Those of you whose day is empty without reading lots of Davy Jones postings know I've recently built a sub using a Peerless 10" XLS driver and passive radiator. You also have been telling all your friends about the sub simulation software I've written. Thanks Ron E!
The sub is in a 29 liter box. Net volume, I'm figuring, is about 26.4 liters. (Good guess?) I bought a PartExpress plate amp with 6dB boost at 30 Hz. (Seemed like a good idea at the time.) But playing around with the new software, it looks like I might be better off with an amp with no boost at all. The downside (snort) would be that to get the crossover point in the right position, between 70 and 80 Hz, I would need to turn up the volume and set the crossover to 50 Hz rather than 75 or so. The lowpass rolloff would therefore be reduced from 12dB/octave to maybe 9dB/octave.
My question: Is that acceptable?
See the graph below.
The sub is in a 29 liter box. Net volume, I'm figuring, is about 26.4 liters. (Good guess?) I bought a PartExpress plate amp with 6dB boost at 30 Hz. (Seemed like a good idea at the time.) But playing around with the new software, it looks like I might be better off with an amp with no boost at all. The downside (snort) would be that to get the crossover point in the right position, between 70 and 80 Hz, I would need to turn up the volume and set the crossover to 50 Hz rather than 75 or so. The lowpass rolloff would therefore be reduced from 12dB/octave to maybe 9dB/octave.
My question: Is that acceptable?
See the graph below.
I built a sub using the 10" XLS and PE sub amp and it certainly doesn't need any boost. Just change the 2 resistors in the PE amp to disable the boost....... details should be with your instructions.
Really I can't see what your problem is............ adjust away and will sound much better than with the boost. Give the software the flick and check with the ears.
Really I can't see what your problem is............ adjust away and will sound much better than with the boost. Give the software the flick and check with the ears.
rabbitz said:
Perhaps I did not explain it well enough. If I change the resistors to make the amp play flat, then in order to get the combined response of the system flat, I will have to set the nominal crossover point about 1/2 octave lower than the actual crossover point. That will yield a subwoofer high frequency rolloff of only about 9 dB an octave. I am asking if that will prove unacceptable.
I'll check with the ears, but I'm not going to give the software the flick. It's good stuff.
Paradise_Ice said:
DIY, naturally! Ron E helped me write it. See this thread:
http://www.diyaudio.com/forums/showthread.php?s=&threadid=35291
I think I've hit on a solution employing my AudioControl Richter Scale bass management unit.
The mains are ported, and start to roll off at around 70 Hz. They are down 6dB at 50Hz according to Martin's Mathcad worksheet. The rolloff is -- what? -- 24dB an octave? Effectively, the rolloff of the sub amp's nominal 12 dB low-pass is only maybe 10 dB, because the unequalized sub has a rising response in that range.
Soooo.... I tried running the sub using the Richter Scale, which has a Linkwitz/Riley crossover with a 24 dB/ octave rolloff.
Well folks, however I set the crossover knob on the plate amp (within reason), it sounds reeeeally good, although the Richter Scale is set up to roll off at 90 Hz. Before, if I turned the sub up enough to get the bass flat in the 30-40 Hz range, there was some muddiness in the deep male voices and so forth. Now I can get plenty of low bass without that problem. I think I'll change a resistor in the Richter Scale to put it at a lower crossover point, which should help a bit more. I'm not sure exactly what frequency to select though.
The mains are ported, and start to roll off at around 70 Hz. They are down 6dB at 50Hz according to Martin's Mathcad worksheet. The rolloff is -- what? -- 24dB an octave? Effectively, the rolloff of the sub amp's nominal 12 dB low-pass is only maybe 10 dB, because the unequalized sub has a rising response in that range.
Soooo.... I tried running the sub using the Richter Scale, which has a Linkwitz/Riley crossover with a 24 dB/ octave rolloff.
Well folks, however I set the crossover knob on the plate amp (within reason), it sounds reeeeally good, although the Richter Scale is set up to roll off at 90 Hz. Before, if I turned the sub up enough to get the bass flat in the 30-40 Hz range, there was some muddiness in the deep male voices and so forth. Now I can get plenty of low bass without that problem. I think I'll change a resistor in the Richter Scale to put it at a lower crossover point, which should help a bit more. I'm not sure exactly what frequency to select though.
Dave,
To answer your question about books, you need to check out elementary books on circuit analysis and solution of differential equations with LaPlace Transforms to really get a handle on all this stuff. THese are sometimes called systems analysis books or spring-mass-damper classes. After you learn those, books on control systems will cement the stuff in your mind....
This stuff is usually taught in sophmore-junior level engineering courses in most US universities. I don't know what your education level is, but tech school books that cover this stuff may be more accessible than university textbooks.... to be sure, check out your local library.
To answer your question about books, you need to check out elementary books on circuit analysis and solution of differential equations with LaPlace Transforms to really get a handle on all this stuff. THese are sometimes called systems analysis books or spring-mass-damper classes. After you learn those, books on control systems will cement the stuff in your mind....
This stuff is usually taught in sophmore-junior level engineering courses in most US universities. I don't know what your education level is, but tech school books that cover this stuff may be more accessible than university textbooks.... to be sure, check out your local library.
Ron E said:
I'm up on the Laplace transform stuff. (I have a master's degree in math.) Could you name some titles for the other stuff? I have Optimal Control and Estimation by Robert F. Stengel, but I find it rather rough going. I have trouble following his notation. Something very application-oriented would be welcome.
I had a 10 week course in ckt analysis and a 10 week course in applied analog and digital circuits and active components like Diodes, BJTs, FETs - the course was for ME's. I kept the book for the second course as it contained a good review of the first course. It is called "Principles and Applications of Electrical Engineering" and it is by Rizzoni. There were some speaker or audio related examples in there. In the last section on AC motors, a rather naive model of a loudspeaker is generated.
A crossover is just a voltage divider with components which vary in resistance with frequency according to the following relationship:
Component - Impedance
Resistor - Z=R
Inductor - Z=sL
Capacitor - Z=1/(sC)
BTW, what are you using to program and make the graphs - it looks a little like FORTRAN syntax (procedural language).?
I just use Excel, once you add the analysis toolpac from teh installation disc, you can do complex-valued math and make nice graphs, if it is a bit cumbersome.....
A crossover is just a voltage divider with components which vary in resistance with frequency according to the following relationship:
Component - Impedance
Resistor - Z=R
Inductor - Z=sL
Capacitor - Z=1/(sC)
BTW, what are you using to program and make the graphs - it looks a little like FORTRAN syntax (procedural language).?
I just use Excel, once you add the analysis toolpac from teh installation disc, you can do complex-valued math and make nice graphs, if it is a bit cumbersome.....
Ron E said:
The system is called Python. I can't recommend it highly enough. This is coming from a guy who has been a full time professional programmer since we programmed the paper tape with our belt buckles. For well over a decade, programming systems development was my specialty. I am not easily impressed. I'm telling you, Python is good stuff.
And the price is right - $0.00. There's even free online documentation. It runs on lots of platforms. There is a wealth of free library code available, much of it with detailed examples. Check it out.
http://www.python.org/
To make the graphs, I used a Python extension for a program called Gnuplot. Gnuplot and the Python extension for it are separate from the main Python distribution. Finally, Gnuplot uses a Python extension called "Numeric" that I don't think comes with the main distribution either.
Long before I heard of Python, I was using Gnuplot. I am marginally proficient with it. There is learning curve. You might want to look into wxPython, which is the Python extension for wxWidgets (a.k.a. wxWindows). That is a full-blown, platform-independent windowing and graphics system.
"Python - Why settle for snake oil when you can have the whole snake?"
peerless XLS10 with 400g radiator in 20 effective litter does not need any bass boost when properly placed in room.
but using a DSP like behringer DSP1124p help to solve room mode, cutting your sub with an strong high pass below 25 Hz will give much power to your system.
For bass...no boost, just a good eq in room !
here's my freq response in room after eq (red color) :
I must precise that response is resulting of summing sub+loudspeakers, crossover is 80 Hz with soft slope (6 or 12 dB, i don't know, it's AV amplifier wich does it)
but using a DSP like behringer DSP1124p help to solve room mode, cutting your sub with an strong high pass below 25 Hz will give much power to your system.
For bass...no boost, just a good eq in room !
here's my freq response in room after eq (red color) :
An externally hosted image should be here but it was not working when we last tested it.
I must precise that response is resulting of summing sub+loudspeakers, crossover is 80 Hz with soft slope (6 or 12 dB, i don't know, it's AV amplifier wich does it)
Dave, I'm sorry if I sounded abrupt but what I failed to say in my post that the software graph would go out the window when the room modes come in. Not knocking the software.
I understand more what you are after now........ have fun.
I understand more what you are after now........ have fun.
- Status
- Not open for further replies.