Contour Enthusiasts Group Archives Forums Modifications Audio The effect of parallel versus series speaker wiring on amps.

My subwoofer amp, a Profile BAJA 100 a CC special, at one time powered one rear deck mounted TC sounds 6.5 inch midbass driver playing the role of free air subwoofer. The amp at 75 watts per two channels and 150 watts bridged proved good enough for powering that driver setup
Over the weekend I took a 6X9 speaker box and placed two 6.5 inch Audiobahn AMD60 onto drilled sides of the box and then mounted the box below the rear deck opening. These free air mounted driver each have a 3ohm rating. I wired each plus and minus terminal directly to the amp. Did I just described a parallel circuit or a series circuit. Parallel I think. When I began to play the stereo again I was really happy with the additional 3dbs of sound. Yes I still could bottom both drivers but the added bass was a plus. Then it happened. While playing some bass heavy music the bass output simply dropped. What had happened. It seems that the heat sensing circuit breaker tripped for all I had to do was turn off the stereo for a while letting the amp cool and the sub amp came back on. So I pose this question. Should I wire the speakers in series so that the amp sees 6 ohms or should I get a fan to mount on the amps heat sinks to circulate the heat better when the amp sees 3 ohms from drivers wired in parallel.

Lastly what is the cheapest 1 ohm stable amp on the market for I ask this question because I plan to add two additional drivers in the future mounted in another 6X9 inch box mounted on the other side of the rear deck in free air form.

I also was consider whether buying a JBL b300.1 amp would fix my problem but I have not decided yet.

If I wired the speakers in series I will resolve resistance issue but will I not also at the same time lower the spl output of the two driver combination?

All comments are welcome.

Is each speaker connected to the same + an - terminal on the amp?
If so, then each speaker is in series with the amp. So you're amp is running 100W to each speaker at 3 ohms.
If the speakers are both connected to the same + and - terminal, then you are in parallel. So you're amp is running 1.5 ohms and providing 200W.
If this is the case, then this is why your amp cut-out. It is unable to provide that much power for long periods of time. Also putting a 1.5 ohms load on an amp no designed to go that low is harmful to the amp.

I am confused for you seem to say the same thing twice. Yes the amp has two wires going to each positive and negative terminal one positive wire from each driver and one negative wire from each driver. So is this a series circuit or parallel circuit Sleeper?

Tripping the amp's heat sensing fuse too many times will or will not hurt the amp?

For those of you out there that are members of the treat your amp properly campaign I just wanted you guys to know until I resolve this issue the volume is turned down some what (so that the amp will not shut off) in the car for now.

Tell me Sleeper what is/are the pros and cons of series and parallel driver wiring to an amp if any?

Parallel:
Speaker 1 plus -> Amp +
Speaker 2 plus -> Amp +
Speaker 1 minus -> Amp -
Speaker 2 minus -> Amp -
Total impedance w/ two 4-Ohm speakers: 2 Ohms

Serial:
Amp + -> Speaker 1 +
Speaker 1 - -> Speaker 2 +
Speaker 2 - -> Amp -
total Impedance w/ two 4-Ohm speakers: 8 Ohms

Now, if you BRIDGE the Amp, each of the two bridged channels "sees" only half the impedance of the above, i.e. 1 ohm/4 ohms respectively.

Wiring two 3-ohm speakers in parallel will produce 1.5 ohms in normal mode, or .75 ohms per channel in bridged mode.

Many Amps are only 2-Ohm stable, i.e. they will not handle the current that comes with a lower impedance setup for a very long time. The higher current produces more heat and the amp can not dissipate the heat quickly enough.

It is normally not a problem if the overheat protection shuts the amp off multiple times (my sub amp does it quite regularly when I run it at full power for an extended period of time). However, if the amp heats up too quickly you can still fry some transistors before the protection circuit reacts.

HTH
Joerg

Yes Joerg Walzenbach I think I understand for I do have a Parallel circuit here. Since you so clearly explained the difference between series and parallel as far as what the amp sees please explain other benefits of each in particular the difference within output level for if I am correct with a parallel connection there is no loss of sound pressure level there is a gain actually where as with a series connect there is a loss within sound pressure level. Am I correct here Joerg?

To start, if you amp is not rated for 1 ohm opperation, then you are damaging your amp.
This is probably the case, since your thermal protection keeps shutting off your amp.
You may end up damaging your speakers permanently as well too.
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The main benefit with a parallel circuit is more power, if your amp can put it out. Parallel is better for bass. The main con is the stress on the amp.
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Series results in less power, but puts less stress on the amp. Series circuits are more suited for higher frequency ranges.
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My suggestions to you are;
1) run each of your 6.5" speakers on a seperate channel of a 4 channel amp, providing
75W/channel.

or

2) get a 2 channel providing 150W per channel, and run two speakers in series on each channel of the amp.

Both suggestions will give you 100W of power and won't over stress an amp.

I agree with sleeper on this.

Here is some more background info:

Your amp is driven from the 12 Volts your car battery provides. There is a power supply inside the amp that jacks up the 12 V to something in the 30-40ish range. This is done to reduce the electric current that has to be delivered by the amplifier's transistors. When you look at the formula used to calculate electrical power

P(Power[watts]) = U(Voltage[volts]) * I(Current[amps])

You can see that you can either increase voltage or current to produce more power.

However, transistors for high-current (many amps) applications are expensive (or not even available), so the designers of the amp use transistors that can only handle so much current.

This is, btw, the reason why the output of a HU without an external amp is so limited. The HU does have an internal amp (usually not individual transistors, but rather an integrated circuit), but it runs on 12V only, and if it were to deliver more than the peak 4x40something watts it would fry the internal amp, since the integrated circuit amp inside the HU can not handle the higher current.

Generally, the more current you run through any circuit, the more heat it will produce, until - eventually - some component in the circuit is destroywed by over-heating. This is why the availability of high-current transistos is limited; there are just none available that can physically handle very high currents. Anyways, I get carried away here.

So, the more viable way to increase output power is to increase the Voltage supplied to the Transistors of the amp. That is why you have the internal power supply.

Now lets just assume the power supply in your amp delivers 30 Volts to the transistors in the amplifier. It is quite obvious that the maximum VOLTAGE output of one amp channel is 30 Volts as well, since nowhere inside the amp are more than 30 Volts available.

Now we look at another formula, known as "Ohm's law":

R(Resistance[ohms])=U(Voltage[volts]) * I(Current[amps])

or, solved for I:
I = U/R

The impedance of the speaker you connect to the amplifier is also rated in ohms. Impedance and Resistance are closely related in electrical engineering, and for this explanation we can just say they are the same. When you hook up a 4-ohm speaker to the hypothetical 30 Volt amp described above, you will produce a current of (up to) 30V/4Ohm = 7.5 Amperes (see formula above). If we insert this into the power formula first used, you produce 30V * 7.5 Amperes = 225 watts of peak output power.

If you use two speakers in parallel, resulting in only 2 ohms resistance, you would produce

30V/2Ohms = 15 Amps
15Amps*30Volts = 450watts

and with a 1 ohm load
30V/1Ohm = 30Amps
30Amps*30Volts = 900watts

PEAK Power PER CHANNEL.

Now, doesn't that sound great? Hook up 4 speakers an quadruple the output power of your amp? Well... in theory only.

In practice the following will happen: The power supply inside the amp is designed to deliver a specific maximum current of, shall we say, around 12 Amps (the components used inside the power supply are don't really like high currents that much either, and the more current the power supply can handle,m the more expensive it will be).

For the original application with a 4 ohm load, everything is well within design limits, and the amp works just fine (Power supply supplies 7.5 Amps PEAK power, which is well within capacity).

With a 2 ohm load, 15 Amps peak power are drawn from the power supply. Much more heat is generated. Heat increases the resistance in an electrical circuit; in return creating even more heat. At the same time the increased resistance reduces the output VOLTAGE: The power supply will no longer supply the full 30 Volts, but maybe only 20-25 of them. If you follow my original argument above, it is quite clear that the amp no longer produces the peak power of 450 watts we calculated, but it will rather be in the 350ish range in reality. At the same time it will produce MUCH more heat.

With 1 ohm, the scenario is the same, but worse. Eventually so much heat is produced that either some protection circuit shuts off the amp, or if the protection circuit is not fast enough (or not there at all), some internal component is fried.

How low a load you Amp can handle is a design feature of the Amplifier. Some can handle 2 Ohms, some can handle 1. A higher load is never a problem, but obviously you don't use the amplifier to its full potential then. This may be a good idea since the sound quality certainly becomes worse when the amplifier approaches its load limits. Not so important for subwoofer applications, though.

Now, as for parallel vs. serial: This really is a matter of taste and testing. You get the most power out of your amp when you run it near the lowest impedance that it can handle (with a decent amp this should be noted in the manual). Generally most power = most noise, but not neccessarily best sound quality.

Another thing you often hear about is "bridging" the amp, where you use two channels simultaneously to drive a speaker setup. Bridging is generally not possible with the high-power output of a HU directly, but only with an external amplifier with an integrated power supply. The bridged mode doubles the output by adding the Voltage of the two bridged channels.

Basically the output looks like this:
Left+ = +30V
Left - = Ground (0V)
Right + = Ground (0V)
Right - = -30V

When you now connect a speaker to left + and right -, you have a total voltage DIFFERENCE of 60 Volts between the two terminals. Currency (Amps) is not affected that way.

Hope this helps a bit. I am not an electrical engineer, so some of the statements above are pretty general.

Joerg

From now on, you will be refered to as Sir Joerg Ohm.

whoa David speaks

take note members Dave is not the only expert here,

great Joerg you have given some direction to future modifications. Yes I will take the time to rewire the two 3ohm audiobahn amd 6.5 inches to a series circuit from a parallel one allowing the bridged amp to see a 6ohm load versus a 1.5 ohm load so that in the future I can add another 6x9 inch box containing another two 6.5inch midbass drivers wired in series and then I will wire the two boxes in parallel to give a 3 to 4 ohm load at the amp, maybe.

Yet still Joerg the issue of which circuit, series or parallel, absolutely produces the highest spl from the speakers per a specific input voltage has not been answered.

Dave can you take it from here?

I wasn't before Joerg showed up either. There are quite a few knowledgeable people here.
If your amp can handle lower resistance applications (high current) then a parallel wiring configuration should be the louder of the two options because it will lower the resistance and increase the output of the amp.

Here is one way too look at it.

When you go from 1 to 2 speakers, you theoretically get a 3dB increase in output with the same power input. But since an amp doesn't normally give the same output into different impedances, the overall output would change. So, if you were to wire in parallel, you would theoretically double the power (+3 db) and by wiring in series, you would cut the power in half (-3db). The final result of going from `1 to 2 speakers is a 6dB increase in power from the parallel option and a 0 dB increase with the series option.