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post #1 of 20 Old 03-16-2013, 01:02 PM - Thread Starter
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Hello,
I've been lurking around and doing quite a bit of research with the goal of building one helluva sub for my finished basement. We use it to entertain, watch movies, etc. so the sub will be used as part of a 7.1 system that is 70/30% for tv/movies / music. I am not an audiophile, but getting there. I am a musician and music educator. Sound quality is very important to me.
I am decently handy. I already have the enclosure designed and partially built: 9 cu. ft. (8.5 after bracing) MDF rectangular shaped, originally with the Dayton HF390 15" and SPA 500 plate amp in mind.
I am hesitant to continue as originally planned because I have some concerns. With my box partially built, (base, sides, and back) I am having the following issues:
Though the freq. response should be incredible with my design, unfortunately it puts the driver at 19mm xmax at 25 hz. This is with a 500 watt signal. At 300 watts, it puts the driver at only 15mm xmax at 25 hz. So...is this a legit concern? Should I consider the 15" Ultimax driver instead? For the price, nothing can really touch the freq. response of the HF390, but I can't afford to replace the driver if it is driven past its limits.
Also, how much more cu. ft. can I expect to "falsely gain" when I insulate the box? I have heard conflicting ideas as to how much the drivers performance is actually affected by acoustical polyester, insulation, etc. I appreciate your help in advance.
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post #2 of 20 Old 03-16-2013, 01:05 PM - Thread Starter
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Here's a photo showing where I'm at so far. Not too late to make adjustments. Why yes, it's going to be big. smile.gif
I'd like to eventually put 4" legs on it and use it behind our wrap around sofa as an oversized end table.

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post #3 of 20 Old 03-16-2013, 01:14 PM
 
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Quote:
Originally Posted by **OptimusPrime** View Post

Also, how much more cu. ft. can I expect to "falsely gain" when I insulate the box? I have heard conflicting ideas as to how much the drivers performance is actually affected by acoustical polyester, insulation, etc. I appreciate your help in advance.
You don't falsely gain anything, there's no such thing as a free lunch. Cabs are lined with damping to control internal reflections. If the Q is higher than 0.8 or so they can be stuffed to lower Q, to help tame humped response. The Qtc of your cab is .64, so stuffing isn't called for. But if anything the cab is too big, 6 cu ft will work just as well.
I wouldn't be concerned about the xmax. At 300 watts you'll seldom see actual content that would push it past xmax, let alone approach xlim.
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post #4 of 20 Old 03-16-2013, 01:30 PM - Thread Starter
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Thanks, Bill. I understand what you're saying. I guess I thought that maybe if the stuffing "tricked" the driver into thinking it was in a bigger enclosure, this would somehow help with the cone excursion.
But - if I have nothing to worry about - than I can proceed!!

So...300 watts, we're good. Would the 500 watt amp be too much?
I read comparisons between the Bash 300 and the SPA 500, and they are all mostly positive reviews.

Do you think the 500 watt amp is too much for this driver?

Thanks again.
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post #5 of 20 Old 03-16-2013, 01:37 PM
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the amp likely has a high pass filter in it around 20hz or so. no guarantees, but you are likely back to about 14mm at full power considering that.

Listen. It's All Good.
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post #6 of 20 Old 03-16-2013, 01:53 PM - Thread Starter
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So...I should probably just stop freaking out and just build the damn thing. Right? smile.gif
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post #7 of 20 Old 03-16-2013, 03:28 PM
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yeah, but also read up on sub placement and room modes.

you have a good driver there and a large enough enclosure for it to sound very clean, but rooms can have standing waves and resonances that make subs sound less than ideal. juts don't kick yourself if it doesn't sound quite right the first instant that you fire it up or the sound changes as you walk around the room (expected).

and use lots of bracing. :-)

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post #8 of 20 Old 03-16-2013, 03:46 PM - Thread Starter
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Yep. The bracing, I've got a good plan for that. And, I'll be sealing the heck out of it too. Amazing how MDF really stiffens up with good bracing and old fashioned carpenters glue. Used coarse 2" drywall screws and recessed them in, which really pulled the boards together nice and close.
I was gonna use painters caulk to seal, unless you can recommend something better.
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post #9 of 20 Old 03-16-2013, 05:40 PM
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the spec sheet on the bash 300 shows that it comes with a 17.7hz high pass filter built in with a minor amount of boost above that.

http://www.parts-express.com/pdf/300-750.pdf

caulk is fine, pl premium expanding super adhesive is another option.

Listen. It's All Good.
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post #10 of 20 Old 03-16-2013, 05:55 PM - Thread Starter
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Quote:
Originally Posted by LTD02 View Post

the spec sheet on the bash 300 shows that it comes with a 17.7hz high pass filter built in with a minor amount of boost above that.

http://www.parts-express.com/pdf/300-750.pdf

caulk is fine, pl premium expanding super adhesive is another option.

Hmmm. Interesting. I was looking at the SPA500 mostly because of its build quality, adjustabilty, and that it matches well to the specs of the driver. But, I have heard that it doesn't take much to power the HF390, so, I'm still kinda stuck with which amp to choose. Suggestions welcome.
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post #11 of 20 Old 03-17-2013, 10:38 AM
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the xmax in the spec sheet of the driver is around 14mm. 300 watts in your enclosure pushes that driver to around 19mm. the driver *should* be okay up there, but you wouldn't want to put more power on it unless you had some really good idea of what you were doing. :-)

does that make the decision easier?

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post #12 of 20 Old 05-05-2013, 03:30 PM - Thread Starter
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So...it's been awhile but I figured I'd update my original post with some pictures and let you all know that I completed my project!!

Here is a pic of the box with the legs. I actually used the legs as bracing, and it worked out amazingly well.
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post #13 of 20 Old 05-05-2013, 03:31 PM - Thread Starter
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The back cut-outs.
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post #14 of 20 Old 05-05-2013, 03:32 PM - Thread Starter
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And the front.
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post #15 of 20 Old 05-05-2013, 03:34 PM - Thread Starter
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Several coats of paint and good old-fashioned mattress foam.
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post #16 of 20 Old 05-05-2013, 03:36 PM - Thread Starter
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Driver, amp, and port installed!
Everything sounds/performs better than originally planned!!
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post #17 of 20 Old 05-05-2013, 03:52 PM
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Glad you like it. The leg concept was a great idea.

The purpose of listening shouldn't be to respond as much as it should be to understand.
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post #18 of 20 Old 05-05-2013, 03:56 PM
 
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Quote:
Originally Posted by **OptimusPrime** View Post

So...it's been awhile but I figured I'd update my original post with some pictures and let you all know that I completed my project!!

Here is a pic of the box with the legs. I actually used the legs as bracing, and it worked out amazingly well.
I don't want to be a downer, but your braces are placed where they're least effective, in the corners of the cabinet, rather than where they're most necessary, connecting the middles of the opposing panels. If you don't have any panel vibration problems all well and good, but if you do you now know what has to be done to fix them.
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post #19 of 20 Old 05-05-2013, 04:02 PM - Thread Starter
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Nope! No vibrations, buzzes, etc. Solid as can be! I was skeptical at first too, thought I would need more as you said. But man, did it work out well!! Couldn't be more pleased.
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post #20 of 20 Old 10-05-2013, 09:39 PM - Thread Starter
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It's been a while, but the sub is holding up just fine and has really been put to great use!! I trimmed it out and my wife ACTUALLY likes it! It currently doubles as an oversized end table behind our sectional sofa. Thanks to all who contributed their thoughts to my project.
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