Should amplifier output be restricted to the max power rating of the speaker?

[Pareto Pragmatic]

As others have said, not really much of a concern. However, there are ways it can be a concern.

One that I never thought about before reading about it here is that if one is using a DAC as a preamp, some failure might send full power to the speakers. I don't know if that is likely from a circuit glitch or a software glitch that switches modes without warning or input. Or from user error.

If such a precaution is prudent, what is recommended when working with power amps that do not have a gain knob?

If one has the knowledge, it is possible to get a volume control that fails in a way that breaks the circuit, not that lets full power through. Think fail safe, not fail proof.

You can also put fuses in place to protect drivers, which is going to cover things like people turning up the volume way too high.

Me? My main speakers will take the full power of my amp without breaking. I did not buy them for that reason, but I certainly like that is how it worked out. Because I am using my DAC as a preamp.

I was hoping for clear guardrails so that I’d be able to know I wasn’t risking my drivers if I stayed below such-and-such a level. While the tests described in the document sound onerous, they don’t provide a clear safe/not safe boundary. I guess the situation is too complex to allow for the simple specification I’d been seeking.

Now I’m not clear on how useful the max power spec is for any driver.

Keep hoping! I've found that there is depth to pretty much every topic that seems simple. In all fields.

Given triamping, I think you are safest looking at max voltage for each driver, and using that to guide you.

 

[Dave TR3A]

Are you speakers active or passive?

My speakers are passive.

They are 1986 Klipsch La Scala speakers. I've removed the Klipsch crossover (Klipsch calls it a "balancing network") and have connected the drivers directly to my 3 stereo (2 channel) amps. One amp serves the L&R tweeters, the second serves the L&R midrange, and the third serves the L&R woofers.

The only thing between the drivers and the amps are two capacitors: a 13 uF in series with the tweeter and a 100 uF in series with the midrange. The capacitors are there to protect those drivers against DC in case the amp were to fail.

• the 13 uF capacitor is in series with the 8 ohm tweeter. It was sized to filter frequencies below 1530 Hz (about 2 octaves below the 6000 Hz cross over to the midrange). I have since changed the crossover to 4500 Hz but have left the 13 uF capacitor in place. I ought to replace it with a 17uF or 18 uF capacitor.
• the 100 uF capacitor is in series with the 16 ohm midrange. It was sized to filter all frequencies below 100 Hz (2 octaves below my 400 Hz cross over to the woofer).
• I did not protect the woofer with a capacitor (because I figured the woofer was beefy enough to withstand a little DC and if it didn't it was easy to replace). One sized for a 4 ohm load and serving as a LPF 2 octaves below an 80 Hz crossover (i.e., a 20 Hz LPF) would be around 2000 uF.

 

[EJasonC]

Correct me if I’m wrong:
It is my understanding that an underpowered amp is more detrimental than one with more power.
In other words, it is better to have more power with more headroom.
Less power risks clipping and hence more chance of damage.

 

[wadude]

Correct me if I’m wrong:
It is my understanding that an underpowered amp is more detrimental than one with more power.
In other words, it is better to have more power with more headroom.
Less power risks clipping and hence more chance of damage.

See post #16 above.

 

[Pareto Pragmatic]

1986 Klipsch La Scala

Just how much power to you need to put through those for your room? A watt?

A watt into those would be ~10 into my vintage horns, and ~100 into my main speakers. All of which would destroy my hearing in my room.

 

[mhardy6647]

I had wondered how manufacturers determined the power ratings for drivers. It’s helpful to know that exceeding the specified power limit will cause damage by overheating the voice coil.

It's a black art.

Unlike, e.g., excursion.

 

[Everett T]

My speakers are passive.

They are 1986 Klipsch La Scala speakers. I've removed the Klipsch crossover (Klipsch calls it a "balancing network") and have connected the drivers directly to my 3 stereo (2 channel) amps. One amp serves the L&R tweeters, the second serves the L&R midrange, and the third serves the L&R woofers.

The only thing between the drivers and the amps are two capacitors: a 13 uF in series with the tweeter and a 100 uF in series with the midrange. The capacitors are there to protect those drivers against DC in case the amp were to fail.

• the 13 uF capacitor is in series with the 8 ohm tweeter. It was sized to filter frequencies below 1530 Hz (about 2 octaves below the 6000 Hz cross over to the midrange). I have since changed the crossover to 4500 Hz but have left the 13 uF capacitor in place. I ought to replace it with a 17uF or 18 uF capacitor.
• the 100 uF capacitor is in series with the 16 ohm midrange. It was sized to filter all frequencies below 100 Hz (2 octaves below my 400 Hz cross over to the woofer).
• I did not protect the woofer with a capacitor (because I figured the woofer was beefy enough to withstand a little DC and if it didn't it was easy to replace). One sized for a 4 ohm load and intended to filter below, 25Hz - 50Hz would be around 800 uF to 1600 uF.

Since it's passive (with no real audible advantages) you're still getting the power divide in passive crossover board/s. The woofer will determine overall sensitivity and usually impedance.how did you split the signal to the amps? (More curiosity than anything else)

 

[Jose Jimenez]

My speakers are passive.

They are 1986 Klipsch La Scala speakers. I've removed the Klipsch crossover (Klipsch calls it a "balancing network") and have connected the drivers directly to my 3 stereo (2 channel) amps. One amp serves the L&R tweeters, the second serves the L&R midrange, and the third serves the L&R woofers.

The only thing between the drivers and the amps are two capacitors: a 13 uF in series with the tweeter and a 100 uF in series with the midrange. The capacitors are there to protect those drivers against DC in case the amp were to fail.

• the 13 uF capacitor is in series with the 8 ohm tweeter. It was sized to filter frequencies below 1530 Hz (about 2 octaves below the 6000 Hz cross over to the midrange). I have since changed the crossover to 4500 Hz but have left the 13 uF capacitor in place. I ought to replace it with a 17uF or 18 uF capacitor.
• the 100 uF capacitor is in series with the 16 ohm midrange. It was sized to filter all frequencies below 100 Hz (2 octaves below my 400 Hz cross over to the woofer).
• I did not protect the woofer with a capacitor (because I figured the woofer was beefy enough to withstand a little DC and if it didn't it was easy to replace). One sized for a 4 ohm load and intended to filter below, 25Hz - 50Hz would be around 800 uF to 1600 uF.

Do you connect the woofer polarity 180 degrees from that of the midrange or tweeter because of the capacitors? Are all the amplifiers input fed full range or do you apply any active crossover as such or pass filtering before being amplified?

 

[Jose Jimenez]

Correct me if I’m wrong:
It is my understanding that an underpowered amp is more detrimental than one with more power.
In other words, it is better to have more power with more headroom.
Less power risks clipping and hence more chance of damage.

You can damage speakers either way. I would agree that an amplifier with sufficient power would be a benefit for the reasons you stated. To the others, aren't we mature enough to know when enough is enough?

 

[Dave TR3A]

Just how much power to you need to put through those for your room? A watt?

A watt into those would be ~10 into my vintage horns, and ~100 into my main speakers. All of which would destroy my hearing in my room.

Since I lack power meters on my amps (boy, would I ever like some), I’ve had to estimate the power. Here's how I've calculated it:

Situation

• I have tri-amped La Scala speakers. Klipsch rates the La Scala as delivering approximately 105 dB SPL @ 2.83V @ 1m (i.e., 1 W at 1m when going into an 8 ohm load).
• All of the drivers in the system are also rated at roughly 105 dB SPL @ 2.83V @ 1m
• I am listening to 2 speakers
• My listening positions are about 3m (10 feet) from the speakers.
• I seldom listen at much more than 90 dB SPL.

Calculation

Recall:

• while dB power is calculated as 10log(P2/P1), dB amplitude (such as SPL) is calculated as 20log(A2/A1).
• adding a second speaker increases SPL between +3 dB (for incoherent/out-of-phase sources) and +6 dB SPL (for coherent/in-phase sources)

105 dB SPL --- SPL produced from 1W
+ 3 dB SPL --- additional SPL from second speaker (worst case, assumes speakers are incoherent)
108 dB SPL --- total SPL from both speakers
- 9.5 dB SPL --- SPL reduction at 3m distance (i.e., 20log(3/1) = -9.5 dB SPL)
98.5 dB SPL --- SPL at 3m when both speakers are driven with 1 watt

From information provided by Crown alongside one of their calculators, we find two formulae that can help us:
1) dBW = Lreq - Lsens + 20 * Log (D2/Dref) + HR
2) W = 10 to the power of (dBW / 10)

Where:
Lreq = required SPL at listener
Lsens = loudspeaker sensitivity (1W/1M)
D2 = loudspeaker-to-listener distance
Dref = reference distance
HR = desired amplifier headroom
dBW = ratio of power referenced to 1 watt
W = power required

If we remove the contribution of the second speaker, the SPL at the listening position should drop from 90 dB SPL to 87 dB SPL.

Populating formula 1, we get:
dbW = 87 - 105 + 20log(3/1)+0 (since we are not interested in amplifier headroom at this time, HR can be ignored)
= 87 -105 + 9.5
= -8.5

Using that result, we populate formula 2 as follows:
W = 10^(-8.5/10)
= ~ .141

Therefore, my speakers should each be drawing about 140 mW to produce 90 dB SPL at my listening position.

The amps that I am using deliver roughly 50W (before clipping) when driven by a 0.5V input (the measured input sensitivity of the amp) into 8 ohms. That would be about 17 dB more than what the La Scala delivers at 1W (i.e., 10log(50W/1W)=17 dB). Since I typically listen at less than 90 dB SPL (which I've calculated as requiring 0.14W), I ought to have about 25.5 dB "headroom" (i.e., 10log(50W/0.14W) = 25.5 dB) above my typical listening level. That should be loads of headroom.

 

[Talisman]

But why are you making your life so complicated? Dividing the amplifiers makes sense only if they are truly separate and if an upstream DSP manages the power distribution, but what do you want to achieve? You might as well use the original crossover, install a good low-watt amplifier, and simply enjoy the music.

 

[Dave TR3A]

aren't we mature enough to know when enough is enough?

I'm guessing you don't have kids or teenagers.

 

[Jose Jimenez]

I wish there were more icons than the thumbs up like on ASR. We need 'WOW' and "LOVE" and the rest of them! Some of the replies here on ASR would have gotten me banned on Audiokarma for certain. But I am enjoying the humor, and it keeps me away from all the politics on Townhall, Gateway Pundit, Breitbart, etc.

 

[Jose Jimenez]

I'm guessing you don't have kids or teenagers.

I raised two, one each on my own after the divorce. Now they are in their 30s. I fought for them hard, and in gratitude they watched and learned. I never needed to worry so I guess I did right by them.

 

[Dave TR3A]

Since it's passive (with no real audible advantages) you're still getting the power divide in passive crossover board/s. The woofer will determine overall sensitivity and usually impedance.how did you split the signal to the amps? (More curiosity than anything else)

There are no crossovers in the speakers. That function is provided by a DSP upstream of the amplifiers.

 

[Everett T]

There are no crossovers in the speakers. That function is provided by a DSP upstream of the amplifiers.
View attachment 520680

Gotcha thanks..

 

[Pareto Pragmatic]

The Aiyima has an analog pot for volume control iirc. So you're safe from sudden full signal incidents.

 

[NTK]

There are no crossovers in the speakers. That function is provided by a DSP upstream of the amplifiers.
View attachment 520680

Since you are using a Flex 8, have you considered/tried using the compressor?

Compressor - miniDSP Flex Eight / Eight-N User Manual

docs.minidsp.com

 

[Dave TR3A]

But why are you making your life so complicated? Dividing the amplifiers makes sense only if they are truly separate and if an upstream DSP manages the power distribution, but what do you want to achieve? You might as well use the original crossover, install a good low-watt amplifier, and simply enjoy the music.

@Talisman That's a long story.

When I got my La Scalas I was disappointed with how they sounded. I tried 5 different passive networks (AL, AA, ALK Universal, AA/4500, ALK Universal/4500) but none of them brought any magic to the sound.

In desperation, I decided to experiment with DSP and tri-amping. The results were astounding. I've tamed (some might say corrected) some of the deficiencies of the La Scala, mitigated some of the challenges posed by my listening room, smoothly integrated my two subwoofers, and created a number of "house" curves to suit my preferences.

My amps can deliver a lot more power (really voltage) than the drivers are rated for. What started this thread was my curiosity about whether it was prudent to restrict amplifier output so that it couldn't exceed the rated specs for drivers.

What I've learned from this thread is:

1. the driver (or speaker) max. power ratings can't be trusted to be useful
2. most of the time, the power being used is so small that the concern is more hypothetical than real

 

[Dave TR3A]

The Aiyima has an analog pot for volume control iirc. So you're safe from sudden full signal incidents.

Yes, that's what I'm using now. It's set so that the amp can never provide more voltage than the driver could handle (as per the driver specs). In my case, that meant keeping the knob below about 2-3 o'clock.

What prompted this thread was curiosity about whether or not such a restriction was a prudent precaution or unnecessary.