What Every Residential Integrator Needs To Know About 70-Volt Systems

Transcription

1 P R E S E N T S What Every Residential Integrator Needs To Know About 70-Volt Systems NEAR is a Division of Bogen Communications, Inc.

2 70V A Bad Reputation Typically 70V systems have poor sound Usually found only in commercial settings How did 70V get that reputation? - It earned it - Most 70V installations use cheap speakers & transformers

3 Why You Need To Know About 70V 70V systems can sound better than you think Easier to install multi-speaker 70V systems than low-impedance systems Can overcome coverage problems with sound sculpting

4 How 70V Works Amplifier outputs constant voltage (70V) - Similar to power grid - Minimizes power loss NEAR 6XL - 600W Power Amplifier

5 How 70V Works Transformer on the speaker steps down voltage just like the transformer outside your house steps down high voltage AC grid power

6 How 70V Works Transformers can be built-in or Added to any low-impedance speaker Power taps select maximum power going into the speaker

7 70V Benefits Less power loss over long wire runs A 55 foot length of 16-gauge speaker wire will lose 21% of available power to a 4-Ohm load speaker. The same speaker in a 70V system can be on a 2687 foot wire before losing the same % of power. In prachcal terms, there is virtually zero speaker wire power loss in 70V systems.

8 First 70V Benefit You can hook up more speakers to an amplifier channel Why do you need more speakers? - More even sound coverage

9 Two Medium Directivity (120 dispersion) Speakers Cannot Uniformly Cover a Large Outdoor Area

10 Four Medium Directivity Speakers in a Large Outdoor Area Better Coverage

11 Six Medium Directivity Speakers in a Large Outdoor Area Even Better Coverage

12 Typical Wiring Most installers wire multiple speakers in parallel System Impedance (X) = 1/(1/R1+1/R2 +1/R3, etc.) Two 8-Ohm speaker example: X = 1/(1/8 + 1/8) or X = 1/( ) or 1/.25 = 4 Ohms Fine for two 8-Ohm speakers, but what if you need more speakers to achieve uniform sound coverage? And then there is

13 The Dirty Secret About Impedance It is not constant It s usually lower than you think Can increase the odds of amplifier failure due to low impedance of speakers wired in parallel Nominal 8-Ohm speakers are not 8-Ohms at many frequencies

14 Alternative Solutions Use more amplifiers - expensive Series/parallel wiring (illustrated at right) can get the impedance right but is inconvenient to wire speakers to each other

15 70V A Better Solution Can run many more speakers off an amp channel safely & reliably

16 70V A Better Solution Sound Sculpting Pool Dining Desired SPL: 0dB Desired SPL: +9dB BBQ Pit Desired SPL: +6dB

17 Sound Sculpting W = +9dB 8W = +6dB 4W = +3dB 2 W = 0dB 2 W = 0dB 50 Watt Amp Doubling power = +3dB Total power = 32W. Do not draw more power than 90% of total available power.

18 70V Configuration

19 70V Benefits Summed Up Negligible power loss over long wire runs Can run more speakers off an amp for more uniform sound coverage No low impedance and amp failure worries Sound sculpting puts the right amount of volume in each area But miracles come at a cost

20 70V Downsides Cheap transformers sound bad Easily saturated = distortion Severe roll-off of lows and highs

21 70V Downsides Even good transformers roll off bass 30Hz

22 70V Downsides Even good transformers roll off highs dbspl 110 SPL vs Freq kHz 50 9K Hz 10K 20K 92: 8 ohms (low impedance)

23 70V Downsides But these 2-3dB losses at frequency extremes are not musically significant compared with the benefits 110 dbspl SPL vs Freq K Hz 10K 20K 92: 8 ohms (low impedance)

24 Hybrid Systems Running subwoofers at 8-Ohms and mid/high speakers in 70V mitigates potential bass loss of 70V transformers. To do this run 70V on one channel and low impedance on the other Use a direct drive (no output transformers) power amplifier

25 Hybrid Systems

26 70V Pros - Allows longer speaker wire runs - Allows use of smaller gauge speaker wire - Allows many speakers to be run off of each amplifier channel without endangering system reliability - Allows sound sculpting different volume for each speaker 70V Cons Summing Up - Higher distortion (with low quality transformers or when high quality transformers are over-driven) - Low frequency roll off - High frequency roll off (with low quality transformers) - Variability (low quality transformers)