Bigger the Port the better!!

[bkolfo4]

There are a couple of formulas for port area based on cone area, Xmax, and frequency. Power can be considered, but would really have to be modeled, since power vs. excursion changes with box size. You might reach Xmax with only 200 watts, or it might take 500.

http://www.diysubwoofers.org/misc/portcal.htm

http://www.carstereo.com/help/Articles.cfm?id=31

[bkolfo4]

You guys also need to remember how much cabin gain factors into the equation and variations between cars.

If you truly want to test and learn, do it outside in open space. . .

[TeamHT]

But what happens once you go from open space back to am environment with cabin gain factors? I mean, to say it's not operating as it should hence the flatter response...wouldn't that still translate to flatter response? Even properly tuned and functioning ports still experience incredibly flat responses

[RooTxBeeR]

In for info

[mrd6]

I've always understood the smaller port giving a "flat" response as follows:

If you imagine your frequency response graph of your normal ported box there will be a large hump around tuning and a quick roll off below and a slightly slower roll off above. When you shrink the port area on the same box, what you will see is a drop in the peak resulting in a flatter response. So, this smaller port does make for a flatter response but it does not do so by adding gain to any frequencies further away from tuning. It gets flatter because you are getting less gain at tuning. You lose overall output.

That is my understanding at least...it could be incorrect lol

[Omega5002]

Good thing I bought myself the Loudspeaker Cookbook to learn about this in better detail.

[bkolfo4]

The peak at tuning has nothing to do with the port size. It has to do with the system Q.

The box size, tuning frequency, and driver t/s parameters determine the peak vs. frequency response.

Here is a quote from Dan Wiggins (pretty sharp guy when it comes to subwoofer for those of you that don't know):

Qtc > 0.707 will have a bump in the response, loses some accuracy (tightness) and bass extension. The higher the Qtc (0.8, 1.0, 1.3, etc) the less accurate and the less deep bass you get.

Qtc=0.707 is called the Butterworth alignment. It provides the most bass extension you can get without the bump. Good all-around compromise alignment.

0.707 > Qtc > 0.577 is considered overdamped. Better accuracy, a bit less bass extension as compared to the Qtc=0.707 alignment.

Qtc = 0.577 is considered best transient accuracy. It's also known as the Bessel alignment. This alignment has the flattest group delay, which means that signals in the passband go through the speaker at the same speed, so everything stays coherent.

0.577 > Qtc > 0.5 are considered heavily damped. They offer some additional benefits, such as less overshoot and ringing, which can be desireable in higher order systems.

Qtc=0.5 is critically damped. This is the point where you finally reach zero overshoot in the signal. You will have no ringing. Considered "transient perfect", because there is no overshoot, IMHO it's not a significant gain over the Qtc=0.577 situation.

Qtc < 0.5 is considered overdamped. You're not ringing, but you're taking longer to reach the final state of the system. Things get slow down here.

GENERAL NOTES:

The lower the Q, the shallower the "knee" in the response. The slower the transition from flat to rolling off.

The lower the Q, the tighter the sound (to a point).

The higher the Q, the more midbass output, and the higher the peak SPL.

The higher the Q, the boomier the response, and the less accurate the response.

IN GENERAL: responses around 0.7 are considered "ideal" for car use. They are typically considered audiophile grade, with very good accuracy and extension. Higher Qtc values are considered more SPL oriented, lower Qtc values are considered more musically/SQ oriented.

Qtc variances of 5-10% are basically inaudible; you'll be hard-pressed to hear the difference between a Qtc=0.66 box and Qtc = 0.74 box.

Hope this helps!

Dan Wiggins

Adire Audio

[Omega5002]

I thought qtc only applied to sealed enclosures, not ported, I can't find anything on qtc for a ported enclosure.

[bkolfo4]

Sorry - should have clarified that.

Yes - the explanation from Dan is for sealed box.

A similar thing happens with ported boxes.

For a given box size, the tuning can be adjusted too low and cause a dip between the port tuning and driver Fs (and the port peak will not be as high as the "flat" response), but with the correct tuning/enclosure size and driver with the correct t/s parameters, you can really extend the low end response without losing too much output. Like a HT sub in a large box tuned several Hz below Fs.

Or, the tuning can be adjusted for an optimum "flat" response where there is no peak but a nice smooth response above port tuning.

Or, it can be tuned higher and give a nice peak at tuning. The higher you tune, the higher the peak to a certain point.

For ported systems, you will hear it referred to alignments, not Q.

Modeling software can be your friend. Even the simple excel spreadsheet on diysubwoofers.org works great.

[Neckbeard]

this should be pinned