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Author Topic: 70V or Not ?  (Read 12439 times)

sureshmadan

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70V or Not ?
« on: January 23, 2005, 12:52:29 pm »

Seeing that there have been quite a few posts recently on 70V /100V systems I would like to pose a rather rudimentary question.

At what point do you decide to use a CV system ?

Example.

For an upcoming installation we have a maximum length of 100m between the amps and the speakers. Speakers are 50W 8?.

Is it better to use 70V CV distribution or just lay in 1.5mm cable in this instance ?

Thanks

Suresh Madan
Spatial MultiMedia Pvt Ltd
New Delhi, India
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John Roberts {JR}

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Re: 70V or Not ?
« Reply #1 on: January 23, 2005, 01:38:45 pm »

For the simple case of one speaker drop the overhead of bumping up to and down from 100v may not be worth the trade off of simply investing in heavier wire and/or a slighly larger power amp.

One hybrid approach worth consideration if there are two speakers in use is to wire the speakers in series creating a 16 ohm load which would have lower current draw and lower subsequent wire losses.


JR
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Tom Young

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Re: 70V or Not ?
« Reply #2 on: January 23, 2005, 02:28:02 pm »

In this example one of the most important question is: how many ldspkrs are you using ?
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sureshmadan

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Re: 70V or Not ?
« Reply #3 on: January 23, 2005, 11:33:28 pm »

Thank you for your responses.

The installation has 12 independent zones.

Of these 6 have 1 speaker each. (50W 8?)

Of the balance 6 the number of speakers varies from 2-5 per zone.

The cable runs from the Amps vary from 20m to a maximum of 100m.

The speakers are the EVID 3.2 (50W 8?)

Do you think it is advisable to just lay down heavier cable rather than use a 70V approach. Presumably this would also improve the frequency response of the system.

I propose to use twisted pair with shield cable between the amps and the speakers.

1. Is this the correct approach ?
2. Will using a shielded cable help to avoid picking up interference along the leg th of the speaker cable ?
3. Where should the shield be terminated at both ends (speakers have ABS cabinets).
4. What cross section of cable should i use?

Thanks

Suresh Madan
Spatial MultiMedia Pvt Ltd
New Delhi, India
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John Roberts {JR}

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Re: 70V or Not ?
« Reply #4 on: January 24, 2005, 11:31:54 am »

At a glance it sounds like CV would be useful.

No, you typically don't need to use shielded cable for speaker cables. While CV systems are higher Z than low voltage systems they are still relatively low impedance. Shielding adds capacitance to the load which could further reduce HF response and potentially destabilize amplifiers.

How you divide up the system depends on how independent the zones need to be. In large systems the economies of scale come from using one amplifier for the whole job, there are too many variables unexplored to determine what precise combination is ideal for you.

JR
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sureshmadan

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Re: 70V or Not ?
« Reply #5 on: January 24, 2005, 12:48:27 pm »

Since the zones are running independent source material using a single channel or amplifier is not possible.

It seems like a waste to use transformers for single speakers but if the 100m cable runs requires it I guess it will have to be.

Interestingly another installer I spoke to swore of the benefits of using shielded speaker cables. I believe, unless I misunderstood him, though, that he was referring at that time to low impedance 8? signals.

So would it be correct to say that with low impedance signals shield cables could offer some potential benefits and with high voltage signals they are not desirable.

While on the same subject what are the potential advantages of standard 2 core cable against 2core twisted pair ?

Suresh Madan
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Hal Bissinger/COMSYSTEC

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Re: 70V or Not ?
« Reply #6 on: January 24, 2005, 01:12:43 pm »

I think the answer here is "it depends". I assume that you will be using 12 amps (or amp channels) to supply the 12 zones. Question is what is the reason for separate amps? Are they necessary because each zone will handle different program material? If not consider one amp with output switching for the zones. CV would certainly be helpful in this case especially if you do the switching at the zone locations.

If you are concerned about frequency response consider that there are amps that will feed the CV line directly without an output transformer.

If you must go the 12 amp or channel route, certainly a single speaker 20m from the amp could be run directly but for groups 100m away CV would be beneficial.

-Hal

Kevin Maxwell AKA TheMAXX

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Re: 70V or Not ?
« Reply #7 on: January 25, 2005, 03:32:41 pm »

The Evid 3.2 version are 8ohm speakers (150 watts) the 3.2t version have the transformer needed to use these with a 70v system. This is according to EV web site.
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sureshmadan

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Re: 70V or Not ?
« Reply #8 on: January 25, 2005, 04:54:56 pm »

Ok ! Things get even more interesting !

The EVID general brochure downloaded from the site says the EVID 3.2 are 150W 8?.

The EVID 3.2 Specification Sheet downloaded from th e site also says that these are 50W 8?.

Just spoke to EV technical support and they say these are rated for 75W continous and 150W peak performance at 8?.

Now what do you say to that ?!

Anyone have real life experience with these ?

Suresh Madan
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Jim Cutshall

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Re: 70V or Not ?
« Reply #9 on: January 26, 2005, 12:35:09 am »

I've installed a lot of 4.2 and 6.2 Evids.  The 3.2 sounds good (IMO) but most customers seem to want a little more lows and that's why we've installed the bigger ones.  

I have (5) 3.2's in my house for my surround sound and they work great.

If your doing a CV system with them, they do make a transformer version but I don't remember if it is a 3.2 or 4.2 or both.

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Jimbob

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Re: 70V or Not ?
« Reply #10 on: August 19, 2005, 07:31:59 pm »

Suresh:

The main reason for using a 70V output is more efficient transfer of power to the speakers.  Using 100m of speaker cable in an 8-ohm system depending on the wire guage, more voltage is being dropped on the cable than the speakers.  70V systems raise the voltage, causing a proportionate drop in the current (Ohm's Law).  The amount of power you can send through a wire is a function of the current not the voltage.  So if the voltage is 10 times as great, the current is 1/10th as great. Therefore the efficiency would be 10 squared or 100 times as great!!! P=I^2R.  Also speakers can be connected in parallel without having to worry about impedance. The only drawback is that frequency response below 70Hz is reduced.
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Ivan Beaver

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Re: 70V or Not ?
« Reply #11 on: August 20, 2005, 05:28:28 pm »

sureshmadan wrote on Tue, 25 January 2005 16:54

Ok ! Things get even more interesting !

The EVID general brochure downloaded from the site says the EVID 3.2 are 150W 8?.
The EVID 3.2 Specification Sheet downloaded from th e site also says that these are 50W 8?.
Just spoke to EV technical support and they say these are rated for 75W continous and 150W peak performance at 8?.

Now what do you say to that ?!

Anyone have real life experience with these ?

Suresh Madan

That is exactly what Kevin Maxwell said.  What he didn't directly say (but kinda suggested) was that if you didn't have your speakers already-AND you were going to go the 70V route-THEN he suggested the model# for the ones with the transformer already inatalled-so you don't have to use an external one.
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Rick Johnston

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Re: 70V or Not ?
« Reply #12 on: August 22, 2005, 02:59:23 pm »

12 zones? The headend sounds like a job for IED products.
http://www.iedaudio.com/

They make rack-frame dual 100-watt amp cards that will drive a 70-volt system. Each card can be bridged to become a single 200-watt amp. Signal sources can be routed to any or all zones via several different IED controllers.

You'll probably home-run the cabling for each zone back to the head-end. Might as well run them all to the head end.

The EV speakers can be ordered with transformers.

Regards,
Rick Johnston

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