I believe it’s reasonable to think that you start getting effects from basket structure and magnet from 500 Hz and upwards on a 5-8 inch driver. Everything (almost) I’ve learnt about dipoles comes from SL. Look at measurements of the Phoenix (main panel, p3) System Test
I think William used the same setup and kept constant distances between mic and speakers as I did. So, the higher distance of the 2nd speaker to the mic could have some impact? Second, apparently the distance between both speakers in the compound have an impact on the output.
All in all I am tempted to do some measurements as well, just don't know when
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I know Erik - time is always the issue isn't it!
This is such an interesting problem - I actually am quite surprised that no-one in the audio community has done these kind of experiments before!
We don't know if we are dealing with a 'virtual baffle' of sorts, an isobaric set up with the 'slug of air' loading both drivers, or the two drivers behaving individually and summing as they would if side by side.....
We have at least confirmed the increase in output beyond that to be expected if there was no summing of the drivers (i.e. an increase beyond the expected 3 dB of increased amplifier power).
Even if this is just behaving as an isobaric set up - as I have previously said - this finding could save people significant costing and labour - no requirement to create an air tight, sealed volume between the drivers.....
Perhaps your smoke idea might also be useful - this would demonstrate if the 'slug of air' is indeed contained between the drivers.
I still cannot see how the two drivers can be 'linked' by this 'slug of air' without containing said 'slug' in a sealed enclosure to pressurise it - I think that the drivers will still create pressure and rarefication waves from the spacer gap - i.e. acting as two separate dipole sources.
This is such an interesting problem - I actually am quite surprised that no-one in the audio community has done these kind of experiments before!
We don't know if we are dealing with a 'virtual baffle' of sorts, an isobaric set up with the 'slug of air' loading both drivers, or the two drivers behaving individually and summing as they would if side by side.....
We have at least confirmed the increase in output beyond that to be expected if there was no summing of the drivers (i.e. an increase beyond the expected 3 dB of increased amplifier power).
Even if this is just behaving as an isobaric set up - as I have previously said - this finding could save people significant costing and labour - no requirement to create an air tight, sealed volume between the drivers.....
Perhaps your smoke idea might also be useful - this would demonstrate if the 'slug of air' is indeed contained between the drivers.
I still cannot see how the two drivers can be 'linked' by this 'slug of air' without containing said 'slug' in a sealed enclosure to pressurise it - I think that the drivers will still create pressure and rarefication waves from the spacer gap - i.e. acting as two separate dipole sources.
I hope not.
The dipole peak is not shown in those plots. Perhaps I should have left it in.
This might be useful if anyone can figure a way of creating two dipoles Ripple Tank Simulation If you click on "example:single source" at the top right you can see the options.
I don't think so. There was no sign of pressure or vacuum acting on the tape. Indeed the test sounded exactly the same whether the tape was there or not.
I'm quite sure the back of driver A saw the back of driver B as the return path and not the front of driver A. There was no low pressure zone in front of driver A when driver A was moving backwards. The nearest low pressure zone was the back of driver B. A seal around the drivers was not required for this to look like an isobaric pair.
If it is a slug of air "bonding" the 2 cones together, you wouldn't expect there to be too much effect on excursion, given that the air load is significantly smaller than the cone mass (isn't it?)*. But it would have some effect. Maybe this is working in conjunction with some positive effect on the dipole radiation?
In which case, there wouldn't necessarily be a universal 6dB improvement.
* Unlike a traditional isobaric arrangement, where the drivers are contending with the compliance of the air in a box of fixed size.
In which case, there wouldn't necessarily be a universal 6dB improvement.
* Unlike a traditional isobaric arrangement, where the drivers are contending with the compliance of the air in a box of fixed size.
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Actually this would be a great way to prove you are right - can anyone see any issues with me laying a sheet of toilet roll over the top 180 degrees of the spacer gap, and then firing up the subs with a 40hz sinewave?
If the toilet roll doesn't move - I am proven completely wrong - correct?!
If the toilet roll doesn't move - I am proven completely wrong - correct?!
Absolutely - it could be a more like a waveguide/horn - increased output over a defined region but similar total power response?
This would be very interesting - kind of a 'super dipole'
It will move. The junction between the moving air and the stationary air around it will be turbulent.
But the air load on each driver is lower than if it were alone in free space.
I think this will need more explanation for me - if the toilet paper flies up into the air, or is instantly sucked into the gap - how do we explain this without concluding there are sound waves emanating from said gap?
You said the tape didn't move at all - so there must be virtually no pressurisation or rarefication in the gap given this was just tape?
I can restrict the toilet roll to literally just the gap - my spacers are 15cm.
That's an incorrect oversimplification.
Picture the operation of a pair of 6" drivers 1M apart, vs the same pair with a connecting tube. The behavior would be very different. The latter would behave like a dipole with D equal slightly over 1M, the former would be an acoustic mess.
A pair of 6" drivers 25mm apart vs a pair on each end of a tube would be quite similar.
Noted and it was to this second configuration I was referring.
No-one that I am aware of builds isobaric constructions 1M apart
I predict the toilet paper will rustle, not be sucked in and out. Eagerly awaiting your video!
I predict the toilet paper will rustle, not be sucked in and out. Eagerly awaiting your video!
Yes!!! This is the most excited I have been about something audio in a long while!
I must be a very sad individual.....
Noted and it was to this second configuration I was referring.
No-one that I am aware of builds isobaric constructions 1M apart
I was creating a mental picture to prove a point. Your statement was an oversimplification. I have built a dipole with the two 12" drivers on either end of a 15" long encosure and it worked very well. If the enclosure wasn't there it wouldn't have worked as expected.