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The One Millionth "My Sonosub Is Done" Post!


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#1 of 14 OFFLINE   BrianW

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Posted January 27 2001 - 08:53 AM

Okay, maybe this isn't the millionth one, but it seems that way. Posted Image

It's a flexy sonosub meaning that it is held together with three all-thread rods connecting all the pieces together. I took pictures during final assembly showing its design. I'll put a web page up soon, but in the mean time, here are a couple of pictures to drool over:

Posted Image Posted Image

It's a 190 liter Tempest sub tuned to 19Hz. It's 18" in diameter (tube) and 5' tall.

I just cobbled it together, but I can't calibrate or listen to it because the rest of my family is asleep (and sick) upstairs. The anticipation is killing me!!!!!!!!!!!
-Brian
Come, Rubidia. Let's blow this epoch.

#2 of 14 OFFLINE   Anthony F.

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Posted January 27 2001 - 11:56 AM

Congratulations! The workmanship looks great. If you get a chance it'd be nice to see some pictures that give the sub a sense of scale. It's hard to imagine the visual impact of a sub as tall as my wife. Posted Image

#3 of 14 OFFLINE   Patrick Sun

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Posted January 27 2001 - 03:24 PM

Is that enough gap between driver and bottom plate? I thought 3" is the minimum, and that's pushing it. Maybe I'm overly cautious.


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#4 of 14 OFFLINE   Greg Monfort

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Posted January 27 2001 - 05:00 PM

I hope you used some form of sealing, as just squeezing the pieces together won't make for an airtight design. Looks mighty fine though! Posted Image

Pat: the rule-of-thumb is that you need, at minimum, the equivalent Vd of the driver between the baffle and a parallel surface at whatever max p-p excursion is used, so assuming:

Tempest = ~173in^3 if Xmax isn't exceeded, or ~173in^2 if it is converted to an infinitely thin flat plate. Divide the baffle's perimeter into this value to determine the minimum. If it's ~20" in diameter, then 20*pi = 62.83". 173/62.83 = ~2.75" between the baffle/opposing surface.

Really though, the distance should be based on the driver's Xsus to minimze any additional distortion due to loading the squish area, while still having a small amount of help at Xmech if needed.

In his case, a minimum applies at the top also, and may need more than at the bottom, if it's a large/long vent.

GM


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#5 of 14 OFFLINE   BrianW

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Posted January 27 2001 - 05:28 PM

[quote]

I hope you used some form of sealing, as just squeezing the pieces together won't make for an airtight design.

[quote]The fit of the MDF plates is EXTREMELY tight. I could never have gotten it together (and I tried!)without the benefit of being able to torque everything in place with a long wrench. I had obtained O-rings to put into channels routed in the MDF, but the fit was too tight for them, so I left them out. But with a blank plate in place of the driver (and with the port plugged up), I was able to presurize it to 15psi (the lowest reading my gauge reads), and it held it there for three hours. I'm not worried about leaks anymore.

For further speculation, the port is a 6" PVC sewer pipe, 26" long. (Or is it 22"? I can't remember.)

Gee, I hope it sounds good! Posted Image
-Brian
Come, Rubidia. Let's blow this epoch.

#6 of 14 OFFLINE   Greg Monfort

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Posted January 27 2001 - 05:47 PM

Ok, the grooves help, but I guess I should have stipulated 'over time', as the rapid compression/rarefaction of the trapped air, which isn't the same as a constant pressure, should wreak havoc on the joints AFAIK due to the relative compressibility of the cardboard composite. Then again, the glue binder in the cardboard may keep it sealed if the wall clearances are very small.

It will be interesting to see how well it works, or how often you have to re-torque them. Posted Image

GM

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#7 of 14 OFFLINE   Patrick Sun

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Posted January 27 2001 - 07:42 PM

Thanks, Greg, for the info/formulas. It still "seems" too narrow, but, I'm sure Brian will give us a glowing review once he gets to play with it soon. Posted Image


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#8 of 14 OFFLINE   chris hunigan

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Posted January 27 2001 - 08:20 PM

BrianW, Nice job on the sonosub! It's nice to see someone who wanted to have a different look to their sub. Well mine is going to be very conventional. Hopefully, it will be complete within the next few weeks. For those who didn't remember, here are some highlights of what my sub is going to consists of: *(4) high excursion drivers (no it isn't a Shiva, nor PE DVC) *Sonotube is 30" dia x 48" high *I am going to use a black laquer for the end caps *The tube is going to be wrapped in a black "rib trim" cloth *I am going to add a base similar to your sub *GOAL: TO COMPLETE THE SUB WITHIN 2 WEEKS So this what I have planned so far. Overall, nice job and it looks great, based on the pics you sent. cree

#9 of 14 OFFLINE   BrianW

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Posted January 27 2001 - 10:47 PM

Thanks, everyone, for the comments.

Greg, thanks for your thoughts about leakage. You may be right about it leaking over time, and I didn't know that "sound wave leaks" could occur where "constant pressure leaks" defy detection. Thanks for the info. However, I'm pretty sure that even if the MDF/Sonotube barrier breaks down, the ends of the tubes are compressed really tightly against the overhanging red oak plates, and this is the barrier I'm counting on holding in the long run. I suspect that this seal will hold long after the MDF fails to stop leaks. And if the Sonotube itself shrinks or breaks down over time, I suspect I could torque the enclosure back to performance spec once or twice during the lifetime of the sub. Of course, since I've never done this before, I'm really only guessing. Posted Image Even so, it was interesting building a "Flexy" Sonosub, and if the design is a failure down the road, I can always convert it to a conventional design. (I have lots of Sonotube left over!)

As for the tube being too small, you're absolutely right. The design started out as a 12" Shiva enclosure, but when the Tempest subs became available for preorder, I couldn’t resist the temptation to "upgrade." Unfortunately, the 18" diameter tube maxed out my SAF credit, and I couldn't upgrade the enclosure. Alas, it's a compromise I must now live with. I tried to minimize the effects of the small-diameter tube by stuffing it liberally with fiberglass. (I also did this to dampen the all-thread rods, which I feared might "ring" since they are under considerable tension.) I hope it's effective.


Okay, I've been home a few hours, and here's my report:

After listening to sweep tones for two hours trying to adjust the x-over and find the perfect balance between boosting LFE and boosting bass redirected from the other speakers, I must say I'm very pleased. From 80HZ down to 22HZ, the response is flat, +- 3db. At 22Hz, it trails off until the response at 20Hz is -5 to -6db. I don't have any test tones that go lower than 20Hz, so below that, I have no idea what it can do.

After calibrating, I had time for just one or two scenes, so I picked the opening scene and Ice Crystal scene from Titan A.E.. As I turned the volume up during the THX trailer, I feared the worst since a number of people have reported subs bottoming out during these scenes. A few even said that they back off the sub's boost by 10db when they play this movie. Nevertheless, I threw caution to the wind and turned it up until the dialog was almost uncomfortably loud. I had my thumb on the mute button, ready to abort the test at the first sign of VC clattering. And all I have to say is…

HOLY BLESSED NACHOS!!!

This thing doesn't mess around!


NO sign of bottoming out, NO sign of distortion, NO boominess… just house-shaking, chest-pounding, brain-puddifying sonic bliss! I couldn't believe the volume at which I was listening to these scenes, and I had no idea that those ice crystals sounded so MASSIVE! Had I not heard it, I would not have believed that this soundtrack could be so loud, yet so clear and clean.

Breaking my promise not to shake the house after 11:00 PM, I also auditioned a few music CDs and DTS CDs, albeit at a much lower volume. To be honest, the transient response of this sub isn't perfect. But it's just barely noticeable as less than perfect, and only because I know this music extraordinarily well. But since this is my one and only complaint, and since the sub in every other respect has exceeded even my wildest dreams, I'm very happy.

Yeah, I know, everyone likes their Sonosubs. Everyone writes glowing reports about how their subs sound so great. No news here. But it is a HUGE thrill to finally experience what you guys have been talking about all these years. I finally understand the passion.

Thanks to all of you who educated and inspired me. You guys are the best.
-Brian
Come, Rubidia. Let's blow this epoch.

#10 of 14 OFFLINE   TerryC

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Posted January 27 2001 - 11:46 PM

Looks cool. Very different. What kind of wood did you use? Terry

#11 of 14 OFFLINE   Andrew Pratt

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Posted January 28 2001 - 07:59 AM

Congrats and welcome to our world Posted Image

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#12 of 14 OFFLINE   BrianW

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Posted January 28 2001 - 08:25 AM

Thanks, Terry. The exposed wood is .75" red oak, pickled, and finished with water-based poly. The black offsets are PVC pipe, painted flat black. There's one place on the port plate where I scratched the wood royally during assembly. I tried to sand it out, but it was too deep. Eliminating the scratch would have required power sanding the whole piece, restaining, and refinishing it - something I can't do now because of the weather, and something I don't have the patience to do a week or two down the road. Oh, well. I can live with it.
-Brian
Come, Rubidia. Let's blow this epoch.

#13 of 14 OFFLINE   Greg Monfort

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Posted January 28 2001 - 05:11 PM

>Greg, thanks for your thoughts about leakage. You may be right about it leaking over time, and I didn't know that "sound wave leaks" could occur where "constant pressure leaks" defy detection. Thanks for the info.
====
That's not quite what I said. Posted Image The high speed pressure differentials (pumping) should (in theory) weaken the joint over time, eventually causing a leak.
====
>And if the Sonotube itself shrinks or breaks down over time, I suspect I could torque the enclosure back to performance spec once or twice during the lifetime of the sub.
====
Agreed. I'm just curious as to how long it will take, if ever. Caulking it during assembly means never having to wonder. Posted Image
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>As for the tube being too small, you're absolutely right.
====
??? Seems big enough to me.
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>I tried to minimize the effects of the small-diameter tube by stuffing it liberally with fiberglass. (I also did this to dampen the all-thread rods, which I feared might "ring" since they are under considerable tension.) I hope it's effective.
====
This isn't a good idea, as it kills too much of the bottom octave's output, and the rods can't 'ring' because there's nothing in a sub at a high enough frequency to excite them.
====
>To be honest, the transient response of this sub isn't perfect. But it's just barely noticeable as less than perfect, and only because I know this music extraordinarily well. But since this is my one and only complaint, and since the sub in every other respect has exceeded even my wildest dreams, I'm very happy.
====
Since the cab volume is larger, and lower tuned than Q = 0.7, plus stuffed, further reducing Q, I find this a very interesting observation. Sounds like the room is affecting it too much. Are other locations an option? If not, then it could probably benefit from lower tuning.
====
>But it is a HUGE thrill to finally experience what you guys have been talking about all these years. I finally understand the passion.
====
Ahh! Another one with the hook sunk deep! Posted Image So when's the upgrade? Posted Image

GM

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#14 of 14 OFFLINE   BrianW

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Posted January 28 2001 - 06:21 PM

Greg, I can't thank you enough for taking the time to evaluate my project and to make such meaningful suggestions. Since I have the ability to take this thing apart, I plan on doing some experimentation to see if I can take advantage of your expertise.

As for the imperfect transient response, I found the problem. In my hurry to hear this thing, I hooked it up before my "proper" sub amp arrived by using a long-retired (and dusty) Yamaha integrated amplifier. I split the line level going into the receiver and each front channel output went to a VC on the sub. Unbeknownst to me, one of the fakey DSP theater/concert hall modes was still engaged. I didn't pick up on this at first because the only indication on the receiver's display was a single digit number identifying the DSP mode. (This thing is about 20 years old, mind you, so no fancy-shmancy displays here.) I turned it off, and Presto! Perfect Sub!

I couldn't be happier!

[quote]

So when's the upgrade?

[quote]
Funny you should mention that! I happen to have another Tempest driver just sitting around doing nothing, and I already have preliminary drawings of a new subwoofer and equipment rack that will be hidden away in the garage which is adjacent to the theater. My garage has a "work area" that can be walled up and claimed for just such a purpose. I've got room for about a 22 ft^3 sub, and the equipment will be neatly hidden away as well behind a hidden panel.

I'll get started on it right away!

...right after I finish watching a few movies.
-Brian
Come, Rubidia. Let's blow this epoch.




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