Some Design Help Please!

[bri1270]

Hi All,

I've been lurking for a while trying to take as much in as I can before actually posting a question. I am NOT a math guy at all, so some of this stuff is making my head spin.

I eventually would like to go with an IB, but I'm really not up for ripping into my wall right now, and there may be a problem with the location of my mains (they're only a foot from the wall where the IB would go).

I'm using Ascend Acoustic CMT340's for my mains and center. My room is 16x16 with an 8 foot ceiling which is actually a loft that extends about 2/3 over the listening area and then opens up to about 24'.

Right now I have an Earthquake Kompressor S12. It's a pretty good sub for $370 shipped, but I can't help but want more after reading all the DIY acclaim. What I am thinking of doing is using an Ascendant Atlas 15 with an O-Audio 500W BASH Amp. I'd like it to be musical, but I really want some good slam for movies. My EQ actually does a pretty good job at both for a sealed sub.

My thought was to get the Atlas 15, so that later, if I do decide on an IB I just need to get another one, and start ripping apart the family room (which I just finished remodeling last spring).

I can't seem to come up with a viable enclosure using WinISD. It's probably my steep learning curve.

I think I am entering the T/S parameters incorrectly or something.

Anyway - box size isn't all that much of a concern, but I'd like to keep it reasonable (2x2x3 or so). I have no preference as to sealed or ported, as long as you can tell me what the port diameter and length needs to be. If a ported design is suggested, then I would also like it to be a front firing design, as I get the best reponse in the front right corner, but a rear port definitely gets booming (which is why I went with the sealed EQ). If there's anything I can add to help someone help me then let me know.

Thanks,
Brian

[Tweeker]

Atlas 15 in 2*2*2 cube, tuned to ~19hz with 2 4" diameter ports 19 inches long each perhaps? Dont give it more than ~300watts, cant bottom the voice coil but can cook it.

[DougL]

There is a sugested Sealed box for Q=.5 that looked sweet on the AA website. There is also a ported allignment.

I have no reason to beleive that the box volumes are not "spot on" unless you want something very unusual.

YMMV

Doug

[bri1270]

Thanks Tweeker and Doug. I saw those recommendations, but I wasn't sure about the tuning portion of the vented box. I like output on both so I guess it comes down to personal preference.

At 20hz the ported sub tuned to 19hz is at 88db and the Selaed with a Q of 5 is 86db but the sealed sub seems to keep up within 2db or so all the way down to 10 at which point the sealed is actually 3db higher than the ported sub. I thought the opposite was supposed to be true?

If a sealed sub is producing good bass at the levels I want, isn't that the way to go because of "clarity" for lack of a better word?

Thanks Again for your help.

[bri1270]

One last question on the Amp portion. I like the O-Audio because it has the built in parametric Eq. But I also like the Parts Express 250W amp because it's $128 and I won't overpower the driver. That being said, if I went with the O-Audio, and kept the gain in check, would that prevent a meltdown of the voice coil? Also, I've seen in other threads something about staying away from "bass boost," why is that?

Thanks,
Brian

[Tweeker]

Ported subs roll off quickly below tuning frequency as the driver becomes unloaded. Output just above tuning is higher though. Are you sure your read the 6.5 cu foot sealed box graph correctly? I see 82dB for it @ 20hz, vs 88dB ported. At 30hz 91dB ported, 87 sealed. Also the ported sub has half again the power handling for a smidgen over 1 more dB.

Yes if you keep the gain down youl be fine with the O-Audio. Id suggest looking at the 350 watt Rythmic Audio amp for $160.

Edit- bass boost can cause you to quickly run out of excursion, it may sound wretched doing it but you cant hurt an Atlas sub this way as the magnet wont allow the voice coil to bottom out.

[bri1270]

Sorry I was looking at the .57 Qts with a 7.8 cubic foot box. That Rythmic Amp looks like a pretty good deal. Would you reccomend adding the LT to the amp? Or just get the 350 Basic?

[Tweeker]

Ah, I see, I got confused, I was looking at the sealed enclosures that had .57q, rather than the ones where the driver had .57q.

Theres soo much you can fiddle with on Atlas subs. Actually you could even switch back and forth between the 7.8 cu foot .57 qts driver setup and the ported alignment I suggested just by blocking the ports and changing driver q, or aperiodic by putting a sock in it.

I dont think you need LT given how much box size you have to work with and the Atlas drivers flexibility. If you want a great parametric eq look at Behringer Feedback Destroyer Pro $100.

[bri1270]

Thanks Tweeker

[simon5]

The Atlas 15 seems to want a really big box to be flat down low.

Since you are limited by 2x2x3, I would go with 10 cu.ft internal tuned to 18.4 Hz using two standard Precision Port 4" diameter ports with full length center tubes. I would also use a Rythmik Audio 350W amplifier since you can't use more than that to stay into linear excursion.

Brace the box correctly and you will be satisfied, especially if you put that box in the corner.