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March 2nd, 2017, 7:25 pm
I would expect that if the DCR of each of the voice coils 3 ohms then you can speculate that their characteristic impedance is 4-ohms each.
Since the woofers are not enclosed, but mounted on an open baffle, then their free-air resonance prevails. If I recall correctly, Carver used woofers with a free-air resonance of about 5-Hz.
When auditioning a pair at Soundscape many years ago I recall that they did go deep (as advertised).
March 2nd, 2017, 8:32 pm
A word of caution about characteristic impedance. It is a good guide generally with mids and tweeters but not so much for woofers. If you look at the data sheet I previously loaded for the woofer you can see that at a few points the impedance is the 4 ohms specified as the characteristic impedance. But, if you were going to design a crossover for that driver at lets say 200 Hz the impedance is over 7 ohms. That would definitely affect your choice of component values.
For comparison I'm attaching the impedance curve of the SB Acoustics 6.5" Satori midrange I will be using in the "egg" speaker that is my next project. You can see the impedance is very flat once beyond the resonance point. Also resonance is 31Hz and I will be using it in the range of 200 to 2,500 Hz so I will not be anywhere near the resonance impedance peak.
- Satori mid impedance curve.pdf
- (347.77 KiB) Downloaded 195 times
March 3rd, 2017, 7:03 am
I read somewhere that the woofers Bob Carver had built for these "Amazing" speakers are high "Q"
They are very small magnet, reasonably long VC. I have not seem specs on the woofers themselves
But I understand the high Q allows these to go low in freq in an open baffle config. But also I think I remember they are also slow.
I am see this whole system being rebuilt as two separate columns separating the ribbon from the woofers.
Stock these speakers suffer from the same problem are the stock Maggy's. They are not very physically stable and are very floppy. The stand is way too week for the weight of the speaker.
It looks like Bob used had mdf and at least 1 inch thick. The panel is fairly stiff but the thin steel base is crap. If I decide to keep these that would be the first thing I would address after they are up and running
March 3rd, 2017, 9:48 am
The woofers were high Q and were done that way to produce a bump at resonance which is where they were rolling off because of the dipole configuration. High Q speakers were also popular back in the day when cheap output transformers on tube amps also resulted in dropping low frequency response and the bump produced some bass even though not very good. When used with an amp with good or no output transformers they sounded tubby.
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