Need to remove speaker shielding

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DYohn

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Joined: April 22, 2003

Location: Arizona, United States

Posted: December 27, 2006 at 8:51 PM / IP Logged

Man, talk about a hack job. I would NEVER recommend removing the bucking magnets from shielded speakers and then expecting them to work properly.... but to each his own I guess.

The amplifier is always loaded with the effective impedance of only ONE speaker if the crossovers are properly designed. That is the function of the crossovers. This is a gross over-simplification, but think of a crossover as "connecting" only the speaker that is appropriate for the instantaneous frequency of the signal at every given moment.

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geepherder

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Posted: December 27, 2006 at 8:53 PM / IP Logged

Haem is correct. Let me take a crack at this. Let's try using an analogy. We'll assume you're high pass and low pass cutoff points are both 3,000 hertz. The woofer plays all frequencies below 3 kHz, and the tweeter plays all frequencies above 3 kHz. This is dictated by the crossover.

The filters in the crossover wired to the woofer create an "infinite" impedance above 3 kHz since those frequencies are effectively blocked. The filters wired to the tweeter create an "infinite" impedance below 3KHz since those frequencies are effectively blocked. This means the amp only "sees" the woofer (8 ohms) below 3KHz, and only "sees" the tweeter (8 ohms) above 3KHz.

Since the seperate drivers never play the same frequency, there only appears to be one 8 ohm driver to the amplifier, even though they're playing at the same time. This is not a technically accurate post, but it should give you a basic understanding of why this works.

For a better understanding of crossovers, read over this: https://www.the12volt.com/caraudio/cross.asp.

Dave, I see you beat me to it.

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DYohn

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Posted: December 27, 2006 at 9:11 PM / IP Logged

But your explanation is more complete geep. Need to remove speaker shielding - Page 2 -- posted image.

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Sad, little man

Copper - Posts: 125

Joined: January 28, 2005

Posted: December 27, 2006 at 10:26 PM / IP Logged

Ok, thanks, I understand now. I wasn't thinking about the frequency cutoffs. Well, I guess 8ohms it is then. As far as the shielding, I know it's not the best idea, but I really needed the speakers to fit inside the door. I'm not hacking my car to pieces to fit a set of speakers. I'd rather hack up a pair of $60 speakers to fit the car.

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geepherder

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Posted: December 28, 2006 at 6:39 AM / IP Logged

Consider cutting some spacers out of wood to bring the speakers farther away from the door metal. Just ensure you've got enough clearance away from the door panel.

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stevdart

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Posted: December 28, 2006 at 8:22 AM / IP Logged

Sad, little man wrote:

Sure, here are the crossover schematics.

Highpass

Lowpass

A good crossover design is one that is 1) appropriate for the system it is designed for, and 2) simpllified, as much as possible, to that degree. Neither of which applies with this one. The designer should ask himself a series of questions after the initial design to find out how much of an overhaul is needed. With this one, I would ask, "Why can't I achieve proper results with a 2nd order crossover? Are the drivers I'm using the best choices to use? Could a replacement woofer be the key to eliminate the added impedance compensation network? Can I find satisfactory results by using just one component of an available value rather than two or three extra components wired together to achieve the same result?....."

But you've already built them, so... Watch your wiring polarity at the tweeter. The diagram doesn't show it, but the drivers should probably be in opposing polarity in this network. Usually, the tweeter is reversed, with the neg terminal connected to the pos side.

You will likely have woofer damage due to the removal of the shielding. For replacement woofers, look for the same model woofer without the shield for closest results.

Build the box so that it performs well in the worst case scenario and, in return, it will reward you at all times.

Sad, little man

Copper - Posts: 125

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Posted: December 28, 2006 at 8:29 AM / IP Logged

Why opposing polarity, wouldn't they be out of phase? Also, using spacers wouldn't work. That was the original plan, but the door panels won't fit back on with the speakers sticking out from the door.

stevdart

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Posted: December 28, 2006 at 8:59 AM / IP Logged

No, sorry, that shouldn't apply with a 4th order. The phase shift should be 360 degrees, which equals 0 degree phase shift, thus no reversing of a driver.

http://www.apicsllc.com/apics/Misc/filter2.html#fourth

Build the box so that it performs well in the worst case scenario and, in return, it will reward you at all times.

geepherder

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Posted: December 28, 2006 at 5:28 PM / IP Logged

Others on this forum have had success spacing the window track back a little for extra clearance. I probably wouldn't try more than about a 1/2 inch or so- that way the window should still function reasonably well.

My ex once told me I have a perfect face for radio.

Sad, little man

Copper - Posts: 125

Joined: January 28, 2005

Posted: January 02, 2007 at 12:17 PM / IP Logged

So it turns out that the tweeters I just installed are just too loud in relation to the mids. I went ahead and ordered one of these variable L-pads that I plan on wiring into the tweeter circuits so I can have control of the tweeter volume independent of the mids right on the dash. As I understand it, for each channel, one of the three terminals is for the speaker signal positive, one is for the tweeter's positive wire (this terminal is hooked to the wiper inside that slides across the coil and varies resistance)and the third terminal just couples the tweeter negative wire with the negative wire from the source. Is that about right? And if so, what is the point of the negative terminal? Couldn't you just bypass the whole thing on the negative side?

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Need to remove speaker shielding

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