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Nuance, this is the first I have heard about such a huge dip in TC driver. What could account for it? Also you applied 15db of boost?! so 10w @30hz == 320w @60hz? Did you try walking around the room with an SPL meeter? I had a similar huge dip in F/R and found that the power was just elsewhere in the room (not at the listening position). Mine of course was a room interaction. I also didn't see info on the design of your box that the TC is struggling with.
I did not walk around the room with my SPL meter, no. I had to do all this the manual method with a tripod, so I wasn't going to do any more work. :)

You're probably right, though, as it was probably a combination of room and driver. I thought you were saying it was only the room node, in which case boosting at 63Hz wouldn't have raised it one bit.

My enclosure is 20" ^3 with solid bracing. It's internal volume is about 3.3 cu ft. My buddy's TC2000 sub (same enclosure and bracing) rolls off pretty steep at the same frequency. The TC 2000 and 3000 drivers are known to roll off pretty quickly after 60Hz, but I never thought it would interact in such a way that it would be a 15dB drop. :scratch: Anyway, I've got an M-Audio MobilePre USB set to arrive on Tuesday, so I'll use REW then and nip this in the bud.
 

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The TC2K is not that bad on the top end really. Illka measured them as about 4db down at 100hz, which is about what I saw at the GTG. This is compared to the SDX 15 which is about 3db down at 100hz, so it should be a tiny bit better in the top end. The TC3K on the other hand hasn't been measured by someone as reputable as Illka but it has been shown a # of times to be about 12db or more down at 100hz due to a huge 60hz LE induced peak. In comparison the LMS5400 and Ultra drivers are flat at 100hz. I'd expect the AV15's to be pretty good like an LMS or SDX in that regard.
 

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Oh yeah, anechoic measurements are pretty good, but it always seems that people have issues with large drops after 60Hz when using TC2000's in sealed enclosures and measuring at the listening position. Is it really room interaction, and if so, why can it be EQ'd up then (as room nodes aren't suppose to be fixable)?
 

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I would disagree. 3dB is very noticeable. Now, 1 dB is barely noticeable. And the ancient research into volume change vs. perceived level is obscure and only mentioned indirectly. So it's not even clear the exact methodology used in this research(which must have been from the early 1900s).
the reason we have the dB scale as a logarithmic scale is because that is how we hear changes in volume.

If you used a linear scale for a volume knob it would be almost useless with very little range of control. Volume knobs are much better when scaled logarithmically for a reason.

Describing something 3dB louder as having 40-50% more output is pretty misleading.
 

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I measured my TC3000 QVC 15" sub corner loaded with REW. I would bet dollars to donuts that the majority of problems in the midbass area is from the phase change from a ported main speaker that transitions over to the subwoofer.

I posted the meausured response over at the AVS forums, but I have to dig it up.
 

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I don't have 5 posts under my belt yet, but if you search under TC 3000 on the AVS forum, you will find it. Once I have a few posts I will post the link.
 

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You are probably right, Michael. I had a huge phase issue near the crossover, but a polarity reversal fixed it. As for the midbass hump, that's all the driver IMO. Word is it was intentionally designed that way (I am talking about my TC2000, by the way).
 

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If you look at the rate of change of phase from a vented loudspeaker near tuning, you can often see around 80 degrees rotation from a half octave or a bit better. If you crossover in this area, you can often see quite a bit of cancellation unless you use an steep or elliptical filter.

Without taking that into account, you can often see a dip near your crossover area.
 
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