How much does an Inactive Speaker Affect side by side A/B Testing?

[tengiz]

When comparing speakers side by side, how much does the inactive speaker interfere with what we hear? It’s easy to assume that if it's not playing, it's harmless - but is that really the case?

Clearly the short answer is that it does have some effect. A ported or even sealed speaker can act as a passive resonator - its woofer and cabinet reacting to sound pressure from the active speaker. That may smear low frequencies or introduce other artifacts. Plus, the inactive speaker’s cabinet reflects and diffracts sound, especially in the mids and highs, which might alter imaging. etc.

And then there’s the issue with dipoles where the rear radiation is essential to how they image. Having another large object nearby could block or reflect that rear wave in ways that would never happen in normal listening conditions.

So the question isn’t whether it affects the sound - it clearly should - but how much? Is it enough to sway our impressions in a meaningful way during side-by-side A/B tests for us mere mortals who cannot afford proper labs with carousels that mechanically move speakers being tested ? And if so, has anyone here come up with practical ways to deal with it without completely tearing down the setup between comparisons?

Curious to hear what others have tried or measured - does this end up being a real-world issue, or is it more of a theoretical concern?

 

[kemmler3D]

as anyone here come up with practical ways to deal with it without completely tearing down the setup between comparisons?

Fair points here although I'm not sure if the inactive speakers will really resonate much while hooked up to the amp, and either way that contribution would be quite small given that most speakers are designed to resonate as little as possible.

I think the diffraction / reflection question is pretty pertinent if you were doing this for real.

IIRC Harman used a huge turntable to move the speakers in and out of position. Should be no problem to fix one up at home using a large dinner table relieved of its legs and replaced with wheels.

 

[DVDdoug]

Probably insignificant but measurable.*

Generally there are pretty BIG differences between two different speakers and any differences caused by a speaker (or other object) in the room will be tiny.

And good speakers, most speakers, don't resonate like a musical instrument. ...You probably won't hear the resonance of an acoustic guitar sitting the room unless you put your ear up to the sound-hole.

It's probably similar to blind-testing speakers. It's usually easy to "pass" an ABX test because there is enough difference in sound to identify which as A and which is B. But it's still helpful if you can keep it blind so don't know the brand, price, size, appearance, etc.

* I was doing some experiments once with high frequency tones and an SPL meter on a mic stand. When I moved around, or just slightly moved my head the sound level varied by a LOT as the direct & reflected waves, and the waves from the left & right speakers, went in-and-out of phase. That "effect" didn't really surprise me except it's something you don't normally notice with music or other program material. What DID surprise me was seeing the measured SPL level change by several dB as I moved around BEHIND the mic stand!

 

[Chris A]

When comparing speakers side by side, how much does the inactive speaker interfere with what we hear? It’s easy to assume that if it's not playing, it's harmless - but is that really the case?

Actually...this touches on what I consider to be an interesting topic--room reverb effects due to high output impedance amplifiers--and passive loudspeakers in-room re-radiating acoustic energy with a delay (mostly--the effects of their woofers re-radiating, but it can include horn/drivers--if any--that match the high acoustic impedance of the horn's driver to the air in the room).

Again--anecdotally--one of my acquaintances on another forum who had worked in a fairly extensive hi-fi shop that had a lot of loudspeakers in-room described the effect as a pleasant reverb effect that added extra spaciousness to the room.

But note: we're talking about a room stuffed full of loudspeakers, not just one extra pair of stereo loudspeakers.

Chris

 

[tengiz]

And good speakers, most speakers, don't resonate like a musical instrument. ...You probably won't hear the resonance of an acoustic guitar sitting the room unless you put your ear up to the sound-hole.

I think at least a ported speaker enclosure, when inactive, should behave as a Helmholtz resonator with a tuning frequency and Q close to those of the system in normal operation. It will "ring", but the question is would it matter?

 

[SIY]

A ported or even sealed speaker can act as a passive resonator - its woofer and cabinet reacting to sound pressure from the active speaker.

Short the terminals of the inactive speaker. This will vastly decrease any resonant effect.

 

[Chrispy]

Inactive?

 

[tengiz]

Short the terminals of the inactive speaker. This will vastly decrease any resonant effect.

I understand that it will suppress baffle/driver resonances. But would it have any effect on the port/Helmholtz resonance?

 

[tengiz]

Inactive?

I meant the speaker that's disconnected or muted.

 

[tengiz]

Again--anecdotally--one of my acquaintances on another forum who had worked in a fairly extensive hi-fi shop that had a lot of loudspeakers in-room described the effect as a pleasant reverb effect that added extra spaciousness to the room.

I can imagine

 

[Chrispy]

I meant the speaker that's disconnected or muted.

Weird term. Thought you meant a passive speaker (i.e. not an actively crossed/powered speaker)

 

[tengiz]

Weird term. Thought you meant a passive speaker (i.e. not an actively crossed/powered speaker)

Yes, I got it. It was not the best choice indeed.

 

[SIY]

I understand that it will suppress baffle/driver resonances. But would it have any effect on the port/Helmholtz resonance?

Yes, though not as much (obviously) as the cone.

 

[Hayabusa]

I would assume if they would be closer that the baffle width it would influence the 'baffle step'.

 

[somebodyelse]

IIRC Harman used a huge turntable to move the speakers in and out of position. Should be no problem to fix one up at home using a large dinner table relieved of its legs and replaced with wheels.

A turntable was used for this small monitor blind test. IIRC Harman had an automated rig like sliding floor tiles, with unused speakers against the back wall and the used speaker further away from the wall, all this behind an acoustically transparent screen to keep the speakers hidden. There's a picture on here somewhere, but I can't find it.

 

[Elkerton]

As I recall from early double-blind screen testing at NRCC, as long as there was at least 6" (15.24 cm) between speakers, there was little influence on the sound of the playing speaker. Less separation audibly increased the baffle area.

 

[MattHooper]

Actually...this touches on what I consider to be an interesting topic--room reverb effects due to high output impedance amplifiers--and passive loudspeakers in-room re-radiating acoustic energy with a delay (mostly--the effects of their woofers re-radiating, but it can include horn/drivers--if any--that match the high acoustic impedance of the horn's driver to the air in the room).

Again--anecdotally--one of my acquaintances on another forum who had worked in a fairly extensive hi-fi shop that had a lot of loudspeakers in-room described the effect as a pleasant reverb effect that added extra spaciousness to the room.

But note: we're talking about a room stuffed full of loudspeakers, not just one extra pair of stereo loudspeakers.

Chris

Along a similar line…

A few years ago when I introduce some subwoofers into my two channel system I had to place one of them behind me and the other one along the same wall as my Home seat, projection screen, and my LCR home theatre speakers.

I was only trying to integrate them with my two channel floor and speakers that were also in the room.

But I noticed when I started playing back music and movies on my surround system that suddenly the bass was thick, sludgy and boomy. It didn’t make sense cause it had never sounded like that. And the subwoofers weren’t even on when I was playing the home theatre speakers.

I wondered whether for instance, the subwoofer placed between my big centre channel and my right home theatre channel had created some sort of based node or something just buy it position. But that didn’t seem to make that much sense to me.

And then looking it up on the net I found people mentioning the effect of passively, resonating drivers. Especially with large subwoofer drivers the idea that the unused subwoofer driver could be resonating in sympathy with the bass frequencies of the rest of the loudspeakers in the room.

And if so, that made more sense of things.

Once I got rid of the subwoofers, that problem went away.

I didn’t have any measurements on this so I can’t say actually for sure what was going on, but that was my perception.

 

[Frank Dernie]

I think at least a ported speaker enclosure, when inactive, should behave as a Helmholtz resonator with a tuning frequency and Q close to those of the system in normal operation. It will "ring", but the question is would it matter?

This is the case.
It will absorb some sound at the frequency the enclosure/port are tuned to.
Probably not that audible unless it happens to be at a room mode, then maybe a help.
If the diaphragms are behaving as microphones there will be a small loss, any reflections in the room will obviously depend where the speakers are.

 

[Purité Audio]

Compared multiple speakers side by side and have been thoroughly criticised for doing so by the ‘remove your wristwatch /single speaker in the dem room crowd’ but never noticed anything untoward certainly no different to having a piece of furniture next to the speakers.
Keith

 

[Mart68]

Compared multiple speakers side by side and have been thoroughly criticised for doing so by the ‘remove your wristwatch /single speaker in the dem room crowd’ but never noticed anything untoward certainly no different to having a piece of furniture next to the speakers.
Keith

I recall that claim from Linn - that even the tiny loudspeaker on a digital watch would affect the sound. So stupid, and then it turned out that Ivor could not tell if there was a whacking great JBL sat behind him or not.