Rythmik Servo ported.

[Exocer]

Hey guys,
I've already tried the Rythmik servo in a sealed allignment and am happy with the results. My next step is to try it in a vented enclosure. RA's site recommends an enclosure size of 3ft^3 for a vented allignment. I would like to use PE's precision 4" port/s if possible, but am not sure how to enter the measurement for ports into unibox. If i used an inside port diameter of 4" (or 10.16cm) How does this take into account actual port length?



Edit: the above graph is with 6" port.
Edit: Can someone explain that 1db boost @ the tuning point? Whenever I remove it, the FB changes to 18hz automatically. There is definitely something not right.

[Jack Gilvey]

the above graph is with 6" port.

Pretty long port.

Can someone explain that 1db boost @ the tuning point?

The FR graph is a product of the driver specs and chosen Vb/Fb. I don't get that hump when I sim the same driver/alignment, though. Can you list the specs you're using?

Whenever I remove it, the FB changes to 18hz automatically.

Typically, lowering Fb will get rid of such a hump, so that's probably what the program is doing if you optimized Fb for a 0dB peak...is that what you did?

[Exocer]

yeah, i did optimize fb for a 0db peak, to try and get rid of the 1db hump. When i get back from work/school i will post the specs I used for the driver. Must get to work now :T be back

[Exocer]

Heres what I used.
Fs : 26
Re : 2.80 Ohm
Qms : 7.42
Qes : .53
Sd : 530cm^2
Vas 88L
X max : 19.3
Le : 1.00mH

When I mention using a 6" port, this is the inside port diameter I inserted.AKA, i dont know how to determine port length from the data.

[ThomasW]

Just enter the box size, the tuning frequency, and the diameter of the port. The program calculates the length of the port.

[Exocer]

It seems that with "walls covered" damping, I get the 1db peak. When I choose "heavy fill" The peak disappears.

I've since switched to two 3" ports but it says "min port dia!" of a size larger than 3". What does this mean?

Edit: i was looking at the port diameter min for the standard design...oops

The problem was in "external components" re was .5ohm...that caused the hump.

[Exocer]

Latest graph attached. 5cu.ft enclosure with 32" long 6" port (anyone say sewer pipe or sonotube? )

[derekbannatyne]

How are you gonna fit a 32" port in a 5 cubic foot box/sonotube? That would be really long and skinny.

[ThomasW]

Heavy fill isn't used for ported boxes, it's used for sealed.

I've since switched to two 3" ports but it says "min port dia!" of a size larger than 3". What does this mean?

As you've discovered it means the program is recommending a larger diameter port to lower the Mach numbers. You can ignore it or switch to a single port that has a larger diameter.

[Exocer]

How are you gonna fit a 32" port in a 5 cubic foot box/sonotube? That would be really long and skinny.

You're right. Probably fugly as well...

Thomas, would it be the worst thing in the world if I used a port diameter just slightly smaller than what Unibox suggests? It seems that going with a larger port diameter exponentially increases port length as well.

[Scott Simonian]

Exocer - Would you be able to post the same graph with "FR affected by Le, Le2, Re2" checked? Don't forget to check the "include effect of port resonance" too!

It would show a more accurate picture of alignment.

[Exocer]

Here

[Amphiprion]

A 4" port should be fine for a 12" driver with that kind of excursion. Alternatively you could use three 3" ports like SVS does. I personally do not like ports much over 18" in length (I tried a 28" port one time, and it had a weird sound to it. Shortened it down to something like 22" and it fixed it).

If you are using the PP flared ports, I believe you need to add about an inch to account for the flare's effect. I think they come with a formula sheet that tells you how to do the correction, but it's been a while since I've ordered one.

You should use light fill for a ported box. I did some measurements of stuffed ported boxes a while back, up to 50% fill. I have the impedance curves somewhere. If you know how to calculate Ql from an impedance curve, you can see that stuffing totally screwed it to hell. It did kill out all the standing waves in the box though (large box, 9cf or so).

ETA: .5ohms may be a little high for series resistance.