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Old 18th June 2002, 03:36 AM   #1
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Default Biamping without active x-over?

This is my first post and hopefully is not too dumb a question. I have an Alpine car amp which accepts speaker level inputs from the car CD/radio. I would like to go with a component speaker system (DIY parts), driving the tweeter and midrange with separate amp channels.

Am I correct in thinking that I can get away with a passive crossover between the CD/radio and the amplifier? After all, the radio output has sufficient current capacity to drive 4 ohm speakers, and the amp input impedance is reasonably high. Am I missing anything? What benefits would an active crossover buy me over a passive one between the two gain stages? TIA.
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Old 18th June 2002, 04:08 AM   #2
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No sorry this will not work.
You really need an active crossover to get something acceptable and a normal speaker xover will not work.
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Old 18th June 2002, 04:10 AM   #3
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Passive crossover between 2 gain stages becomes an active one.
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Old 18th June 2002, 06:36 AM   #4
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You mean the passive network I built into the input of my amp won't work!? Damn, better go rip it out. [joke]

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Old 18th June 2002, 07:05 AM   #5
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Default Re: Biamping without active x-over?

Quote:
Originally posted by ngee
This is my first post and hopefully is not too dumb a question. I have an Alpine car amp which accepts speaker level inputs from the car CD/radio. I would like to go with a component speaker system (DIY parts), driving the tweeter and midrange with separate amp channels.
If 1st order or (maybe) 2nd order will do, have a look at this Passive Line Level XO Article. If you need more than that you can use inductors & caps to build a text-book passive XO but you have to pay attention to the input impedance of your amps -- you would likely need to wind your own coils (with the high input impedance of the amp they would be quite small).

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Old 18th June 2002, 09:21 AM   #6
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With an active filter you will not need any coils and you can still get the order you want. Check out the Linkwitz-Riley filters on www.sound.au.com, they are quite nice.

/Marcus
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Old 18th June 2002, 06:34 PM   #7
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Thanks for all the useful advice. Now, time for some thinking and then doing.

It's amazing to me the depth of technical knowledge in this forum and in the DIY high end audio world overall. I haven't found anything close to this in the car audio world. The usual discussion is around kick panels for speaker placement, dampening various surfaces with viscoelastic membranes, etc. And, there's certainly little emphasis on selecting component drivers and designing crossovers. Why is that? Maybe I just haven't found the right places to look so any recommended links would be greatly appreciated. Again, thanks.
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Old 18th June 2002, 08:43 PM   #8
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If the reason for wanting to bi amp is to get more power to woofers I would guess that if you could split your stereo signal, keep your drivers less woofers set up as is and use one extra amp with a passive low cross on your woofers. I have a very simple 4 channel stereo FM/CD in my truck and if I was interested in adding something for bass extension I would go that route 1st because it is cheapest and if it doesn't work I can move on still being able to use the amp and woofers I just bought. A thing to remember is that a good sounding 30 to 40 Hz will sound much better than a 15 to 20 Hz if you are really wanting to listen to music. The numbers in Hz tells you how long the wave length is. A 30 Hz wave is around 45 feet. One fourth of that is 11.25' which is the amount of room you need to be able to hear it. You will still feel it. In other words if your auto is only large enough to do a quarter wave of 40 Hz that is basically how low you will hear your bass. After that you feel the concussion of the air being compressed and the vibrations of the woofer through the air. If you want to go real low what you are deciding is how much compression and vibration you enjoy as the sound won't change with your windows up. A good way to look at it is a sealed speaker cabinet. Sounds good set up in your living room, but how would it sound being inside the box? A sealed car full of speaker drivers becomes a rolling acoustic suspension speaker with you sitting in it.
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Old 19th June 2002, 07:23 AM   #9
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Thatch_Ear, I'm looking more for fidelity than SPL in this system (although my car is rather noisy, unfortunately). The reason for considering biamping is it appears to provide sonic benefit. I've never tried it and am intellectually curious. I'm still in the planning stages and in the process of selecting drivers and designing the crossover. Next will come the hard part of interior disassembly and experimenting with driver placement.

Right now I'm planning on just a 4"-5" midrange/bass and a 1" tweeter. I would like to go larger but the car (an '87 Corvette) will not easily accommodate much more in the door panel. The Delco Bose system uses a 4" driver in that location. There are no other drivers up front. Furthermore, the windshield has a steep slope so I'm not sure an A-pillar mount for the tweeter would work well. Later on, I was planning on adding a pair of 6.5"-8" woofers for the lower notes in the rear, as you suggested.

I know that the automobile environment is a difficult one to design for. One thing that I'm considering is an equalizer to help with the dips and valleys in frequency response. Is this a good idea? And which is the worse sonic evil, flat frequency response with weird phase response introduced by the equalizer, or living with the lower bass emphasis and dip at around 100Hz? The OEMs have selected the former. Wondering what your views are.
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Old 19th June 2002, 04:34 PM   #10
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Try Harrison Lbs fmods.Good,cheap,inline rca xovers.
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