Installs Impedance Matching Speaker Selector

[Les]

Does anyone have any advice on purchasing an impedance matching speaker selector? It would need to be 4 or 6 zones, with volume control for each zone.

Zone 1: Two 8 ohm speakers; possible wired parallel (4 ohm load)
Zone 2: Two 8 ohm speakers; possible wired parallel (4 ohm load)
Zone 3: Two 8 ohm speakers; possible wired parallel (4 ohm load)
Zone 4: One 4 ohm paging horn (Can substitute 8 ohm if needed)
Zone 5: Empty
Zone 6: Empty

The zones would all be used at once, and total impedance should not drop below 4 ohms. I bought and received this unit, but looking at the impedance chart leaves me to believe that it will not drive the amp at a safe level with all zones selected.

 

[jkowtko]

I just upgraded our Niles SVC-4 to the SSVC-6 ... hooked it up to a Niles SI-245 amp, and it sounds pretty good with 6 pairs of speakers. I think all of our speakers are 8 ohms. There should be a switch on the back that adjusts overall impedance ... on the Niles it is presented as a "# of speakers selection" switch ... but if you switch it back and forth you can hear based on the volume change in the speakers that the switch simply adjusts how much impedance is added to the overall system.

The Niles amps are supposed to be 2 ohm stable, which means you can get a fair number of speaker sets without overworking the amp.

I am very happy with my Niles setup. I have purchased an SI-275 so I can get a bit more power.

Fyi if your amp has a protection circuit, then that should kick in if you have too little impedance in your overall system. But there should be an impedance selector switch on the back of the speaker selector unit.

 

[Les]

Thanks for the reply! I've actually been looking at the Niles SSVC-6. A little pricey, but it seems to cover all the bases. Looking back on the Pyle unit, there are no impedance selectors so I am pretty sure it's just a dumb passive splitter - luckily B&H has a good return policy. Unfortunately, I don't have the Niles amp. This is the intercom system for a small business, and we've been running on this old thing: The Realistic MPA-90 which has a rating of 100w at 4 ohms minimum.



It has actually been serving us quite well for the last year or so, and it currently drives four 20w 8 ohm paging horns mounted above a grid ceiling. They're wired in series-parallel and the amp has seemed happy with plenty of power - never really has to be driven above 50%. I'm hoping to keep it in the system since this project isn't a high priority and doesn't have much money allocated to it.

However, I am tired of the airport-like sound quality of the paging horns above the office which have to broadcast in various directions to somewhat cover the office area so I am replacing them with six 20w 8 ohm ceiling speakers in key areas. Hopefully they will be able to run at a lower volume and provide more direct and intelligible sound. I also added a doorbell annunciator for our various doors and shipping/receiving bays, which has highlighted the need to improve the system coverage since it is also tied in to the intercom.

I could wire each speaker to an output so every splitter channel has an L+R, but I would rather wire pairs in parallel just to save on how much wire has to go all the way back to the telecom room. I am also adding a 15w 4 ohm Atlas paging horn in the warehouse, but do have access to a similar model in 8 ohm if needed. So... Worse case scenario is that I have 4 zones of 4 ohm loads, which needs to not drop below 4 ohms for the amp. Does that sound doable?

 

[FMEng]

The way such a system would normally be built is to use the 70V output and speakers with 70V matching transformers. The MPA-90 has a 70V output. Then, simple switches can be used to turn on or off zones without any significant level changes. Just set the speaker transformers so that the total taps don't exceed about 80 Watts.

 

[Les]

The MPA-90 has a 70V output.

Unfortunately (and surprisingly), it doesn't. The smaller MPA-25 actually does, but I'm not sure why they left that off of the MPA-90.

 

[FMEng]

Unfortunately (and surprisingly), it doesn't. The smaller MPA-25 actually does, but I'm not sure why they left that off of the MPA-90.

The photo of the back panel I found must have been miss identified. Rat Shack left it off because an output transformer of that size adds some cost, size, and weight to the product. You can still do it with a 100 Watt transformer at the amp to drive the line.

Use something like
http://www.parts-express.com/70v-100w-high-power-speaker-line-matching-transformer--300-225

http://www.fullcompass.com/prod/264...t-pti=264061&gclid=COTC_LCRgc4CFYqPfgod4gsJiw

 

[Les]

Ah, I see. Well, I already had the ceiling speakers which don't use a 70v transformer. I'm wondering if I should just say goodbye to the faithful old Realistic and buy a cheap Bogen PA amp [like this one] online (even eBay) and purchase some 70v ceiling speakers. When running at 70v, those speakers only use like 5w, right? Meaning I probably won't need anything above a 60w amp for a system of 6 speakers plus horn.

@FMEng - you mentioned setting the transformer taps. This is essentially how the volume is determined, correct?

 

[RonHebbard]

Ah, I see. Well, I already had the ceiling speakers which don't use a 70v transformer. I'm wondering if I should just say goodbye to the faithful old Realistic and buy a cheap Bogen PA amp [like this one] online (even eBay) and purchase some 70v ceiling speakers. When running at 70v, those speakers only use like 5w, right? Meaning I probably won't need anything above a 60w amp for a system of 6 speakers plus horn.

@FMEng - you mentioned setting the transformer taps. This is essentially how the volume is determined, correct?

There was a time when I never would have spoke against Bogen but I'll make the following couple of comments.
In the 1960's Bogens were workhorses. Built with vacuum tubes and quality components. Buy once, cry once ruled. Even their first two solid state generations were still quite solid. You'd see Bogens in the kitchens of 'greasy spoon' diners, often coated in grease above deep fryers and still chugging away. A few decades passed and I recommended a brand new Bogen to a community theatre to serve monitor / page duties for their makeup and dressing areas. This would've been around 2005. It wasn't cheap but they came up with the funds on the basis of buying a real Bogen. They were thrilled for a few years then noticed one of the mic input pots was getting a little picky. Eventually they had a couple of pots that were getting really temperamental. Silly me. Acting on the group's behalf, I phoned my contact at our Canadian Bogen distributor only to learn they no longer stock replacement parts. Neither do they offer in warranty service. Nope! No longer built in New Jersey. Built in Mexico. If it failed in warranty, an entire new replacement amplifier would have been supplied. Once past warranty, bin it and buy a new unit OR repair it yourself. Sourcing suitable replacement pots, even better pots than their OEM components isn't a big deal. At least you can install pots worth cleaning a couple of times over the next 10 years. Nope! The Bogens of today aren't the Bogens of my childhood. I shouldn't be surprised. Victrolas no longer have the large horns and the little dog either.
I guess my point is: If you've currently got an amp that's solid, even if it's branded Radio Shack, if it's still serviceable I'd keep it in preference to replacing it with any of today's Bogens.
Toodleoo!
Ron Hebbard.

 

[Les]

There was a time when I never would have spoke against Bogen but I'll make the following couple of comments.
In the 1960's Bogens were workhorses. Built with vacuum tubes and quality components. Buy once, cry once ruled. Even their first two solid state generations were still quite solid. You'd see Bogens in the kitchens of 'greasy spoon' diners, often coated in grease above deep fryers and still chugging away. A few decades passed and I recommended a brand new Bogen to a community theatre to serve monitor / page duties for their makeup and dressing areas. This would've been around 2005. It wasn't cheap but they came up with the funds on the basis of buying a real Bogen. They were thrilled for a few years then noticed one of the mic input pots was getting a little picky. Eventually they had a couple of pots that were getting really temperamental. Silly me. Acting on the group's behalf, I phoned my contact at our Canadian Bogen distributor only to learn they no longer stock replacement parts. Neither do they offer in warranty service. Nope! No longer built in New Jersey. Built in Mexico. If it failed in warranty, an entire new replacement amplifier would have been supplied. Once past warranty, bin it and buy a new unit OR repair it yourself. Sourcing suitable replacement pots, even better pots than their OEM components isn't a big deal. At least you can install pots worth cleaning a couple of times over the next 10 years. Nope! The Bogens of today aren't the Bogens of my childhood. I shouldn't be surprised. Victrolas no longer have the large horns and the little dog either.
I guess my point is: If you've currently got an amp that's solid, even if it's branded Radio Shack, if it's still serviceable I'd keep it in preference to replacing it with any of today's Bogens.
Toodleoo!
Ron Hebbard.

Well that's crappy. Especially since I was just eyeballing this on eBay!

 

[FMEng]

The Realistic would work fine by adding a transformer, but I can also understand not wanting to add cost to keep an old unit. TOA amps seem good and reliable. I have one that's been running continuously for 7 years and hasn't skipped a beat. As long as I hear music in the halls I don't even look at it.

You are correct that 5 Watts per tap is plenty for paging. The taps adjust the relative level of each speaker. If a certain area needs a bit more level, use a higher tap. a smaller or quieter room gets a lower tap. The volume control on the amp adjusts the over all level.

 

[Les]

I decided to just go with a 70v system, scavenged off eBay. I found a set of 12 ceiling-mount paging speakers with brackets for super cheap (and locally), and ordered a pair of Atlas AP-15 Vari-tap paging horns off eBay for $20. Also a nice, modern commercial amp for $38. The 12 ceiling speakers should be more than enough - in fact, I will probably only use ten. The suite next door to us sells security systems so I should be able to get a roll of Class 2 wire from them. All in all, I think I'll end up with a decent intercom system for just a few hundred bucks, and it will be a more industry-standard installation.

I'm hoping to put the components in a desktop equipment rack like the one below. I had everything in a small rack that our POE switches and camera POE lives in but I don't want to crowd it and generate more heat.

 

[RonHebbard]

I decided to just go with a 70v system, scavenged off eBay. I found a set of 12 ceiling-mount paging speakers with brackets for super cheap (and locally), and ordered a pair of Atlas AP-15 Vari-tap paging horns off eBay for $20. Also a nice, modern commercial amp for $38. The 12 ceiling speakers should be more than enough - in fact, I will probably only use ten. The suite next door to us sells security systems so I should be able to get a roll of Class 2 wire from them. All in all, I think I'll end up with a decent intercom system for just a few hundred bucks, and it will be a more industry-standard installation.

I'm hoping to put the components in a desktop equipment rack like the one below. I had everything in a small rack that our POE switches and camera POE lives in but I don't want to crowd it and generate more heat.

View attachment 13563

You're writing "intercom system". I'm trusting this is a one way paging system although I've been wrong many times.
With the sloping rails and flat bottom, I gather you're mounting shallow depth rail supported gear near the bottom to avoid it colliding with the bottom of the rack. Presumably you've no requirements for plenum rated cables.
Congratulations on going 70 volt.
Toodleoo!
Ron Hebbard.

 

[Les]

You're writing "intercom system". I'm trusting this is a one way paging system although I've been wrong many times.

You'd be correct. Basically just for paging as well as a doorbell annunciator. I should stop using those terms so interchangeably on a technical theatre forum. Back in elementary school it was always "no talking while the principal is talking on the intercom" so I guess that's where it comes from.

With the sloping rails and flat bottom, I gather you're mounting shallow depth rail supported gear near the bottom to avoid it colliding with the bottom of the rack.

Yeah, the amp is the deepest component and I was planning on mounting it toward the middle. I'll probably put a 1U power conditioner near the top. The rest will be populated with airflow blanks. Good point though!

Presumably you've no requirements for plenum rated cables.

Nope - this is basically just a large tilt-wall industrial building with offices built in to one end. There's at least 15' of open air above the drop ceiling. Too bad they didn't go two story when they built it out!

Congratulations on going 70 volt.
Toodleoo!
Ron Hebbard.

Thanks! It'll be a neat learning experience.

Edit:

In fact, both my amp and speakers have a 25v tap, so I might even go that route. Might make the NEC happier and I'll sleep better at night.

 

[RonHebbard]

You'd be correct. Basically just for paging as well as a doorbell annunciator. I should stop using those terms so interchangeably on a technical theatre forum. Back in elementary school it was always "no talking while the principal is talking on the intercom" so I guess that's where it comes from.



Yeah, the amp is the deepest component and I was planning on mounting it toward the middle. I'll probably put a 1U power conditioner near the top. The rest will be populated with airflow blanks. Good point though!



Nope - this is basically just a large tilt-wall industrial building with offices built in to one end. There's at least 15' of open air above the drop ceiling. Too bad they didn't go two story when they built it out!



Thanks! It'll be a neat learning experience.

Edit:

In fact, both my amp and speakers have a 25v tap, so I might even go that route. Might make the NEC happier and I'll sleep better at night.

Two points: Your fire folks may consider anything above your ceiling to be a plenum.
When you mention filling the remainder of your rack with vents, keep in mind your amplifier's air flow whether by fan or convection. You often see people making amplifier cooling errors such as two different amps placed above one another; one pulling cooling air in its front with heat out the rear while the other's trying to pull cooling air in the rear and blow it out the front. People have been known to have two amps heating the heck out of each other. Some amp manufacturers spec' amps to be racked adjacent to one another with either minimal clearance or solid blanks. This is common for amps sharing identical air flow designs where they want all of the fans combining to haul air in the rear and out the front for one example.
All the best with your project.
Toodleoo!
Ron Hebbard.

 

[Les]

Two points: Your fire folks may consider anything above your ceiling to be a plenum.

That's a good point. I've interfaced with our fire marshal a lot, and he seems pretty lax. The facility is 1/2 office and 1/2 warehouse (about 13k square feet total) and the attic and warehouse airspace is all connected.

Funny story; the previous tenants expanded the office portion without approval and got caught. Fire Marshal made them add sprinklers but otherwise let them slide. They also left what seems like hundreds of feet of dead Cat5 laying above the grid -- oh yeah, none of the Ethernet is supported. It is a total mess (not our doing).

I'm planning on zip-tying the 25/70v wire to the suspension wires for the grid but I'll be honest, it is so tempting to lay it in like everything else...

 

[JD]

Plenum rules apply if the space above the ceiling is used for airflow. If, for example, air is supplied via ducts but return air simply returns in the area above the ceiling, then that is considered Plenum space. If air is delivered by ducts and returned by ducts, then it is not. The plenum rules are to prevent toxic gasses from burning plastic cable to enter the airflow and be moved to other areas.

 

[RonHebbard]

That's a good point. I've interfaced with our fire marshal a lot, and he seems pretty lax. The facility is 1/2 office and 1/2 warehouse (about 13k square feet total) and the attic and warehouse airspace is all connected.

Funny story; the previous tenants expanded the office portion without approval and got caught. Fire Marshal made them add sprinklers but otherwise let them slide. They also left what seems like hundreds of feet of dead Cat5 laying above the grid -- oh yeah, none of the Ethernet is supported. It is a total mess (not our doing).

I'm planning on zip-tying the 25/70v wire to the suspension wires for the grid but I'll be honest, it is so tempting to lay it in like everything else...

And we KNOW you won't be securing to the sprinkler pipes. ;^)
Please let us know how this all works for you when you're finished.
Toodleoo!
Ron Hebbard.

 

[RonHebbard]

Plenum rules apply if the space above the ceiling is used for airflow. If, for example, air is supplied via ducts but return air simply returns in the area above the ceiling, then that is considered Plenum space. If air is delivered by ducts and returned by ducts, then it is not. The plenum rules are to prevent toxic gasses from burning plastic cable to enter the airflow and be moved to other areas.

Understood. That's definitely how it's supposed to be but I've always opted to never argue with AHJ's, Fire Marshalls, et al.
Toodleoo!
Ron Hebbard.

 

[Les]

Haha - most definitely won't be interfering with the sprinkler pipes. If I had my way, everything would be in cable trays but it's too far gone. We run a lot of PoE and wireless, but those last tenants must have had everything hardwired and hundreds of phone lines on top of that. My theory is that the old company moves out, just cuts their lines, removes the actual gear and then they're gone. New renters arrive, need to install their own infrastructure, and just throw it on top of the abandoned stuff. We must be the 5th tenant since the dawn of Ethernet. There is a 5" bundle of Cat5 above the telecom room that appears to have been cut with a hacksaw. It branches out to who-knows-where.

Oh and it's definitely not a plenum. All our AC returns are run straight up to the RTU's.

One last question. Since I have the option of doing either one, should I do 25v or 70v? The office is actually not very large, only requiring two loudspeakers in the largest rooms. It's a quiet office with the only loud portion being the warehouse. The amp is 100w and either way, I'll probably only be pushing a small portion of that with my 11 speakers total. My thought is that 25v is safer/less liability than 70v.

 

[RonHebbard]

Haha - most definitely won't be interfering with the sprinkler pipes. If I had my way, everything would be in cable trays but it's too far gone. We run a lot of PoE and wireless, but those last tenants must have had everything hardwired and hundreds of phone lines on top of that. My theory is that the old company moves out, just cuts their lines, removes the actual gear and then they're gone. New renters arrive, need to install their own infrastructure, and just throw it on top of the abandoned stuff. We must be the 5th tenant since the dawn of Ethernet. There is a 5" bundle of Cat5 above the telecom room that appears to have been cut with a hacksaw. It branches out to who-knows-where.

Oh and it's definitely not a plenum. All our AC returns are run straight up to the RTU's.

One last question. Since I have the option of doing either one, should I do 25v or 70v? The office is actually not very large, only requiring two loudspeakers in the largest rooms. It's a quiet office with the only loud portion being the warehouse. The amp is 100w and either way, I'll probably only be pushing a small portion of that with my 11 speakers total. My thought is that 25v is safer/less liability than 70v.

If it was me, I'd go straight to 70V for several reasons: Possible future growth, less line loss, I could go with a smaller gauge cable, 70V is, arguably, more common, (If I had to shop for another speaker or two for instance.) yada, yada. BUT I'm in Canada and not dealing with folks in your locale.
Toodleoo!
Ron Hebbard.