does bridging drop impedance
Printed From: the12volt.com
Forum Name: Car Audio
Forum Discription: Car Stereos, Amplifiers, Crossovers, Processors, Speakers, Subwoofers, etc.
URL: https://www.the12volt.com/installbay/forum_posts.asp?tid=99696
Printed Date: May 01, 2024 at 5:36 PM
Topic: does bridging drop impedance
Posted By: davngr
Subject: does bridging drop impedance
Date Posted: December 05, 2007 at 7:10 PM
a little back ground on my question, i made a bet with a salesman at my job that bridging a two channel amplafier into one channel would cause the amplafier to *see* half the ohm's actually connected to it (ie. 4 ohm load = 2 ohm load) any how this was told to me many many years ago when i was just starting to install and thru out the years when mentioned none ever opposed to that theory. untill now, a salesman at my job disagrees with it and in turn says it makes no difference if an amp is bridged or not that the amp *sees* waht ever ohm's the speakers are at (ie 4 ohm's = 4 ohm's). the reason i ask here is because when trying to make my point it became painfully obious to me that my knowledge on the theory was here say. so knowing that there are plenty of guys on these forums that konw amplafier internal workings far better than myself i decided to post my newby question. does bridging cause the amplafier to *see* a lower ohm load than that of the speaker. ps. i really hope im right on this one, coz it's gonna hurt to have to buy this mustard salesman lunch :(
Replies:
Posted By: ferretvw
Date Posted: December 05, 2007 at 7:30 PM
Since the speaker is the load the amplifier will see whatever the sub is so a 4 ohm sub will be 4 ohms at the amp whether it is bridged or not.
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2008 Scion xB
Pioneer AVIC-D3
RF 3Sixty.2 sound processor
Stock speakers (for now ;))
Posted By: techman93
Date Posted: December 05, 2007 at 7:34 PM
Looks like you are out $ for betting on an assumption that someone told you some mystical secret wisdom of car audio electronics when they were only blowing smoke up your bum and making you as dumb as them. 
Bridging an amplifier only makes two channels into one. The ohm's depends on speakers or woofer connected to that single bridged channel. ------------- 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
Posted By: haemphyst
Date Posted: December 05, 2007 at 7:35 PM
When bridging, the voltage across the terminals doubles, thus demanding twice the current.
This 2X current demand is what makes the amplifer "see" twice the effective load, even though the load is still EXACTLY the same.
It is the same, mathematically and electrically, as running the amplifier at twice the load, in stereo. If you start with 4 ohms, and your output is X amps, and you halve the impedance, your current will go to 2X amps.
::::EDIT::::
ferret and techman are trying to throw you off the trail. This is the reason that your amplifier SEES twice the load, or half the impedance.
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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."
Posted By: davngr
Date Posted: December 05, 2007 at 7:43 PM
haemphyst wrote:
When bridging, the voltage across the terminals doubles, thus demanding twice the current.
This 2X current demand is what makes the amplifer "see" twice the effective load, even though the load is still EXACTLY the same.
It is the same, mathematically and electrically, as running the amplifier at twice the load, in stereo. If you start with 4 ohms, and your output is X amps, and you halve the impedance, your current will go to 2X amps.
::::EIDT::::
ferret and techman are trying to throw you off the trail. This is the reason that your amplifier SEES twice the load, or half the impedance.
thanks for the technical answer bro, it's waht i was looking for. just to make sure im understanding it right, the amplafier does work twice as hard when bridged but it does not actually see less ohm's so when i was told the amplafier sees a greater load it was right but the ohm's thing was not? again thanks much for the reply.
Posted By: ferretvw
Date Posted: December 05, 2007 at 8:54 PM
The question wasn't about demand on the amplifier though it was specifically about impedance which does not change, the amplifier is pulling twice as much current yes but that current is going into the speaker which is still presenting the same load to the amplifier. So I guess it really depends on how the question is asked.
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2008 Scion xB
Pioneer AVIC-D3
RF 3Sixty.2 sound processor
Stock speakers (for now ;))
Posted By: DYohn
Date Posted: December 05, 2007 at 10:25 PM
ferretvw is correct. No matter what someone may do or not do to an amplifier it will not change the impedance of the speaker. 4-ohms is 4-ohms. haemphyst is correct. Placing a load across two bridged amplifier channels will cause each channel to operate at the same level as the equivalent of 1/2 the total load. davngr, the amplifier does not "see" anything. It is an electrical device. Bridging a 2-channel amplifier with 4-ohms total is the same as loading each amplifier channel with 2-ohms. I think you and your pal should buy each other lunch.  ------------- Support the12volt.com
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