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Box tuning question

 

Bronze Member
Username: Nevertoomuchbass

Virginia Beach, VA

Post Number: 86
Registered: Aug-10
im getting 2 Fi Q 12's and on the Fi website, it says the Fs of it is 34.2 Hz. but for a ported box it says to tune it to 28-33 Hz. i thought you werent supposed to tune the box below the Fs of the sub due to the risk of excessive excursion. is this not really true or what?
 

Gold Member
Username: Southernrebel

Monroe, Louisiana Team Audible...

Post Number: 8274
Registered: Mar-04
Well, that can be true....to a point.

Port and sub loading is actually FAR more important than 'on paper' tuning. For instance, say you have a port 5x12 cross area in a 4cuft box 26" long firing back in an SUV. 'On paper' it may tune to ~35hz.

But, load that port into the back hatch of the vehicle ~4" from the hatch and it will react like it is tuned lower. Likely around 32-33hz or even lower depending on the distance you are from enclosure (distance from source to listening point)

Also, the cabin acoustics of the vehicle will change in-cabin tuning and response.

If you dig deeper into enclosure design, you will find that Helmholtz resonance (aka box tuning or Fb) can mean next to nothing when you take into account the actual in-cabin response of a subwoofer.

Build for the car/sub/listener's needs, not just some random 'tuning freq' that manufacturer's throw out there in their (narrow minded) tech papers.

In essence, when designing a ported box in a vehicle...you are not building a ported box. But rather something more along the lines of a series tuned 6th order enclosure....given that the cabin of the vehicle acts like the forward chamber in a bandpass box. You have to account for the 'leaky' forward 'sealed' chamber the cabin creates.

Ever notice how the low freq seems to be FAR louder when you roll the windows down in a vehicle? That is because the windows are actually PORTS! And your in-cabin tuning totally changes when you roll them up or down.
 

Bronze Member
Username: Nevertoomuchbass

Virginia Beach, VA

Post Number: 87
Registered: Aug-10
well my subs are always in trunk so im not sure the lows really are much louder with the windows down. so im putting 2 fi q 12's in the trunk of my lesabre. the port will probably be ~6 inches from the rear of the car when the trunk is closed. ive talked to some people on the fi forum and they think that 32 Hz is the optimal tuning for most output fir Q's. so should i tune it more like 35? this an SQ system. i couldnt give a s*** about SPL. that loud higher bass just hurts my ears.
 

Platinum Member
Username: Rovin

1 15 = 153 DBs ...Trinidad & T...

Post Number: 16698
Registered: Jul-05
how about doing it sealed for a nice flat sq response ....
 

Bronze Member
Username: Nevertoomuchbass

Virginia Beach, VA

Post Number: 89
Registered: Aug-10
because I still want some showoff ability. but untill i get this ported box done ill just be runnin them sealed
 

Gold Member
Username: Skdooley

Roanoke, VA Usa

Post Number: 1214
Registered: Oct-09
32 Hz should work out nicely for those subs and help give you some peak at the lower frequencies.
 

Bronze Member
Username: Nevertoomuchbass

Virginia Beach, VA

Post Number: 91
Registered: Aug-10
so tuning below the Fs of the sub is okay?
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