CurtPalme.com Home Theater Forum

[ecrabb]

Finishing... Definitely some lessons learned. #1: Don't try to use rattle-cans to spray something this size. They turned out pretty damn nice, but damn... Probably nearly $40 worth of rattle cans. Should have taken a photo of the PILE of overspray I swept off the floor. Can you say waste?

Makeshift spray booth


Primer


Texture coat


Coat of black


Baffle in black... Yeah, that's overspray in the bottom of the sub.


Drying. There's a little mottling from uneven coverage, but I don't think you'll ever see it in the theater even with the lights up.


Size reference. Yeah, they're kinda big. I think I'll call them "the twins" in honor of Art and Cliff's stack. This is probably as close as I'll ever get.


SC

[ecrabb]

[greg_mitch]

[tri_joel]

[ecrabb]

Thanks, Joel... When I moved the subs from the sawhorses to the furniture dolly, I picked them up by the bracing... So, we're talking probably nearly 70 pounds, or 35 pounds on each of my arms and the braces, and they didn't budge a bit. There are eight of those plus the simple cross-bracing in the center... I think I'll be OK.

SC

[Brad S]

Looking good! Can't wait to hear them.

[-Pjackso]

Ok,
Due to the lull in the thread, I thought I'd toss out a few more tid-bits:
...and possibly a recommendation.


Steve's goals:
1) The design goal was flattest frequency response I could get.
2) The sub needs to be able to run about 100dB or so.
3) Preferred: Flat in-room response down to around 18-20hz at around 101-102dB.


So, Let's look at what we've got so far...
The given hardware:
1) Dayton Audio RSS390HF
2) Box info: 1 Driver per box, sealed configuration, box volume (after bracing) is 8167 in^3
3) You're using a 500W amp per each box.

See pictures: Dayton single -1a and Dayton single - 500W.
We've got decent flat frequency response, with -3 db rolloff at 31 hz.
The max SPL is 114 db, with 105 db @ 20 hz - Driven at 500W,
As stated earlier, at 500 watts of power the speaker cone excursion exceeds manufacture limits at 37hz and below.
So the speakers are unusable below 37hz (at 500 watts). This requires active equalizer limiting, box size modification, or lowering power input to a lower wattage.

To keep the cone excursion within factory limits, the power amplifier needs to be reduced to about 200 watts.
This reduces max SPL to 110 db, with 101db @ 20hz.
See pictures: Dayton single - 200W.
If you use two subwoofer boxes (kits), you'll get a +3db gain in SPL. So 113db max, and 104 @ 20hz.


So far...
This design meets the stated goals.
Although, you need to be very careful about the power input - as it would be very easy to overdrive the subs and possibly damage them. (200W max, recommended).

[ecrabb]

Hey, you're back, Paul!

Yeah, your measurements jibe with mine, and you're absolutely right... 200w is about the limit with the large enclosure volume. After testing the first sub, I confirmed your (and my) initial suspicion that the amp would easily push the driver beyond xmax with very modest power inputs... It was fine with music (presumably because there was no signal much below 30hz), but throw in Dark Knight, and it was obvious that I could use less than a third of the gain knob.

Note...
Since I'm sure some would question the choice of 500w amp, I thought I'd explain... I could have saved $70 per plate amp ($140 total) if I'd gone with the O-Audio 300w amp as opposed to the 500w amp. However, I felt the 500w amps were worth it - even though I wouldn't be using some of the power - for dynamic power headroom, to have in case I decided to do something different later, and because the 500w amp has a single-channel parametric EQ and sub-sonic filter in addition to the 300w amp's simple LP filter. I thought all those factors easily justified the modest additional cost.

Anyway, after a little testing, I did decide to go ahead and reduce the internal volume. The enclosure is just too limiting to overall output, and I think it would be very difficult just to calibrate to prevent over-excursion. So, in the first sub (the only one pseudo-completed at this point), I used some temporary filler to reduce net internal volume to the 3.5 cuft ballpark. In the second, I'll build a "wall" into the inside of the second sub to reduce overall enclosure volume down into the 3.5 cuft ballpark. If that works well, I'll go back and do the same to the first.

The reduced volume will give me additional power-handling (350w ballpark, IIRC) at the expense of some extension, but the subs should be easier to calibrate and I'll be less concerned with the driver.

I also decided to go ahead with a long-term plan to pick up a Behringer DSP1124P. I should be able to dial down some negative gain in the 50-80 range, and achieve my desired goals.

Regarding the first sub which mostly complete... After the little bit of playing around I've done so far, having done zero calibration or level-matching - just playing around - this sub utterly DESTROYS my old subs. There is NO comparison. The old subs had so little output at 30hz, it was essentially non-existant. Now? It's rattling the door in the door frame. I can hear rattles I've never heard. It shakes the floor upstairs and sounds like a kid is in the driveway with the stereo system in his Civic cranking. Yeah, isolation fail. This is with ONE sub, mind you. Yes, this one single sub obliterates my TWO old M&K subs. At first blush, it's not quite as musical or accurate, but the output and extension makes up for it, and I'm hoping the musicality and integration improves once I've done some EQ and level-matching.

So far, I'm thrilled. Lots of work to do this weekend, though. Hoping to do some calibration tomorrow night with both subs, and I'll post my impressions.

SC

[-Pjackso]

Steve,
I've got some AWESOME INFO YOU YOU!!!!
I was playing a little more with WinISD, and I came across a possible modification that will have some ***HUGE*** enhancements.
If you're willing to modify the box just a little more...


Modifications:
USE THE SAME BOX!
1) Box info: ** 2 ** Drivers per box (IsoBarik configuration),
2) Add a port 4" diameter x 18" long (tuned at 18 hz).
(This reduces the box volume to 7928 in^3 after bracing **AND PORT**.)
*I also subtracted the volume of the internal driver. That's why the screenshot is slightly different. It doesn't change the results either way.


Results:
See pictures: Dayton IsoBarik -1a, Dayton IsoBarik -2a, and Dayton IsoBarik - 4.
We've got decent flat frequency response, but now with a -3 db rolloff at 18hz. (ALMOST 15hz LOWER THAN BEFORE!)
The max SPL is 109 db, with 107 db @ 20 hz - Driven at 500W.
Speaker cone excursion is safe down to 14hz - which is well below required usage. ...And that's using the full 500W power amp.
The port air-velocity stays below the 110 ft/s - so very little concern about port noise.

NOTE: I compared the IsoBarik 500W with the original configuration 200W. I did that because this is a subwoofer project - and the goal is to get down to 20hz (and be safe).
The original configuration 500W exceeded manufacturer limits and was not a real bullet-proof solution. ...Well, not without special work-arounds.
Hence, the original configuration 200W was the "Safe" approach that I used for comparative purposes.



This IsoBarik configuration is safe for the speakers regardless of how high the amp is turned up to. (max setting? oh Hell ya!)
...No need for active equalizer, No limiting the power, No limiting input signal, No worries, ...All smiles...


Let review the original goals:
1) The design goal was flattest frequency response I could get.
-The IsoBarik provides a "flat" response similar to the original, but the IsoBarik drops the flat range by almost 15hz lower.

3) Preferred: Flat in-room response down to around 18-20hz at around 101-102dB.
-The IsoBarik provides 107db at 20hz. This meets, exceeds, and blows away the expectations.

...Oh ya, the best part:
You only need 1 box in the theater to get the same SPL. (@20 hz you actually get a GAIN of +3db!)
...And did I mention "Bullet-proof"?

[-Pjackso]

Nice....
With the IsoBarik configuration, you can install a 1000 watt amp - and still be within Xmax limits down to 16hz.
...totally safe. MAX power, throwing whatever you want at it - .... TOTALLY SAFE.

(@1000 watts) Max SPL is 112db, with 110db @20 hz.
The port air-velocity raises above 110 ft/s below 22hz - so you might have some port noise. But only during the really low-hitting notes.
But then again, with the volume cranked up that high - you may not ever hear it at all...

I guess you could just add a second identical port, and it's back down to 82 ft/s. (Way below the 110 ft/s rule)
But I'm not sure it's worth the hassle.


EDIT: the drivers have a max wattage of 800 watts (500W RMS). So maybe 1000W would be a bit too much.

[ecrabb]

Thanks for doing that, Paul!

Hmm.... I've always been leery of vented enclosures because they're so damn hard to get right. I suppose I've heard so many bad examples of big, boomy, ported subs that have that one-note sound, it's hard to get that out of my head.

I have always been intrigued with isobarik alignments, specifically M&K's push-pull variation.

I do have a hard time getting my head wrapped around this, though... The idea that a single driver in this enclosure can easily exceed Xmax with only 200w, but adding yet another driver (with twice the mechanical power) AND cutting a hole in the enclosure will now allow the subs to handle so much more power. Where does the mechanical impedance come from? Obviously, I need to read up more on vented enclosures.

I'm really interested in checking this out, but definitely not in the short-term. I have this meet coming up in a week, so I need to have things wrapped up and performing well for that. Once that is over, and I get a few other things off my plate, I'll certainly consider this, though... Getting rid of an enclosure and selling an amp would be nice.

SC

[greg_mitch]

[-Pjackso]

DISCLAIMER: Make no mistake - I make NO claim to be an expert at speaker building.
All through High School and College - I couldn't build a speaker box to sound good if my life depended on it.
...That didn't stop me from trying - but that's mainly due because of being young and stubborn. (...not smarter)
Years ago, I finally conceded that making it SOUND good was black magic. ...and I didn't have the touch.

Then I found WinISD. I played with it some, tested some old projects, and I can work the basics (box 101).
I plugged in some of my old projects, and sure enough WinISD said "THIS SUX"! ...So it verified some of my past experiences.
I don't know WHY speakers/boxes works the way it does. ...But sometimes, you just have to say "I believe" - and move on.
(So I can't answer your questions....)



If you're wanting to do a quick and dirty test:
Un-mount the amp (but still connected electrically)
Build a wooden temporary plug (where the amp was) and mount the port in the plug. (if necessary, some of the port can actually protrude outside the box - i.e. NOT FLUSH with exterior)
Add the second woofer, ...and test it out.

If/when you test the IsoBarik configuration, I would appreciate your feedback in this thread.
I still have my subwoofers that I built from college (which sound awful) and I've been thinking of replacing them with another sub.
This project configuration looks DAMNED GOOD (on paper), and has got me a little stoked.
If you have the time - test it out with your sound meter and verify the response.


As for the second cabinet/amp:
If the IsoBarik works, then finish the second (ported) cabinet. I bet you could sell the cabinet and amp here at CP. (reference this thread of course).
You could recoup the amp, cabinet materials, and maybe some of your effort.
If you test the IsoBarik quickly (before the meet), you might be able to sell it ***AT*** the meet!

[-Pjackso]

I'm still interested in how this turns out, but as a fair comparison...
Is this sub-woofer a good value? Let's compare the costs:



***TOTAL*** materials and costs:
- Qty (2) - Dayton Audio RSS390HF, cost: $160 each, so x2 = $320 total.

- Qty(1) - Bash 500 watt subwoofer amp Cost: $239 here, or $239 there.

- Box materials: 2 sheets of MDF, wood glue, screws, misc... (Is 3/4"x4'x8' MDF $20 each?)
I estimated $40 for MDF, $10 for glue & screws. $50 total.

- Top coat finish: Paint? Vaneer? Stain?
I estimate $40 for paint.

-YOUR TIME is worth money. I know mine is.
Base your estimate on your ability and estimated time to build the box. Are you fast? slow?
How about $/hr for your free time: $20? $40? (How much would you charge your neighbor to build this for him? i.e. Price per hour) ...Or I think about it this way: How much would I pay to NOT have to do it? If you'd do it for free, that's fine too.
I estimate 12-20 hrs @ $15 per hour. Total labor: $180-300.


Ok so total costs are:
$320 + $239 + $50 = $609. (Drivers, Amp, and Wood)
+ $40 for topcoat = $649 (Or leave it bare if you don't care)
+ labor ($180) = $829 total. (Your time and cost may change)
So the range is $609 low-side to $829 high-side.

Let's keep the search to:
1) 18-20hz F3 rolloff,
2) approx 107db across full range down to 20hz.
3) $609-$829 or lower.
(Sub size, # of drivers, and wattage are negotiable, ...providing they meet the above requirements)
I'd even be interested in MULTIPLE sub-woofer boxes, providing the above requirements and meet - including TOTAL price. Note: Doubling the number of subs only increase the SPL by +3db.


Anybody know of any good competitors?
(107db @ 18hz is pretty good!)

[greg_mitch]

If you will accept a pretty dramatic increase in box size...the THT from Bill Fitzmaurice might do it!

http://www.billfitzmaurice.com/THT.html

[ecrabb]

I don't have time to go into all the detail right now, Paul... But, a couple of quick comments...

First, I wouldn't include labor in the prices... The reason is that this is a hobby - not something mundane. It's not mowing the lawn, cleaning the sewer line, or repairing gutters - it's something we enjoy... If you go down the "time is money" road, then a lot of DIY projects stop making sense financially. Even at a measly $20/hr, I can't even imagine what I "spent" researching, designing, and building my home theater!

However, in the case of the subs, I think they're pretty impressive even if you do include labor. Parts-wise alone, I had around $450 in each sub... Actually probably closer to $400. Since I'm only using half the amp's power, I could have substituted the O-Audio 300w amp for $60 less, or the PE BASH amp for even less, and put total parts cost under $350.

Now, the cheapest commercial sub that's even in the ballpark cost/performance-wise with ONE of the subs I built is probably the eD A5-350 at $800 shipped. 500w, ~4.7 cuft vented cabinet, -3dB point at 18hz... I don't recall the max SPL at 18, but I think I remember Ben telling me that 115-120dB in-room in the 25-30hz ballpark shouldn't be a problem.

Now, after getting these two subs running for the meet, I'm thrilled. I haven't done extensive testing yet - I just spent an hour or two playing around on Saturday afternoon with REW to try get response flattened out a little... But, between REW, a $100 Behringer DSP1124 (which I've wanted a long time, anyway), and a few filters, I'm getting >110dB at 30hz in my listening position, and still getting close to 100db at 20hz, and good usable response even at normal listening levels below 20hz.

I know the numbers didn't say the enclosures were ideal, and I'm sacrificing a lot out output for extension, but the amount of bass I have at this point is truly astonishing... The rear wall of the theater and the ceiling (floor of living room above) is moving, now... A lot. Large explosions or big bass notes are now moving the projector (and projected image). I don't think I'm exaggerating when I say the middle of the rear wall is probably deflecting 1/8" with large LFE effects. It's AWESOME. Considering I sold my old subs for $400, and spent less than $500 to do the upgrade...

I attached the graph from REW of where I called it "good enough" on Saturday. I set it up to handle reference levels (100/110) for "demo mode"... For where I normally listen (~ reference -15dB), I think I can set up another memory in the DSP1124 with a second set of filters and get the in-room response close to flat down to around 18hz @ 95dB, which is almost exactly where I wanted to be!

So, would your design have been better for the money? Maybe, though I'm pretty happy with how these turned out, and honestly - I do NOT need any more bass... Would a single sub's response have been as smooth in the room? Not sure, but I know the two subs sound a lot better than one.

OK, those comments weren't so quick...

SC

[ecrabb]

Greg's here... Greg was at the house on Sunday... What did you think? Don't worry about hurting my feelings... Seriously, what did you think?

If anything, I think my priorities at this point are now placement and treatment to try to even out response in the room...

Oh, it's worth noting... The response is better practically everywhere in the room as you move away from the listening position... The back row is probably another 3dB or so at 30hz...

SC

[WanMan]

But Paul is getting at something like what if I wanted you to make me a pair what would I be charged.

Mind you my time, even when I am wasting it, is about $45-50/hour. When I decide DIY vs. paying for it (even paying someone else to DIY) money speaks loudly in the stated rate of my time. Heck, wiping my butt is measured in this way.

[ecrabb]

I know what you're saying, Wan... But, looking at all your endeavors in terms of billable time implies there's an opportunity cost to everything you do. I don't know about you, but I *HAVE* to poop - I have no choice in the matter. So, to me at least, there's no opportunity cost. There's no way I can avoid wiping my ass, and I can't hire somebody to wipe my ass any more cheaply than I can do it myself, so there's no opportunity cost with wiping my ass like there might be with mowing the lawn, doing laundry, or some other menial task.

Back to the subs and something more serious... I can't or won't work 24/7, therefore the opportunity cost isn't "my usual hourly rate", hence Paul's suggestion of $15-20/hour, or even free if I so choose. I'd state "free"... Not because I'd do this for my neighbor for free (I wouldn't), but because I get a 100% time discount on hobbies I enjoy.

SC

[WanMan]

All I am saying is that I cannot find anyone willing to wipe my ass for $5-10 for every visit to the can.