I have been able to use REW and apply corrective filters thanks to some very helpful people from this forum. I am going to investigate a small sub to fill the low end better and hopefully balance some room modes.
Can some equally helpful individual kindly help me understand how to do it? The pre-out from my amplifier will be feeding the subwoofer. Is it a case of siting the sub and tweaking the crossover and level? Do I need to do further measurements in REW?
Thank you
Sort of that simple.
Are you going to cross your speakers higher once you get a sub?
Are you going to run your sub a little higher spl level than your speakers or flat? (most like a little higher spl).
Let's say you choose a 80hz acoustical (acoustical = as measured by microphone at your listening position) crossover and choose to have a 6-10db spl gain on your subs over your speakers.
At your main listening position you want the crossover to be at 80hz and be about 6db down from your overall curve.
This is an example (note this was from a vehicle but same principles still hold true)
These are using acoustic Linkwitz Riley 24db/oct filters for phase integration reasons
To get this, The midbass is crossed around 80hz but the sub, since it runs higher spl, is crossed at like 50hz. This way it is 6db under the overall curve by 80hz to match the midbass.
Once you have something like the above, you can start working on the timing/phase aspect of each.
Usually you need to delay your speakers more due to internal processing of the subs amplifier.
To check this without a way to easily measure phase (REW can but it gets tricky to get good results), you can start the RTA screen and play band limited pink periodic noise for about 40hz to 120hz (the +/- 10db overlap region). You will then most likely need to delay your main speakers until that response gets to be the best summation possible.
This will get your subs integrated as best as possible just by using REW.
If you do the above, you should get something that looks like this for phase integration (this was using SMAART to measure phase in real time)
The level of the subwoofer looks high in this diagram, but I forgot to lower it by 6db (both woofers playing adds 6db compared to a single woofer) before taking the measurement. Otherwise the sub is 10db louder than both woofers playing individually. Lowering the sub level back down doesn't change the phase though so I didn't bother to do it and take a screenshot, although I did check it to confirm it didn't.
Notice the middle graph is the phase response graph and ideal phase would have all three speakers lines completely overlapping to where it looked like a single line.This is pretty darn close to that.