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[Alan Reynolds]

Our small church's 20 year old audio system needs replacement. None of us are real audio pros, so I've been studying as much as I can...

We're working with a local A/V installer who as come up with some great ideas for video (something I do understand). But for sound reinforcement for our 400 seat fan-shaped sanctuary he's proposed:
- QSC 70 volt amplifier
- 2 SoundTube HP12i 2-way high power speakers, center mounted
(plus a bunch of other conventional stuff)

From everything I've read, 70 volt systems are typically used for distributed sound (like a nursery feed) or where there are so many speakers that impedance becomes a problem. (We have maybe 100' between the current amp location and the speakers.) Also, I read that they are typically used for speech and background music, as the required transformers (built-in on these units) will take some of the frequency response off.

I've pushed our installer, and he insists this system will rock, even as we add more contemporary music. Anything will be better than the creaky system we have now, but our small church gets one shot at audio, and I don't want to mess up.

- Is a 70 volt system reasonable, or totally nuts?
- Anyone have experience with SoundTubes as primary speakers?

Thanks so much.

[john abney]

Ask your installer why he is recommending a 70 volt system. It's been a long time since I've done AV installs (just remember to always wash with COLD water after crawling around in fiberglass ) but I recall there are advantages to 70 volt systems if you plan to incorporate a lot of speakers. You can keep adding speakers until you reach the power rating of the amp.

You don't have to worry about impedance with 70 V. From reading your posting though, we may be talking about two different things. There is speaker impedance wherein wiring two speakers in parallel cuts the impedance in half (series doubles it). This is highly critical, you can kill an amp with too low a load. Then there is cable length impedance which in practice only starts to get real important if things get absurd (such as 1/2 mile runs using 18 gauge zip wire). 70 V does allow you to use much smaller gauge wire than non-70 V and it allows you to forget about series vs. parallel.

From a Google search, it appears the Soundtube can run off either a 70 V tap or an 8 ohm tap. If nothing else, insist on robust cable of decent quality (12 or 14 gauge) and try the system both ways. Maybe the transformers add a nice coloration to the sound. You never know until you listen.

What else has he specified for the job? What do you have in the church now?

[John Roberts {JR}]

Dazed and Confused wrote on Mon, 09 August 2004 11:22

Our small church's 20 year old audio system needs replacement. None of us are real audio pros, so I've been studying as much as I can... We're working with a local A/V installer who as come up with some great ideas for video (something I do understand). But for sound reinforcement for our 400 seat fan-shaped sanctuary he's proposed: - QSC 70 volt amplifier - 2 SoundTube HP12i 2-way high power speakers, center mounted (plus a bunch of other conventional stuff) From everything I've read, 70 volt systems are typically used for distributed sound (like a nursery feed) or where there are so many speakers that impedance becomes a problem. (We have maybe 100' between the current amp location and the speakers.) Also, I read that they are typically used for speech and background music, as the required transformers (built-in on these units) will take some of the frequency response off. I've pushed our installer, and he insists this system will rock, even as we add more contemporary music. Anything will be better than the creaky system we have now, but our small church gets one shot at audio, and I don't want to mess up. - Is a 70 volt system reasonable, or totally nuts? - Anyone have experience with SoundTubes as primary speakers? Thanks so much.

70 V systems will reduce wire losses over long runs and simplify managing power balance between multiple speakers. Conversely running the audio through transformers on each end requires lots of iron for very low frequency linearity.

I suspect an adequate system could be assembled with or without 70V capability, YMMV.

JR

[Tom Young]

You are in for bad audio if you pursue this course.

The Soundtube ldspkrs are of far more concern to me than the 70V issue.  But both are inappropriate and completely unnecessary.

The Soundtube product line is based on wide coverage designs that are completely wrong for 95% of sound reinforcement applications.  They also may not provide the SPL, power handling and frequency response that you need.

I strongly suggest you employ someone else to design and provide your sound system needs.  This provider may know video but he has NO clue about live sound.

[Alan Reynolds]

Thank you -- you have helped confirm my suspicions. We have now engaged the services of different firm with significant church experience, and he said pretty much the same thing.

It is tough to get good advice when you are small church with amateur technicians, but we are learning.

[john abney]

Hi dazed and confused,

I trust you weren't referring to me when you said that your suspicions had been confirmed. My first (fleshly) thought when I was preparing to respond to your initial posting was to crack wise about a man with hammer seeing every problem as a nail. As I said, I've worked in AV and I know that 70 V is common there. But then I thought (hopefully a little more spiritually) that saying something like that about a product I had never heard (the Soundtubes) might be bearing false witness simply for the sake of sounding clever or wise. I have heard QSC's better amps and they sound OK (fairly neutral) - especially for the weight, current draw and the money. So I decided to research the other product you mentioned a little before answering.

I did a Google search, and the first listing had several install-type loudspeakers with the Soundtubes being the most expensive ($700+) and described as suitable for stadiums and football fields at high SPL (the same could have been said about some Western Electric horns). Seems like it's probably an efficient speaker since the power rating is less than 200 watts. The appearance would not be what I would choose for a Gothic or a colonial building, but you said fan-shaped so I'm guessing your church's interior is modern. Perhaps the Soundtube's modern look would fit right in. I didn't research in depth, so I didn't know that the dispersion pattern was especially wide, but it seems that would be something you might want in a fan-shaped room.

Questions? Absolutely. That's why I was interested in three things: why he recommended 70 V, what else he recommended that you buy from him (that will tell a lot about his available vendor pool) and what you already have that he's suggesting you discard (it would tell a lot about his taste if - for example - he told you to get rid of that old fashioned White EQ).

But it seems - and please forgive me if I am jumping to conclusions - as if you decided to fire the guy from at least the audio portion of the job without giving him a chance to explain and defend his design decisions. Did he recommend a lock-out panel on the EQ? If so, maybe he's learned from experience and is trying for 'bombproof.' I don't know you or your fellow sound crew, but you have identified yourself as "Dazed and Confused" which happens to be a Led Zeppelin title - a loud, heavy, speaker-stressing Led Zeppelin title. Not exactly the "I Come to the Garden Alone" vibe, now - is it .

I've never heard the loudspeakers he recommended and I seriously doubt I've ever heard the first installer's work. The more important question is, have you? Are you planning on reimbursing the man for the time he spent designing a sound system for your church?

[Alan Reynolds]

JAbney,
Thank you as well for your comments. I think the best description really is "a man with hammer seeing every problem as a nail." When asked to see similar sites, we were pointed at a successful installation at a gymnasium. Needless to say that doesn't look like our church. The explanations left me concerned enough to want to learn more (there was no specific design work per se).

Having done a lot of study over the last two weeks, I've learned that a 70v system doesn't make a lot of sense for a central two-speaker cluster (it could work, but why do it that way?), and that the wide-dispersion Soundtubes are great for open-field or PA, but will cause problems with reflections in our church sanctuary. In addition, I now know how to do the math to determine that they won't get loud enough for blended worship in our facility (too high a ceiling, wide a space).  

I'm no expert, and the AV contractor is a nice guy, but I knew one of us had to be wrong about something. It was good to hear from someone like Tom Young that this doesn't make sense. That pushed me to seek out a church-audio specialist, who said the same thing (unprompted).

I'm not the speaker-stressing type (at least not a church!), but we are really looking for intelligibility and room to add more contemporary worship music. It's going to take a little more, but we'll get there -- I'll post the results.

[Adam Kane]

I would strongly reccomend against the soundtubes.  I've never seen them used anywhere except places like stores, gyms, theme parks and the like.  They seem to have a sort of Bose approach:  lot of sound from a small package.  

You're right in stating that the wide dispersion would cause problems.  Not just with poor house sound, but imagine the feedback from all of the mics on stage.  

The whole idea of a 70volt front of house system makes me cringe.  Even the best 70volt speakers with the best transformers can't come close to the clarity and punch that live music requires.

The whole idea of installing a nice system is to put the sound where you want it with minimal reflections.  Most of the sound tube speakers I've seen disperse around 360-degrees.  Wouldn't this kind of defeat the purpose?

[Wayne A. Pflughaupt]

Quote:

The whole idea of a 70volt front of house system makes me cringe. Even the best 70volt speakers with the best transformers can't come close to the clarity and punch that live music requires.

During my time as a pro audio installer, we only did one 70V system in a church.  It was for a traditional denomination in a vintage 1930s sanctuary, and they understandably didn’t want some monstrous cluster hanging from their vaulted ceiling.

We installed small Ramsa speakers near-field under the pews, every-other row, set on delay zones, and it was a beautiful thing.

But it was primarily a vocal-only system.  For live music – can’t imagine using a 70V system. "Makes me cringe" - aptly put!

Regards,
Wayne A. Pflughaupt

[AV Tech]

In my own church building and in others where I have installed sound systems, I have used the nominal 8 ohm output for 1-6 8 ohm speakers (using various series/parallel wirings to keep impedance between 4 and 8 ohms), and used a simple separate amplifier with 70 Volt output for multiple speakers going to nurseries, vestibule, and kitchen/fellowship hall, sometimes on hundreds of feet of 16 gauge wiring.  In one such installation I successfully used a 10 watt Bogen amp, and Radio Shack makes a 40 watt one for under $100.
In my own church we are using our Peavey mixer/amp to drive the center cluster and on its Monitor output an old 60 watt TOA with 70 volt output to drive 4 other speakers with transformers in custom installed ceiling speakers for even distribution (only 10' above the floor), plus 5 other speakers with L-pad volume controls in other rooms throughout the building.  Our sound reinforcement needs are modest, as we worship with only congregational acapella singing.  We occasionally have need to play recorded music or amplify a soloist for wedding or funeral, or to present a video program.
I have yet to find two churches, chapels, auditoria (sorry, my 9th grade Latin lessons stuck), or other space where exactly the same equipment prescriptions were ideally matched to another different space.

[ProSoundWeb Community]