[Inspiron]

Hi guys, nice forum

I'm planning on building a subwoofer for my home theater (surround sound only). In my country I can get the Ascendant Audio chaos 15" in a relatively good price but only in the dual 2ohms version. To order the SDX15 will cost about 50% more.
I have a crown CSL800 amp that outputs 640W into 4 ohms. My room is 13ft. X 15.5ft.

I was thinking of building a ported enclosure of 200 liters tuned to 20Hz for the chaos 15 OR and if the added expense really justifies it, a 225 liters enclosure tuned to 18Hz for the SDX15.

The chaos 15's t/s parameters are:

Re: 1.5 Ω
Fs: 27.1 Hz
Qms: 6.62
Qes: 0.47
Qts: 0.43
Mms: 260 g
Sd: 810 cm^2
Vas: 121.8 l
SPL: 89 1W/1m
Bl: 16.9 Tesla Meters
Xmax: 21mm (one-way)
RMS: 800W

What do you guys think?

Thanks.

 

[SteveCallas]

How much more is 50% more? Those specs look like the driver should be able to do a decent job, but if 50% more only equates to say $70 more, you might be better off with a known performer.

 

[Inspiron]

It's about 200$ more.

 

[Mike P.]

What country are you in?

 

[Inspiron]

Israel.

 

[Mike P.]

The Subs model fairly close with 640 watts input power. Go with the Chaos 15.

 

[Inspiron]

Yeah, I taught so too. Would you change anything in the enclosure or does it look good to you?

 

[Mike P.]

I have the modeling file on another computer, I'll have access to it tonight. Have you figured out the porting yet?

 

[Inspiron]

No, I've just "played" with the volume and tuning frequency and actually I'd like help with figuring out the porting.
I'd like to build an enclosure that will sit under my projection screen and that the center will sit on top of the sub so the height should be no more than about 42cm (I still need to measure it exactly) and I thought of making it about 100cm wide.

Thanks for the help

 

[Mike P.]

Your sub will require a High Pass Filter (rumble filter) at 15 hz to prevent over excursion at the lower frequencies.
Porting can be done with two 4 inch round ports 21 inches long. Maximum air speed is 25 m/s.
The ports displace 2 liters, you'll have to add the dispacement of the sub and bracing also to give you the required internal volume of the cabinet.

 

[Inspiron]

How much does a rumble filter cost? Will I need one if I'll use the SDX15? Is there something I can change in the design so I won't have to use a filter? Do I need to flare the MDF around the ports?

I gather that the design looks good to you?

Thanks!

 

[Mike P.]

It doesn't matter which sub you use, the sub will exceed Xmax in a HT application. Reckhorn has a B1 bass management system, they are located in Germany. You'll have to check and see where the closest distributor to you is.

http://www.reckhorn.com/index.php?ln=en&prod=b1

Flaring the ports is always a good idea. It helps keep the air speed down. Here's how to make flares with a router.

http://www.subwoofer-builder.com/flares-10mm.htm

200 liters tuned to 20Hz is what I would do with this sub, it models well in that size and tuning.

 

[Inspiron]

Thanks.

Is there some kind of guide about the required MDF thickness and bracing?

 

[Mike P.]

MDF should be 3/4 inch thickness. Bracing will depend on the size and dimensions of the box. Figure out the external box size and we'll take it from there.

 

[Inspiron]

I've just went and measured and the maximum height of the sub should be 15.75" (40cm). The driver overall diameter is 15.625" and the cutout diameter 14.125". So if I subtract the thickness of the MDF from 15.75" it's 14.25" so I should be fine right? I'd like the sub to fire to the front.

The driver displacement is 0.17 CF (4.81386 l) so if I add the port displacement you gave and let's say some bracing it should be about 210l or maybe more. If so the outer measurements I'd like using 3/4" MDF should be 15.75"X39.37"X25.24" The only measurement that I can't change is 15.75"

In winisd with two 4" ports I get a peak velocity of about 40m/s, what's the reason I got a different velocity?
I was also thinking of maybe doing a slot port on the side of the front panel. Because my enclosure will be fairly deep maybe I'll be able to make one without a bend (just to make it a little bit easier). How much clearance do I need from the end of the port to the back panel? I thought about a port of about 14.25"X1.77" which according to winisd pro should be 20.48" long.
If I'll have to bend the port do I measure its length in the middle of the port?

BTW do you prefer the measurements in inches? I'm used to metric.

I hope I didn't make calculation mistakes, it's after 2 a.m. - good night

 

[Mike P.]

Your numbers look right. 2 four inch ports 19.5 inches long will do the tuning. As for your high air speed, check the cone excursion graph. You have to add a HPF to keep the sub within its Xmax limit and that will reduce the air speed.

If you do a slot port, you measure its length through the center of the port.

 

[Inspiron]

How much clearance do I need from the end of the port (round or slot) to the back panel?
I ran the slot port height and width in winisd pro and beta and in the next calculator and each gave me a different length result (14.25"X1.8"):
http://www.carstereo.com/help/Articles.cfm?id=31

Which one is more accurate?
You've changed the port length from 21" to 19.5", why? Is it because I wrote that the gross volume will be about 210l? The net volume is still 200l.

What about the braces? should I just see what other members did and do something similar?

One last thing, is a rumble filter a real necessity or is it more of a safety measure? I currently have a ported shiva with 200W and I don't feel I need much more spl so I'm pretty sure I won't abuse the chaos.

 

[Mike P.]

For clearance it's recommended you stay one port diameter away from any surface
.
There are small variations in port length from program to program. Differences of 1 inch n length won't have any noticeable effect of the performance of the sub.

Port length should be 21 inches for 200 liters. I thought the net volume had changed to 210 liters.

Window pane bracing works well. Find a similar sized box and see how it was done.

As for the rumble filter, try the sub and see how it performs. That will tell you if you need the HPF or not.

 

[Inspiron]

And for a slot port of 14.25"X1.8" which has about the same cross area of the two 4" ports will a clearance of 4" be fine as well? Is there a rule for slot ports?

Thanks

 

[Mike P.]

Long narrow ports run the risk of port noise. 10" x 2.5" would be a better choice. 6" clearance should be good. Rounding over the ends as well as smoothing out the corners, if there are any, is recommended.