We only have two samples but the same issue with both.
and I have different rooms with different subs system but have the same null in Z axis TR@15hz. At the point where we have the highest or a peak in SPL, we have the lowest TR. It happens to be at the same frequency for both our rooms. This can be explained simply with Correlation. In this case positive and negative correlation. What is that? Very simply if you have two variables and when one variable is moved to the positive, and the other does as well, thats a positive variable. Negative variable is the opposite, when one variable moves to the positive, another moves to the negative. The other important thing is to find the causation of the particular problem or issue were having. We have to identify the cause if we are to come up with a solution. Let’s review to this point.
This is my response with and without Time Alignment.
Time Aligning multiple subs allows you to achieve the maximum spl at the MLP. This show my frequency response from 5-50hz. Notice the peak around 40hz. Theres a corresponding gain in TR that matches the FR over the band the subs in. We have a positive correlation. You turn up the volume, it gets louder and TR increases. All pretty simple.
But………. low frequency tactile response seemed much weaker. Playback of ULF heavy media, War or the Worlds, Incredible Hulk, Edge of Tomorrow all felt weak with time alignment. zeroing TA made a huge improvement to the tactile feel of the clips. It also flattened the peak. Trying to identify the problem with Omnimic proved frustrating and fruitless. This wasn’t working. I needed to find the right tool. The rest is history.
This is the tactile response.
Above 24hz, we have a positive correlation but below that, theres a negative correlation and the opposite happens. So now that we know the effects, we need to identify the cause. Correlation doesn’t always lead to causation or it could lead to more than one. in this case theres more than one. There is indeed a primary and a secondary causation. In In my room you clearly see a larger trough than in DD’s room. On the EoT test clip I have a 20hz and 15hz null and in DD’s room just the 15hz null, where his SPL was highest and TR was the lowest. So DesertDome’s and my room have something in common and something that isn’t. Eliminating the TA delay remedies the 20hz null. Thats demonstrated very clearly and easily. Lets call this the secondary causation. With it eliminated, TR improved dramatically at 25 and 20hz. Now both rooms mirror each other with a significant Z axis null at 15hz. DesertDome’s room is different as well as his type of subs and placement. But our rooms share a common denominator. What is that? I believe the Z axis is the answer, and very simply the Z axis is the rooms height. This may be the one and only thing ours rooms have in common, the height. With basement theaters ranging from 7-8ft or more and single or two story HT ranging from 8-10ft on average, it makes sense that our rooms TR would match fairly close in the Z axis. I believe if we measure more rooms, we may see a pattern there in the Z axis. If that proves to be the case, then it would stand to reason that room height is the single biggest deterrent to TR@15hz or near that frequency depending on height. If thats the case, then the primary causation of TR dip is the boundary. For the record my room height is 9ft. At this point its too early to talk solution(even though eliminating boundaries appears early on to be the answer, or using and equalizing axes specific tactile transducers), even causation because we’re still trying to figure a test protocol. Actually we are in the experimentation phase. BTW, as a by product of this research, it appears we have stumbled on a way to identify the frequencies that we need to excite by way of TT’s. Now that we have a way to meter and set TT’s, they can be expertly set and blended seemlessly with a sub’s and room’s natural response and eq’d accordingly. If this is the only solution, so be it. It would be a noteworthy accomplishment.