I added 9.2 Ohms of series resistance to my OB sub, a Hawthorne 15" Augie. I was basically trying to see what the Amazing Loudspeaker might have sounded like and squeeze more deep bass out of the Augie. There was a suitable resistor (e.g. 9.2 Ohm 1% 50 watt) available at a local surplus supplier
www.halted.com for $1.75/ea, so I decided to give-er-a-go. Fancier circuits could have been and still can be implemented that waste less power, but this was quick and easy.
My baffle is 2 ft tall by 3 ft wide which is larger than most anyone uses with an Augie and considered more than optimal by most Augie users. I just had not bothered to cut the board I bought for the purpose of baffling the Augie b/c it used to fit so well under the TV. The theory of operation at HA, which is not new, is that you can use a thinner baffle than what would be calculated to mount a highish Q woofer b/c the added bass boost at resonance will compensate for the roll-off caused by the the baffle width. The 2 will then combine and make a nice, smooth, extended bass response to somewhere near driver resonance. From my limited understanding it seems reasonable enough. So the Solo/Duet is 24" wide and the Amazing Loudspeaker, from what I can find on the web, is 30" wide at the bass but thinner at the top. Not all the different but the frequency extension of the Solos is usually measured somewhere between the mid 40s to 50s by the users capable of doing so while the Amazing supposedly does 20Hz. I don't recall anyone stating how deep the Augies went in their rooms. I know from experience that it sounds deeper then the PSI by itself.
The Qts of the Amazing woofer according to many sources on the Web is around 3, the PSI and Augie are more near a normal 0.9. The resonance of the Augie is 27Hz where as the Amazing woofer is usually stated as 22Hz. The equation for adjusting woofer Q with series resistance according to
www.trueaudio.com is given as Q(tc) = Q(tco) ( (Re + Rg)/ Re ). The relevant Augie specs according to the
www.hawthorneaudio.com are given as Re: 5.69 Ohms and Qt: 0.92. Plugging the numbers into the equation with the 9.2Ohm resistors gives us Q(tc)= 0.92 ((5.69+9.2)/5.69). Our new Q(tc) is then 2.4 if I did my math correctly. That's close enough to the Amazing IMO to see what the effect may be and my additional baffle width will maybe compensate for my lower Q(tc). Of course my Resonant Frequency is also 5Hz higher, but I just don't feel like cutting my baffle today
.... This also means that I have virtually no DF, but prior experience has let me unconvinced of it's worth anyway. YMMV
I have no measuring equipment, but listening impressions basically go like this: Augie w/o resistor is putting out a lot more midrange, but apparently less deep bass. As far as bass quality goes (the usual fast vs. slow bass argument) I can't tell the difference. YMMV on that one as well. Many people claim to hear the effect, but
I discovered today that I really cannot. At least not easily. Sort of a bummer. Just yesterday I thought that the quality of bass was mostly determined by Q(tc). Now I don't know what to think. I mean I also thought that OB bass was less affected by the room than boxed bass. Perhaps this is untrue as well?
Just a note on the set-up: I've got a 24 db/octave x-over set just below 60Hz, a 250 watt amp driving the Augie and 25 watt amp on the PSI.
More listening sessions are needed for sure and measurements would be nice, but it's been a fun experiment so far.
Dan
