ampfixer
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Phase cancellation with passive radiators (ANSWERED)
Didn't know where else to post this one. Does anyone understand how they overcome phase cancellation when using a passive radiator in a speaker enclosure? An example would be the Celestion Thames Ditton series. One active 12" driver and one identical driver with no voice coil being used as a passive radiator. One is mounted directly above the other. In the confined chamber the passive radiator moves forward only when the active driver moves backward. The air colomn pushes the passive radiator. If a 2x12 guitar cab was wired to do this it would sound horrible, thin and broken. The Celestion monitors sound huge. How do they overcome the phase cancellation in this Hi-Fi gear and studio monitors?? Many thanks.
post edited by ampfixer - 2011/07/07 22:50:03
Regards, John I want to make it clear that I am an Eedjit. I have no direct, or indirect, knowledge of business, the music industry, forum threads or the meaning of life. I know about amps. WIN 10 Pro X64, I7-3770k 16 gigs, ASUS Z77 pro, AMD 7950 3 gig, Steinberg UR44, A-Pro 500, Sonar Platinum, KRK Rokit 6
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quantumeffect
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Re:Phase cancellation with passive radiators
2011/07/07 21:01:24
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Yes, the phase issue is an inherent disadvantage in the passive radiator / drone cone design. In a passive radiator design the whole system is carefully tuned where the passive radiator excites at low frequencies. There is no way around the phase issue so very careful design and optimization (taking advantage of certain psychoacoustic effects) is the major contributor to great sounding PR designs.
On the other hand I don’t think your comparison to the guitar cabinet is a fair comparison. Wiring 2 active speakers out of phase is not exactly the same thing as a mass moving in response to the air in the speaker cabinet. Also, cross-overs (I know this because I have built them), depending upon their roll-off, wire the woofers, mids and tweeters out of phase.
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quantumeffect
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Re:Phase cancellation with passive radiators
2011/07/07 21:09:28
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... one last very important point ... the speakers should be placed on concrete plant stands!
Dave 8.5 PE 64, i7 Studio Cat, Delta 1010, GMS and Ludwig Drums, Paiste Cymbals "Everyone knows rock n' roll attained perfection in 1974. It's a scientific fact." H. Simpson "His chops are too righteous." Plankton during Sponge Bob's guitar solo
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ampfixer
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Re:Phase cancellation with passive radiators
2011/07/07 22:49:21
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Thanks, that's a pretty easy to understand explanation. I figured you would need to design the system mathematically and then tune the physical components mechanically to make it work.
Regards, John I want to make it clear that I am an Eedjit. I have no direct, or indirect, knowledge of business, the music industry, forum threads or the meaning of life. I know about amps. WIN 10 Pro X64, I7-3770k 16 gigs, ASUS Z77 pro, AMD 7950 3 gig, Steinberg UR44, A-Pro 500, Sonar Platinum, KRK Rokit 6
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Karyn
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Re:Phase cancellation with passive radiators
2011/07/08 06:01:18
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Another point...
Wiring two speakers out of phase will result in them being perfectly out of phase, hence sounding horrid.
A passive radiator is being driven by the air behind it, which is "soft" and compressable. Add to this the distance between the main driver and the PR (which can be lengthend by internal baffles) and the PR will actually work IN phase with the main driver at the design frequencies.
Mekashi Futo. Get 10% off all Waves plugins.Current DAW. i7-950, Gigabyte EX58-UD5, 12Gb RAM, 1Tb SSD, 2x2Tb HDD, nVidia GTX 260, Antec 1000W psu, Win7 64bit, Studio 192, Digimax FS, KRK RP8G2, Sonar Platinum
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The Maillard Reaction
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Re:Phase cancellation with passive radiators
2011/07/08 07:51:40
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It is an old timer practice to "weight" a passive radiator with something gooey as an act of "tuning" the *diaphragm* to the system so that the air spring helps out. The goal is to increase the range of bass response... but the basic design predates all the Thiele Small math so there is often times a lot more experimentation done before it's finished.
As mentioned, the energy coming off the radiator is much much lower than that which is coming from the the front of the driver.
best regards,
mike
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Rbh
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Re:Phase cancellation with passive radiators
2011/07/08 22:04:29
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I vote for Karyn's response being closest. I have an older par of JBL Lancer 77's. They have an active and passive 10 " drivers. Nice sounding speakers still... I think theyr'e from the mid 70's
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Jonbouy
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Re:Phase cancellation with passive radiators
2011/07/08 22:29:05
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quantumeffect
... one last very important point ... the speakers should be placed on concrete plant stands!
Columnal, with Greek style fluting work best.
"We can't do anything to change the world until capitalism crumbles. In the meantime we should all go shopping to console ourselves" - Banksy
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The Maillard Reaction
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Re:Phase cancellation with passive radiators
2011/07/09 09:23:07
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I owned a pair of these from 1978 thru 2009 when I gave them to an old stereo hobby friend. Genesis II+  I replaced the drivers and radiators twice in that period... and used a putty to tune non factory spec radiators each time. My dad built his first pair of passive radiator speakers back in the late 1930s. As I say, traditionally the tuning is done by trial and error and listening tests. Ported speakers are also known as bass reflex systems... their design can benefit from the discoveries of Thiele and Small. In practical terms... wiring two drivers out of phase will create a noticeable drop in SPL, but at the risk of seeming disagreeable, I will say that I have encountered instances where installs had obviously been running like that for quite some time with few people sensing that there was a horrible problem. For example; I once ran a large rig with two brands of amps that no one acknowledged used opposite hot pins on the inputs. What tipped me off (half way through the first set) was that when I pushed the sub cabinets... the SPL wouldn't rise as much as I expected. When I looked at the amp rack during break I saw the two different brands of amps mix and matched in the racks and I was able to compensate for the input pin out mismatch by swapping the output cables (we are still allowed to use bare wire on speakers over here). anyways.... best regards, mike
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