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Need to remove speaker shielding


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Sad, little man 
Copper - Posts: 125
Copper spacespace
Joined: January 28, 2005
Posted: December 26, 2006 at 1:19 PM / IP Logged  
I'm trying to mount some 8ohm speakers in my doors, (with the way I'm wiring things I needed some 8ohm spekers) but since they're more of a home audio speaker they have big magnetic shields on the magnets. Anyone know of a good way to get them off without damaging the speakers so I have a little more room? I think I may have to mount the speakers on the back of the door panel instead of dropping them into the holes for the sake of mounting flush, and getting the speakers in place inside the door is not going well so far.
haemphyst 
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Joined: January 19, 2003
Location: Michigan, Bouvet Island
Posted: December 26, 2006 at 9:52 PM / IP Logged  
The chances of you getting them off, without damaging the speaker is pretty slim. The epoxy that is used to attach the shielding cup is usually the same epoxy used to assemble the motor structure... What I am saying is this: JUST as strong, and just as solvent resistant.
You will have much better luck actually using different speakers. Just don't use shielded versions.
It all reminds me of something that Molière once said to Guy de Maupassant at a café in Vienna: "That's nice. You should write it down."
coppellstereo 
Silver - Posts: 785
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Joined: November 21, 2005
Location: United States
Posted: December 26, 2006 at 10:11 PM / IP Logged  
what way are you wiring in such that you need 8ohm speakers?
haemphyst 
Platinum - Posts: 5,054
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Location: Michigan, Bouvet Island
Posted: December 26, 2006 at 10:15 PM / IP Logged  
Doesn't matter, really... That's not why he came here. Need to remove speaker shielding -- posted image.
I have 8 ohm speakers in my car, and are you gonna grill me, too? ROFL
Take that in the spirit in which it is intended, please.
It all reminds me of something that Molière once said to Guy de Maupassant at a café in Vienna: "That's nice. You should write it down."
Sad, little man 
Copper - Posts: 125
Copper spacespace
Joined: January 28, 2005
Posted: December 27, 2006 at 8:29 AM / IP Logged  
I'm putting a tweeter and woofer in each door. I also have a pair of custom fourth order crossovers built for them, so they need to be wired in parallel. So in order to not fry my HU, they both need to be about 8ohms in order to give the HU the 4ohm load it's looking for. The crossovers also have zobels in them made for the woofers, so I'd really rather not change speakers.
Either way, I managed to get the magnets off. Haemphyst, you were right. Very strong epoxy. The magnets chip off before they break cleanly off. The motor came detached on one of the woofers in the process, but I centered everything back up so the coil moves freely without binding up, and as long as the motor holds up, I'm not going to worry about it.
stevdart 
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Location: Pennsylvania, United States
Posted: December 27, 2006 at 9:00 AM / IP Logged  
I'm interested in having a look at that crossover schematic.  Can you find a way to post that info up here?
Build the box so that it performs well in the worst case scenario and, in return, it will reward you at all times.
haemphyst 
Platinum - Posts: 5,054
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Joined: January 19, 2003
Location: Michigan, Bouvet Island
Posted: December 27, 2006 at 11:58 AM / IP Logged  
Sad, little man wrote:
I'm putting a tweeter and woofer in each door. I also have a pair of custom fourth order crossovers built for them, so they need to be wired in parallel. So in order to not fry my HU, they both need to be about 8ohms in order to give the HU the 4ohm load it's looking for. The crossovers also have zobels in them made for the woofers, so I'd really rather not change speakers.
If I am understanding completely what you are saying, that's incorrect. With the crossover in place, the HU will be seeing 8 ohms. The crossover presents to the amplifier (basically) 8 ohms ABOVE the crossover point, in parallel with (effectively) an infinitely high impedance below the crossover point.
This same electrical phenomenon with the woofer section, only in reverse.
Your HU will be seeing an 8 ohm load.
It all reminds me of something that Molière once said to Guy de Maupassant at a café in Vienna: "That's nice. You should write it down."
Sad, little man 
Copper - Posts: 125
Copper spacespace
Joined: January 28, 2005
Posted: December 27, 2006 at 1:57 PM / IP Logged  
Sure, here are the crossover schematics.
Highpass
Lowpass
I can't take credit for these though. Someone who goes by Nizidramanii'yt on the miata.net forums designed this whole system for his car, and I'm duplicating it. I did make those schematics though so I could get a better picture of how they were going to be wired. I guess they're technically two crossovers, but I have them wired up in one box with input and output wires. All of the capacitors are just in parallel to match the values I was given with what was avalible, they could be made with fewer capacitors if you found the right values. And the resistors on the high pass side are just there to even out the tweeter and woofer volumes. There are two in parallel so they don't blow. I don't know about the impedence issue. I don't know enough about it to know if it would be four or eight ohms wired up like this. I can't test it with a multimeter since those capacitors on the high pass side screw up the true impedence. If you test the highpass side from the crossover input it's something ridiculous like 1 mega ohm, which definitely isn't what the HU truly sees.
haemphyst 
Platinum - Posts: 5,054
Platinum spaceThis member has been recognized as an authority in Electrical Theory. Click here for more info.spaceThis member has been recognized as an authority in Mobile Audio and Video. Click here for more info.spacespace
Joined: January 19, 2003
Location: Michigan, Bouvet Island
Posted: December 27, 2006 at 3:03 PM / IP Logged  
Above the crossover point, the amplifier (whether external or deck) will see about 7.5 ohms, and below the crossover point the amplifier will see a little over 8 ohms. The reason the tweeter is reading 1M is because capacitors block DC (and they are wired in series, for purposes of testing thus effectively blocking DC), which is what the VOM uses for reading Ohms.
It all reminds me of something that Molière once said to Guy de Maupassant at a café in Vienna: "That's nice. You should write it down."
Sad, little man 
Copper - Posts: 125
Copper spacespace
Joined: January 28, 2005
Posted: December 27, 2006 at 4:52 PM / IP Logged  
I guess I still don't get it. You have two 8ohm speakers per channel. One woofer, one tweeter. Each of them go through their own filters totally electrically separate from each other in the crossover. The only time their circuits meet is at the amplifier (HU) where they're wired in parallel. How is this different from two 8ohm speakers in parallel? Are you saying somehow the filters change their impedance? Maybe professionally built crossovers work differently, but my highpass and lowpass are totally separate, so I don't see how it comes out to 8ohms total load. I'm not saying you're wrong, I'm just saying I don't understand how it works. I know that if I test the lowpass circuit's resistance it's about 8ohms on its own. I can't really test the highpass circuit like we said, but I can only assume with the 6ohm tweeter and the 1.5 ohm resistance in the crossover it comes out to about 7.5ohms total. So I have a circuit I know from testing is 8ohms, and one that I assume is in the 8ohm ballpark, so parallel those, and....?
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