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Case Study: Constant Beam Transducer Speakers in Commercial Project


Staff Member
CFO (Chief Fun Officer)
Feb 13, 2016
Seattle Area
This was an article I wrote for the local magazine that gets sent to high-end designers, builders, and architects. It had to be very short and not too technical. It is also designed to be a bit of advertorial for my company so I hope you don't mind that aspect :).
Bringing Science to Commercial Projects: The Seattle Great Wheel
By Amir Majidimehr

[Note: this article was originally published in the Premier Builder Magazine.]

The covered area where the music plays as patrons wait to board.

The bulk of innovations in our industry go toward residential projects. As a way of example, we routinely design home theaters that outperform most commercial movie theaters! Residential projects are often driven by the dreams of people to achieve the best in life with less consideration to cost. The commercial side though is often driven by utility and return on investment which tends to stymie innovation. That is a shame as much can be done to increase the function and customer enjoyment of such projects. Fortunately there are some exceptions. This article is about one of those, namely, the Seattle Great Wheel. Standing tall at 175 feet (the tallest on the west coast), the wheel sports a beautiful modern design. The client wanted to make the process of waiting to board the wheel as enjoyable as possible with background music.

If one wanted to just throw something together this would be an easy project. Put some outdoor speakers there with a few amplifiers pushing the sound to them and you would be done. But there are problems with this solution. This being an outdoor situation means you need a lot of power to fill the area. Now consider a law of physics when it comes to speakers: sound power drops proportional to the square of distance. This means that if you double the distance from a speaker, you get four times less sound. Triple the distance and you now have a whopping eight times less power. Now imagine a person standing next to a speaker and another 20 feet away. You can imagine one going deaf while the other hearing normal volume. Not exactly the good experience you want to have when you are aiming for an enjoyable experience for your customers in such a landmark.

A related problem is that the sound quality of a speaker changes depending on whether you are standing in front of it or to its side. The higher frequency tones are more directional meaning if you move to the side of the speaker you will not hear them as much. This translates to the sound being muffled in those areas versus standing directly in front of the speaker. In this situation customers are walking around the line as they get closer to the boarding point as opposed to, say, you enjoying music at home always in your favorite chair. So ideally we would have the same fidelity for everyone in the line and not something that changes up and down.

Turns out there is a solution to these problems but not one that you or your typical AV supplier is aware of. Its origin dates back to 1970s when navy researchers aiming to improve underwater communication and sonar invented a new type of device called a Constant Beam Transducer or CBT for short. By utilizing an array of speakers specially configured to work as one, a “wall of sound” is generated that moves in a much more efficient and focused manner that nearly solves all the problems I mentioned above. Specifically, sound energy coming out of a CBT drops at a rate proportional to distance travelled and not the square of it as is the case with conventional speakers. So if you are three times away from the speaker, now the sound level is only three times less, not eight. That is a dramatic improvement.

Listening to a CBT speaker for the first time is an uncanny experience. As you walk up to it the sound level seems to not change at all. Nor does it change in quality as you move around it. Try walking up toward your home speakers and note how it does not act this way. CBTs as such are perfect for amplification of sound in large spaces.

Close up of the JBL CBT speaker showing how nicely it blends into the
architecture of the wheel.
Alas, what is good for the government is not always good for commercial deployments where costs have to be manageable. Fast forward a few decades later and JBL, the company that produces the vast majority of speakers and electronics for outdoor concerts, commercial theaters and recording studios, tamed the complexity of CBT devices by a patented process and produced a series of speakers that are quite reasonably priced yet preserve all the qualities of CBTs. The manifestation is a highly robust outdoor speaker with superb power handling and reliability together with all the benefits of CBT technology.

For the Great Wheel, we strategically positioned these speakers in the waiting area. They are mounted on the columns and nearly completely blend into the structure of the wheel. Since there is little sensation of the music changing in volume as customers get near or away from the speakers, the patrons are simply unaware that these speakers even exist. Yet they hear enjoyable music, reducing the anticipation of waiting in line.

Here is the full shot showing the CBT speaker in location:


Not visible are a set of subwoofers delivering the low frequencies (since those are not directional the subwoofers can be placed where convenient which in this case meant out of sight). Amplification is provided courtesy of Crown which is a sister division to JBL. We like them because they have built in processing that we use to optimize the sound, route the appropriate signal to each speaker, and to provide equipment protection (limiters).

This project is not without irony. Research that was aimed at underwater navy vessels is being harvested for this beautiful project which itself towers over the waters of the Puget Sound. When you visit the wheel next time with someone, you will have a great story to tell of the technology that powers its sound system!
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Staff Member
CFO (Chief Fun Officer)
Feb 13, 2016
Seattle Area
Thread Starter #2
Here are a couple of other shots that did not make it into the article. It was a dark and cold day so tried to make the best of it due to deadline for the article :).
Jun 7, 2020
I followed this link happenstance, when I was reading your x4700h review thread. I was surprised and delighted to see your use of JBL CBT speakers in this project. I first heard these speakers in a Kansas City AMC Prime Cinema and absolutely loved them! That was my favorite commercial cinema experience, and at the time my friends and I commented on just how amazing those speakers sounded. They also looked the part, which doesn't hurt. ;)


I set an eBay alert for JBL CBT 70j-1 and waited close to three years before I found a deal on 13 of them from a single seller I could afford. He had used them in a commercial 5K race audio setup and strung them along the full length of the race course due to their design characteristic retention of SPL at distance and broad uniform coverage. The seller was fortunately local and the sale made. I bought 13 of his 34 for use in my home theater, and really enjoy them for the characteristics and sound quality they offer. This purchase was about 2 years ago at this point, and I've been pleased as peach with the outcome.

I can put my AVR in all channel stereo and walk nearly anywhere in the room and the sound is identical. It's really unique and novel, and I like to show that unique CBT line array aspect off for my HT guests. Another neat factor is that because the sound is spread among so many different drivers top to bottom I can play a media clip at reference level and walk right up to any particular speaker and not feel blown back by the volume. Instead of one tweeter trying to play reference, that will make you cringe if you put your ear up to it based on the required SPL, there are 16 soft dome tweeters sharing the load and so any particular single one is not nearly as loud. This allows for great surround field speaker placement because it doesn't blow that closest seat out with obnoxious SPL!

I've suggested a pair of these to a friend for his giant, beautiful, pool setup, and for our church sanctuary for obvious reasons. Broad coverage of uniform sound, plenty of SPL capability, waterproof even (for the pool use setting).

My HT room is not big enough to really need these specific characteristics, and I only have a single row, yet I think these speakers are the cat's meow (panther's meow?), and it's fun to have something reminiscent of my favorite commercial cinema experience memory.

I adopted AMC's cosmetic fanfare too, and installed RBG 5050 lighting strips in them controlled by Alexa, so I can make the speakers glow. I can say "Alexa, it is showtime", and she turns off the speaker reveal lights behind the screen and dims the in speaker RBG lighting to 5% brightness on all the surrounds for my movie watching, or "Alexa the movie is over" which brings the lights back up to full!

Here are a few pictures to show how they are setup in my HT room:

Inexpensive RGB 5050 mod with Alexa based controller

Putting the speaker back together

I wired the RGB 5050 lighting up to CAT5e jacks for a clean look to the wallplate. Brave was the first movie I watched in Dolby Atmos at the AMC Prime commercial cinema, and they had a Dolby Rep there that introduced the Atmos technology before the movie and gave everyone a Brave poster, so it gets a special spot in my HT.

Just one view of the HT

and another

and a third

The movie Gravity, with the RBG 5050 lights turned to turquoise to show the JBL CBT 70J-1 speaker placement behind the screen.

Anyway, I thought I'd share my own experience with these special speakers since they happened to be the focal point in your unique commercial install! I think they are also a fun/exceptional choice for HT.

I've only recently started to explore your site. I appreciate your expertise (and the way you handle conflict) as you share your impressive knowledge with the audio enthusiasts community.

Thanks for what you do!

AVS Forum HT room thread:


Addicted to Fun and Learning
Forum Donor
Sep 19, 2019
What do you have, 8 sub woofers? Might be a bit thin...
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