Questions about Sub with Passive Monitors

If you hear nothing from the sub but something from the amphion at 20 hz, I'll be interested to know that explanation ? it suggests that the amphions are not actually creating a 20 hz cycle, jus an audible artifact ?

Pulled this from an old post I wrote on the other site. Hope it makes sense for you.

When you use a sub with any system make sure your phase response at the crossover is correct. That means - 80hz is at 40 degrees phase at the LR speakers but because of the sub displacement (distance) 80hz from the sub is at 70 degrees phase. This kind of combination will cause a comb filter on up though the frequency range. The numbers I picked are random, your system will be different.

Most subs come with a phase switch or knob that you can adjust. You want to send a sinewave though your system at the crossover frequency. (Your crossover frequency is the frequency that is -6dB at the natural low roll off of the speaker) For fun take a walk around the room and listen to the changes. Now invert the phase on the sub 180 degrees and move it around until the level drops at the listening position, this will take two people to make short work of it. Once you have found the position that creates the greatest reduction in level, switch the phase back to zero. If your sub has a phase knob - invert the LR speaker phase, and adjust the knob until you have a level drop at the listening position - correct the polarity on your LR speakers and take a listen. You should have a fuller, richer bass responce, since your Sub is now truly reinforcing the LR speakers. You also want to adjust the level of the sub to create as smooth and flat transition as you can into its range.

Advanced dual channel FFT programs will allow you to do this much quicker and more accurately like SIA's Smarrt.

This is not to say that you don't need more bass trapping. Put as much as you can! It will also help to aline the sub with the LR speakers as you will reduce the ringing in the room, and let you hear when you have cancelation.

Hope this helps

PS make sure that the sub and speakers are level matched before testing the phase.

JK, put the 20hz sine wave through the sub, crank it up to where you think it would be loud(be careful), and then walk around the room, you will hear the 20hz(or any freq for that matter, from around 75hz down)tone in some places, and it will disappear in others, and it will be even louder in other spots, especially corners(even trapped corners), these are called nodes and antinodes, and the only way to rid yourself of them is with some serious room treatments in the form of bass traps, i know you already have some in there, and they do help, but 6" corner traps are not going to cut it most times, i have 3 absolutely huge bass traps in here, and my walls have 3" of roxul underneath the slat diffusors, my room is pretty good, but it STILL has hot and cold spots.
   Beside lots of acoustics tuning, the best way to eliminate these problems is by monitoring at low volume, you can try the phase switch and see what happens? if it works in your listening position? then use it. You should get someone over there to help you run some sweeps with room eq wizard, it can only help you understand where you room is lacking, and then you can either fix it, or compensate for it.

kcatthedog It's totally normal that the amphions are hitting 20hz and below(it will be rolled off, but it will be very much there), i just was hearing/feeling/watching my HR824's kicking at 7hz. The reality is humans can hear/feel a bit above 20k as long as there are many multiples of freq's involved, and they surely hear(mostly feel) down to 7hz, big people even lower! check this out, get it down there and be careful as you turn it up, you will have to turn it up BE CAREFUL! and don't forget to turn it back down or the next time you use your rig, you're gonna shit your pants lol
plasticity.szynalski.com/tone-generator.htm

I also should add that if 20hz is showing up weird, it makes sense that harmonics can do weird stuff as well, you should also check the frequency plot of the amphion 1 18's and set your crossover point of your sub accordingly, sometimes if they are crossed too high a fight breaks out, no influence on the 20hz thing though, I don't know about you guys, but I usually hard filter off just about everything below 25hz anyway.