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Sound Reinforcement - Forums for Live Sound Professionals - Your Displayed Name Must Be Your Real Full Name To Post In The Live Sound Forums => LAB Lounge => Topic started by: Douglas Cyr on July 13, 2021, 08:29:19 PM
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Hello again everyone,
This is a pretty basic question but something I'm not clear on:
How do I set limiters for passive speakers that are daisy chained/linked in parallel?
I use this formula for a single speaker:
Loudspeaker Voltage = Square Root of Continuous Watts Divided by Nominal Impedance
Example: 700x8=5600, sq.root 5600=74.83Vrms
-Convert voltage to dBu if necessary
I know two 8 Ohm speakers in parallel will become 4 Ohm nominal, but then what do I do with that voltage figure?
Using the example above:
Wattage times two, impedance divided by two
(700+700)4=5600, sq.root 5600=74.83Vrms
So based on the calculation, the limiter setting/voltage will be the same for the two speakers in parallel as one?
Thanks for any insight,
Doug
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This will get the dogs barking :)
What you are asking can be a simple as you want it to be or as complex.
I hesitate to dive into the pool. Let me offer you this, assuming the power amplifier is within the range of the speakers in terms of power output - set the limiter to what the amp can deliver at rated power. But, then there's the attack and release times and that's something you will also want to understand.
To answer your question "So based on the calculation, the limiter setting/voltage will be the same for the two speakers in parallel as one?"
The setting for a pair of loudspeakers in parallel -vs- a single loudspeaker depends upon the amplifier. It will be the same or lower depending upon performance at 8 ohms load -vs- performance at a 4 ohm load. For most of today's amps the setting would be the same, but not always.
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This will get the dogs barking :)
What you are asking can be a simple as you want it to be or as complex.
I hesitate to dive into the pool. Let me offer you this, assuming the power amplifier is within the range of the speakers in terms of power output - set the limiter to what the amp can deliver at rated power. But, then there's the attack and release times and that's something you will also want to understand.
To answer your question "So based on the calculation, the limiter setting/voltage will be the same for the two speakers in parallel as one?"
The setting for a pair of loudspeakers in parallel -vs- a single loudspeaker depends upon the amplifier. It will be the same or lower depending upon performance at 8 ohms load -vs- performance at a 4 ohm load. For most of today's amps the setting would be the same, but not always.
My knowledge on this topic/formula is based on an old Ivan Beaver post somewhere on this forum, and if I remember correctly the attack and release should be based on the HPF corner for the speaker in question. I don't remember the specifics though honestly.
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I experimented with limiters the other day for some subs.
Took a look around in various presets from a manufacturer and it looks like they have common RMS and Peak limiter setting regardless of how many speakers you connect in parallel. This is in line with what I've learned through the years, but there may be different approaches.
I ran the drivers at a fairly loud level for 20mins with pink noise, took a transfer function of the box and increased the level in 1 min intervals until the TF changed, set a RMS and Peak limiter level from that.
RMS limiter attack/release is 2/8 seconds, for the Peak limiter attack/release I used numbers from a XTA(I think) manual I found years ago.
Tested those settings with various pieces of music, the limiters kick in about the same time as the driver starts to sound stressed.
Planning on running these settings for a while and take it from there.
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{...} So based on the calculation, the limiter setting/voltage will be the same for the two speakers in parallel as one? {...}
My mind goes the opposite direction: short of some very strange speaker/amplifier interactions (or a very, er, "esoteric" amplifier design that varies voltage with impedance), why wouldn't the settings be the same?
Voltage is what makes a speaker driver move (or move to too far), and voltage (when squared and divided by impedance, a.k.a. watts) is what makes a speaker driver heat up. The voltage that an amplifier applies to speaker is going to be basically the same regardless of how many speakers are wired to that amplifier in parallel (within the power capacity of the amplifier, at least).
So, if voltage is what we're trying to limit, and the voltage applied to a speaker is the same regardless of the number of speakers wired in parallel, then why would the settings need to change?
-Russ
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Hello again everyone,
This is a pretty basic question but something I'm not clear on:
How do I set limiters for passive speakers that are daisy chained/linked in parallel?
I use this formula for a single speaker:
Loudspeaker Voltage = Square Root of Continuous Watts Divided by Nominal Impedance
Example: 700x8=5600, sq.root 5600=74.83Vrms
-Convert voltage to dBu if necessary
I know two 8 Ohm speakers in parallel will become 4 Ohm nominal, but then what do I do with that voltage figure?
Using the example above:
Wattage times two, impedance divided by two
(700+700)4=5600, sq.root 5600=74.83Vrms
So based on the calculation, the limiter setting/voltage will be the same for the two speakers in parallel as one?
Thanks for any insight,
Doug
The answer is "it depends".
As long as the amplifier can deliver the voltage (the limiter voltage), into the lower impedance of multiple cabinets, then you are fine using the same voltage.
However, if the amplifier cannot deliver the voltage into the lower impedance load, then you need to set the limiter voltage a little below what the amplifier can provide for the lower impedance. The amplifier being the "limiting" factor here, not the loudspeaker.
Now whether or not you want to raise it to get an extra dB or so out of a single speaker, that is up to you.
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I experimented with limiters the other day for some subs.
Took a look around in various presets from a manufacturer and it looks like they have common RMS and Peak limiter setting regardless of how many speakers you connect in parallel. This is in line with what I've learned through the years, but there may be different approaches.
I ran the drivers at a fairly loud level for 20mins with pink noise, took a transfer function of the box and increased the level in 1 min intervals until the TF changed, set a RMS and Peak limiter level from that.
RMS limiter attack/release is 2/8 seconds, for the Peak limiter attack/release I used numbers from a XTA(I think) manual I found years ago.
Tested those settings with various pieces of music, the limiters kick in about the same time as the driver starts to sound stressed.
Planning on running these settings for a while and take it from there.
Off topic (slightly).
But this is an interesting approach! Similar to M-Noise testing.
Did you find the voltage level to be similar to conventional limiter approach? (1/3 or 1/4 power for thermal)
The peak limiter... How did you determine that voltage? 6dB over thermal?
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Off topic (slightly).
But this is an interesting approach! Similar to M-Noise testing.
Did you find the voltage level to be similar to conventional limiter approach? (1/3 or 1/4 power for thermal)
The peak limiter... How did you determine that voltage? 6dB over thermal?
I set the peak limiter after the continuous W for the driver (like I used to do before I got processing with RMS limiters).
RMS limiter threshold ended up around 1/3 RMS W.
It was pretty audible that the driver was struggling right after I observed a change in TF. There seemed to be a pretty good correlation between RMS and Peak limiting playing music from Spotify.
I think this limiter is ok for people mixing by their ears, not for those mixing by the amount of red lights flashing.
I'll admit that my RMS attack and release times are a guesstimate, learned 2s attack/4s release from a friend a few years back. But I think the 4s release was too audible, moving to 8s release gave a more "musical" limiter.
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I'll admit that my RMS attack and release times are a guesstimate, learned 2s attack/4s release from a friend a few years back. But I think the 4s release was too audible, moving to 8s release gave a more "musical" limiter.
Eight seconds release time? I've heard songs that were that long ;^)