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[George Dougherty]

I'm thinking 12 feet from the ceiling. That doesn't sound very far.

The rule of thumb I'd heard was within 2 ft or further than 8ft for your typical sub to not have major cancellation issues caused by boundaries.  That goes for walls and ceilings though the distance also depends on the frequency response of the sub.  I think that covers the typical down to 40 sub, maybe a bit lower.

[George Dougherty]

Am I missing something here? Maybe floor cancellation if the subs aren't flown 50 feet in the air?

Regarding the no-go-zone 2-8ft from a boundary, your typical stage is going to put the sub right within that region which will cause cancellations at all kinds of frequencies.  Most people don't consider it, but I've had improvements in response just by rotating a sub 90-180 degrees which was sitting near a wall.  The cabinet depth put the driver (when facing the audience) into the +2ft range and caused cancellations.

[Merlijn van Veen]

Regarding the no-go-zone 2-8ft from a boundary, your typical stage is going to put the sub right within that region which will cause cancellations at all kinds of frequencies.  Most people don't consider it, but I've had improvements in response just by rotating a sub 90-180 degrees which was sitting near a wall.  The cabinet depth put the driver (when facing the audience) into the +2ft range and caused cancellations.

+1

If you can't beat them, join them.

By all means, if the boundary is sufficiently large enough to reflect all frequencies ergo wavelengths of interest AND is stiff and rigid (no diaphragmatic action) then couple with it. Just leave reasonable air gap between the front of the speaker and the surface.

[Scott Harris]

After turning your sub around changing it's distance by 2 feet, do you then adjust the time delay of your tops to bring them into phase alignment?   :-)

[Merlijn van Veen]

Depending on the XO frequency I might.

[George Dougherty]

After turning your sub around changing it's distance by 2 feet, do you then adjust the time delay of your tops to bring them into phase alignment?   :-)

In this particular case I was trying to polish a turd.  The subs were a pair of MRX528S's 15 feet from each side of a stage in a fan shaped room and about 5 feet from the nearest seating running parallel to the front wall. The Mains were some decent quality EV tops flown in several day lines above the stage front and 2 rows further back with atrocious spacing for coverage.  There was no aligning anything except the flown mains to each other and the best I could do with little slack on the sub lines hanging out of the wall was even out the coverage on either side by rotating the subs.  Next time I went back someone had "corrected" my mistake for me. 

For the best footprint I really wanted to face them, flip the polarity on one and delay it to align with the other but I figured that would be too placement sensitive and I didn't have the DSP handy to do it anyway.  I mentioned the idea of flying them with the mains but that had issues with line-of-sight to stage from lighting instruments.

Oh well...

[Luca Rossi]

So this PROVES (at least to me) that the whole idea of "getting more bass" when the subs are on the ground OR simply that you can "add a magical 6dB" to a whole space measurement is simply false.

Since the mic (or person listening) is already in half space, you get the loading.  But no additional loading when both are in half space.

I think you need to consider that listening ear are at least 1.6 meters above the ground level. Then comb filter interaction will cancel some frequencies.

As you can see there are two deep holes. The first one is at 80 Hz and the second one is about at 240 Hz, (of course the last one is well above frequency xover). This is obvious depends on the height of both subs and listener ear. Another think to consider is that as you move away from the flying source, the comb tends to tilt up. This means that only further away people can be considered fully in half place.

caricare immagini

[Ivan Beaver]

I think you need to consider that listening ear are at least 1.6 meters above the ground level. Then comb filter interaction will cancel some frequencies.

As you can see there are two deep holes. The first one is at 80 Hz and the second one is about at 240 Hz, (of course the last one is well above frequency xover). This is obvious depends on the height of both subs and listener ear. Another think to consider is that as you move away from the flying source, the comb tends to tilt up. This means that only further away people can be considered fully in half place.

caricare immagini

So have you EVER seen a spec sheet that said the mic was at ear height?  And what is "ear height?  Sitting or standing?

I have never seen that.  Every one I have seen says full or half space. 

THAT is the reason for the measurement.

I do want to redo the test-with more measurements, but that is not going to happen soon.  I have to many things going on.

But others are welcomed to do their own measurements and post the results.

Models are nice-but they DO NOT represent everything that is going on in real life.

[Luca Rossi]

Models are nice-but they DO NOT represent everything that is going on in real life.

Yes, that simulation represent what's going on in that particular condition. However other situations make no substantial difference with flying subs. The effect is the same, unless the mic is perfectly against the floor as you rightly did for your measurements.

[Bill Hornibrook]

There are a lot of different factors involved in "tests" like this.

For example.  Room modes.  The room modes can often have a greater effect on sub performance than anything.

And the reflections (which are part of room modes) can greatly affect the output at different locations.


I will agree that in some cases, putting them on the floor results in greater output.  But it could be because of something other than in the air vs ground.

With my test, there was only 1 variable-since I was outside and pretty far from reflections.

What I was addressing was the "general statement" about half space vs whole space.

And unless you were in a very LARGE room, when the subs were on the stage-there were nowhere near whole space.

So-as usual-it depends.

Ok so I'm trying to get my head around this. Is what you're saying is that there's no such thing as an advantage to half space loading versus full space? That the reduction in low end that we all experience when we raise tops on stands or put subs on a stage is caused by room modes? And that the low end would return if we could just get the cabs high enough  - and far away enough -  from boundaries?

In a way, that actually all makes sense. It's just looking at an observed phenomenon from another perspective.

And I know you're going to say "it all depends" In general...

[ProSoundWeb Community]