Which XO Config?
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Silver Member Username: NuckParkhill, Ontario Canada Post Number: 297 Registered: Dec-04 | How do I determine the XO configuration I have? Not that it matters in a bought product, but I blew a tweeter XO and am trying to spec a new ceramic resistor(cooked) and add a heat sink, and it seemed a good time to ask. Thanks. |
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Silver Member Username: Timn8terSeattle, WA USA Post Number: 631 Registered: Dec-03 | A little more info would be helpful, such as, a description of what you're looking at. (Disclaimer) My responses are going to be generalities. (End disclaimer) A resistor is not "really" part of the crossover. A resistor is used to attenuate the driver, not control the frequencies delivered to it. Inductors and capacitors are used to limit frequencies delivered to the driver. A single inductor (L) in series with the driver is a low pass filter (limits highs) and a single capacitor (C)in series with a driver is a high pass filter (limits low frequencies). These are basic first order filters. A single component(L or C)in series followed by another component in parallel is a second order filter. Use two second order filters in succession and you have a fourth order filter. After that there are a multitude of variations but that's the basic stuff. What do you have? |
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Gold Member Username: Jan_b_vigneDallas, TX Post Number: 6561 Registered: May-04 | Nuck - Did you blow the resistor in both speakers? If not, you could always open up the other speaker and look at the components which are still surviving. If you destroyed a resistor, you probably don't need a heatsink as much as a higher wattage resistor. Or possibly a governor on that volume control. What'ja think, Tim? About the resistor I mean. |
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Silver Member Username: NuckParkhill, Ontario Canada Post Number: 302 Registered: Dec-04 | The offending)offended) item is a ceramic resistor. The Tweeter XO board has a coil, a cap(Hanlan 100v, 15uf, bp+- 10 %. The now unreadable resistor is wired into the tweeter XO. The lower XO is for 2x bass driver.and also capped at 15uf. My meter doesn't do cap, but the smoke is still inside, and the tweeter is at nominal 5 ohms. Overpowered, but seems to be no damage beyond the release of smoke. power into the board is to the cap, cap feeds the resistor, resistor out feeds the coil, coil is neg out. The tweeter leads are across neg(coil out) and - pwr in. The board is marked as HPC 22-c |
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Silver Member Username: NuckParkhill, Ontario Canada Post Number: 304 Registered: Dec-04 | Thanks Jan. I had just rewired the posts, and got a little rambunctious. The speakers are 4 ohm rated, and the Rotel took advantage of that, along with SRV. oops. If thats the worst, and I need to replace a $3 part, I will add a sink and see what gives next. BTW, The specs say I was giving them about 180wpc at the time, for 15 mins, so I am not worried about the rest of the gear(smiley). On a tip, I replaced the metal bands with speaker wire as bi-amp links, and put the hot lead to the highs, the low lead to the lows. Works great! Thanks |
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Silver Member Username: Timn8terSeattle, WA USA Post Number: 633 Registered: Dec-03 | "What'ja think, Tim? About the resistor I mean." Getting the value from the other speaker would be the best, otherwise an L-pad could work and at the same time provide addtional adjustment to taste. As for a heat sink or governor, I'm thinking Polymeric Positive Temperature Coefficient Thermistor. |
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Silver Member Username: NuckParkhill, Ontario Canada Post Number: 305 Registered: Dec-04 |  That sounds about right |
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Silver Member Username: NuckParkhill, Ontario Canada Post Number: 306 Registered: Dec-04 | L-Pad? Does that mean an output pot, with the sweep acroos the speaker feed? I dont find l-pad anywhere. |
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Gold Member Username: Jan_b_vigneDallas, TX Post Number: 6563 Registered: May-04 | How to find L-pads in an I-pod world? Yeeeesh!!! |
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Silver Member Username: NuckParkhill, Ontario Canada Post Number: 309 Registered: Dec-04 | hehe, not kiding Jan. I plan to move the XO to external on a breadboard, since the one I have is baked. All original parts(plus a sink for the toast resistor). Would the L-pad be useful? Or just more junk in the way? Still wondering about the XO I described earlier, or did I describe something wrong? Mucho Appreciado |
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Anonymous | It seems to me that now would be the perfect opportunity to switch your speakers to a first order x-o. |
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Silver Member Username: NuckParkhill, Ontario Canada Post Number: 311 Registered: Dec-04 | Please supply wiring and specs, anon. |
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Silver Member Username: Timn8terSeattle, WA USA Post Number: 634 Registered: Dec-03 | It sounds like 2nd order but I would expect there to be 2 inductors and 2 capacitors. The resistor is attenuating the tweeter and I would guess the polarity on the tweeter is reversed so the positive in from the amp is going to the negative terminal on the tweeter. If you're going to externally mount the XO, then just experiment with resistors until you find a value that sounds right to you. Start with about 5 ohms and see where it takes you. Don't be surprised if you end up with a resistor value much higher than that. Or use a L Pad http://www.partsexpress.com/pe/showdetl.cfm?&DID=7&Partnumber=260-248 |
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Anonymous | Tim already did Nuck. |
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Anonymous | Tim already did Nuck. The rest is just experimentation to see which values work best. |
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Silver Member Username: NuckParkhill, Ontario Canada Post Number: 312 Registered: Dec-04 | Thanks again, Tim. The external XO will give my wife another reason to go batty, and another chance to learn sommore. I shall seek a suitable breadboard tomorrow. It may be highschool stuff, but I find it very interesting. |
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Silver Member Username: NuckParkhill, Ontario Canada Post Number: 313 Registered: Dec-04 | Happy shopping at the electronics supply house in the city.(thats what we call it here in the sticks) LARGE Ceramic resistor, same 3.3 value, but 25watts.(wonder why the manufacturer didnt do that). Have breadboard, will solder. I also have 2.7 and 3.9 value resistors, I will evaluate and let y'all know. Now down to the laboratory. Mbooowhahaha |
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Silver Member Username: NuckParkhill, Ontario Canada Post Number: 315 Registered: Dec-04 | All is well again. Made a board, and added a large 25w resistor in place of the 10w original. Stevie Ray lives! Thanks for the help, folks, much appreciated! Details at www.greatwhitena.blogspot.com |
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Silver Member Username: NuckParkhill, Ontario Canada Post Number: 358 Registered: Dec-04 | So a single cap and a resistor in series( a +tap for the driver there), with a coil past the tap to driver - would be 1st order/ |
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Silver Member Username: NuckParkhill, Ontario Canada Post Number: 359 Registered: Dec-04 | And how will bench resistane help me determine the dynamic inductance of a driver, if at all, or is that where experience(and productspecs) come in. Just hadda ask. |
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Silver Member Username: NuckParkhill, Ontario Canada Post Number: 360 Registered: Dec-04 | http://www.lalena.com/audio/electronics/rcl/ or I will start here.(smiley) |
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Silver Member Username: Timn8terSeattle, WA USA Post Number: 641 Registered: Dec-03 | A single cap is a first order filter. A single inductor is a first order filter. A single cap in series followed by an inductor in parallel is a second order high pass filter. An inductor in series followed by a cap in parallel is a second order low pass filter. Inductance of a driver is not a fixed amount. As you've pointed out, it is dynamic and is measured on a curve spanning the drivers frequency range. Note the FR and Inductance graph for this driver. http://www.madisound.com/pdf/fostexdrivers/f200a.pdf Driver inductance and frequency response can be combined with the XO filter to result in a steeper rolloff than just the filter alone would produce. So, a filter may be second order electrically but combined with the driver may result in 3rd order acoustically. |
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Silver Member Username: Timn8terSeattle, WA USA Post Number: 642 Registered: Dec-03 | I just noticed I left out some words on my descriptions of first order filters. A single cap in series is a first order high pass filter. A single inductor in series is a first order low pass filter. Sorry about that. |
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