Box tuning below vs. above drivers Fs

[Phendyr_Loon]

I've search both this site and the rest of the interweb with no definitive answer. I've use several port calculators and none could get me close to understanding nor answering my specific questions.
What are the pros and cons to tuning an enclosure both above or below the resonant frequency of the driver? What is the relationship between the enclosure tuning (port frequency) and the resonant frequency of the driver?
I know the drivers Fs exists to, with the assistance of the ports, to slow down the cone at he point of max excursion. What are some rules of thumb to account for proper enclosure tuning using such variables as Fs, Xmax and enclosure size?

[bigboote]

i was pretty confused about this as well. eventually just gave up and tuned the ports to the driver's Fs. sorry to not answer your question, but my box does sound good!

[Phendyr_Loon]

Originally Posted by bigboote

i was pretty confused about this as well. eventually just gave up and tuned the ports to the driver's Fs. sorry to not answer your question, but my box does sound good!

That's what I considered as an option too. It makes sense as I understand the fundamentals of how the system works. Thanks for the reply!

[rpsands]

My recollection is that tuning has to do with a multitude of factors (the driver's Q plays a big role in where you should tune it; lower Q drivers start rolling off much sooner in most cases, so you want to tune them higher to counteract that). For a good comparison try comparing the 3012HO and 2512 II in winIsd.

My understanding of Fs is that it's the resonant frequency of the cone and plays a big role in how low the driver goes (based on cone stiffness relating to low end reproduction). But the frequency at which a driver "unloads' or whatever is going to be different based on enclosure parameters for every driver, so it's not necessary to obsessively worry over whether you're tuning below Fs or not.

The best way to figure out a good tuning frequency is to model the drivers, and then use an adjustable tuning mechanism to validate (port tubes are very useful for this but it is doable to design a removable shelf port so you can change the length).

[Bassmec]

Well port tuning is only ideal when used to extend the frequency response rather than add to resonant frequencies.
So lower than fundamental resonance is the only direction.
How much by is the big trick and one that may require fine tuning in as close as you can make of an anechoic chamber more than in a software modeling system. (Look at the graph
look for a smooth -3db point and tune to that)
You may cut a few port tubes before you get it as right as a total compromise can be.
Some cabs my son Henry makes are well beyond current software's ability to accurately predict results of:

Henry's original 12 X 15" 30hz hexaport design plays all the notes down there very nicely equally loud.

[billfitzmaurice]

Originally Posted by Phendyr_Loon

What are the pros and cons to tuning an enclosure both above or below the resonant frequency of the driver? What are some rules of thumb to account for proper enclosure tuning using such variables as Fs, Xmax and enclosure size?

Every driver is different, so there are no rules of thumb. Designing a speaker cabinet is like juggling eight balls at a time: the only way to get it right is through practice and experience.

[Petebass]

Originally Posted by Phendyr_Loon

What are some rules of thumb to account for proper enclosure tuning using such variables as Fs, Xmax and enclosure size?

It's a very good question, except for one thing - it's searching for a rule of thumb shortcut where none exists. And unfortunately the answer to your question requires the writing of an entire textbook.

Have you looked at the different cabinet tunings for the different alignments? If not that's your next lot of googling. Have a look at the alignment tables and the way the relevant "factors" for tuning are determined by the speakers QTS.

[Alexander Eddy]

Originally Posted by Bassmec

Well port tuning is only ideal when used to extend the frequency response rather than add to resonant frequencies.
So lower than fundamental resonance is the only direction.
How much by is the big trick and one that may require fine tuning in as close as you can make of an anechoic chamber more than in a software modeling system. (Look at the graph
look for a smooth -3db point and tune to that)
You may cut a few port tubes before you get it as right as a total compromise can be.
Some cabs my son Henry makes are well beyond current software's ability to accurately predict results of:

Henry's original 12 X 15" 30hz hexaport design plays all the notes down there very nicely equally loud.

Wow! More info please!!

[bgavin]

By definition a BB4 or SBB4 tuning has the box at Fs for a driver optimized for a vented box (EBP > 75).

This gives a very tight transient response, similar to a D2 sealed alignment for a driver optimized for a sealed box (EBP=50). The tradeoff is a fairly high rolloff point.

[fdeck]

One thing to consider about Fs is that it represents the resonant frequency of the cone in free air. That resonance will move upward -- possibly by a substantial amount -- when the driver goes into a box. Thus, the port resonance in most practical systems is likely to end up well below the driver-in-box resonance.

Another thing is that for a useful bass speaker, the port tuning can't be too far away from 40 Hz. As a result, design options are not unlimited, and if you "try" drivers by modeling them into practical sized boxes and looking at the response curves, you end up eliminating a lot of drivers from consideration.

[DukeLeJeune]

Just use whatever tuning it takes to get the target response and power handling you want, and don't worry about where the tuning frequency ends up in relation to the driver's resonant frequency.

[fdeck]

Originally Posted by DukeLeJeune

Just use whatever tuning it takes to get the target response and power handling you want, and don't worry about where the tuning frequency ends up in relation to the driver's resonant frequency.

Dang, what's with all of this practicality all of a sudden? How are we going to argue endlessly about theory if you keep that up?

[DukeLeJeune]

Originally Posted by fdeck

Dang, what's with all of this practicality all of a sudden? How are we going to argue endlessly about theory if you keep that up?

Well, if "someone" hadn't posted an Excel spreadsheet on his web page that makes it easy to look at frequency response, thermal power handling, and mechanical power handling all at the same time...

;^) <-----oldschool wink