Thanks Ron! Yeah, I did initially go down the 8
ohm rabbit hole of trying to
throw together an unconventional
system. The original goal was to average the
impedance to a safe
level for the amp, plus the ability to control the over all volume of "zones" was a big plus in that I could have the larger rooms louder than the hallways, for example.
Luckily, the 70v
system makes that easy. I just tapped the transformers for 2w in the larger spaces or where I wanted more volume. I didn't bother to calculate the ceiling height to determine
spacing between speakers and all that, because honestly, perfect coverage isn't that crucial in this environment. I just made sure to have a
speaker within 25-30' at all times (8-9' ceiling) which ends up being more than adequate for paging duties. I tapped most other speakers at 1/2-1w depending on the space and think I did well with that. The amp is only running at 5/10 on the master volume and I might have to turn it down (we'll see on Monday once I really hear it in use).
I wish I could divide up this thread and move the 8ohm talk to its own thread since the 70v discussion is good, but some might not think to look here. In fact, I think I have another old thread from when I was first designing the
system I just replaced. Probably should see about sticking the first half of this thread over there.
Anyway, all's well that ends well and I appreciate everyone's patience and assistance!
A few more 70 Volt thoughts for you; not that you need these now but they may be of use to you in the future.
Let's say you've got a quantity of small dressing rooms to do. Maybe you've got four floors worth with 8 per floor. Maybe they're each specified to have two speakers. You may consider putting two 8
Ohm speakers in parallel and using only one 70 volt to 4
Ohm line to
speaker transformer and always locating the xfmr on the
speaker closest to the door. The plus to this is, if / when you need to re-tap the xfmr's for any reason, you've only half as many speakers to pull out of the ceiling, change taps, and re-install. By always consistently locating the xfmr's on the
speaker closest to the doors you won't waste time pulling out the wrong
speaker.
Sometimes you'll have dressing rooms with showers and toilets at one end and a cot / script study area at the other. In these cases you'll want transformers on every
speaker to finesse the relative levels above ambient within the rooms. You'll also learn to install speakers with moisture resistant cones in shower areas.
Here's another silly situation to file away: (This is from my 'made that mistake once' file.) Had a room off the
lobby. The architect designed this as a private lounge with kitchenette for high-ranking patrons, benefactors, board members, etcetera. As such, the architect was willing to allow one
speaker and one attenuator to intrude on his 'landscape' and he wanted it to be part of the
FOH Manager's
lobby paging and recall chime
system.
The
theatre's owners, Artistic Director and
Production Manager, foresaw this space being useful for small, intimate, private rehearsals and, as such, wanted the
speaker and attenuator affiliated with the backstage
monitor system with SM's
page override. The architect stomped his little hoofies and DECREED he'd tolerate zero additional blights on his 'landscape'. I ended up installing a single ceiling
speaker with a dual
voice coil. Dual voice coils are normally intended to allow
speaker impedance flexibility; both coils in parallel = 4 Ohms, one or the other = 8 Ohms, both in series = 16 Ohms. In this application the thinking was the visible attenuator would drive one coil and be part of the
lobby system. A second attenuator, located out of sight in the kitchenette, would drive the other
voice coil as part of the backstage
monitor /
page system.
Sounds like a good plan when you say it fast but I'll never make that mistake again.
When
speaker manufacturers wind two electrically separate voice coils on one
voice coil former, keeping them from magnetically coupling like a
transformer never enters their minds. Granted, two tiny voice coils
in one 8" ceiling
speaker don't afford great magnetic coupling but they do couple none the less. It took a
bit of head scratching to eventually figure out where the two separate paging systems were 'talking to each other'. If the ambient was high in the
lobby, nobody heard the backstage
system buried far below the
level of the
lobby pages. If the ambient was high in the dressing areas, nobody noticed the
lobby recall chimes. 'Mr. Murphy' prevailed, as he always does. If the
lobby was quiet during the day, people would hear the occasional backstage
page. Likewise, if a 'star' was trying to grab a
nap, they'd occasionally grumble at an SM about the annoying
lobby recall chimes.
Congrats again Les and welcome to the world of 70 Volt paging systems. If you graduate to systems in international airports and / or large hospitals, please come back and revile us with your tales.
Toodleoo!
Ron Hebbard.
.
