Speaker Related Projects

   Vector2
(A T-line and ribbon tweeter 2-way. August-2012)

   Polaris
(A tall, thin, upwards firing omnidirectional speaker. May-2010)

   Shiva_PR15
(A powered subwoofer using a 12" driver and 15" passive radiator. Jan-2010)

   Can-Less
(A computer speaker; redux. December-2005)

   Can-Can
(A computer speaker in a light canister. Jan-2005)

   Sonosub
(10" vented subwoofer in a cardboard tube, powered by a Parapix amp. May-1999)

   MTM Center Channel Speaker
(A Madisound design. Nov-1997)

   2-way Surround Speakers
(5" woofer and 1" tweeter. July 1997)

   3-piece mini system
(6" DVC bass module mated to 4" car speaker. June 1997)

   3-way Vented Floorstanding Speaker
(vented 10" woofer, 5" mid and 1" tweeter in a 4 ft tower. Summer 1995)

   NHT1259 Subwoofer
(A 12" woofer in a sealed architectural pedestal. Winter 1994-95)

   Inexpensive Speaker Stands
(Particle board, sand and spray paint. Fall 1994)

   2-way satellite
(6.5" woofer and 1" tweeter. Summer/Fall 1994)

Electronics Related Projects

  900 MHz Audio Receiver
(Better use for bad headphones. Jan-2008)

  Buster - A Simple Guitar Amp
(Perfect for the beginner. Jan-2010)

  A PC-based Audio Console
(Use a PC to play tunes. Jan-2010)

  LM-12 Amp
(Bridged LM-12 opamps. Aug-2003)

   CeeDeePee
(A CD player and FM tuner from spare computer parts. Oct-2002)

   Quad 2000 4-Channel Amp
(Premade modules by Marantz. May-1998)

   Zen Amp and Bride of Zen Preamp
(by Nelson Pass. Apr-1997)

Articles

  Backing-up LPs to CD-R
(Whiningdog.net 10-Dec-2002)

  Using Wood in Speakers FAQ
(Work in progress)

   MDF FAQ for speaker builders

   Woodworking Tools for the DYIer
(HomeTheaterHiFi.com Oct-1998)

  Some Thoughts on Cabinet Finished for DIY Speakers

   Large Grills Made Easy

   Some Parts Suppliers
(Outdated)

Other Useful Stuff

   DIY Audio Related URLs

  Veneering Primer
(by Keith Lahteine)

   How to get a Black Piano Finish
(by DYI Loudspeaker List members)

   Sonotube FAQ
(by Gordon McGill)

   Excerpts from the Bass List
(Oldies but Goodies)

DIY Loudspeaker List

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  DIY Loudspeaker List Archives

Shiva+PR15 Subwoofer

2-January-2010

Time flies! It's been over 6 years since I last updated this page. The subwoofer is done... sort of, and is now in use. Guess it's time to write it up!

The final configuration is downward firing woofer with a front firing passive radiator. Ideally, I'd use 2 PRs and fire them in opposite directions for balance but I did what I could with what I had on hand. Adire Audio is no longer in business and getting another PR15 and adding the same amount of additional mass was just more work than I wanted. As it turned out, the results are more than adequate. Power is from an Adcom GFA545 II amplifier. The LM-12 based amplifier is collecting dust and may be salvaged for parts. I never could get rid of the last bits of hum and unless I can think of a good use for it, I see no reason to even try to debug it further.

Final Design

The final design called for an 89 liter (3.1 cubic feet) box containing the Shiva woofer and PR15 passive radiator. The Shiva is a dual voice coil driver and both coils are made available for hookup. The PR15 has the same 726 grams of added mass (for a total of 1011 g). Using Adire Audio's LspCAD software, the modeled response is F3=28Hz and F10=17Hz. I could have lowered F3 by removing some mass from the passive radiator but that would also raise F10. It's a tradeoff of F3 vs. F10 and how much more work I want to do. I opted to leave the PR mass as-is.

Construction

This box was built using parts from the previous prototype. The new box is bigger so I kept the cutouts for the driver and PR and used that as the basis for sizing the box. Ultimately, the box topped out at roughly 18 x 28 x 15 inches before adding the final trim.

Internally, the box is heavily braced with shelves. The woofer is downward firing and takes up pretty much all of the room on the bottom. This meant the cabling terminals would have to go onto a side panel. The PR is left exposed on one side without any grill. The exterior is either painted black or veneered with Pau Ferro - a beautiful dark red wood. I've had this veneer for many years and this is the first time I've used it. A few month after I built the sub, I noticed that much of the veneer was cracking and peeling off the MDF substrate. The original veneer was very warped and required a lot of treatment to flatten it. Apparently, it didn't work. I have to go back and correct the finish.

Active Crossover

The subwoofer found a home in my living room behind the armoire that houses the TV. The big problem is that I don't own a "home theater" receiver through which the AV signals go through. All audio is fed to a 30 year old Technics SA-200 2-channel AM-FM receiver. Antiquated, yes; but I love the old gear with the analog tuning flywheel dial. And it's built like a tank and will likely outlast any other component I have. So I needed a crossover.

The Shiva driver is a dual-voice coil design and both coils are exposed for hook-up. I decided to only use one voice coil (for now). Power for the subwoofer comes from an Adcom GFA-545 II amplifier. I found this beauty at a garage sale for $10. It had a blown fuse in one channel that was fixed with a trip to Radio Shack. It's rated at 100 watts per channel into 8 ohms, 150 watts into 4 ohms.

The active crossover is housed in the same Stardent box that I used for my Zen preamp.

Internally, the active crossover is very simple. There are two parts to the unit - a power supply and the crossover circuitry. There are 2 sets of inputs in the rear - Left/Right line level and Left/Right speaker level. I used RCA jacks for both tpes of inputs (probably not a good idea but the connectors were readily available from Radio Shack and easy to retrofit into this case). There is a single RCA jack for the output (at the far right of the above picture, just off the picture).

The power supply is pretty standard - 7812/7912 pair to deliver +/- 12V from a small toroidal transformer. It is fused and wired to the existing power cord receptacle in the box. There are two power switches - one is on the side (at the lower right of the left picture) which was original to the case, and the other is a front panel push-button switch I added for ease of use. Both must be on for use. The yellow patches in the right picture is self-adhesive paper I added to act as an insulator - just in case something shorts out with the case!

The active circuitry is likewise pretty straight forward. A front panel four pole, double throw (4PDT) switch selects the input source. Speaker level inputs go through a voltage divider network. The selected input is summed by an op-amp then fed to two 2nd order Salen Key unity gain low-pass stages with a corner frequency set to 75Hz. The output is fed to a variable gain buffer controlled from a front panel gain/volume control pot.

The front panel has the power switch, power LED, gain, and input selector.

Results

It's great! We don't use it often; usually just for watching movies. But when it's on, you know it. The current speakers are my 2-way surrounds which were put into service for space reasons. They don't go that low so there's a dip in the response between the sub (75Hz) and the speakers (100Hz). I'll fix that when I have the time. For now, action movie just rock the house!


3-August-2003

It's been over 2 years since I made the first test box. I wasn't too thrill with its un-equalized response and the size of the box made it rather unappealing. The next step was therefore to shrink the box to about half the original size. Using the original box, I made a new one measuring 16-5/8 x 15-1/8 x 18-7/8 inches on the outside for an internal volume of just over 2 cubic feet (not accounting for the driver's and passive radiator's rear volumes). But that still wasn't quite right.

Here is the new smaller prototype box.

The real problem is that I don't really have a use for this sub yet. The original use for this sub fell through and so this project has had no calling. And so the new smaller box is partly to allow the drivers to be stored on a baffles while I decide what to do with it ! I placed the drivers in adjacent faces of the box mainly to allow me to place the unit in a particular place in my house for "temporary storage". The box is still nothing more than 3/4 inch MDF with absolutely no bracing of any sort. No attempt was made to "do the job right" since the probability is high that a new box will be built once a final plan is made. This box does however provide a reasonaly test platform for designing the EQ and crossover circuitry that will eventually be needed.

Like the sub, the amplifier for this unit has also languished. Here is the current state of the LM-12 based amplifier.


19-July-2001

I've owned a original Adire Audio 12 inch Shiva (not the Mark II) since 1999 and up until recently, it sat quietly on the floor in its original box. The only more lonely looking thing was the 15 inch PR15 that sat beneath it. Both cried out to be used but my original plans for a home theater subwoofer were stalled for various reason I won't go into.

As luck would have it, we had a need for a subwoofer in the office lab. This was the perfect excuse to use these drivers.

What follows is work in progress and may take some time for the whole thing to come together. The overall plan calls for a powered subwoofer using a passive radiator. A built-in equalizer will boost and flatten the low-end and allow for level of "tuning" to allow usage in both large and small rooms.

Prototype

The prototype is a simple box used to get up and running. It's the largest box I intend to use and during future tuning, I will decrease the volume of the box by adding blocks inside the cavity.

June 24, 2001

front of Shiva and PR15 Here is the Shiva 12 inch woofer (left) and PR15 passive radiator (right)

Back of Shiva and PR15 Here is the bottom of the 2 drivers. Note the space in the cardboard tube at the center of the PR15.

PR15 with added weight I added 726 grams of mass to the passive radiator by adding ninety (90) 3/8 inch zinc hex nuts with 4 ounces of wax. This is pretty easy to do. I melted two 4 oz of wax into a clean tin can by heating the can it in hot water. Layers of nuts were then added to the space in the center of the passive radiator and held in place with melted wax. Each layer was allowed to cool and solidify for a few minutes. Both the nuts and wax container were carefully weighed before use. When done, the wax container was weighed again to determine how much wax was actually used. Added to the original mass of 285 grams, the new PR has a moving mass of 1011 grams which is the upper bound of what I expect to have. The final mass will be determine through further tuning.

June 25, 2001

open box Here's what the prototype box looks like. It is made from 3/4 inch MDF and has internal dimensions of 30 inches (height) by 15 inches (width) by 13.5 inches (depth). This creates a volume of 3.5 cubic feet or 99 liters (not counting anything else that takes up space in the cavity). The small rectangular hole in the rear of the box is for the terminal cup. Another identical (unseen) hole is located just beneath it for a second cup (one per voice coil).

box with bracing For this box, bracing consists of just 3 dowels that tie opposite side panels together. Screws from the outside hold things in place.

wheels on the bottom of the box These four casters are supposed to make the unit easier to move. The sad truth is that they are cheap wheels and don't turn well. If they continue to bother me, I'll replace them with better ones.

June 26, 2001

terminal cup and wiring Here are the other parts that make up the prototype. Once installed, the wires were taped to the bracing dowel to keep them from rattling :)

prototype with test amp The completed prototype with a test amp sitting on top.

Prototype next to 1258 sub Here it sits next to my NHT1259 sub for size comparison.

Amplifier

The current plan is to build an amp using a pair of National Semiconductor LM12 power op-amps in a bridged configuration.

Equalizer

Details TBD

Real Box

The "Real Box" is the final box built. Its characteristics will be determined through testing of the prototype.

Details TBD

 

02-January-2010


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