Impedence?

Okay so I went to my JL dealer today to check on my VR-series speaker repair and see what they had in the way of comps and what-not.. when I get into a conversation with one of the sales guys he explains to me.. I guess.. that 2 woofers need to be 8-ohm woofers to be wired to 2-ohms @ the amplifier.

So I'm sort of confused, because, he really is quite insistent about this. So I tell him that as long as I've messed with cars, I've always wired 2 4-ohm subwoofers for a 2-ohm load on a monoblock. I mean, this is sort of one of the first thing I learned.

Now, I'm aware that if you BRIDGE two channels, say off an A/B amp, the amp will see half-of what the speakers are wired at, but the monoblock?

Wouldn't this ruin the "monoblock" purpose? So the guy starts walking around the store talking about "how long he's done this" and then dares me to prove him wrong. "Okay" I think, and I pointed his dandy computer right at sounddomain.com and opened that handle little "Subwoofer Wiring Guide Selector" and sure enough, two 4 ohm speakers is wired at any given monoblock for a 2-ohm load.

Not So! Claims this guy, then he starts telling me how the guide is totally wrong and it is because Circuit City and Best Buy control the industry and Rockford had to change its lines all around and thats why everyone thinks that two 4-ohm speakers in parallel wire to 2-ohms when it really wires to 1-ohm.

Can anyone tell me what this guy was talking about?

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"I'm finished!" - Daniel Plainview

Hes wrong, if two 4 ohm resistors are wired in parallel, the resistance in the circuit is 2 ohms. I dont know what that guy is trying to tell you, but cc and best buy did no come up with or change ohms law.

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6th gen Celica | Alpine CDA-9827 | Pioneer GMX962 | CDT CL components | JBL 600.1 | Infinity Reference 12

I think that guy hit the crack pipe or bong a little bit too much.

Best Buy and Circuit city have nothing to do with ANYTHING.

Two four ohm loads wired in parallel will create a 2Ohm load.

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Right Right but this guy was telling me that "internally" the amplifier is really operating at 1-ohm because all a monoblock is a bridged amp so its really at 1-ohm.

He kept saying "amp sees half of what the box sees."

Can you even guess at what he meant?

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"I'm finished!" - Daniel Plainview

good question...now i'm curious myself.  Is a monoblock amp the same as a bridged amp?  if so then wouldnt the 2 ohm load actually appear to be a 1 ohm load (assuming a monoblock is the same as a bridged amp)  but if it is the same then why put terminals for 2 subs ( 2- and 2+)  on a monoblock?  if a monoblock was a bridged amp then wouldnt there only be a need for 2 terminals (1- and 1+) or would both sets of terminals on the monoblock be bridged meaning u could hook up 2 sets of dual 4 ohm subs, each putting out a load of 1 or 2 ohms?  I'm confusing myself here now, but if a monoblock is the same as a bridged amp then why would they sell both?

Mono = one channel.  No relationship to a bridged stereo (2-channel) amp.  They are different animals.  Amplifiers don't "see" anything, they supply voltage and current into an impedence load.  If you connect a 2-ohm load to an amp, it operates into a 2-ohm load.  Poormanq45 had it right: too much crackpipe or bong action happening somewhere.

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The guy is very confused.

https://www.bcae1.com/bridging.htm

Print that out and give it to him. He probably won't understand it.

I'll try to give him the bridging for idiots explanation:

First: Mono amplifiers aren't necessarily bridged amplifiers.

Second: The box doesn't see anything. Tell the guy this statement makes him sound like an idiot.

Third: The load the amplifier "sees" has nothing to do with what's in the stupid amplifier. It has everything to do with how the resistors (speakers) are wired together.

Fourth: quote from bcae1.com, because this is the most important part: "If we take a single 4 ohm speaker and bridge it on that same amplifier, the amplifier will be able to apply twice the voltage across the speaker. This is because while one speaker terminal is being driven positive (towards the positive rail), the other terminal is being driven towards the negative rail. This will allow the entire power supply voltage to be applied to the speaker's voice coil. It will now be able to drive the 4 ohm speaker with 40 volts instead of 20 volts..."

Fifth, and finally: another quote from that page, because I'm lazy: "The same amount of current flows through the output transistors whether the amplifier is driving a 4 ohm mono load or 2 ohm stereo load. As far as the amplifier is concerned, they are the same load. NOTE: Some people say that when an amplifier is bridged onto a 4 ohm load, it 'sees' a 2 ohm load. While it is true that the same current flows whether the amp is bridged on a 4 ohm load or a 2 ohm stereo load, the amplifier is driving a 4 ohm load across its outputs. A single 4 ohm speaker can never be a 2 ohm load."

In other words: Just because the output transistors have the same amount of current running through them when bridged doesn't mean that the amplifier "sees" a different speaker load!

The wiring guides all over the internet are correct and have nothing to do with Circuit City and Best Buy. The fact that he came up with some conspiracy theory like that to explain something he obviously doesn't understand ... is well, really freaking funny. You should laugh at him.

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New Project: 2003 Pathfinder

The guy used to wander up and down the street talking to himself and yelling at his imaginary demons...then he was tagged to sell subs.  Go figure.

or maybe the demons werent imaginary and its all a dastardly evil plan to have him corrupt the minds of all who want to know the TRUTH about audio.

lol, you never know.  ;-)

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New Project: 2003 Pathfinder

Why is it so hard for some people to believe that a heatsink can have one dedicated channel of amplifier in it? A mono amp is just that mono - meaning ONE! It has nothing to do with bridging or not bridging. If you have a 2 ohm net load, HOWEVER you achieve it (1 @ 2 ohms, 2 @ 4 ohms, 4 @ 8 ohms... whatever) THAT is the load a mono amplifier will see. This guy really was stoned, (or just a MORON - this is the likely scenario) and he can suck a fart out of my ass if he thinks he knows more than the people here. He is simply and completely WRONG. I know people are always bragging about "how long I've been doing this"... I see it in Bakersfield all the time, but 90% of those people never stayed awake in class (let alone absorbed anything), and can't find their own asses with both hands when it comes to understanding electricity.

--Sorry for the language, but people like that piss me off. It makes it harder for people (like kfr01, DYohn, Steven, Stevdart (anybody else I may have forgotten - sorry) and myself) who really *DO* understand to help people who *DO NOT* understand.

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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."

Man, you could really mess with the guy.  You could bring up DCR, or better yet JL voice coils which have a 3 ohm impedance.

Steven Kephart

Adire Audio

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kfr01:

This wasn't freakin funny at all! Man it felt like the I was in the twilight zone or something! I'm standing in the the highest volume shop in town (i'd post a link but I still want a deal on a set of Boston Pros ) and the guy is *insisting* that two 8-ohm woofers are needed for a 2-ohm load on my monoblock and then snickering to himself and saying "Well if its always worked for you before..."

This wasn't amp specific either, he was gesturing to all the amps saying that no one really understands how they work and they are all really 1-ohm stable, and, because of the way the industry has taken shape, when monoblocks say "2-ohms" its really because companies assume ppl will just hookup 1-ohm loads thinking they are hooking up 2-ohm loads (because even tho the circuit is at 2-ohms, the amp 'sees' 1) and no one really knows any better. Thats when he got off on Circuit City and Best Buy controlling the industry.

What Placid Warrior said was the crux of his argument; that monoblocks have the 2 - and 2 + outputs so when you only use two of them, you are bridging them for a net load that halves what the speakers come to... I think, I mean he kept using the phrase "bridged internally."

Steven Kephart:
This actually all started because I was asking him about wiring up 3 JL 10w3's... like, I said I wanted to wire three 10's.. 4-ohm DVC's, for a net of 2.6 ohms .. he responded "why would you do that? you'd waste alot of power" to which I said "well, its only about 200-watts and I was looking at real high efficency drivers anyway, I think I can get the volume I want from 600 watts." So then he moves on to trying to sell me two Boston 12's.. DVCs with those new goofy jumpers that let you set the woofer to 2 or 8 ohms.. I say "do these come in SVC version, if I ran 2x12's I'd want all 800-watts from my amp"

To which he looks at me funny and starts explaining that 2 8-ohms woofers in parallel *would* be a 2-ohm load.... nevermind that a minute ago *three* 8-ohm woofers in parallel would be "wasting power"...

What is DCR anyway?

So yea I have to go back up there tommorow and talk to some other guy about my broken-speaker.. I'm really tempted to show him this thread..

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"I'm finished!" - Daniel Plainview

sedate,

Bottom line is this salesman does not know what he is talking abouit and needs to go back to school.  It is people like this who give car audio a bad name.

What store and what town may we find this brainiac?  What's his name?

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sedate wrote:

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he was gesturing to all the amps saying that no one really understands how they work and they are all really 1-ohm stable....

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Actually he is correct in this statement. All amplifiers are 1 Ohm stable as long as the maximum power and thermal capacity are not exceeded.

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I understand your point Poormanq45 but that's not strictly correct.  Many amps can sustain a 1-ohm load that are not rated for it, but many others are not 1-ohm stable at all and will go into a shorted condition at less than rated load levels.  Some amps have short-circuit protection set at 1-ohm.  Others will simply fry the output transisters with 1-ohm load as soon as power is applied.

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Poormanq45:
"all amps are 1-ohm stable"
As has been my expierence as well... I've hooked up a 2-ohm mono load to a 6-channel I have on numerous occasions with no problems.. As my friend did with his amps all the time..
The "meat" here is that he was telling me that that to get the maximum *rated* power from my amp(480wattsx1@4-ohms,800wattsx1@2ohms), two 8-ohm woofers in parallel would do that. If I'd been doing it differently, he was "glad its worked for me."

DYOhn:
I really don't want to smear the store, they've always given me real good deals and I think (would like to believe) the guy was earnestly trying to help.. even if he was dead wrong, or confused, or not explaining himself well enough... and a wee bit smarmy about it.

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"I'm finished!" - Daniel Plainview

sedate wrote:

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DYOhn:
I really don't want to smear the store, they've always given me real good deals and I think (would like to believe) the guy was earnestly trying to help.. even if he was dead wrong, or confused, or not explaining himself well enough... and a wee bit smarmy about it.

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I was being a bit facetious and agree it is never good to publicly impugn a business... but it might be good for you to express your experience to the store manager and let them know some of their employees seem to be spreading bad information.

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Sedate: I'm moderately confident he is confused because of the reasons I listed earlier. I seriously think you should print the bcae1 page out for him and watch his eyes widen. :-) Highlight with yellow highlighter the lines I quoted.

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New Project: 2003 Pathfinder

DYOhn, kfr01:

Naww, like.. the guys that work this store are *real* jerks. I know that if I went into this store trying to complain about *anything* it would work out horribly. This is the kind of place where the management would say "well screw you get out then." Like.. I'm kinda used to car buffs being sort of snotty and elitest, but the guys at this store are just totally over the top. I dunno what their deal is.   I've gotten some really bad advice at this shop as well... nevermind the whole woofer-shopping debacle that resulted in this whole thread.

I'm thinking I will probably wash my hands of the shop after my speaker gets fixed...    As much as I love car audio, I really dread going to this place.

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"I'm finished!" - Daniel Plainview

Thats probly the best thing to do...u shouldnt be dealing with a place like that anyways.  If people u know ask where u buy your stuff then they'll probly go to the same place thinking its good cause u got your stuff there.  We have a place like that where i am and plenty of people go there...and come out with crap systems.