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Multi-Way Conventional loudspeakers with crossovers

Selecting Amp's power
Selecting Amp's power
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Old 8th January 2019, 10:16 AM   #1
Gaussem is offline Gaussem
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Default Selecting Amp's power

Hello,

I almost finished the design of my speakers but I have a doubt about power.

The speakers are Monotoring type. I don't know yet if I will make them amplified or build a seperate amplifier espacially for it.

My question is, how do you determine the max power (based on RMS) of a 2 or 3 way speaker, depending on the drivers selected ?

I understand that it depends on the impedence of each driver. For example, if the woofer is 4 Ohms and the tweeter 8 Ohms, the woofer will receive 67% of the power and the tweeter 33%.

However, I also heard somewhere that it also depends on the frequency.
I'm a bit lost.

Basically, what is the rule to choose the amplifiers so that there is no risk for the tweeter or the amplifier itself ?

I was going to choose an amplifier with the power rating of the woofer but I want to be sure I won't burn the tweeter.

Thanks and have a nice day.
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Old 8th January 2019, 10:33 AM   #2
TBTL is offline TBTL  Germany
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That would be true if the woofer and tweeter play the same frequency range and get the same input voltage. But it doesn't work that way. Music is a signal of which the power is distributed across all frequencies, with a bias towards low frequencies. How much power a driver will get depends on which frequency range it plays, its efficiency and how loud it is asked to play. And of course the spectral content of the music.

The signal that is going to the tweeter has got a high crest factor (peak to average power) and its amplifier must be sized based on the peaks. As the continuous power rating of a tweeter is only a few watts, it is almost always possible to damage the tweeter if you drive the amplifier into heavy clipping or if you play sine waves. It is not uncommon to drive an actively filtered 5 watt dome tweeter with a 50 watt amplifier. If you want to protect the tweeter from user errors, some form of limiter (placed before the amplifier) works.

If the crossover is passive, you could base the amplifier power rating on the woofer power rating, multiplied by some factor to account for the dynamic range of the signal. If the crossover is active, it gets more difficult.

Last edited by TBTL; 8th January 2019 at 10:47 AM.
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Old 8th January 2019, 10:45 AM   #3
Gaussem is offline Gaussem
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Thanks for you answer.

Is there a simple rule / calculation to limit the risk as much as possible ?
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Old 8th January 2019, 10:53 AM   #4
TBTL is offline TBTL  Germany
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Is the crossover passive or active?

If passive you could use the following guideline. The loudspeaker input power is a bit larger than the woofer power handling.

Quote:
Originally Posted by JBL - Sound System Design Reference Manual
A persistent question is: what amplifier power rating do I choose for use with a loudspeaker of a given power rating? The detailed answer is addressed in JBL’s Technical Note Volume 1, Number 16A; here, we will only summarize those recommendations:
1. For systems that will be stressed with full amplifier output for long periods of time, we recommend that the amplifier’s continuous output rating be chosen to be equal to the loudspeaker’s input power rating. Situations of this sort occur primarily in music reinforcement, where a constant, wide-band signal predominates.
2. For applications, such as speech reinforcement, where there is an operator who controls levels carefully, we can confidently recommend an amplifier with output capability that is twice (3 dB greater) than the loudspeaker’s continuous rating. The rational here is that peak power requirements, often slightly in excess of the loudspeaker’s continuous rating, can be handled with no problem, and it makes sense to provide amplification accordingly.
3. For certain critical monitoring applications, as in recording studios or film postproduction environments, amplifiers may be chosen that can deliver four-times (6 dB greater) power than the loudspeaker can withstand on a long-term continuous basis. The rational here is that the loudspeakers can ordinarily handle midrange and high frequency peaks of short duration that are much higher in instantaneous power than the long-term continuous rating of the loudspeaker.
See section 7.5 https://www.jblpro.com/pub/manuals/pssdm_1.pdf
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Old 8th January 2019, 11:59 AM   #5
Gaussem is offline Gaussem
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Sorry but file stops at section 5. I can't find the section you talk about.

What I don't understand is what power the tweeter will receive and how to estimate it (not too precisely with complicated calculations)
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Old 8th January 2019, 12:05 PM   #6
TBTL is offline TBTL  Germany
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Ah, I'm sorry, I did not check it.
Here it continuous. Section 7.5 is on page 25. http://www.jblpro.com/pub/manuals/pssdm_2.pdf
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Old 8th January 2019, 12:09 PM   #7
Gaussem is offline Gaussem
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Thanks

It talks about "loudspeaker" but my concern is more about the tweeter.
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Old 8th January 2019, 12:49 PM   #8
Gaussem is offline Gaussem
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I also read that monitoring speaker like Pioneer's are "Bi-amplied".

Is there an advantage with this system ?
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Old 8th January 2019, 01:25 PM   #9
PeteMcK is offline PeteMcK
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Why Do Tweeters Blow When Amplifiers Distort?

BiAmp (Bi-Amplification - Not Quite Magic, But Close) - Part 1
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Impedance varies with frequency, use impedance plots of your drivers and make crossover calculations using the actual impedance of the driver at the crossover frequency
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Old 8th January 2019, 03:15 PM   #10
TBTL is offline TBTL  Germany
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Could you show us your speaker? Which drivers do you use? Active or passive crossover? At what frequencies?
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