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Author Topic: Bridged amps and stereo playback  (Read 6848 times)

Luke Geis

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Re: Bridged amps and stereo playback
« Reply #30 on: October 14, 2016, 06:39:37 pm »

There is an old trick in which running an amp in bridge mono mode and simply connecting two speakers to each channel ( with channel two's connections reversed ) would net you a gain of about 15% more power. The downside is that you won't have stereo. This is great if you are splaying speakers together or have a line array. The debate is on whether this is a practical and viable option?

The problem is the need to invert the connection on one half of the amp which adds to confusion. The second is that even if 15% more power is gained, is it really worth it? I prefer to go with the K.I.S.S theory and simply keep it simple. 15% more of 1000 watts is only 150 watts. Since you need double the wattage to net a 3db increase in SPL, 150 watts is going to get you pretty much nowhere. It won't even get you a full db more in SPL, which means no appreciable gain for the extra work involved.

Pretty much the only time you should desire to bridge mono an amp is if you need to drive that much power into several speakers that will work within the amps minimum ohm rating, or you simply can't afford to acquire an amp big enough to power what you currently have in the conventional way. Subs are a prime example of speakers that are often powered by a bridge mono amp. Many subs these days are rated for a peak rating of between 3000 to 6000 watts! Not too many amps will deliver even 3000 watts per channel at 4 ohm's. So the only way to get ample power and save money is to use an amp with a bridge mono rating that will get you the wattage you need.
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Tim McCulloch

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Re: Bridged amps and stereo playback
« Reply #31 on: October 14, 2016, 06:54:24 pm »

There is an old trick in which running an amp in bridge mono mode and simply connecting two speakers to each channel ( with channel two's connections reversed ) would net you a gain of about 15% more power. The downside is that you won't have stereo. This is great if you are splaying speakers together or have a line array. The debate is on whether this is a practical and viable option?

The problem is the need to invert the connection on one half of the amp which adds to confusion. The second is that even if 15% more power is gained, is it really worth it? I prefer to go with the K.I.S.S theory and simply keep it simple. 15% more of 1000 watts is only 150 watts. Since you need double the wattage to net a 3db increase in SPL, 150 watts is going to get you pretty much nowhere. It won't even get you a full db more in SPL, which means no appreciable gain for the extra work involved.

Pretty much the only time you should desire to bridge mono an amp is if you need to drive that much power into several speakers that will work within the amps minimum ohm rating, or you simply can't afford to acquire an amp big enough to power what you currently have in the conventional way. Subs are a prime example of speakers that are often powered by a bridge mono amp. Many subs these days are rated for a peak rating of between 3000 to 6000 watts! Not too many amps will deliver even 3000 watts per channel at 4 ohm's. So the only way to get ample power and save money is to use an amp with a bridge mono rating that will get you the wattage you need.

Running a loudspeaker at the "rated" power for more than brief instances will ultimately result in the destruction of that loudspeaker.  You might as well use an amp 1/4 the size and let it clip - and frankly that's what we did 20 years ago with the "big" Crest 8001 - 750W @8 Ohms.

Especially on bass-reflex subwoofer designs any distortion from clipping was masked by the substantial harmonic distortion of the subwoofer itself.

The programme material and ability of a loudspeaker to dissipate heat have far more to do with the selection of amplifier power than mere published specifications.
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Luke Geis

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Re: Bridged amps and stereo playback
« Reply #32 on: October 15, 2016, 02:43:27 pm »

Running a loudspeaker at the "rated" power for more than brief instances will ultimately result in the destruction of that loudspeaker.  You might as well use an amp 1/4 the size and let it clip - and frankly that's what we did 20 years ago with the "big" Crest 8001 - 750W @8 Ohms.

Especially on bass-reflex subwoofer designs any distortion from clipping was masked by the substantial harmonic distortion of the subwoofer itself.

The programme material and ability of a loudspeaker to dissipate heat have far more to do with the selection of amplifier power than mere published specifications.

While I was slightly vague about what wattage you NEED, that topic is well documented at this point of course. The point of the comment being that the average guy can't afford Powersoft K10 or K20 amps to power their subs rated for 6,000 + watts peak in two channel stereo mode. Granted , NO you DO NOT need to power a sub with its peak rated wattage, but affordable options are few and often bridging an amp is required to get the needed wattage.

For example: You get yourself a nice, pretty, new JBL STX dual 18" passive sub. It has a peak wattage rating of 8,000 watts! Ideally, you want to power it with about 4,000 watts, but can go as much as 6,000 watts if you want to go for all out performance. Depending upon needs and application you may even desire to power it with an amp that produces around 2,000 watts? Either way you have a few different ways of powering it and each has it's pro's and cons.

There are plenty of amps that you can buy that will provide 2,000 watts in dual channel operation. There ARE NOT as many affordable amps that will provide 4,000 watts in dual channel operation. So you are left with two choices. You can either pony up to get the Lab Gruppen, Powersoft and upper end Crown offerings, which will cost more than the speaker you're powering them with, or you can buy lower end products and run them in bridge mono mode to get the needed wattage?

I believe that powering a speaker with at least its program rating is the best all around option, certainly NEVER use an amp rated for the same peak wattage as the speaker it is powering. Subs these days are power hungry and the average peak wattage is sitting around the 6,000 watt range. This means that most will need an amp that will produce around the 3,000 watt per channel at 4 ohm mark. There are not too many options that will do that. There are lots that will produce that wattage cheaply in bridge mono mode though.

Most are not fans of running amps in bridge mono mode however. It increases potential distortion, reduces the damping factor and makes the amp work harder, lessening its life. At the cost of making more power, it sacrifices quality and itself to do so. Another downside is that you will need multiples to power multiples of anything. So if you have 4 subs, you will need 4 amps. It is possible that buying 2 higher end power house amps is cheaper than buying 4 smaller amps? If you need several amps the weight and space consumption goes up. If you can buy 2 amps that do the job of 4 and have similar investment cost, you can see the obvious gains in doing so. I am not a fan of running in bridge mono myself, but when you don't have another option and you have to run what you have, you do what needs to be done.

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Tim McCulloch

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Re: Bridged amps and stereo playback
« Reply #33 on: October 15, 2016, 04:57:55 pm »

Luke, my point is that one does not need 3000 or 6000 Watts and that for most uses, doing so puts one into the territory of diminishing returns.
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Ivan Beaver

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Re: Bridged amps and stereo playback
« Reply #34 on: October 15, 2016, 06:31:20 pm »

There is an old trick in which running an amp in bridge mono mode and simply connecting two speakers to each channel ( with channel two's connections reversed ) would net you a gain of about 15% more power.
Not necessarily.  It depends GREATLY on the power supply of the amplifier.

If the amp has common power supply, then you can get a slight increase in power-less than 1 dB.

If the amp has dual power supplies, (the channels don't share a common supply), then there in no increase in power.

It also depends on the type of power supply.  Is it an old transformer/bridge/cap power supply or a switching supply that operates at a high freq?

It all has to do with how fast the power supply can recharge.

There "might" be a increase in power that is not noticeable by anybody, or no increase at all.

The possibility of getting quite a bit LESS sound (by wiring it incorrectly) is MUCH higher, and in my opinion, not worth the effort.

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Don Boomer

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Re: Bridged amps and stereo playback
« Reply #35 on: October 15, 2016, 06:56:07 pm »

Don,

There are countless songs mixed with hard-panned tracks, if you don't properly combine left/right, you get a random lack of something or other.

While reading your reply, was listening to Jimi Hendrix' "If 6 were 9".
The main vocals are only in the right channel, guitar left.
Which channel do you choose to omit, vocals, or guitar?


Right is wrong, but Hendrix played right hand guitars left handed...

Art

Agreed. It depends on the material and how important or non important the background music is. But you'd also need to watch if you played Jimi in stereo and a listener was near one stack or the other where they would also only hear one side. ;)
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Don Boomer
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Re: Bridged amps and stereo playback
« Reply #36 on: October 15, 2016, 07:05:25 pm »

Running a loudspeaker at the "rated" power for more than brief instances will ultimately result in the destruction of that loudspeaker. 

My experience says otherwise. First, you are likely to never run full rated continuous power to a speaker using "program" rated amps. In fact it's not likely that you'd even ever deliver half power continuously. Furthermore both AES and EIA power tests run full power for 2 hours and 8 hours respectively without speaker damage.

I remember running tests where we ran speakers with amps 5x the rated power (500w AES rated speakers with 2500w power amp) into clipping (limiters bypassed) for a few hours (until we got shutdown by the cops).  We took the speakers back into the shop and broke them down. There was no damage to those.

We DID use proper high pass filters however.
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Don Boomer
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John Roberts {JR}

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Re: Bridged amps and stereo playback
« Reply #37 on: October 15, 2016, 07:21:26 pm »

There is an old trick in which running an amp in bridge mono mode and simply connecting two speakers to each channel ( with channel two's connections reversed ) would net you a gain of about 15% more power. The downside is that you won't have stereo. This is great if you are splaying speakers together or have a line array. The debate is on whether this is a practical and viable option?




Google Dave Rat trick, or Dave Rat article.

How much louder do you think 15% is?

JR 

PS: Can we just number these? That old #29 coming through again.
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Ivan Beaver

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Re: Bridged amps and stereo playback
« Reply #38 on: October 15, 2016, 08:51:41 pm »



PS: Can we just number these? That old #29 coming through again.
:) :) :) :) :)

Didn't we talk about #3 last week???????;) ;)
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Ivan Beaver
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Re: Bridged amps and stereo playback
« Reply #38 on: October 15, 2016, 08:51:41 pm »


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