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Old 10th February 2013, 04:02 PM   #11
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It must be remembered that an un-eq'd f3 of 37Hz sealed is quite respectable. Room gain helps sealed subwoofers a lot.

Here's what I'd do.

Make the box as small as you can while eq'ing the low end (you'll need to simulate a Linkwitz Transform for this) to whatever you like.

Set the cabinet size such that excursion and thermal power handling run out at about the same time.

Power input is just a matter of how hard it is to move the cone at a given frequency. A small cabinet makes it harder, so you'll run out of power handling before excursion.
A big cabinet is more efficient: it lets the cones move more freely, so excursion runs out before power handling.

When both run out simultaneously, you have the smallest cabinet that still allows you to get all the SPL available out of your drivers.

Chris
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Old 10th February 2013, 05:41 PM   #12
OscarS is offline OscarS  United States
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Quote:
Originally Posted by Ron E View Post
Is this for a car or a house? If a Car, probably best to just use a smallish sealed box - I have heard subs with Qtc up to 1.3 sound quite acceptable in a car.
176/((1.3/.45)^2-1) gives about 24liters per woofer for a punchy sound - although about 55 liters per woofer is probably going to sound more neutral.
I'm sure you agree that "acceptable" is in the eye of the beholder. If you listen to heavy metal at ear-melting levels like I do, all of a sudden quick double-bass drum blasts don't sound so distinct if you run a Qtc that high and would sound quite aweful. It all just depends on the listening material and the preference of the user.
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Old 10th February 2013, 06:35 PM   #13
Ron E is offline Ron E  United States
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Quote:
Originally Posted by OscarS View Post
I'm sure you agree that "acceptable" is in the eye of the beholder. .
Try it, room modes and/or road noise will swamp any overhang you might care to imagine.
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Old 10th February 2013, 11:21 PM   #14
djk is offline djk
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In 0.5 cu ft stuffed the Qtc=1.0 F3=65hz, this might be OK in a car.

A smaller BP4 box, 95.3dB/2.83V/1M

Driver Properties
Name: Polk 12
Type: Standard one-way driver
No. of Drivers = 1
Fs = 23.9 Hz
Qms = 3.034
Vas = 176.2 liters
Cms = 0.442 mm/N
Mms = 100.4 g
Rms = 4.968 kg/s
Xmax = 8 mm
Xmech = 12 mm
P-Dia = 259.8 mm
Sd = 530 sq.cm
P-Vd = 0.424 liters
Qes = 0.538
Re = 3.204 ohms
Le = 2 mH
Z = 3.845 ohms
BL = 9.473 Tm
Pe = 250 watts
Qts = 0.457
no = 0.431 %
1-W SPL = 88.49 dB
2.83-V SPL = 92.47 dB
-----------------------------------------
Box Properties
Name:
Type: Bandpass Single-Tuned Box
Shape: Prism, Bandpass
with two chambers
Chamber 1 - lower-freq.
Vb = 1.5 cu.ft
Fb = 54.23 Hz
QL = 6.589
F3 = 34.77 Hz
Fill = heavy
Chamber 2 - upper-freq.
Vb = 2.113 cu.ft
Fb = 54 Hz
QL = 6.761
F3 = 85.03 Hz
Fill = minimal
No. of Vents = 1
Vent shape = round
Vent ends = two flush
Dv = 6.012 in
Lv = 5.929 in
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Last edited by djk; 10th February 2013 at 11:26 PM.
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Old 10th February 2013, 11:34 PM   #15
OscarS is offline OscarS  United States
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Quote:
Originally Posted by Ron E View Post
Try it, room modes and/or road noise will swamp any overhang you might care to imagine.
been there, done that. Tried it about 15yrs ago, and I didn't like it personally.
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Old 10th February 2013, 11:36 PM   #16
sreten is offline sreten  United Kingdom
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Hmmm.........

A BP4 box with the low pass section bigger volume
than than the high pass section ? not good IM0.

Paper design hardly ever reflects the real build,
the things are so damn sensistive to parameters.

With room gain -3dB at 37Hz is very good for sealed,
though F-6dB actually matters more for a speaker,
and F-10dB (with power handling) for a subwoofer.

rgds, sreten.
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Old 11th February 2013, 01:41 AM   #17
djk is offline djk
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"A BP4 box with the low pass section bigger volume
than than the high pass section ? not good IM0."

Tell that to Polk, they sell many subwoofers designed like this. Mathew Polk wrote a technical paper published in Audio magazine a few years back and offered free ($5 to ship and cover the disc cost) software for designing BP4 enclosures.

High mass, high Qts drivers work well in BP4 designs when done as per Polk suggestions..
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Old 12th February 2013, 07:40 AM   #18
Siorus is offline Siorus  United States
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Quote:
Originally Posted by OscarS View Post
A speaker with a relatively large Vas and an average Qts, will naturally tend to give a maximally flat response in a large-ish box at or near it's reference sensitivity
Thanks, that makes sense.

Quote:
Originally Posted by just a guy View Post
To expand on this a bit, WinISD doesn't "want" anything.
"Wants" was a poor choice of words on my part; "suggests as a starting point" would have been more accurate.

Quote:
Originally Posted by Ron E View Post
Is this for a car or a house?
This is for my living room.

Quote:
Originally Posted by chris661 View Post
It must be remembered that an un-eq'd f3 of 37Hz sealed is quite respectable. Room gain helps sealed subwoofers a lot.
Objectively speaking, you're absolutely right. a 37Hz f3 isn't half bad. But I'm a little OCD and I have a somewhat (but not completely) arbitrary set of specifications that I want to hit. Mainly an F3 under 25Hz and a theoretical maximum SPL (with the drivers operating at their full RMS input power rating) >125dB, while retaining good sound quality.

That's a fairly tall order, and I know it. Power won't be an issue, though; I've got a pile of amps that are credibly capable of shoving 1000wpc (if not comfortably more than that) RMS/continuous into 2 or 4 ohm loads with both channels driven. The Crown CE4000 on the bottom of the pile will actually do 3,600w into 4 ohms if I need it to, and I've been looking for an excuse to pick up one (or several ) MA-5002VZs or big Crests or something anyhow. Just a matter of finding drivers and a couple of boxes.

And I've always considered "room gain" a cop-out. It's like running nitrous on an otherwise mildly built car. It'll get the job done but it's a halfassed way of doing it. If you want a f3 of, say, 30Hz, build the system for 30Hz. Whatever you get from room gain is a bonus. Just how I see it. *shrug*

Quote:
Set the cabinet size such that excursion and thermal power handling run out at about the same time.
(...)
When both run out simultaneously, you have the smallest cabinet that still allows you to get all the SPL available out of your drivers.

Chris
How do I go about determining that, though? Is there some formula that can be applied to calculate whether a given speaker/enclosure combination is going to hit the driver's xmax before it hits its max. power handling or vice/versa? OscarS mentioned that some enclosure modeling software has the ability to predict cone excursion, but that's not something that I see either WinISD beta or WinISD Pro alpha being capable of; is there some other software that's worth considering? I know PE carries a couple different programs but the reviews of them seem to be pretty mixed.
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Old 12th February 2013, 09:31 AM   #19
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Quote:
Originally Posted by Siorus View Post
How do I go about determining that, though? Is there some formula that can be applied to calculate whether a given speaker/enclosure combination is going to hit the driver's xmax before it hits its max. power handling or vice/versa? OscarS mentioned that some enclosure modeling software has the ability to predict cone excursion, but that's not something that I see either WinISD beta or WinISD Pro alpha being capable of; is there some other software that's worth considering? I know PE carries a couple different programs but the reviews of them seem to be pretty mixed.
Its a bit trial-and-error.

I'll run some numbers and see what happens.

...
Remember that WinISD provides (IIRC) groundplane simulations: I think you can gain 6 & 12dB of boost from wall- and corner-loading respectively.

I can tell you immediately that 4x12" sealed won't hit 125dB @25Hz. The displacement-limited SPL is ~108dB at 25Hz.

Ported box required.

Ported can pretty much get you into the 120s, without any boost from walls etc. 0.9 cubic metres (900L), tuned ~22Hz.
Maximum SPL drops to around 117dB at 28Hz, as cone excursion becomes a problem above port tuning as well as below. Infrasonic filter definitely needed at these power levels: the ports will give very little resistance to <20Hz stuff, and the drivers will bottom out immediately.


Given correct eq, you could get (corner loaded) 120dB from 25Hz upwards from a 100L sealed cabinet.
You could stick all 1400w into it, and the drivers would hit 9mm one-way travel around 18Hz.
You'll need an infrasonic filter, or <20Hz stuff will take up all the headroom: a Linkwitz Transform set for f3=25Hz, Q=0.5 is used (the lower Q reduces the boost needed, and integrates better with room gain).

The Linkwitz Transform is essential.

HTH

Chris
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Old 12th February 2013, 10:05 AM   #20
djk is offline djk
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123.8dB/1KW/1M in 2Pi, no room gain.

Driver Properties
Name: Polk 12
Type: Standard one-way driver
No. of Drivers = 4
Mounting = Standard
Wiring = Series-Parallel
Fs = 23.9 Hz
Qms = 3.034
Vas = 176.2 liters
Cms = 0.442 mm/N
Mms = 100.4 g
Rms = 4.968 kg/s
Xmax = 8 mm
Xmech = 12 mm
P-Dia = 259.8 mm
Sd = 530 sq.cm
P-Vd = 0.424 liters
Qes = 0.538
Re = 3.204 ohms
Le = 2 mH
Z = 3.845 ohms
BL = 9.473 Tm
Pe = 250 watts
Qts = 0.457
no = 0.431 %
1-W SPL = 88.49 dB
2.83-V SPL = 92.47 dB
-----------------------------------------
Box Properties
Name:
Type: Bandpass Single-Tuned Box
Shape: Prism, Bandpass
with two chambers
Chamber 1 - lower-freq.
Vb = 11.6 cu.ft
Fb = 41.83 Hz
QL = 5
F3 = 24 Hz
F6 = 21 Hz
Fill = heavy
Chamber 2 - upper-freq.
Vb = 8.453 cu.ft
Fb = 41.83 Hz
QL = 5.378
F3 = 73.62 Hz
Fill = minimal
No. of Vents = 1
Vent shape = round
Vent ends = two flush
Dv = 12 in
Lv = 7.493 in

This is in 2Pi, if you push it up against a solid wall you could pick up 3dB~5dB or so. Will handle 1KW down to 30hz without exceeding 8mm on sine, much more on real program material. It could be made as a 34" cube (external), but I would make one dimension 30" so it could fit through a standard home doorway (roughly 36x36x30). The drivers could be mounted push-pull pairs (not isobaric) for lowest distortion, and perhaps a triple chamber design would be best, or two separate sub cabinets.
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Last edited by djk; 12th February 2013 at 10:12 AM.
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