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Author Topic: Crossover, L-Pad, Impedence, Resistance question  (Read 12117 times)

Tim McCulloch

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Re: Crossover, L-Pad, Impedence, Resistance question
« Reply #40 on: November 22, 2017, 11:02:26 am »

Mac,
I've no idea where you got that from, but it ain't right.

Bridging an amplifier gives you 6dB more output from the amplifier.
You're effectively putting the two channels of the amplifier in series, doubling the voltage output.

Since P=V*V/R, when you double V (voltage), P (power) quadruples. That's your +6dB.

Sure, there are downsides. Each side of the amplifier effectively sees half the load impedance, so the amp is working harder. Pretty much anything will run bridged into 8ohm, though - each side is seeing 4ohm, which is fine. If you want to bridge into 4ohm, each side is seeing 2ohm, which is a tough life. A lot of amps will do it for "easy" program material, but if it was EDM at the limiters all night I'd have to have something really durable to start the gig bridged into 4ohm (or on 2ohm/ch). MA5k as a minimum.

I'd also argue there's an increase in system flexibility. Bridging amps means you've got spare channels that are currently in use. You can free them up by switching to normal output. You'll lose some output, sure, but you've got your emergency amplifier channels right there.

Chris

Bullshit.

Where does the extra power come from, the Amplifier Fairie?  Does she swoop in and leave a bigger PSU and extra output transistors under the pillow?
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Chris Grimshaw

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Re: Crossover, L-Pad, Impedence, Resistance question
« Reply #41 on: November 22, 2017, 11:13:26 am »

Bullshit.

Where does the extra power come from, the Amplifier Fairie?  Does she swoop in and leave a bigger PSU and extra output transistors under the pillow?

Are you for real?

You double the voltage swing by bridging. If the amplifier can source the current, you'll get 4x the power.

When bridging into 8ohm, that's the case for any amp worth having in the rack. Bridging into 4ohm, as I've noted, becomes more difficult as you're driving down at 2ohm/ch which some amps aren't always happy about.

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Even if you're gonna disagree with me, lets keep it vaguely professional and polite.

Chris
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Jeff Schoonover1

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Re: Crossover, L-Pad, Impedence, Resistance question
« Reply #42 on: November 22, 2017, 11:20:23 am »

^THIS ^^RIGHT ^^^HERE
Staying in 2 channel mode also makes for fewer "hey, why isn't this working" interruptions to the work day.
Agreed - to a point.  Always willing to learn though, convince me further?  My low box is 2x18" with each driver at 3,600W program power, 1,800 AES RMS.  Right now I'm set up with a dedicated Crown XTi-6K, set at 6KW bridged into 4-ohms. I can also stereo at 1.2KW into 8-ohms.  The amp is dedicated to this box, so either or is fine.  Would Bi-Amp-ing outweigh the benefits of "more power" in bridge-mode? Will it be audibly better?
Links are fine if we don't want to get off the original topic too much.  :)
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Tim McCulloch

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Re: Crossover, L-Pad, Impedence, Resistance question
« Reply #43 on: November 22, 2017, 11:24:26 am »

Agreed - to a point.  Always willing to learn though, convince me further?  My low box is 2x18" with each driver at 3,600W program power, 1,800 AES RMS.  Right now I'm set up with a dedicated Crown XTi-6K, set at 6KW bridged into 4-ohms. I can also stereo at 1.2KW into 8-ohms.  The amp is dedicated to this box, so either or is fine.  Would Bi-Amp-ing outweigh the benefits of "more power" in bridge-mode? Will it be audibly better?
Links are fine if we don't want to get off the original topic too much.  :)

Think about this:  how does the amplifier suddenly have MORE power?  POWER is not voltage.
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"Practicing an art, no matter how well or badly, is a way to make your soul grow, for heaven's sake. Sing in the shower. Dance to the radio. Tell stories. Write a poem to a friend, even a lousy poem. Do it as well as you possible can. You will get an enormous reward. You will have created something."  - Kurt Vonnegut

Jeff Schoonover1

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Re: Crossover, L-Pad, Impedence, Resistance question
« Reply #44 on: November 22, 2017, 11:27:52 am »

... you're driving down at 2ohm/ch
  Not sure about this?  One, two, or fifty speakers doesn't matter, a 4-ohm load is a 4-ohm load, right?
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Jeff Schoonover1

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Re: Crossover, L-Pad, Impedence, Resistance question
« Reply #45 on: November 22, 2017, 11:29:40 am »

Think about this:  how does the amplifier suddenly have MORE power?  POWER is not voltage.
Agreed, and understood.  But, doesn't an amp only using one channel of two possible channels, only use half of the power available to both channels?
Also, isn't a 4-ohm load twice as efficient as an 8-ohm load?  Meaning, if I use each channel independently, and only drive one driver, my impedance is 8-ohms per channel.  Parallel-ing them halves the impedance, making the overall load of the box more efficiently driven?
« Last Edit: November 22, 2017, 11:34:14 am by Jeff Schoonover1 »
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Tim McCulloch

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Re: Crossover, L-Pad, Impedence, Resistance question
« Reply #46 on: November 22, 2017, 11:34:07 am »

Agreed, and understood.  But, doesn't an amp only using one channel of two possible channels, only use half of the power available to both channels?

You either use the other channel, or not.  But the amplifier has only so much current it can deliver into a particular load regardless of voltage swing.  This is EXACTLY what Mac is saying - you get what appears to be a +6dB increase, but it's in the gain (or input sensitivity, if you will) when bridged.  The amplifier isn't automagically capable of additional current and that is exactly the notion that we've spent 20 years dispelling on the LAB and its subforums.
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"Practicing an art, no matter how well or badly, is a way to make your soul grow, for heaven's sake. Sing in the shower. Dance to the radio. Tell stories. Write a poem to a friend, even a lousy poem. Do it as well as you possible can. You will get an enormous reward. You will have created something."  - Kurt Vonnegut

Tim McCulloch

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Re: Crossover, L-Pad, Impedence, Resistance question
« Reply #47 on: November 22, 2017, 11:37:00 am »

Are you for real?

You double the voltage swing by bridging. If the amplifier can source the current, you'll get 4x the power.

When bridging into 8ohm, that's the case for any amp worth having in the rack. Bridging into 4ohm, as I've noted, becomes more difficult as you're driving down at 2ohm/ch which some amps aren't always happy about.

ProSoundWeb, remember?
Even if you're gonna disagree with me, lets keep it vaguely professional and polite.

Chris

If you can't take the heat, disconnect the load...

Dispelling bullshit has been a major part of these forums from the very beginning.  Don't stub your toe on the Dave Stevens (LAB founder) Anvil of Reality.
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"Practicing an art, no matter how well or badly, is a way to make your soul grow, for heaven's sake. Sing in the shower. Dance to the radio. Tell stories. Write a poem to a friend, even a lousy poem. Do it as well as you possible can. You will get an enormous reward. You will have created something."  - Kurt Vonnegut

Jeff Schoonover1

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Re: Crossover, L-Pad, Impedence, Resistance question
« Reply #48 on: November 22, 2017, 11:39:34 am »

You either use the other channel, or not.  But the amplifier has only so much current it can deliver into a particular load regardless of voltage swing.  This is EXACTLY what Mac is saying - you get what appears to be a +6dB increase, but it's in the gain (or input sensitivity, if you will) when bridged.  The amplifier isn't automagically capable of additional current and that is exactly the notion that we've spent 20 years dispelling on the LAB and its subforums.
Do you have a link? I understand that TOTAL amount of current an amp can deliver remains the same.  But think of it this way, If you're only using half of the amp, aren't you leaving the other half on the table?  My understanding is that the potential current it can deliver is divided into half - one half for each channel?  Doesn't the channel limit its consumption before drawing more than it's been alotted?  Otherwise, there wouldn't be any 'clipping,' the channel would just keep drawing more until it blew up?  Not being stubborn, just learning.
« Last Edit: November 22, 2017, 11:57:45 am by Jeff Schoonover1 »
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Tim McCulloch

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Re: Crossover, L-Pad, Impedence, Resistance question
« Reply #49 on: November 22, 2017, 12:06:36 pm »

Do you have a link? I understand that TOTAL amount of current an amp can deliver remains the same.  But think of it this way, If you're only using half of the amp, aren't you leaving the other half on the table?  My understanding is that the potential current it can deliver is divided into half - one half for each channel?  Doesn't the channel limit its consumption before drawing more than it's been alotted?  Not being stubborn, just learning.

This requires logic, not a link...

As I said, if you don't use the other channel, that's up to you.  If you don't *need* the power there is no harm in "leaving power on the table" and you have a spare channel if something else takes a dive...

There are a 2 or 3 ways to power a dual transducer box, I'll use an example of subs - you can wire the loudspeakers in parallel, wire them in series, or separately power each loudspeaker (which is commonly done in Big Dog dual driver subs - more copper means less resistance and therefore less loss; the higher the load impedance also means maintaining a higher damping factor).

We've had amp racks of XTI6002 on sidefill duty (KF850 over SRX728).  I didn't plan or build these racks and the guy who did chose to bridge the sub amps, blissfully unaware that the subs go into power compression with a sustained input of around 500 Watts or so per cone.  Yesterday we started putting the sub amps back into 2 channel mode and pulling an amp out of each rack.  This also means I can now send out VerTec 4880 subs instead of SRX728 with these racks.

Perhaps a water analogy will work:  think about a fire truck that carries 2000 gallons of water.  The pressure out of the hose is very high (voltage) but when the water tank is empty, it's empty regardless of the pressure.
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"Practicing an art, no matter how well or badly, is a way to make your soul grow, for heaven's sake. Sing in the shower. Dance to the radio. Tell stories. Write a poem to a friend, even a lousy poem. Do it as well as you possible can. You will get an enormous reward. You will have created something."  - Kurt Vonnegut

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Re: Crossover, L-Pad, Impedence, Resistance question
« Reply #49 on: November 22, 2017, 12:06:36 pm »


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