Could it be tuned as claimed? (27Hz)

michaelpage26 · 16th June 2008, 06:11 PM

My speaker designer has built a 18.5L trapezoid enclosure for each of my loudspeakers. It has a 8.5cm/3.3" diameter port and the port length is 11cm/4.3". The woofer is the 10" Revelator coated paper. In this enclosure there is a closed enclosure for the mid which is about 1.9L. I think i have to subtract it from the 18.5L to find the actual net volume for the Woofer (The dimensions are internal)

So we have 16.6L.
I used this formula to find where my loudspeakers are tuned...

Quote:

Lv = (23562.5*Dv^2*Np/(Fb^2*Vb))-(k*Dv)

where,

Dv = port diameter (cm)
Fb = tuning frequency (Hz)
Vb = net volume (litres)
Lv = length of each port (cm)
Np = number of ports
k = end correction (normally 0.732)

http://www.diysubwoofers.org/misc/portcal.htm

So after calculations

Fb=root(1702390.6/((11+6.22)*16.6)=root(5954.80)=77Hz

He claims that it is tuned at 27Hz...

Is something wrong? Is the formula applicable to floorstanders or is it only for subwoofer designs ?

Thanks in advance for any help!

kelticwizard · 16th June 2008, 09:57 PM

For what it is worth, WinISD agrees with you completely, 77 Hz it is.

michaelpage26 · 16th June 2008, 10:04 PM

So that means the 27Hz couldn't be the case for that speaker!
He lied ?

badman · 16th June 2008, 10:21 PM

He's likely just totally incompetent.

augerpro · 16th June 2008, 10:24 PM

18.5L is incredibly small for this driver. That's like a small bookshelf speaker. Are you that is correct?

michaelpage26 · 16th June 2008, 10:42 PM

My bad! I did wrong the conversion from cm^3 to liters

Now it seems too large ....When I asked him he said 30-40liters. Anyway it seems he is doing it empeirical. And when I said that Klang & Ton recommended 60L bass reflex for this one he said "Oh If i do what they say, the bass driver will bottom out or be loose and not tight, due to huge enclosure...,or something like that"

I will do the calculations again...
The dimensions are:

Big base : 39cm / 15.3"
Small base : 21cm / 8.26"
Trapezoid Height: 107cm / 42.12"
Depth : 35cm / 13.77"

Oh it is 112L! Sorry am a noob in stereometry too

sreten · 17th June 2008, 08:45 AM

Hi,

I suspect those may be external dimensions, not internal.
FWIW 27Hz tuning with 85mm diameter / 110mm length = 130L.

/sreten.

16th June 2008, 09:57 PM	#2
kelticwizard diyAudio Member Join Date: Sep 2001 Location: Connecticut, The Nutmeg State	For what it is worth, WinISD agrees with you completely, 77 Hz it is. __________________ "A friend will help you move. A really good friend will help you move a body." -Anonymous

16th June 2008, 10:21 PM	#4
badman Custom Title diyAudio Member Join Date: Sep 2003 Location: Sunny Tustin, SoCal	Probably not a lie He's likely just totally incompetent. __________________ I write for www.enjoythemusic.com in the DIY section. You may find yourself getting a preview of a project in-progress. Be warned!

16th June 2008, 10:24 PM	#5
augerpro diyAudio Member Join Date: Aug 2006	18.5L is incredibly small for this driver. That's like a small bookshelf speaker. Are you that is correct? __________________ ~Brandon DriverVault Soma Sonus Old Driver Tests

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16th June 2008, 10:04 PM	#3
michaelpage26 diyAudio Member Join Date: Mar 2004 Location: Athens	So that means the 27Hz couldn't be the case for that speaker! He lied ?

16th June 2008, 10:42 PM	#6
michaelpage26 diyAudio Member Join Date: Mar 2004 Location: Athens	My bad! I did wrong the conversion from cm^3 to liters Now it seems too large ....When I asked him he said 30-40liters. Anyway it seems he is doing it empeirical. And when I said that Klang & Ton recommended 60L bass reflex for this one he said "Oh If i do what they say, the bass driver will bottom out or be loose and not tight, due to huge enclosure...,or something like that" I will do the calculations again... The dimensions are: Big base : 39cm / 15.3" Small base : 21cm / 8.26" Trapezoid Height: 107cm / 42.12" Depth : 35cm / 13.77" Oh it is 112L! Sorry am a noob in stereometry too

17th June 2008, 08:45 AM	#7
sreten diyAudio Member Join Date: Nov 2003 Location: Brighton UK	Hi, I suspect those may be external dimensions, not internal. FWIW 27Hz tuning with 85mm diameter / 110mm length = 130L. /sreten.

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