Room gain low frequency anomaly

[meestercleef]

I tried out my Stereophile test discs. The low frequency tones are 1/3 octave warble tones at -20 dB at 200, 160, 125, 100, 80, 63, 50, 40, 31.5, & 25 Hz (maybe 20 Hz, too, altho it don't matter to my spkrs). I tested it on my Polk AW spkrs ("B" spkrs on my stereo rcvr), my MB Quart QL S530 bookshelfs ("A" spkrs on same), & my el cheapo HT in a box (I am too ashamed to identify it, but in self-defense, I'll say that it's fairly priced & Bose would charge twice as much for the same thing). "A" spkrs are placed correctly for 2-ch bookshelfs. "B" spkrs (Polks) have drivers tilting upward, so they are on carpeted floor below the "A" bookshelfs. The front L/R HT cubes are on top of the "A" spkrs with the bass module on the floor beneath the TV shelf.

Overall, response was smooth & consistent from spkr to spkr. The Polks started dropping drastically right when they should (their - 3dB range is 79 Hz), the MB Quart did the same (specs give 44Hz as bottom range, no +/- dB given), & the HT in a box had the expected gap in the 100-200 range (the 125 Hz tone was noticeably weaker than the 160 & 100), where sub & cube don't quite meet (crossover not adjustable on this model).

Here is my issue--all 3 sets of spkrs seemed to "jump" at 50 Hz. This was hard to detect on the Polks (since they aren't even rated that low), but it was there, and was more obvious on the MB Quart & the HT in a box. The 50 Hz tone didn't seem to warble as much as the others, but was more like a smooth rumble, & it was a little louder than the 63 Hz tone. My amateurish attempts to diagnose this led me to the possibility of a room gain anomaly at that frequency.

If this is what it is, any ideas how to fix it? Or if it's not a room gain anomaly, what could it be? A bad test tone?

[meestercleef]

Well, got one answer to this on another forum. The suggestion was to get an equalizer. Since my receiver is a $400 Marantz 2-channel, I don't want to spend a lot. The Audiosource EQ-100 is a hundred bucks at Best Buy. 2-yr manufacturer warranty. Any opinions re equalizers in general and/or this one in particular?

[Aaron]

I would try to avoid an EQ is at all possible. I would try to correct the problem with room placement first. You could also try some isolation techniques like spiking the speakers on the speaker stand. I doubt this will accomplish much, though. The next step would be to get some tube traps. That should solve the problem without adding any piece of electronics in the chain to degrade things.

Aaron

[gidrah]

I hate to ask this, but is your Loudness on?

I've ran an EQ or 2 (at a time) in the past. I like your choice.

[meestercleef]

there is no loudness button. tone controls and balance are all at high noon. will try messing w/placements some more, but the presence of the problem in different speakers in different spots leads me to think that it's more than a placement issue. thanks for feedback.:(