room problem : I get more deep bass when inverting phase of one speaker

[entoine]

I noticed that when I do a phase inversion on the signal of one of my speakers I got a lot more bass frequencies (wich is the inverse of what I expected ). globaly it is awfull but in the deep basses, it's seems way better... more open

so are my questions : is this due to room modes wich cancels bass frequencies? Is this due to my monitors position (I tried different placement with no convicing results), or because of the room itself ?
If I build bass traps, can I have more bass by "fixing"an eventual room mode??

(if this is the case (need basstrap), suggestion how to build on myself are welcome )

regarding room modes, I noticed that I have more bass in the whole room, not only at listening position.... weird, maybe more speaker position so...!?


by the way, my monitors are ADAM P33A wich are on K&M Stands.

do you have any suggestion or experience with such problems?
(sorry for my aproximative english)

[AkustikArkitekt]

The phase problems are much more noticeable at the low frequencies. Try open the two out of phase tracks, one 100% to left, and the other, 100% to the right, and keep them in phase. See what happens, try to analyze the pure sound and its behaviour.
The Room modes can create ressonances and standing waves. The way to minimize its effects is to change the room proportions, an expensive solution, or try the find the ressonance frequencies, place a bass trap equalized with that frequence and get a little better sound.
You dont speake english very weel? We both. Where are you from?
Im an architect and audio fanatic from Brasil. Check my recording company, ok?
::. Area 13 Studios .::

[entoine]

Hi AkustikArkitekt,
thank you for your reply
I'm french. I went on your website. I'm not very good in english, but I'm worse in Portuguese, so I looked at the pictures .
Your studio is very cool. It sounds better than my room. I can see it on the pictures .
I will try some other speaker placement, and test signals tomorow. But I can't smash the walls to modify the proportions of my room. So bad..

[theblue1]

I'm sure you've considered the obvious: a reversed connection somewhere that flipped the polarity.

A quick way to check the polarity alignment is to put a mono signal up with some low bass, move the speakers next to each other and reverse the polarity. By putting the monitors near each other you are enhancing whatever cancellation occurs when one has the polarity reversed.

[TheArchitect]

Originally Posted by theblue1

I'm sure you've considered the obvious: a reversed connection somewhere that flipped the polarity.

I second this. I think the issue is far more likely an inverted connection than a room node

[jwl]

I would agree that a phase reversal somewhere in the chain is a possibility, except that he states that it's only the deep bass that is affected with an apparent boost, and everything else sounds worse.

I think that, even if there *is* a phase problem, setting the room up properly will help. In general, there are three basic steps you can do that can improve the sound of the room tremendously.

First, arrange the room in an acoustically beneficial way. This generally means a symmetrical setup, particularly from the listening position forward, with the listening position 38% back from the front wall, in the center of the room between the side walls. The speakers should make an equilateral triangle with your head, ideally with the tweeters at the same height as your ears. This setup will give you optimum stereo imaging, and the placement within the room minimizes the effect of room modes on the bass. For more detail on this step, read How To Set Up A Room.

Secondly, you need to control the low end of the room, to even out the bass response it all parts of the room. This is most easily accomplished in almost all rooms by adding bass traps to as many corners of the room as you can manage, including wall/ceiling corners or even wall/floor corners if it is feasible. There are many threads in various forums about how to build these yourself if you wish to take the time to learn what to do and do the construction yourself. Alternatively, you can buy products designed to optimize bass trapping. Visit us at RealTraps - Home to see some great examples of these products, or if you'd like a more detailed explanation of this step you can read Acoustics: Facts & Fiction.

Finally, you will want to create a Reflection-Free Zone to make the stereo imaging as clear as possible. This is most easily done by placing more absorbers at the first-reflection points of your room. You can easily find these with the help of a friend and a mirror. Sit at the mix position and have the friend move along the wall with the mirror. Anywhere you can see your speakers in the mirror, put absorption there, this will be on the side walls and the ceiling (and also possibly the floor, depending on room furniture) in most rectangular rooms. For more detail on this step, read Creating a Reflection-Free Zone, and visit RealTraps - Home to see examples of products designed to do this task. And again, there are plenty of DIY examples on this forum; do a search.

I hope this gets you started, keep reading and post back with follow-up questions.

[Wayne]

Originally Posted by entoine

I noticed that when I do a phase inversion on the signal of one of my speakers I got a lot more bass frequencies (wich is the inverse of what I expected ). globaly it is awfull but in the deep basses, it's seems way better... more open

This will be interesting to see how this turns out once you have heard them both ways (one side intentionaly inverted).
It's unlikely, but what if it was just one of the woffers flipped?

[theblue1]

Originally Posted by Wayne

This will be interesting to see how this turns out once you have heard them both ways (one side intentionaly inverted).
It's unlikely, but what if it was just one of the woffers flipped?

Good catch... I hadn't even got to the good bass/bad mid-hi conundrum -- but that would certainly account for something like that on paper.

And, where humans are involved, I think it's fair to think that one in x number of woofers will be reversed (along with everything else that's relatively easy to get wrong).