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Old 25th September 2013, 12:26 AM   #1
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Default Need advice for 12" studio build

I've been working on a semi budget recording studio setup. I have a relatively well treated room with several bass traps. My monitors are Equator D5s.

After looking at reasonably priced studio subs, I've decided I want to build one because anything less than $1000 seems lame.

So, obviously flat response is important, down to 30Hz if possible (Flat to 30, not F3=30). I guess I don't need much volume compared to a big home theater room or something.

My first idea was a Eminence Lab 12 in a 3.5cuft vented box (their "large vented" design). It seems pretty sweet. Paired with a Dayton SA230 and a MiniDSP 2x4 for crossover.

Then I saw the CSS SDX12, which produces an almost identical frequency response graph as the Lab12, but in a 1.8cuft box. However, the Xmax on that thing is mental, so port air speed quickly becomes an issue. I'd need a big slot port, or elbows in round ports.

Once question I have is:

-Is the SPL graph absolute? For example, the 1.8cuft SDX12 vs the 3.5cuft Lab12 (both tuned to 25Hz) look identical - will they sound identical? It seems like the SDX12 is more for home-theater boom rather than music?

-An SDX10 build with a 1.7cuft box tuned to 25Hz has again, a very similar frequency response, but with significantly less port air velocity. Would this be a better choice? I have a feeling winISD is lying to me - it shows a flat response all the way past 10khz...



help!
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Old 25th September 2013, 01:22 AM   #2
OscarS is offline OscarS  United States
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It depends on how the SPL graph was generated.

Sound has more dimensions than just frequency response.

WinISD is not "lying". WinISD is a very basic low-frequency simulation program (with many great features, I might add). This is because Thiele-Small parameters are solely for determining the response below the midband. This is because T/S analysis is based on electrical high-pass filter theory. Above the midband, it is all but impossible to predict and must be measured.

WinISD is reasonably accurate with respect to low-frequency response, but you have to include enough parameters in the "electromechanical" section in order to generate the SPL graph and not just Transfer Function Magnitude. Both plots are dB vs Hz, but they are different in that transfer function magnitude is normalized to "zero" which references the driver's reference sensitivity via the Eta-zero spec. Then you have to equalize the power input by making sure both simulations receiving the same power (watts).

Last edited by OscarS; 25th September 2013 at 01:24 AM.
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Old 25th September 2013, 05:55 PM   #3
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Your expectations, (...or questions) might be well out of sync. or not, maybe you are almost there with wrong woofer/sub. Maybe asking first; are you going to use EQ, BR or other type of enclosure. Do you have a limited footprint for the speakers? It looks that yes. How is it going to blend with the main speakers in the frequency domain? Is always better if it's a studio to use the room gain calculators, besides are you going to chose the type of system/sub or letting us helping you... It looks you have a close idea of systems volume (net) and air speed, in the case of BR you have to check for ports also. Also check the needed amp W you will need for the finished system, sealed are different from BR and max amp W you are going to use/need, for max airspeed also. And, also important, I'm not mentioning the right Qt at this point because you are not mentioning it. So let's give an easy answer, after all. But first what's your max volume internal (net)/external (need extra ports vol. for BR), for the sub? I would use it as my starting point and after getting an appropriate woofer I would model for room gain. I would recheck again for my system/room gain and move to another sample/enclosure like the CSS if it's the case. You are going to be very far from flat in your studio, just my guess. For that do the modeling.

(example #1) You are going to use a sub with no EQ in a BR type system/sub, and no limited space (or driver size), flat to 30Hz (?), as you said for Eminence Lab 12:
That's not a very flat alignment with a hump @35Hz that will react with room gain.

(example #2) Lab 12 compromise, flat to 30Hz (+/-0.5dB),
VB = 99.1 L, FB = 22 Hz
(3.5ft³ = 99.109L)
2x4" ports (length 89.97cm = 35-27⁄64in) This alignment doesn't look so bad besides the length of the ports, if you can afford to add to the total volume.

(example #3) CSS SDX12, flat to 30Hz (+/-0.5dB), in a VB = 51.0 L, FB = 22.0 Hz (1.8ft³ = 50.970L)... but problematic with the ports. Some use aperiodic ports for remediation. Probably will modify response in frequency a lot from the 30Hz objective.
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Old 25th September 2013, 06:24 PM   #4
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Hey Guys,

Thanks for the replies.

The largest available space I have is approx 24" tall, 16" deep, by 16" wide ish. I think this provides around 3.5cuft (external, anyway). Smaller would be OK too I guess.

I'm not going to lie, many of the speaker params are outside my level of understanding at this point. I was hoping to rely on modeling/advice to get me by. I have a problem over-researching things and then failing to reach a decision. When I found the Lab12 and a decent vented box design that looked to have a nice flat response, I had all but decided on that and tried to avoid looking at other stuff. Then I saw the SDX12 and it all went to crap

I've been using REW and a condenser mic (not ideal, I know) to gather room stats. My monitors are quite flat, room response is good. I have used Roxul Safe&Sound extensively - bass traps floor to ceiling in all 4 corners, 4'x4'x3" cloud, 4'x4'x6" panel on rear wall above a fluffy couch, 4x4x3" on either wall beside desk, etc.

I plan on using a miniDSP 2x4 for crossover and DSP/room correction, along with REW to maintain the flat response.

I have no preference on amp/etc. The miniDSP removes the need for any filters/etc on the amp itself, but it seems difficult to find a decent amp that'll work for sub duty for a cheap price. I looked into building one from individual components, but that requires a power supply etc etc and it gets complicated and expensive fast. Thus, building a passive box, using an SA230, and the miniDSP will keep things clean and easy.

Your example #2 was my original plan, but with 2x 3" round ports.
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Old 25th September 2013, 07:18 PM   #5
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Here's another driver. This is the one that's better for your amp too.
Dayton Audio SA230 230W Subwoofer Amplifier
156 watts into 8 ohms, 233 watts into 4 ohms

(example #4) SB Acoustics SB34SWNRX-S75
SB Acoustics :: 12'' SB34SWNRX-S75-6 The Madisound Speaker Store
30Hz - (+/-0.8dB)
VB = 85.0 L, FB = 22.8 Hz
net: 85L = 3ft³ (+ports/driver/all internals)
3x3" ports, length: 84.31cm = 33-3⁄16in

(example #5) Scan-Speak 32W/4878T Revelator 13" Subwoofer
The Madisound Speaker Store
30Hz - (+/-0.8dB)
VB = 94.3 L, FB = 22 Hz
net: 94.3L = 3.33ft³ (+ports/driver/all internals)
2x4" ports, length: 97.91cm = 38-35⁄64in

Last edited by Inductor; 25th September 2013 at 07:22 PM.
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Old 25th September 2013, 07:30 PM   #6
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Wow, thanks a ton!

Can you send me specifics on Example #4? Where the design came from etc?
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Old 25th September 2013, 07:37 PM   #7
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My alignment. You can simulate with WinISD or others. Best.
What ply you will be using, for end calculations?
Ports - internal dimension for diam used (in this case 3").
1x port volume = ~18.25L, 3x port volume (18.25L) = 54.75L
85L + 55L (ports) + 2L (driver) = 142L internal total
142L = 5.0ft³ net
ply + bracing will give external dimensions (+/-).

Last edited by Inductor; 25th September 2013 at 07:51 PM.
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Old 25th September 2013, 08:15 PM   #8
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Quote:
Originally Posted by Inductor View Post
My alignment. You can simulate with WinISD or others. Best.
What ply you will be using, for end calculations?
Ports - internal dimension for diam used (in this case 3").
1x port volume = ~18.25L, 3x port volume (18.25L) = 54.75L
85L + 55L (ports) + 2L (driver) = 142L internal total
142L = 5.0ft³ net
ply + bracing will give external dimensions (+/-).
Edit: Sorry I used Radius (distance from center to rim) instead of Diameter for the ports volume.
That's the problem with calculators. Let's try again;

1x port volume = ~4.45L, 3x ports (4.45L) = 13.35L
85L + 13L (ports) + 2L (driver) = 100L internal total
100L = 3.5315ft³ net
ply + bracing will give you the final external dimensions (+/-).

Last edited by Inductor; 25th September 2013 at 08:21 PM.
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Old 25th September 2013, 08:20 PM   #9
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Ah, that's a bit more doable

Thanks again, I really like this solution. And the driver is available in Canada for a reasonable price.

Cheers!
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