alot of my boxes worked best being tuned into the 60hz+ range while car's peak always stayed around 55-56hz.

anyone? Peter?

 

Got my paper and pen out ....

 

Is there a theory or calculation to this, or is it all trial and error? Make the box and start changing the ports length?

Could it be the parameters of the sub that play a part in the tuning.

 

Because.

 

like Ive mentioned last time you brought this up in a post....

because...

lol..

no really

at port frequency your cone excursion is at its minimum(which normally would give you lowest impedance)...but the impedance is actually lower a few hertz just below the port frequency causing your amplifier to output more power... now this partially caused by the loading of the port and cone ...your results should change when you open your doors and depressurise the vehicle

try to see how the box peaks in an open field not loading off any surfaces not even the ground... you will find your box peak will be totally different

btw this is also a reason alot of guys blow their crap up when demoing their burp box with doors open using hteir burp frequency


does this make sense? or am I just rambling?

 

you notice a difference on this behavior at a lower power?

if yes, this is related to a change on speakers parameters at high power.

 

I asked this same question to an acoustical engineer a few years ago.

The quicky version of the answer; was that in a pressurised air environment sound travels at a lower speed and the relative port tuning frequency becomes lower in a pressurized environment.

Basically your 60Hz open air tunied box. is really more along the 55-56hz tuning when pressurized. The more pressure, the lower the relative tuning becomes.