Important considerations for your 70-volt speaker + sub install


As our AC.SUB is an excellent choice for such 70-volt installations, we thought you should know why 70-volt subs are more complex than you might think.

There are few downsides to a 70-volt audio system when you’re talking about installing lots of speakers, particularly using long wiring runs. But there is one issue of concern when you’re talking about high performance (or high fidelity, if you’re an old timer). The copper wound transformers used to convert the 70-volt signal at the speaker is critical to the ultimate fidelity of the system. Most 70-volt transformers are low quality, low fidelity devices chosen for their low cost above all. This may not be a big deal in a distributed sound system at the local department store because fidelity doesn’t matter there. But it is a big deal in your client’s back yard when they’ve paid big bucks for a high performance system.

When you’re installing any 70-volt system you should try to ensure the speakers are using high performance, high quality transformers like the heavy American made ones in the Terra AC Classic and AC FIVE series. If you don’t, you’re shorting your clients of the best performance available. In particular, when it comes to subwoofers, this issue gets really serious. High power low frequency signals will cause typical 70-volt transformers to create lots of distortion ruining the bass detail and impact. The transformer core simply overloads which is also called saturation. [SEE NOTE BELOW]

We’ve spent significant effort working with our transformer supplier to come up with a transformer capable of handling high power levels at very low frequencies to eliminate the possibility of core saturation. We have chosen a 400 watt, 11.8 pound monster that can handle pretty much anything that you can throw at it so you can be sure that your clients will get all the bass performance they’re looking for in their outdoor distributes audio system.

You can order the AC.SUB in 70-volt now. There is an upcharge for the transformer, of course. We can also provide a built-in heavy-duty choke as a 100Hz passive crossover for the sub. However, there are so many benefits to active bi-amplification with a low-level active crossover that we strongly urge you to go that route using a device like our Crown CDi 1000 DSP high efficiency amplifier.

Note for the technically minded: Low quality transformers become very non-linear at low frequencies due to core saturation. The transformer core is made of ferrous metals (iron). Within that iron there are tiny regions that act like little magnets with their North and South poles haphazardly oriented. As current is passed through the copper windings wrapped around the core, the random magnetic fields within the core begin to align parallel to the magnetic field generated by the current passing through the windings. When full alignment is reached, the transformer becomes non-linear, creating harmonics and intermodulation distortion. The effect is dramatically exacerbated by high power low frequencies.

In order to overcome core saturation you must use a very large, very heavy transformer with a core that won’t saturate with high power, low frequency signals. Big transformer, lots of copper equals big bucks. The massive Terra transformer incorporates M6 29 gauge line grain oriented steel laminations hand assembled and wound using heavily insulated, pure virgin copper magnet wire. It will pass serious levels of high fidelity bass without distortion for your client’s maximum enjoyment and satisfaction.