All speakers are NOT created Equal(ized)

By John Strohbeen • Ohm Speakers • Tuesday, April 4, 2017


Speakers that require active, electronic equalization to work properly have been around for a very long time, but with mixed success in the market place. This is changing. I believe it will become the dominant style of speakers even in the highest quality category. The concept behind an electronically equalized speaker is that if you build an integrated, complementary, amp-and-speaker system, the designer has better control over the balance of the system.

History: Back to Bose-ics.

In 1966, Bose introduced its 2201. This speaker had 22 drivers on the face of a 1/8 sphere and was designed to nest in a room’s corner. The built-in 50-watt amplifier was equalized to get the sound desired by Bose and its guiding force, Amar Bose. This model was not a commercial success. I believe there were several reasons for its failure, including its appearance, placement requirements, sonic balance and the fact that the retailer did not get to match a profitable amplifier to the speaker.

Ed Marchino, the world’s best salesman of 2201s, was recruited to help address these problems. Bose designed a much, much smaller, nine-driver system. It eliminated the amplifier, but retained an equalizer to get the desired balance. Marchino established the “proper” balance by choosing what sounded best in his showroom. Christened the 901, the speaker was introduced in 1968.

Bose Corporation then hired Marchino and sent him on extensive sales trips recruiting dealers. Thus began the commercial success of Bose audio products. The 901 was updated five times over the years including shifting from an acoustic suspension design to a vented design in 1976 after EV demonstrated the benefits of venting with the EV Interface Alpha 1974 (an equalized small box with powerful deep bass using A.N. Thiele’s principles.)

Ohm G.

Ohm also learned from EV, and introduced the Ohm G as the first vented Walsh speaker. The EV Interface A’s 8” driver in a small box with 12” passive radiator (vent substitute) and an equalizer could produce the bass output of a big acoustic suspension speaker with a 12” woofer. Marty Gersten, Ohm’s founder, took the top section of the Ohm F 12” driver and truncated it to an 8” system. Then he tested the Thiele parameters and built an appropriate box. With a bit more tweaking, the Ohm G was nearly completed.

Marty took a close look at the benefits and problems of the Bose and EV equalizers. Both drastically improved the bass and somewhat improved the treble. While the EVs sounded OK without the equalizer, the Bose truly needed the equalizer at all times. A further problem was that many dealers did not demo the speakers with the equalizers and many users skipped the equalizers, severely degrading the delivered sound. Marty chose to go with the EV style and make the equalizer an enhancement to the Ohm G’s sound. While the equalizer was not needed for good sound, it would add both more deep bass and extended treble while adding protection below the tuning frequency of the cabinet/vent. In my experience, very few Ohm G equalizers were sold.

Allison Electronic Subwoofer.

In the late 1970s, Roy Allison introduced an equalizer for his line of acoustic suspension speakers. The speakers sounded good without the equalizer; but when the equalizer was added to a pair of Allisons, they provided the low bass of the new vented systems being offered by other manufacturers. The Electronic Subwoofer could also be used with many other well-designed acoustic suspension designs such as the popular AR3a. It was only a few years later that Allison Acoustics was closed. I have often wondered if the equalizer helped the company by extending the bass or hurt it by acknowledging the need for deeper bass.

Home theater increased the demand for deep bass, as there is never enough to reproduce a train wreck or atomic bomb. With the introduction of a subwoofer output in Dolby Pro Logic II (1980s) and standardization of a Low Frequency Output for DVDs (early 1990s), the popularity of subwoofers drastically increased. Adding a powered subwoofer both extended the deep bass and allowed the main speakers to play much louder when they (and the main amplifiers) did not have to reproduce the bass. The subwoofer amplifier could have a built-in equalizer allowing much smaller cabinets than un-equalized speakers with the same deep bass. It also allowed the user to control the bass/midrange balance to fit the room and listener’s taste. All are real improvements.

An extreme example was the Sunfire True Subwoofer introduced in 1996. When Bob Carver asked me to design the driver that could get the sound of a 15” subwoofer from an 11” cube, he promised 2400-4000 watts if it was really needed for the output. I built him prototype woofers that had the excursion required and Bob confirmed one woofer with a matching passive radiator was easier to drive than two woofers in a dual-drive acoustic suspension configuration. The Sunfire True Subwoofer went into production and met with great demand. Powered subwoofers have demonstrated their benefits in the home and have become the standard for home theater systems.

Pro Sound Monitors.

These are the speakers which recording engineers use to listen to the results of their work. The Yamaha NS 10 series became the near universal “small monitor” with limited frequency range. To reproduce the full frequency range, studios often had gigantic, built-into-the-wall systems. As basement/garage project studios have taken over the industry, powered monitor speakers that are equalized to extend their frequency range have become popular even in the lower price ranges. Yamaha has followed with the current HS series. Now, the recording engineer can get the performance (if not the sound level) of the giant speakers with a small box speaker sitting on his recording console.

Sound Reinforcement

Sound reinforcement arrays for large venues have always used lots of big speakers and big amplifiers. These systems can reproduce the sound levels considered necessary for an impressive “live” performance. Today’s systems have amplifiers with built-in DSP to match levels, provide equalization and manage crossovers, as well as controlling directivity and protecting the speakers from damage. These systems can provide even distribution to thousands of listeners – all at high sound levels.

My experience at the Barclay Center — while listening to Bob Dylan’s show from across the basketball court — demonstrated the ability of these new systems to play loudly, without distortion at levels higher than my ears could tolerate. Yes, my ears distorted before the sound system did while listening hundreds of feet from the speakers. Remarkable and painful.

Wireless.

Portable wireless speakers that stream music from your smartphone or iPod have become very popular because they can deliver amimpressive amount of bass for their size. This is partially because ICs have been developed with DSP and small, high efficiency digital amplifiers are on the same chip. You can get a lot of sound on one charge of the batteries.

The Future.

Looking into my crystal ball is always interesting, although usually a bit cloudy. I was recently told that the primary concern when designing drivers to be used in DSP equalized, powered speakers was efficiency. This is because the frequency range and balance can be adjusted to the designer’s taste using DSP, while the battery lasts a lot longer with high efficiency drivers and you can use a smaller amplifier. For home stereo, I do not feel this is significant concern since the speakers will be plugged into the 120V wall outlet – never needing recharging. Still, small size and deep bass are major benefits when used in the home. This is where DSP equalized and self-powered speakers have an advantage. I believe “purists” will not initially accept these designs because the amplifier is no longer a wire-with-gain and the drivers’ raw frequency response is not flat-as-a-pancake. The amplifier will have a very strange response – the complement to the strange response of the drivers. These two far-from-flat curves match each other, like two fitting pieces of a jigsaw puzzle, to give the designer the target response. Choosing this target response will continue to be a problem for the designer as the room interaction remains a major variable. There is more work to be done…

See you in two weeks, until then,

Enjoy & Good Listening,

John

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