I am trying to get a house curve that does not stop @20hz. At the moment I can get a nice house curve down to about 18hz and after that it goes flat due to my receiver's EQ only applying filters down to 20hz.What are you trying to achieve? Boosting such low frequencies could also boost offsets and create problems with DC if the cutting slope is not steep enough.
How would I go about doing a shelf boost at those frequencies? And what is a Marchand Bassis? (Off to see what google has to say)Dave,
I would not use parametric eq below 20Hz anyway. Not really a good idea. Use a shelf boost with a knee in the 15-20Hz range if you must. Basically an LT type filter. You must be very careful messing around with EQ that low or amps and speakers will get damaged. Most any unit with a shelf filter can produce this type of boost. You could always get a Marchand Bassis
Prolonged subsonics may give 'some' people a headach, but bowel control? I was under the impression that that was an old wives tail???5Hz? Let me give you a hint. There is a reason a standard 33 band PA eq does not go that low. You should not. If you must prove why to yourself, You probably need to build a box as even the eq boxes you could modify have the DC servo higher that that or if not servo, will have blocking caps at much higher cutoff. For a house sound system, 25Hz HP is far more reasonable. If you succeed, about all you will do is find out that subsonics give people a horrible headache and can sometimes cause issues with bladder or bowel control.
Now to dive deeper into your question? Yes. There are numerous opamp audio filter calculators and tutorials on the Net that discuss "active opamp audio filtering." Elliot Sound Products (ESP) has some great schooling, example, and projects that will help you in your quest. Personally, I like his site a great deal.
JapanDave,
If you are after just the sensation of ultra low bass like in a movie why not just go with some shakers that could be a simpler solution. Not like your going to hear anything this low, but you do feel the vibration in your body. I see in some of the latest movie theaters here they are putting individual shakers on each seat in the theater. Doesn't take up all the space of a low frequency enclosure either.
This might not be the best place for this discussion btw.