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How do you know if a sub or midwoofer is good and not dead without playing it?

I know 2 ways.

1. Cone movement, quick tap, more information below.
2. Measure Resistance. More below


Measure resistance with a DMM, it should measure the nominal resistance value. If it is rated at 4 ohms, it should measure close or just over that, if there are 2 of them both should measure the same, a 0.2 -0.4 difference is OK, One ohm or higher measurement can indicate an issue with the connector and coil leads and not a bad coil issue, and it could be an easy fix but the topic is not fixing those issues, simply check for a faulty driver.

Sometimes it may take a few seconds to get a steady reading, no need to panic or be impatient, sometimes we may just get a peak reading of the lowest reading within a 0.1-0.3 ohms, that is also Ok and sometimes a solid steady reading, it all depends on the pressure applied or the part of the connectors used to measure it.

The other method is to push or tap gently on the cone, if you hear no sound and it feels smooth, it is good, if it makes a sound like when you tap on an empty food can with a few coins inside or like a metal rattle sound, that means the voice coil is dead. If there is no cone movement, the motor is out of alignment, seized or broken.

About Cosmetics
Regarding punctured surrounds, that will affect the resale value, it can be fixed with a special glue and hold and perform like if there was no puncture in it.


I hope this helps and you should not shy a way for buying used expensive subs or speakers.
 

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This is correct and very interesting for many who do not know, another quick way if you don't have a dmm is by using a 9v battery and giving a quick tap. The positive to positive will make the cone pop up and negative to positive will make the cone pop down and like this you can test a dual voice coil sub to see if both coils work.
 

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This is correct and very interesting for many who do not know, another quick way if you don't have a dmm is by using a 9v battery and giving a quick tap. The positive to positive will make the cone pop up and negative to positive will make the cone pop down and like this you can test a dual voice coil sub to see if both coils work.
Excellent tip for "toning out" multiple speakers in a system too. When you have a mess of wires and don't know what goes where, this is a great trick.

Just to be on the safe side... 9V into 8ohms is ~10watts. And since we are talking DC.... be cautious!

No speaker, regardless of power handling, "likes" DC across its coil(s). Short bursts are OK for just about everything except a tweeter - so DC is a no-no across their fragile voice coils. 9V batts are convenient cuz their terminals are close together, making a tap across most speakers easy, but its safest to use 1.5V batt with a short length of wire. If someone is gonna test a tweet thru a crossover, the cap protects the VC from DC, but once the cap is "charged", no current will pass thru it. A discharged cap will allow a micro second of DC to reach the coil so listening closely is required, otherwise, nada. BTW: to discharge a charged cap in a cross over: use any conductor across it. You'll sometimes get a visible spark too, depending on how big the cap is. Make sure theres no ignitable fumes around. And NEVER short the terminals of a large cap, anything in the single digits (like a 1uF) can knock a full grown man and his date to the ground.
 
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