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Old 20th March 2014, 06:26 PM   #1
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Default Total subwoofer Q

Hi again everyone, I'm designing a sub woof box around the Parts express 15" Titanic 4 I received for my birthday. I listen to Classical and jazz and I love tight base, little overhang and bass extension, no boom lol. I know 0.7 q is ideal but I was wondering since I have the space would a 4.5 cubic box ( I have almost all the materials for this size and 400 watts rms power how would a q of around 0.64 please me? No chance of boom here . Have a great day!
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Old 20th March 2014, 06:49 PM   #2
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What're you using as a crossover?
Where will this be placed in your room?
Do you have any eq available?
What will be powering it?
Do you have any particular low-end cutoff in mind?
What's the rest of your system?

Chances are you'll probably like it, but you haven't told us nearly enough for us to tell you what exactly it'll do...

Chris
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Old 20th March 2014, 07:13 PM   #3
sreten is offline sreten  United Kingdom
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Hi,

Sealed and well stuffed might add about 20% to cabinet
volume and drop Qbox a little lower. If you like it tight
and extended then dropping Qbox below 0.7 will be
absolutely fine if you don't mind the larger cabinet.

Anywhere between 0.6 and 0.7 will be fine.
FWIW some would argue the best sealed alignment
is near Bessel *, Q=0.58. However many subs that
are suitable for sealed boxes need impractically large
cabinets for Qbox = ~ 0.6, compared to ~ 0.7.

rgds, sreten.

* It has the flattest group delay of sealed boxes.
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Old 20th March 2014, 08:17 PM   #4
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Why not a second order Linkwitz-Riley profile with Q=0.5?
Minimal excursion, extended low-end and a good phase behaviour...
Well... perhaps you need a LT but you have enough power in your amp.
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Old 20th March 2014, 09:43 PM   #5
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Default Type of alignment

Here is my thinking. The box will be filled but not stuffed with acoustic fill. That would make the interior closer to about five square feet and lower the Q to about 5.6, a little weak perhaps but fast and tight with little boom. Mitigating the fact that it will be a little weak is the fact that I must employ corner spacing and the fact that the room is small, 10x13x8 so I'll get room gain there. I would expect about 18Hz minus about five or 6db from a baseline 105 db. Any one see a flaw?How do most feel regarding a .07 alignment verses Bessel allignment of .058? Oh buy the way I have almost unlimited eq available Up to 18 db boost or cut at 20 Hx 25Hz, 30 Hz and up. One channel of a big Crown amp is the driver. Thanks again Mark

Last edited by markbark; 20th March 2014 at 09:55 PM.
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Old 20th March 2014, 10:07 PM   #6
sreten is offline sreten  United Kingdom
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Hi,

Stuff it bigtime. If you don't like the Q reduce the box size.

Corner placement is poor but you've fortunately got a
reasonable set of room ratios, allowing about 25%/
30% placement along a back (preferably) or side wall.

Low Q (0.5) is about using room gain, Q 0.7 isn't as much.

And FWIW when you get to Qbox = 0.5 there are loads
of deep tuned vented alignments that do a quasi 1st
order rolloff to match typical room gain and offer a
substantial increase in the low bass maximum SPL.

rgds, sreten.
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Last edited by sreten; 20th March 2014 at 10:21 PM.
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Old 21st March 2014, 02:56 AM   #7
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Quote:
Originally Posted by sreten View Post
Low Q (0.5) is about using room gain, Q 0.7 isn't as much.
Room gain is always there and you cannot choose when to use it just by changing the Q value.

Quote:
Originally Posted by sreten View Post
And FWIW when you get to Qbox = 0.5 there are loads
of deep tuned vented alignments that do a quasi 1st
order rolloff to match typical room gain and offer a
substantial increase in the low bass maximum SPL.
AFAIK it's impossible to approach a 1st order rolloff by using any vented aligment which is a 4th order one...
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Old 21st March 2014, 04:27 PM   #8
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Interesting comments about using Q with room gain by sreten. We should (OP) know (and model) the room (dimensions) then (with the driver).
More on Q by Tony (wintermute@diyAudio) and pics below for OP.
New program for Room Response Simulation
Cabinet size help
Attached Images
File Type: gif ROOM GAIN - TROELS - box simulation and room-gain.GIF (48.3 KB, 166 views)
File Type: jpg QTC courbe 2_petoindominique.jpg (138.9 KB, 166 views)
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Old 21st March 2014, 04:59 PM   #9
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Quote:
Originally Posted by markbark View Post
Hi again everyone, I'm designing a sub woof box around the Parts express 15" Titanic 4 I received for my birthday. I listen to Classical and jazz and I love tight base, little overhang and bass extension, no boom lol. I know 0.7 q is ideal but I was wondering since I have the space would a 4.5 cubic box ( I have almost all the materials for this size and 400 watts rms power how would a q of around 0.64 please me? No chance of boom here . Have a great day!
There's something awkward about a 4.5 cubic ft enclosure.
Quote:
The re-tooled motor focuses even more magnetic flux in the gap, for a lower Qes and Qes. This allows for the same performance as a Titanic Mk III 15", in a much smaller box. Where the Mk III needed at least 2.44 cubic feet of net internal airspace for a Qtc alignment of 0.707 and an f3 of 43 Hz, the Mk 4 needs 1.67 cubic feet of internal airspace for the same Qtc alignment and f3 (when used with two pounds of Acousta-Stuf fill).
Is that the Titanic Mk III or Mk 4?!
Dayton Audio TIT400C-4 15" Titanic Mk III Subwoofer 4 Ohm | 295-420
Dayton Audio TS400D-4 15" Titanic Mk 4 Subwoofer 4 Ohm | 295-405
Plus the data is not the same in the Dayton Audio driver website vs. pdf and they need to correct this because is not the same driver specs or measurements where than with different drivers.
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Old 21st March 2014, 05:30 PM   #10
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You get a benefit (using the pdf parameters above for simulation) from a Qtc of 0.7 to a Qtc of 0.6 but you don't gain nothing going lower than that (Qtc 0.5) in terms of output and extension.
DAYTON TS400D-4 Titanic Mk 4,
VB = 107.0 L, QTC = 0.706, F3 = 35 Hz (107L = 3.8ft³)
VB = 175.0 L, QTC = 0.600, F3 = 37 Hz (175L = 6.2ft³)
VB = 240.0 L, QTC = 0.550, F3 = 39 Hz (240L = 8.5ft³)
Your enclosure of 4.5ft³ = 127.5L with QTC = 0.66 (F3=35Hz) is adequate to me. You only need 330W to achieve max excursion (driver is 900 RMS).
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