[Early B.]

I'm assuming an amp can more easily power speakers that are not burdened with the lowest octaves. Let's say you have two scenarios for a low-wattage SET amp:

1.  the amp is powering 95dB monitors that drop off at around 70 Hz
2.  the amp is powering 95dB fullrange speakers with bass into the 20's

 How do you determine the extent to which the amount of bass impacts the amp's ability to properly power it?

[opnly bafld]

Reproducing sound/music into the 20's? 
While I have owned speakers that can go that low (none at 95dB 1 watt) no music I listen to goes that low.

More realistically into the 30s - Depends on many things including how loud you want to go 80 dB, 90, 100?
If someone wants to listen to pipe organs and special effects at live levels an SET is not the proper tool.

FWIW I had a pair of one of kind (company owner's personal speakers) Legacy Classics (90? dB) with dual 10 inch woofers that went to the low 30s and powered them with a 15 watt McAlister Audio SE32 PSE. At MY listening levels the combination had more and better bass than several @100 watt amplifiers I tried. An EK Eagle 2 had slightly better bass, but I preferred the tube amp overall.

[Early B.]

Reproducing sound/music into the 20's? 
While I have owned speakers that can go that low (none at 95dB 1 watt) no music I listen to goes that low.

More realistically into the 30s - Depends on many things including how loud you want to go 80 dB, 90, 100?
If someone wants to listen to pipe organs and special effects at live levels an SET is not the proper tool.

Let me see if I can clarify my question.... if a low-wattage amp doesn't have to produce low bass, the amp should always have plenty of power reserve. However, if this amp has to power a bass-heavy speaker, there's a greater strain on the amp's capacity, even for high-efficiency speakers. The question is about how to determine the balance between an amp's power and a speaker's power need relative to its bass output and sensitivity.
   

[opnly bafld]

That's like asking if a low power engine can go up a hill at 60 mph.
There are factors that need to be considered before a correct answer is given.
Any amplifier, no matter how powerful, has limits.

A system is always limited in absolute spl by the lowest output section.
If an amplifier can reach the desired spl within it's (the amps) ability without strain, how would more unused potential help?

[Saturn94]

I'm assuming an amp can more easily power speakers that are not burdened with the lowest octaves. Let's say you have two scenarios for a low-wattage SET amp:

1.  the amp is powering 95dB monitors that drop off at around 70 Hz
2.  the amp is powering 95dB fullrange speakers with bass into the 20's

 How do you determine the extent to which the amount of bass impacts the amp's ability to properly power it?

My understanding is unless you place a high pass filter before the amp to filter out low frequencies, the amp will try to amplify whatever the recording calls for regardless of the speaker’s ability to reproduce it.  In other words, without any bass filtering before the amp, the bass capability of the speakers doesn’t matter to the amp (assuming all else equal) in this scenario.

[Early B.]

In other words, without any bass filtering before the amp, the bass capability of the speakers doesn’t matter to the amp (assuming all else equal) in this scenario.

Oh, so the amp's power requirement for a particular set of speakers is independent of the amount of bass the speaker produces. Gotcha.

[Saturn94]

Oh, so the amp's power requirement for a particular set of speakers is independent of the amount of bass the speaker produces. Gotcha.

Yes.  So if you want to reduce the demand on the amp, the bass frequencies need to be removed/reduced (using a high pass filter) before they get to the amp. 🙂

[Early B.]

Yes.  So if you want to reduce the demand on the amp, the bass frequencies need to be removed/reduced (using a high pass filter) before they get to the amp. 🙂

No, I don't want to reduce the demand on the amp. I want to know how to determine the extent to which bass impacts the demand on the amp. For instance, if an amp puts out 8 watts into a 92dB speaker that drops off at 80Hz, it will have plenty of headroom to drive that speaker. However, if the same amp has to drive a 92dB speaker that goes down 30Hz, how much headroom is diminished as a result of the need to drive this additional bass?
   

[Saturn94]

No, I don't want to reduce the demand on the amp. I want to know how to determine the extent to which bass impacts the demand on the amp. For instance, if an amp puts out 8 watts into a 92dB speaker that drops off at 80Hz, it will have plenty of headroom to drive that speaker. However, if the same amp has to drive a 92dB speaker that goes down 30Hz, how much headroom is diminished as a result of the need to drive this additional bass?
 

The amp will send the same bass level to both speakers in your example.  The amp doesn’t know if the speakers can output 30hz or not.  From the amp’s perspective, there is no additional headroom availability for either example (to keeps things simple, let’s assume the amp is designed to put out equal power across the entire audible range, 20hz-20khz).    If the recording has a 30hz signal, the amp will amplify it and send it to the speakers.  The speaker that can handle/reproduce the 30hz signal will output it.  The speaker that can’t handle/reproduce the 30hz signal will not output it (and potentially be damaged if the 30hz signal from the amp is powerful enough).

The important thing here is whether the amp has sufficient clean power to drive the speakers with a given efficiency rating, regardless of the speakers frequency response abilities.  The headroom available from an amp depends on the speaker’s efficiency, not it’s frequency response.

[Early B.]

OK. I've always heard that an amp doesn't work as hard if it doesn't have to reproduce the lower frequencies, but I suppose that's another one of those audio myths.

 

[Saturn94]

OK. I've always heard that an amp doesn't work as hard if it doesn't have to reproduce the lower frequencies, but I suppose that's another one of those audio myths.

It is true that an amp doesn’t have to work as hard if it doesn’t have to amplify bass frequencies (which generally are much higher level than mid/high frequencies in a recording.  This gets into how our hearing is much less sensitive to bass frequencies, so they have to be at a higher level to be perceived as the same level as the mid/high frequencies).

But in the case you cited, the amp IS producing the bass frequencies, it’s just that you won’t hear them from the speaker that’s unable to produce the low bass that the amp is sending to it.

My apologies if I am unclear.  I’m not sure how else to explain what I am trying to convey. 

[Letitroll98]

Sounds very clear to me.  The only way to not load the power amp with low frequencies is to cut them off before they reach the amp.  Today this is done with various types of digital filters.  The most common implementation is the LFE output on a HT receiver. 

[FullRangeMan]

Most of Fender basses energy are around 70Hz on rock tracks.

[Tyson]

Sounds very clear to me.  The only way to not load the power amp with low frequencies is to cut them off before they reach the amp.  Today this is done with various types of digital filters.  The most common implementation is the LFE output on a HT receiver. 

Correct.  Another way to do it is put a small cap in line between the preamp and the amp.

[Saturn94]

Sounds very clear to me.  The only way to not load the power amp with low frequencies is to cut them off before they reach the amp.  Today this is done with various types of digital filters.  The most common implementation is the LFE output on a HT receiver.

Thanks.  Well put.