Can it be that simple? 3/8" hole in cab lowers F3 by half an octave?

[Tom V]

I am working on my design for computer speakers using the Aurasound NS3-193 8ohm 3" speakers.

I am using the enclosure calculators referenced on the Madisound site.

Sealed 2.5L sealed enclosure has an F3 of 86Hz. Not bad!

Now for a vented enclosure:

mh-audio.nl - Vented System

F3 is 57Hz but the vents are way too big. So I try sucessively smaller port diameters until I get down to 3/8" (.95 cm). That puts the port length at .54".

Can I really drill a 3/8" hole thru the 1/2" thick side of the cabinet and get an F3 of 57Hz? Fantastic if true!

Thanks for any input!

-Tom-

 

[TheSeekerr]

Small ports have higher resistance, so they model more like sealed enclosures than you'd expect. So no, you probably won't get as much extension as you're modelling.

Also, model the port velocity at reasonably high volumes - I'm guessing it'll be pretty high, which would result in undesirable noise from the operation of the port.

 

[Tom V]

Apparently it wasn't that simple. On the same site I found a Port Calculator and that got me a minimum diameter of over an inch.

So latest theory is 1-1/4" port (the cardboard tube from a roll of wrapping paper) about 8" long. This preserves the 57Hz model number.

Sound more reasonable??

 

[planet10]

Make sure you account for the volume of the port when you calculate the gross volume of the box.

dave

 

[Tom V]

>>Make sure you account for the volume of the port when you calculate the gross volume of the box.

Yup, my rough calculation was about 170 cm**3.

Thanks to TheSeekerr, and Planet10 for the great advice.

 

[Tom V]

It's done and it works!!

Bringing this thread to a close, here is the completed Soundbar, using a 7.5" cardboard tube as the bass reflex port, and attaching a Dayton DTA-1 T-amp as power.

First pic is assembly details with the internal dividers, port tube, and padding in place. Glue from the hobby store worked just fine.

 

[Tom V]

The other two pics show the completed soundbar. The bottom edges were cut off at a 15 degree angle.

 

[chuyler1]

So how does it sound?

 

[Cal Weldon]

Looks good Tom.

 

[Tom V]

Sounds pretty good. Lots of bass, maybe just a tad uncontrolled, and lacks "sparkle" on the high end. But very pleasant sound.

And it sure sounds better than the built in speakers in that laptop!

 

[chris661]

Looks very nice - like the kind of thing you could go out and buy......

If the bass isn't quite right, you might want to experiment with stuffing the ports a little, or playing with stuffing in the box itself.

Chris

 

[borispm]

Try stuffing it almost completely with fiber glass to control the bass a bit. If it's still bad try stuffing the ports too. The Aurasound speakers have a highish Q so they play happier in sealed cabs. If you try to model it through WinISD, you'll find that the group delay is quite large when ported.

 

[AndrewT]

looks very good!

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