Need Quick Help if Possible (Question And Design)

[Rounder]

First the question.
This is my first time building and I am building floorstanding home theatre speakers. When a driver states its Vas as being a specific value, is that meant to be the cabinet volume required for the driver? Whate are the affects of increasing size or decreasing size?

Next the bigger problem.
Somewhat related is a woofer issue im having with designing a cabinet for the woofer in the dimesions required for my floorstanding speakers. The inside volume i have to work with for the woofer is 6.5 inches wide, 13 inches deep and 25 inches tall. Both the driver and the port must shoot forward in the end. Yes it must be ported. The driver i have has a link listed below with its specs. The reason i havent been able to design an appropriate enclosure is because no matter what route i choose i end up with one critical flaw. WHether, port whistling, or having the port end withing 3 inches of an interior wall (i hear its bad) or port length issues. Im open to any suggestions or ideas. And please correct me if im wrong with ne of my statements. I have attempted using some basic programs which all prove to cause some flaw. Once again any help is appreciated!!

[kelticwizard]

Originally posted by Rounder
First the question.
This is my first time building and I am building floorstanding home theatre speakers. When a driver states its Vas as being a specific value, is that meant to be the cabinet volume required for the driver?

What is the Vas? It is a specification which is essential in calculating the proper volume for your woofer's enclosure. In most cases, the proper enclosure will not be the same volume as the Vas, though it might be. It all depends on the other specifications, such as Qts and Fs, of the woofer.

[kelticwizard]

In one post, I cannot give you a complete tutorial on Thiele-Small parameters.

However, myself or someone else can give you the proper box size for your specific woofer if you post:
A) The Thiele-Small parameters, (Qts, Fs,Vas, etc)
B) How big a box you want-you said ported
C) Dimensions of the box, approximate, you are interested-tall and skinny, or box like?


If I am not still up, some other person will be able to give you a good box size for your woofer.

[Rounder]

DIAPHRAGM MTL Paper
SURROUND MTL Rubber
NOMINAL IMPEDANCE 4 W
DCR IMPEDANCE 3.6 W
SENSITIVITY 1W/1m 83 dB
FREQUENCY RESPONSE 35-800 Hz
FREE AIR RESONANCE 38 Hz
VOICE COIL DIAMETER 38.5 mm
AIR GAP HEIGHT 4 mm
NOMINAL POWER 70 W
MUSIC POWER 140 W
FORCE FACTOR, BL 8.67 TM
MAGNET WEIGHT (oz) Neodymium
MOVING MASS 34.91 g
FERROFLUID ENHANCED No
SUSPENSION COMPLIANCE 423.31MN-1
EFFECTIVE PISTON AREA 0.0140m2
Levc 0.34mH
Zo 33ohm
X-max 13 mm
Vas 11.78 Litr.
Qts 0.40
Qms 2.65
Qes 0.47

i was hoping the enclosure would fit in the dimensions of my original box that i listed in my first post if possible.

[kelticwizard]

Hee hee hee, this is funny.

Having just explained to you that Vas is not necessarily the volume you build the box for, it turns out from your other specs that, in this case, the Vas happens to be exactly the volume you build your box for.

A ported speaker, with a driver of Qts between 0.38 and 0.4, should be built with an internal box volume equal to the Vas and tuned to the Fs-in this case, 38 Hz.

The box you want to build is about three times the Vas of your speaker, and the usual box volume for that speaker.

If you want to wait until tonight, (playoffs are on), I can run a more complex program which can tailor the design to the exact dimensions you are building.

I believe that a ported box can be designed for your woofer-we might just have to change the tuning a little.

[kelticwizard]

Both the driver and the port must shoot forward in the end.

Not sure what you mean by this. Are you mounting the woofer on the top of the enclosure, and want the port to be on the same side, (6.5" by 13" side)?

[Rounder]

Thanks alot for your help. Your making my life much easier. No big rush with the final dimensions, so enjoy the playoffs, but what i meant is that both the sub and the port would have to be front firing. On the same face as the tweeter and mid. Im not sure if its possible but if it is that would solve all my problems. ONce again thanks for all your help.

[richie00boy]

An alternative is to install a shelf to reduce box volume. This would also stiffen it up as a side benefit. You can accomplish long vents by fitting 90 degree angle bends.

[Rounder]

Y does every port calculator claim that its crucial to have the port end at least three inches form every inside wall... Whats the negative effect?

[kelticwizard]

A) Usually the walls of a reflex are lined with stuffing, so if the port ends up next to a wall with stuffing on it it blocks some of the air going in.

B) If the interior of the cab wall is bare and the port opening abuts it, it somewhat changes the tuning.

Do you want the sub driver on the bottom of the front? So the mid/tweet is near the top of the cabinet?

Also, how big is the mid and how big is the tweeter? Trying to get a picture of how much space I have to work with here.