SPL's vs. Low fequency

I'm designing my first subwoofer for my. soon to be, surround system. My experience with designing speakers for movie sounds/music is minimal.
The question that puzzles me in making a decision is the balance or choice between extreme low frequencies (down to 15/20 Hz) at moderate SPL levels (85/90 db) and High SPL levels (95/97 db) with moderate low frequencies (35/40 Hz). This seems to be the choice if your looking at the $200/300 price range for 15" subs.

So, if I've to make a choice between above mentioned (including building a huge speaker to gain extreme lows), what is the best way to go, based on your experience????

Thanks in advance,

Mazz
 

pinkmouse

diyAudio Moderator Emeritus
2002-04-03 7:15 pm
Rotherham, England
Hi Mazz
I have just built an active sub for my home theatre that has its -3db point at 26Hz, and having now tried it with the usual suspects, ( The Matrix, Jurrasic park 3,MIB) it sounds fine.

But I suspect our friends across the water, with rooms the size of a small European country will disagree...
 

roddyama

diyAudio Moderator Emeritus
2002-01-19 9:25 am
Michigan
Hi Mazz,

I would go for the bass extension, partiularly if the room is not exceptionally large. Here's why.

If your calculating the SPL from the param's or making near field measurements, then the SPL values your giving us are for radiation into a half space (the imaginary half sphere in front of the driver). For a sub reproducing frequencies 100Hz or below, its easy to get "free" db's of SPL. By moving the sub to the middle of a wall where it meets the floor, you've changed the radiating sphere to a 1/4 space. You also gain 3db in the process because the same acoustic power is being radiated into half the area. Now move the sub to a corner, and change the sphere to an 1/8 space, and you'll gain 3db more. You gain 6db just from speaker placement. Now you can tune your speaker for the mid-20's and still have wall rattling bass, even in our vast American livingrooms.

Have Fun,
Rodd Yamashita
 
Mazz:

Actually, you are getting most of these free db's at the low frequencies irrespective of where you place your woofer.

Why don't you go to our website

www.kbacoustics.com

and download the demo of our program, Visual Ears.

You can vary the low frequency cut-off of your speaker as well as move it around the fixed sized room. Use the default speaker type and click on the speaker icon to set the low frequency cut-off frequency and slope. You can see, graphically, the resulting frequency response curve at the listening position as you move the speakers around.
 
Go with the low Hz. The only time the thing will become active is at low Hz and it is for pushing the air and vibrating your chair. Just make some good speakers that will be full range from 40 Hz or lower for your five channels and set the sub for special effects only. Put your money and time into the most important speakers which are the ones that are not your subwoofer.
 
Well,

It's obvious now that the way to go is Low Hz.
Actually, if I rethink my question. It's easier to build a second similar sub (With low Hz) to gain higher SPL levels. Than build a complete new one that incorporates both features.:D

Thanks for all your input.

Thatch_Ear. I agree with your statement in building first of all a good set of speakers that only needs sub assistance under extreme sound conditions.


Bill, Nice software, but my system runs under XP.