A dedicated powered subwoofer for mid-sized listening rooms
Discontinued, here for archive only
Conceived of as a mini-tower style subwoofer that can be used either as a stand or in stacks, the Thunder subwoofer is build around the spectacular Peerless XLS-12 woofer, XLS passive radiator, and the North Creek 250 Watt dedicated subwoofer amplifier.
The Peerless XLS-12 is ruggedly built, with a cast aluminum frame, stacked double-magnet motor, paper cone and rubber surround. Both the cone and voice coil are vented to facilitate cooling, and the pole is extended well above the top plate to keep cone motion linear and prevent gap jump. The cone is capable of 24mm peak-to-peak excursion.
The XLS-12 passive radiator is built on an identical platform and is capable of over 30mm of peak-peak excursion.
The core of the system is the North Creek Dedicated Subwoofer Amplifier. It is a discrete 250 Watt class AB amp designed with 6dB of bass boost at 23 Hz and an integral third order roll off below 20 Hz. The amplifier also has discrete phase and low pass frequency selections, which are precise and much better sounding than the continuously variable adjustments one finds on most subwoofer amplifiers. Stereo and mono inputs are provided for low-level (via gold-plated RCA's) and high level (via heavy duty gold plated binding posts). The North Creek Dedicated Subwoofer Amplifier is the only plate amp on the market that surpasses all of the DST/Peerless performance requirements.
The Thunder cabinet has a net internal volume of 35 liters (overall internal volume is 41 liters). Ladder bracing is employed to stiffen the side walls, while the front and back are a double-thick MDF/Plywood laminate. The cabinet is extremely stiff and weighs in at a hefty 48 pounds.
Thunder Normalized Amplitide Response
This system was designed to reproduce the deepest bass with authority. By carefully optimizing the box volume to perfectly match the passive radiator tuning and amplifier bass boost, the Thunder has flat response down to 20 Hz. Furthermore, the even at its maximum of 250 Watts, the amplifier can not overdrive the XLS-12 woofer. Because the amplifier has 6dB of boost at 23 Hz and a built in third order high pass filter below 20 Hz, the passive radiator is about one third lighter than would be required by an unassisted alignment, while at extreme low frequencies both the passive radiator and woofer are protected from overexcursion.
Thunder Cone Displacement
The Thunder can reproduce bass down to 20 Hz at 105dB and do so cleanly.
North Creek Thunder Subwoofer Kit
Includes the Peerless XLS-12 subwoofer driver and XLS-12 passive Radiator, North 250-Watt Dedicated Subwoofer Amplifier, connectors, genuine DuPont Dacron stuffing, grill fasteners, all required screws, North Creek Big Toe spikes, gasket tape, power chords, etc. Everything except the wood.
Discontinued, here for archive only
I originally undertook this design after reading the Peerless Application Notes on the DST web site. This is good reading for anyone considering building a serious subwoofer. The link is under "Engineering".
The Peerless engineer's goal was to build a woofer that when used in a correctly sized cabinet with a port or passive radiator, could achieve 105dB of SPL at 25 Hz without destroying or overheating the driver. The Peerless engineer came up with an alignment for their XLS-12 woofer and 625-gm passive radiator in a 35 liter box that achieved this goal. The trade offs for this simulated system is that it would be low in efficiency (requiring over 300 watts of amplifier power, beyond the thermal limit of the woofer), that the passive radiator - with a cone of nearly a pound and a half - would be slow, that the suspension may be liable to warp over time, and that some sort of external filter was required to prevent the system from going out of control from any input below 20 Hz.
The DST simulations were done with HT Audio's very powerful "Bass Box Pro" software, and excellent simulation package. Two limitations of this software are that it does not allow the user to specify parameters of an external filter when used with a passive radiator system, nor can the user specify the exact frequency response contour of an external filter when used with a vented box system. This made simulations difficult as the North Creek Dedicated Subwoofer Amplifier does not fit any of their models. None the less, after working with the software for some time, routes around these issues were discovered and it became possible to apply our amplifier to the simulation and come up with a superior system.
The problem with the original Peerless simulation is that the tuning was so low that the passive radiator became too heavy to be well controlled, and so much amplifier power was required that the driver became at risk. Because the North Creek Dedicated Subwoofer Amplifier has 6dB of bass boost at 23 Hz and a third order roll off below 20 Hz, we were able to use a much lighter passive radiator and a slightly larger cabinet to get flat frequency response to 20 Hz, while still keeping both the woofer and passive radiator below their excursion limits. We were also able to get higher SPL with less amplifier power, which keeps the woofer within its thermal envelope. The key was to perfectly balance the bass boost, box volume and passive radiator tuning in order to protect the woofer. The third order roll off below 20 Hz is critical in keeping the system stable.
A simulation is not reality. I was a little apprehensive when building the prototype that I may have made an error circumventing the HT Audio software, and would be spending the near future blowing up $150 woofers. Most 12" woofers would not be stable under these excursions, regardless of what the software implies. The Peerless XLS-12 is better than most because its pole piece is extended beyond the forward excursion limit, and should be stable even at 250 Watts.
When all was said and done the system worked beautifully. The bass is in unbelievably powerful, deep and clean even at the highest SPL's, and conveys a wealth of texture and subtlety. This is THE SUB for individuals who love deep bass loud and clear.
-George Short, President
You may recall I purchased a pair of Thunder Kits a few months ago. We had a few conversations about construction. I've been remiss in not getting back to you to let you know how they turned out. In a word, superb! I even managed to veneer them using simple hand tools and advice from a web site I found (woodmiser or something like that). They look great.
More important the sound is awesome. They go deeper and subjectively sound much smoother and more articulate than my single _____ Sub Two that I was so pleased with for 4 or 5 years.
I couldn't be happier with these beauties. I'll get a picture to you as soon as I can.
Thanks again for another amazing product.
Joseph B., CT
The Thunders are finished and looking good. They sound good too. My son helped my build them and his comment was "I thought they would be louder than that". I guess a life time spent listening to booming car audio has ruined him because when we put the sound pressure meter on the test tone from the receiver, the subs were a full 6db louder than the mains after we set the levels listening to some metal CD of his. I have since reset those levels!
I am listening to "Supertramp - Crime of the Century" as we speak and those low rips on the fretless bass rock the house. A door slamming in a movie yields a visceral "punch in the gut" sensation. I am going to have to fix the closet door which buzzes in resonance during the flight deck scene of "Top Gun"....
Here is a pic taken before I rub out the ribbon mahogany finish a few weeks from now. When I do that and do a final clean up, I will send another. Note that I made front and back fascia’s and out set them as shown in pics on your web site. I held the interior volume to with 0.5% of the original. The idea was to create a standard "look" for future N.C. speaker projects...
I have finished my work on Thunder Subwoofer speaker following your plans.
Now I want to thank you. My English is not enough good for describing, how happy I am. It’s absolutely the best home bass sound I ever heard. It’s so natural deep and clear, unbelievable :-)
The source of power for my speaker is my self build amplifier with about 600W RMS@6ohm (220V)
The cabinet has clear internal volume of 38 liters ant it works perfectly.
Here is a photo of my speaker and I am proud of this part of my home theater.
Thank you again
I've been enjoying my Thunder kit for almost a year now and am ecstatic about the performance. My friends and family are really impressed!! My only wish is that I built 2 at the same time. Once I build up the CM-77's I will see about adding another.
Jeffrey S., CT
I thought I would share a few words about my initial listening session with the Thunder sub.
First of all, It is gorgeous as you said. No let down there. The wood working is excellent.
Since my intended use for home theatre is not complete my initial listen was in my 2 channel system.
It is bi amped with an active digital crossover so flexibility with the woofers is easy.
I disabled my woofer section entirely, (which consists of 4 (2 per side) 10" Focal woofers in 5 cubic foot ported boxes).
My woofer section plays deep and loud and has always kept me happy.
The Thunder alone played up to 140 hz and gave way to a 7" Kevlar Focal midrange and a Dynaudio D-260 Tweeter.
The bass in this configuration was amazing. Rivaling the output of my 4 focal woofers.
While not providing quite as much slam (understandable given the differences between systems including there intended purpose), the deep bass (lower octave or 2) was considerably smoother, cleaner, and just plain better.
The Thunder truly delivers deep, clean bass as it is intended.
And after going back and forth comparing it to my reference set up several times, I added the spikes.
After adding the spikes I listened to CD after CD for 2 or 3 hours and never switched back for comparison once.
I just listened to all my favorites with only the Thunder playing the bass.
Everything I have ever purchased from you, crossover parts, drivers, or whatever has been top notch!
I wish I could afford those matching Manifest demos you have. They must be georgeous too!!
And they probably don’t sound too bad either, huh?