DJNUBZ said:
It threw me for a loop when essentially the same thing was posted in another thread. I went back to 1st principals (and ignoring change in impedance) couldn't convince myself it wasn't true. So i've been sitting back holding my tongue & noodling on it. I'll be interested to see if GMs explaination snaps things into place.
dave
DJNUBZ said:
Greets!
If you mean Dave's, it appears he assumed that 0.78 is 'liters', but I believe it's 'ft^3' so while the basic response is ~right if there's no series R, the amplitude of the peak won't be as high. Still, it will be severely underdamped so some form of series R will be required to flatten out the response.
?! What's series connected got to do with any of this? As I've noted, all my calcs, observations assumes either none or various amounts of resistance in series with parallel connected midbass drivers.
That said, if two 93 dB/W/m (AKA 93 dB/~2.83 V/m) drivers are wired in series, then we now have two drivers that sum to 96 dB/2 W/m, so yes, their combined efficiency will stay 93 dB/W/m due to the 3 dB loss from a 2x higher R which negates the +3 dB gained over whatever BW the two are closely coupled acoustically (<WL/pi, or more commonly referred to as <1/3 WL).
Drivers in series:
10*log(2/1) = ~ +3 dB due to doubling Sd
10*log(4.9/9.8) = ~ -3 dB due to series wiring
net change = o dB
Drivers in parallel:
10*log(2/1) = ~ +3 dB due to doubling Sd
10*log(4.9/2.45) = ~ +3 dB due to series wiring
net change = +6 dB
Another advantage of parallel Vs series wired is Le halves Vs doubling, so parallel wired has a flatter response (better acoustic phase).
GM
GM said:
Thanks GM,
Everytime I've said that parallel was better, people have told be I didn't know what I'm talking about. Now I have some ammo.
Back to the topic. I don't think either Nubz or myself want to use up any power with series resistance, since we don't have any to spare. If I decided to monoblock 2 of my amps, then I like the idea of Dave's bipole TQWP, but that's down the road. If I go OB, then I'll add helper woofers. A BR with an F3 in the 100hz range is just not acceptable, but a -3db at 40hz and -6db at 30hz that the TQWP showed me seems much more palatable. I want to leave BSC out of the equation for now other than to substantially widen the baffle at the driver level and maximise the kit drivers' potential on it's own merits without any correction circuitry and add bass drivers later, if necessary.
On OB they sound like all drivers do once you get them out of the box, more open and natural. I'm going to fill in the bottom with the 10" woofers that I'm using with my FE206's, but I'll need to start the roll off of the woofers a little lower because the Parkers are a bit fuller on their own due to the slightly higher Q. I can't finalize everything until I have my new room ready. I'm going to flatten 2 sides of the tweeters' mounting plates to better match the woofers and enable closer mounting. Hopefully that will help the sound blend into a single wave front at 9ft or so, my new listening distance. They won't work in my current nearfield setup because of that issue.
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