The cable I was refering to is connecting the input side of the amp and has nothing to do with the outputs.

I answered this thread because I had every good intention to help our friend. However, it seems as my six years working as a car audio installer, as well as my graduate degree in Electrical Engineering and my four years working in the Engineering field,(most of which has been devoted to the design of amplification stages), are not enough credentials for answering such a simple question. Since there are other people who are way more knowledgeable than myself, It seems appropriate at this time to move on to some other subject. I will not be checking this thread again.

public enemy - sorry, thanks for all your help
kuan - thanks

my next question is....what does it mean to be clipping? and is there a way to measure watts? what is the benefit of having more watts?

Publicenemy,

Please forgive me if I've come across as argumenative. If you read my posts, I seem to be absolutely sure that I know how to bridge an amplifier. I even tried to explain why I thought I was correct. I only know what I know through high school physics class. I only had one question throughout this whole thread which was: How come you can't bridge an amplifier by connecting the output section in parralel? There's a good possibility that I'm wrong, and if I am, I want to know why. That's all.

Kuan

ISh: Clipping means distortion.

Crutchfield sells or used to sell a triway or trimode speaker-level crossover that takes a stereo (2 channel) output and converts it to stereo high pass channels and a mono low pass channel. If this device can be used with any amp, then Ish can use it with his amp to bridge the output for a subwoofer. It shouldn't matter that the high pass channels are unused.

I think public enemy means that an amplifier is a lot more complicated than a battery, light bulb or speaker, and will likely be damaged if the outputs are wired together in series or parallel. So don't try it

Sixto
91 300SE
... definitely not an electrical engineer or auto sound pro

hi everybody,
i have a on and off switch for "hi pass". is this what were talking about? other than that i have no other switches. so far this is what i tried...
1) connecting both pos from both channels into the pos terminal of the sub, same with the neg...all i get is basically nothing but a weird sound.
2) i connected the neg from one channel into neg of sub and pos from the other channel and into sub. the sub works but i'm not sure if it has 300watts. how do i know?

what should i do(try) next? sorry if i missed any info from the early post! thanks again

Alright folks, everyone who has met me knows that patience is not one of my virtues so that is why I decided to not continue being part of this discussion. However, it seems as it would be more appropriate for me to contribute a few more things to the subject for the purposes of clarifying a few things as well as providing some information on some basic electricity concepts.

So here we go:
First of all, some very basic electricity principles: The power the speaker consumes, (I should also point out here that whenever I use the term power in this reply, I mean RMS power), is equal to the voltage difference across the speaker terminals squared and divided by the impedance of the speaker. (V^2/R). Example: If there is 10 volts across your 4 OHM subwoofer then the power consumed by the subwoofer would be 10 squared which obviously equals 100 divided by 4 which equals 25. So, your subwoofer is consuming 25 Watts RMS from your amplifier. Now on to the next level. Lets assume that we are cranking up our amplifier to produce a voltage difference of 20 Volts across our same speaker. Now the power jumps to 20 squared which equals 400 divided by the 4 OHMS of our speaker which now equals 100 Watts.
Now lets move on to another basic concept which will come handy in a few moments. This is the basic principle of connecting voltage sources in parallel and/or in series. For the purposes of this reply (or I should say article), an amplifier will be considered a voltage source. Now if we have two identical voltage sources for example two batteries each one of which is 10 Volts and each one of which can supply a current of up to, lets say, 2 Amperes, and we want to use them to power a hypothetical light bulb, we can do the following things:

1) We can use only one of those batteries to drive our bulb. In this case our bulb will light up as a result of the 10 Volts that the battery developed across it and consequently it will consume a current from our battery. The amount of the current that it will consume will depend on the internal resistance of the bulb. Obviously we have selected a bulb whose internal resistance is such that it will never require a current of more than 2 Amperes otherwise our battery will go "BANG...".

2) We can connect two of those same batteries in a serial configuration. A serial configuration means attaching the positive pole (+) of one battery to the negative pole (-) of the other battery and then connect the remaining negative and positive poles to our bulb. In this case our bulb will light up but instead of the 10 Volts that were across it before, it now has 20 Volts because our batteries are connected in series and the voltage is doubled. Obviously our bulb will now shine much brighter. However there is a problem. The doubling of the voltage across it is accompanied by a doubling of the current that it will require from our batteries. This is due to the well known OHM'S Law which states that any time we double the voltage across the SAME load the current also doubles (R=V/I). So now our bulb is asking for twice the 2 Amperes in other words it is asking for 4 Amperes. But wait a minute. Our batteries are connected in series in other words whatever passes through one of the batteries will also pass through the other. In other words, now 4 Amperes will have to pass through each battery. You see, its similar to the links of a chain. If the weight hang by a chain is 100 lbs then these 100 lbs pass through every link of the chain. If the load increases to 300 lbs now 300 lbs are passed through every link of the chain. Same here: 4 Amperes pass through each of our batteries. But as we said in the beginning our batteries can only tolerate 2 Amperes. So, connecting our batteries in series in order to power this bulb, will damage them.

3) We can connect our batteries in parallel. That means connecting the positive (+) pole of one battery to the positive pole of the other and the negative (-) pole of one battery to the negative pole of the other. Then, we connect these two positive poles (which have now been connected into one) to one end of our bulb. In a similar way we connect the two negative poles (which have now been connected into one) to the other end of our bulb. Now our bulb has 10 Volts across it and consequently according to OHM's Law will pull a current of 2 Amperes as in case (1) above. However, in this case we have increased the ability of our batteries to provide current to twice that of one battery, in other words our batteries can provide up to 2 times the 2 Amperes which obviously equals 4 Amperes. But do we make use of it since our bulb still only requires 2 Amperes? NO, of course not. Using the chain example mentioned above we are still using the same 100 lbs weight but now we are hanging it from two identical chains one connected in parallel with the other. Our chains can now hold twice the weight but we really do not make use of this capability.

Now lets see how this applies to our speaker example: Connecting the two amplifiers in series would double the available voltage across our speaker in the same way it was doubled across the bulb. Now, as in the case of the bulb, our speaker will require twice the current which will destroy our amps the same way the bulb did to its batteries.

What if we connect the amps in parallel? Again in total analogy to our bulb case number (3) above, our speaker will see the same voltage that would see with only one amp across it which consequently will still make it pull the same current as with one amp. Since the voltage across the speaker as well as the current are still the same, our speaker will still consume the same power. So putting the two amps in parallel will not double the power.

O.K. folks, those of you that are still reading, I have tried to make things as simple as possible so that everyone can understand them. In reality things are more complicated but getting into this is totally out of the purposes of this discussion and anyway requires some degree of intermediate level mathematics. The reason is that the output of an amplifier is actually producing AC (alternating current) in contrast to the DC current produced by a battery. AC currents and voltages do not add in the simple way that DC voltages add. That is because of a property of the AC current called "phase". So unless our two currents are "in phase" with each other, they can not be added in such a simple way.

One last thing: There are other reasons, too, that the amplifiers can not be connected in parallel, but again this is getting complicated and out of the purposes of this discussion. Suffice it to say, that an amplifier possess properties such as very low output impedance and therefore connecting two of them in parallel will make one amp act as a load on the other, in other words the first amp will try to consume all the output current that the second will produce. This in turn will place a tremendous strain on the second amp and will probably destroy it unless this second amp has a protection circuit like this Kenwood has. In this case the protection circuit will sense the tremendous strain on the amp and will kick in to protect it as it happened when "ISh" connected his two amps in parallel and heard that "Thump, thump..." sound.

O.K. enough for now, I am getting seriously hungry so I am stopping here. I will check again, in case anyone requires any more info.

wow that must be the longest post i have ever read! haha okay...just to make sure that everybody is on the same foot. i am using ONE amp with FOUR channels, i am trying to put TWO channels together so i can have double the watts. after reading the facts on series and parallel, is it saying that it isn't possible? or doubling the watts won't do anything?

Ish, when you are taking the negative (-) from the left output channel and the positive (+) from the right output channel you are not connecting the amplifier in series nor in parallel. The two channels still work independently, however by using the (+) of one channel and the (-) of the other you are able to get substantially more power. However, as I mentioned in an earlier post, doing this only takes care of the output stages. You also need to wire the input of the two channels correctly. As you said, you were only using one channel to power the subwoofer and that the other channel was disconnected. That means that the output of one channel was NOT connected to any speaker. How about the INPUT of this non-used channel? Was there an RCA cable going to it? If it was, then disconect it and let it hang there because it is NOT going to be used again.

In order to bridge the two channels of the amp, you should first put them in MONO mode. This is usually accomplished by a switch. Now in your case there is no such switch so you have to do this manually. This is where that Radio Shack cable comes in. You will need a cable that has ONE FEMALE RCA plug on one side and TWO MALE RCA plugs on its other side. This cable takes the input from the female RCA plug and splits it into the two male RCA plugs. (This is a small cable aproximately 6 inches long with three plugs hanging from it and if I remember correctly it is either black or grey in color). The Radio Shack guys should know what you are talking about.

Connect these two male RCA plugs of the Radio Shack cable to the inputs of the two channels that you are going to bridge.
Also connect the female RCA plug of the Radio Shack cable to the RCA plug that you had attached to the channel that was driving your subwoofer before.
Thats it. Of course, if you have not already done so, you will also need to connect the negative (-) output of the LEFT channel to the (-) of your subwoofer and the positive (+) output of the RIGHT channel to the (+) of the subwoofer.
Now your amp should be bridged and you should be able to get way more power than before.

Again, I need to caution you. This is the way that MANY but NOT ALL amps in the market get bridged. Some amps have different output stage design and bridge differently. Some others do not bridge at all. That is why I keep insisting that you should contact Kenwood's technical support and find out in what way your amp gets bridged. However if you want to experiment yourself do as I am describing above and you will PROBABLY be fine.

Finally as far as measuring the output power of the amp, well this is done in the following way: The amplifier's output is not connected to the speaker but instead it is connected to a dummy load (this is a load comprised of non-inductive resistors that have a total resistance equal to the impedance of the speaker, in this case 4 OHMS). Then the amp is driven with a sinusoidal wave of a known frequency (obviously a frequency that the amp can produce) and the input level is raised to the point where the amplifier JUST starts clipping. It has to be at this exact point nothing more nothing less. At this point the voltage at the output of the amp is measured and then the power is calculated by the formula I gave in the beginning of the previous long post, (Voltage squared over resistance).
This is nothing very difficult, however it requires the use of an oscilloscope in order to be able to determine the EXACT point were the amp starts clipping. I assume that you do not have such a scope handy but if you do then you can calculate the power by using the above steps.

[Edited by public enemy on 04-25-2001 at 02:04 AM]

THANKS public enemy!
i'm gonna give that a try later tonite, i'll keep you guys informed...

For the record, clipping is when an amplifier's output reaches the maximum voltage that the power stage is able to provide. The sine wave now has a nice flat spot at the top and bottom of it. In other words, DC voltage. Running DC voltage through a voice coil on a speaker produces tremendous heat which WILL melt the insulation and thus short circuit the coil. When an amp clips, it is no longer reproducing the signal that was provided it. Slight clipping can be inaudible in a subwoofer, so setting an amplifier's gains correctly is a must for prolonged equipment life.

Publicenemy,

Thanks for the explanation! It didn't occur to me that connecting the two sections in parallel would be like having one try to drive the other. That should have been quite obvious.

Kuan

Hi everybody...sorry it took me sooo long to figure everything out. okay this is what i did. it used one of those 1 to 2 connected and connect my amp. then i connected the right speakers pos to the sub and the left speakers neg to the sub...so far right? to me it sounds the same, is it supposed to be unnoticable? i also contacted kenwood by email and they responded that the model isn't valid. interesting.... so they were absolutly no help to me. thanks to everybody that replied!!!

It seems as you did the correct thing and everything is fine. If the connections were wrong it wouldn't have worked. Now as far as not playing louder is concerned, here is what is probably happening:
When you bridge your amp on a 4 OHM speaker (I assume that your subwoofer is 4 OHM, most are) the amp now plays at 2 OHM.
There are two kinds of "2 Ohm" amps in the market. The one that claims it is "2 OHM stable" and the other that claims it produces more power at 2 OHMS. The first one can play at 2 OHMS with no problem but it will not produce any more power than it would at 4 OHMS. The second one will not only play at 2 OHMS but it will also produce significantly more power (up to twice the power it produces at 4 OHM).
Your amp probably belongs to the first category and although it will play at 2 OHM it will not give you any more power. If that is the case, then I would use the regular 4 OHM configuration (the one you had before) because it will give you SLIGHTLY better quality bass.

You may have to adjust the gains on your amplifier. The gains may have been set too low initially and you can't tell the difference.

One good way to tell whether you are getting enough power or not is to connect the subwoofers in 4 ohm mode (not bridged) and drive the speakers until clipping is heard (sound begins to distort...although admittedly this is more difficult to determine with subwoofers). After determining the level at which clipping takes place, subsequently connect the subwoofers to the amp in bridged mode. You *should* be able to play the subwoofers louder. Unless your subwoofer has far less power handling than your amp, you would be able to play louder due to "cleaner" power.