The Rule of 10
If we cannot hear above 20kHz why do engineers insist on building amplifiers with ever higher bandwidths?
While I can’t tell you why designers other than our own like to extend amplifier bandwidth into the ultrasonic regions I can explain why we do. It’s called the Rule of 10.
The rule of 10 is a lofty engineering goal that simply states we should strive to build products with 10 times the required average use case. So, for example, if we want to make sure we can deliver flat frequency response out to 20kHz then we should try and extend the amp’s bandwidth by a factor of 10, or 200kHz. In the same vein if we want to be flat to 20Hz we’d make certain to extend that by a factor of 10, to 2Hz.
We don’t always get what we want nor do we use the Rule of 10 as a strict formula, only a guide. The reasons for this are simple. By stretching the parameters beyond requirements we gain headroom, staying within the comfortable bounds of an amp’s abilities. Taken too far in any one direction this goal can actually make things worse. For instance, demanding too much ultrasonic performance can require design changes that have negative impacts elsewhere.
The Rule of 10 is valuable advice if it is kept in balance and harmony with the rest of the design.
Without design compromise
Origin stories of Infinity’s flagship loudspeaker, the IRS, have as many variations as M&Ms but this is the one I was told.
It all took place over a dinner attended by Infinity partners Cary Christie and Arnie Nudell along with their international sales manager Leon Kuby. It was Kuby who challenged Arnie to consider building a line source loudspeaker without design compromise. Nudell is reported to have scoffed at the idea saying such a speaker would be absurd, taking up most of the room and costing a king’s ransom. Over time the challenge moved from the absurd to the possible and finally to the practical.
From TAS’ Jim Hannon:
“Like Infinity’s previous flagship loudspeakers, the goal of the formidable seven-feet, six-inches-tall, four-tower, Infinity Reference Standard (IRS), introduced in 1980, was to reduce “the musical distance between the live performance and its reproduced illusion.” Its sole design objective was to “achieve the world’s highest level of musical accuracy, and to develop the new technology needed to attain that objective.” Originally conceived as a statement of what a large line-source dipole without any design compromises could achieve, the IRS attained surprising commercial success, and served as HP’s long-time reference. That alone should be enough for the IRS to reach iconic status!”
In fact, Stan and my first meeting with HP of the Absolute Sound was at a time when this very speaker was his reference. We had come to visit Harry and show off our new little phono stage, a $120 silver box about the size of a pack of English muffins that was our sole product. Harry kept promising to give the phono preamplifier an audition while we sat transfixed by the sound of the IRS—but the audition never happened. When 2 a.m. rolled around we were all tired. Stan and I went back to California the next day changed by those speakers. Our horizons had been forever extended as we witnessed what few people ever get the chance to do: be in the same room when the musical distance between a live performance and its reproduced illusion had been reduced to near nothingness.
The IRS loudspeaker system changed my life and the lives of others. It was a seminal work that deserves its place in history. It will live in permanency at our new building with its own dedicated room. Sometimes history has to be preserved so we can understand our roots.
Kevin in Wappinger Falls New York (wherever that is) asked me an interesting question recently.
“Arnie Nudell popularized the line source loudspeaker design and many of his most revered Infinity speakers such as the Quantum Line Source, the IRS 1B, the IRS V, and the Genesis 1 (and apparently at least the two larger members of your forthcoming AN series loudspeakers) are all line source designs. Why don’t we see more line source loudspeaker designs? Is it strictly due to the cost because of the many more drivers, the larger cabinet, the increased manufacturing labor cost – or are there other attributes that have made them less popular?”
This is a really good question and one we don’t talk about much. Perhaps it’s a good idea to first get on the same page. The classic two-way or three-way loudspeaker has two or three drivers in a box. The multiplicity of drivers—tweeter, midrange, woofer—is needed to break apart the frequencies so each driver only has to handle a specific range: tweeters handle the higher frequencies about 2kHz and the woofer handles everything from that point down.
A line source handles the frequency divisions in exactly the same way—tweeters, midrange, and woofers—but instead of relying upon a single driver for each range multiple drivers are instead employed, typically with a line of many tweeters and sometimes many midranges. The advantages of multiple drivers in a line are manifold: each driver has fewer demands and the waveform comes out in a long, vertical, cylinder rather than a single driver’s ever-expanding circular wave.
The advantages of a line source vs. a point source can be summed up fairly easily. A point source sound radiates in all directions from the driver and quickly loses energy as it floods the room in a 180˚ plane. Worse, this expanded radiation pattern hits the ceiling, walls, and floor and reflects back into the room out of synch (time) with the initial launch. Only those listeners in a narrow sweet spot get to enjoy the best sound. A line source radiates a more focused pattern in the shape of a tall vertical cylinder that, above about 500Hz, has nearly no floor, ceiling, or sidewall reflections to dissipate energy and add to sonic confusion.
All that said, tomorrow we’ll look at some older Infinity designs.
Is your stereo system setup a circus or a naked exhibition? I’ve certainly seen both.
By circus I mean a cluster of well-intentioned objects intended to enhance the room’s sonic performance. You’ve seen these sometimes magnificent temples: two speakers, a disparate equipment stack, a forest of traps, wall hangings, pucks, dots, and carefully placed shapes designed to reflect, reduce, and distract the sound from those speakers. For the most part, these are terrific sounding rooms, especially given all the effort that’s gone into them. Perhaps this describes your room.
Then there’s the minimalist’s approach. The mostly empty room that sports a pair of speakers and a neat collection of gear. It is bereft of anything resembling sound modifiers. It relies instead on furniture, precise placement, and a lot of luck.
Finally, there’s the middle ground like my system and perhaps yours: A decently dimensioned room with a few diffusers and a smattering of accouterments to coax out the best possible sound.
What’s lovely about what we do is the variety in the mix. The amazing efforts we each go through and the many different paths to get where we hope to go.
Only passionate people care enough to work at making things great.
Middle of the road is as its name implies. Boring.
Extreme, on the other hand, is far more exciting. When we take it to the edges we’re excited to see our horizons move and our expectations exceeded. We’d much rather know that the tweeter in our new speakers is better than “a reasonably good driver” and much happier to learn “state of the art with extension beyond human hearing”. Extremism, where it matters, is a good thing.
Yet sometimes taking things to the extreme is at the expense of the intended. A little salt enhances the food, too much and its unedible.
Recently I’ve been hearing about extreme solutions to the problems of achieving clean AC for use in our home stereo systems. There’s everything from battery power, ultra caps, isolation transformers, exotic rare earth filters, to expensive mystery boxes intended to clean the hash and noise riding on our home AC. Several of these are extremely good at what they do, but all of them do their work at the expense of addressing AC power’s real problem. Missing energy from the sine wave and unregulated power.
Clean power is good. Regulated, low distortion, regenerated power is what really matters when it comes to enhancing performance.
Extreme solutions to the wrong problems often times steer us in useless circles.
The last full paragraph is exactly how I did my own listening room.!!
Building a room
In early September we’ll be moving much of the company into our new building across the street. We’re pretty excited. We’ll do our best to make our move as seamless as possible from your standpoint: keeping the phones live, using remote access for emails, reducing downtime to nearly nothing.
Once the offices, engineering, and production have moved the next phase will be the building of the Music Rooms of which there are 3 planned. Our original hope was to have the music rooms as well as our offices, production facilities, and engineering all humming along at the same time but what is it they say about plans for mice and men?
Starting with Music Room One, the largest of the three. It’s 16′ 6″ wide and nearly 30 feet long. On one end of this room sits Arnie Nudell’s reference loudspeaker prototypes and on the opposite side whatever new PS loudspeaker we’re working on at the time. Just to the right is Music Room Two the new home for the Infinity IRSV. It’s a foot wider than our existing room at 16′ 2″ and about the same length of 22 feet. To the right again will be Music Room Three with our Affordable AN3 loudspeakers (or the new Sprout Speaker) and a Stellar Stack in combo with a nice little showroom so visiting folks can see what we make.
Note how the center wall between rooms One and Two is slightly angled and that each corner too is angled. These angles, along with a pitched ceiling, will greatly reduce standing waves by virtue of limiting the parallel wall bounce.
Much more to come as we progress.
I use some pro audio gear, specifically Urei Equalizers, but agree that audio equipment for the home is and should be different than pro audio stuff.
Pro vs. home
Our knee-jerk reaction to pro vs. home is that the former is better than the latter. After all, the pros make their living using equipment and we amateurs don’t. Ergo, a pro drill must be better than a Black and Decker, a chef’s knife superior to a Popiel offering.
Of course, not all pro gear is better than home gear and for a good reason. They are often intended for different tasks. Take professional loudspeakers and subwoofers vs. home versions: neither would work well in the other’s application.
Pro speakers intended for concerts and public events focus on loud and efficient at the expense of frequency extremes and performance qualities precious to an audiophile. Home speakers are the opposite. A home subwoofer, for example, will try and plumb subterranean depths while a pro version is intentionally rolled off at 40Hz to 50Hz. There’s no need to go lower in a crowded live setting and doing so requires a ton of amplifier power.
A pro tool might better suit a carpenter but it’s unlikely pro audio gear will ever sound as good in our homes as simple “amateur” products do.
Multiple stab wounds
I recently enjoyed the latest version of Murder on the Orient Express. I’m certain everyone’s seen at least one version of this Agatha Christie classic but if you haven’t, it’s alright because I won’t tell you who done it.
The antagonist in the film is named Mr. Ratchett but his real identity is Cassetti, an infamous child abductor, murderer, and all around jerk. In this version, he’s well played by the actor Johnny Depp. The protagonist in the story, our hero, the affable Hercule Poirot, has to figure out who killed Mr. Ratchett after he had been stabbed 12 times. It’s a good film.
Stabbing someone 12 times is the epitome of overkill, as Poirot affirms. Apparently, the first stab did the job quite well.
We’re often concerned with overkill, afraid that too much will gild the lily or somehow become a futile attempt at improving that which does not need help.
The most common source of angst when it comes to overkill is with audio amplifiers. Second on our list just might be audio cabling, and subwoofers a close third. It’s common wisdom you don’t need 1,000 watt amplifier on a pair of bookshelf speakers, $1,000 cables on a cheap off-the-shelf receiver, or a pair of 24″ woofers in a small room.
I would argue poppycock. There is no power amplifier with too many watts just as there are no cables too expensive for the job or a woofer too big for a room. The increase in amplifier headroom is always welcome in my book. The real crime is pushing an amplifier close to its limits.
Fear not the overkill, but be wary of too little. A wounded beast is dangerous indeed.
The finishing touch to a several hour’s long meal preparation might be the setting of the table. The last little bit of work capping off hours of preparation.
When I roll my sleeves up to muscle loudspeakers around a listening room, swap audio and AC cables, restack audio equipment, and rough tune a system the last step is the finishing touches. Tidying up, making sure the eye candy on the front wall is perfectly centered, ensuring visual symmetry qualify as the last bits to get everything just so.
Those finishing touches are important. I’ve witnessed poor reactions to system setup at a show when those touches have yet to be applied. When we’re in the middle of setup at a consumer show the room is generally in chaos with packing materials, poorly dressed cables, and chairs scattered helter-skelter. Walk-in listeners have trouble separating the clutter from the beauty of sound. They quickly leave promising to return after we get the system dialed in. What they miss is the system was dialed in, though without the finishing touches.
Often, it’s those last bits of polish that create the sparkle.
Why do we build some things while not others? A sleek red car with a big and powerful engine’s probably not what you’d design for mom to take to the market just as a lumbering minivan might not win the Daytona 500.
We design with purpose to satisfy a need or a desire. The strength of any product depends on how close to filling those needs or desires we get.
Take the PS Audio P20 Power Plant as an example. It was purpose-built to fit a very narrow need: clean, tightly regulated, AC power for high-end audio systems. It’s big. It’s expensive. It’s likely not something you’d ever find in an industrial equipment catalog. Yet, it is so purpose-built that it prompted Tone Audio publisher Jeff Dorgay to comment: “I’m gonna violate the prime directive and tell you to get one. You won’t be able to un-hear it, and you won’t be able to live without it.”
The first step in the design process has to be intent. Who’s the product intended for and what does it hope to accomplish. Take our new Sprout Speaker we’re developing as another example. It’s a 2-way under $1,000 pair of speakers in a small enclosure designed to fill an entire room with uncompromised sound. That’s a pretty tall order for a pair of 18″ tall boxes that are generally targeted for small rooms, desktops, and bookshelves.
Traditional manufacturers of 2-way “bookshelf” speakers aim for a broad general purpose audience and find themselves swimming in a sea of competition.
The more narrow the targeted use the better chance designers have for success. The downside to this approach, of course, is missing the mark.
There’s much more power in a single bullet only if it hits its mark.