Originally Posted by woody777
Interesting information, Brian. I don't know the video mikepos is referencing, but that sounds exactly like the issue I've been having. My FV15HP has tons of air movement and the loud flapping at 20Hz and moderate volumes. I am an Audyssey user. I wonder if it's possible to unplug the sub, run Audyssey, then plug the sub back in. Any EQing could be done on the sub itself. This is obviously not an ideal work around (I think Audyssey is fantastic for the most part), but maybe a possibility to use Audyssey and keep it from messing with the sub.
I finally got to flight in Denver and visit Woody777(Adam) and check out his subwoofer and see why he heard this flapping noise. I felt the urgency of solving this problem as it may not be perceived correctly from other potential customers.
We first listen to a 2 ch song and immediately I find the music bottom heavy. I suggested Adam to reduce the SUB level by 3db and then he told me boosted the SUB level after the Auddsedy calibration by 3db. So I am not against messing around with SUB level. But the foremost important thing is the sound has to be musical.
We then go though manual warble tone plotting. Everything seems to be fine except there is a -3db drop at 80hz. Audyssey calibration set the subwoofer distance to be about 2ft closer than the physical distance and Adam uses LFE inputs. So that is normally. I explain because he has Ascend 340s which can extend much lower than 80hz, so in order to get phase alignment, Audyssey needs to add phase compensation to the sub, which is equivalent to setting the sub distance closer. So "adding phase delay to sub" = "setting subwoofer distance closer"; "subtracting phase delay from sub" = "setting subwoofer distance farther". In short, we try different sub distance and it turns out the best result is what Audyssey has set after calibration. So we leave that unchanged.
Then we go on to the movies. We play a few movies that cause the sub to flap. The first one is the new THX demo track. It sounded again very bottom heavy. For me, all I hear is the boom when the floor is shaking and moving during crescendos or no bottom end at all at other times. There is nothing in between. So I immediately suspect it is the LFE mixing level not set up correctly. He and I went through all adjustment menu from Onkyo AVR and we did find the LFE level adjustment menu and Adam set them to 0db. My Denon receiver does something different so I was looking something similar on Onkyo. We play “Inception” and I again notice the bottom end is just too heavy. I asked him to reduce the sub level by 4db and listen again and the sound is much more natural now. We then played Dark knight rises. Every time the scare crow speaks, we can hear faint flapping noise when the cone moves about 3/4" without generating any audible noise (it is definitely a subsonic signal). That was with Dynamic EQ off and master volume level set to -12db. He comments that noise is actually less than what he normally would have experienced with Dynamic EQ on and master volume level set to something like -20db. So we tried that and indeed it was actually worse than higher master volume setting without Dynamic EQ. So this becomes the first problem, that DynamicEQ boosts the amount of bottom more than 6-8 db at the bottom end, which to me is a shock. I will come to this later in this report. But I ask Adam to search the internet again to see if there is anything related to LFE discussion of Onkyo AVRs and he eventually finds the mentioned of -10db LFE setting and he tried that and now everything is back to normal.
Here are a few thigns we learn:
Edited by Rythmik - 2/24/13 at 4:43pm
- If you have Onkyo AVRs and your bottom is too heavy, check the LFE level again. LFE LEVEL does not equal to SUB LEVEL So boost LFE by 10db is not same as boosting SUB level by 10db. If we were to boost SUB by 10db and make it sound unnatural, we would have noticed that even with normal music. But if we set the LFE level too high by 10db, it sound like every special effect is a mini earthquake. It is just not fun to watch movies like that and we may not have noitced the incorrect LFE LEVEL setting as it only happens during movies's special effect. So identifying where the problem occurs helps us to find root casue.
- Dynamic EQ implementation is not fool proof. I commented several times in the past I am totally against using dynamic EQ as it was same as the "loudness" control in the old days and it was already proven not working. Here is the fundamental problem. Regardless your master volume setting, the bottom signal strength is always changing. Sometimes it is -60db, sometimes it is -20db, that means the dynamic EQ, if done truly to compensate loudness curve, would have to changing the gain dynamically on the fly. That is a nonlinearly operation. It is like chopping the time axis into smaller intervals and check the bass signal strength of each interval and apply different compensation based on the signal strength. It is a clearly nonlinear option. Now if the software does not do that. It just apply a fixed EQ boost based on master volume level (which is exactly what we had in the old days), it does not address the loudness compensation issue at all.
- I really suspect the flapping noise each time the scare crow speaks is caused by the internal clipping by erroneously apply 10db boost to the LFE signal. It overloads the DSP and also the digital to analog converter, which has the same effect as "clipping". The effect of boosting LFE by 10db plus turning on Dynamic EQ is the reason to cause the signal path to saturate and clip. This is very different from the flap due to over-excursion (or being over-driven).