Subsonic may be faulty?

[Hell-Razor 0]

Well I just started today really trying to tweak everything on my amplifiers to get everything working correctly. I started with my big amp setting the gain with a DMM. all that went well but I noticed that my subsonic may have been off. So I popped in a tone to 33hz to try and make it cutoff at that point and its not. I cranked it up to 60 hz (has a range of 10-60hz) and it is still not cutting that signal out. Is it possible I have a faulty SSF?

I have a SAZ-3500D and a SAX-50.4

[Impious 1,476]

What do you mean by "not cutting the signal out"? Is it not affecting the voltage at all?

To set the SSF to a specific frequency, turn the filter all the way down (10hz) and disconnect the sub. Turn the volume on the HU up to some arbitrary level (the volume level itself doesn't matter), and play the 33hz test tone (if that is what you are trying to set your SSF to). Measure the voltage output of the amplifier with a DMM. Then multiply this voltage by .707. So if you measure the voltage output and it's 2V, then you would multiply 2 * .707 = 1.414. With the test tone still playing and your HU at the same volume level, turn the SSF knob up until the voltage drops to your calculated voltage, in my example that would be 1.414V. This will set your SSF to 33hz.

The SSF is not a brick wall. It will not eliminate the signal below 33hz. It simply attenuates those frequencies at a certain rate based on the slope of the SSF. A SSF is nothing more than a highpass filter.

[Hell-Razor 0]

To set the SSF to a specific frequency, turn the filter all the way down (10hz) and disconnect the sub. Turn the volume on the HU up to some arbitrary level (the volume level itself doesn't matter), and play the 33hz test tone (if that is what you are trying to set your SSF to). Measure the voltage output of the amplifier with a DMM. Then multiply this voltage by .707. So if you measure the voltage output and it's 2V, then you would multiply 2 * .707 = 1.414. With the test tone still playing and your HU at the same volume level, turn the SSF knob up until the voltage drops to your calculated voltage, in my example that would be 1.414V. This will set your SSF to 33hz.

Very nice. I did not know this, I thought it was a "brick wall". Anyway, why .707? I have never seen this number in car audio. But then again I am a novice towards this kind of stuff.

[Hell-Razor 0]

I am so confused right now. I started playing a 33hz test tone, put the SSF at 10hz and I measured the output terminals with a DMM. It came up as 6v. so then 6 x .707 = 4.24200. I then went and put the SSF at about where it looks like it should be on the range and it showed that the voltage went from 6 to 10.25. What the... Its supposed to go down, not up.

[Impious 1,476]

Very nice. I did not know this, I thought it was a "brick wall". Anyway, why .707? I have never seen this number in car audio. But then again I am a novice towards this kind of stuff.

.707 is actually a pretty popular number. It's derived from 1/SQRT(2). In this case, multiplying the voltage by .707 would provide you with the necessary voltage for a -3db decrease in the signal, the -3db point being the crossover point for most amplifier crossovers (or any other Butterworth filter, the crossover point is defined differently for different crossover types). Just as a proof, we can use basic ohms law. Just to make the math simple, lets assume you have a 1ohm load and we'll use your 6V example

Power = Voltage^2/Resistance

6V^2/1 = 36w

4.242^2/1 = 18w

10*log(36/18) = 3db

.707 is also used to calculate RMS voltage and current from peak voltage and current. Vpeak * .707 = Vrms, Ipeak*.707 = Irms

.707 is also used Q of Butterworth filters (crossovers) and Butterworth enclosure alignments.

Overall, it just comes up a lot

I am so confused right now. I started playing a 33hz test tone, put the SSF at 10hz and I measured the output terminals with a DMM. It came up as 6v. so then 6 x .707 = 4.24200. I then went and put the SSF at about where it looks like it should be on the range and it showed that the voltage went from 6 to 10.25. What the... Its supposed to go down, not up.

I'll have to ponder this a little. Off hand I'd wonder if maybe you were adjusting the lowpass filter rather than the subsonic.

[Hell-Razor 0]

I'll have to ponder this a little. Off hand I'd wonder if maybe you were adjusting the lowpass filter rather than the subsonic.

Nope. I am positive on this one. I even thought that as well but I am adjusting the subsonic. I just set it at a hair less than halway becuase halfway on a 3500D is 35hz.