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Old 18th January 2012, 08:28 PM   #41
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Quote:
Originally Posted by Djim View Post
Hi guys,

Just wondering, how does a rotary sub play 2 tones in the same time? "Real sound" is an even more complex signal so how does a rotary sub handle 'everything' below 40Hz?
I also wonder.
BTW - I don't understand follow term in case of movie sound effects:
"most realistic"
this term is for me only clearly to understand in case of the reproduction of classical concerts and acoustical instruments.
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Old 18th January 2012, 08:37 PM   #42
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Default Complete explanation of Rotary Sub

Quote:
Originally Posted by Djim View Post
Hi guys,

Just wondering, how does a rotary sub play 2 tones in the same time? "Real sound" is an even more complex signal so how does a rotary sub handle 'everything' below 40Hz?
Here is a link that will explain, in detail, the rotary sub.Page Title

International Audio Review (Titled the ONLY SUBWOOFER) as reviewed
by Peter Moncrieff
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Old 18th January 2012, 08:40 PM   #43
TheGimp is offline TheGimp  United States
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I would expect the angular rotation of the vanes to follow any electrical signal within the specified bandwidth, thus producing the frequencies within the specified bandwidth. This would include any complex mix of such frequencies.

Imagine an electrical signal on an oscilloscope. Now, let the instantaneous voltage represent the instantaneous angle of the blades. The blade angle follows the signal profile.
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Old 18th January 2012, 08:42 PM   #44
Djim is offline Djim  Netherlands
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Quote:
Originally Posted by tiefbassuebertr View Post
I also wonder.
BTW - I don't understand follow term in case of movie sound effects:
"most realistic"
this term is for me only clearly to understand in case of the reproduction of classical concerts and acoustical instruments.
Hi tiefbassuebertr,

"Most realistic" doesn't have a technical definition like a standard, so it can be used without stating anything specific.

Most ultra/infra low frequencies used in movie fx is artificial generated by down pitched samples. This technique is used widespread since it the best way to control low frequency sound. If there is usable (occasionally that happens) low frequency on a recorded track they still use this sample technique and put it on top of the original recorded sound. This way they have full control over the signal and they can make the impact of the total sound as large they want.
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Old 18th January 2012, 08:54 PM   #45
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Default The sound of thunder

Quote:
Originally Posted by tiefbassuebertr View Post
I also wonder.
BTW - I don't understand follow term in case of movie sound effects:
"most realistic"
this term is for me only clearly to understand in case of the reproduction of classical concerts and acoustical instruments.
As one example I have a recording of a thunder clap, and the rotary
subwoofer recreates this with astonishing fidelity. The first time I
played this recording it scared my wife (her first reaction was to look
out the window for a approaching thunder storm.) My wife was in the
kitchen at the time and when I told her that this sound was coming
from my sound system, she said that it completely fooled her!

This is what I meant when I said "most realistic"
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Old 18th January 2012, 08:59 PM   #46
Djim is offline Djim  Netherlands
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Thanks for the link awraudio.
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Old 18th January 2012, 09:00 PM   #47
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Quote:
Originally Posted by Djim View Post
Hi guys,

Just wondering, how does a rotary sub play 2 tones in the same time? "Real sound" is an even more complex signal so how does a rotary sub handle 'everything' below 40Hz?
The fan blades vary in pitch (angle of attack) with frequency, in the case of two (or any number of tones) the low tone causes a larger pitch change, the higher tone is an oscillation (“wiggle”) in the blade during the pitch change.
As the blades pitch while rotating a pressure wave is generated, the degree (angle) of pitch determines the amplitude of the pressure wave.
The power amp modulates fan pitch and frequency, the fan rotates at a constant speed, the rotational motor does the “heavy lifting”.
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Old 18th January 2012, 09:21 PM   #48
Djim is offline Djim  Netherlands
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Thanks Art. It seems to be less difficult than I thought. Wonder why they are not used in post production studio's.
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Old 18th January 2012, 10:56 PM   #49
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Quote:
Originally Posted by Djim View Post
Thanks Art. It seems to be less difficult than I thought. Wonder why they are not used in post production studio's.
Rotary subwoofers are quite expensive, require an extensive ductwork with a separate location, the TRW, for optimum performance, requires a huge box enclosure, much larger than even the largest enclosures employed by conventional subwoofers.
They don’t sound like a conventional loudspeaker, so from a monitoring standpoint would not be compelling to base your mix on a system that only a miniscule amount of listeners use.

The TRW-17 Maximum Acoustic Output: is only 115 dB , not up to the levels used in a large monitoring facility. It is recommended for use below 25 Hz.

At loud levels its fan blades go to a steeper pitch, and this creates air turbulence around the fan blade tips, which sounds “like a bird flapping its wings”.

The link araudio provided compares the rotary subwoofer to subs with a 1” peak to peak movement, at the time it was written that may have been a high Xmax sub, but now 18” drivers with 38 mm Xmax (just over 3” peak to peak) are available.
Multiples can easily surpass the TRW fan down to 15 Hz, low enough for the biggest organ pipe, and in much smaller size than the TRW.

Since music and soundtracks have little content below 15 Hz, and that range is so expensive to pursue, theaters and home systems will seldom be built to achieve that, especially using a system that has problems above 25 Hz.
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Old 18th January 2012, 11:09 PM   #50
TV7 is offline TV7  Australia
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Originally Posted by theophile View Post
You'll have to come back yesterday,they're on back-order.
They're only available two days before the day after tomorrow.....
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