Component Reviews

Component Reviews, Part 3 of 4

Published on July 1, 2004

July-August 2004, Part 3 [Pt. 1] [Pt. 2] [Pt. 4]

Thorough Bass Inc. Magellan VI SU Subwoofer

Thorough Bass Sub power amp rear
Thorough Bass inc. Subwoofer
Thorough Bass Inc.
341 England Pl NE
Marietta GA 30066 USA
1-770-516-8540  1-877-828-7829  (Toll Free USA)
FAX: 1-720-559-5556
General Information:
Web site:


SENSITIVITY 90db 1w/1m @ 35Hz
DRIVER 6.5” Convex Single Piece Aluminum Cone
CONNECTION 5-way binding posts
IMPEDANCE 8 ohms nominal
ACCESSORIES Brass Vibration Isolators-Standard Large Rubber Feet
WIDTH 14.5 inches (368.3 mm)
DEPTH 14.5 inches (368.3mm)
HEIGHT 5.5 inches (139.7mm) no feet (7 inches w/spikes)
WEIGHT 15 lbs. (6.8kg)
SRP $800


FREQUENCY RESPONSE 10 Hz –150 Hz (-3db x-over @ 150 Hz)
POWER OUTPUT 200W 4 ohms (150W 8 ohms)
CONTROLS Level—Phase–Crossover 50 Hz-150 Hz (18db/oct)
CONNECTION 5-way Binding Posts
WIDTH 6.25 inches (158.75mm)
DEPTH 8 inches (203.2mm)
HEIGHT 6.75 inches (171.45mm)
WEIGHT 6 lbs. (2.72kg)
AC INPUT REQUIREMENT 120V- 240V 50-60-Hz (Internal Jumper Selectable)
355 VA max
SRP: $450


I have looked forward to reviewing this subwoofer since I saw it at CES 2003. First I feel it necessary to discuss what a subwoofer does and the problems encountered in doing it. A subwoofer is made to fill in the bottom octaves below what a standard speaker is not capable of. Many speakers claim to go down to 30 or 40 cycles; almost none in reality come even close to that in a real room. Most two-driver systems are lucky to be good down to 80 cycles. Three-driver systems can go down to 60 cycles. Trying to get frequency response below this highly compromises the total sound of the speaker. Most audiophiles do not bother to try to go below this because the sound of most subwoofers is not very musical. They usually sound like rumble generators or flatulence emitters. Some of the really expensive speaker systems have rows of large woofers to create their bass. They have the problem of a single note coming from a large area of sound. This makes the bass overly large and out of proportion.

Many smaller subwoofers use the corners of the room to reinforce the bass volume. Usually the harmonics of a note ride on the fundamental’s waveform. If a fundamental is produced three or more feet away from the harmonics it is not likely that the sound is going to be very natural. Another problem is air movement. Deep bass requires a lot of power and air to be moved. Large speakers do this best, but suffer from slow response speed. There are those that would tell you that speed is not as important at low frequencies. A 32-cycle note is about 34 feet long. This means 34 feet between full positive excursion and full negative excursion. Doing this 32 times in one second takes both speed and control. The larger the speaker the more speed and control is needed. There are also room acoustic problems with deep bass. Low bass can cause the room and objects in the room to shake or vibrate. Room having sustained low frequencies need to be reinforced structurally not to be damaged. One audiophile found that his big subwoofer system was tearing the sheet rock from the studs on his walls! There is also the noisy shaking of doors and windows.

Now I want to discuss what you hear down in the subwoofer range. Probably less than 1 percent of music is below 50 cycles. One of the first things that people think of is the organ. Many large organs have a 32-cycle capability. Far fewer have a 16-cycle capacity. One in Australia has an 8-cycle note. These notes are however seldom used in actual organ music. A large grand piano has a 25-cycle note. The Bosendorfer Imperial Grand can go down to 16 cycles. A bass guitar can go down to 17 cycles. Various contrabass brass and reed instruments go to between 17 and 50 cycles. A B-flat tuba can go down to 25 cycles. A standard doublebass goes down to 41 cycles. These notes and /or instruments are seldom used, except double bass and bass guitar. Notes that are this low are usually used for a musical foundation. In the last twenty years the synthesizer has become a main source of low frequency notes.


These woofers have a 6.5 inch one-piece aluminum driver with Low Mass. It fires up into the box cavity below the top the sub and exits the box through a port. The very Low Mass driver requires little diaphragm travel to produce long wavelength signals in this patent pending design. This combination of attributes provides a platform for fast launching of the low frequency waves. This combination of low mass and travel eliminates the need for big powerful amps to drive the woofers. The hybrid alignment combines the best attributes of reflex and transmission line designs. For more details on the theory go to the site.

Initial Inspection

I received two of the Magellan VI SU passive subwoofers and a TBI 200 SU Subwoofer Amplifier/ Crossover. I noted the high quality finish and build quality of the subwoofers and amp. The subs came with both rubber and spiked feet; I used the spiked feet. As you can see from the dimensions above both amp and subs are fairly small in size. Their instructions were minimal and could use some expansion. The amp came with a removable power chord, which was nice. I used a Kimber power cable on the unit. The speaker wire connectors on the subs were quiet good. The speaker-cable binding posts on the amp were not so good. You need to wrap the wire around the center post or modify a smaller than normal ring connector. The amp allowed for phase adjustment, 0 or 180 degrees. It would be useful to have continuous phase adjustment. Output volume and crossover frequency, 50 to 150 Hz with 18 dB per octave crossover, is also available. Unfortunately the amplifier sums the right and left line inputs to mono. It would have been interesting to try stereo bass.


I used some 16 gauge Monster cable for speaker cable. I ran an 8-foot pair of Jena Labs interconnects between preamp and amp. I ran a Y connector out of my preamp sub-out output. I was using a Paradigm 8-inch subwoofer before. It mated well with my electrostatic array, but had little response below 40 Hz. My electrostatic arrays have 5 – 9×22 inch bass panels on each side, which give strong bass response to 50 Hz. Crossing my panels at about 80 Hz made them sound clearer however. I first placed the subs just to the inside of right and left arrays, with the port pointed straight back. My big screen RPTV was about three feet behind the subs. This is far from the recommended setup for a subwoofer. I have never however liked the sound of subs in the corners or even near walls. It slows the sound down and does away with proper harmonic alignment. This position gave me the best integration and system sound. In this position there was a resonant problem at about 32 Hz. The room became very reactive and my big screen TV started rattling. Not Good! I then placed the subs outside of each array. The bass was stronger and a little deeper – it sounded a little slower and not as tonal. The general sound of the system also seemed to be a little less focused. I then moved the woofers back inside the arrays, but pointed the ports diagonally between speakers and the TV. This proved to be the best compromise. Getting the best sound from any speaker in a particular room is a matter of trial and error.

How They Sounded

I used a bass sweep cut on a test CD to determine the frequency response. I good strong response down to 27 Hz and audible response at 24 Hz. I could still hear the tone at 21 Hz. The woofers were working hard and there was a cabinet resonance at 32 Hz. A 25-pound lead brick on each woofer eliminated the resonance. This is truly amazing response for a unit this small. Best of all, the sound had tonality at these frequencies. Something I have not heard from a subwoofer before. I did note that the subs in this position did not do well above about 55 Hz. I am not sure if that this was because of crossover settings in my preamp or that they need wall reinforcement for these frequencies. I lowered my preamp subwoofer crossover point to 60 Hz and eliminated the problem. One really strong point of the woofers is how well they integrated with the electrostatic array. This is no easy accomplishment. I have eliminated a number of subs just because they were too slow to mate with them. An audiophile friend of mine said that he had never heard a subwoofer mate that well before.

On Gorecki Symphony #3 the first movement starts off with a 60 Hz note played by the double basses at a low volume and gradually increases. The note underlies most of the first movement. Without a subwoofer it is awhile before you even hear the note. Even after you start hearing it, it has little weight or presence. With this sub, you hear the note earlier and it is more solid and has more sense of life. I felt like I was hearing the movement for the first time. It brought out much more emotion from the music. On the 50 Hz note at the start of Also Sprach Zarathustra sounded much better through the sub. It was not only more solid, but also had tonality. You could hear the bass note move through the Hall. I feel that the speed at which these subs create bass allows you to hear more detail in the bass. The sub offered a lot more emotion when used for AV use. In the DVD Star Gaze, it added excitement to video. It is a video of pictures from the Hubble Telescope with synthesized music added. I watched it at a friend’s house that has a near state of the art video projection system. He has a very modest sound system. The video was very nice, but not all that involving. The music seemed like a Musak add on. When I played the disc at home with deep bass capabilities, the enjoyment of viewing the disc was greatly enhanced. The music now had emotion and power. The subs also added tension and emotion when watching movies. It’s gratifying how well defined low bass adds tension and a sense of power to a movie. After listening to this quality of bass, it will be much harder for an audiophile to stand the bass put out in most movie theatres.


First we have subs that create defined tonal deep bass. Then you have units that will not dominate the listening room. I feel that they have a much better mate acceptance factor than normal subs. I feel the approach of having the amp separate from the subs is a good idea. After going to substantial steps to isolate your components from vibration, it seems counter productive to put amp on a vibrating speaker. TBI does offer this woofer with amp and crossover attached if you do not want to bother with an extra box and speaker cable. They also offer the larger Magellan VIII, for more bass. I hope to get two of these for a comparison review. These woofers may not be the ultimate for big macho bass, which knocks you against your seat or makes your pant legs flap. If however you like high quality realistic-sounding bass, this may very well be your subwoofer. The only thing that might get these subs out of my system is their larger model. This is the most musical sub that I have heard and the only sub that will create the low frequencies and mate well with quick-sounding main speakers. Highly recommended!

– Clay Swartz

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