FAQ's

Question: Why was the Lubell Labs LL916 Underwater Speaker chosen over all other brands and types of underwater speakers for the 2000 Olympic Games?

Answer: Sound Engineers representing the Olympic Committee were looking for an underwater speaker that would faithfully reproduce the entire audible audio spectrum from 200Hz up to 20kHz at a level that was both safe and sufficient, from as few units as possible, at a legal voltage (30 Vrms or lower). Synchronized swimmers are entitled to a proper full frequency response from 200Hz to 20Khz at a sufficient level of 180dB maximum so they can hear all the music and all the cues. If the Olympic Committee installed an underwater speaker that did not reproduce the music faithfully, then this shortcut would have caused many problems, including an unfair handicap to many swim teams. The Lubell LL916 fit the committees minimum requirements with flying colors -- from a single reasonably priced unit! For reasons of redundancy, two units were used during the competition. Competing units could have been used in large quantities (20 - 50 units depending on brand) in order to obtain sufficient sound levels and/or a proper frequency response, but the cost and unsightliness of so many speakers, cables, amplifiers, and equalizers would have been staggering.

There are many other cases where the Lubell design has proved useful. For instance, the NASA Neutral Buoyancy Simulator (MSFC and JSC) required just ONE Lubell underwater speaker to fill their 1.3 million gallon training tank with powerful sound clearly heard by the divers (astronauts) at a cost of about $1500 for speaker and amplifier. (In contrast, 20 competing units requiring a plethora of amplifiers, cabling, and processors were sold for tens of thousands of dollars to another space agency just to come close to the sound level and response of ONE Lubell speaker.) Another instance is Disney's Epcot Living Seas Aquarium, where just ONE Lubell speaker and 35 watt amplifier is used to fill their 5.3 million gallon tank with powerful sound clearly audible by SCUBA divers and dolphins. (Epcot has also developed a cutting-edge communication system for dolphin research that utilizes ONE Lubell underwater speaker.) And yet another instance is the UNC's Aquarius Underwater Research Habitat, where ONE Lubell underwater speaker connected to a Raytheon 30 watt hailer is used to recall divers in a 500 meter radius. Note: A "competitor" of Lubell Labs showed up at Aquarius and dropped off a "free" gift of their underwater speaker and 100 watt amplifier, then (without UNC's authorization), posted a picture of Aquarius on their web page, and published claims that Aquarius was a user of their product. ("Well they DID try it" -- Ed.) The product was tested and rejected for poor performance, and the company was served notice to remove any reference to Aquarius from their web site.)

The efficient Lubell LL916 and the Lubell LL9816 are the ONLY broad-band Piezoelectric Tonpilz Underwater Speakers in the world that are M.S.E.E. designed, patented, and US Navy tested to powerfully cover a much wider portion (200Hz-20kHz) of the audible frequency spectrum than any other commercially available product -- guaranteed!! (Bass frequencies below 200Hz are avoided with swimmers and divers, as they are Navy documented as leading to swimmer and diver disorientation.) Competing moving-coil magnetic type speakers are very inefficient and physically incapable of producing any usable power in the critical mid to high frequency range.  And competing quasi-flexural-disk (flat shaped) piezoelectric speakers are not capable of reproducing broad-band music -- most of their energy is concentrated in a narrow-band peak (typically centered around 4kHz), resulting in a weak low and high frequency response accompanied by high distortion and a tendency to go "kaput".

The Lubell LL916 and LL9816 also provide the maximum safe sound pressure level (per US Navy) of 180dB/uPa/m -- up to 60dB higher than the competition, and a "must have" for hearing the subtle musical cues that synchronized swimmers key-in on during complicated, fast paced routines.

The Lubell LL916 and LL9816 also operate at a safe maximum speaker cable voltages of 20 volts rms -- well within the 30 volt international legal limit. Compare this to the Oceanears DRS-8 running at 750 volts on the speaker cable via their 125 watt transformer box. Whew!

Any manufacturer can make fantastic claims about their products. But out of all the underwater speaker manufacturers in the world (Clark Synthesis, Coomber, Dal-Bay, Malux, Multisound, Oceanears, Spector-Lumenex, Uetax, just to name a few), only Lubell Labs backs up their superior performance specifications by actually publishing impartial test data provided by a respected and accredited underwater acoustic measurement facility (US Navy Dodge Pond detachment). Note: If you are one of these manufacturers and you do decide to publish impartial test data from an accredited deep water facility, please let us know and we will post this data here for review.



Question: What type of AC powered amplifier may be safely used with an underwater speaker for swimming pool use?

Answer: The amplifier must under law have the following minimum design features:

These amplifiers are commonly referred to as P.A. (public address) amplifiers, and are readily available on the market by manufacturers including Peavey, TOA, EV, Inter-M, and Bogan. For the convenience of our dealers and customers, we offer Peavey, Inter-M, TOA, and EV amplifiers for use with our underwater speakers. Amplifiers should be installed in equipment rack and connected to GFCI in air conditioned pool office, where they will not be exposed to humidity. When starting a new synchro program at high schools and university, we suggest consulting with a certified professional audio contractor first (or Lubell Labs if local service not available), who can design and provide a complete air and underwater sound system using genuine Lubell underwater speakers.

Amplifiers NOT TO USE with underwater speakers for reasons listed: Palca PA-7550 (not UL listed, owner said "do not use with underwater speaker"); Oceanears labeled/modified amplifiers (not UL listed, typically Palca amplifier with Oceanears label covering Palca label, probable high voltage output transformer added internally by Oceanears that far exceeds 30 Vrms worldwide legal limit); Mi-Pro MA-707 (Not UL listed, oddball series external speaker jack resulting in ungrounded underwater speaker and unusable terrible sound with piezoelectric speakers); Radio Shack MPA-50 (output "chip" unstable with piezoelectric speaker and will likely burn out)...


Question: I am a synchronized swimmer that travels to several different venues and would to prefer to carry a compact self-contained system -- do you offer anything?

Answer: Yes we do -- the battery-powered Anchor Liberty with choice of University UW-30 or Lubell LL916 underwater speaker. Also the battery powered digital Anchor Explorer Pro with choice of Clark AC339, Lubell LL9816-AC201CXA, or Lubell LL916C-AC201CXA underwater speakers.

Here is some background on portable systems: Over the last 35 years, we have obtained and evaluated many portable systems as they became available. Many of these systems use cheap thumbnail sized audio output chips, which are not designed for use with capacitive piezoelectric underwater speakers due to inherent instability and subsequent burn out. None of the systems tested used the acceptable standard of discrete audio output transistors found in standard commercial sound amplifiers. And only a few (from Japan and Taiwan) used large-die audio IC's rated for use with capacitive loads. One of the systems we tested was the Palca PA-7550 ($579 - NOT UL LISTED), which had an impressive 50 watt rms rating (20 volts rms @ 8 ohms) yet weighed only 18 lbs! Unit used a massive Toshiba IC, and switch mode power supply. Although this unit seemed very nice, and tested very well (as provided from factory) with the Lubell LL916 and AC205C or AC203/4 transformer box, it did not meet the important circuit safety standards (including UL certification) legally required for powering underwater speakers. We spoke to the owner of the company, who kindly explained that the unit was never designed for use with underwater speakers, and should be used in classrooms only. He also said that they would not be interested in having the product tested or redesigned for UL certification (since their intent is to only offer these items for use in classrooms) and not to use with underwater speaker. So in other words, please do not use any underwater speaker with the Palca PA-7550 or with any self-contained AC powered system that does not have UL approved circuitry and UL listing.

Warning: It has been brought to our attention that a company may be performing factory unauthorized modifications to the PALCA PA-7550, which include installing an internal high-voltage output transformer, and adding various jacks and controls. DO NOT CONNECT a Lubell underwater speaker or any underwater speaker to this system as the transformer may be stepping up original 20 volt rms speaker output to a voltage greatly in excess of 1200 volts rms (maybe even 2500 volts rms!), which ends up on the underwater speaker cable. (FACT: The international legal limit for swimming pool speakers is 30 volts rms.) Here is what the Palca PA-7550 is supposed to look like when it leaves the Palca factory. If it looks any different, please discontinue use immediately and have an electronics technician at your local stereo shop measure the REAL maximum output voltage (not what the modifier claims). If voltage is found to be in excess of 20 volts (+/- 3 volts), please return the system immediately to place of purchase, and inform the Palca factory and Lubell Labs so that safety authorities and synchronized swimming organizations can be warned.



Question: My Telex UW-30 underwater speaker (formally University UW-30) is rated at 30 watts @ 8 ohms. If I connect it to a PA amplifier rated at 30 watts @ 8 ohms, how much voltage would be measured on the speaker cable?

Answer: First make sure you are connecting to a commercial sound amplifier having an 8 ohm transformer isolated output tap (such as the Peavey UMA352 available from Lubell Labs). Next make sure you are looking at the amplifier's speaker rms output rating (30 watts rms @ 8 ohm) found in the specification section of the manual, and not the amplifier's power consumption rating by the power cord. Using a calculator, take the square root of the wattage (30 watts rms) times the impedance (8 ohms) which equals a voltage of 15.492 volts rms. This is well under the 30 volt rms international legal limit.



Question: My Clark AQ339 underwater speaker is rated at 135 watts @ 4 ohms. If I connect it to a Lubell PA amplifier rated at 120 watts @ 4 ohms, how much voltage would be measured on the speaker cable?

Answer: First make sure you are connecting to a UL listed commercial sound amplifier having a grounding power cord and a 4 ohm transformer isolated speaker output, such as the Lubell InterM A120 offered by Lubell Labs. Next make sure you are looking at the amplifier's speaker rms output rating (120 watts rms @ 4 ohm) found in the specification section of the manual, and not the amplifier's power consumption rating by the power cord. Using a calculator, take the square root of the wattage (120 watts) times the impedance (4 ohms) which equals a voltage of 21.91 volts rms. This is WELL under the 30 volt rms international legal limit.



Question: My portable Lubell LL916 with AC203/4 transformer box has a nominal rating of 35 watts rms @ 8 ohms. I notice the manual repeats this nominal power, but says that an amplifier up to 50 watts may be used. Under what conditions would the higher power be necessary, and how much voltage would appear on the underwater speaker cable with these amplifiers?

Answer: We recommend a 35 watt amplifier because this is usually all the power you need to provide outstanding sound levels (~178dB/uPa/m) for synchronized swimming practice and meets. But an amplifier up to 50 watts can be used if you also expect to be doing lap swimming, or performing routines in an extremely large pool. Using a calculator, take the square root of the wattage (35 or 50 watts rms) times the impedance (8 ohms) which equals a voltage of 16.733 volts rms and 20 volts rms. These are the voltages that actually appear on the Lubell LL916 underwater speaker cable, since the AC203/4 transformer does not step up the voltage to the LL916. This is well under the 30 volt rms international legal limit.



Question: My installed Lubell LL916 with AC205 transformer box has a rating of 25 volts. What does this mean and what amplifier should be used?

Answer: Commercial sound amplifiers including the Peavey, TOA, EV, and Bogan brands have transformer isolated speaker output taps including common terminal, 8 ohm tap, 25 volt tap, 70 volt tap, 100 volt tap (Europe). The AC205 was designed to connect to the low voltage 25 volt/common tap only, of amplifiers rated from 37.5 watts up to 300 watts (depending on how many speakers are to be connected in parallel to these terminals). Allow at least 37.5 watts of power consumption for each AC205 and LL916 connected to the 25 volt & common terminals. Following are some examples of multiple LL916/AC205 boxes connected in parallel to the 25 volt speaker terminals, and the required amplifier power/impedance: 1/37.5W/16 ohms; 2/75W/8 ohms; 4/150W/4 ohms; 8/300W/2 ohms. In every case cited previously, the AC205 steps the 25 volt line down to 20 volts on each speaker cable. This is well under the 30 volt rms international legal limit.



Question: Do I have to use the Lubell LL916 underwater speaker with the included AC202, AC203/4, or AC205 transformer box?

Answer: Yes you do -- failing to use the box is unsafe, and will damage the equipment and void the warranty. The transformer box performs many important functions: 1) It has an isolation transformer that isolates the speaker from the amplifier, preventing power line voltages which might appear on the chassis of a defective amplifier from reaching the speaker; 2) It provides impedance matching for proper amplifier load (so amplifier will not be overloaded); 3) It has a series power resistor which limits electrical current and flattens the frequency response; 3) Provides isolated deck speaker output jack and volume control (AC203/4 only) which allows adjustment of the air speaker from no sound to full blast.

The AC202 or AC203/4 may be connected to amplifier rated up to 50 watts rms @ 8 ohms (20 Vrms), which will provide no more than 20 volts rms on the connected LL916 underwater speaker cable. The AC205 may be connected to an amplifier rated up to 75 watts @ 8 ohms (25 Vrms), which is stepped down to provide 20 Vrms on the speaker cable. The maximum voltage on the LL916 cable must be limited to 20 volts rms (which by the way, provides a whopping 180dB/uPa/m sound level that is ample for any synchro program!)



Question: How do I compare underwater speakers in a logical manner?

Answer: Look for a frequency response, output level, and depth rating that meets your specific minimum requirements from a reputable brand that does not exceed 30 volt international legal limit on the underwater speaker cable. A reputable company will always publish and provide impartial test data graphs on their underwater speaker(s), so that commercial and scientific customers can make an informed purchase. Unlike air speakers that are tested in air filled anechoic chambers, underwater speakers must always be tested in underwater acoustic test facilities (such as the US Navy's Dodge Pond Acoustic Measurement Facility). For a nominal fee, the facility will measure the underwater speaker's impedance (in ohms) vs. frequency, and the on/off axis frequency response vs. sound pressure level (SPL). If the underwater speaker manufacturer will not provide this data for you, then we would be pleased to arrange a test for you at cost of $2000.



Copyright 2004-2007 Lubell Labs Inc. All information subject to change without notice. E-mail your FAQ questions to

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