Car audio Crossovers
EDY19, Thu Jul 27 2006, 05:19PMI just got a new head unit in my car (kenwood MP332) and I like it, but I would like to add a small subwoofer at some point. The amp has front and rear preouts, but it does not have a subwoofer preout. I think I can get an amp (or make one
)that has a low filter so only the lows get put through to the sub (from one of the front or rear preouts) , but how would I go about filtering out some of the lows from the other 4 speakers? If i filter out some of the lows, they can get more of the high freq. stuff, and less stress will be on them. I looked at using a single capacitor as a high pass filter, but the cap would have to be 265uf for a 4 ohm speaker and 176uf for a 6 ohm for a crossover freq of 150Hz, which seems really high- and physically large.Re: Car audio Crossovers
HV Enthusiast, Thu Jul 27 2006, 05:27PM
You could always go with an active high pass butterworth filter using a single op-amp a a few resistors and capacitors. This will give you good roll off as well, but does require a power source, which might not be any big deal anyways since you have 12V readily available.
Do a search on active and passive audio filters on GOOGLE. There is LOTs of info out there. . .
HV Enthusiast, Thu Jul 27 2006, 05:27PM
You could always go with an active high pass butterworth filter using a single op-amp a a few resistors and capacitors. This will give you good roll off as well, but does require a power source, which might not be any big deal anyways since you have 12V readily available.
Do a search on active and passive audio filters on GOOGLE. There is LOTs of info out there. . .
Re: Car audio Crossovers
EDY19, Thu Jul 27 2006, 06:26PM
Aren't these active crossover designs for preouts, not speaker level outputs (22W)?
EDY19, Thu Jul 27 2006, 06:26PM
Aren't these active crossover designs for preouts, not speaker level outputs (22W)?
Re: Car audio Crossovers
HV Enthusiast, Thu Jul 27 2006, 11:58PM
Yeah, your right. A series capacitor should do the trick, although its just a simple first order filter, and yes, the capacitor will be pretty big uF wise.
Even a 2nd order filter using an L and C will still require a pretty big C for around 120Hz corner frequency.
HV Enthusiast, Thu Jul 27 2006, 11:58PM
Yeah, your right. A series capacitor should do the trick, although its just a simple first order filter, and yes, the capacitor will be pretty big uF wise.
Even a 2nd order filter using an L and C will still require a pretty big C for around 120Hz corner frequency.
Re: Car audio Crossovers
Steve Ward, Fri Jul 28 2006, 01:51AM
Look at motor run caps, some of them are pretty large uF wise and not too expensive if you look in the right place.
An active crossover is the better solution of course.
Steve Ward, Fri Jul 28 2006, 01:51AM
Look at motor run caps, some of them are pretty large uF wise and not too expensive if you look in the right place.
An active crossover is the better solution of course.
Re: Car audio Crossovers
EDY19, Fri Jul 28 2006, 02:58AM
I would do that, but I don't have a 4 or 2 channel amplifier for the speakers, so using the onboard amp in the reciever is my only option right now- My stock speakers handle suprisingly well, so maybe I'll turn up the mids and the highs to them(+8db), then leave the bass at 0db, then send one of the preouts to an amplifier for the subwoofer, and use a low pass there so the amp still gets plenty of signal, and the the lows are somewhat "cut" from the 6x9 and 6.75 inch speakers.
EDY19, Fri Jul 28 2006, 02:58AM
I would do that, but I don't have a 4 or 2 channel amplifier for the speakers, so using the onboard amp in the reciever is my only option right now- My stock speakers handle suprisingly well, so maybe I'll turn up the mids and the highs to them(+8db), then leave the bass at 0db, then send one of the preouts to an amplifier for the subwoofer, and use a low pass there so the amp still gets plenty of signal, and the the lows are somewhat "cut" from the 6x9 and 6.75 inch speakers.
Re: Car audio Crossovers
HV Enthusiast, Fri Jul 28 2006, 10:48AM
For your head unit which i'm guessing puts out less than 30W per channel RMS, you only need a low voltage capacitor, so its still going to be quite physically small. You probably only need a capacitor rated to about 20V and this is pretty tiny, even at a few hundred uFs. If you have an audio shop near you, they usually stock these types of capacitors (usually bipolar) and are very inexpensive - couple of bucks each.
HV Enthusiast, Fri Jul 28 2006, 10:48AM
For your head unit which i'm guessing puts out less than 30W per channel RMS, you only need a low voltage capacitor, so its still going to be quite physically small. You probably only need a capacitor rated to about 20V and this is pretty tiny, even at a few hundred uFs. If you have an audio shop near you, they usually stock these types of capacitors (usually bipolar) and are very inexpensive - couple of bucks each.
Re: Car audio Crossovers
Steve Conner, Fri Jul 28 2006, 10:58AM
Meh, filtering the head unit's speaker level outputs doesn't solve the problem, that the bass will make the head unit's power amps clip early. It needs to be filtered out before the power amps. All the more so, because they're relatively low power, so their power should be saved for mids and treble to help them keep up with the subwoofer.
Doesn't the head unit have an option to do that? My cheap crappy car CD player didn't, and I never got round to busting it open and installing an active crossover inside. (just as well really, because it broke and my work would have been wasted.)
Steve Conner, Fri Jul 28 2006, 10:58AM
Meh, filtering the head unit's speaker level outputs doesn't solve the problem, that the bass will make the head unit's power amps clip early. It needs to be filtered out before the power amps. All the more so, because they're relatively low power, so their power should be saved for mids and treble to help them keep up with the subwoofer.
Doesn't the head unit have an option to do that? My cheap crappy car CD player didn't, and I never got round to busting it open and installing an active crossover inside. (just as well really, because it broke and my work would have been wasted.)
Re: Car audio Crossovers
EDY19, Fri Aug 11 2006, 05:41PM
I just got around to playing with my bass guitar amplifier, the speaker is a 4 ohm impedance. I found that a 150uf capacitor does about what I want, I used a cap from a computer power supply rated at 400V so the voltage reversal wouldn't hurt them, although It probably wouldn't anyway because if was fairly low volume. I figured that a 150uf cap and a 4 ohm load cuts frequencies centered around 260Hz. I then put a 6 ohm speaker (the 6x9 inch ones in my car) into the equation with this 260Hz, and found that a 100uf capacitor would suffice for my needs. Could I use some of these high voltage polarized electrolytics in my high pas filter? It does work really well
And I'm not too concerned about serious clipping as the volume control goes up to 35, and I only have had it up to 20 for any period of time.
EDY19, Fri Aug 11 2006, 05:41PM
I just got around to playing with my bass guitar amplifier, the speaker is a 4 ohm impedance. I found that a 150uf capacitor does about what I want, I used a cap from a computer power supply rated at 400V so the voltage reversal wouldn't hurt them, although It probably wouldn't anyway because if was fairly low volume. I figured that a 150uf cap and a 4 ohm load cuts frequencies centered around 260Hz. I then put a 6 ohm speaker (the 6x9 inch ones in my car) into the equation with this 260Hz, and found that a 100uf capacitor would suffice for my needs. Could I use some of these high voltage polarized electrolytics in my high pas filter? It does work really well
And I'm not too concerned about serious clipping as the volume control goes up to 35, and I only have had it up to 20 for any period of time.
Re: Car audio Crossovers
Steve Ward, Fri Aug 11 2006, 07:02PM
The output of an amplifier is AC, you are using a DC cap. Expect it to sound like garbage, and or, the cap to fail in short time. DC caps will only stand maybe 2-3V reverse before they basically go short circuit and no longer act as a capacitor, so they wouldnt do much good for filtering.
Steve Ward, Fri Aug 11 2006, 07:02PM
The output of an amplifier is AC, you are using a DC cap. Expect it to sound like garbage, and or, the cap to fail in short time. DC caps will only stand maybe 2-3V reverse before they basically go short circuit and no longer act as a capacitor, so they wouldnt do much good for filtering.
Re: Car audio Crossovers
EDY19, Fri Aug 11 2006, 07:14PM
I thought it was a percentage of the full voltage rating, not 2-3V no matter what the voltage of the cap, but I could easily be wrong!
That was the reason I used a 400V rated capacitor. It doesn't sound like crap by any means, and the cap hasn't failed yet... I guess it did help me find out what the value should be even If now I have to go buy some from somewhere.
EDY19, Fri Aug 11 2006, 07:14PM
I thought it was a percentage of the full voltage rating, not 2-3V no matter what the voltage of the cap, but I could easily be wrong!
That was the reason I used a 400V rated capacitor. It doesn't sound like crap by any means, and the cap hasn't failed yet... I guess it did help me find out what the value should be even If now I have to go buy some from somewhere.Re: Car audio Crossovers
Steve Ward, Fri Aug 11 2006, 09:17PM
I just realized that what made me think the reverse voltage was so limited was actually something else. You see, at one point i accidentally hooked up my DRSSTC power supply backwards, and it was clamping my charging to like .5V. The .5V was really the IGBT diode drop, not the caps... "d'oh!".
I guess now that i think of it, ive seen lytics end up with -10's of volts when abused in coilguns and stuff. I dont think its good for the cap at all, so id still suggest finding a suitable "AC" capacitor.
Also, if you dont have the volume up much, you might just be running like 1V peak output from the amp.
Steve Ward, Fri Aug 11 2006, 09:17PM
I just realized that what made me think the reverse voltage was so limited was actually something else. You see, at one point i accidentally hooked up my DRSSTC power supply backwards, and it was clamping my charging to like .5V. The .5V was really the IGBT diode drop, not the caps... "d'oh!".
I guess now that i think of it, ive seen lytics end up with -10's of volts when abused in coilguns and stuff. I dont think its good for the cap at all, so id still suggest finding a suitable "AC" capacitor.
Also, if you dont have the volume up much, you might just be running like 1V peak output from the amp.
Re: Car audio Crossovers
Steve Conner, Fri Aug 11 2006, 09:57PM
They make "Bipolar Electrolytic" caps to do what you want. I once had a 100Hz crossover for a sub, and the only components in it were a 6mH iron cored coil, and a 188uF one of these caps. They look like regular axial electrolytics except with rubber bungs in both ends.
If you can't get hold of that, you can try two ordinary lytics in series, back-to-back, with a diode across each to clamp any reverse voltage.
Steve Conner, Fri Aug 11 2006, 09:57PM
They make "Bipolar Electrolytic" caps to do what you want. I once had a 100Hz crossover for a sub, and the only components in it were a 6mH iron cored coil, and a 188uF one of these caps. They look like regular axial electrolytics except with rubber bungs in both ends.
If you can't get hold of that, you can try two ordinary lytics in series, back-to-back, with a diode across each to clamp any reverse voltage.
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