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

Tom V · 9th February 2010, 04:26 AM

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 · 9th February 2010, 05:50 AM

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 · 9th February 2010, 03:03 PM

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 · 9th February 2010, 05:36 PM

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

dave

Tom V · 9th February 2010, 08:08 PM

>>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 · 4th March 2010, 11:52 PM

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 · 4th March 2010, 11:55 PM

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

chuyler1 · 5th March 2010, 03:48 PM

So how does it sound?

Cal Weldon · 5th March 2010, 03:54 PM

Looks good Tom.

Tom V · 6th March 2010, 12:01 AM

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!

9th February 2010, 04:26 AM	#1
Tom V diyAudio Member Join Date: Jan 2010	Can it be that simple? 3/8" hole in cab lowers F3 by half an octave? 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-

9th February 2010, 05:36 PM	#4
planet10 frugal-phile(tm) diyAudio Moderator Join Date: Oct 2001 Location: Victoria, BC, NA, Sol III Blog Entries: 4	Make sure you account for the volume of the port when you calculate the gross volume of the box. dave __________________ community sites t-linespeakers.org, frugal-horn.com ........ commercial site planet10-HiFi p10-hifi forum here at diyA

5th March 2010, 03:54 PM	#9
Cal Weldon Speakerholic diyAudio Moderator Join Date: Jan 2004 Location: British Columbia	Looks good Tom. __________________ Next stop: Margaritaville Some of Cal's stuff \| Cal Weldon Consulting

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9th February 2010, 05:50 AM	#2
TheSeekerr diyAudio Member Join Date: Jan 2008	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.

9th February 2010, 03:03 PM	#3
Tom V diyAudio Member Join Date: Jan 2010	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??

9th February 2010, 08:08 PM	#5
Tom V diyAudio Member Join Date: Jan 2010	>>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.

5th March 2010, 03:48 PM	#8
chuyler1 diyAudio Member Join Date: Feb 2006 Location: Massachusetts	So how does it sound?

6th March 2010, 12:01 AM	#10
Tom V diyAudio Member Join Date: Jan 2010	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!

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