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Old 6th March 2011, 03:37 AM   #41
Lerg is offline Lerg  Canada
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Going to an 8 ohm version only does seem like it might be a reasonable choice. It makes parallel wiring more feasible for dual driver designs, and single drivers are an easier load for some amplifiers that might not have liked 4 ohms.
If there are any other benefits to an 8 ohm coil that would be good to know.

Those shiny new connection terminals that you have on the alpair 7 and other new drivers looks kind of nice too if we getting a wish list in here. I can't tell for sure but it looks like you might have included it from what I can see of the new frame.
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Old 6th March 2011, 03:49 AM   #42
AEIOU is offline AEIOU  United States
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If you wire/install two identical 8 ohm drivers in parallel on the same baffle, your increase will be 6dB not just 3dB!

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Originally Posted by germpod View Post
Making it 8 ohms makes it so you can use two drivers to get an extra 3db of efficiency which is quite appealing, to go along with the other benefits of using two drivers.

Ed Robinson
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Old 6th March 2011, 04:54 AM   #43
Lerg is offline Lerg  Canada
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You still get a 3db increase in sensitivity, and both series and parallel wiring get you another 3db from increased power handling. No overall difference there.
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Old 6th March 2011, 05:40 AM   #44
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Neither of you have it quite right...(wired in parallel)

You get 3 dB increase in efficiency from doubling th number of drivers.

You get 2 x the power (3 dB) if you are using a voltage amp capable of delivering the current needed for the lower impedance (something akin to this is the case with most store bought SS amps -- typically amplifier distortion also doubles)

You get half the power (-3 dB) if you use a current amp (or most output transformerless tube amps).

You get about the same power with a typical transformer coupled amp.

dave
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Old 6th March 2011, 06:10 AM   #45
AEIOU is offline AEIOU  United States
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Efficiency and sensitivity are two different things and can easily be confused. And it certainly depends on whether or not we are talking about constant voltage or constant power.
Most modern high powered amplifiers have no problem delivering more current into lower impedances. Theoretically by the numbers, you double the current when you half the impedance provided their is no voltage drop.

If you place two drivers in parallel that are rated at 90 dB/2.83V/Meter then the combined output would now be 96 dB/2.83V/Meter. All box modeling software or crossover design software that allows you to model two drivers in parallel will calculate it this way. It's very easy to measure with actual drivers too, and confirm that this is true, and if it wasn't then even order crossovers would not sum to +6 dB at the crossover point and D'Appolito's MTM would not work right either. However, in this example our parallel pair at 2.83V is drawing twice the Wattage as a single driver. Therefore, if we reduce the Voltage until the Wattage draw is the same as for a single driver then we would find that our parallel pair is only 93dB/W/Meter more "efficient."
The problem here is two-fold, first we had to reduce the drive voltage to get here and second, since solid state amplifiers are constant voltage sources Voltage sensitivity (dB/2.83V/M) is the only way to compare two drivers accurately.


Quote:
Originally Posted by planet10 View Post
Neither of you have it quite right...(wired in parallel)

You get 3 dB increase in efficiency from doubling th number of drivers.

You get 2 x the power (3 dB) if you are using a voltage amp capable of delivering the current needed for the lower impedance (something akin to this is the case with most store bought SS amps -- typically amplifier distortion also doubles)

You get half the power (-3 dB) if you use a current amp (or most output transformerless tube amps).

You get about the same power with a typical transformer coupled amp.

dave

Last edited by AEIOU; 6th March 2011 at 06:16 AM.
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Old 6th March 2011, 06:54 AM   #46
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Quote:
Originally Posted by AEIOU View Post
since solid state amplifiers are constant voltage sources Voltage sensitivity (dB/2.83V/M) is the only way to compare two drivers accurately.
Most SS amps at least approximate voltage sources, not all. Do a poll, i bet you'll find that a significant number of Mark Audio users have tube amps. Matter of fact i can think of no Mark Audio uses in my local area that are using anything but. Mark does (at least at home). Tony does.

Sensitivity is, in IMHO, started as a ploy by marketers to get a higher dB number. Real efficiency should be specified, 1w/1m. Sensitivity could also be specified. Efficiency is agnostic (any amp may apply). Sensitivy is misleading unless you have a true voltage amp.

dave
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Old 6th March 2011, 07:04 AM   #47
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Quote:
Originally Posted by planet10 View Post
Most SS amps at least approximate voltage sources, not all. Do a poll, i bet you'll find that a significant number of Mark Audio users have tube amps. Matter of fact i can think of no Mark Audio uses in my local area that are using anything but. Mark does (at least at home). Tony does.

Sensitivity is, in IMHO, started as a ploy by marketers to get a higher dB number. Real efficiency should be specified, 1w/1m. Sensitivity could also be specified. Efficiency is agnostic (any amp may apply). Sensitivy is misleading unless you have a true voltage amp.

dave
I actually do have a little tube amp that definitely works best with 8 ohm loads.
But I also have a solid state receiver and a solid state amp under construction.
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Old 6th March 2011, 08:41 AM   #48
djanci is offline djanci  Croatia
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Efficiency/sensitivity are NOT amplifier (topology) dependent values!

Efficiency is expressed in % as output(acoustical) power/input(electrical) power ratio.

When defining sensitivity, acoustical power is expressed as SPL in dB measured on-axis one meter from the speaker and electrical (input) power is set to 1W. Basically, sensitivity is some kind of normalized efficiency.

Also note that efficiency/sensitivity of speaker varies with frequency, so when manufacturer say that sensitivity is 90dB/W/m that value is almost meaningless.

You don't gain efficiency with 2 speakers! They are consider as a system so 1W is now applied to a system ie. 1/2W to each speaker. With a half power on each speaker SPL (NOT sensitivity) of each drops by 3dB, but as there is two of them combined SPL rise by 3dB. So -3dB+3dB=0dB. No gain of sensitivity but gain in power handling ie. 3dB gain in maximal SPL.
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Old 6th March 2011, 09:04 AM   #49
Ian444 is offline Ian444  Australia
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Quote:
Originally Posted by planet10 View Post
i bet you'll find that a significant number of Mark Audio users have tube amps. Matter of fact i can think of no Mark Audio uses in my local area that are using anything but. Mark does (at least at home). Tony does.
Another tube amp user here, so what will it mean for tube amp users if future CHR-70 models are 8 ohm? I would have thought 8 ohm voice coils would be welcomed with great enthusiasm, as it seems to be a more common load? I would think an 8 ohm voice coil would generate more sales (which makes the final unit more economical or generate more profit) but, and a big but, how would the HT manufacturers like the change to 8 ohm?

I am so happy with the gen 1 units, any improvements would be fantastic, and if the gen 3 could drop straight into my existing speaker boxes I would probably buy a pair at the drop of a hat, and build some other boxes for the gen 1 units. I am glad to hear the CHR-70 has been a sales success, it really is a pleasure to listen to. I do hope this model continues for a long time.
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Old 6th March 2011, 09:23 AM   #50
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Quote:
Originally Posted by planet10 View Post
Where the fixing holes moved so that they aren't so close to the driver cutout?

dave
Yes. That should be fixed with the EL70 aswell. That's the only bad thing with the EL70.
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