clamping amp

[dbjunior 10+ year member]

4.4ohm is possible for a box rise try it at different frequencies start at 35 and step up by 5 Hz and your clamp needs to be true rms. Or. It. Wont be accurate. Unless it's. 60hz

 

[splwj47 10+ year member]

4.4ohm is possible for a box rise try it at different frequencies start at 35 and step up by 5 Hz and your clamp needs to be true rms. Or. It. Wont be accurate. Unless it's. 60hz

how do u tell if its true rms, it has no manual since it is not mine

 

[dbjunior 10+ year member]

It should say it right on it. If not 60hz is the only frequency that will be accurate. The impedance. Changes at different frequencies so you will get. Different. Readings

 

[splwj47 10+ year member]

the meter is a power fist dt 266

 

[splwj47 10+ year member]

i found the manual on the net here and it says in there ac current: frequency responce 50-60hz

 

[splwj47 10+ year member]

AC CURRENT

20A

200A

1000A

Resolution

10mA

100mA

1A

Accuracy(50Hz - 60Hz)

+ (2.5% + 8)

+ (2.5% + 5)

+ (2.5% + 5) for 800A and below

If >800A, the reading is only for reference.

AC Current

Frequency response: 50~60Hz

Indication: Average (rms of sine wave)

Overload protection: 1200A within 60seconds,

Jaw opening: 2"(5cm)

 

[splwj47 10+ year member]

???

 

[maylar 10+ year member]

Seems like you have a 4 ohm load if everything is working OK. The amp clamp aught to be reasonably close at 50 hz.

 

[splwj47 10+ year member]

so that means that they are only seeing 135rms then?

 

[splwj47 10+ year member]

i guess nobody knows?????

 

[vector 10+ year member]

What that means is you do not have a true rms clamp meter, so it is only accurate around 60hz as was mentioned before. If while measuring a 60hz tone you see a max of 5.5 amps on your clamp meter and your second DMM is reading 24.4, then your amp is pushing out 134 watts and seeing a resistance of 4.4 ohms at 60hz and level you have selected.

That is the basic explanation. There is a much more accurate and detailed explanation which follows but you can ignore if your question was already answered.

First to find out how much clean or undistorted power an amplifier is putting out you need an oscilloscope measuring the 60hz wave while you clamp it.

First measure the output of your head unit for clipping. Find out at what voltage or output level the head unit clips at or if it does (some manufacturers will set the internal gain so that you will never have clipped or distorted output from the head unit low level outputs). Next feed a 60hz test tone to your amplifier from the headunit making sure to never go above the point at which you measured clipping from the head unit. Turn the amplifier up until you see the signal start to turn into a square wave. This is the actual undistorted output power of your amplifier.

Second, your subwoofer will change impedance throughout its frequency range. The impedance given from the manufacturer is its nominal impedance or a rough median impedance characteristic. Impedance is also affected by the enclosure that you mount your speakers in which is sometimes called box rise. This can be minimal or quite pronounced such as with horn designs where, when operated over a specific frequency range present a very high impedance load to an amplifier.

Find an impedance curve graph of your subwoofer to give you a good idea of how what you are seeing at 60hz relates to the impedance over the rest of the frequency range.

 

[vector 10+ year member]

Also what is the input voltage to the amplifier while clamping? If you are running off the battery while clamping than this seems very reasonable.

You have an amp that is rated at 300watts rms into 4 ohms at 12.5 volts. That means that with two subs hooked up they will be seeing 150 watts each. Your amplifiers is seeing 4.4 ohms and if this test was done at 12 volts that is probably exactly what you should expect from the amplifier.

 

[vector 10+ year member]

It is strange that your amp is seeing that high of an impedance though. What type of box are you using? What make and model of subwoofer?