The higher the Q value the sharper and narrower the bandwidth.
Q = 0.7 is about equal to one octave - the width of a typical band on a "10 band graphic equalizer".
Higher Q values are sharper/narrower; lower Q values are shallower/wider.
There are various technical reasons why especially high Q values are generally avoided or discouraged.
1.
Filters with very high Q values tend to produce more unpleasant "side effects".
This actually varies with the specific type of filter involved but in general higher Q values are more likely to negatively impact sound quality.
(And anything over about Q=20 is considered to be really worth avoiding.)
2.
Deep narrow notches in measured frequency response are most often caused by unwanted acoustic cancellations.
(For example when, due to speaker placement, sound reflecting from some surface cancels sound from the speaker, at a very specific frequency.)
In many cases these cannot be corrected by simply applying a sharp narrow boost to compensate.
They also tend to be far less audibly annoying than wider errors in "tonal balance".
And, in many cases, attempting to correct a deep narrow notch with a powerful narrow boost will introduce more audible problems than it fixes.
(This is why most room correction algorithms place a limit on the amount of EQ they will apply to attempt to do so.)
3.
Sharp narrow peaks are often the result of ringing...
And, again, this can be compensated for, but cannot be fixed entirely, by EQ.
(You cannot stop a bell from ringing by turning down its volume... you can only make it ring more quietly.)
Most room correction will try pretty aggressively to correct this... because a very sharp deep notch tends to be less audible than ringing.
However, if you have this sort of problem, you're really better off solving the actual problem than trying to compensate with EQ.
Let me expand on that last issue a bit...
It has to do with something called energy storage...
If you tap a bell, the energy from your tap enters the bell, which then stores it, and releases it at its characteristic frequency, over some period of time.
This is exactly what you
DON'T want a loudspeaker to do.
You want a speaker to pass on some of the energy you send it to the room... "burn" the rest... but
NOT store any and release it later.
Unfortunately this is exactly what happens when you have a subwoofer, in a room, that has "a bad room resonance".
Your nice subwoofer has become a really big low frequency bell (technically more like a bell in an organ pipe).
And, if you simply turn down the level using EQ, the overall system will simply ring more quietly.
(You can get the average level right but the bass will still sound "a bit slow and thundery".)
What EQ and room correction can do is to turn down the overall level... which can make it sound a lot better.
As a result, if the effect is relatively minor, EQ applied in moderation can mostly cancel it out, and provide a pleasing result.
But, at that point, while the average level may come out OK, it will start out a little bit too quietly, and still drone on a tiny bit too long.
It will be a lot better... but still not perfect.
That's why, if the problem is really serious, the only really good solution is to fix the actual problem.
(Which probably means moving that sub to a better location in the room where it doesn't "want to ring".)
Out of curiosity, as Q rises does the effective width get narrower or wider? Keith mentions that a Q of 10 is only about 1/10th of an octave wide, so I'm curious about that relationship.
Sorry, I could have searched it online but perhaps a response here includes Emotiva-specific details that are useful to me and other Emotiva owners.
