CurtPalme.com Home Theater Forum

ecrabb · Posted: Wed Apr 13, 2011 3:10 pm Post subject:

-Pjackso · Joined: 31 Mar 2006 Posts: 791 Location: Oklahoma

Steve,
How did you take your SPL reading? ...and what is REW?
I'm curious how your readings would compare to what WinISD would show.... (as a means of validating how well the software works)
I know you used both subs (2 boxes).
Did you use the original 8167 in^3 box? Or the smaller 4000 in^3 box (effective volume)?
Can you estimate input wattage (per box)? 500W max! or 200W?

As for the costs:
I fully understand your "free" labor comment. I'm not trying to make your efforts sound like a bad investment.
You think it sounds bad-ass, your happy with the results, and you had a good time building it. Maybe in your mind - that's not a cost, but maybe it's a benefit! (sort of like model airplanes)

...Although, not everyone can say that.
So for the other people following this thread, and considering building the same - is it the best bang for the buck?
That's why I showed my math, and provided the costs "without labor" ($609 min), and "with labor" ($829?). You pick your number.

It's to give 'OTHERS' a ballpark $ figure to compare with commercially available sub-woofers.
For the total costs involved, can I go down to Best-Buy and purchase a sub-woofer (or 2?) that would provide equivalent results?

I think your subs look good. And I'd probably have fun building it too.
Congrats!

greg_mitch · Joined: 03 May 2006 Posts: 5320

ecrabb · Posted: Thu Apr 14, 2011 3:25 am Post subject:

Hey, Paul -

REW is RoomEQ Wizard... Awesome free software for acoustic measurement.

http://www.hometheatershack.com/roomeq

Most guys use REW for two main things: Measuring system frequency response and equalization to compensate, and for measuring room resonance (RT60), finding problem frequencies and mitigating them - with placement, acoustic treatment, or with equalization. It uses a sweep sine wave and

I used REW with a Radioshack SPL meter, and the calibration file that goes with it. There are much more accurate measurement mics, and I may upgrade to one at some point, but this was good enough for now.

If you wanted to compare the built cabinet with the WinIDS plots, you'd need either an anechoic chamber, or you'd have to go outside in a big open back yard or something, and take calibrations from a calibrated mic at 1 meter. I'm not so interested in that... It's academic, anyway... If the T-S parameters for a given driver are accurate, then the WinISD models will be very accurate. It's pretty simple math, actually.

But yes, I used two boxes (and two amps), so +6dB over a single sub/amp. I did reduce the volume of the boxes (with an internal baffle) to get net volume back down to the 3.25cuft/5600cuin ballpark. According to the numbers, it's still a little big for max SPL, but I'm not gong for max SPL... I can use the EQ to dial back the really low-frequency stuff when I want to run in "demo mode", and let it breathe a little running at normal listening levels.

I'd estimate I'm using right around 250-300w of the O-Audio 500W plate amp. With that driver in a large enclosure, you can easily get by with the 300w amp... Especially with two of them. That's why I say you can build these bad boys for under $400 apiece (for everything) if you wait for one of the sales that run practically every month at Parts Express.

Given that price and the performance we're talking about here... No, BestBuy doesn't have anything remotely comparable. Might be a couple of good 40hz output, and decent 30hz output, but nearly 100dB in-room at 20hz? No way. There just isn't much like that in the mainstream audio market.

Subs with the performance we're talking about here are almost exclusively built by specialty vendors that cater to the HT market - companies like HSU, SVS, Elemental Designs, Epik, and Seaton Sound. Many of those subs are capable of good sub-20hz output, but most come with price tags in the $1500 ballpark. Seaton gets two-large for the Submersive!

If you have the money to drop on a sub like a Submersive, it's worth every penny. If you don't have that kind of money, but you still want really high-perforamance LFE, not only is DIY an option, it's the only option.

SC

ecrabb · Posted: Thu Apr 14, 2011 3:33 am Post subject:

MikeEby · Joined: 24 Jun 2007 Posts: 5237 Location: Osceola, Indiana

ecrabb · Posted: Thu Apr 14, 2011 4:10 pm Post subject:

I thought about doing that at one point, Mike... But, I don't think my center would even fit between the screen and ceiling, and even if it could, it would probably sound like ass for everybody being crammed right against the ceiling... At least yours has some room to breathe.

Doesn't it sound weird coming from so far overhead? I mean, that's WAY outside the plane of the mains...

SC

MikeEby · Joined: 24 Jun 2007 Posts: 5237 Location: Osceola, Indiana

ecrabb · Posted: Thu Apr 14, 2011 6:59 pm Post subject:

Heh heh... Sorry, Mike!

Hey, at least AT is an option for you! My room just isn't big enough. I'd have to move the projector AND lose three of my six seats. I just don't have the room for a 2-foot deep false wall.

Next house, next room...

SC

greg_mitch · Joined: 03 May 2006 Posts: 5320

ecrabb · Posted: Thu Apr 14, 2011 7:01 pm Post subject:

I agree with Greg... Having been in several rooms now (from reasonable to über-expensive) with AT/scope setups, I truly think it's the new standard in HT.

SC

WanMan · Joined: 19 Mar 2006 Posts: 10270

I do not think I can ever go back to anything but AT/scope.

-Pjackso · Joined: 31 Mar 2006 Posts: 791 Location: Oklahoma

Hi Steve,
Ok, I just plugged in the info into WinISD Using:
1) Dayton Audio RSS390HF
2) Box info: 1 Driver per box, sealed configuration, box volume (after bracing) is 5600 in^3
3) 300W amplifier per each box.

The frequency response is very similar to the 8167 in^3 boxes. The -3db rolloff is still at 32hz.
Using the smaller (5600) box at 300 watts (max), the Xmax (cone excursion) stays within limits. So looks good there!
...but it is really moving at 30hz and below.

Just out of my curiousity, I compared your REW readings to the WinISD model. The two are really close, and illustrates the slight driver/room interactions.
It shows (to me) that the WinISD model is fairly accurate to real world results.
...Although, when you did the REW reading - did you only use (1) sub for the reading, or both?
The results are right in line for (1) sub, but doesn't show the +3 db increase ***IF*** you used (2) subs. Imagine the green line moved up 3 db.
(Ok, wait a minute. Due to the magnitude of the Y-axis scale - it wouldn't move much. So nevermind.)

Summary: 32hz F3 rolloff, approx 108db down to 32hz, (-7db at 20hz, ouch!).
Building two boxes will not help the F3, but WILL increase the SPL.

Total costs for ONE sub is:
$160 + $150 + $50 = $360. (1-Driver, 300W Amp, and Wood)
+ $40 for topcoat = $400 (Or leave it bare if you don't care)
+ labor ($150) = $550 total. (Your time and cost may change)

So just like you said, you could build one for $400~ish if you don't count the labor. Or even cheaper if you find the equipment on sale.