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#### onebluec5

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Is there a correlation?

Assuming equal power output and amp quality, let's say the difference between a 4ohm speaker being driven at 4ohms vs a 4ohm speaker being driven by a bridged amp (with an effective 2ohm load).

#### Sarthos

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Umm, can you give a more "concrete" example?

ie: You're saying like running a pair of speakers on an amp rated 100 RMS x 2 @ 4 ohms, vs running each speaker on its own amp that does 100 RMS x 1 @ 4 ohms bridged?

#### onebluec5

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Let's say I have two amps - same brand/series/etc...

Amp A (1ch) - 100W x 1 @ 4ohm
Amp B (2ch) - 25W x 2 @ 4ohm, 100W x 1 @ 4ohm bridged

If I ran a speaker off Amp A vs Amp B bridged, would there be a SQ difference?

Sorry if I am not explaining this correctly!

#### Sarthos

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Okay that's what I thought. The main difference is gonna be that Amp B is gonna heat up a lot more than Amp A. Namely since Amp B is likely gonna be about half the size, with half the heat dissipation capabilities, then add in the fact that Amp B is gonna be driven at a lower resistance, making it less efficient. Might make a warm amp.

#### onebluec5

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Okay that's what I thought. The main difference is gonna be that Amp B is gonna heat up a lot more than Amp A. Namely since Amp B is likely gonna be about half the size, with half the heat dissipation capabilities, then add in the fact that Amp B is gonna be driven at a lower resistance, making it less efficient. Might make a warm amp.
Would there be any hypothetical difference in SQ?

#### nick650

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"can" higher the impedance less the amp has to work to produce it and if you can run it higher, do so.

#### Sarthos

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Hypothetically? Well hypothetically it might not matter cause an elephant could drop out of the sky and smash your car on your way to work tomorrow, destroying the car and killing you.

It can make a difference, likely a small one though. Namely because there can be some small differences in the outputs of the two channels that get bridged, but the biggest difference in SQ is the one where you have no S cause the amp overheated and went into protect.

#### ChrisB

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Would there be any hypothetical difference in SQ?
If both amplifiers measure within 1 decibel of each other over the entire audible spectrum (20Hz to 20kHz) and have inaudible distortion levels (less than 1%), I'd be willing to bet that you would NEVER be able to discern the difference between the two in a properly designed double blind listening test. Now, let's further compound this by tossing these amplifiers in a mobile environment where you are subjected to extraneous noise out of your control (generally 50 decibels or greater) and reflections from the vehicle's glass and various interior points. What I am getting at is there are a lot more things at play regarding sound quality in the mobile environment than one properly designed quality amplifier versus another.

#### minbari

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If both amplifiers measure within 1 decibel of each other over the entire audible spectrum (20Hz to 20kHz) and have inaudible distortion levels (less than 1%), I'd be willing to bet that you would NEVER be able to discern the difference between the two in a properly designed double blind listening test. Now, let's further compound this by tossing these amplifiers in a mobile environment where you are subjected to extraneous noise out of your control (generally 50 decibels or greater) and reflections from the vehicle's glass and various interior points. What I am getting at is there are a lot more things at play regarding sound quality in the mobile environment than one properly designed quality amplifier versus another.
^this!

95% of people will never know the difference, except where there wallet is concerned. the bridged amplifier will more than likely cost less.

#### sqshoestring

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There are a lot of threads on this here, some explain exactly what types of distortion this affects. Bridging does increase THD in the amp but it is such a small amount it is not an issue except certain situations. Maybe you run very efficient horns at low power they might pick it up, maybe you have a crappy quality amp and doubling the distortion makes it that bad (though unlikely), or have the quietest car on the planet. It also depends on the range you run; most run midbass no problem but your ears are going to be most precise in the vocal ranges.

I will say many 4ch are not as robust as comparable 2ch. Running low loads will make more heat and the amp will be less efficient per watt. Running 4 ohm bridged is the same as 2 ohms not bridged far as the (a typical amp) amp is concerned.

#### HondAudio

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Would there be any hypothetical difference in SQ?
No.

Impedance is a quantifiable electrical measurement.

Sound quality is a completely subjective measurement. You might think your install sounds great, and your buddy might think it sounds like crap. You'll be biased, of course, but the "quality" of the sound can only be measured by what somebody thinks of it.

#### ezutel

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THD level at 2 ohms (4 ohms bridged) is 10x than at 4 ohms...so if you are running at 0.01 % THD at 4 ohms and 0,1 % bridged it´s no audible diference

#### sqshoestring

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Most amps have excellent sonic quality, until they clip. Long as you are not talking really old/crappy or the cheapest amps you can find.

Most differences in amps are power or frequency response, not sonic quality, so always figure out if you have those two things first (and differences in FR are typically slight and people EQ everything anyway, but some do notice a slight difference). Overhead means the amp has power to spare, if you have an overhead problem you have too small of an amp.

Some say amps have different dynamics, and they can though likely slight. But its not something that is commonly measured, if there is a good way to measure it.

#### onebluec5

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No.

Impedance is a quantifiable electrical measurement.

Sound quality is a completely subjective measurement. You might think your install sounds great, and your buddy might think it sounds like crap. You'll be biased, of course, but the "quality" of the sound can only be measured by what somebody thinks of it.

By SQ, I mean accuracy to the original source.

I completely understand that the difference would probably be so minute that it is indistinguishable to the human ear, but I'm curious of the true physics/science behind what happens when the impedance is lower.

If I'm reading correctly, THD increases as impedance is lower. Is there a point wherepast the THD actually increases as impedance is higher?

#### Sarthos

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Hmm, that's a good question. I can't think of any off the top of my head. I mean obviously if you have an amp that's rated 4x100 @ 4 ohms and try to run it 4x100 @ 16 ohms you'll be clipping and that'll cause HUGE THD.

As far as how impedance can cause a difference in sound quality, think of it like this... If I can remember how to explain it...

Imagine that the amp's signal is a car traveling forward. The mass of the car is proportional to the impedance on the signal. Now, imagine EMI interference as being wind traveling perpendicular to your car. If you have a lightweight car (low impedance) the wind will shake your car a ton, or the EMI will be more effective. If you have a heavy car (high impedance) the wind (EMI) will be less effective.

But that's only part of it, I'd just avoid running amps at low impedance so you don't fry the amp over time.

#### andrave

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There is a lot that goes to sound quality beyond thd. You can "hear" things like damping factor. I believe that I can "hear" the difference between a class AB and a class D on subs. Class D amps have a looser sound than the same class AB, and they usually have a lower DF... I believe its an audible difference.

#### cubdenno

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There is a lot that goes to sound quality beyond thd. You can "hear" things like damping factor. I believe that I can "hear" the difference between a class AB and a class D on subs. Class D amps have a looser sound than the same class AB, and they usually have a lower DF... I believe its an audible difference.
You realize that the reason behind the rise of class D amplification is they are more efficient, smaller in size therefore cheaper and sonically indestinguishable from the other classes that do not add anything to the signal?

Damping factor has been disgussed here ad nauseum. Andy from JBL explains Damping factor the best. Cliff's notes version. It is a marketing tool to sell uninformed people stuff. Search for Damping factor.

Some of the most highly praised amplifiers out there are tube amps. DF is single digits.

#### Sarthos

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Some of the most highly BASHED amplifiers out there are also tube amps FWIW

#### minbari

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You realize that the reason behind the rise of class D amplification is they are more efficient, smaller in size therefore cheaper and sonically indestinguishable from the other classes that do not add anything to the signal?

Damping factor has been disgussed here ad nauseum. Andy from JBL explains Damping factor the best. Cliff's notes version. It is a marketing tool to sell uninformed people stuff. Search for Damping factor.

Some of the most highly praised amplifiers out there are tube amps. DF is single digits.
I will add that if you do that math on most amplifiers, even ones that claim dampening factor greater than 100. once you put a speaker on them, they are less than 20 and some in the single digits. still plenty since most impedance are less than 4.

By SQ, I mean accuracy to the original source.

I completely understand that the difference would probably be so minute that it is indistinguishable to the human ear, but I'm curious of the true physics/science behind what happens when the impedance is lower.
if the amplifier is doing its job, then there is really no science to it. you put in a signal, it comes out the other end bigger if a change in imepdance from 4 ohms to 2 ohms actually makes a sonic difference, then the amplifier is NOT really 2 ohm stable.

#### sqshoestring

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Low loads increase current flow and lower efficiency, but they should not change THD much. The transistors might function slightly different under the higher output but the amp is not a very good one if the difference is significant. What the amp is optimized to handle really depends on amp design. Really all a low load does (providing you don't have a new regulated output amp) is let more amperage flow through the amp and speaker. The voltage stays the same. A low load rated amplifier is just capable of making enough power to supply the increase in current flow. However transistors and many things tend to be less efficient at more amperage and make heat, while more voltage is not so much that way.

When you bridge that is a different story, you are putting two channels together into one. One is inverted, so when the normal channel goes positive the inverted goes negative. There is no ground anymore so if the synchronization of the channels is off a little you can get a type of distortion, plus you add together the inherent distortions of both original channels and running them at a lower load. But in the scope of things making an amplifier is a very basic task, it is a decades old technology so its only a matter of making it cheaper mostly. They are massively ancient compared to that phone in your pocket, from an engineering standpoint. That does not mean someone can not make a crappy one, but even a pyramid amp should have low THD numbers. It may lack in other areas like ratings and noise protection and build quality and is likely an old design, then again many class AB are old standard designs, I mean they work so why screw with them? The only new designs today are mostly full range class D and Hybrids. In cheaper amps there are piles of them with the same board in half a dozen cases, and they even change that board to fit other cases but use the same circuit. Most of those are class AB. This may not be so true of more accomplished amp makers, but most of them do not sell the same amp under various names.

I'd say in most cases what you get with an amp you buy, is just what they wanted to make. If it is not perfect, they did not want it to be.

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