Can you correct nulls with acoustic treatments.

Onhwy61,

Understand your first point. I am trying to look at trends over 20 to 30 hz. ranges. Started with the LF as it seems from previous threads that is where the largest gains for the effort come from.

I was thinking about your second point last night and wondering the same thing. Am I misusing or misunderstanding the info? The CD I am using for LF is from Real Traps. The CD has a white noise track to set a start level. I have assumed that start level would correspond to an SPL baseline and db. readings above that baseline level were bumps and below were nulls. That may be correct, but not necessarily so. If not correct, the data is valid (the amplitude swings are still there), but the description and amplitude I had assigned to null and bump are invalid.

Anyway, I should have done a little more prep work and broader data gathering before posting. I may have jumped the gun. Back to work on it.

Audiotomb,

Yeh, I wish I had 1800sq.ft. to play with. It is an odd shaped room that follows the contours of an irregular foundation. Because of the backwards L shape with a few extra zig-zags thrown in, the usable space is much smaller There are framed in steel support columns and beams. Also seperate rooms for laundry/storage, furnace/water heater and a bathroom with a Jacuzzi. Why the previous owners put the Jacuzzi in the basement is anybody's guess? Sounds a lot bigger than it is.

Thanks for your observations.
Jim S.

I'm with Onhwy61....you probably have typical room bass boost. You need to tone down those bass bumps rather than boost 80 to 300 Hz.

Secondly, above 200 Hz...you are dealing with wavelengths of roughly 5 feet...don't expect any kind of smooth response here as movements of a couple of feet of the SPL meter will give you nulls when playing pure test frequencies. (for example quarter wavelength cancellations off the back wall behind the speakers is typically evident with a series of nulls from 40 up to 500 Hz depending on speaker placement)

See this link Quarter Wave Cancellations Explained

The above is why I have soffit mounted my speakers into a heavy braced wall cabinet. This is most important for larger three way full range speakers and is why you see soffit mounting of studio main speakers in almost all studios. (The difference is very audible as you can imagine by looking at the frequency response curves shown in the URL example I gave you above)

Finally, I suspect a 1 Hz pure single frequency test tone with an SPL meter is likely to lead to frustration unless you are an expert like Rives and know how to interprete it.

For example, imagine (in theory) that your speakers are perfect ( zero distortion ) then you will get enormous peaks and nulls with single pure frequency test tones (as the ONLY frequency in the room is exactly what you input to the speaker).

Alternatively, imagine your speakers are more normal or typical (with 50 % distortion in bass frequencies when played at louder SPL levels ) then you will get a beautifully smooth balanced SPL response when playing pure single frequency test tones (because not all the harmonic distortion will be affected by the room in the same way as the fundamental - and SPL meter will pick up the average)

How's that for counter-intuitive.....two different speakers placed in the same position in the same room and the better speaker SHOULD measure far far worse!

How's that for counter intuitive....an amplifier with higher amounts of harmonc distortion may actually sound more balanced compared to a perfect amplifier with zero distortion, as it is less ruthless on room modes.

All this is because nulls will be their very worst when you have pure single frequencies....

So be very careful interpreting 1 Hz pure frequency test tones! (It is unlikely that kind of purity is actually coming out of your speakers unless they are incredibly good and you have an amplifier with very low harmonic distortion)

Ok, I got it. To do a really serious analysis and correction, I am in way over my head and resources.

But, believe it or not, what everyone has generously posted makes sense and has helped my understanding. I just don't know enough to know how to make a direct quantum leap in results (it ain't gonna happen overnight). I do know that a little knowledge is dangerous, so I will go slow, keep studying, keep measuring, and keep experimenting. I will post the setbacks and breakthroughs.

Thanks and Best Regards to All,
Jim Still

Jim:

I like your attitude--and I think it's exactly right. You won't make that quantum leap overnight--but you can read, understand, try some things, and make progress over time. I wish everyone would deal with their room. Whether they hire a professional or take some sound advice (pun intended) and work through the issues themselves over time, the room is almost always the limiting factor in good sound.

I would recommend the book Alton Everest Master handbook of Acoustics. It's available through Amazon and is an excellent overview on the subject.

I had a deep null in mid to low bass right where I wanted to sit. Then I noticed that the bass would almost blow your hair back in other parts of the room. I made a series of bass traps and I wouldn't have believed anything could be so effective. It's still slightly peaky at certain frequencies but not bad. I'll probably get a digital eq eventually.

BTW, my listening room (built before I moved into the house) is of horrendous dimensions. Very close to 1 x 2 x 4.