I am listening to my Lafayette LA-375 amp with a small pair of Automatic Radio speakers.

I have the loudness switch turned on and the speakers sound better. That got me to thinking.

I wonder if some manufacturers of amps chose the loudness boost frequencies for use with certain speakers?

No, it was to boost low and high pressure when volume was reduced, to make speakers more adaptive to human ears. They tried. But it was a crapshoot depending on which speakers in which room with the particular ears in question. Also known as damping. Strange brew it is.

An issue with marketing 'packages' which was how stereo systems were sold in bulk in
the 60's and 70's, to most people who were not audiophiles, was the speakers.

Large retailers realized that Japanese import amplifiers and receivers were good enough
and cheap enough to literally give away at cost, in a package. Where the money was
made was in the speakers, that could be manufactured locally. They were styled to look
the the high end types, and most sounded quite good.

There was a difference in geographic areas in preferences to sound, and to an extent, style
too, but since speakers cabinets could be made almost automatically in low capital plants,
by the use of tenoner machines, and sheets of veneer faced particle board, things could be
rather nimble in keeping ahead of the competition. Everyone in the market could sell,
the amplifiers, but the house brand speakers allowed stereo packages that only one
chain of stores had.

When you combine a beefy amplifier, with a boom-sounding speaker, you aren't going to
play a record very loudly, without acoustic feedback, in a small room with the loudness
switch on.

I do know it was to boost the treble and bass, but was it standardized as to the boost frequencies?

I can see where maybe a brand of amp would have a loudness control that would maybe work best with that particular brand of speaker.

The "Loudness" control on a hi-fi amp was tailored to have the boost points approximate the Fletcher-Munson curves of human hearing response. These controls were an attempt to match apparent system frequency response to the perception of the human ear, given a certain amount of gain.

http://en.wikipedia.org/wiki/Fletcher-munson_curve

-O.B.

" Loudness is function of the Fletcher-Munson. curves, and as such a true loudness switch would
involve a tapped volume control.

Here's parts of my article in Electron Oct 1965 that discusses this.

Cool. The Yamaha receiver I have has a variable loudness control which either attenuates the midrange or boosts the bass and treble. Works good for the four Fisher speakers (late 60's or possibly early 70's) I have.

I am going to be the odd man out.

Although a loudness circuit properly compensates for deficiencies in how the human ear works at low volume levels, and does this by boosting the bass, there is a penalty, and that penalty is phase shift.

People will keep the loudness switch on, even when playing music at higher volume levels, where the deficiencies depicted in the Fletcher-Munson Curves do not come into play. Since most loudness circuits are fairly unsophisticated, they muddy up the phase relationships not only in the bass domain, but in the midrange. And the midrange and upper midrange are the frequency domains that affect imaging. By imaging, I refer to the capacity of the hearing apparatus that allows the brain to differentiate a complex field of sound into specific voices and instruments, and that allows the brain to localize the placement of these voices and instruments in the overall panorama of sound.

Muck with the phrase relationships, and all pretensions of high-fidelity are lost.

Now some people don't care about high-fidelity. For example, the above points are not relevant to a 1950's monaural tube radio. But if, for example, a person is running a Scott LK-72 integrated amplifier into highly efficient Klipsch speakers, phase relationships become highly relevant, and there is a pronounced audible sacrifice in imaging the instant that the loudness function is activated.

Fred
repairing audio gear since the Pleistocene

It is amazing how stupid Avery Fisher and H.H. Scott were. It's obvious they didn't know a thing about sound, all this time I thought that when the volume control was advanced the loudness circuit had less effect as the brush pulled away from the loudness tap.

The unit of loudness is the Phon and at 1 kHz a Phon equals a Sone. And 40 Phons is
equal to 1000 loudness units.

The reason loudness is included as a feature is to compensate for the insensitivity of the human hearing apparatus in the bass domain at low volume levels. This is a well understood fact.

There was nothing stupid about famous makers including this feature, and I resent the sarcasm. I get this kind of flaming every time I bring up the argument against using the loudness function. You would think that I was advocating some kind of Satanic ritual.

Many customers at my audio service business leave the loudness function on all the time, even when the sound is fairly loud and bass compensation is not needed, not realizing that they are sacrificing imaging by doing this. For many, when I switch the loudness off, they are delighted at the improvement in sound.

The loudness tap on a volume control does not imply that when the wiper in the control is "above" the tap, that the loudness function is off. It merely means that, as the volume is advanced beyond the tap, the "loudness effect" is progressively reduced. However, in a typical receiver, when the volume is set at, say ten o'clock, the loudness effect is still somewhat pronounced, and the resulting phase shift is clear and obvious to a sensitive pair of ears.

* * * * *

Now most garden-variety loudness circuits boost the bass indirectly. In other words, the circuit does not literally boost the bass. It achieves this effect by cutting the treble. This is done using simple R-C networks. The phase of the treble and midrange components of the composite audio signal are thus shifted relative to the phase of lower-frequency sounds. You can model this as shifting the phase of the bass relative to the midrange and treble, or as shifting the phase of the treble relative to the midrange and bass. Either way the phase coherence in the midrange domain suffers.

Unfortunately, sonic localization in the midrange and treble domains is achieved via the subtle timing difference between when a sound reaches one ear and then the other. It is precisely this that the loudness function confounds.

Regards to all,

Fred
Owner
Classic Audio Repair

Satanic ritual? Wow, lighten up Fred, and don't be so insecure with a little obvious light hearted sarcasm. I laughed and winked when I wrote that and didn’t mean to hurt your feelings.

Some manufacturers referred to it as automatic loudness compensation. There is a reason it has a switch to turn it off just like there are adjustable tone controls, to compensate for different conditions and different recordings. Those that leave it turned on don't hear or don’t care about the difference. I rarely sit front dead center of a sound system. I turn it on and crank it up while I'm busy doing stuff around the house. It's on almost all of the time and when something comes on that I want a little more bass or less treble, I walk over and adjust accordingly. It’s very convenient and I can "pretend" that it's real high fidelity.

With some smaller speakers such as my pair of Automatic Radio speakers the loudness control does help extend the bass response of the speakers.

The only amp that ever made those speakers sound good with the loudness control off is my Scott LK-72.

One one thing about loudness switches, the left and right speakers may or may not be in phase.
Many people with setups with terminals rather than plugs on speaker lines never noticed or cared
if the speakers were out of phase. The loudness switch wont do much if the speakers are out of
phase.

Yep. pretty apparent to tell when a speaker is out of phase even without the loudness switch on.