Basic question about subwoofer build (sanity check)

[boinger]

So I have a entertainment center that is roughly 84" x 40" x 20".

I wanted to build a sealed subwoofer with the same dimensions underneath that. And put all the electronics on top. One would this damage the electronics?

Two would that be too big of an enclosure? Comes to something like 38.9 CF

I am looking at the UM-18 from parts express.

Should I use 2 maybe?

I plugged it into winisd and it looks very smooth fall of to a f3 of 23hz

But I really don't know what I am doing in all these design tools. So someone smack me if I'm wrong.

[Bear]

The magnetic fields won't hurt, but vibrations over time might. Adequate bracing would be good. Depending upon your goals, 2 - 4 big subs could fit in that space and still leave plenty of room for electronics. Depending upon the sub and enclosure, 2 - 8cf is plenty for each unit (e.g., a Dayton 15" HF needs ~3cf sealed, fully stuffed).

I haven't modeled a UM18, but it won't be an order of magnitude bigger, unless you go with a ported cabinet. Unibox or some other modeling tool will help you work through various scenarios.

[boinger]

Oh I think you misunderstood.

The rack that is 84" x 40" x 20" is going to sit on top of the sub I wanted to build a box with the same rough dimensions.

84" x 40" x 20"

And put that underneath, are there any cons to building a sub box that big?

[Bear]

Oh I think you misunderstood.

The rack that is 84" x 40" x 20" is going to sit on top of the sub I wanted to build a box with the same rough dimensions.

84" x 40" x 20"

And put that underneath, are there any cons to building a sub box that big?

Moving it. People do all sorts of fun things with subs if they have the space (horns!). Look at total cone area (really piston volume -- area times stroke) and count amp channels. Multiple subs will work better than a single sub, but the incremental cost usually starts at high and climbs rapidly.

In other words, if you do it well, the only real downside is that you're creating something bulky and heavy.

[1Michael]

The size of the box is dictated by the driver {s} you are using. You do not have to use the entire volume for the drivers that you model.

[Philzeemon]

Had built 2 sealed cabinets for ultimax 12's,.... Those dimensions would be huge for a sealed setup-(IMHO)-

[boinger]

Could someone help me with a sanity check I think I got everything right in winisd.

Edit: I guess can't upload winisd files I configured my enclosure at 12.7 cf with a tune of 16hz.

3 vents at 2.5" x 9"

Filters para eq 16hz, q=2, gain= 2.8db

lowpass buttenworth n=4, fc=110hz

highpass butterworth n=1 fc = 14hz

para eq fc 35hz, q=2, gain = -0.4db

Also for the bracing does it have to be this style of bracing or can it just be like 2x1 sticks?

That would be much easier. I couldn't find much information on bracing.

[1Michael]

Bracing is a matter of personal preferance. The bracing pictured would be the best choice however 2x1's will work just fine.

[rick844]

Your box design is interesting. What are the overall dimensions?

[boinger]

Your box design is interesting. What are the overall dimensions?

The box size is H 24 x W 30 x L 40

Planning to use it as a side table.

[TEK]

What is the thickness of the cabinet walls?
When it comes to bracing, with a cabinet that big it is quite important to have good bracing, meaning that the breacing should lock off the cabinet in all directions.

[boinger]

What is the thickness of the cabinet walls?
When it comes to bracing, with a cabinet that big it is quite important to have good bracing, meaning that the breacing should lock off the cabinet in all directions.

I am planning to use 3/4" MDF or 3/4" baltic birch. Not sure yet.

[boinger]

Anymore advice or does the design look good?

Here is the modeled response.

The red line is the ported version.

[fbov]

Bracing: Rule of Thumb is a cross brace every 8-10" across all surfaces. Problem with pole braces is getting both ends tight to the wood. Frame braces have more contact area for gluing, but add a lot of mass.

Isolation: I would not mount electronics on a conventional subwoofer. Plate amps are made for it, and it's too easy to isolate. Look at any of the subwoofer isolation products.

I have a big TV sitting on a subwoofer, but it's vibration isolated (springs). Overkill for your needs.

HAve fun,
Frank

[Evil Twin]

Could someone help me with a sanity check I think I got everything right in winisd.

Edit: I guess can't upload winisd files I configured my enclosure at 12.7 cf with a tune of 16hz.

3 vents at 2.5" x 9"

Filters para eq 16hz, q=2, gain= 2.8db

lowpass buttenworth n=4, fc=110hz

highpass butterworth n=1 fc = 14hz

para eq fc 35hz, q=2, gain = -0.4db

Also for the bracing does it have to be this style of bracing or can it just be like 2x1 sticks?

That would be much easier. I couldn't find much information on bracing.

[ATTACH=CONFIG]29557[/ATTACH]

[ATTACH=CONFIG]29558[/ATTACH]

While you mentioned planning to build a sealed subwoofer, perhaps we should point out this is a bass reflex enclosure with a folded port; the port entry at the back and exiting the front.

[boinger]

While you mentioned planning to build a sealed subwoofer, perhaps we should point out this is a bass reflex enclosure with a folded port; the port entry at the back and exiting the front.

Yes the original sealed enclosure plan was supposed to be around 40CF. But when I was calculating the weight via MDF etc. it seemed rather impractical so I changed to a ported design for louder spl at a lower frequency. According to the model.