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Need amp to run six or eight JBL control 1 speakers at an exhibition

 

New member
Username: Earthplane

Cricklewoood, London United Kingdom

Post Number: 1
Registered: Apr-12
I am helping a friend set up a sound installation in an art centre (in South Africa) and am getting so many contradictory messages about what we need. The room is about 40 feet X 18 X 12.5. The ceiling is made of wood.
The idea is to hang either three or four pairs of speakers (JBL Control 1s) on the ceiling and keeping the amp in the office. It will be more than background sound. There will be interviews as well as music and nature sounds. The audio will be on a loop running on an iPod.
I was looking at the Teac AG-980 because it can accommodate eight speakers without having to use a splitter or any fancy (parallel or serial) wiring. Then someone recommended something very inexpensive at an electronic chain (http://www.maplin.co.uk/slimline-5.1-av-amplifier-227609). But when I called to confirm a colleague said that would not be nearly powerful enough. I am totally confused about how much power is needed. I heard 100watts is more than enough and then I heard you it must be 100watts for each speaker. That would mean 600-800 watts. The amp must be rugged. It would be on for eight hours a day in dusty conditions. Please help!!!
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Platinum Member
Username: Jan_b_vigne

Dallas, TX

Post Number: 17195
Registered: May-04
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What's the budget? More than the cost of the Teac I hope.
 

New member
Username: Earthplane

Cricklewoood, London United Kingdom

Post Number: 2
Registered: Apr-12
Thanks, Jan. The budget could be more but not a lot more. It is a charity in the middle of nowhere. The equipment needs to be as uncomplicated and robust as possible. My main question is how much power do we need. This is where the conflicting advice has come. Do we need !00 amps of power for each speaker? Again, this is not for a concert it is for an art exhibition. We will never be blasting the speakers, and yet it will be more than "background music". I'm in the UK and the time difference is six or seven hours. I'm grateful for your help.
 

Platinum Member
Username: Jan_b_vigne

Dallas, TX

Post Number: 17196
Registered: May-04
.

Most listening requires only a handful of watts. More importantly, what determines how much volume you can achieve is more based upon the speaker's ability to convert electrical energy into acoustic energy than it is just how many watts you have on hand. This ability of the speaker is measured by the "sensitivity" specification of the loudspeaker which measures "how much in" produces "how much out". The JBL's are rated at 87dB which is slightly above average and provides an advantage of requiring less power overall. If we assume you wish to have an average listening level in the low to mid 90dB range - conversational but not background - then the leap from 87dB output with only one watt input into the JBL's to, say, 93dB would require less than five watts. That would be your "average" wattage output and you would like to have some headroom for dynamic peaks. But a decently constructed 35-50 watt amp should do the job you're asking of it. Driving off an iPod playing MP3's would reduce that requirement slightly given the compressed dynamic range of MP3's. MP3's also cut your sound quality by a considerable margin and are not generallly considered a decent source for even a modest audio system. As background the MP3 would be OK but, if this is meant as a system where the music is of value to the event, even a portable CD player would outshine the iPod IMO. But I understand the hours of music from the iPod probably outweighs the sound quality advantages of a single CD player. You could record your playlist to the iPod at a higher bit rate (such as WAV or FLAC) which would increase sound quality while still leaving hours of playing time on even the smallest iPod.


Watts alone don't buy you much volume and trying to buy volume by buying watts alone is a somewhat futile effort. As power increases by double (2 to 4, 20 to 40 or 50 to 100) the increase in acoustic output is only 3dB for each doubling - noticebale to the attentive listener but not enough to say there would be a substantial increase in volume since the advantages of more power are to handle loud peaks and not to increase the average program levels.

I would say in the space you describe two pairs of speakers each placed approximately one third of the length of the room would be enough for the sort of listening you describe. With that mounting scheme there would still be a speaker about every thirteen feet along the length of the room. Adding the third pair would present some problems to many amplifiers as that would either drop the load on the amp down to four Ohms (parallel wiring) or double the load to sixteen Ohms (series wiring). Most solid state amps in your price range like neither. You would then be best advised to insert a speaker selector switch box with a protection device which would maintain a steady load on the amp. Figure another few hundred for a good switch worth buying. My suggestion would be to try the two pairs mounted as described and determine whether you'll have sufficient volume once the room is filled with warm bodies which absorb some acoustic output. If you determine you would prefer slightly higher volume levels, add a third pair with one speaker each at either end of the room. If the amplifier shuts down with that load - I would suggest a series connection on the third pair which will raise the impedance load and, therefore, make for a more stable load - you can add the switch box with a load protection device at that time. The alternative to the load issue is a much beefier amplifier - read; a much more expensive amplifier.

You might want to consider a stereo to mono transformer on the amplifier outputs. This would negate any differences perceived as a listener walked the length of the room pointing out left/right interferences. It's not a big deal, can always be added at a later date and only adds a small amount to the cost of the system.


While the Teac is probably a decent enough amp for a short term exhibit, I would be looking at something that offers a more likely issue of reliability over the long haul should this exhibit be more than temporary. I would also have a backup plan in mind should the amp fail and you need sound. Buying over the internet (or even in person) will mean days or possibly weeks of delays in getting a replacement as most manufacturers would send the unit off for repairs first and provide a replacement only if the amp continued to fail. Some retailers offer extended warranty plans which cover a loaner for emergencies. You might consider this to be a reasonable expense rather than having to either go without sound or to buy another amp to continue to have msuic.

You don't need the tuner (radio) function of the Teac and while it's not costing a lot to include it in the package, you could probably do better with a multi-channel amp meant for whole house distribution systems. Something along the lines of this; http://www.hometech.com/hts/products/audio/amplifiers/nv-d460.html would work.

You could also go the "T-amp" route which would be several small integrated chip amps such as; http://www.amazon.com/Dayton-DTA-100a-Class-T-Digital-Amplifier/dp/B004JK8BDK These are cheap and cheerful amps with good sound and very good reliability. Buy an extra as a back up at the price. Once you get over the size of the amp vs the sound it produces, this would be a good choice IMO.

You might want to consider some volume controls for each pair of speakers to sort out the needs of the day as people congregate in various areas of the room. Those can always be added later of course.

You can also consider a self-powered speaker which would negate the need for separate amplifiers. http://audioengineusa.com/Store/Audioengine-2 Most music instrument shops and pro sound shops should have a wide selection of self-powered speakers to choose from at virtually any price range.

If you stick with the JBL's, you would do well to consider adding a small subwoofer to the system. A powered sub doesn't need to be much, just something to add a bit of thump to the bass since the JBL's are only spec'd down to 80 Hz which isn't very much bass. Even more so when you place them in such a large space and even more so yet when that 80Hz has no defined roll off point. The spec just says "80Hz" as far as I can see which could mean there's really no bass from that small speaker beneath about 150Hz. IMO a small sub is almost mandatory if you want this to be more than background/restaurant conversational levels.




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