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Product Review - Osborn "Monumental" Active Subwoofer - May, 2000

David Wurtz
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Specifications

Driver

300mm (12 inch)

Sensitivity: 92 dB for 1 Watt @ 1 Meter

Fs: 30 Hz

Impedance: 6.5 Ohms

Amplifier

195 Wrms Continuous Output Power

350 Wrms Short Term Power

Frequency Response: -3 dB @ 1 Hz and adjustable from 20 Hz to 200 Hz with a 12 dB per octave slope.

Input sensitivity: 220mV for 175Wrms

S/N: >110 dB (amp) > 85 dB (overall)

Slew Rate: 35V/uS

Overall

Frequency Response: 20 Hz – 125 Hz (usable bass to 15 Hz)

Variable Active Crossover 20 Hz – 120 Hz

Weight: 55 Kg

Dimensions: 710mm H x 440mm W x 450mm D

MSRP: $3,300 AUS


Osborn Loudspeakers, 17 Hammersley Court, Taylors Lakes Victoria, Australia. 3038 Tel. +(613) 93901564. Fax. +(613) 93904775; Email osspeak@ihug.com.au http://www.osbornloudspeakers.com.au/; USA and Canada Contacts: NuView Marketing, Karl Schaefer, Phone 1-877-361-3630; Fax: 250 833 4332; E-Mail
nuview@shuswap.net

Introduction

Very few people I know really, and I mean really understand the benefits of having a high quality subwoofer compared with one of lesser or average quality, within their hi-fi system and home theater. A lesser quality unit gives the indication that it’s reinforcing the bass, but generally it feeds you boomy, undefined bass instead of a fast, tight, controlled kick in the guts. Greg Osborn from Osborn Loudspeakers is well reknown for producing full-range loudspeakers that have tremendous amounts of impact as well as loads of well-controlled bass. The Osborn "Monumental" subwoofer, which I have under scrutiny in this review, is the middle choice of three such subwoofer units in his range. Does it live up to Osborn’s reputation for quality bass? Let’s see . . . .

The Driver

The 300mm (12") Focal driver was selected because it is considered by the designer to be one of the world’s best. This driver makes up the bottom end of some systems selling for between $50,000 and $200,000. It also makes up the bottom end of Greg's most expensive loudspeakers, the "Grand Monument Reference". The gray-colored, foam-roll speaker surround measured 30mm. The cone actually has a diameter of 260mm measured with my trusty flexi-tape for a total cone area of 531 cm2. The poly-glass cone has a 77mm voice coil former, edgewound with flat copper wire. The cone's overall weight is a miniscule 94.6 grams, and the driver's total weight is 13.5 Kg.

The Amp

Ian Robinson from Redgum Audio has been charged with the responsibility of powering this unit. He produces some of the best power amps available anywhere and at any price. A 300 VA high-speed toroidal transformer was chosen, and extremely high-grade power MOSFETS (Metal Oxide Silicon Field Effect Transistors) are used for the output stage. The power supply has 18,800 F of capacitance and a 63 V DC rail for total energy storage of 76 joules. The amps were produced in 180W, 300W, and 500W versions, but it was found that the 180W version is more than sufficient.

The amp and associated crossover electronics remain on at all times (although there is a power switch if you must turn it off) and at optimum operating temperature. An auto-switching circuit is not an option because Ian feels they don't perform very well. If there is no signal for a short time, the amp would turn off and not be 100% ready for the bass info coming down the road. Power consumption at idle was measured at 410 mA.

The built-in active crossover is a simple "frequency feed-back" op-amp (operational amplifier) design, attenuating at 12 dB/octave above cut off frequency, variable between 20 Hz and 200 Hz. Other "more standard" crossover designs were tried, but the op-amp configuration performed and sounded the best. The crossover allows the use of high (speaker) level and low (line) level inputs. This makes the sub able to fit into nearly any audio situation, as it is with most modern subs. Finally, there is a level control and a phase switch. Interestingly, the level control, once configured with the aid of an SPL meter, was set to about 10:30, allowing plenty of adjustment up. In my experience, having this much "available adjustment" just tends to give inexperienced users inaccurate indication of bass levels and response as it is usually set far too high. To be completely accurate, the use of as SPL meter is essential. The fundamental reason for having such a wide level of adjustment is for "matching" sensitivity levels to all loudspeakers.

The Package

The cabinet is constructed of 32mm (1 ") custom-wood, veneered with a 6mm ( ") solid piece of Australian Redgum. As with all Osborn products, the "Monumental" is also available in Tasmanian Blackwood and a South African Bubinga. There is a 5% extra charge for the quilted Bubinga veneer. The veneer samples are available for perusal on the Osborn Web page (http://www.osbornloudspeakers.com.au/files/veneers.html).

The cabinets are heavily braced, with the whole package coming in at 55 Kg or 121 lbs. This is one of the heaviest subwoofers in the world, and in the subwoofer kingdom, heavy is good.

The solidity of the cabinet ensures that there are not any spurious vibrations, completely isolating the baffle (the board that the driver is mounted on) and the port at the rear. "Any spurious cabinet vibration will result in a lack of definition and sonic purity," says its designer and builder Greg Osborn. The overall appearance of the Redgum cabinet is nothing short of spectacular. I only wish the photographs I took did it as much justice as the finish truly deserves.

The Sound

After the obvious but reasonably minor difficulties I had removing and positioning such a heavy speaker box, I was ready to go (kid with the new toy syndrome). At first, I used the AVIA test DVD to generate the various tones required to set the levels, crossover point, and phase between my mains (JBL 4410s) and the sub. After about 15 minutes of futzing (Author’s note: This is great verb from the Dr. John E Johnson collection), I was happy with the overall levels. Not a single rattle or buzz out of the box was heard while sweeping frequencies down below 20 Hz at high SPL.

Time to play some music. The Rockmelons CD "Form One Planet" is usually the first disc I play when I test subwoofers. I listened . . . and "I love this sub" is all I want to say. But knowing that you guys, my Editor-in-Chief, and the Monumental’s designer will read this, I had better elaborate a little.

I am quite fond of the sound of my main speakers (JBL 4410 Studio Monitors), and I was very impressed at the lack of coloration at the bottom end when the Monumental was in the circuit. The sub blended in seamlessly with them. In adding the bottom octave (20 Hz – 40 Hz), it gave the music a huge boost in dimensionality. The Monumental was just as accurate, distortion free, speedy, and musical as my mains. In other words, the mains and the sub became one.

I proceeded to play several pieces of classical music. Fast paced Baroque was handled exceptionally well. "Classic Beethoven", a new disc from the DTS collection (20-bit 5.1 channel) shook the room in its fullest splendor, the sub having no problems in expertly reproducing and reinforcing the 0.1 LFE channel. Shane Howard’s (a well-known Australian artist of the band named "Goanna") solo album "River" has fantastic warmth in the bass section of the mix. Most lesser quality subs I’ve heard tend to make this a rather warm (floppy or loose), or too bassy (too much harmonic distortion) sounding recording. The Monumental masterfully handled the bass on this album, giving me a wonderfully accurate representation of what the producer actually had in mind when he mixed the album.

This unit should first and foremost be used for its musical qualities, but it is also a killer for the home theater. In this area I was just as excited. The DVD-movie "The Matrix" literally had me on the edge of my seat again. (Quite amazing, seeing that I have seen it many, many times before.) The scene where the helicopter crashed into the building startled me when it exploded. With all this available "sub level" at my fingertips, it was hard not to give the level knob a little "tweak up" to increase the bass level and make the room and windows shake more. This was less than ideal for accurate reproduction, but nice to have in reserve for explosions and car crashes in my action movies.

At no point did I drive the Monumental hard enough to hear any noticeable distortion. Although bass distortion is less audible than mid-range or high frequency distortion, boominess and chestiness are characteristics of a subwoofer driven too hard. I really gave it a workout in my room, but the Monumental just kept on delivering clean, accurate bass. For the Monumental, it is a combination of an extremely high quality driver, and a massive enclosure, along with a high-performance amplifier. Bravo!

Conclusion

I was a little reluctant to finish this review, because it meant I would have to send the Monumental back to the manufacturer. The fact is, I’m not done enjoying the sound from this beautiful piece of equipment. This is as close to the finest all round subwoofer that I have ever heard. Do yourself a favor and have a listen!

- David Wurtz -

 

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