# Bridging vs. Stereo SQ



## bamelanc (Sep 13, 2009)

Is SQ adversely affected when bridging vs. simply running an amp in stereo. Lets say I had two amps, bridge them both and put one on each channel. Will there be a significant difference between that and a similarly powered 2 channel? (100 watts bridged vs. 100 watts per channel)


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## Hillbilly SQ (Jan 26, 2007)

It will make the amp run hotter and increase thd. Other than that it depends on the amp and who you ask.


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## minbari (Mar 3, 2011)

nope. ussualy the difference is .01%THD vs .1%THD neither are audible.

there is no magic in bridging. you are just taking the left channel and summing it with right channel (inverted). the sum of the 2 channels gives you a theoretical 2X power than the 2 channels do by themselves. (this has to do with how it loads more than anything.) in reality you will get 1.5x-1.8x . That summing effect also magnified the THD, since you are getting both channel THD into one channel.


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## Hillbilly SQ (Jan 26, 2007)

I have my popcorn ready. This could get entertaining.


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## minbari (Mar 3, 2011)

Hillbilly SQ said:


> I have my popcorn ready. This could get entertaining.


pass the salt


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## simplicityinsound (Feb 2, 2007)

u r going to get vastly differing opinions on this.

i have met people who swear both ways...some refuse to ever bridge due to the increase THD, though as mentioned it is doubtful that a human ear can pick it up, however, we often make other decisions based on other similar differences, perhaps the better question is if you had two amps, one is rated at 1%THD and one at .01 or .001THD, but the former is 30 percent cheaper, produces 30 percent more power. (often the case of a medium 4 channel bridged versus a big two channel)...which would you choose?


on the flipside, i know people who loves bridging because they claim better headroom and better stereo separation. of course dependant on amps as above...but thats their take when talking about quality gear.


to me, if there is a two channel of sufficient power, size and price that fits the bill, i usually use it, or better, a dual mono. but if not, i dont hesitate to bridge.

i have really yet to hear a difference..my own car for example, usea a 4 channel bridged to send 250 watts to each midbass.

i think personally, if you use top shelf gear, you will be fine with either method.


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## Hillbilly SQ (Jan 26, 2007)

Say someone wants to cheap out and bridge a fleamarket amp.

I personally am not a fan of "cheap" power. Quality parts and plenty of rail voltage goes a long way.


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## BrianAbington (Jul 27, 2012)

When I was competing I took my 4ch amp from running tweets and mids using internal x/o's to using the passives and bridged and on the whole everything got better simply because the head room went up. I felt that placement was better and I noticed that my tweeters didn't distort as easily because I could keep my gains lower.


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## minbari (Mar 3, 2011)

Hillbilly SQ said:


> Say someone wants to cheap out and bridge a fleamarket amp.
> 
> I personally am not a fan of "cheap" power. Quality parts and plenty of rail voltage goes a long way.


garbage in garbage out. cheap fleamarket amps dont sound good un-bridged


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## lizardking (Nov 8, 2008)

I know the Mcintosh MCC404 bridged is .007% THD vs .005% unbridged and that is at rated power from 250 milliwatts to rated power. I guess it depends on the quality of amp you chose.


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## chad (Jun 30, 2005)

I'm fairly competent in the understanding of these things but I fail to understand how .005+.005=.007

Yall understand that you are adding to channels correct, literally.

Now given that noise is random and the channels are out of polarity to bridge one could argue that some will cancel out... bit no less than half of one channel which still equates to .0075


Now lets take a head-count of who can hear the difference? between .005, .007, and .01

This guy can count them on all his fingers


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## lizardking (Nov 8, 2008)

The MCC302 is also .005% THD at rated power unbridged and .008% bridged at rated power. Who knows how they do it, but it's a Mcintosh.


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## minbari (Mar 3, 2011)

love it. Let's see how many can hear the difference between 0.5% and 1%. I bet the results are the same

Sent from my phone using digital farts


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## chad (Jun 30, 2005)

lizardking said:


> The MCC302 is also .005% THD at rated power unbridged and .008% bridged at rated power. Who knows how they do it, but it's a Mcintosh.


well that's .0075 rounded up, so the random and cancellation hypothesis may just hold water.


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## lizardking (Nov 8, 2008)

Mcintosh states that running their amp bridged provides a more powerful stereo reproduction with two full frequency range 400 watt amplifiers. MCC404M/404 model for example.


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## bamelanc (Sep 13, 2009)

lizardking said:


> Mcintosh states that running their amp bridged provides a more powerful stereo reproduction with two full frequency range 400 watt amplifiers. MCC404M/404 model for example.


Would this be true for a 4 channel amp...or for two completely separate amps?


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## chad (Jun 30, 2005)

lizardking said:


> Mcintosh states that running their amp bridged provides a more powerful stereo reproduction with two full frequency range 400 watt amplifiers. MCC404M/404 model for example.


if that's the case then they are admitting to ****ty crosstalk which is rather rare n modern amplifiers 

Here's a hint, don't believe everything an audio manufacturer's marketing department tells you.

In other words, you're fuken-A right it sounds better, you spent twice as much money with them


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## ChrisB (Jul 3, 2008)

In my old Civic coupe, I ran one amp bridged per door on the components run passive. I'd be willing to bet that any distortion I heard was from the speakers themselves versus the amplifier doubling in distortion by bridging. I went from 60x2 to a conservative 240x1 per door.


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## simplicityinsound (Feb 2, 2007)

does damping factor drop signifcantly when bridging?


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## WRX2010 (Jun 11, 2011)

simplicityinsound said:


> does damping factor drop signifcantly when bridging?


oh no . . . this thread is going to get interesting. 

Does bridging make the amp sound different than in stereo??? :laugh::laugh:


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## lizardking (Nov 8, 2008)

Mcintosh seem to be pretty darn good at building amps. I'm sure the amps they design and build do exatcly what they state. The question becomes does it really matter? I would guess that its all unaudiable.


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## ChrisB (Jul 3, 2008)

WRX2010 said:


> oh no . . . this thread is going to get interesting.
> 
> Does bridging make the amp sound different than in stereo???  :laugh::laugh:


Why not turn this into a panned monophonic discussion versus time aligned stereo while we are at it?


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## minbari (Mar 3, 2011)

simplicityinsound said:


> does damping factor drop signifcantly when bridging?


does it matter? once you connect a speaker to an amplifier the dampening factor drops like a rock. if it had a DF of 4 instead of 5, would you hear it?


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## chad (Jun 30, 2005)

minbari said:


> does it matter? once you connect a speaker to an amplifier the dampening factor drops like a rock. if it had a DF of 4 instead of 5, would you hear it?


The load is part of the DF, it's not the speaker that makes it drop. 

DF is the load impedance/output impedance.

Since output impedance doubles in bridged the damping factor is cut in half.

But since DF is as moot as the number of midgets in America divided by the number of gay goats in Australia then... Make your own case.


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## minbari (Mar 3, 2011)

I think we are arguing the same point here though


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## trojan fan (Nov 4, 2007)

Hillbilly SQ said:


> I have my popcorn ready. This could get entertaining.





minbari said:


> pass the salt



x2....:snacks:


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## EVcelica (Dec 30, 2008)

Wow, that was an interesting read. 
THD doesn't double because you are adding two channels together, first of all it is a percent!!! So this theory of adding them would yield the same THD percent, not double. 
If you bridge your amp to run one four ohm speaker, each channel will be seeing two ohms since they share the load. So THD increases since you are decreasing the impedance. Your power should at least double, even quadruple on some amps, meaning instead of [email protected] 4ohms, you would get [email protected]; but each side would see only 2 ohms. much like if you ran 2 ohm stereo speakers the amp would be [email protected]


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## sqshoestring (Jun 19, 2007)

chad said:


> But since DF is as moot as the number of midgets in America divided by the number of gay goats in Australia then... Make your own case.


:laugh: Thanks for making my day Chad lol.

IIRC it was the noise floor that made most amps higher THD bridged, but since it hardly matters I think I forgot....but I know the tech details are posted here likely many times someplace.

Well of course I would take the larger amp that did not need to be bridged all else equal, why not.

You should not get more heat bridged unless you lower the ohm load, which would double to stay the same to the amp internals. So if you ran one amp 2x4 ohms then two amps bridged on same, you would double the heat because you have two amps now and more heat yet because they are running at 2 ohms effective (2x4ohms=4 ohms/ch; 1x4ohms=2 ohms/ch). More of a consideration for older amps though.

Beyond all that what would I do in practice, and having run stuff both ways? I have heard amps that did not sound as good bridged on highs/mids. I think if you ran a Mac it would not matter at all. Midbass and subs you need a really crappy amp to tell the difference in SQ from bridging. Make sure you are not including clipping distortions you have because your amp is too small, always ear test at a medium volumes. So yeah, if I needed to bridge on mid/highs I would do some testing first and not do it unless I needed to. No, I don't have amps like Macs sitting around to use anymore lol, but many amps are very capable of bridging and being below audible noise levels.


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## jguthrie (Nov 14, 2011)

But isn't the point of running bridged to get the sub to hit on both L/R signal? Or, a better way of putting it, you might only have 1 sub so you don't want to run off L or R, but both.


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## sqshoestring (Jun 19, 2007)

jguthrie said:


> But isn't the point of running bridged to get the sub to hit on both L/R signal? Or, a better way of putting it, you might only have 1 sub so you don't want to run off L or R, but both.


Yes but lot of people here will bridge two amps and run say 150+rms out of each to the left and right components....or midbass. One amp per speaker or comp set however they set it up.


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## Richv72 (May 11, 2012)

Does bridging an amp cause the signal to noise ratio to lower?


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## sqshoestring (Jun 19, 2007)

Bridging an amp uses two channels to run one channel, so you get the noise from both. An amp runs the pos wire (sometimes pos) with both pos and neg signals to move the speaker the other side is ground of its power supply (which is not necessarily ground of the car). Bridging takes that 'ground' and uses another channel to run that out of phase. So you double the signal. But only certain types of noise from the amp, for example you would reduce clipping significantly at high volumes because you double the power. You would be more likely to hear noise at low volumes, but in reality amps are pretty clean these days and have been for some time. It would take a crappy amp. Just the same I have done it and not liked the sound but that was with an older amp so maybe that was why. The difference was minimal even then.


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## avanti1960 (Sep 24, 2011)

Do gain adjustments ever drift enough to be audible? I have a 4-channel amp bridged to my front midbass drivers as well. Since each pair of channels have their own gain adjustment, this opens up the potential for left / right drift that coincides with gain drift if possible, assuming the gains were initially DVM level matched (which they were). I could swear that my center has and does drift on occasion. Maybe it's psychological.


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## sqshoestring (Jun 19, 2007)

I've never had that issue, but SPL systems often take them out and replace with resistors....so strapped or parallel amps then have exactly the same output level.


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## 14642 (May 19, 2008)

Dampening factor. I love that. 

Additionally, If you have ten apples and you give me 10% of your apples and then I go to your neighbor's house who also has 10 apples and he gives me 10% of his apples, how many apples do I have? 

Now, if one apple was made of apple, and the other apple's flesh was made of apple anti-matter, then I'd have two things that looked like apples, but when i mashed them together to make apple sauce, the flesh of both apples would "cancel" and I'd be left with seeds stems and skins. 

OK, so now that we have that out of the way, let's say 20,000 of us are going to bungee jump and everyone's weight is slightly different, but the bungee cords are identical. We're all going to jump off the same platform at the same height. The platform is made of wood but it's slightly warped. The platform is 100 feet in the air and is warped by 0.1 inches in a few places. That means that some of us start a maximum of .1" higher than others. (Granted, it would be difficult to get 20,000 people on the platform, but this is theoretical). Some of us whose weights are very similar are perfectly damped by the elasticity of the bungee cords and when we reach the ground, we're able to let go--a smooth landing. Jumpers who weigh less go up and down and up and down before being stranded in mid air. Jumpers who weigh more crash into the ground and are killed. 

Now, let's say that we send someone to find new people who weigh exactly the same as the people who were killed in the first jump. While they're searching for volunteers, a couple of us plane the platform so that it's perfectly flat. The new (and potentially doomed) jumpers arrive and we all jump again. How different will the results be now that we've eliminated the .001% "distortion" in the platform?


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## amalmer71 (Feb 29, 2012)

As far as THD, bringing that up is irrelevent in this matter. When an amplifier is bridged the total amplifier output can only be glamorized as being "doubled" if the percentage of THD is raised.

I'd like to see someone test a 2 channel amplifier that's rated at being able to produce twice as much power, bridged, than it produces to each channel in stereo, and see how much power it puts out bridged @ 4 ohms, when using the same THD percentage as when it's ran in stereo @ 4 ohms on each channel.

That's what CEA-2006 was supposed to make happen, but the problem is they don't require a 2 channel amplifier to be rated that way, bridged. The only requirement to become "compliant" are at 4 ohms on each channel, indiviually.

E.G. A monoblock amplifier can be rated at 500 watts RMS @ 4 ohms x 1 channel @ 1% THD+N and be CEA-2006 compliant. After that the manufacture can rate it at 1,000 watts RMS @ 2 ohms and 1,500 watts RMS @ 1 ohm without using a THD percentage and still be CEA-2006 comliant.


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## avanti1960 (Sep 24, 2011)

Interesting to note that JL audio rates the 300/4 V2 amplifier at 2X the power per channel bridged (75 X 4 and 150 X 2)- 

Yet the HD900/5 is rated at 100 X 4 and 150 X 2 bridged @ 4ohms.


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## jimbno1 (Apr 14, 2008)

avanti1960 said:


> Interesting to note that JL audio rates the 300/4 V2 amplifier at 2X the power per channel bridged (75 X 4 and 150 X 2)-
> 
> Yet the HD900/5 is rated at 100 X 4 and 75 X 2 bridged @ 4ohms.


Huh? Per the 900/5 manual

Rated Power (Main Channels / Stereo):
100W RMS x 4 @ 4Ω (11V - 14.5V)
75W RMS x 4 @ 1.5-3Ω (11V - 14.5V)
Rated Power (Main Channels / Bridged):
200W RMS x 2 @ 8Ω (11V - 14.5V)
150W RMS x 2 @ 3-6Ω (11V - 14.5V)


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## avanti1960 (Sep 24, 2011)

jimbno1 said:


> Huh? Per the 900/5 manual
> 
> Rated Power (Main Channels / Stereo):
> 100W RMS x 4 @ 4Ω (11V - 14.5V)
> ...


thanks, my mistake as edited above. 

the point is that the slash amp does not lose power when bridged but the HD900 loses 25% @ 4 ohms.


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## t3sn4f2 (Jan 3, 2007)

avanti1960 said:


> thanks, my mistake as edited above.
> 
> the point is that the slash amp does not lose power when bridged but the HD900 loses 25% @ 4 ohms.


Why is that "interesting"?  They are just playing around with optimization in order to have enough wattage headroom left over for the sub channel. The HD600/4 behaves the same way as the Slash 300/4 with respect to power to impedance ratios.


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