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How to check Impedence of Subs?? 

 

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 Post subject: How to check Impedence of Subs??
Posted: Sat Dec 16, 2006 2:09 pm 
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I have had a problem with my amp lately and it has been into service twice in a month. The first time to fix and the other time under warranty. I have been told that if it comes back again that they will charge me.

Anyways the part they replaced was output fets and power supply fets. I am unsure as to what these are??

Anyway they have told me to check The Impedence (Ohms) of the Speakers including sub. It is a monoblock amp and all I am running off are 2 subs.

I have double checked the instructions and it says for a 2 speaker system that Subwoofer (min TOTAL 4 ohms) and that is hooked up to one speaker connection and the same for the other side speaker slot Subwoofer (min TOTAL 4 ohms). I hope this all makes sense.

I think I am running it all properly, becuase I have had this amp for about 2 years and the fault only occured in the last few months, so I am thinking it was the actual amp that gave way.

So to get to the point how do I check the impedence (ohms) of speakers/sub??
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Posted: Sat Dec 16, 2006 2:22 pm 
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I can't be sure, however going from my engineering days, get a multi-meter, set it to resistance and connect 1 lead to 1 wire and the other lead to the other wire.

 

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Posted: Sat Dec 16, 2006 8:02 pm 
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^ that'll get you a good enough reading, as in most cases the voice coil resistance is almost the same as the impedance.

You could of course check the specs on the sub itself. It'll tell you what it should be.

If after testing the resistance you find the coil is significantly different from what it should be, you've got a dead sub, and it may be killing your amp too.

BTW: What amp is it? If it's a monoblock it's a rather poor one if it's minimal impendance load is 4ohm. Most are good down to 1 ohm. If you've wired your two subs up in parallel (two 4Ohm subs) the amp will see 2Ohm (and yeah you'll overload the amp).

Lets us know what equipment you have so more info can be provided.

 

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Posted: Sat Dec 16, 2006 9:03 pm 
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use an impedance multimeter, a normal one on resistance will give u a good indication of weather or not the sub is working, but wont give u a proper reading

 

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 Post subject: Re: How to check Impedence of Subs??
Posted: Sat Dec 16, 2006 9:45 pm 
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Bluexr6 wrote:
Anyways the part they replaced was output fets and power supply fets. I am unsure as to what these are??


FET stands for Field Effect Transistor. They are high power transistors that would be used as the output stage of your amp and also to supply high current from the power supply.

Your speaker impedance roughly equates to their resistance which can be measured with a multimeter .

As data_mine said, if you parallel the speakers you will halve their impedance, which means too much current might be drawn causing the power supply and output FETs to fail.
(Current=Voltage/Resistance)

I don't know if you are bridging the amp but that might effect it too. I have an amp that will run bridged into 8 or 4 ohms but not 2 ohms. (Mind you it's not a car amp - 830W RMS bridged!- but the same principle should apply.)

 

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Posted: Sun Dec 17, 2006 9:43 am 
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Thanks for the replys.

Okay the amp is a Sony XM-DS1600P5 Monoblock. Subs are 2x12" Pioneer, 800w max. 400w nom. 4ohm impedence Model no. TSW305C.

The only info I know about car audio is how to wire it up. When it comes to the technical stuff I don't really know much.

I forgot to mention that from the first time I got it fixed it worked for about 2 1/2 weeks before it played up again.

The way I have the subs wired up is, each speaker is wired on their own terminal on the amp. ( if this makes sense).

Where is the best place to check the ohms from?? Do I conect the system up and check it from the back of the speaker when the system is runnng??
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Posted: Sun Dec 17, 2006 11:49 am 
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To check the speakers, make sure they're disconnected (and off of course).

Specs for the amp says it can handle either 2 or 4 Ohm.

Specs fro teh subs confirm they are 4 Ohm each. So wired in parallel like they're supposed to be, will result in a 2 Ohm load on the amp.

So check the subs, make sure they're reading around 4 Ohm each. And get back to us.

 

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Posted: Sun Dec 17, 2006 12:01 pm 
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data_mine wrote:
To check the speakers, make sure they're disconnected (and off of course).

Specs for the amp says it can handle either 2 or 4 Ohm.

Specs fro teh subs confirm they are 4 Ohm each. So wired in parallel like they're supposed to be, will result in a 2 Ohm load on the amp.

So check the subs, make sure they're reading around 4 Ohm each. And get back to us.
ok I have checked the two subs individually. One had a reading od 3.3ohms and the other3.4 ohms. I got my multimeter out and set it on the ohms section. I put one lead form the voltmeter on + and the other one on -. Is this is how I was suppost to get the reading??
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Posted: Sun Dec 17, 2006 12:04 pm 
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Yep, and both those figures are ok for a 4Ohm impedance sub. (impedance and resistance are similar, but different, so the numbers won't match).

 

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Posted: Sun Dec 17, 2006 12:19 pm 
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Well supposedly the amp can put out 900W RMS @ 2Ohm...so wiring the 2 subs in parallel will see a 2Ohm load on the amp. If you wired the subs in series before and tried to pump it harder then the amp could handle, then that may have caused the failure of the amp. the amp only supplies 500W RMS @ 4Ohm so it may have struggled supplying the power to the subs if in series.

Anyways if wiring it in parallel and running it at 2Ohms still causes trouble, I think you should get a new amp seeing your subs seem okay with a 3.3Ohm resistance.

Even though you didn't ask for an opinion, I will give you one anyway...Sony were never good with Car Audio products and their stated power ratings and figures are usually over rated and they don't seem to last the distance as you can see.

phong =P~

 

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Posted: Mon Dec 18, 2006 9:59 pm 
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So with my subs having the reading of 3.3 and 3.4, I should be able to connect it as per instructions and nothing should happen to the amp this time if everything is within specification and per instruction

Only problem if something happens again I might lose the $390 I spent fixing the amp. Stupid me for taking it to a sony authorsied repairer. If it breaks down again I will have to try and recover the money.

Just a quick question though. If the reading as I have discovered is for example 3.3 ohms and the amp says that for a two speaker system that it needs per speaker min total 4 ohms then is it enough and should the subs have a greater reading for everything to work together.

Also if the amp has worked for the better part of two years then it really shouldn't be the way I have hooked it up, it would be the amp that has given up?? Would I be safe in assuming this?
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Posted: Mon Dec 18, 2006 10:02 pm 
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Thanks for all your patience with the questions i am asking
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Posted: Mon Dec 18, 2006 11:41 pm 
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The specs for the amp (I looked them up) say it's good for 2Ohm as well.

The resistance of the subs voice coil and it's impedance are NOT the same, however they are normaly close. So it's safe to assume that with readons of 3.3 and 3.4 Ohm of resistance, the impedance will be close enough to 4Ohm each, that they'll be fine.

Wire teh two in parallel to the amp, the amp will see abotu 2Ohm of impedance and be happy. If the amp dies again, fight Sony, get you're money back, then bin it. You're not (from what you've told us) doing anything wrong.

 

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Posted: Tue Dec 19, 2006 7:51 am 
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You should have no problem connecting those subs to an amp stable for 2ohms.
The resistence of the subs when they are operating will be higher than that anyway.

Box up the sony and grab another amp, i've had nothing but trouble from Sony Car audio.

Home audio on the other hand they makle some nice gear.

 

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Posted: Tue Dec 19, 2006 10:26 pm 
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Thanks for all the replys guys much appreciated.

I am gonna set my system up again in the next couple of days. If it breaks again then I will be definately talking to sony about getting my money back.

Yeah I'm not gunna touch Sony car audio products ever again.

What do you think of soundstream equipment??
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