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The 'Circles of Doom'.....Open baffleless full range speakers.
The 'Circles of Doom'.....Open baffleless full range speakers.
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Old 22nd July 2021, 08:12 AM   #301
ayebee is offline ayebee  Sweden
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Quote:
Originally Posted by ErikdeBest View Post
So do you think that the measured peak and valley are due to the magnet being between driver and mic?
I believe itís 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) Iíve learnt about dipoles comes from SL. Look at measurements of the Phoenix (main panel, p3) System Test
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Old 22nd July 2021, 08:12 AM   #302
ErikdeBest is offline ErikdeBest  Switzerland
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Originally Posted by bushmeister View Post
We are squinting at these charts - William has shown a 4.5-5dB increase in output.

I have shown an ~6dB increase.

There is 1-2dB differences here that we are drawing conclusions from.

I am the only one to use two separate amps with the same power and output with the same ohms per amp - a proper, like with like comparison.

Can someone please repeat my measurements with two amps and the same loads per driver?! Please?
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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Old 22nd July 2021, 08:24 AM   #303
bushmeister is offline bushmeister
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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.
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Old 22nd July 2021, 08:37 AM   #304
cowanaudio is offline cowanaudio  Australia
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The 'Circles of Doom'.....Open baffleless full range speakers.
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Originally Posted by Juhazi View Post
Yep sorry William (are you perhaps a member of the Royal family?).
I hope not.

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Originally Posted by Juhazi View Post
I was surprised that f of axial peak and null didn't change. That fights agains virtual baffle D change... really strange and interesting issue!
The dipole peak is not shown in those plots. Perhaps I should have left it in.
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Old 22nd July 2021, 08:42 AM   #305
Jazz Man is offline Jazz Man
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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.
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Old 22nd July 2021, 08:42 AM   #306
cowanaudio is offline cowanaudio  Australia
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Originally Posted by bushmeister View Post
Perhaps your smoke idea might also be useful - this would demonstrate if the 'slug of air' is indeed contained between the drivers.
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.

Quote:
Originally Posted by bushmeister View Post
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'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.
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Old 22nd July 2021, 08:43 AM   #307
bushmeister is offline bushmeister
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Amazing!
So all isobaric constructions to date have been based on a falsehood!?

I can try some simple stuff like putting some toilet roll over the gap and videoing it!!

Last edited by bushmeister; 22nd July 2021 at 08:46 AM.
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Old 22nd July 2021, 08:51 AM   #308
keithj01 is offline keithj01  United Kingdom
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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.

Last edited by keithj01; 22nd July 2021 at 08:55 AM.
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Old 22nd July 2021, 08:51 AM   #309
bushmeister is offline bushmeister
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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?!
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Old 22nd July 2021, 08:53 AM   #310
bushmeister is offline bushmeister
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Quote:
Originally Posted by keithj01 View Post
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.
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'
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