Subwoofer Electronic Assistance?

Andre Money (---None of it?) Gold Member Username: Arande2 Rattle your ... Missouri Post Number: 2893 Registered: Dec-06	Posted on Thursday, July 24, 2008 - 03:14 GMT You could create circuit using opamps and other components that can "fix" the BL and all the driver parameters, then you can a circuit that makes it flat to 10hz (anechoic at this point), then limits it as the driver reaches limits. After that you add a room compensation circuit that can compensate for the room. Then if the subwoofer is designed to be run from a current source (= low Q), you could eliminate power compression and other problems with a voltage source. Of course, the driver and enclosure should be designed well (to the room and have capability) to avoid much EQ overall. The circuit, as I would imagine, has to be very complicated, but I am sure its possible to make. Do you think this could make a great improvement to a subwoofer overall?
Jan Vigne Platinum Member Username: Jan_b_vigne Dallas, TX Post Number: 12846 Registered: May-04	Posted on Thursday, July 24, 2008 - 11:02 GMT . Virtually every driver already in use has been designed to operate from a voltage source, which is what most amplifiers are. http://www.passdiy.com/pdf/cs-amps-speakers.pdf .
Andre Money (---None of it?) Gold Member Username: Arande2 Rattle your ... Missouri Post Number: 2896 Registered: Dec-06	Posted on Friday, July 25, 2008 - 00:26 GMT That was an interesting read. Did you google that or have it as your own reference? Or? On the subject of current/voltage sources, I might make a tester to put inline with my speakers to find its parameters.
Jan Vigne Platinum Member Username: Jan_b_vigne Dallas, TX Post Number: 12852 Registered: May-04	Posted on Friday, July 25, 2008 - 01:23 GMT . The whole Pass DIY site is bookmarked along with the information regarding the products. Pass has always been and is a very innovative thinker. "On the subject of current/voltage sources, I might make a tester to put inline with my speakers to find its parameters." What "parameters"? .
Jan Vigne Platinum Member Username: Jan_b_vigne Dallas, TX Post Number: 12853 Registered: May-04	Posted on Friday, July 25, 2008 - 01:52 GMT . "Then if the subwoofer is designed to be run from a current source (= low Q), you could eliminate power compression and other problems with a voltage source." I'm not sure what you are considering when you say "current source" but I'm sure it's not the transconductance design such as the Pass amplifier. But here's how you minimize power compression; http://sound.westhost.com/articles/pwr-vs-eff.htm This is a revised edition of an article Elliot had on his web site for years. The bottom line is thermal compression is the most common cause of power compression. Thermal compression is caused by the heating of the voice coil and in the case of a mutliway system the crossover components. Heating of the voice coil and crossover components will alter the values of the components, the vc being a form of inductor, which then changes the total resistance of the circuit. Just as adding a resistor to the line in front of a driver will pad down its output, so too the change in resistance within the circuit lowers the output of the driver/system. The change is not linear and the resulting loss might be as much as -12dB at certain frequencies where current draw is at its highest point. In the original article Elliot made it clear the best way to avoid power compresion was to start with the highest efficiency driver/system possible. If the high efficiency driver also was one of high impedance magnitude, the resulting changes in resistance would have minimal effect on the overall output levels. So, Andre, start off with a 106dB, 16-32 Ohm driver and power compression is all but negible. If you've read the Pass article, you should understand that it is not truly possible to simply switch between a current source and a voltage source amplifier with the same driver/system. The rest of your scheme is "possible" but highly impractical. You are roughly describing the servo systems which have for several decades been used to control driver response. Servos have the basic fault of only correcting once the problem exists (and typically only correcting one problem at a time) and then generally not being fast enough to actually catch the problem until it's too late and over-correcting which becomes a vicious cycle as the servo then sees its own error as in need of correction. .
Andre Money (---None of it?) Gold Member Username: Arande2 Rattle your ... Missouri Post Number: 2897 Registered: Dec-06	Posted on Friday, July 25, 2008 - 01:59 GMT Parameters? Ohh I meant Thiele/Small (or something to that effect) and I meant their parameters not "its." The particular one was the impedance curve of the woofer chamber. There would be a pair of ~200-ohm resistors inline with the speakers. I would then attach a voltmeter at the speaker terminals. A 10-second test tone sweep from 20-200hz would be run. The meter would be watched for the highest voltages (the highest impedances within those frequencies). Then after that, I would play a smaller range that covers the curve between the two high impedances caused by tuning and driver fs so that I can find the system resonances. I am sure you know that stuff, but I like talking about it anyway. I could probably get some switches so that I could add different properties to the circuit. I like to play around with stuff. You know that.
Andre Money (---None of it?) Gold Member Username: Arande2 Rattle your ... Missouri Post Number: 2898 Registered: Dec-06	Posted on Friday, July 25, 2008 - 02:10 GMT Oh yeah servo I forgot to mention that in my post. I am not sure about servo since I've heard a servo sub (3 high-excursion 10" drivers at 120-degree angle of each other) playing along with some Studio 60s. When it was switched on, it just seemed that the bass suddenly appeared and it's the best bass I've ever heard. I can't say anything about it because I don't know much. It seems it's best to implement it in the lowest octaves, probably <30hz. I did read the article, but probably not slowly enough. It just seemed to me that, with at least a reistor in-line with a driver, that when the impedance rises due to heat, then the voltage would increase to stop the output from being lost. I guess the best solution is going to be an extremely well-designed driver in a very well-designed and construction enclosure. I'm starting to wonder about transmission lines and infinite baffle type alignments..
Jan Vigne Platinum Member Username: Jan_b_vigne Dallas, TX Post Number: 12854 Registered: May-04	Posted on Friday, July 25, 2008 - 03:23 GMT . http://sound.westhost.com/tsp.htm
Andre Money (---None of it?) Gold Member Username: Arande2 Rattle your ... Missouri Post Number: 2899 Registered: Dec-06	Posted on Friday, July 25, 2008 - 04:17 GMT Oh thanks that helps a lot... I really should be looking this stuff up before I post
Jan Vigne Platinum Member Username: Jan_b_vigne Dallas, TX Post Number: 12858 Registered: May-04	Posted on Friday, July 25, 2008 - 16:24 GMT . That's a thought.

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