Vifa Pl18w

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diyAudio Moderator Emeritus
Joined 2001
I second Transducer, above. WinISD is very easy. Since you seem to like building boxes, I would think you will find it fun. You can download it from the following link:
http://www.linearteam.dk/

Nonetheless, I assume you have your reasons for not having an enclosure program, so I have done some ported boxes for you.
They are in the chart, below.

Red is 0.5 cu. ft box tuned to 45 Hz.

Blue is a 0.75 cu ft box tuned to 40 Hz.

Green is a 1 cu. ft box tuned to 37 Hz.

Gold is a 1.25 cu. ft box tuned to 34 Hz.

Let me know which one appeals to you, and I can give dimentsions of the port.

Good luck!
 

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diyAudio Moderator Emeritus
Joined 2001
Also, I would certainly recommend using Transducer's link for the crossover. Remember to keep the spacing between the centers of the woofer and tweeter the same as in the sealed project, and then copy the crossover, using the identical Seas tweeter, of course.

Center-to-center spacing is important in crossovers. In this case, it is 6 1/8 inches.

Whether the woofer is sealed or ported will make no difference up around the crossover frequency. Only in the bass region will the electrical characteristics be any different.

One thing: this is the PL 18W 8 ohm version, correct? It also comes in a 4 ohm version. I ran the graphs for the 8 ohm version-the 4 ohm version might have different numbers. Please let me know.
 
:angel: Thank you again KELTICWIZARD. Yes it is the 8 ohm version. I think I like the 1.25cu ft. please let me have the dimensions and port size. YOU are right, because I use my office equipment and do not want to mess things up. When I fix my own, then I will download the software. Boy, that will be fun.
 
diyAudio Moderator Emeritus
Joined 2001
Thank you for the kind words.

One thing, though. I got a little carried away with those boxes and forgot that I was dealing with only a 7" woofer with a .16" excursion, plus or minus.

Small woofers have limited air-moving capability, and the amount of air you move determines how much bass you can produce.

Your woofer, at full excursion, moves 3.25 cubic inches of air. To produce 112 dB at 34 Hz, the woofer must move 50 cubic inches of air. To produce 112 dB at 40 Hz, it must move 35 cu inches of air.

If your woofer has a symmetrical magnetic field-I don't know if it does, it might-you can cut the amount the woofer must move by four. A bass reflex woofer, at it's tuning frequency, only has to move one-fourth the amount of air a closed box woofer does to produce the same sound level.

So now, at 40 Hz, the woofer must move only 8.5 cu inches of air to produce 112 dB. It can't do that, but with the Vifa's capacity to move 3.25 cu inches, it can produce 103 dB. This is at 40 Hz.

If both woofers are working together in the bass range-records are recorded for that to occur-you can produce 109 dB at 40 Hz and above.

Which is pretty good for two 7" woofers, I think. 42 Hz is the lowest note a bass guitar normally plays. Tuning the box to 34 Hz would waste the benefit the port gives you by trying to reach too far. At 34 Hz, you would only be able to produce 106 dB for the two woofers.

I think a 1 cubic foot enclosure tuned 40 Hz would be the way to go. The choice is yours-I'll give you the dimensions for the 1.25 cu ft enclosure if you want.
 

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diyAudio Moderator Emeritus
Joined 2001
For a 1 cu ft box internal volume, the vent for your Vifa should be 2" diameter by 3.75" long. I can calculate metric pipe sizes if you give me the metric internal diameter-I don't know how they measure pipe over there.

Also, two 35mm ports 100 mm long will give lower noise than the above single port.

For 3/4" building material-18mm, here are the dimensions:
Width: 34.5 cm
Height: 53 cm
Depth: 22.1 cm

For 1" building material-25 mm:
Width: 35.9 cm
Height: 54.44 cm
Depth: 23.54 cm

Obviously, you can round off the fractions. If you actually want the 1.25 cu ft box tuned to 34 Hz, let me know, I'll give the dimensions. If only metric size pipes are available, let me know the size, I'll recalculate.

You might consider using a flared port, wihich gives the low noise level of a port twice the cross sectional area. Not really necesary, but nice to have. Other members have said to increase the length of the port by 1" is you use flares.

Falcon Acoustics over there has ports, I don't know if they are flared at the end or just go straight into a flange. You might want to call them if flared ports are not available locally-which I think they would be in London. Again, flares and flanges not necessary-you can just use PVC pipe for your port.
http://www.falcon-acoustics.co.uk/

Good luck! :)
 
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