Mounting crossovers in trunk

[Hoot 10+ year member]

Is it preferable, or even significant, to mount passive crossovers near the drivers? I'd like to mount the crossovers for my front speakers in the trunk next to the amps, where I can easily tweak 'em, but I don't wanna compromise anything if it is not advisable.

Thoughts?

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[TeenWolf 10+ year member]

I don't think it matters where you put the crossovers. Having them by the drivers or amps shouldn't make your sound quality any better or worse. I would go with your original plan for easy access.

 

[johnecon2001 5,000+ posts]

Udually places where there are the least changes in the physical environment are best. A bad idea would be inside a door. You have moisture and extreme heat and rattles galore. So anything inside the car on "stable" surfaces is usually good.

 

[Hoot 10+ year member]

What do you these comments lifted from the ICIXSound.com forum in the CDT section? (In answer to the same question posed, here.)

"A passive network has problems that has to do with their impedance. Impedance restricts power transfer; it's like resistance, only frequency sensitive. In order for the passive network to work exactly right, the source impedance (the amplifier's output plus the wiring impedance) must be as close to zero as possible and not frequency-dependent, and the load impedance (the loudspeaker's characteristics) must be fixed and not frequency-dependent (sorry -- not in this universe; only on Star Trek). Since these things are not possible, the passive network must be (at best), a simplified and compromised solution to a very complex problem. Consequently, the crossover's behavior changes with frequency -- not something you want for a good sounding system.

One last thing to make matters worse. There is something called back-emf (back-electromotive force: literally, back-voltage) which further contributes to poor sounding speaker systems. This is the phenomena where, after the signal stops, the speaker cone continues moving, causing the voice coil to move through the magnetic field (now acting like a microphone), creating a new voltage that tries to drive the cable back to the amplifier's output. If the speaker is allowed to do this, the cone flops around like a dying fish. It does not sound good. The only way to stop back-emf is to make the loudspeaker "see"a dead short, i.e., zero ohms looking backward, or as close to it as possible -- something that's not gonna happen with a passive network slung between it and the power amp, and if the crossover is closer to the amp the impedance can't be zero ohms, but will be closer when the crossover is closer to the speaker, maybe not still exactly zero but better since the speaker cable distance has been eliminated. Now what about phase, impedance/inductance, frequency response slope, damping factor, transient response, attenuation due to distance of the capacitors, amplitude, etc. as other factors? (Man I'm getting a head ache-why did you ask this question of me?).

In other words to make it a little more visual:

A. Speaker X-Over

( o )------------------------------------------------------------------------------[__]-----AMP

B. Speaker X-Over

( o )------[__]-----------------------------------------------------------------------------AMP

In the A. scenario it exhibits what occurs in the above description. I'd rather have the amp be the workhorse.

In the B. scenario as the crossover does not have to deal with any loss of frequency or phasing or loss of slope or any extra impedance issues to have to push the frequency over a distance. Maybe in a lab there is an effect like I said but my electronics gut seems to tell me B. is a better approach."

 

[TeenWolf 10+ year member]

That was a mouthful. Still think it's a good idea to put the crossover where you originally planned. Also think it's a good idea to keep them away from the door panel b/c it gets moist in there (as mentioned above).

That guy seems to know what he's talking about, but I wouldn't say that the crossover is the workhorse when you place it close to the amp. Crossovers filter, amps provide the power.

Technically, a crossover (or any break in your line) will reduce original quality from the amp, but not enough to notice in a 10 foot speaker wire and certainly not detectable by the human ear.

 

[Hoot 10+ year member]

Technically, a crossover (or any break in your line) will reduce original quality from the amp, but not enough to notice in a 10 foot speaker wire and certainly not detectable by the human ear.

In my case, the wires will be more like 15 feet (and they'll be three sets > mid, tweeter, and supertweeter). So, here, instead of running 15 feet from the amp to a crossover that is located near the front of the car, and then running three sets of roughly 2-3 foot wire to three different drivers (roughly 20 feet of speaker wire per speaker), I am now going to be running roughly 50 feet of speaker wire to each driver from the rear of the vehicle. Overall, I am hopeful that the resistance -- or anything else -- won't cause any undesirable effects - anyone think otherwise?
FYI: I am currently using 12 guage speaker wire.

 

[TeenWolf 10+ year member]

I still don't think you will notice a sound difference wiring it either way. A lot of guys here will tell you that wire is wire. 12 guage is plenty - I would use that guage if I were wiring my entire house and using 100's of feet of wire. As I said before, there will be more resistance using a lot of wire or having a bunch of breaks in the line, but you'll probably only notice this using an electronic reader.

 

[Hoot 10+ year member]

I guess it is fair to say that nobody disagrees with this assertion? //content.invisioncic.com/y282845/emoticons/smile.gif.1ebc41e1811405b213edfc4622c41e27.gif

 

[adam71 5,000+ posts]

I know I don't disagree. In my second car I have a passive 3 way and I kept them in the trunk with NO problems.

"A passive network has problems that has to do with their impedance. Impedance restricts power transfer; it's like resistance, only frequency sensitive. In order for the passive network to work exactly right, the source impedance (the amplifier's output plus the wiring impedance) must be as close to zero as possible and not frequency-dependent, and the load impedance (the loudspeaker's characteristics) must be fixed and not frequency-dependent (sorry -- not in this universe; only on Star Trek). Since these things are not possible, the passive network must be (at best), a simplified and compromised solution to a very complex problem. Consequently, the crossover's behavior changes with frequency -- not something you want for a good sounding system.
One last thing to make matters worse. There is something called back-emf (back-electromotive force: literally, back-voltage) which further contributes to poor sounding speaker systems. This is the phenomena where, after the signal stops, the speaker cone continues moving, causing the voice coil to move through the magnetic field (now acting like a microphone), creating a new voltage that tries to drive the cable back to the amplifier's output. If the speaker is allowed to do this, the cone flops around like a dying fish. It does not sound good. The only way to stop back-emf is to make the loudspeaker "see"a dead short, i.e., zero ohms looking backward, or as close to it as possible -- something that's not gonna happen with a passive network slung between it and the power amp, and if the crossover is closer to the amp the impedance can't be zero ohms, but will be closer when the crossover is closer to the speaker, maybe not still exactly zero but better since the speaker cable distance has been eliminated. Now what about phase, impedance/inductance, frequency response slope, damping factor, transient response, attenuation due to distance of the capacitors, amplitude, etc. as other factors? (Man I'm getting a head ache-why did you ask this question of me?).

The only way to take the breaks out of a line is to go active and believe me it made a huge difference in my current setup.

 

[Hoot 10+ year member]

Thanks for your post, Adam. What do you feel were the most significant improvements in the sound when you ditched the passives in your system? Also, do you think the MTX crossovers might have had anything to do with the improvement? (Never had any experience with anything MTX other than their early 90's old school amps and subs (both pretty good stuff).

 

[adam71 5,000+ posts]

Actually, in the past system I never had MTX passives. I had a MTX LSX-2 active xover and I had MB Quart passive, bi ampable 3 way crossovers. Going totally active made every channel for every speaker ALOT more flexible. I can change the xover frequency in 1/3 octave steps. And I can change slope from -6db/oct to -36db/oct. This is all something a passive system cannot do. Which in all made the system sound ALOT better.