Why flea power is often enough

[tube fanatic]

Joseph Marshall, who was very prominent in the audio world of the 50s, said this in 1956.  I agree with him based on my own experiences through the years,  particularly when Klipsch speakers are used.

 

 

Maynard

 

 

[jjptkd]

I was quite surprised when I was running my Chorus II's with the Carver TFM amplifiers that have watt meters to see that "normal" listening levels at that time barely registered on the meters floating around 2-3 watts.

[henry4841]

Nelson Pass has the same experiment in his listening room with full range speakers with less efficiency then horn speakers and the meters only reach 1 watt on peaks when the listeners say turn it down. Admittedly from my personal experience  bass is better with more watts but that is not to say bass is not good with just a few watts. I have been listening this week with my SE 45 tube amplifier with only a couple of watts and enjoying it immensely using a sub with my LaScala's to round out the spectrum. Another reason could be that when a tube amplifier, with just a few watts, clips it is not unpleasant like when a SS amp does. 

[VDS]

Hi, I, like so many others I’m sure, have been pondering low watt SET amps. I think it’s clear 2-3 wpc is enough to get 96db+ speakers loud, and SET has a certain “magic” but what boy other qualities, power, scale, bass, etc?  Can a flea watt serve as a general purpose, everyday, all types of music solution. Any of you using small amps like this? Reflections? Thanks

[henry4841]

23 minutes ago, VDS said:

Hi, I, like so many others I’m sure, have been pondering low watt SET amps. I think it’s clear 2-3 wpc is enough to get 96db+ speakers loud, and SET has a certain “magic” but what boy other qualities, power, scale, bass, etc?  Can a flea watt serve as a general purpose, everyday, all types of music solution. Any of you using small amps like this? Reflections? Thanks

The 45 tube in a SE amp is considered by many as one that you can close your eyes and it is as though the singer is in the room with you but it is limited by a couple of watts. The sweet spot for me in an all around SE amplifier is 5 or 6 watts. Really nice bass and fantastic mids and highs. Naturally ones choice in music comes into play. If one likes hard rock and modern pop bass strong music a SE amp is probably not going to be a great choice for them especially if they like to shake walls. If you like to listen like when people were limited to just a radio and not television as more of background music they will be perfectly happy with less than a watt amplifier that Maynard loves so much. For what they do they do it fantastically. If a one watt amplifier is not good for horn speakers exactly what are they good for? Same for the popular SE 300B amps people shell out big bucks to buy that only have 5 or 6 watts. The EL34 family of tubes in SE are another good choice. 

[jjptkd]

1 hour ago, VDS said:

Hi, I, like so many others I’m sure, have been pondering low watt SET amps. I think it’s clear 2-3 wpc is enough to get 96db+ speakers loud, and SET has a certain “magic” but what boy other qualities, power, scale, bass, etc?  Can a flea watt serve as a general purpose, everyday, all types of music solution. Any of you using small amps like this? Reflections? Thanks

I would think there are just too many variables to slap a "good enough" label on something like this. I've never had a "flea watt" amp but have had a few 20-30 watt tube amps and integrated amps and one thing I can say for sure is your room is a huge factor in itself.

 

I had a little Jolida 101brc? 20 watt integrated running my Chorus II's in a bedroom system 13x14 iirc and it was the bee's knees, did everything right sounded fantastic could not turn the volume up past 11 o'clock or things would literally start falling off the walls in other rooms, I was tickled pink.

 

I moved to a slightly larger room 13x15? in an old farm house and that little Jolida would not drive those same speakers for nothing, sadly disappointed not even the same sound and no where near loud enough or any bass to speak of. Everything was the same in the system except the room, had that been my only experience with that Jolida I'd just have written it off as junk.

[MicroMara]

Each loudspeaker has a different voltage and current requirement, depending on efficiency or core sonic pressure and impedance.

 

Power

 

The expression "performance" always contains a time component. If you manage to achieve a certain result either with the same effort in a shorter time or in the same time with less effort, you achieve a higher performance. In electrical engineering, the power P is the product of voltage U and current I, in short: P = U ∙ I. The time component is contained in the current, which is defined as charge per time. Together with Ohm's law - resistance R is voltage divided by current, in short: R = U ∕ I - the power can also be calculated using the formula P = U² ∕ R

Power primarily affects the amplifier. These are usually designed to provide a constant voltage. To maintain a functioning circuit, Ohm's law also requires a certain current to flow, which is essentially determined by the driven load - keyword "impedance".The relationship is inversely proportional: the smaller the impedance, the higher the current demand. And under the premise of "constant voltage", a higher current demand is directly related to a higher power demand. Accordingly, loudspeakers with low impedance require more current stable amplifiers.

 

Efficiency vs. characteristic sonic pressure

 

The term "efficiency" is problematic in this respect, because it is actually used in an imprecise way in the language. Normally, it is used to describe the ratio of effort and benefit - or more precisely: the quotient of "supplied divided by emitted energy (or power)". The Greek lower case letter η (pronounced: eta) is used as the symbol for the formula. In most cases, the result is expressed as a percentage and quantifies the efficiency of the converter. Electric motors, for example, achieve very high efficiencies of more than 90 percent. This means that they can convert the vast majority of the electrical energy supplied to them into actually used mechanical energy.

 

Loudspeakers are supposed to convert electrical energy into acoustic energy, which unfortunately can only be achieved with enormous losses due to the poor power transmission from the membrane to the air - this is called mismatch. A large part of the energy is lost in the form of heat development in the chassis. For this reason, loudspeaker efficiencies as defined above are somewhere in the single-digit percentage range and are rarely explicitly stated in this form.A more suitable figure is the characteristic sound pressure level, which is also called "sensitivity". The characteristic sonic pressure indicates the sound pressure level produced by a loudspeaker at a distance of one meter along its main radiation direction when an electrical power of one watt is supplied to it. The correct dimension is therefore "decibel per watt and metre (abbreviated: dB/W/m)".

 

The value indicates - to put it casually - how loud the box is. In terms of measurement, however, it is usually easier to supply the loudspeaker with a constant voltage. For one watt this voltage is roughly the root of the nominal impedance, at 8 Ω it's 2.83 Volt, at 4 Ω exactly 2 Volt. In the laboratory  measures every passive loudspeaker with an excitation signal of 2 volts, regardless of its nominal impedance. The characteristic sound pressure level is then calculated from the mean value of the frequency response between 100 and 4000 Hz.

 

For the same input signal the speaker with the higher characteristic sonic pressure level is louder. On the other hand, this method of measurement means that two loudspeakers with the same characteristic sound pressure level do not necessarily have the same power output, since this is also dependent on the impedance, which also fluctuates depending on the frequency.

 

 

Left: With the Cornwall III, Klipsch has one of the most powerful hi-fi speakers in the industry. In the laboratory the speaker delivered 94 dB/2 V/1 m. Only 4 W are needed to extract 100 dB from it. Right: The PMC Fact 12 only achieved 78 dB/2 V/1 m, making it one of the weakest speakers. For 100 dB it needs a whopping 106 W.

 

Voltage requirement

 

Let's look at two extreme examples from practice. The Klipsch Cornwall III provided an axial frequency response in the lab (left diagram, red curve), with the amount oscillating somewhere between the 90-95 dB line over most of the transmission range. The averaged characteristic sound pressure is 94 dB/2 V/1 m, which is a very high value for hi-fi speakers. In order to achieve the reference level of 100 dB at the same measuring point with this speaker, the input signal must be increased from 2 Volt to about 4 Volt.

The exact value of 4.1 Volt is shown below the diagram and is additionally visualized by a red bar. The longer the bar, the lower the voltage requirement and the higher the characteristic sound pressure.The PMC Fact 12, on the other hand, barely exceeded 80 dB at 2 Volts, and its averaged characteristic sound pressure is a very weak 78 dB/2 V/1 m. The voltage requirement for 100 dB was correspondingly high, and the amplifier had to provide a full 25.3 Volts. The diagram shows such a voltage requirement with short red bars, which ideally should touch or overlap the red bar of the amplifier.

 

 

[tube fanatic]

I exist in a world where 1 watt is high power.  It all depends on listening level and distance from the speakers when listening.  Speakers with fairly low sensitivity can often be used very successfully in small room or near-field applications.  One does not need to reproduce the levels of live rock concerts to enjoy the music, and the guys I know (except for the guy down the road whom I have mentioned in the past) cannot even tolerate such levels at this point.  My own listening requires only a few milliwatts, so a 100mw capability provides all of the headroom needed.  I will gladly post the link to the thread on how to measure the power you require if anyone is willing to do it.  You could be very surprised at how little you really need!

 

 

Maynard

 

 

 

[MicroMara]

24 minutes ago, Jeffrey D. Medwin said:

You need a speaker of about 101 dB efficiency, to REALLY play the small power amplifier game at its best. 

 

Jeff Medwin

According to the technical data sheet, the Klipsch RF 7 MK II has a sonic pressure rating of 101 dB

[henry4841]

1 hour ago, tube fanatic said:

I exist in a world where 1 watt is high power.  It all depends on listening level and distance from the speakers when listening.  Speakers with fairly low sensitivity can often be used very successfully in small room or near-field applications.  One does not need to reproduce the levels of live rock concerts to enjoy the music, and the guys I know (except for the guy down the road whom I have mentioned in the past) cannot even tolerate such levels at this point.  My own listening requires only a few milliwatts, so a 100mw capability provides all of the headroom needed.  I will gladly post the link to the thread on how to measure the power you require if anyone is willing to do it.  You could be very surprised at how little you really need!

 

 

Maynard

 

 

 

I have 103db LaScala's and have played around with a full range open baffle speaker with 96db efficiency and only noticed a slight difference in output. I doubt there is a only a significant difference in volume until one gets below 90db. Firstwatt amplifiers are recommended for 90db and above speakers. Of course there always exceptions depending on multiple things, room, loudness one likes, etc. I have run test on power use at my house with volume so loud one cannot talk and found only a watt or two of average use with my speakers. I use to think more watts means better when I was younger but now know it is just a selling point to fool the consumer. 

[jcmusic]

My system is all active and using one amp that produces 1 wpc, another amp is at 2 wpc, and the speakers are 118db padded down to about 108 db.... The sound quality is excellent!!!

 

[robert_kc]

Here’s my thoughts that I posted on another forum.   (Many of these issues have already been discussed by others in this thread.)

 

• Speaker sensitivity is specified on a logarithmic scale.  To put this in perspective, some owners of highly sensitive speakers (e.g., Klipschorn, 105dB) are satisfied with a 2wpc tube amp, whereas some people require 100 times that power because their speakers have a low sensitivity rating, and based on other important factors discussed below.
• Speaker/amp synergy.  This is black magic, as far as I’m concerned.  IMO, you basically have to audition amps and speakers together to hear if they “play well together”.
• Tubes vs. solid-state.   Analogies are dangerous, but in a sense, this is like the difference between a diesel vs. gas engine when pulling a heavy load.   Tube watts “go farther” than solid-state watts. 
• Room size.  If you double the length, width, and height, the room has 8 times the volume, meaning much more acoustic power is needed to fill the room.
• Distance from listening chair to speakers.  Sound level is inversely proportional to the square of the distance – i.e., if you sit far away, you need more power.
• Listening volume.  Some people listen at volume levels that causes hearing damage.  Again, logarithmic – meaning if you want insane volume level, it takes a lot of power.  (FWIW, I don’t recommend that people damage their hearing, or be inconsiderate of neighbors.)  
• Genre of music.   Large scale orchestral music can have tremendous dynamic range.   Some large-scale classical compositions go from whisper to as many as 200+ musicians playing fff.   Classical music can therefore place a relatively large demand on an amp and speakers.   Folk music – not so much.
• Mastering of a recording.   Modern hi-res recordings of classical music typically are not compressed, and can include significant dynamic range.  OTOH, a lot of pop music is highly compressed, resulting in less dynamic range and less demand on an amp and speakers.  (In other words, with some pop music, you can listen at a lower volume level and hear everything because there are no soft and loud passages in the music.)
• Technology of the consumer deliverable.   Modern hi-res consumer deliverables like Blu-ray DTS-HD MA 5.1, 24bit/192kHz download, and SACD are capable of delivering to the consumer the tremendous dynamic range of modern hi-res classical recordings of large-scale classical music.  OTOH, some consumer formats (e.g., LP) are capable of less dynamic range, and therefore place less demand on an amp and speakers. 
• Whether or not a subwoofer cross-over is installed before the amp, thereby off-loading power-hungry bass from the main amp and speakers.  (I use my Oppo UDP-205’s bass management feature, and line-level subwoofer connection.)
• Surround sound 5.1 vs. stereo.   If you have 3 identical speakers (LCR) across the front, plus rear speakers, and subwoofer(s), you’ll have more acoustic power than 2 speakers.   In some surround-sound installations multiple amps are used, in which case each amp is doing only part of the work
• Bi-amping.   In some cases, not only are separate amps used for each channel, but some people bi-amp or tri-amp individual speakers.   Again, each amp is doing only part of the work.  (For example, a “flea power” SET tube amp may be adequate to drive a K-402 horn, while a more powerful amp drives the associated bass bin.)
• Ambient noise level in listening room.  In a very quiet room, it is easier to hear the quiet passages in classical music, and therefore the volume doesn’t have to be turned up as loud.

In my basement system (average size room), I have no problems with dynamics or deep bass, for any music.   Front, center, and left speakers are Klipsch RF-7 II.  A single rear speaker is a Klipsch RF-7.   Subwoofers:  SVS SB16-Ultra, Klipsch R-115SW.  Source:  Oppo UDP-205 universal player, playing hi-res recordings of large-scale classical music.  (The Oppo provides the bass management function, meaning that the power-hungry bass is off-loaded from the main amp and speakers.)   I have multiple tube amps in this system.   If I use, for example, a Scott 296 to drive the left and right channels, and a Fisher KX-200 (or Scott 272) to drive the center and (single) rear channel, there is dynamic range and frequency range approaching a live concert in a symphony hall.   (These tube amps each produce approximately 30 - 40 wpc.  If I want more muscle, I’ll use my LK150 which produces about 58wpc.)   No problems with dynamics, or deep bass, for any genre of music.  For big-band music or folk music, my 8wpc single-ended pentode amp is adequate.

 

Bottom line, there’s a big difference between playing an LP of a “little girl with a guitar” in a small listening room, vs. delivering in a large listening room an experience that approximates the live performance of Mahler Symphony 2 - i.e., uncompromised dynamic range and frequency range - when playing this modern Blu-ray that features an uncompressed DTS-HD MA 5.1 audio track:

 

[J M O N]

I have and have had multiple 2A3 SET amps putting out a whopping 3.5 watts/channel.  With high efficiency horns, they played more than loud enough for most of my listening needs with startling dynamics.  As an example, I could get live volume levels with life-like dynamics of a drum set in my room with this system.

 

[J M O N]

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Edited September 7, 2020 by JMON

[flm]

Keep in mind if you are not getting enough bass from a 45 or 2A3 probably the amp's output transformer is not up to snuff!

Edited April 1, 2023 by flm

[KT88]

I thought that this article (link below) is very interesting when it comes to the interakton between amp, speaker and music program. It was a link at the end of the recent review about the LaScala AL5 in Stereophile magazine. On the last page under the ending of John Atkinson's measurements.

Who is interested because it highlights some of the dynamic relationships e.g. impedance.
I want to give this link because it can be fun to deepen my knowledge, or as a basis for further discussions here.
I personally think that in some cases a small amp can play very nice and musically with the right partner as speaker.

 

https://www.stereophile.com/reference/707heavy/index.html

[henry4841]

1 hour ago, KT88 said:

I personally think that in some cases a small amp can play very nice and musically with the right partner as speaker.

 

https://www.stereophile.com/reference/707heavy/index.html

Absolutely. I remember a fellow member here who was also a reviewer for some publications, forget which ones, that reviewed a 1 watt amplifier on his K-horns and claimed they sound the best he had ever heard them. 

[Marvel]

My 2A3 amps were stunning on my La Scalas. After I got the MWM cabinets with dual 15 inch woofers in the room, I disconnected thd LS woofers and connected the MWMs. For a lot of music they were fine, bass very good. They just couldn't be pushed as well. Connected to my modified Crown D-45 (25 wpc), the system was powerful, clean and deep.