[Bookerman]

Hello!


How much space do you need in between the woofer and floor?

My floor is carpet over underpad over concrete in my basement.

When I first got my down-firing sub (Mission M3as), I noticed it sunk into the carpet under the weight. The sub has legs so the woofer was still off the ground but it seemed smothered. I felt like I was getting unclear bass and it just seemed to rumble and vibe underneath my feet which would bother me.

Since then I've attached the spiked feet and placed them on dimes to prevent them from sinking into the carpet. This added an inch more clearance and I noticed less vibration under my feet and clearer bass. I've been fiddling between a 80Hz and a 100Hz crossover. I now have about a 2" or so in clearance between the woofer and carpet.


I'm wondering if I should get something like hockey pucks under each spike and raise the sub a further inch or so off the ground. I wonder if that will help in the clarity of the bass?

Alternatively, I have a piece of MDF the size of my sub and thinking of laying that down and placing my sub on top of it with spikes and all. That way, I recover the distance caused when the sub sinks into the carpet. The carpet's really springy! Would the MDF also act as a decoupler? I would prefer not to feel the vibes under my feet. I guess I won't really know until I try but I'm new to this bass stuff and a lot of it seems to be based on theory. I've read more about wavelengths and frequencies in the last week than I did all during highschool it seems

Oh and another question: I use the YAPO mic that comes with my Yamaha receiver to configure my system. It seems pretty accurate and calculates distance spot on. However, when I run my test tones to check out how well the YAPO did after a calibration, the test tone coming out of the sub seems a lot lower than the rest of my speakers. For example, if I did it by "ear", the sub setting would be a lot higher than if I did it with the YAPO. Is that just a perception though and low frequency trickery?! Do most people who've correctly calibrated their subs with an SPL meter perceive the test tone coming from the sub to be lower than the other speakers? If not, then my YAPO is not doing a good job at setting the subs level.


Any help would be appreciated!

Thanks!

 

[ggunnell]

Your 2" clearance is probably enough. Working out the minimum distance is not hard -- here's an example:


You don't want the air to have to compress after leaving the face of the woofer, so you don't want the area of the space between the lowest point of the woofer (usually the mid-point of the surround) at the woofer's maximum excursion and the floor/board/top of carpet to be less than the piston area of the woofer.

Lets take a 12" woofer with a 10" distance from the top of the surround roll on one side to the top of the surround roll on the other side. We'll call that the effective piston diameter, so the piston area is 5 squared times pi = 78.5 sq.in..

The circumference of the surround at its peak is 10" x pi = 31.4" You need 78.5 square inches, so 78.5 divided by 31.4 = 2.5". But many woofers these days "excurse" quite a bit -- if you know the maximum one way excursion add that, or use 1/2 inch as an estimate -- add that to the 2.5" so that minimum clearance will be maintained even at peake excursion. In this case we'd want 3" minimum clearance between the woofer surround and the surface beneath.


Try the MDF and see if it helps or hurts.


Most folks run their subs a little 'hot' -- go with what sounds best to you.

You may find you like more sub volume on movie effects, less on instrumental music.

 

[ericgl]



Quote:
Alternatively, I have a piece of MDF the size of my sub and thinking of laying that down and placing my sub on top of it with spikes and all.

Worth a try.

Quote:
For example, if I did it by "ear", the sub setting would be a lot higher than if I did it with the YAPO.

A RS SPL meter is always a good idea. If done by ear, probably 99 people out of 100 would set their sub too hot.