AMM-1 trouble... help please

[tboorn]

So as stated i was curious as to how much power my Rockford Fosgate T400.4 was putting out to my set of Focal P165v30 door speakers. Let me start by saying how everything is hooked up because i feel like that may have something to do with it, although another part of me feels like it shouldnt. I have a prs80, RCA's coming from the Front Left & Right output on the h/u, and into channel 1 & 2 on the amplifier. It is a 4-channel but has a switch for 2-chan or 4-chan input. The switch is on 2-chan, which the owners manual says is the way to do it if you are using all 4 channels, but only 2 inputs. Next, since im only running one set of component speakers, i have the right components bridged on chan-1 + and chan-2 -, and the left components bridged on chan-3 + and chan-4 -. The speaker wire coming out of the amp goes into my crossover, and then to the woofer and tweeter via the crossover outputs. Both speakers do work perfectly and so does the amp. I used the speaker wire coming out of the amp that goes into the crossover through the AMM-1 for testing, and hooked the probes up to the right speaker +/-. Upon powering up the system and the AMM-1 i was able to see readings for AC VA & Power Factor, AC Freq & Impedance, AC voltage and AC current. But once i reached either dyno mode or live power mode, i got no reading whatsoever. I played music, and a 400hz test tone at near full tilt. I will also add the AMM-1 was only registering around 3-5 volts of AC while the tone was playing, which by my math guestaments wouldnt add up to what should be outputted from the amp.

any insight is well appreciated, thanks!

also ive ran the amp using only chan 1 & 2 for the speakers, and obviously, its not nearly loud enough, so bridging is the best way for me to go, i havent tried dynoing it that way to see if it works, but it wouldnt do me much good because i want to see how much power the speakers are seeing bridged.

Edited February 29, 2016 by tboorn

[3vil]

I am no expert at all, but I've always been taught to run HU>EQ>Amp(s). The idea being you're not amplifing the signal before the EQ.

[tboorn]

I am no expert at all, but I've always been taught to run HU>EQ>Amp(s). The idea being you're not amplifing the signal before the EQ.

im not quite sure what youre referencing. I agree that is correct but im not using an EQ in this scenario. ah i think you mistook me saying "crossover" for an EQ, i mean the crossover that is used/came with my component set, which consists of a tweeter, a mid-bass, and a crossover to separate the signal for the two. Its purely analog and has no signal changing capabilities. heres a link if yourne not getting it.

http://www.focal.com/usa/en/expert-archives/332-p-165-v30-3544053750156.html

[tboorn]

but that was one of things i felt could cause trouble with the AMM-1, since the speaker wire goes into the crossover im not sure if the impedance rise is facilitated back to the amp, or just stays at the crossover and the crossover sends a constant impedance to the amp.

[3vil]

Totally my bad, to many bourbon and cokes had me jumping lines on the wall of text you posted. I apologize for any confusion I may have caused.

[tboorn]

anybody??

[tboorn]

helpppppppp

[TonyD'Amore]

A two way passive crossover as an example separates the low frequency audio and the high frequency audio. It does so by placing magic resistors in line with the tweeters and with the woofers. The magic is that these resistors change resistance (impedance) with frequency.

For the tweeter we use a magic resistor that gets higher in impedance as the frequency decreases. At 10kHz this resistor might be 0 ohms, at 5kHz it might be 1 ohms, and at 2.5kHz it might be 4 ohms and at 1.25kHz it is 12 ohms, at 612Hz it is 48 ohms; and so on. If we are using a 4 ohm tweeter and the magic resistor hits 4 ohms at 2.5kHz, this means only half of the power will be going to the tweeter at 2.5kHz vs when the magic resistor isn't active. This half power point is called the -3dB point or the crossover point. Also notice that as the frequency halves, the impedance of the magic resistor goes up by 4x. This indicates a 6dB per octave crossover. In a 12dB per octave crossover the magic resistor goes up by 16x per frequency half.

The same thing happens with the woofer, but the magic resistors used for this work the other way. As frequency goes up by 2x, the impedance goes up by 4x. (6db per octave).

So with our 2 way component set lets do an example of what happens with impedance vs freq. We will use a 2kHz crossover point and a 12dB per octave crossover for high and low pass. We will also use 4 ohm woofers and tweeters. We are going to ignore impedance rise of the drivers themselves for this example. This will demonstrate how a properly designed component set can maintain 4 ohms at any frequency even.

Frequency Impedance of Woofer + magic R Impedance of Tweeter + magic R Parallel impedance (what amp sees)

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

31 Hz 4 ohms 12 Mohm 4 ohms

63 Hz 4 ohms 1 Mohm 4 ohms

125 Hz 4 ohms 84 kohms 4 ohms

250 Hz 4 ohms 6916 ohms 4 ohms

500 Hz 4 ohms 580 ohms 4 ohms

1 kHz 4.3 ohms 52 ohms 4 ohms

2 kHz 8 ohms 8 ohms 4 ohms

4 kHz 52 ohms 4.3 ohms 4 ohms

8 kHz 580 ohms 4 ohms 4 ohms

16 kHz 6916 ohms 4 ohms 4 ohms

This magic resistor is made from capacitors and inductors; and sometimes resistors too.

So as to how this relates to the AMM-1, it depends if you are trying to measure the actual power going to one of the speakers in the component set, or if you are trying to measure the amplifier output into the complete component set.

[tboorn]

thank you for the incredibly detailed explanation of how the crossover works. That puts fact to what i assumed to be true i just had no justification. but as stated in my example/question i had the AMM-1 hooked up to the speaker wire that is coming directly from the amp, into the 2-way passive crossover. From your explanation it seems that since the amp is seeing a constant 4 ohm load, the AMM-1 should also register a 4ohm load when calculating its figures. Yet i have been unable to get a proper live, or dyno, power reading from the AMM-1 with this configuration. So if i am trying to measure the complete output from the amplifier to the component set, what have i done wrong?