Regulating output wattage

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Say I have an amp that has X amount of power. The speakers can't actually handle that power but I still want to use the amp. How is an amp properly adjusted to limit the output to the speaker's capabilities?

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[Firewalker]

By using a DMM and the voltage method. Use the link below to figure out what it would be on the DMM and set the voltage on the amplifier accordingly.

Ohm's Law Calculators and Formulas

www.the12volt.com

 

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So I connect the meter with the speaker connected and the amp gain turned down then adjust and watch the voltage on the meter? I calculate using 4 ohms impedance? I'm confused.

 

[Firewalker]

On the right use the voltage calculator. Take the RMS power of the speakers x 4 ohms and it will give you the voltage.

So say the for the sub amplifier 3,000 watts at 1 ohm would be 54.72 on the DMM for voltage.

For the 4 channel say the total RMS is 200 watts between both speakers, take 200 then 4 ohms would be 28.28 on the DMM. As Channel 1 should control the voltage for left and right front with channel 2 controlling rear left and right speakers. Or if you are using the front with components only then you put the tweeters on the front channels and the mid-bass on the rear channels. Works perfectly and you set the voltage on 1 for the tweeters and 2 for the mid-bass. Did mine that way for awhile always works.

FYI you set your head unit to 75% and make sure you are using a test tone as well to set the voltage on the amplifier. If the head unit has BT use a test tone generator on your phone and connect it that way. I set mine that way and it works or buy the test tone cd from SMD if you want.

 

[Water Bear]

The math is like this: Ohm's law is P (power) = V^2 (voltage squared) / R (impedance). (This is only true under some pretty strict assumptions, namely that you can represent your speaker as an RLC circuit. Let's not worry about this too much).

Without giving a science lesson on impedance, the point is that it depends on the frequency of alternating current. Your "4 ohm nominal" speakers won't measure 4 ohms on a DMM. We're going to assume that they present a 4 Ohm impedance at least some of the time during normal operation.

Soooo...hook your DMM up to your amp's speaker outs. Solve the equation sqrt(P * R) = V. Example: For a 100 watt speaker at 4 ohm, one channel should output sqrt(100 * 4) = 20 Volts. Set your head unit volume to whatever you tune at, turn up your gain until your DMM reads 20 V AC. Boom, you're done. Your amp will produce no more than 100 watts per speaker if you don't exceed tuning volume.

 

[Firewalker]

And why go through all that when you can take 2 seconds to plug in that information on 12 volt and have it done for you these days,lol.

 

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Yeah...I'm just gonna hook it all up and go to the local sound shop and let them set everything. They will set my DSP also.

 

[Water Bear]

Is it that hard to plug P and R into the equation sqrt(P * R) and then turn a gain knob with a DMM? Well, you can't go wrong taking it to a shop.

 

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Is it that hard to plug P and R into the equation sqrt(P * R) and then turn a gain knob with a DMM? Well, you can't go wrong taking it to a shop.

No it's not hard to turn knobs and read meters. But when this is something you have never done and you have thousands invested in a particular thing then you want someone else to be responsible for damaging it. Plus I want to get the DSP setup right. I have never dealt with those. The most technical I have ever gotten is to connect an oscilloscope to my equiment to set gains.

 

[Water Bear]

No it's not hard to turn knobs and read meters. But when this is something you have never done and you have thousands invested in a particular thing then you want someone else to be responsible for damaging it. Plus I want to get the DSP setup right. I have never dealt with those. The most technical I have ever gotten is to connect an oscilloscope to my equiment to set gains.

I get where you're coming from. You don't need a DSP for this, any ol' DMM would do. Reading the AC voltage from your amp's speaker terminals is about the same level of difficulty as reading the AC voltage from a wall outlet in your house, so it's probably easier than you think, but I get it.

 

[HardofWhoring]

Like this:



Not at the speakers, remove the speaker wire, and test at the terminals. (The probes can be secured that way).

 

[HardofWhoring]

I'm a visual learner too, but it's pretty simple when you see it.

On the right use the voltage calculator. Take the RMS power of the speakers x 4 ohms and it will give you the voltage.

So say the for the sub amplifier 3,000 watts at 1 ohm would be 54.72 on the DMM for voltage.

For the 4 channel say the total RMS is 200 watts between both speakers, take 200 then 4 ohms would be 28.28 on the DMM. As Channel 1 should control the voltage for left and right front with channel 2 controlling rear left and right speakers. Or if you are using the front with components only then you put the tweeters on the front channels and the mid-bass on the rear channels. Works perfectly and you set the voltage on 1 for the tweeters and 2 for the mid-bass. Did mine that way for awhile always works.

FYI you set your head unit to 75% and make sure you are using a test tone as well to set the voltage on the amplifier. If the head unit has BT use a test tone generator on your phone and connect it that way. I set mine that way and it works or buy the test tone cd from SMD if you want.

I would disagree with that. You're either cutting down your usable range, making your adjustments have more gap between each adjustment; or you're going to turn it up over where it was set, and then you're going to be sending a lot more wattage to your speakers. One or two below max volume seems more reasonable to me.


OP, I have a kenwood Excelon, and a DD1+. I have tested the output voltage on my head unit. On two of my excelon head units, the max rated voltage is achieved at 34 (out of a max of 35). The range up to 34 is .2v between adjustments. 34-35 is 10% more. (.4 and .5v). It does make a big difference. Also, you can clip from your head unit. If you use that DMM / AC voltage method to set your gain, if you are lower than your rated RMS wattage, then you are also below your rated THD. Your head unit can cause THD. Cheap head units can cause clipping below max volume. Even good head units can clip at max volume, because rated voltage output might be below max volume.

 

[hispls 5,000+ posts]

Which amp and which speakers? What crossover are you using? You may be fine so long as you never push the volume too hard.