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CEILING SPEAKERS

Part 1

The Small Speakers

The airport, hospital, dentist office, supermarket, and local steakhouse all have ceiling speakers. Ceiling speakers are one of the necessary tools that we must use until somebody develops a communicator badge (Beam me up Scotty!). Ceiling speakers are simple, yet complex. They are available in different sizes, packages, power ratings, colors, and prices. In Part 1 of this series we will discuss the 4" cone, 8" cone, 8" with whizzer, and 8" coaxial ceiling speakers. All figures are referenced at 2kHz.

4" Cone

Here is probably the best ceiling speaker for low ceilings, and the least appreciated. Most 4" ceiling speakers have very wide coverage at 2kHz, very smooth frequency response, and take up very little space. Figure 1 shows the 2kHz coverage of a 4" cone (S1), 8" cone (S2) and 8" coaxial (S3). Although the 4" cone coverage can get rather narrow at higher frequencies, it works extremely well for speech on ceilings up to 3m. And the smooth frequency response means fewer feedback problems with live microphones! Advantages: Good fidelity Smooth frequency response Very wide coverage for speech (use fewer units) Small and unobtrusive Disadvantages: Poor coverage at higher frequencies Low sensitivity Low / moderate power ratings Will not get very loud Applications: Low ceiling needs <100dB SPL Critical architectural spaces Figure 1

8" Cone

The 8" cone is the workhorse of ceiling speakers. It is used in every possible application, although it has the weakest fidelity. It is inexpensive and has a narrow frequency response (regardless of what is on the data sheets). The 8" cone ceiling speaker is usually rated at 5W rms, it rarely gets tapped at more than 1W. Coverage is around 90 degrees at 2kHz and gets narrower as frequency increases. Use lots of them! Plenty of installation hardware is available from a number of sources. Advantages: Low cost Wide variety of available hardware Disadvantages: Limited frequency response Poor fidelity (speech only) Applications: paging systems with 3m to 4m ceilings
8" with whizzer cone
Add a little more power, add a miniature megaphone, and you have the next 8" speaker on our list. The whizzer improves high frequency output for a little sparkle. The 8" with whizzer fits into standard 8" hardware and is usually rated at 10W rms. Most will be tapped at 1W. Advantages: Low cost Wide variety of available hardware More HF versus 8" cone Disadvantages: Limited frequency response Moderate fidelity (speech & low level background music) Applications: paging systems with 3m to 4m ceilings and mood music

8" Coaxial

Altec Lansing introduced the concept of a high frequency device mounted in the center of a cone woofer in the 1940's and registered the name Duplex. Others could not use Duplex on their similar devices and had to come up with another term. Coaxial has been used since. The heart and soul of 8" ceiling speakers is the 8" coaxial. A small high frequency device is center-mounted for more sparkle and better high frequency coverage. The 8" coax can do anything from paging to moderate levels of music playback. The good ones will be better at speech versus music. They fit into standard 8" hardware, however, they should be installed in a larger backbox (28.3l) for better low frequency performance. Power ratings are from 16W to 32W. A 32W version can deliver well over 110dB at 1m! Advantages: Moderate cost Higher Max SPL Wide variety of available hardware Better HF coverage Good fidelity (speech & foreground music) Disadvantages: Limited frequency response More expensive hardware suggested Applications: Paging systems with 3m to 6m ceilings and music playback

How do I know what speaker to use and how many?
Question #1: How loud does the system need to be? We usually like to have 10dB more than ambient (background) noise. 85dB is about all most offices need. Question #2: How high is the ceiling? Remember: The listeners are 1m above the floor. The speaker only needs to throw 2m from a 3m ceiling.

Tip #1:

Speakers gain 3dB in SPL each time power is doubled Power @ 1m 1W 2W 4W 8W typical 4" 91dB 94dB 97dB 100dB typical 8" 96dB 99dB 102dB 105dB

Tip #2:

Speakers lose 6dB of SPL when distance is doubled (or speakers gain 6dB every time the distance is cut in half)
In our example we need to deliver 85dB at the listener.
Lets see; a 4" speaker tapped at 2W will deliver approximately 94dB @ 1m. We double the distance and lose 6dB, leaving 88dB. Looks like a 4" ceiling speaker tapped at 2W will do the job. An 8" speaker will deliver about 96dB @ 1W/1m and 93dB @.5W (see Tip #2 above). We double the distance and lose 6dB, leaving 87dB. Looks like an 8" ceiling speaker tapped at.5W will also do the job.

Office with 3m ceiling.

Question #3: How many ceiling speakers are needed? Most 8" ceiling speakers are 6 dB down at 90 degrees. The 6dB down reference is said to be the edge of the usable coverage. 90 degrees of coverage will make a circle diameter twice the distance from the speaker. In our example the listeners are 2m from the ceiling and we should expect the speaker to throw a 4m circle. Spacing the speakers 4m apart places the circles edge-to-edge and looks pretty good on paper (see Figure 6).

Figure 6

6dB down
However, the 6dB down point of a speaker is not measured on a flat surface. The speaker is rotated with the measuring microphone stationary. The 6dB down point is actually located on a circle or arc. Although this makes sense to the guy in the lab, it does not apply to most floors. When the 6dB down point is extended to the listening plane, additional losses occur. (remember Tip #2?)

Figure 7

Figure 8 shows the 6dB down circle is closer to 8 or 9dB down at 1m above the floor! Obviously the 6dB down point on paper is not the 6dB down point in the real world.

Figure 8

Some designers will offset each row of speakers to improve coverage. This method can make the coverage +6dB with spacing 2 x distance-tolistener. This technique has limited applications.

Figure 9

Spacing the 8" ceiling speakers 3m apart gets us +4dB average SPL in this office example with a 3m ceiling (see Figure 11).

Figure 10

Spacing between ceiling speakers 1.5 and 2 times the distance-to-listener will fit most 8" ceiling speaker applications.
Figure 11 A comparison of 4" and 8" ceiling speakers: Here is a 3m x 4m office space. Figure 12 shows how little an 8" ceiling speaker will cover from an 2.4m ceiling. And yet this is very common!
Figure 12 Figure 13 shows how much more area a 4" ceiling speaker will cover. My choice for small rooms, particularly meeting rooms, is always a 4" ceiling speaker. Figure 13
Here are graphs for laying out 4" and 8" ceiling speakers (for those of us that are mathematically challenged)

8" Coverage

Select your ceiling height along the bottom, read speaker spacing on left
0 2.5 2.3.25 3.5 3.4.25 4.5 4.75 5

Ceiling Height in Meters

4dB Variation

6dB Variation

4" Coverage
Select your ceiling height along the bottom, read speaker spacing on left 2.5 2.3.25 3.5 3.4.25 4.5

Summary:

Ceiling speakers are used in applications where communication is needed. Many speakers will do double duty and play background or foreground music. The most common ceiling speakers are 4" cone, 8" cone, 8" with whizzer, and 8" coaxial. Choosing the right model for the job depends on; application, how much SPL is needed, and ceiling height. 4" ceiling speakers cover more area, but do not offer lots of SPL. 8" cone and 8" with whizzer ceiling speakers can get louder, but have limited band width and coverage on low ceilings. 8" coaxial ceiling speakers offer good band width and good output SPL, but have limited coverage on low ceilings. Its your call.