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funny thing, dvc's wired to 2ch amp?


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ibasspro 
Copper - Posts: 95
Copper spacespace
Joined: October 10, 2007
Location: California, United States
Posted: November 24, 2007 at 8:04 PM / IP Logged  

Had something funny come into the shop today. An Atomic AP 12, dual 1ohm (customer said). hooked to a powerbass XA 2150. Customer came in because he didn't think his system hit like it used to. So, I listened, & in the 99 cherokee it shure didn't hit like I expected. So I proceed to the amp (not my install, or any1 I know). It is hooked up in stereo, 1 ch to each voice coil. Sub was in about (I didn't measure) but looked to be about a cube & 1/2, sealed, looked to be a custome made, with nice carpet. Put the test meter on the power cable, & turned it up, engine off, voltage stayed above 11.5, turned it off, & checked the spk terminals, & got 1.35 ohms outta one, 1.34 outta the other. so, I though the amp dropped a chanel, turned it back on, Fluke on AC, & test tone 40z, got 33.x volts out of each channel (at 1.3 I though that was pretty respectable), but it wasn't consistant, it would peak, & cut, & sounded funny. So, I pop the sub out of the box (only other thing I really thought it could be..loose connections...maybe). fluke up to each coil, & same readng as before, suspension felt fine. Grabbed the battery out of my makita, & pop tested the speaker...."shoop" when I first hook it up....then OK, reverse the polarity "shoop".....hmmm, voice coil came unglued from the former.

I told the customer what I had found, & he said that this is the second sub that has done that.....he came to me because he had never herd of it, & thought the last shop he was at (who did not warranty his last sub) were just lying to him.

I just bring this up, because I find it interesting, because the sub is fairly burly, & the amp is decent output, but nothing that should really damage the speaker, & a cube & 1/2 box should be OK for that sub. The only thing out of the ordinary, in my eyes, was that the amp was hooked up in stereo.....although each channel was approx. the same output.

Long story even longer, I told the customer to get a recone kit from Atomic, & I would rebuild it for him.

Shure makes me wonder why 2 subs in a row did that to him? I might hop in & series up the vc's & bridge the amp, when I rebuild the sub, just to see if it makes any difference.

Anything pop out in your folks's eyes that I overlooked? No bass knob (lol distortion knob) Pioneer DEH-p6800 HU, sub out was at +2 (125hz) , bass at +1, & volumne at 42.....customer said 40 was usual listening volumne....42 got max ac out on amp.

used to be loud, used to be fast...now I am married LOL
haemphyst 
Platinum - Posts: 5,053
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Location: Michigan, Bouvet Island
Posted: November 24, 2007 at 10:05 PM / IP Logged  
If you are beating the suspension up, the enclosure is wrong. That's all it can be.
You'll need to get ACTUAL T/S parameters for the driver, and build a PROPER enclosure.
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."
techman93 
Silver - Posts: 591
Silver spacespace
Joined: October 28, 2006
Location: Pennsylvania, United States
Posted: November 24, 2007 at 11:21 PM / IP Logged  
I will have to agree, box must be a tad too large.
Two reasons speakers fail:
A. POOR BAFFLING
Speakers in poor baffles in cars can have an amazingly short life--months. This is often due to mechanical failure, not thermal failure. Thermal failure comes from overheating the voice coil at any frequency. Mechanical failure happens when a speaker cone travels too far in the BASS range. This can happen easily at power levels far below the thermal (wattage) rating of the speaker in bad baffles. (Some manufacturers use a surround and a spider with a limited throw to make long excursions impossible, but that causes two more problems. Limited throw means an increase in bass distortion and a decrease in bass volume.)
# What is a GOOD BAFFLE? A solid box the right size and type for the speaker in it.
# What is a BAD BAFFLE? There are lots of possibilities...
1. NO BOX. Yes, people will lay a speaker down with no box or baffle and play it. Sometimes they hang them up by a wire or string and play them. Then they wonder why they don't get any bass and why the speaker tears apart.
2. A good box, but one with a port or passive radiator tuned TOO HIGH in frequency. On low notes the speaker doesn't know it's in a box. It makes a long throw, but not much audible bass.
3. An OPEN baffle board. This means one board, not a solid box with six sides. These open boards are found in many place--behind the seat of a truck, laying over the well in the rear of a hatchback, covering the trunk area of a hatchback, fastened in place of the rear seat in a sedan, or behind the back seat in the trunk of a sedan.
4. The REAR DECK. (usually for six by nines or four by tens) Not a good baffle for powerful bass.
5. The PANELS in cars, trucks and vans.
6. Any baffle that aims heavy speakers (tens, twelves, or fifteens) UP or DOWN. DOWN is not as bad as UP, but a heavy cone will sag from the pull of gravity and come to rest out of the magnetic gap. This will cause distortion, loss of power, and a possible mechanical failure of the speaker.
As you can see, many people have no choice but to use BAD baffles in their vehicles. Nevertheless, they need to be aware that when they do, they are placing their speakers in mechanical jeopardy. Many people think that a trunk or a door panel is equivalent to a solid box. It's not, and the price to be paid is in poor transient response, failure to generate good low frequencies, and increased risk of premature mechanical speaker failure. Extended usage in bad baffles at high power levels in the bass range can lead to these mechanical failures:
1. The spider can be torn.
2. The surround can be torn or worn out.
3. The voice coil can be thrown out of the magnetic gap, permanently, or temporarily, the latter deforming it and making it useless. (Sometimes this is caused by a VERY large transient.)
4. The voice coil can also be deformed by hitting the bottom of the magnetic structure. This could be a speaker design problem, but good compliant speakers should be able to travel almost one tenth of their cone diameter safely.
It should be mentioned that excessive speaker excursion is not a problem in small sealed boxes. It can be a problem in very large sealed boxes.
B. OVERPOWERING THE SPEAKER LEADING TO A CHARRED VOICE COIL
This type failure can happen at any frequency, not just the bass range. When people talk about blowing a speaker up they usually mean that excessive wattage caused a thermal failure of the voice coil. That type failure means that part of the voice coil became short circuited, or open, or deformed so that continued movement is impossible or very noisy. EVERY speaker voice coil can be burned up.
What does a burned (charred) coil look like? You can't tell until the cone and spider are cut out and the coil pulled out of the gap for inspection. However, sometimes the dust cap can be removed and you can see a melted Kapton voice coil former (It goes at 750 degrees.), or bubbles in a paper or aluminum former, or even charred wire. A new voice coil is a neat little cylinder of bright copper colored wire. When operated at its rated power it turns brown. When operated above its rated power it turns black. The coil could delaminate (come unglued from itself) before it turns black. THIS SHOULD BE COVERED BY THE MANUFACTURER'S WARRANTY. But once it turns black, it s ABUSE. Excessive heat can expand the voice coil wire and the little cylinder will not be neat anymore. Eventually the wire may become unbonded and create a short or open circuit.
Thermal overload cannot be fixed in watts. A speaker takes in heat (watts), and it can dissipate heat into the air. If the air is HOT the speaker can't handle as many watts. Power handling goes way down in the summer with a speaker in the trunk. Don't put a hot amp under a speaker or in the enclosure with it.
The wire I'm test'n isn't doin' what it's supposed to be doin'... I am so glad I printed that tech sheet, with the wrong info.
Do it right the first time... or I might have to fix it for ya
haemphyst 
Platinum - Posts: 5,053
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: November 25, 2007 at 9:15 AM / IP Logged  
Well put!
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."
DYohn 
Moderator - Posts: 10,740
Moderator spaceThis member has made a donation to the12volt.com. Click here for more info.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: April 22, 2003
Location: Arizona, United States
Posted: November 25, 2007 at 9:56 AM / IP Logged  

Excellent post techman93. 

One other possible reason for early speaker failure is poor quality construction to begin with (like "Atomic AP.")

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techman93 
Silver - Posts: 591
Silver spacespace
Joined: October 28, 2006
Location: Pennsylvania, United States
Posted: November 26, 2007 at 6:36 AM / IP Logged  
My reply was taken from a website page I found to have worded what I wanted to say without me having to retype it out. Web Page
written by Toby Guynn
The wire I'm test'n isn't doin' what it's supposed to be doin'... I am so glad I printed that tech sheet, with the wrong info.
Do it right the first time... or I might have to fix it for ya
ibasspro 
Copper - Posts: 95
Copper spacespace
Joined: October 10, 2007
Location: California, United States
Posted: November 26, 2007 at 12:42 PM / IP Logged  
wow, the AP is poorly constructed?
used to be loud, used to be fast...now I am married LOL

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