Vertical Phase Accuracy.
Back in Feb/March '24, I wrote a series of blogs about speaker setup and ended up talking about phase rendering. That is, making sure the position of your speakers was best optimised for time of arrival, to make sure imaging is resolved properly and phase intermodulation is minimised. See that blog here.
But if course there is one other element in this debate and that is vertical phase rendering with speakers using multiple drivers (assuming they are spaced vertically). In those previous blogs I discussed how fine imaging information relies on the phase accuracy of the left and right channels and the sound arriving at your head with minimal time of propagation discrepancy. Any significant discrepancy reduces image accuracy but also brings about midrange harshness. But we need to think in the vertical too.
If you take a typical two way with tweeter mounted above the mid bass driver, well the designer has probably taken some account of vertical phase and intends that you listen with the height of the speakers so that the spot on the baffle in between the two drivers is at ear height. That way, the rendering of the musical information remains intact with lower tones from the mid bass, and their upper harmonics from the tweeter, being correctly in phase. With a three way speaker it is often the midrange driver that is intended to be at ear height.
So have a look at how your speakers are setup with regard to their vertical height. If you’ve been through my previous blogs about speaker setup, or are just about to embark on that task now, then add in the vertical height element too. It might be with stand mounts, you’ve never bothered to get the right height stands or with mid size speakers they might be on the floor when really they should be on short stands. Of course, bear in mind that I am making a generalisation about the designer's intentions here – perhaps there is guidance from your speaker's manufacturer on the matter you can refer too.
The thing to do is experiment. See if you can temporarily raise your speakers up if needed (they’re usually too low), with a stack of a few books say. It’s important work, to discover if you are simply missing the vertical sweet spot. For me, listening to speakers with any significant vertical displacement has often resulted in noticeable phase errors. Get it right and the outcome is usually another step up in tonality, realism and soundstage reproduction.
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