Obi's Tower of Power!! **Updated (new pics)** (1 Viewer)

[Robert George]

They say that necessity is the mother of invention. Well, I just invented one mother of a subwoofer...

In this case, the necessity was to get one of my SVS 25-31CS subs out of a corner and still be able to place both subs on the same side of the room. You see, the corner loading with two subs side by side was introducing some nasty room modes and some serious humps in the lower frequencies. In moving the subs around, I discovered, with the expertise and encouragement of Mike Knapp and another chum with just as accute hearing, Ken Gunlock, that my low bass was overpowering my mid-bass and midrange frequencies and totally muddying up my soundstage. This was much less of a problem with movies than with music, however, with the recent upgrade to some beautiful sounding B&W Nautilus 804 main speakers, my music reproduction has become far more critical.
I've been kicking around the idea of stacking two SVS subs for some time, though not for this reason. My original idea was to use TWO two-sub stacks in a larger theater room so one could get four subs in a room without some of the placement problems that goes with such a configuration. I decided to make a practical application out of my idea with my two subs to see if it would solve the placement problem I had in my room. This is what turned out...

Here's a closer look at the joining of the two subs...

The resulting sound, I am very pleased to report, solved my problem. My bass cleaned up nicely and I didn't lose any impact on movie soundtracks. Music sounds way better. I don't know if I can recommend this application to everyone, but for the record, my wife prefers the "tower of power" over putting one sub on either side of the mains.

 

[rodneyH]

I noticed you have the 804s, I am consirering purchasing a SVS, but haven't decided one a 20-39 or a 25-31, If you were to only have 1 sub, would you still opt for the 25-31, or a 20-39???
btw, I am running cdm7nt (similar characteristics to 804)

 

[Trevor Schell]

I love it!
Looks like you just took off the top grille and added three extra spindles.
Shouldn't be too hard to do.
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Trevor..

Link Removed Sonically Enhanced
*Outdated new pictures
due to recent upgrades!
**Equipment list current

 

[Will]

Obi --- you still live in northern California?
I was going to ask if you were worried about an
earthquake knocking down your tall stack, but then
remembering that the stack consists of subwoofers
thought better of asking that question.

 

[John Morris]

OBI: Cool! It has been suggested but it took YOU to actually do it nicely! It looks like you also left the 4 inches recommended to avoid port compression too!
Are you powering them as independent subs or in parallel or in serial connection? Are they 20-39cs units, or the smaller subs?
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Take Care,
merc
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Link Removed
God Bless America!!!

 

[Robert George]

John:
My subs are rather unusual. They started out as 25-31s, but Tom made me a custom port to lower the tune to around 22Hz. Then, the drivers have been upgraded to the same driver used in the new Ultra. The two subs are still being powered independently (Samson S1000).
Rodney:
I personally would recommend the 25-31 for its higher output in the 27-35Hz range, however, the 20-39 would probably do a fine job as well in most rooms. Also, you should consider what type of music you listen to most often. The 20-39 will go a bit lower than the 25-31, but at the expense of a few dB in what I consider a critical frequency range. Maybe ask SVS if they can provide you with custom porting for the 25-31. That would lower the tune and you would still lose a little around 27-30Hz, but not quite as much as the 20-39.
Trevor:

Looks like you just took off the top grille and added three extra spindles.

Pretty much. The spacers (spindles) are 3 5/8". I used a 6" carriage bolt up from the top plate of the bottom sub. That was enough top go through the top plate of the bottom sub, the spacer, and the bottom plate of the top sub with a hex nut to hold it together. There is a bit more to it the way I did it, though.
The port has to be removed to get to the underside of the top plate. The bolt is held in place with a hex nut (tightened). The spacer is drilled so that the bolt goes all the way through and there is a space drilled in one end so the spacer sits flush over the hex nut. This is done by drilling a 1/2" hole about 1/4" deep then centering the 1/4" hole all the way through. The base plate should be removed from the top sub so the holes can be lined up. Replace the base plate after pre-drilling the holes. Line up the bolts to the holes in the base plate of the top sub (two people recommended) and attach with hex nuts. You would want to paint the spacers before assembly.
Will:
I'm a Florida boy. Not too many earthquakes around here (except the ones I cause

). However, I figure it will have to be a pretty bad flood for me to lose both subs

.

 

[Bruce Hedtke]

Obi,
Very cool and professional looking. I am green with envy.
Bruce
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Welcome aboard the Satellite of Love

 

[Mike Knapp]

I notice that the mains are away from the rug again....dont make me come back up there!
Mike

 

[rodneyH]

tom, you have mail

 

[DonnyD]

SVS is great at everything .....
This is proof that they will go to great lenghts and considerations to keep their users happy. Thanks TomV and Ron for being who you are and for having a product that pleases most of us regardless of price.
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"I am part of all that I have met, yet all experience is an arch wherethru gleams that untraveled world whose margin fades forever and forever...."

 

[Robert George]

Thread edited to return it to original topic.

 

[Robert George]

I've been talking to Tom V. and he has made some suggestions and I've had another idea myself. I'll be posting some pics of the "Tower of Power" Ver. 2.0 in a couple of days. Same basic design, but with a couple of design changes to improve asthetics and, as it turns out, improve (measurable) performance.

 

[Jack Gilvey]

One thing that Dr. Hsu has recommended for years for his TN line is tying them together end-to-end and remounting the woofers in push-pull, cancelling out "reactive forces" in the enclosures and cutting even-order distortion in half.
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[Tom Vodhanel]

push pull is cool, but while it is generally known to lower even orders(due to motor non-linearity)...it's hard to predetermine exactly what the reductions are going to be.I don't think you could assume a 50% reduction across the board though...maybe on paper. And since it's the ODD harmonics that are the bad guys anyway...
reactive cancellation is something else...not related except incidentally. What you're talking about here is...when the driver moves one way, the baffle(enclosure)it's mounted to will try to move the other way. If you have one large enclosure with 2 drivers moving in OPPOSITE directions...the reactive forces will tend to cancel. This holds true for PRs too. In this case, the more resistant the subwoofer design is to these reactive forces...the less you'll gain by implementing it as a modification. I agree, the TN series will benefit. I don't think the SVs would benefit nearly as much though.(I know you know all this JG---just trying to clarify for any lurkers).
TV

 

[Jack Gilvey]

I know you know all this JG---just trying to clarify for any lurkers

Always a bad assumption. I always learn something from your posts, thanks for the excellent explanation.
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[Chris White]

Robert, you should make up a list of possible answers to the inevitable question, "What the heck is that!"
For example,
1) It's an air purifier.
2) It's an antenna.
3) It's a security device. That's all I can say.
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http://www.bus.ucf.edu/cwhite/theater/theater.htm

 

[John-D]

.. reminds me of Shrek
"Do you think he's trying to compensate for something...??"
.... just a joke Robert.... just a joke..

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The things we own end up owning us

 

[Robert George]

Chris:
It is a security device. That's all I can say.

[Edited last by Robert George on September 25, 2001 at 09:33 AM]

 

[Jack Gilvey]

Robert, you should make up a list of possible answers to the inevitable question, "What the heck is that!"

How about: "I don't know, but it's damn happy to see me!"
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[BryanZ]

Robert, you should make up a list of possible answers to the inevitable question, "What the heck is that!"

Why? Do you wish you had one?

Or the other ever so popular answer: I could tell you but I'd have to kill you.