Spkr A/B switch -- matching sensitivity, etc

[redrabbit]

I want to audition 2 pairs of speakers...A/B style....a switch placed between amp, and speakers.
But before I wire the "make-before-break" switch.....

....I have a feeling that speakers with different sensitivity ratings....one pair will sound "louder" than the other. Am I correct ?
I don't want to re-adjust the preamp's level each time I flip between sets of speakers.

....or is the sensitivity "part of the evaluation" ??

=RR=

[analog_sa]

Originally posted by redrabbit
I don't want to re-adjust the preamp's level each time I flip between sets of speakers.

Like it or not, it's the only way to do it without prejuduce to one speaker.

[AndrewT]

two identical power amps with the gain set to match the sensitivity of the speaker.

[redrabbit]

Yes, I imagined that would be a solution.

I also thought about using what I have...different amplifiers:
set up with 2 different amps and the two sets of speakers...set levels, switch back and forth (A/B), noting the differences in speakers.
Then switch amps, and A/B the speakers again....see if my results are similar.
Very informal, and a great compromise, but it's what I have.


Here's an interesting story....

I don't believe there are large sonic differences in the sound of similarly powered SS power amplifiers. This may not sit well with many here.
But it's funny how......
Years ago I purchased a BK ST140 stereo amp. It uses 2SJ50/2SK135 power fets.
Two years later, I purchased some monoblocks (Muse 175). When I got those home, I opened them up, and inside.....2SJ50/2SK135 power fets !! (but more of them).
What are the chances ? Do I eat my thoughts that 'all power amps sound similar' ??
Well, the catch is, I didn't audition those Muse amps. I knew of their great reputation...a deal came up to buy them used, and half price....so I jumped at the deal.

I'll fully admit that I buy amplification based on build quality, and recommendations from those who listen to different amps all-the-time.....because in an audio showroom, I am not able to hear any differences in amps...it does not mean there are none, it just means those differences don't jump out at me, in informal A/B tests.
This is not the case with loudspeakers....I can hear the differences immediately.

[analog_sa]

Originally posted by redrabbit
I can hear the differences immediately.

Why do you need an A/B switch then?

[redrabbit]

Fair question.
Glaring differences, or overall character can be noted in my memory, and does not need a "switch".

I want to listen to specific areas of interest...lower midrange, character of sizzle in the highs, etc. An A/B switch allows these to be compared instantly, perhaps within the same bar of a musical passage.
What spurred me on to considering such a switch, is I am currently trying to integrate some satellites with a sub, and want to listen for "holes" at the crossover frequencies.
Without a switch.....powering down the amp, swapping cables, re-igniting the music....subtle memory is lost. (I have not discounted the "long-term" listening tests either....important too)
I already have (built) a line-level switch box with a relay, that I use for auditioning my headphone amps....or anything stereo that doesn't exceed the rating of the relay.....it switches (near) instantaneously, using a push-button switch. If I cover the LED with tape, I am not aware which source I am listening to....relieving most of the subjective bias.
I was amazed at the subtle differences that identical line drives have...installed with different "audio" opamps.....almost indecipherable.

=RR=

[analog_sa]

In case you are developing a speaker system i can justify a switch. But still i find the idea of A/B -ing wrong. There are many differences which become obvious in such comparisons which are not really important. The brain seems to equalise such differences with ease. Long term perception is what really matters as that's how we listen to music. I have spent countless hours agonising upon trivial sound differences by A/B -ing. Time truly wasted.

[redrabbit]

Originally posted by analog_sa
In case you are developing a speaker system i can justify a switch. But still i find the idea of A/B -ing wrong. There are many differences which become obvious in such comparisons which are not really important. The brain seems to equalise such differences with ease. Long term perception is what really matters as that's how we listen to music. I have spent countless hours agonising upon trivial sound differences by A/B -ing. Time truly wasted.

You are right, we equalize the differences in the long term.
But long term equalization can accustom you to a sub-par sound, ....and because you've grown accustomed to it, it's good, because it's the best one you have. It's only when you hear something better, that your tried-and-true system, sounds lacking. (which is why I don't like to audition gear that's out of my price range)
But if there is a fork in the road (my two pairs of speakers), I'd like to know in what general direction, each will take me......and once down the road, see if my initial suspicions were correct.

An argument against my thinking is, I may be setting myself up for bias....and fall into the trap of 'concentrating on the faults', instead of 'enjoying the merits'.......the Classic Audiophile Syndrome (CAS).

Alternatively, if I find the road (long term listening) to be a pleasurable one, and that my initial tests/opinions proved unfounded...."a mistake"....well then I guess, I learned something.

=RR=

[Ron E]

The ear tends to prefer the louder of two speakers, so equalizing the levels is very important when making judgements.

If you have measurement capability - even just an SPL meter, you can make a determination approximately how much louder one is than the other and use an L-Pad to reduce the sensitivity of the louder one to match the other one - perhaps the best reference would be octave band limited noise around 1kHz.

Note that even differences of 0.1dB are audible if over a very broad bandwidth.

You will at first notice the differences quite strongly, but it is only after a longer period of time that you might decide which is preferable. This is where measurement capability is useful to help correlate your subjective impressions to measurable differences.

In comparisons where you don't hear a difference immediately, the longer period of time is less necessary, IMO.

[BlueWizard]

Certainly, there are psycho-acoustic effects that throw off our perception of music. As has already been noted, we tend to prefer anything that stands out. That's 'stands out' not 'out standing'.

If there is a non-harsh brightness to the treble, that is the speaker our mind prefers. If one speaker has a fuller bass, then we prefer that. And if one speaker is slightly louder, then we prefer that upon first listening. Only in long term listening can we begin to see that our mind is being fooled.

So, to the idea of leveling speaker output loudness. First and foremost you need an accurate SPL meter and probably a pink noise generator.

Next, if you already have a speaker switch box or an amp with an A/B switch, then you could probably just add a variable L-Pad to one or both speakers and balance the sound. Assuming the added resistance, which is good but not quite linear, doesn't color the output.

If you are going to build a custom A/B box with the variable adjustments built-in, then I suspect the total cost will equal simply buying another identical stereo amp,and using the volume control to compensate for levels.

Also, if you build a switch box, are you going to add resistance to the open channels? That is, when you shut a speaker off, is that line going to go completely open, or is an 8 ohms or 16 ohms power resistor going to slide into its place? And, typical 10w and 20w power resistors are probably not going to be enough.

If both speakers are always being used with the same amp, having replacement resistors would stabilize the load to the amp. Not so much of a problem if you alway only have one speaker on line at a time, but if you are shifting between one and two active speakers, this stabilizing resistor might be something to consider. And, it is also something to consider if you have NO speakers on line at any given time. An open circuit on the amp output could start the amp oscillating.

Also, remember that while typical variable L-Pads may be rated at 100watts, it would be unwise to put anything near that through them for a sustained period.

No method is perfect. So, you do the best you can with what you have.

Instead of a true A or B toggle to rotary switch, I suggest two separate press-to-engage switches similar to what you find on stereo amps. If you have impedance problem, then only engage one switch at a time. But the push to engage switches allow A, B, and A+B as options.

Right off the top of my head, and assuming two identical amps are out of the question, a box with two separate switches with variable L-Pads in both speaker lines is probably the best choice.

For what it's worth.

Steve/bluewizard