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Old 29th June 2007, 04:09 PM   #11
sreten is offline sreten  United Kingdom
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Hmmm..........

Making an amplifier bridgeable but only suitable for 8 ohms per
channel in stereo is stupid, though a few chips amps have been
built like this.

A bridgeable amplifier needs to be able to work into 4 ohms (2 ohms
for some some car amps) per channel. Bridged it will drive 8 ohms.

Quote:
"min impedance 8 ohm min bridged impedance 8 ohm".
Is simply wrong one way or the other, per channel is half bridged.

A perfect stereo amplifier say 100W per channel bridged will deliver 400w one channel.

In practice a 100W 4ohm per channel gives 200W 8 ohm bridged.
In practice if the above has 8 ohm speakers its 50W per channel.
Adding a bridging circuit to a 8 ohm min per channel amplifier is a poor idea.

Quote:
can you wire two 4 ohm speakers in series and use them on one bridged
channel provided the stereo has enough power to drive them like that?
In practice is the same as wiring them parallel and driving them
with both channels in parallel, i.e. 4ohms connected to 8 ohm output.

Bridging does not make any difference.

/sreten.
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Old 29th June 2007, 09:47 PM   #12
Sammich is offline Sammich  United States
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I hope I'm not coming over as argumentative, I know quite a bit about troubleshooting and building electronic devices, but it only comes from talent and doing it all my life as a hobby, as the math and science behind most of it I'm just now in the process of learning.

I'm just trying to understand.

For a moment, forget that I mentioned bridging, I think I have the wrong idea of how it works;

Let's say an amp has a min load of 8 ohms per channel, and outputs 100 watts RMS.

If I wire two 4 ohm speakers in series, and connect them to one channel, the resistance would add up to 8 ohms. The current will be equal, and the voltage will be split. IE, if the stereo were outputting a perfect 12 volt 1 amp sine wave @ 1KHz, each speaker would be receiving 6 volts @ 1 amp. How is that bad for the amplifier, if it was meant to drive 8 ohm loads in the first place?

That said, I understand that bridged, it would be the right channel and left channel in series, decreasing the allowable load to 16 ohms. I'm not sure why the amp manual I downloaded said that, maybe I don't understand it. Like I mentioned before, it says; Stereo impedance: 8-16 Ohms Mono (Bridged) impedance: 4 Ohm + 4 Ohm pair". I assumed this meant 8 ohms stereo 8 ohms bridged, but with the way you guys explained everything, I must be reading it wrong.

Am I close or am I totally off?
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Old 1st July 2007, 09:00 AM   #13
AndrewT is offline AndrewT  Scotland
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Quote:
Originally posted by Sammich
Let's say an amp has a min load of 8 ohms per channel, and outputs 100 watts RMS.

If I wire two 4 ohm speakers in series, and connect them to one channel, the resistance (nominal impedance) would add up to 8 ohms. The current will be equal, and the voltage will be split. IE, if the stereo were outputting a perfect 12 volt 1 amp sine wave @ 1KHz, each speaker would be receiving 6 volts @ 1 amp.
that arrangement and your analysis is OK.
It is better if both speakers are identical, better still if the series connecting is done at identical driver level rather than at the crossover + driver (=speaker) level.
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Old 1st July 2007, 11:36 AM   #14
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A lot of good points here.

Why is it that people feel the need to bridge everything and run it at the edge?

What you achieve in output power bridged is dependent upon its design and the power supply limitations. In theory the maximum gain would be X4. In practice however it can be much lower. Generally a X3 power output is more in line depending upon how much power supply sag their is.

Just my .02
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Old 1st July 2007, 01:33 PM   #15
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Quote:
Originally posted by Sammich
Let's say an amp has a min load of 8 ohms per channel, and outputs 100 watts RMS.

If I wire two 4 ohm speakers in series, and connect them to one channel, the resistance would add up to 8 ohms. The current will be equal, and the voltage will be split.
I believe that's where your analysis is going wrong. An amp that's rated for 8ohm operation is rated that way because of limited current capability. When you bridge an amp, it causes a halving of the impedance seen by the amp, therefore doubling the current into the same load. So if you have an amp that's only rated for 8ohm operation, it needs a 16ohm load in bridged mode, so that the amp will see an 8ohm load.

This is a pretty good explanation: http://www.bcae1.com/bridging.htm
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Old 2nd July 2007, 09:58 AM   #16
sreten is offline sreten  United Kingdom
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Quote:
Originally posted by Sammich

Like I mentioned before, it says; Stereo impedance: 8-16 Ohms Mono (Bridged) impedance: 4 Ohm + 4 Ohm pair". I assumed this meant 8 ohms stereo 8 ohms bridged, but with the way you guys explained everything, I must be reading it wrong.

Am I close or am I totally off?
Hi,

Yes. > 8 ohm bridged (one speaker), > 4 ohm (pair of speakers each) per channel normal is what it means.

/sreten.
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Old 2nd July 2007, 10:28 AM   #17
AndrewT is offline AndrewT  Scotland
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Quote:
Originally posted by Sammich
I'm not sure why the amp manual I downloaded said that, maybe I don't understand it. Like I mentioned before, it says; Stereo impedance: 8-: 4 Ohm + 4 Ohm pair".
I have read and re-read those instructions.
I now realise what they are trying to (badly) say.


Quote:
Stereo impedance: 8-16 Ohms
is telling the user that the amp is suitable for 8 to 16ohm speakers.
Quote:
Mono (Bridged) impedance: 4 Ohm + 4 Ohm pair".
is telling the user that the amp can be used with a series connected pair of 4ohm speakers.
Based on electrical requirements this advice is plainly misleading and particularly so for those users with little electrical knowledge.

However, the instructions can be read differently.
Quote:
Stereo impedance: 8
would indicate that the amp is 8ohm capable
Quote:
16 Ohms Mono (Bridged) impedance
and can be bridged into 16ohms. but then the
Quote:
4 Ohm + 4 Ohm pair".
becomes superfluous.

Rely on the general (and always true) rule. Bridging doubles the power into double the impedance.
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Old 2nd July 2007, 01:21 PM   #18
sreten is offline sreten  United Kingdom
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Hmmm..........

The manual or where-ever it says this is a misprint.

It should say :

Mono (Bridged) impedance : 8-16 Ohms

Stereo impedance : 4 Ohm + 4 Ohm pair

It simply should say : bridged > 8 ohm, stereo > 4 ohm.

As I said earlier, if it cannot manage 8 ohms bridged its next to useless.

/sreten.
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