Subwoofers.... one 10" or two 8"?

Due to "group delay" sound impulse leaves the sub usually 8-10 msec later than it leaves the main, even though the electrical impulse hits the sub and the main at the same time. So must be aligned by ear. Using just distance measurement doesn't work. Used to think there was something wrong with my autocalibration when it consistently made sub setting farther away than the actual measurement. Check:
http://www.theabsolutesound.com/articles/subwoofer-basics/?page=3

Someone please explain "time aligned"

@leotis

That's a huge amount of "group delay." I think you are confusing that sub's are often located several feet behind the mains.

As for aligning by ear, great googly moogly no! :) It's far easier, faster and more accurate to fully align with a tool like OmniMic or AudioTools or Room EQ Wizard than by ear! :)

Assuming the room modes are dealt with, the second stage in integrating a sub are to integrate it with the main speaker. This runs into the same issues a speaker designer would have in blending one driver with the next. Meaning, crossover slopes and phase alignment to provide a seamless transition from the subwoofer to the main's output. You should not be able to tell by looking at the frequency response where the sub ends and mains start, it should appear like 1 single speaker.

Best,


Erik

@larstusor

It means a lot of things, but in general it means making sure that each driver you are listening to blends seamlessly with others despite being located at different distances from the listener.  It matters in multi-way speakers as well as in integrating a subwoofer with a main speaker. This really is "phase alignment" but in use it's often called "time aligned." 

In flat baffle designs, each driver has a different acoustic distance from the listener. Phase alignment means you've taken that and the phase of the crossovers into account so that the frequency response has no dips/valleys where they meet.  Here is an example from a speaker I designed, the LM-1.  Look at the second and last chart for more information. 

At it's most stringent, time alignment may mean having a perfect impulse or step response.  Van DerSteen is famous for this type of design.  Look at the step response in Stereophile's review of the Seven and compare it to the LM-1.  Thiel is also a manufacturer that specialized in time-alignment.

Best,


Erik

Hey eric 
. Aren't  reflection points playing a big role there also . When i used treatment on the points . The ole mirror reflection spot gik talks about it helped immensely. Op cant run treatment though