18 inch pro woofer for passive radiator - Page 2 - diyAudio
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Old 27th September 2012, 04:23 PM   #11
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ashok's Avatar
Join Date: Jun 2002
Location: 3RS
I've heard the Extrema's and I found the low end superb ! I don't know what the setting was for the rear driver but we didn't change it while I was there. Don't remember checking what position it was at.
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Old 31st July 2013, 06:12 AM   #12
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Join Date: Feb 2011
Location: Portland Oregon, USA
I built a passive radiator speaker system using two cheap dual cone 8 inch drivers that sounded remarkably good (there was a tweeter for above about 3kHZ too). One driver was active, and the other had a shorted out coil, which caused substantial damping (minimal ringing). If I remember correctly, I did glue a somewhat heavy washer to the center of the non-active driver (with contact cement), but I was truly just guessing at how much weight would be right. This was a very long time ago (the 70's). The box was about 10 x 19 x 9 internal. I gave them to a Dentist friend for work he did on my teeth. Then I moved 100 miles away for a job. About five years later I returned to his town, had him do some work on my teeth, and I had totally forgotten that I had made these speakers for him, which now hung from the ceiling in one of his dental rooms. I was totally proud of how great they sounded. Amazing low end. No sense of screwed up frequency response anywhere. I wish I knew for sure if I actually shorted the coils of the inactive driver, or id I used an 8 ohm resistor across the terminals. and I'm not sure about the details of the washer I may have glued to the inactive drivers coil. I'm thinking that it's probable that I glued in some maybe 1 inch thick steel washers. What I do clearly remember is that they sounded superb. No audible ringing in the bass. It may be that the presence of an inactive driver in the box greatly reduces the peak pressure levels inside the box, which may diminish any internal box resonance effects... just a theory, not something I've verified. I plan to try another one of these active/passive radiator systems after all these years. There may be more magic to it than has been documented. The EE that was with me agreed that they sounded amazing. On paper it's easy to criticize such a method, but when it sounds great, it is great.
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Old 31st July 2013, 06:51 AM   #13
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Join Date: May 2002
Location: Switzerland
I know someone who changed his DIY Manger box from a twin-woofer closed-box speaker into a reflex speker with passive radiator just by using this method. He disconnected the second woofer from the X-OVER (which had to be altered as well). And he also used a damping resistor accross the terminals of the second woofer. The resistor value was chosen by response measurement and listening test.

Before damaging this expensive 18" driver by glueing stuff to it: Did you ever think about using that one as subwoofer driver ? You may probably not be able to use a "textbook tuning" to reach the desired cutoff frequency. But with modern 18" PA drivers there are some choices you have to get good low-end extension.


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Old 1st August 2013, 02:21 AM   #14
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Join Date: Feb 2011
Location: Portland Oregon, USA
I guess the main advantage of using some variation of a passive radiator is to keep the system simple and small. All my speaker projects since the early 1980's have been at least biamp'd, with active EQ on the woofers to get the response I want (flat acoustically to 20HZ). Lately I'm thinkin' simple would be nice too.

I noticed that Jamo has a woofer called the model 800, that has one active 6.5 inch woofer, and two passive radiators on the sides of a cube that is 8 inches on all sides. It's got phase and rolloff freq. adjustments and a built in poweramp), and is even allegedly wireless (not sure if that requires additional product)(for about $500 at Amazon). I wouldn't be surprised if it competed well for it's physical size. I wonder if their passives are actually regular drivers with shorted out coils for tighter bass (?).
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