Please help me design a sub enclosure (1 Viewer)

[Chris Eriksen]

Hello Everyone,
I am in the process of planning a new sub, and I would like to ask for your help with the design. I have built many subs in the past, but the majority of them were for the car audio environment, which presents a completely different set of design criteria. As a result, I am confident in my abilities to build any type of enclosure, but my design skills may need some tweaking.
I will be using a driver with the following T-S parameters:

Vas ----- 235 L
Qes ----- 0.476
Qms ---- 8.086
Qts ----- 0.450
Fs ------ 24.7 Hz
Xmax--- 25.0 mm (linear, one-way)
Mms --- 197.9 g
Sd ------ 890 cm^2
Re ------ 6.8 ohms
Le ------ 1.58 mH @ 1 kHz
BL ------ 10.47 TM
P ------- 500 rms

The sub will be located at the front of the listening area, in the corner. The room dimensions are approximately 27'x14'x12' (LxWxH), and there is one opening on a side wall to an adjacent room. Power is not a problem, as I can feed the sub in excess of 900 watts if necessary. I would like to keep the enclosure size below 7 cubic feet, with smaller sizes being prefereble.
This sub will be used almost exclusively for HT. I am aiming for a sound that is dynamic with good deep bass extension and reasonable transient response. High SPL's are not a major concern - I have a feeling that any design with this driver will be more than enough for my needs.
I will be using a Behringer Feedback Destroyer to tame the room resonances, and if necessary, I can use a Rane AC-22 crossover, which includes an adjustable 0-2 ms delay circuit.
At this point, I am considering a sealed enclosure with a volume around 5.5 cubic feet. Any other suggestions or recommendations would be greatly appreciated.
Thank you in advance,
Chris

 

[Chris_Brunhaver]

That looks likr a nice driver. What kind of driver is it? I wouldn't recommend the box you suggested because the f3 is pretty high at around 46 hz. Unless you are planning on doing active EQ, I wouldn't go with a sealed box. I personally would go with a vented box. The driver looks pretty good in your maximum sized cabinet of 7 cubic feet tuned to 20 hz. That would be one 6" x 22" vent or two 4" x 20" vents.
-Chris

 

[Geoff L]

Hi Chris,
Yes a nice looking line of params. Probley a car drive??? Might I be right, wrong, anyway whos line is it anyway.
Geoff

 

[Dustin B]

Jack, where are you. Looks like another canadite for a LT circuit.
Chris, I don't know much about the LT circuit, but from what I've read in Jack G's thread about the BP1803 I would think this driver would work well with LT circuit as well. Especially since you have 900 watts you can throw at it. In which case you could make a 5-7 ft sealed enclosure work extremely well. Although I could be wrong, you'll have to ask Jack or somebody he recommends to learn more about the LT circuit and whether or not it would work well with the driver you have.
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Dustin
[email protected]
My Adire Tempest Sonosub

 

[Chris Eriksen]

Chris B and Jeff,
Thank you for your quick replies. The driver is an Earthquake Magma 15. I had originally intended to clone the Earthquake Supernova MKIV-15, which has been reviewed favorably by a several magazines. However, after looking at their design, I couldn't help but think that I would be compromising sound quality for size. The Supernova uses one Magma 15 with a very high excursion passive radiator ( HERE ) in a 3 cubic foot enclosure, tuned to 15 Hz. Maybe my simulations are off, but this enclosure seems to be lacking in the low end. I really like the idea of using this PR, but my size would be limited to around 5 cubic feet with a PR, due to WAF reasons involved with a large cube. (If it has to be big, she prefers the Sonosub look.)
Chris B: I think you hinted that I may be able to use an EQ to balance the sub's frequency response. I will be using a Behringer BFD (12-band parametric EQ) for the sub - I assume this would be sufficient? Could this also be used to compensate for an undersized PR enclosure, at the expense of SPL?
Thank you,
Chris
[Edited last by Chris Eriksen on September 23, 2001 at 11:40 AM]

 

[Chris Eriksen]

Dustin B,
Thank you for the suggestion. That is an interesting idea, but I must confess that I do not know much about LT circuits. I have been following Jack's thread on the BP1803, and it sounds like an intriguing concept. I will need to do some research...
Thank you,
Chris

 

[Patrick Sun]

The Fs seems t0o high to get that last bit of low end for HT (18-25Hz) rumble. You'll probably need to EQ the rest of the bass output to get a flat response from 20Hz and above.
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PatCave; HT Pix; Gear; DIY Mains; DIY CC; Sunosub I + II + III; DVDs; Link Removed

 

[Jack Gilvey]

Hi,
I took a look at the driver here:
http://www.earthquakesound.com/magma15.htm
I'm not at home this morning, so I don't have any software to try it in, but it seems like a nice driver. The 0.98" X-max is extremely high if correct, and it doesn't state if it's one-way or P-P (although the strict defintion of Xmax is one-way). It's strange that the driver would only have 500w power handling if that's the case, judging by the other drivers I've seen. The power handling itself might limit its usefulness in a LT circuit.

 

[Rick Chwiendacz]

The Fs seems t0o high to get that last bit of low end for HT (18-25Hz) rumble.

Not necessarily, Pat.
That's one of the great advantages of a vented enclosure - you can have alignments where the F3 is well below the Fs of the driver.
For that driver, the optimum alignment would probably simply be the largest enclosure you can manage (7 cubic feet, in this instance), tuned to as low of a frequency as you can get with a 6" port (or dual 4" ports)
If the x-max data is correct, it should be able to handle pretty much anything you throw at it.
- Rick

 

[Chris Eriksen]

Thank you for all of your replies.
Jack and Rick,
Although not stated on the web site, the xmax is rated as linear, one-way excursion. In the past, my experience has been that Earthquake's drivers are spec'd very accurately. The exception is that their power handling specs are incredibly low when compared to the actual power handling of their drivers. In the car audio world, it is very common to see SPL competitors feeding upwards of 1500 rms to a single Magma 15, and the sub will generally handle it without a problem. So I wouldn't put too much credence in the 500 watt rating.
The consensus seems to be a vented enclosure, tuned to around 20 Hz, in an enclosure as large as the wife will allow.
Jack, do you have any links for information on the LT circuit? Even if I decide not to use it, I am interested to learn how it works.
Thank you,
Chris

 

[Jack Gilvey]

http://sound.westhost.com/linkwitz-transform.htm
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[Chris Eriksen]

Thank you for the links, Jack. I have a little reading to do...

 

[Chris Eriksen]

(double post deleted)
[Edited last by Chris Eriksen on September 24, 2001 at 09:40 PM]