4 replies to this topic

[JohnDB]

Guys,

I have recently built a just over 5 cu.ft enclosure (net) for 2 x subs,when I had it tested on term lab it peaked at 52 Hz, I had intended to tune it to 40 Hz. The port area is 80 sq.in , it is a slotted type of port.

When I checked the port length tonight, I realised that I failed to "measure twice cut once" rule, the port was 16 in long, but should have been 18 in long as per the manufactures specs for a 5 cubic foot box for their subs.

My question is, by making the port 18 inch long, will this tune the box to 40 Hz - or should I go longer?

I had thought about adding 2 inches to the port, then having it tested when we meet again here in WA, then if that's not quite right, add another 2 inches etc etc till it's around 40 Hz?

Anyone got a quicker way to calculate the port length rather than trial and error?

[Sam.Harvey]

I think you will find that your box is infact tuned to or atleast close to the desired 40hz, your car however will resonant and a frequency a bit higher than 40hz, this is why it has brought your peak frequency upto 52hz. My sub box is tuned to 28hz but my car still peaks between 37-45hz area.

[RAD]

For your box to be tuned at 52hz, you'd have to measure 10" too short; 8" length will tune you to 52hz, even 16" will be 42hz.

As Sam mentioned, you're probably finding your cabin frequency, not enclosure frequency.

[TMM]

Just because it's tuned at 40Hz doesn't mean it'll peak at exactly 40Hz. The output from the port will, but the combined output with the subs will be a bit higher up, you have to model it with WinISD / BassBox Pro / etc to find the exact point. And thats not even considering the effects of the cabin yet.

How are you deciding on a tuning frequency of 40Hz? I agree with the others, your cabin is probably peaking at 52Hz. If it's purely an SPL box, tune it up a bit.
I'd guesstimate that if you tune for 48Hz~ it'll fit in nicely with your cabin peak around 52Hz. That results in a port length of 10in.

Edited by TMM, 30 June 2012 - 06:07 AM.

[JohnDB]

Guys,

today I got to run my 2 x Alpine subs in my car on termlab, they peaked at 42 Hz.

My 2 x AQ subs peaked at 52 Hz.

Sam amp, same car , same sensor location for the term lab..............what does this tell me about my cabin frequency ?

I will trying a 3 sub combination in the coming weeks.