Stereo vs bridged mono

J

Jorge Costa

Freshman
Dec 16, 2012
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Santa Rosa , California
Hi everyone , this is my first post in the forum , thanks in advanced for your replies.
I've been running my subwoofer system in bridged mono for the last year , I'm very satisfied with the results so far.
I'm currently using 4 jbl srx718 , each pair running of a QSC plx 3102 in bridge mono . What benefits will I have with my system by running a big enough amp in Stereo mode , besides saving some weight and space ? Will the difference in Sound be noticeable and be worth to spend some extra money on this?


Thanks a lot.
 
Re: Stereo vs bridged mono

The QSC PLX 3102 is rated at 3100 watts at 4 ohms, bridged mono, at 1% THD. Now, you will notice that the THD rating when the amps are driven in stereo is .1%. The sound is cleaner when in stereo mode. Is that enough to make a difference in the sound? Probably not going to be all that noticeable.

Now, getting an amp that can truly deliver 3100 watts per channel at 4 ohms is likely going to ratchet up your budget higher than running the 2 amps that you currently have. You also are getting to the point where plugging the amp into a single 15 amp circuit isn't going to be an option if you plan to drive the amp at any decent level.

In all honesty, if your amps are working for you, and the size isn't a concern, I don't see a reason to spend any money to fix a problem you don't have.
 
Re: Stereo vs bridged mono

Well , my budget is about $2000 for either a qsc pl380 , crest audio pro 9200 or an itech 6000, but I will pull the trigger only if there will be a noticeable improvement on sound , the places where I usually work don't have a reliable source of power , sometimes I'm limited to a couple of 20 amp outlets. I would love to be able to rent one of these amps in my area to do a side by side comparision , but Im afraid I'm not gonna find a place to do that.

thanks for your replies.
 
Re: Stereo vs bridged mono

Brian jojade said:
The QSC PLX 3102 is rated at 3100 watts at 4 ohms, bridged mono, at 1% THD. Now, you will notice that the THD rating when the amps are driven in stereo is .1%. The sound is cleaner when in stereo mode. .
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Actually you are not looking at the specs close enough.

Since an amp in bridged mode is essentially having each side of the amp drive a 2 ohm load. OS if you look at the 2 ohm rating in stereo-it is the same 1% THD.

And if you look at the 8 ohm bridged mode you will see that it is rated at 0.1%THD-the same as when driving a 4 ohm load per channel.

So I don't see anything in the specs that would make me say that running a bridged amp has a higher distortion than stereo.

Now if you are going to compare the same impedance-then you ALSO need to compare at the same output power. Yet the bridged output is over 3 times the stereo output. If we were to turn down the bridged output to the same level-the distortion should go down. ( I can't say for sure on that particular amp).

So you have to compare apples to apples.

But I do agree that the THD in most cases is nothing to "get you panties in a wad" about.
 
Re: Stereo vs bridged mono

Jorge Costa said:
[...]each pair running of a QSC plx 3102 in bridge mono [...] Will the difference in Sound be noticeable and be worth to spend some extra money on this?
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Jorge Costa said:
Well , my budget is about $2000 for either a qsc pl380 [...] but I will pull the trigger only if there will be a noticeable improvement on sound [...]
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In a previous life I did a comparison between a PL236 bridged into 4 (supposedly 3.6kW) and a PL380 dual channel mode into 4 (2.5kW). The improvement going to the PL380 was huge. The PL380 driving just one sub made me feel physically sick. The PL236 had no chance. Hard to describe the perceived difference so here's an ugly hand-drawn pic of what it sounded like. The red is the PL380, the only reason the blue (PL236 bridged) goes higher at the start is because I am assuming it did actually do 3.6kW for the start of the notes... it just couldn't sustain it. To be sure, it was loud, but just in a different ballpark.

I know in a world of measurements and accurate science it might seem a little weird to trust my "chart", but if you have the chance to test the PL380 properly (test it with some EDM, that should show it pretty easily). I just wish I had have measured it on the day 5 years back. Oh yes, after a 5 minute demo to the boss we ordered $100k worth the next day.
PL380 v PL236.jpg

P.S. If anyone needs any technical charting done, I'm thinking of offering it as a new service! :lol:
 
Re: Stereo vs bridged mono

I like to avoid bridging as well, for a few reasons. First, you need twice as many amps which take up twice as much space. There goes any cost advantage. Secondly, I don't think it sounds as good. You're relying on both amp channels to be perfectly matched, including when driven into limit. You're also loading the amp twice as hard, and using much more current through the power supply. Add to that the number of "bridged" amplifiers I have seen configured incorrectly (50%?) and it's not worth the hassle to me.
 
Re: Stereo vs bridged mono

Bennett Prescott said:
I like to avoid bridging as well, for a few reasons. First, you need twice as many amps which take up twice as much space. There goes any cost advantage. Secondly, I don't think it sounds as good. You're relying on both amp channels to be perfectly matched, including when driven into limit. You're also loading the amp twice as hard, and using much more current through the power supply. Add to that the number of "bridged" amplifiers I have seen configured incorrectly (50%?) and it's not worth the hassle to me.
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I know what happens then, lol As far as more current through the power supply.
 
Re: Stereo vs bridged mono

Bennett Prescott said:
. Add to that the number of "bridged" amplifiers I have seen configured incorrectly (50%?) and it's not worth the hassle to me.
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But the incorrect use of bridging is good business for speaker reconers. I know I made a good bit of money off of people simply flipping the bridge switch and then hooking the speaker up normally-which made them OUT OF POLARITY! REALLY bad on subs.
 
Re: Stereo vs bridged mono

Life was simpler in the good old days when men were men and they didn't run amps bridged, or down to 2 ohms. :-(

While most of the discussion so far is accurate it doesn't really address your question, or what your question should be.

Yes, distortion is higher in bridge mode but only very slightly higher, just like running an amp at 2 ohms is higher distortion than that same amp at 4 ohms. So yes, distortion may be higher, but no, it is NOT AUDIBLE in my informed judgement.

One benefit from not running your amps at maximum load normally, is that you can double up in case of an emergency, like a random amp channel crapping out, which does happen even with premium amps. In fully loaded/bridged mode, one channel going down takes out the whole amp... With bigger amps running stereo, just move the speaker, or speakers to another amp, and keep on truckin.

If everything is running bridged and already maxed out you have nowhere to go.

Another subtle benefit from running bigger amps less hard is you have more thermal headroom (so you could play louder longer), and reliability will be better from lower operating temps (MTBF doubles for every 10'C drop)..

JR

PS Running the amps with less headroom, could lead to occasional transient current limiting, that might be too brief to register on meters, but may be subtly audible (like transient clipping), on clean but loud program material.
 
Re: Stereo vs bridged mono

Jorge Costa said:
Hi everyone , this is my first post in the forum , thanks in advanced for your replies.
I've been running my subwoofer system in bridged mono for the last year , I'm very satisfied with the results so far.
I'm currently using 4 jbl srx718 , each pair running of a QSC plx 3102 in bridge mono . What benefits will I have with my system by running a big enough amp in Stereo mode , besides saving some weight and space ? Will the difference in Sound be noticeable and be worth to spend some extra money on this?


Thanks a lot.
Click to expand...


Here, read this then look up the prices.


http://www.diy.poweraudio.ro/albums/userpics/10001/BENCH_COMPARISON_TEST.pdf
 
Re: Stereo vs bridged mono

I'll be using a PL380 this weekend , I was able to get one , let's see how that goes.
Thanks for your replies and thanks for the link Alan , very interesting , powersoft looks good , but expensive.
 
Re: Stereo vs bridged mono

Jorge Costa said:
I'll be using a PL380 this weekend , I was able to get one , let's see how that goes.
Thanks for your replies and thanks for the link Alan , very interesting , powersoft looks good , but expensive.
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Your welcome. Thats the best thing you can do is try a amp before you buy it, or at least find some kinda comparison. I can only warn you if you are going to bridge a amp into 4 ohms, don't use a crest 8200, they sound great don't get me wrong, but I have had 3 fail on sub duty bridged into 4 ohms. Amps all failed in the same area.
 
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