Go Back   Home > Forums > Loudspeakers > Subwoofers

Please consider donating to help us continue to serve you.

Ads on/off / Custom Title / More PMs / More album space / Advanced printing & mass image saving
Reply
 
Thread Tools Search this Thread
Old 3rd April 2011, 11:49 PM   #1
endrek is offline endrek  Spain
diyAudio Member
 
Join Date: Sep 2010
Default :) Check my first Bass Reflex 6 ports, 2 driver standard configuration design :)

Well here i have my first design, could you check it? And tell me if i'm completely wrong? nearly nearly? or good enough to do a test-speaker?

I got one drivers T/S parameters (i know that when i buy the driver Fane Colossus 18XB, i'll calculate T/S parameters instead using the spec from manufacturer ) Cause i want to drivers 2*Vab and 2*Sd right? I'm not sure how to predict, or mesure how Fs will change once they are together (electrically in paralel) any ideas please??

Now i can calculate the Vab,Fb,Fl,Lv, Sv, etc.. for a C4 Alignment for a QL = 3, that gives me a volume Vb(L) =442,14539 . Wich i can verify that my suposition of QL was correct because Vb>80L (atleast this is how my book says to verify your QL)
Important parameter is Lv=0,10997 or 0,112368 or 0,0755 (with constant=23500 proposed by Small) ..... I think i'll get try the first one and start trimming while tunning as they've told me at this forum

Then i divide the Sv by 6 (Sv/6=Sv') because i want to make 6 cilindrical ports. That gives me Sv' and Dv'=0,103m I'll keep the Lv the same right? Or i divide it by 6 too? :S

Well, with a volume of Vb(L)= 442,1453 L and using the golden ratios of 0,62x1x1,62 i get a box dimensions of W=1,23m , H=0,47 and D=0,76 , wich are really bad dimensions, because my driver has a diameter of 0,48m and i kind of draw it in paper and the 2 drivers with the 6 ports don't really fit in 1,23 of width. So i changed a bit the dimensions, keeping the same volume W=1,29m , H=0,54 and D=0,63 .

I think its really really big, and before i start building it, and spent money with the woods, i would like to know some opinions, because this is my first design/construcion of a speaker. And maybe i'm just going completely wrong
here i leave a table i copied from my excel calculations:

T/S param
1 driver Colossus 18XB
2 drivers Colossus 18XB
Fs
33 Hz
33 Hz
Qts
0,337
0,337
Vas
236
472
Xmax
7,5e-3
7,5e-3
a(m)
0,2056605
0,26833131
d (2a ) (m)
0,41151
0,53666266
Sd (m^2)
0,1131
0,2262


C4 alignment
α
1,2616
h
1,1034
q
1,2798
Vab (L)
374,128091
Fb (Hz)
36,4122
Fl (Hz)
42,2334
Vs (L)
34,00864933
Vb (L)
442,14539
Vdmax (m^3)
1,70E-03
dv (m)
0,1940665250,25
Sv(m^2)
((0,25/2)^2)*Pi=0,05
Lv (op1)
0,10997276
Lv (op 2)
0,11233682
















Design with 6 ports

Sv (6ports)=Sv/6Dv (m)
0,103m


Dimensions

W
1,29m
H
0,54m
D
0,63m


Pd: any advice for construction? wich cheap wood is good enough for my test-speaker and won't influence that is cheap on the results?? Wich material should i use for the ports?? Rigid PVC right? any thickness better than other?

And another dumbie question i just though, to trim the ports while tunning to the Fb, do i glue them all time and test? Or how do i stick them, test, and cut ?? Any good method??

Sorry for this long long post and if there are too many questions, and if there are not really smart I'm new, and my english either makes me look dumber

Thanks to all and for all. Really apreaciate your help and this cool forum
You are all invited to our parties if the speakers project succeed

pd: don't be cruel with me jaja i'm a newbie
cheerz from Spain
  Reply With Quote
Old 4th April 2011, 12:23 AM   #2
diyAudio Member
 
Join Date: Nov 2007
First thing's first - I strongly suggest that you don't use 6 separate vents. You're going to REALLY regret doing that once it's time to trim those vents to achieve the target Fb . Instead, I suggest going with a simple shelf vent below the driver - it will be much easier to adjust the length of the "shelf" by designing it to be a simple screw down panel that you can remove and trim if necessary.

Second thing - don't put the two drivers in one chamber. Use separate chambers, one for each driver.

Your end result, if you follow my suggestions, will be two chambers, two shelf vents, and a pretty sturdy box (the shelf vents will act as additional bracing to the panels).

Thirdly, don't worry about the "golden dimensions" when it comes to subwoofers. They will make little difference to the subwoofer's performance. For 18" driver, you may want to consider making the baffle 2ft x (2ft + shelf vent height), then derive the cabinet depth from the net required volume - this approach may result in a cabinet that's deep enough to hold the shelf vent without having to resort to folding it.
  Reply With Quote
Old 4th April 2011, 02:03 AM   #3
diyAudio Member
 
revboden's Avatar
 
Join Date: Feb 2011
+1 Brian

If you put the two drivers in one box they will interfere with each other since no two drivers are exactly the same.

I just modeled that driver in a 221L box with Fb 36.4hz and one .304m (12") diameter port, .522m (20.55") length.

it's a monster
  Reply With Quote
Old 4th April 2011, 07:26 AM   #4
endrek is offline endrek  Spain
diyAudio Member
 
Join Date: Sep 2010
Quote:
Originally Posted by Brian Steele View Post
First thing's first - I strongly suggest that you don't use 6 separate vents. You're going to REALLY regret doing that once it's time to trim those vents to achieve the target Fb . Instead, I suggest going with a simple shelf vent below the driver - it will be much easier to adjust the length of the "shelf" by designing it to be a simple screw down panel that you can remove and trim if necessary.
you convinced me certainly
When you mean a shelf, its a kind of rectangular port under the driver? Or do you have any link to a picture so i can figure what it is? my english is not too god :S
because i google speakers shelf vent, and they only picture me wood furniture

Quote:
Originally Posted by Brian Steele View Post
Second thing - don't put the two drivers in one chamber. Use separate chambers, one for each driver.

Your end result, if you follow my suggestions, will be two chambers, two shelf vents, and a pretty sturdy box (the shelf vents will act as additional bracing to the panels).
I will So do the same design for both and then just like "stick" them together, but with a separation wall so they don't interfere on each other right?


Then i was completely wrong with my night of calculations jeje

i thought that two drivers could go in a box, because i saw the design, G-sub
Speakerplans.com and figured, that if they go in phase... But i trust you more than my little(no) experience

I'll do the calculations again, and see. My 2 drivers Colossus 18XB are on their way
And when i finish this, i want to do 2 Mid-High speakers. (but before lets finish this)

really thankfull to all! Nice to have this free and enjoyfull education
big up free education for all!
  Reply With Quote
Old 4th April 2011, 08:32 AM   #5
endrek is offline endrek  Spain
diyAudio Member
 
Join Date: Sep 2010
Quote:
Originally Posted by revboden View Post
+1 Brian

If you put the two drivers in one box they will interfere with each other since no two drivers are exactly the same.

I just modeled that driver in a 221L box with Fb 36.4hz and one .304m (12") diameter port, .522m (20.55") length.

it's a monster
With a circular port? I just done some calculations, and i got this,

C4 alignment
α
1,2616
h
1,1034
q
1,2798
Vab (L)
187,064046
Fb (Hz)
36,4122
Fl (Hz)
42,2334
Vs (L)
11,75724126
Vb (L)
198,821287
Vdmax (m^3)
9,98E-04
dv (m)
0,1940665250,25
Sv(m^2)
((0,25/2)^2)*Pi=0,05
Lv (op1)
0,20359849
Lv (op 2)
0,23139113

But you said you did a .522m of Lv?? My calculations are wrong?Or did you overdimensioned and then trim it for to tune it?

Another question, if i make a little bigger the Vb, does it have a bad effect on the response? What effect does it make??

thx again for all
  Reply With Quote
Old 4th April 2011, 09:16 AM   #6
sreten is offline sreten  United Kingdom
diyAudio Member
 
Join Date: Nov 2003
Location: Brighton UK
Hi,

What is it for ? i.e. its intended use ? the huge size and relatively
poor bass extension of 2 x 18" 99dB drivers needs good justification.

rgds, sreten.
__________________
There is nothing so practical as a really good theory - Ludwig Boltzmann
When your only tool is a hammer, every problem looks like a nail - Abraham Maslow
  Reply With Quote
Old 4th April 2011, 09:29 AM   #7
diyAudio Member
 
picowallspeaker's Avatar
 
Join Date: Apr 2007
Quote:
Originally Posted by endrek View Post
You are all invited to our parties if the speakers project succeed
That's the story !
  Reply With Quote
Old 4th April 2011, 12:55 PM   #8
diyAudio Member
 
Join Date: Nov 2007
Quote:
Originally Posted by endrek View Post
When you mean a shelf, its a kind of rectangular port under the driver? Or do you have any link to a picture so i can figure what it is? my english is not too god :S
Imagine a rectangular vent. Now imagine a rectangular vent where three sides of the vent's cross-section are formed from the walls of the enclosure. There's your shelf vent.


Quote:
Originally Posted by endrek View Post
So do the same design for both and then just like "stick" them together, but with a separation wall so they don't interfere on each other right?
That's correct.


Quote:
Originally Posted by endrek View Post
i thought that two drivers could go in a box, because i saw the design, G-sub
Speakerplans.com and figured, that if they go in phase... But i trust you more than my little(no) experience
The G-Sub looks like a good design. I'd go further and extend the "A" brace to be a full internal panel, splitting the box into two, and adjust the height or depth of the box to hit the target Vb.

Note: that's going to be one heavy and likely difficult to move enclosure. You may want to consider just building separate enclosures for each 18, and then stacking them. They will be a lot easier to move around .
  Reply With Quote
Old 4th April 2011, 11:09 PM   #9
diyAudio Member
 
revboden's Avatar
 
Join Date: Feb 2011
Quote:
Originally Posted by endrek View Post
With a circular port? I just done some calculations, and i got this,

C4 alignment
α
1,2616
h
1,1034
q
1,2798
Vab (L)
187,064046
Fb (Hz)
36,4122
Fl (Hz)
42,2334
Vs (L)
11,75724126
Vb (L)
198,821287
Vdmax (m^3)
9,98E-04
dv (m)
0,1940665250,25
Sv(m^2)
((0,25/2)^2)*Pi=0,05
Lv (op1)
0,20359849
Lv (op 2)
0,23139113

But you said you did a .522m of Lv?? My calculations are wrong?Or did you overdimensioned and then trim it for to tune it?

Another question, if i make a little bigger the Vb, does it have a bad effect on the response? What effect does it make??

thx again for all
I was just playing with the numbers.

Your Math is good.

I came up with 221L Vb ( Vb = 442.14539L/2 ) + .522m legnth port with .304m diameter port to = Fb (Hz)36.4122. It is the same simulation as your design with one big port, not 3 per driver.

You should try WinISD Pro, free design software. LinearTeam
It will show you what happens when you increase Vb.
it has a very good help menu.
  Reply With Quote
Old 5th April 2011, 01:42 AM   #10
endrek is offline endrek  Spain
diyAudio Member
 
Join Date: Sep 2010
For a Vb=195,56L i choosed a Dv=0.25 => Sv=0,05 => Lv=0,41

Then i dimensioned W=0,609(2ft) x H=0,609+0,081(Height of shelf vent)=0,69 => D=0,4723m

Isn't it too long the port lenght? if my deepth is 0,4723 and the Lv = 0,41?? There is only left like 0.06 for air to flow...
Or you think i did some wrong calculations??
I know i'll have to trim it to tune it to Fb=36Hz but so much?

thx again for all

Last edited by endrek; 5th April 2011 at 01:44 AM.
  Reply With Quote

Reply


Hide this!Advertise here!
Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
Double Driver Bass reflex design endrek Subwoofers 11 11th April 2011 07:46 PM
Design of rectangular ports for Bass reflex box endrek Subwoofers 19 3rd April 2011 09:34 PM
bass-reflex with 2 different ports? andrew24 Subwoofers 6 4th July 2009 02:54 AM
Bass Reflex design wit the new Hemp Acoustics FR8C driver audio_moksha Multi-Way 4 7th March 2007 08:30 PM
Two ports in a 2-way bass-reflex speaker alvinlim Multi-Way 3 15th February 2006 10:41 AM


New To Site? Need Help?

All times are GMT. The time now is 02:45 PM.


vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2014 DragonByte Technologies Ltd.
Copyright 1999-2014 diyAudio

Content Relevant URLs by vBSEO 3.3.2