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Old 23rd February 2004, 03:54 AM   #1
diyAudio Member
 
Join Date: Feb 2004
Location: Australia
Default Subwoofer sanity check

Thanks to other kind forum member's Ive now modified my first ever speaker design as follows. This has brought up a couple of questions, more a sanity check than anything.

Im going to use a Shiva 12" driver in a closed box design for a subwoofer, and once Ive done the basic design (maybe) use a Linkwitz Transform to get a lower response if I feel I need it. Ill be driving with a 300W dedicated amp.

Here are my questions, if someone can give me a hand ?

Firstly :

The output from Unibox suggests Vb of 47L. That's a 36cm cube, leaving only 2cm each side of the driver on the driver face side. Is that reasonable - it just seems a relatively small box to a novice like me, I can certainly accommodate something larger.

Secondly :

In Unibox the "standard design" (as above) shows a Vb of 47L and Qtc 0.707. But "design by Vb and Q" has a "Physical Vb" 32.2L with a resultant Qtc of 0.696. If I manually adjust the latter Vb, I find that 31.0 in fact gives a Qtc of .704 - closest to 0.707. Im assuming I should be using "DESIGN BY Vb and Q", and by adjusting Vb to get the Qtc I want ? It just seems straange that the resultant box volume is EVEN SMALLER (ie only 31L) ?

Thirdly :

Really Im tempted to make the box larger - perhaps not a cube but something taller but less 'deep', and then sort out the response curve with the Linkwitz Transform. But just "making the box bigger" doesnt have much scientific basis - ie it feels like I dont know what IM doing. (Ah, that's because I dont because Im learning).

Lastly :

A max SPL of 112.1dB at 300W (or 87Db at 1W/1M) would seem enough for a standard living room environment ? But I could only really tell you AFTER Ive built it ! Can anyone tell me before I do so ?

Any responses much appreciated - I surely want to get the design right and know why I have that design before I cut any MDF !

Output from Unibox :

Drive Unit Parameters
Audira Shiva MK IV 12"
Fs 21.00 Hz
Re 2.90 Ohm
Qms 6.50
Qes 0.40
Sd 481.0 cm2
Vas 151.0 l
Xmax peak 16.60 mm
Le 2.12 mH
Le2 0.00 mH
Re2 0.00 Ohm
Nominal Power 300.0 W

External Components
Rs 0.00 Ohm
(Lco1) 0.00 mH
(Rco1) 0.00 Ohm
(Cco1) 0.00 uF
(Lco2) 0.00 mH
(Rco2) 0.00 Ohm
(Cco2) 0.00 uF

Closed Box
Standard Design

Vb 47.1 l
Fb 43.05 Hz
F3 43.06 Hz
Qtc 0.707
Response peak 0.00 dB
Max power input 276.5 W

Design by Vb and Q
Physical Vb 30.5 l
Absorption, Qa 5
Leakage, Ql 15
Alpha, a 4.087
Vb 36.9 l
Fb 47.05 Hz
F3 47.42 Hz
Qtc 0.704
Response peak 1.01 dB
Peak at 98.17 Hz

Parameters of Single Unit
SPL at 1 W 1 m 87.4 dB
SPL at 2.83 Vrms 1m 91.8 dB
Max SPL at 300 W 112.1 dB
Qts 0.377
Effective Qts 0.377
Mms 123.60 g
Cms 0.465 mm/N
Rms 2.509 kg/s
Bl 10.87 Tm
Ref. efficiency, n0 0.336 %
Efficiency, n 0.336 %
Applied voltage 29.50 Vrms





==============================================
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Old 23rd February 2004, 09:10 AM   #2
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Join Date: Jul 2003
Location: Newcastle, Australia
Know absolutely nothing about Unibox, but LspCad says Shiva at Qtc 0.707 is 63.9 litres........

I haven't built a sealed box using this program's predictions, but with vented cabinets its ok.

Just some more confusion to add !!!

Cheers
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Old 3rd September 2004, 06:29 AM   #3
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Join Date: Sep 2004
Location: Sydney
I am looking at using the Shiva 12" as well, and when running it through WinISD it recommends a 54ltr box for a sealed configuration...

But, I'm still a Newbie too so am sitting back and taking in all the threads on box design for the Shiva 12" to see what comes up. If anyone has any recommendations then I'd appreciate them. Will probably just go with the 54ltr sealed design for my very first attempt at DIY.

I can source the Shiva 12" in Australia for $273 from Acoustic Concepts and have a choice of amps from various retailers that I'm working through at the moment.

Back in to my box and keep reading all of them threads.

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Old 4th September 2004, 08:27 AM   #4
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Join Date: Mar 2003
Location: brisbane queensland
here is a copy of LSDcad from the adire web site that has the specs for the shivas built in . http://www.adireaudio.com/TextPages/...eFrameText.htm

iam trying to do the same thing . but have learned a lesson about plate amps . have been told by adire audio that my jaycar plate amp is no good with the shivas driver because it has a built in bass boost of 6db@35hz.

most of the jaycar amps have this & so do a lot of the parts express plate amps as well . so beware if you get one with the bass boost it have to be disabled . .

it is easy with the parts express the resistors have to be changed are in the specs .

jaycar is a different story have tried there tech department also the forum on there web site . no answers yet

have you had a look at the techical section of the adire web site for the application notes for the shivas
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Old 4th September 2004, 08:49 AM   #5
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Location: Holland, The Hague
WinISD (Pro alph0.5) here gives 64 l for 0.707. f3 is 40 Hz

Maybe use the old calculator yourself?

http://www.diysubwoofers.org/sld/sealed1.htm

lol, now I get 60 l for 0.707
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Old 4th September 2004, 10:49 PM   #6
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Join Date: Feb 2004
Location: Australia
Default Update

OK, well I have finally completed building the Shiva in a 54L sealed enclosure, with the walls lined. I have never had a subwoofer attached to my system before, so wouldnt have much to directly and scientifically compare it with, but I have to say the result is awesome. It certainly sounds worlds apart from the subwoofers I have heard to date (commercial designs, mostly compact plastic ones), which seem boomy and far less crisp by comparison.

Next I need to either mess around with damping the second voice coil, or putting in a Linkwitz transform circuit to see how it sounds with different values of Q. Whether the shiva is operating at .707 as designed or something less is an interesting (and achedemic !) point.

By the way, I used the 300W subqwoofer amp from Sound west (Rod Elliott) and the result was fantastic - the amp has more than enough power and, with Rods boards, was simple to build and mount and worked first time. Likewise with the active filter I used.

I dont suppose many regulars read the day to day chatter like this, but many genuine thanks to the people that advised me on what to build and how, the result is certainly better than it would have been had I not got the advice I did.

Im no expert at this - in fact this is the first speaker Ive ever built, but if I can help any others like I was, Im only to happy to do so !

Back to some amazing bass (I can no longer listen to my system without the subwoofer, it just sounds empty ! Painting it could be a problem !)

FT
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