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Author Topic: Amps - Bridged or bi-amped, which mode sounds better and WHY?  (Read 6292 times)

Jeff Schoonover1

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Re: Amps - Bridged or bi-amped, which mode sounds better and WHY?
« Reply #20 on: November 25, 2017, 08:39:55 pm »

I am not sure what you mean by dual channel though? One channel for each speaker, or one channel for each whole sub?
in my case, one channel per speaker in the same box, a 2X18" But the same principle would apply to multiple boxes.
I DO NOT suggest running a single channel per speaker in the sub ( re configuring the sub for bi-amp operation ). This doesn't improve the outcome and as I presented, you actually loose 2.4db in potential output. The amp would run each speaker individually with a lower potential.
I'm finding others who would disagree with this assessment, and I'm inclined to agree with them.  Losing 2.4dB (or even 4-5db, as the impedance of each driver alone is 8-ohms Znom) isn't even audible and it's likely that with seperate channels, sound quality would be improved noticeably, even though on paper there are far fewer watts.  It's less taxing on the amp as well.
The third option you presented was running the sub so it has a 16ohm load with the amp in bridge mono.
presented as an option, but I think it's been shown this wouldn't be a good option as the amp is still bridged rather than using independent channels.  The presented impedance of 8 ohms (resistance encountered by both channels in parallel) is better than two ohms, but still presents the same drawbacks others have posted regarding bridged mode.
The last option is running the sub in its normal configuration at 4ohms with the amp in bridge mono. This is the one that most people will go for.
In the past I would have as well, but as I learn more, I think this is clearly the worst option. My ears have told me in the past, and presently with this box that it sounds better when it's not bridged.  Now I'm hearing some great reasons why, instead of just chalking it up to placebo.
It provides the most power,
I believe this is not correct either, as others have posted.  It provides an input gain boost, but not 'more power.'
but has the added cost of making the amp work harder and with a little more distortion.
Based on what my ears have told me, a whole lot more distortion.
The cable you are using is not of detriment to your use.
Agreed, in any case.
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Luke Geis

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Re: Amps - Bridged or bi-amped, which mode sounds better and WHY?
« Reply #21 on: November 25, 2017, 10:53:25 pm »

I won't bullet point things as you have, but will point out perhaps a couple misunderstandings you may have of what I meant.

I need to start from the beginning about SPL potential so it is a little more clear. You have a power potential that spans between 6,000 watts and 1,200 watts. The difference between the two is 7db all else being equal. If you run bridge mono at 4 ohms, you have 6,000 watts and full potential. If you run at 8 ohms stereo ( the bi-amp method you're looking to do ) you will have 1,200 watts at 8 ohms. That is a total of 7db loss in output potential. This is measurable and definitely audible. This is a make or break amount of SPL deficit. When running at the normal 4 ohm, 2 channel mode the amp will provide 2,100 watts and you will have a 4.6db deficit in potential output, this is that 2.4db improvement over bi-amping I speak of. Since you are writing off running in bridge mono, I didn't really factor it before. When you had considered running at 16 ohms bridge mono, the amp will produce roughly 3,000 watts and you will have a 3db deficit. This is only a 1.6db advantage over running in the normal 4 ohm stereo mode. This is not a huge deal. It is these numbers that I use to support that 4 ohm stereo mode is the best compromise between power and sound quality.

The amp in bridge vs. stereo mode. The sensitivity of the amp is increased yes, and the power deliverable to the speaker is higher too. The amp has the same power potential regardless of the configuration, but the way you connect the speakers to it allows for a higher wattage to be delivered. You can put the amp in bridge mono and connect one speaker to each output channel. Both speakers will work and each speaker will get 2,100 watts if they are 4 ohm speakers. The problem is that one of the speakers will be out of polarity. In either case, when ran in bridge mono mode, the amp will allow more power to be fed to a properly connected speaker.

Bridge mono is to be avoided if you can help it. Most buy a sub for its output potential, not so much how it sounds when ran in different non stock configurations. Most aim to power a speaker with around its program power ratting. In this case you would be looking for something around the order of around 3,600 watts each or 7,200 watts for the pair base don teh info we have. You are well under powered if that is the case. The sub sounds like it has a peak wattage rating of about 14,000 watts!!!! If that is a fact, then you are actually considering running the speaker in a way that will reduce its peak potential output by 10.7db!!!!! That is REALLY a make or break difference.

Perhaps we need more info about your sub. Thus far everything is theory and speculation sprinkled with some facts. If you have more sub than your current needs are, then you can stand to lose that potential output. If you are close, then 2.4db may make a dent. I think you won't really be able to tell much of a difference unless you do a very controlled test with all possible configurations. I think you will find that running the sub in its stock form @ 4 ohms utilizing one channel of the XTI 6000 will yield the best performance to sound quality ratio. The added benefit of not having to change anything is a bonus. If in fact the test results did show that the sub performed the best in bi-amp 8 ohm stereo mode, then awesome you have proven to us all that 8 ohms is in fact better than 4 ohms. I don't think it will be measurable to the degree where a clear conclusion can be made. If you can hear 1% THD, the you best be able to hear a 2.4db difference in level. 2.4db is not a make or break amount, but it is still a fair amount to throw away for the sake of nothing else.
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Bob Leonard

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Re: Amps - Bridged or bi-amped, which mode sounds better and WHY?
« Reply #22 on: November 25, 2017, 11:27:50 pm »

This discussion has turned into a science fair project.

OP,
Splitting hairs over a few db isn't going to help you in the end. Do what you will with the hardware you have, and change the configuration if you don't like the results, and IMO, and based on my 50 years of experience, you may want to start by configuring your system using the "rule of thumb" I mentioned above that you brushed off so quickly. You should also make every attempt to keep the impedance seen by the amplifier, bridged or per channel, at a 4ohm minimum. Two drivers per cabinet? Then you should have bought 8ohm drivers. Best to keep these things simple in the end, usually because minute increases or decreases in the maximum output, as proven mathematically, don't amount to a piss hole in the snow in the end.
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Chris Grimshaw

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Re: Amps - Bridged or bi-amped, which mode sounds better and WHY?
« Reply #23 on: November 26, 2017, 10:11:17 am »

I won't bullet point things as you have, but will point out perhaps a couple misunderstandings you may have of what I meant.

I need to start from the beginning about SPL potential so it is a little more clear. You have a power potential that spans between 6,000 watts and 1,200 watts. The difference between the two is 7db all else being equal. If you run bridge mono at 4 ohms, you have 6,000 watts and full potential. If you run at 8 ohms stereo ( the bi-amp method you're looking to do ) you will have 1,200 watts at 8 ohms. That is a total of 7db loss in output potential.

No, it isn't.
The amp is 1200w/ch into 8ohm, so the total power going into the cabinet will be 2x that: 1200w per driver. 2400w total.

With this particular setup, you can either have 1200w per driver or 3000w per driver when you're lighting up the red lights:

2x channels, 1 driver per channel: 8ohm on each channel, 1200w per driver
Bridged, drivers in series - 2400w total bridged output, 1200w per driver
Both drivers on one channel - 2400w into 4ohm, 1200w per driver
Bridged into 4ohm - 6000w into 4ohm, 3000w per driver.

As I said earlier, fire up Hornresp or WinISD and see if the extra power is going to be useful, and go from there.

Chris
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John Roberts {JR}

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Re: Amps - Bridged or bi-amped, which mode sounds better and WHY?
« Reply #24 on: November 26, 2017, 10:23:06 am »

This discussion has turned into a science fair project.


They are keeping each other amused and off the street... all good...

JR
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Jeff Schoonover1

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Re: Amps - Bridged or bi-amped, which mode sounds better and WHY?
« Reply #25 on: November 26, 2017, 10:24:48 am »

This discussion has turned into a science fair project.
Sorry you feel that way.  Your 50 years of doing things are respected. I've been at it for 30, using the conventional wisdom of which you speak.  Others who have presented information in this and in my other thread have made well-documented positions as to why using conventional rules of thumb for 30 years, or more, doesn't necessarily make them best practice.  My interest is WHY and HOW to do things optimally so that I learn more and become better at this craft.
Splitting hairs over a few db isn't going to help you in the end.
Agreed.
you may want to start by configuring your system using the "rule of thumb"I mentioned above that you brushed off so quickly.
Done, and it wasn't brushed off - it's how I've always done things as well. The spec. sheet for the XTi 6000 claims 6Kw into 4 ohms.  The speakers have an RMS rating of ~ 1,800 watts, each. So, by our rule of thumb, I'm more than there. When I assembled the box, I did my testing with one driver per channel, as a safety to keep the power down while I tested.  When I was satisfied with those tests, I re-configured for bridged and 4-ohms. The box sounds audibly worse than when each speaker is run separately, even though the supposed extra power they get is 2.5 times greater.  The effect is absolutely noticeable, it isn't subtle.  The amp soon gets hot and fans turn on high if bass-heavy music is put through it at half (or less) of the levels needed to make full power. Even with a 30Hz roll-off and high-pass filter applied, If I were to place input gain at unity and put any sort of transient like a kick drum through the system, the cones would jump across the room.  That gave me these questions and leads to the idea that this rule of thumb needs to be re-examined, hence this thread.
Two drivers per cabinet? Then you should have bought 8ohm drivers.
I did buy 8-ohm drivers.  I should have bought 4-ohm drivers and not bridged the amp.
Best to keep these things simple in the end
Again, I totally agree.  But it seems that the simple solution isn't the best one.
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Jeff Schoonover1

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Re: Amps - Bridged or bi-amped, which mode sounds better and WHY?
« Reply #26 on: November 26, 2017, 10:42:02 am »

As I said earlier, fire up Hornresp or WinISD and see if the extra power is going to be useful, and go from there.
^ This.  I used WinISD in designing this box and it's been spot on accurate to the smallest detail.  As shown in WinISD, and my experience with this box in real-life, The "extra power" is a mere (and probably not audible) 4.5dB.  It also seems unnecessary, because music or transients at substantially less than "full-power" already look to be able to launch cones out of the box. 
Also what WinISD doesn't tell us, but seems pretty clear from what others in this thread have said and personal experience, there is a substantial audible and amp-stress penalty to be paid for that 4.5dB negligible increase.
« Last Edit: November 26, 2017, 11:04:16 am by Jeff Schoonover1 »
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Ivan Beaver

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Re: Amps - Bridged or bi-amped, which mode sounds better and WHY?
« Reply #27 on: November 26, 2017, 01:15:49 pm »

The "extra power" is a mere (and probably not audible) 4.5dB.

 there is a substantial audible and amp-stress penalty to be paid for that 4.5dB negligible increase.
I don't think I would call 4.5dB "negligible".  People get "hung up" on much less than that.

Generally a 3 dB change/difference is a "goal".  Less that that is not really worth worrying about.

If 4.5dB is "negligible", then how much is enough?  Is it 6dB?

If so, then that is only 1.5dB more than your 4.5dB.  So does 1.5 dB increase somehow make it "enough", but 4.5dB does not?

Just something to think about.
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Keith Broughton

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Re: Amps - Bridged or bi-amped, which mode sounds better and WHY?
« Reply #28 on: November 26, 2017, 02:36:51 pm »

Bridged or dual channel, from my experience, won't sound "different"
However, a setup that delivers 3000 watts to each driver may sound different after power compression takes place.
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Tim McCulloch

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Re: Amps - Bridged or bi-amped, which mode sounds better and WHY?
« Reply #29 on: November 26, 2017, 06:02:33 pm »

Popcorn for the show, anyone?
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Re: Amps - Bridged or bi-amped, which mode sounds better and WHY?
« Reply #29 on: November 26, 2017, 06:02:33 pm »


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