porting mid-bass question on port size

[tRidiot 10+ year member]

That's not the question. The question is: Is it possible to estimate the possible gains from larger airspace? Also, I have already started construction of the box. It was originally meant to be ported, so its already got lots of airspace. So is there a certain level where the larger the volume, the worse the sound? How do I find that level, if it exists?

And you can estimate the "sound" of a sealed enclosure, it's called the total system Q. Larger sealed enclosures have better low-end response at the expense of less powerhandling. Smaller enclosures will have greater powerhandling, often at the expense of a slight "bump" in the frequency response. This is often described as a "peaky" sound, the driver being overdamped and not reaching full excursion at lower frequencies.

Optimal is often touted to be a total "Q" of .707 - there is a mathematical formula you use to determine system Q, but I can't recall how to do it right now.... it's 5AM and I'm up waiting for my cold medicine to kick in so I can go back to sleep. //content.invisioncic.com/y282845/emoticons/wink.gif.608e3ea05f1a9f98611af0861652f8fb.gif

Good luck!

 

[helotaxi 5,000+ posts]

System Q mathematically describes the shape of the bottom of the response graph where the driver is high passed by the enclosure. As was mentioned, a Q os 0.707 is considered optimal by most. It approximates a simple first order filter on top of the drivers natural roll off. The result is a smooth transition from reference level to a 12dB roll off on the bottom end. A higher Q (smaller box) has a hump at the system resonance and rolls off faster than 12dB. Lower Q (larger box) rolls off slower.

Ported boxes behave a bit differently. The problem that you are going ot run into trying to use something other than one of the standard ported alignments is that group delay is going to become audible. The higher the frequency, the less delay has to be present or it to become audible. You'll have strong midbass, but it will sound muddy and not match up with the midrange correctly. WinISD will plot group delay as well.

 

[2004alpinewhite 10+ year member]

ok, trying to use winISD... Here's the specs I typed in...

Qts: .46

Vas: 14.9 L

Fs: 64.7 Hz

Re: 2.83 Ohm

Le: .45

Xmax: 3.3 mm

Z: 4 Ohm

Qms: 2.62

Qes: .56

SPL: 91.9 dB

Pe: 60 W

BL: 4.71

dia: 6.5 in (should it be 6.75?)

Sd: 138 cm2

I can't get the curve to look like the one on their print out and I dont understand it?? I have it at .6 cubes and 50hz and the graph cuts down far before they say it will.. Have I entered a spec wrong or something??

 

[helotaxi 5,000+ posts]

Nope. You got it right. Their plot is in-car. You have to add cabin gain.

 

[2004alpinewhite 10+ year member]

Nope. You got it right. Their plot is in-car. You have to add cabin gain.

Is there any way to adjust for this in the program? If not, then is there a certain formula typical of cabin gain that I should apply to all of the graphs?

 

[2004alpinewhite 10+ year member]

If they say that ideal is .707 for box Q, then would there be a particular reason that all of the boxes they recommend are around .75 or .76? Would I like it better at .707?

 

[2004alpinewhite 10+ year member]

And why is it that if you say 2 drivers the curves go to hell? Should I be trying to find the right curve with just one driver or 2?