Overview of the two Morrison Audio speakers and associated sub woofers. This image is not a technical drawing but simply meant for comparative purposes.
Model 53 Sub–Woofer
The topic of sub-woofers around the dinner table can indeed be a perilous one.
Dad envisions huge enclosures while mom hopes they are the size of teacups, preferably tucked away out of sight. When she spots photos of some of the larger cabinets you can be assured that she will not be amused by the prospect of having two garden sheds in the living room. Comments peppered with “Over my dead body” will sneak into the conversation. The laws of physics will conspire against those shirt pocket-sized subs. They may indeed reach down to 20 hZ but the output will be down 80 dB relative to 100 hZ. It takes a doubling of power to reach a 3 dB increase. Millions of watts will be required to make up the 80 dB deficit. In fact, a handheld calculator and some back of the envelope scribbling tells us that the shortfall can be made up by pumping in 29,225 volts or 106,768,827 watts into an 8 ohm load! As you can imagine the voice coil or anything in the same postal code will be vaporized in a nanosecond. Great strides have been made in the last while with long throw drive units. Not cheap but they give you a fighting chance to plumb the depths.This allows a decent low end response out of a reasonably sized cabinet thus pleasing both Mother Nature and hopefully spousal units. The addition of a sub should not be to simply add low frequency extension to the main speakers but to relieve the mains from working their tails off. Looking at the distortion graphs of any mid-sized full-range speaker we see the distortion sprouting out of the lower left side almost exclusively below the 100 hZ point and certainly at 50 hZ and lower. In some instances the distortion at 90 dB in a full range speaker at 50 hZ can be just 10 to 20 dB below the program material! The louder you play it, the worse the distortion gets.
That’s where the sub comes in to assist. The mains can now have reduced excursion requirements and thus reduced distortion. All the heavy lifting is left to the sub. Why do so many subs sound like the bottom of a barrel? Usually because of price and/or shoddy workmanship. Cheap cabinets, poor bracing, nasty rattles,cheap drivers, mistuned ports will all add to the sonic disasters.
A sub-woofer with a built in power amp is convenient. The trade-off is performance. Why shoehorn an amp into the cabinet and sacrifice the structural integrity? They all have air leaks around the edges of the amp. What happens when the amp goes on the fritz and you have to ship the whole shebang back for repairs? What are the chances of having an A.C. outlet near the powered sub?
Keeping the amp external is the cure.
The Home Theatre market has enabled the makers of lo-fi gear to flourish. Car chases, gun fights, explosions, and dinosaur footsteps are all thrilling.
They have nothing to do with music. Here’s a dirty little secret. Shut off the video portion of your home theatre rig and play some music through it. Sounds pretty awful when you’re not distracted by the action. The video system allows you to have a surround sound effect for a few hundred dollars.
You wouldn’t dare listen to your Beethoven through it.
An accurate sub-woofer will blend with the main speakers and become unobtrusive. In other words, totally disappear. The sonic illusion should be that the main speakers are reaching down into the 20 hZ region.
The subjectivist audiophile will prattle on about “fast” woofers. Ain’t no such thing. What matters is the behavior of the woofer when the signal stops. The woofer should shut up. One of the worst examples of “Shutupability” is the planar type of speaker. There is simply not enough force over area to control the diaphragm and bring it to a stop. The light weight of the diaphragm won’t solve this problem.
A ported sub will have slightly better efficiency but not at 20 hZ. Below resonance, a ported box displays a 24 dB/ octave slope. A sealed cabinet has a 12 dB/octave slope below resonance. A perfectly optimized tuned port at 1 watt will display different characteristics at a 4-watt input. Like a moving target. After much R & D over several months and testing more subs than I’ve had hot dinners the final product displays performance that neither myself or my associates thought possible.
Reading reams of papers on sub-woofer design it would appear that far too many so-called experts have never plunged into actual design work. They simply keep quoting some of the errors of past writings. No kidding. Some of the notes quoted: “because of the long wavelengths of low frequencies the act of stuffing the cabinet with sound absorbent materials is ineffective.”
Complete and utter drivel. An accurate sub-woofer design can only be achieved by using a solid well damped sealed cabinet. It needn’t weigh 16 tons. The following questions must be addressed:
1). Do you put stuffing in the box?
2) If so, what kind of stuffing?
3) How much stuffing?
4) Do you use the same density of stuffing throughout?
5) Where do you locate the stuffing?
6) What shape of stuffing?
The object of stuffing the box is to reduce the impedance hump as flat as you can without destroying the low-frequency excursion of the drive unit. The lower impedance hump results in the best recovery of the cone when the signal stops. ie: “SHUTUPABILITY”.
The Model 53 sub is a sealed optimally damped cabinet with a long linear excursion (low distortion) 10-inch drive unit. The sub fires downward and is loaded by a one-inch gap at the floor level.
Using a pair of Model 53s in the system will offer the biggest improvement when using correct stereo recordings. If the venue is a large hall or a church for example there will be another layer of realism. Room ambiance, footsteps, and general low-frequency sounds are captured in their glory. The net result is an extension of low frequencies which the listener may not have even been aware of.
The audio system now takes on a sense of effortlessness. This is due to the reduction of low-frequency excursion requirement from the main speakers. At no time are the main speaker voice coils being driven into a non-linear area of the magnetic gap. The distortion can be reduced accordingly. The main speakers can now be played much louder with lower distortion. Since the long excursions are now taken over by the subwoofer the intermodulation distortion is now substantially reduced in the main speakers as well. This is the type of distortion in speakers that the listener never notices until it is removed. A welcome relief. A deft hand with a smidgeon of room correction will scotch the gremlins of pretty much any room placement and will provide a reasonably flat and solid response into the mid-twenties with minimal distortion in a domestic setting.
Dimensions are 13” X 13” X 21” tall. Takes up about 2 cubic feet of real estate if you’re counting. Tips in at about 57 lbs. 69 lbs. shipping.
The input connector is a Neutrik 2-pole Speakon.
Satin black finish. Impedance curves are provided with each unit shipped. Optimum results with a power amp of 200 watts and higher.
As with all Morrison Audio speakers each one is tested and measured by the most miserable critic of the product. That would be me.
Model 61 Sub–Woofer
The Morrison Model 61 subwoofer is a scaled-down version of the larger
Model 53. It uses the same drive unit. The measurements of the 2
subwoofer models are in lock step from 90 hZ up. At 30 hZ the Model 61
is exactly 3 dB lower in output than the Model 53. Physics dictates
that the Model 61 requires twice the power at 30 hZ to achieve the same
loudness as the Model 53.
The Model 61 is 13" X 13" X 13" tall. Satin black finish.
Tips in at about 42 lbs.