Bridging vs bi-amping

[josko]

I understand that bridging a power amp produces more power, while bi-amping reduces interference between the two speaker sections at the expense of total power output. Aside from that, what are the factors that make a difference in deciding whether to bridge or bi-amp speakers? Thanks in advance.

 

[Loren42]

I am not sure I understand your question.

I think they are two different things. Bridging an amp simply utilizes both sides (left and right) of a stereo amplifier to drive a single load (i.e., speaker). You are in effect combining the output transistors of two separate amplifiers to work as one larger amplifier. The reason you bridge an amplifier is to generate more power into a single load.

Bi-amping is simply a technique for driving each transducer in in a two-way speaker system with its own independent amplifier. The reason you bi-amp is for negating or eliminating the passive crossover network, which is replaced with an active crossover that is placed before the power amplifiers.

Bi-amping doesn't reduce power, but it does mandate that you employe more amplifiers (one for each driver).

The advantage of an active crossover versus a passive crossover is another subject altogether.

 

[markw]

Bi-amping requires a speaker with two sets of speaker terminals, one for high, the other for lows. Each terminal set is run to a separate power amp. If you do not use a powered crossover before the power amps, it's called "passive" biamping and all amps should have the same gain.

Bridging is when two channels of a stereo amp that's made to allow for bridging are combined into one more powerful channel. The down side is that this bridged amp "sees" the speaker load as one half it's rated nominal impedance so it works harder. Another thing to keep in mind is that not all stereo amps are made to be bridged.

 

[Midcow2]

If you need more power get and external amplifier Behringer EP2500

I understand that bridging a power amp produces more power, while bi-amping reduces interference between the two speaker sections at the expense of total power output. Aside from that, what are the factors that make a difference in deciding whether to bridge or bi-amp speakers? Thanks in advance.

When you bridge, you usually reduce your 7.1 down to 5.1 because you are using power from two separate channels to drive one speaker.

Bi-amp ( or even try amp) typically means you are driving the dofferent ranges within one speaker as separate channels, example bass= one channel, mid range a second channel and tweeter a third channel. I wouldn't say it reduces the interference between speaker sections; just that you have moved the crossover from the speakers to the AVR.

I personally am not a fan of bi-wiring, b-amping or bridging.

====

First, if you AVR does not have pre-outs, then you cannot add an external amp. And typically if a AVR doesn't have pre-outs, then a lot of times it also does not have the capacity to bridge .. so it may be time to upgrade. If you can bridge for more power, it is typically a stop gap.

With pre-outs you can drive external amps and if your front speakers are power hungry you can provide more power. Remember that power is logtihmic db ratio = 10 Log(p1/p0) so to increase your power you need to significantly increase the power output. For example to double 100 watts
to 200 watts only provides a 3.01 dB increase. So if you bridge a 100 watt receiver you can achive a 3 dB increase.

If you have very low impdenace front speakers, nominal 4 ohms or less, then you possible need separates or an external amp. With pre-out you could add a Berhinger EP2500 for less than $300 at B &H Photo and provide
•750 watts at 4 ohms (per channel)
•500 watts at 8 ohms (per channel)
•1200 watts at 2 ohms (per channel)

Emotiva also makes some very good amps, higher quality but higher cost.


Good luck!

MidCow2

 

[Djizasse]

I wouldn't say it reduces the interference between speaker sections; just that you have moved the crossover from the speakers to the AVR.

How does this work? Do you have to select the crossover frequency? And what about the filter slopes used?

 

[josko]

I guess my question assumes I have two suitable power amplifiers which can drive the speaker within spec in either configuration.
What audible differences would I notice between the two configurations (bridged vs bi-amped)? I realize the bridged speaker could play louder, but at lower settings and same speaker sound levels, would there be an audible acoustic improvement in the bi-amped configuration?

 

[Loren42]

I guess my question assumes I have two suitable power amplifiers which can drive the speaker within spec in either configuration.
What audible differences would I notice between the two configurations (bridged vs bi-amped)? I realize the bridged speaker could play louder, but at lower settings and same speaker sound levels, would there be an audible acoustic improvement in the bi-amped configuration?

I tried to explain this earlier, but the two situations you are asking about are apples and oranges.

Let's pretend you have a stereo amplifier that has the ability to be put in bridge mode.

Right now you have two speakers; a left and a right. Each speaker has its own channel. Now you bridge the amp and you now have two speakers connected to only one channel that has the sum of power from left and right channels, but only one output. In other words, instead of stereo, you have monoral.

Will that sound better? Probably not. So why do it? Answer: you shouldn't.

Let's talk about bi-amping. Bi-amping requires four amplifiers for stereo sound. Two channels are assigned to the left and right woofers and two other channels are assigned to the left and right tweeters.

Why would anyone do this? Well, it is not because you get more power. You do this because you eliminate some nasty side effects that would normally be present from passive crossovers. The primary problem with crossovers is that you get phase delays at the crossover frequencies that muck up the sound a bit.

When you bi-amp your system you use an electronic (active) crossover that allows you to adjust the exact crossover point and you get very little phase delay. As a bonus many electronic crossovers allow you to "time" align the tweeter to the woofer.

Time alignment is also a phase issue present with many speaker systems. At and near the crossover point the same frequency sounds will be produced by both the woofer and the tweeter. If the two drivers are physically at different distances from the listener (usually the woofer is slightly further than the tweeter from your ear) the note that arrives to you will have a distortion created by the two speakers being slightly out of phase. This causes a distortion in the note's waveform because of the lack of time alignment. Think of it as two ripples on a pond that are made when two stones are dropped simultaneously. If one stone is closer to you than the other, the closer stone's wave reaches you first, but the second stone will be close behind. As the ripple mix they will either reinforce or cancel each other out to some degree.

The disadvantage of bi-amping is mainly cost because you need more amps and an electronic crossover. You have to either have speakers that are made to be bi-amped or you must modify them (remove the crossover and add a second set of speaker terminals). And there is a lot of work to set up the system to make it play correctly. Bi-amping is not plug and play. You need to set the crossover frequency, set the gain for each speaker's driver, and set the time alignment for each driver, too.

The advantage will be better sound in the end, but getting there is not a trivial task.

If this doesn't help or make sense, then I would recommend going to a library and reading anything you can get your hands on about the subject in general.

 

[josko]

Thank you. That's just the information I was looking for. Could you point me to some sitable electronic crossovers? Would you also know of an article that discusses phasing calibration? I'm also curious at just how big a difference i could expect to find.

FWIW, my plan all along was to use two amplifiers (ML 334) to drive each speaker (B&W803); I just wasn't sure if I was better off bridiging them or bi-amping. You've confirmed it's a tradeoff between sonic accuracy and output power, which is what I was hoping it would be.

Sounds like I need to roll up my sleeves and figure out the calibration procedure.

 

[lsiberian]

How does this work? Do you have to select the crossover frequency? And what about the filter slopes used?

You will need an active crossover. One such example is the CX2310. And of course are familiar swiss army knife of crossovers the DCX2496. One could never own to many of those IMO.

 

[Loren42]

Thank you. That's just the information I was looking for. Could you point me to some sitable electronic crossovers? Would you also know of an article that discusses phasing calibration? I'm also curious at just how big a difference i could expect to find.

FWIW, my plan all along was to use two amplifiers (ML 334) to drive each speaker (B&W803); I just wasn't sure if I was better off bridiging them or bi-amping. You've confirmed it's a tradeoff between sonic accuracy and output power, which is what I was hoping it would be.

Sounds like I need to roll up my sleeves and figure out the calibration procedure.

This is a good read. It is primarily for passive crossovers, but it is a good foundation if you can follow it.

Another link to consider is this one.

Peavey offers an interesting article on Bi-amping here.

 

[mr-ben]

Thank you. That's just the information I was looking for. Could you point me to some sitable electronic crossovers? Would you also know of an article that discusses phasing calibration? I'm also curious at just how big a difference i could expect to find.

FWIW, my plan all along was to use two amplifiers (ML 334) to drive each speaker (B&W803); I just wasn't sure if I was better off bridiging them or bi-amping. You've confirmed it's a tradeoff between sonic accuracy and output power, which is what I was hoping it would be.

Sounds like I need to roll up my sleeves and figure out the calibration procedure.

Personally, I'd avoid getting into active bi-amping of your speakers. The crossovers are an important part of the speakers, especially in your 803's, and you're talking about going through a lot of effort and expense to get potentially worse sound.

If you already own two ML 334 amplifiers, I suggest you try bridging them (so you have two mono-block amps) and listening for several hours. Then try passively bi-amping them, and listening for several hours. Pick what sounds best to you. This won't cost you anything but time and perhaps a second set of speaker cables. Also, don't assume that a single ML334 won't be capable of driving both speakers just fine on its own.

 

[josko]

Well, we messed around with it last night, and settled on biamping with the ML 334 driving the lower and and a bridged Mac 275 the upper, leaving the internal crossover intact. The difference in sound between the tube and solid state amp on the high frequencies was appreciable. And beautiful.
We weren't so sure about the lower end; I felt the Levinson amp sounded a bit better than the tubes on some very low frequency stuff; my buddy disagreed, and many more beers will be needed to fully resolve this dilemma.
So now I'm in the market for a pair of Mac 275's.

I'm intrigued by the prospect of bypassing the internal crossovers, but I think I'll leave it for a bit, both because B&W probably built in something decent, and because I'm not sure what signal distortion or dynamic range issue an active crossover would have. Has anybody seen a review of active crossover systems?

 

[Midcow2]

depends on what sounds good to you

How does this work? Do you have to select the crossover frequency? And what about the filter slopes used?

If you have a speaker that internally has multiple speakers for bass, mid and treble then the speaker itself usuallu has internal crossovers to swithc between the various input frequencies.

If you connect one set of AVR speaker outputs too, for example treble/tweeter, then you are depending on the AVR to limit the range. If you have built-in equalizer or and external equalizer then this is possible. In many cases the crossover frequency is limited between the front speakers and subwoofer. However other more espnsive AVRs has full equlaizer bandwidth for all speaker outputs. and yes if you tweak it this way you would select the frequency ranges, whic in effect would be the crossover frequencies ( upper and lower). You can add an external equlizer, such as a Alesis DEQ-230 Programmable Digital Stereo Graphic EQ, http://pro-audio.musiciansfriend.com/product/Alesis-DEQ230-Programmable-Digital-Stereo-Graphic-EQ?sku=182533

Filter slopes is another matter, most filters are not notch or Zobel fliters and you really wouldn't want that anyway. You typically have somewhere around a 6 dB rolloff per octave. The ideal is the two overlap an have both speakers playing the frequency when it is in their dynamic sound range ( in other words when it sounds good on that particular speaker) for example even though a tweeter is mainly for high frequencies , it can still sound good with upper mid frequencies.


Good Luck!

MidCow2

P.S. - ...and then to complicate matters further there are active and passive crossovers

 

[Loren42]

Well, we messed around with it last night, and settled on biamping with the ML 334 driving the lower and and a bridged Mac 275 the upper, leaving the internal crossover intact. The difference in sound between the tube and solid state amp on the high frequencies was appreciable. And beautiful.
We weren't so sure about the lower end; I felt the Levinson amp sounded a bit better than the tubes on some very low frequency stuff; my buddy disagreed, and many more beers will be needed to fully resolve this dilemma.
So now I'm in the market for a pair of Mac 275's.

I'm intrigued by the prospect of bypassing the internal crossovers, but I think I'll leave it for a bit, both because B&W probably built in something decent, and because I'm not sure what signal distortion or dynamic range issue an active crossover would have. Has anybody seen a review of active crossover systems?

Keeping the internal passive cross overs wired into the speakers will defeat what you are trying to do by b-amping. The passive cross overs still induce a $h!t load of phase shifting.