Determining acoustic center in a nearfield monitor

[THUMP LUMP]

I searched around a bit and couldn't find an answer to this. I know on "normal" speakers that it's desirable to have the acoustic center of each driver "inline" with each other. This makes sense for a larger room with varying listening positions. But, in the case of a nearfield monitor, where the listening position is fix, wouldn't it make sense to align the acoustic centers of the drivers to where the ear is and not to each other? Doing some quick measurements, my listening position is 30" from the front baffle with the woofer on axis and the tweeter 5.5" above (center to center) which gives about a 10 degree off axis listening position. This translates to, relative to the ear, an acoustic center that is just under .5" closer than if the drivers were aligned to each other.

So, I am building new enclosures for these nearfield monitors and am wondering about which route to go. Align to each other or to the listening position? Or am I nit picking and .5" off in acoustic centers is not worth being concerned with?

 

[THUMP LUMP]

Guess I'll have to figure it out the hard way.....

 

[norman bates]

eh.

To me it is only important in a 6db or a 24db crossover design.

 

[THUMP LUMP]

Huh? How is that used to determine whether the acoustic centers are aligned to each other or equal-distant to a singular listening position?

 

[GM]

http://www.rane.com/pdf/ranenotes/Linkwitz_Riley_Crossovers_Primer.pdf

GM

 

[Sangram]

The other problem with nearfield is that maintaining the listening axis over a listening session is generally quite difficult. It is desirable to use a low crossover point and closely spaced drivers, which are possibly contradictory goals unless we are talking cost no object drivers.

I used an offest tweeter with a 1.6KHz, 24dB crossover and I angle them in quite a lot, partly because my listening distance is much shorter. The very short distance means the tweeter is not straining at high listening levels, and the offset takes care, to some extent, of the time alignment required for a 24dB/oct crossover.

Even so, I do find that it takes a lot of concentration to mix correctly with such a setup. Super-nearfields under 1m are great for setting faders. levels and EQ, but not so much for more delicate work like reverb and compression (IMO). A nice set of midfields are essential to complete the toolkit.

 

[THUMP LUMP]

So it doesn't matter if they (the acoustic centers) are not on the same vertical plane inside the enclosure, but rather that they are the same distance from the listening position (or "the sweet spot").

 

[Sangram]

That is my understanding, yes. In my vase this 'axis' is the surround of the mid woofer, whereas if the tweeter were in the center it would have been lower. Putting me further off-axis, as it were.

 

[GM]

So it doesn't matter if they (the acoustic centers) are not on the same vertical plane inside the enclosure, but rather that they are the same distance from the listening position (or "the sweet spot").

Well, only in the sense that any XO, etc., delay is accounted for WRT the speaker's polar response as explained in the Rane doc..

This once popular wall mounted studio monitor and its more recent concept clones acoustically projects only the mids/HF down at the LP @ 10 deg, but all these types typically have < ~800 Hz XOs, so with higher XO points up in our acute hearing BW it's best overall to design for on axis alignment and tilt/toe in the monitors as required to get the desired coverage angle [double click images to enlarge]: 9844

That said, for near-field apps, some folks skip this extra design work and just toe in and tilt back the speakers to get the desired time delay.

GM

 

[THUMP LUMP]

Great....Thanks. I was wanting to know for enclosure construction considerations, with placement and any Xover adjustments in the back of my mind. I figure, start out as close as one can to being correct, then there is less to make up for later on.