I have my own ideas as far as
setting up Subs, others may differ. But I do offer some guidelines that
may be useful.
Two Are Better Than One
May I make this point again, that too Subs are better
than one. At the frequencies that Subs operate and
located as shown below, the quarter wave-length is much larger than the
spread between the Subs. The effect is that they act as a Line Source.
Also for the same reason there is an addition +3dB Acoustic Boost, which
improves headroom and lowers distortion for any given SPL level.
The cutting sheet I have supplied (2400mm x 1200mm -
25mm Thick MDF) allows for two subs from a
single sheet. I have built two for myself and
this is how I have set them up:
Inside or Outside?
Having two subs, they can be placed either inside the
Main Speakers or as I have done, outside. In my case
they were not as close to the corners as shown.
Check for Correct
Phase
My two Monoblock Power
Amplifiers are non-inverting (Zero) Phase
wise. The Main Speakers have also been
checked that they are in-phase at Low Frequencies. This can easily be
checked with a 1.5V Battery. Place the 'Positive' of the Speaker to the
'Positive' of the Battery and the 'Negative' of the Speaker to the
'Negative' of the Battery. Then the bass cone should move noticeably
forward (outward). If the cone moves back then the
Phase is
wrong, then reverse the
Speaker Wires. Once
this is sorted out, then set the Sub Amp to Zero Phase
(this is only a starting recommendation).
Single Sub Operation
If you are only using a single Sub, then I must insist that the correct
location is dead centre between the Main Speakers. If you are
not able to put
it there, then you are very much on your own as I cannot be expected to
know how the Sub will behave.
Adjusting Frequency,
Volume & Phase Controls
Now this is a very difficult area, how to set up a
Sub-Woofer is not easy and requires patience and persistence.
Since I have access to both 1/3rd and 1/6th RTA
measurements, this is much easier for me. But that is a luxury most don't
have.
There are some interesting setup suggestions here:
www.diysubwoofers.org/misc/sub_integration.htm
If you find a setting that seems pretty good but
want to try other things, then take notes that enables you to return to
it (don't forget to record Phase position as well). That way you can, even over time, try different things but not loose
anything you have gained. You can always go back and even A-B the results.
Have fun!
