Hey guys,
I recently attended to acoustics of my room. Problem is the treatments are only effective above around 200hz and somewhat effective to 100hz. Below 100hz and there's problems.
Allow me to show a before and after snap shot at the listening position of the right speaker only then I'll explain the problem:
Before treatment
After treatment
As can be seen, there's a very nice improvement in overall damping of the upper bass and higher frequencies but after running sine waves and listening to music there's something weird going on at around 50-90hz and its at its worst around 70hz. The bass at the listening position is very strong and strangely appears not to come from the speaker but from the rear and left side of the room as opposed to the front right where the speaker is located. Also just turning your head from looking straight forward to looking 90degrees right makes the bass completely disappear! But move your head straight or to the left and it comes back.
After a process of elimination and measurements I've narrowed down possible candidates to the cause. Before treating the room there was no cabinet at the front and between the speakers so no problem at 70hz back then. I dropped the cabinet face down onto the floor then ran a tone generator with sines through the right speaker as before and the weird phasey boom around 70hz disappeared. The exact cause is the cabinet creates two small alcoves that the speakers partially sit within and this appears to be where the problem is created.
For now I've come up with a bandaid just to make the system listenable, actually its much better but I'm still aware of a problem in the bass. What I've done is put a high Q and deep notch filter in at 70hz along with digital room correction. Oddly despite the deep notch showing as a severe drop in the frequency response its not that noticeable because its filled in by the resonance. Hardly fidelity though since your listening to controlled boom at 70hz.
Here's some possible solutions I've come up with:
- The problem will be smoothed once the left channel is playing thus placing another low frequency source within the room. Usually such a move would smooth bass problems. But I'm not at all confident this will be true since the left channel is in a mirror image situation with the right so it makes sense that the same problems will be present.
- I was wondering about membrane traps located in the alcoves where the loudspeaker sit? Each alcove could accommodate 1x 60cm x 170cm panel and 2x 40cm x 170cm panels. All with a max total depth of 4". Can these be tuned low enough to affect 50-100hz with the concentration around 70hz?
- What about multiple small subs? I could very easily and quickly build 3 small sealed cubes based around the unused Peerless XLS10 drivers I have already. I've read the Harman paper about multiple subs for smoothing room response and one at the mid point for side walls and rear wall looks promising. These would work from around 80-90hz.
Any thoughts on these idea's?
I like the idea of trying the membranes around the speakers first 'cause its cheap and no problems building them.
