the internals of an amplifier works. What really happens is you have two supply rails inside an amplifier +Vcc and -Vee. Normally each channel uses one of these rails and a point considered 0. Not necissarily ground.
When you bridge an amplifier you use both +Vcc and -Vee so you now have twice the voltage swing for a given input. I could explain how this "excepted" rule came about but dont have the time. I'll leave this up to you. Try calculating the current thru the coil and you will see where it came from.

You will not be able to hook a 2ohm bridged load to an amplifier that is 2ohm stereo stable. On an amplifier you can only hook up twice the load of the min stereo load to a bridged amplifier.

acuradriva

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by nsxxtreme &raquo;</TD></TR><TR><TD CLASS="quote">

You will not be able to hook a 2ohm bridged load to an amplifier that is 2ohm stereo stable. On an amplifier you can only hook up twice the load of the min stereo load to a bridged amplifier.</TD></TR></TABLE>

Exactly. so if an amp is 4 ohm mono are you telling me that you can't hook up a 4 ohm sub to it because the amp will "see" 2 ohms. or do the manufacturers know this? so they tell the public that a 2 ohm stable amp is only 4 ohm stable to compensate for when the amp "sees" 1/2 the load. Your thinking makes no sense. 4 ohms is four ohms and the amp "sees" what ever is hooked up to it.

acuradriva

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by nsxxtreme &raquo;</TD></TR><TR><TD CLASS="quote">

There is an error in your logic you have half the impedence on each channel to get the same power as the bridged channel. Put 4 ohms on each channel then put a 4 ohm bridged load on the amplifier compare the output.

</TD></TR></TABLE>

This is exactly what i am talking about you get differennt power because one is bridged and 1 is stereo. say 4 ohm mono will get you 500 watts, 4 ohm stereo would be 125x2. its not because the amp sees half on the bridged set up. Its because it is half of that stereo set up.

Maybe these guys can explain it better for you. http://forum.sounddomain.com/f...00005


Modified by acuradriva at 12:13 PM 10/9/2003

nsxxtreme

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by acuradriva &raquo;</TD></TR><TR><TD CLASS="quote">

Exactly. so if an amp is 4 ohm mono are you telling me that you can't hook up a 4 ohm sub to it because the amp will "see" 2 ohms. or do the manufacturers know this? so they tell the public that a 2 ohm stable amp is only 4 ohm stable to compensate for when the amp "sees" 1/2 the load. Your thinking makes no sense. 4 ohms is four ohms and the amp "sees" what ever is hooked up to it.</TD></TR></TABLE>

A 2ohm stable amplifier will only be able to power a 4ohm bridged load.

nsxxtreme

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by acuradriva &raquo;</TD></TR><TR><TD CLASS="quote">

This is exactly what i am talking about you get differennt power because one is bridged and 1 is stereo. say 4 ohm mono will get you 500 watts, 4 ohm stereo would be 125x2. its not because the amp sees half on the bridged set up. Its because it is half of that stereo set up.

Maybe these guys can explain it better for you. http://forum.sounddomain.com/f...00005


Modified by acuradriva at 12:13 PM 10/9/2003</TD></TR></TABLE>

No that is not why.When you bridge an amplifier you use both supply rails. So the voltage doubles. If I have time later I will try to post pictures to try to simplify it and make it easier to understand. Save comments till the end.

acuradriva

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by nsxxtreme &raquo;</TD></TR><TR><TD CLASS="quote">

A 2ohm stable amplifier will only be able to power a 4ohm bridged load.</TD></TR></TABLE>

a 2 ohm stereo stable amp would only be able to powre a 4 ohm bridged load. did you even read that link i posted?

This is from http://www.eatel.net/~amptech/...g.htm

2 Ohm Stereo vs 4 Ohm Mono Loads

There seems to be some confusion as to why a 4 ohm mono and a 2 ohm stereo load are the same, as far as the amplifier is concerned. When two 4 ohm speakers are connected to each channel of a 2 channel amplifier, the amplifier is capable of driving the speakers with half of the total power supply voltage. If the amplifier has a power supply which produces plus or minus 20 volts, it will not be able to drive the speakers on a single channel with any more than 20 volts at any point in time. If we have a 2 ohm load on each channel, at the highest point on the waveform the amplifier will apply 20 volts to the speaker load. Remember that we are only considering a single point in time for this example. If we go back to ohms law...

I=V/R
I=20/2
I=10 amperes

If we take a single 4 ohm speaker and bridge it on that same amplifier, the amplifier will be able to apply twice the voltage across the speaker. This is because while one speaker terminal is being driven positive (towards the positive rail), the other terminal is being driven towards the negative rail. This will allow the entire power supply voltage to be applied to the speaker's voice coil. It will now be able to drive the 4 ohm speaker with 40 volts instead of 20 volts in the previous example. Back to Ohm's law...

I=V/R
I=40/4
I=10 amperes

The same amount of current flows through the output transistors whether the amplifier is driving a 4 ohm mono load or 2 ohm stereo load. As far as the amplifier is concerned, they are the same load.


--------------------------------------------------------------------------------


NOTE:
Some people say that when an amplifier is bridged onto a 4 ohm load, it 'sees' a 2 ohm load. While it is true that the same current flows whether the amp is bridged on a 4 ohm load or a 2 ohm stereo load, the amplifier is driving a 4 ohm load across its outputs. A single 4 ohm speaker can never be a 2 ohm load.


Modified by acuradriva at 3:42 PM 10/9/2003

nsxxtreme

I don't need to read a link I am an EE, I think by now I know ohms law. I also know how the internals of an amplifier work. So what we are arguing here is simantics. As I mentioned before it is easier for people to understand than trying to teach them how an amplifier works. In the end you accomplish the same thing porperly sized amps and speakers. One method requires less knowledge from the end user. How many people do you know go into a stereo shop and ask what the voltage output is on an amplifier. Or ask What are the rails of the amplifier. How many people do you think would put a 2 ohm load on a bridged amplifier if you tell them it is 2 ohm stable. There are a lot of not exact science in the audio industry. For example power output is measured differently through out the industry. When if you wanted to be **** there is only one way to measure it. This is what happens after it get in the hands of marketers.

What does two ohm stable mean? This is another example of a made up term. There is no such term used when designing these things.


Modified by nsxxtreme at 2:08 PM 10/9/2003

rjr162

you both realize you're saying the same thing.

NSX: you're saying a 2 ohm stereo stable amp won't be 2 ohms stabled bridged, which is true. He's saying the amp is going to see 4 ohms bridged and be fine... I think you are both mis-reading each other.

Manu's list amps as 2 ohm stable as a marketing trick... which they really are but in stereo. Basically a 2 channel amp is two mono amps sandwitched together. Think of it that way. most mono amps are two ohm stable, so each channel is "two ohm stable".

as for the rails, just think of a transformer.

a 10:1 transformer that takes 120 volts to 12 volts typically has 2 input wires (for the 120) and 3 output wires. The output wires are wound so the voltage difference between the first and 2nd wire is 6 volts, and the difference from the 2nd wire to the third wire is -6 volts. disreguarding the fact the output from the tranny is AC, you could hook a + wire to the 2nd wire, reguarded as 0, and negitive to the 3rd wire, and you'll end up with 6 volts. Same with using the first for pos and the middle (0) for neg. 6 volts. So if you link between the first wire and the last wire, not using the middle (0), the voltage difference between the two outputs is 12.

Sort like using stereo channels on an amp compaired to bridging the outputs.
The stereos would represent 6 - 0 - -6 outputs, which if you total both "channels" is 12, and if you bridge between the outer two it ends up being 12 volts.

acuradriva

say the amplifier power supply puts out +/-20 volts. a 2 ohm speaker will produce 10 Amps. If the internal componets cant handle more than 10A then the amp is said to be stable at 2 ohms. if the load was dropped to 1 ohm the current would double with the voltage remaining constant.

but like i said in the beginning if you want to make it easier for new people to understand what you are talking about the amp "sees" 1/2 the load on each channel. a load of 3.43 would be like 1.71 per channel.

nsxxtreme

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by rjr162 &raquo;</TD></TR><TR><TD CLASS="quote">you both realize you're saying the same thing.

NSX: you're saying a 2 ohm stereo stable amp won't be 2 ohms stabled bridged, which is true. He's saying the amp is going to see 4 ohms bridged and be fine... I think you are both mis-reading each other.</TD></TR></TABLE>

No I am being a typical engineer I am sure you know what I mean

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by acuradriva &raquo;</TD></TR><TR><TD CLASS="quote">say the amplifier power supply puts out +/-20 volts. a 2 ohm speaker will produce 10 Amps. If the internal componets cant handle more than 10A then the amp is said to be stable at 2 ohms. if the load was dropped to 1 ohm the current would double with the voltage remaining constant.

but like i said in the beginning if you want to make it easier for new people to understand what you are talking about the amp "sees" 1/2 the load on each channel. a load of 3.43 would be like 1.71 per channel. </TD></TR></TABLE>

No you would get 20 amps 40/2=20. The word "stable" is another made up word. Audio amplifiers are voltage amplifiers which means the voltage is what is going to be amplified. You have two type of amplifiers inside an audio amplifier. The first stage takes the 14.4 V battery voltage and amplifies it to +60 and -60 by using pulse width modulation. This now becomes the rail voltages. You know have the second stage of amplification which takes the input and amplifies it by a gain factor. Say your input is 1V. Now the amplifier has a gain of 35.56 dB or 60 you take that 1v and multiply it by 60 you now have reached your maximum voltage swing. Any input beyond 1v and you have "saturated" your amplifier. The word stable comes from being able to use the entire input voltage swing without saturating your amplifier. When you bridge an amplifier you would have a gain of 120. So that 1V input would now be multiplied by 120. It also comes from as you metioned a certain amplifier can only supply so much current. If you keep droping the impedence the current will keep going up. This is usually caused by th PWM power supply not being able to source enough current and not the actual audio amplifiers problem. There are other factors that create "stable" issues but I simplified it here.

I think you are missing where the voltage doubles. When you bridge an amplifier you double your supply voltage. Current is just a side effect from the load and voltage supply.

Now which is easier to understand all of our dribble or the other method. How many people do you think actually care what is going on. There are so many problems with terminolgy in the audio industry that I am not going to try to fix them. Exspecially when you have millions of advertising dollars going up against you. As long as someone knows that they can't run a 2 ohm bridged load on a 2 ohm "stable" amplifier that is all they care about.