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Serial and Parallel drivers
Serial and Parallel drivers
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Old 30th May 2013, 05:45 PM   #1
bvbellomo is offline bvbellomo
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Default Serial and Parallel drivers

I know this has been asked many times before, but there are many different answers and a lot of wrong information. Is the following correct or incorrect about series or parallel drivers?

If I connect 2 drivers in series:
1) 3db louder at the same wattage
2) half the current at the same voltage
3) twice the impedance
4) twice the wattage before distortion
5) twice the wattage before damage

If I connect 2 drivers in parallel:
1) 3db louder at the same wattage
2) twice the current at the same voltage
3) half the impedance
4) twice the wattage before distortion
5) twice the wattage before damage

The rules for connecting a set of drivers already wired in series or parallel are exactly the same as for connecting individual drivers.
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Old 31st May 2013, 12:47 AM   #2
Dissi is offline Dissi  Switzerland
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Hi bvbellomo,

It's always tricky, but I would say 100% correct.

From a practical point of view we could add:

If I connect 2 drivers in series:
6) same spl at the same voltage

If I connect 2 drivers in parallel:
6) 6 dB more spl at the same voltage
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Old 31st May 2013, 07:08 AM   #3
wolf_teeth is offline wolf_teeth  United States
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Quote:
Originally Posted by bvbellomo View Post
I know this has been asked many times before, but there are many different answers and a lot of wrong information. Is the following correct or incorrect about series or parallel drivers?

If I connect 2 drivers in series:
1) 3db louder at the same wattage (This should say +3dB efficient, as louder is incorrect in terms of voltage sensitivity being no difference in perceived output level.)
2) half the current at the same voltage
3) twice the impedance
4) twice the wattage before distortion
5) twice the wattage before damage

If I connect 2 drivers in parallel:
1) 3db louder at the same wattage (Again- +3dB efficient, +6dB sensitive)
2) twice the current at the same voltage
3) half the impedance
4) twice the wattage before distortion
5) twice the wattage before damage

The rules for connecting a set of drivers already wired in series or parallel are exactly the same as for connecting individual drivers.
Wattage is usually equated with efficiency, and voltage with sensitivity. See my alterations or comments above.

Later,
Wolf
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Old 31st May 2013, 08:26 AM   #4
tinitus is offline tinitus  Europe
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2 woofers in series may not give you more output in terms of measured/calculated SPL

but if they are of smaller size it should give better power handling and lower distortion
and you might experience this as being more powerful, and louder

not multiway woofers, but I once in my youth connected two 6" fullrange drivers in series
and it sound better than when in paralel
somehow smoother

but it was common knowledge not to series connect drivers
so I didnt, even when it sounded like better
I guess that was a mistake

I also have some small Foster tweeter horn drivers
sounds like crap one by one
even worse in paralel
but connected in series they sound quite sweet really
but who wants two series connected tweeters
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Old 31st May 2013, 09:43 AM   #5
AndrewT is offline AndrewT  Scotland
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A driver will give a certain SPL for a watt of input.
Two drivers each with half a watt of input will give the same SPL.
Except, when the drivers comply with very rigorous conditions. Sometimes the SPL can be upto 3dB louder than the wattage predicts. This is due to the way the air loads the driver. Two drivers very close to each other relative to the frequency they are being asked to reproduce will affect the air loads of each other. When the frequency is low enough there is a full 3dB of extra output due to this air load interaction.
As the reproduced frequency rises the extra 3dB gradually falls off to nothing extra.

This all makes conclusion 1), in both sets, wrong for most conditions of operation.
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Old 31st May 2013, 01:04 PM   #6
bvbellomo is offline bvbellomo
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Quote:
Originally Posted by wolf_teeth View Post
1) 3db louder at the same wattage (This should say +3dB efficient, as louder is incorrect in terms of voltage sensitivity being no difference in perceived output level.)

1) 3db louder at the same wattage (Again- +3dB efficient, +6dB sensitive)

Wattage is usually equated with efficiency, and voltage with sensitivity. See my alterations or comments above.

Later,
Wolf
Can you please define "efficiency" and "sensitivity" in the context of your comments? "3db louder at the same wattage" is well defined, as an SPL meter measure db and I can measure watts too. If you want to nitpick "3 more db at the same wattage" is a better way of wording what I wanted to say, as it is entirely objective.
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Old 31st May 2013, 01:11 PM   #7
bvbellomo is offline bvbellomo
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Quote:
Originally Posted by tinitus View Post
2 woofers in series may not give you more output in terms of measured/calculated SPL
Going by what I posted, at the same voltage, they won't.

Quote:
Originally Posted by tinitus View Post
2 woofers in series may not give you more output in
but if they are of smaller size it should give better power handling and lower distortion
and you might experience this as being more powerful, and louder
I meant this as a theoretical question, 2 smaller woofers might or might not sound better than 1 large one, but that is outside the scope of what I wanted to ask.

Quote:
Originally Posted by tinitus View Post
not multiway woofers, but I once in my youth connected two 6" fullrange drivers in series
and it sound better than when in paralel
somehow smoother

but it was common knowledge not to series connect drivers
so I didnt, even when it sounded like better
I guess that was a mistake
This is why we need to understand the theoretical, instead of relying on other people's advice.

Quote:
Originally Posted by tinitus View Post
I also have some small Foster tweeter horn drivers
sounds like crap one by one
even worse in paralel
but connected in series they sound quite sweet really
but who wants two series connected tweeters
IMO comb filtering is more feared than it should be. Of course, this is something else people would benefit from understand the theoretical, instead of just going by standard practices "Never use multiple tweeters" or "Never more than 1/2 wavelength between drivers".
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Old 31st May 2013, 01:15 PM   #8
bvbellomo is offline bvbellomo
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Quote:
Originally Posted by AndrewT View Post
A driver will give a certain SPL for a watt of input.
Two drivers each with half a watt of input will give the same SPL.
Except, when the drivers comply with very rigorous conditions. Sometimes the SPL can be upto 3dB louder than the wattage predicts. This is due to the way the air loads the driver. Two drivers very close to each other relative to the frequency they are being asked to reproduce will affect the air loads of each other. When the frequency is low enough there is a full 3dB of extra output due to this air load interaction.
As the reproduced frequency rises the extra 3dB gradually falls off to nothing extra.

This all makes conclusion 1), in both sets, wrong for most conditions of operation.
This is very interesting, do you have links to further information on this? Am I correct in saying everything I said is still correct as long as the drivers are far enough apart not to affect the air loads of each other?
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Old 31st May 2013, 01:21 PM   #9
bvbellomo is offline bvbellomo
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What I am really surprised at is no one commented on 4) and 5), which were guesses on my part, and really important with something like a line array. Suppose I have 16 drivers that individual start distorting enough to sound bad at 20 watts and explode at 40. Using my logic above, the line array should handle up to 320 watts. Different logic can give wildly different power handling numbers, and unless this is well understood, line array builders will either blow all their drivers or never play them near full potential.
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Old 31st May 2013, 01:25 PM   #10
AndrewT is offline AndrewT  Scotland
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No !!!!
the drivers need to be VERY close together to get advantage from the coupling of Sd and this only applies at the low frequency end of the passband for that driver combination.
Sometimes the frequency is so low relative to the driver spacing that the +3dB effect is only available below the passband of the driver.
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