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Help with understanding speaker Impedance (please).

GURU

Well-known member
Nov 7, 2008
3
0
11,510
I'm sorry if this comes across as being somewhat naive but I was wondering if someone could assist in explaining how adding a Supertweeter to my speakers - may, will, does, could, etc, change/affect the load that my amplifier recognises?

The Supertweeters (rated at 8 ohms) have their crossovers and would connect to the main speakers HF binding posts (tri-wireable speakers - three sets of binding posts - LF, M and HF) via "piggy backing" banana plugs.

The main speakers are also listed as 8 ohms (and according to the manufacturer ATC have a flat impedance curve allowing easy load for amplifiers).Flat impedance curve allowing easy load for amplifiersFlat impedance curve allowing easy load for amplifiers

Further, if I was biamping (passive) the main speakers with bridged amplifiers* - one connected to LF binding posts "driving" the bass driver, and another connected to the M and HF binding posts "driving" the midrange driver, and tweeter (and in effect the Supertweeter), how does/would this impact on the amps, in terms of the load they see, and could this cause the amps to stress?

Thanks in advance

*It may or may not help, but In the manual, the amps aren't rated in relationaship to being able to drive 2 ohm speakers (in bridged mode) so I assume they would struggle or simply can't.
 

davedotco

New member
Apr 24, 2013
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0
OK.

Most of the information given in you post is irrelevant.

The supertweeter will have a simple high pass filter as a crossower so above this frequency your amplifier will be seing your regular tweeter and your supertweeter in parallel.

Without impedence curves it is impossible to be accurate but you are dealing with two 8 ohm drive units in parallel, so a nominal impedance of 4 ohms will result.

Demands on your amplifier at supertweeter frequencies will be minimal, so there should be no discernable stress on your amplifiers.

Go on, annoy you dog and give it a go.
 

GURU

Well-known member
Nov 7, 2008
3
0
11,510
Davedotco

Thankyou for your reply

With the two 8 ohm drive units in parallel in essence it halves the impedance thus creating a nominal impedance of 4 ohms, just so I am clear (I'm not that electrically minded and as such sometimes I can appear slightly thick), does this mean that only the amp driving the tweeter & supertweeter see a load of 4 ohms or will the entire main speakers impedence essential drop to 4 ohms and thus both amps will see this load of 4ohms?

Also, just for confirmation..."Demands on your amplifier at supertweeter frequencies will be minimal, so there should be no discernable stress on your amplifiers"...the fact that the amp or amps are in bridge mode won't creatie a problem (doesn't bridging in effect halve the impedance seen)?

Oh, I don't own a dog, but perhaps next doors cats will steer clear for a while. :)

.
 

davedotco

New member
Apr 24, 2013
20
0
0
GURU said:
Davedotco

Thankyou for your reply

With the two 8 ohm drive units in parallel in essence it halves the impedance thus creating a nominal impedance of 4 ohms, just so I am clear (I'm not that electrically minded and as such sometimes I can appear slightly thick), does this mean that only the amp driving the tweeter & supertweeter see a load of 4 ohms or will the entire main speakers impedence essential drop to 4 ohms and thus both amps will see this load of 4ohms?

Also, just for confirmation..."Demands on your amplifier at supertweeter frequencies will be minimal, so there should be no discernable stress on your amplifiers"...the fact that the amp or amps are in bridge mode won't creatie a problem (doesn't bridging in effect halve the impedance seen)?

Oh, I don't own a dog, but perhaps next doors cats will steer clear for a while. :)
Resistors in pararell are calculated by, 1/R1 + 1/R2 = 1/R3 Where R1 is the impedance of the tweeter, R2 the impedance of the supertweeter and R3 the impedance of the combination.

Strickly speaking that is for DC not AC music signal but in this instance it is close enough. This only applies above the crossover frequency where the amplifier 'sees' both units. The crossover increases the impedance at lower frequences so has little to no effect on the overall impedance of the system.

In theory the 4 ohm impedence of the two tweeters is a bit low for amplifiers in bridge mode but the demands made by a music signal at these, very high, frequencies should not be an issue, unless your amplifiers are pretty unstable at high frequencies. Very rare in a competent design these days.

Give it a go, but keep an eye (hand?) on the temperature of the amplifier, if it is not happy it will get pretty warm, pretty quickly so stop.

Very unlikely though.
 

GURU

Well-known member
Nov 7, 2008
3
0
11,510
Ok, I will definitely give it a go, but will be very conscientious re the amplifiers temperature.

Thankyou once more, your assistance is truly appreciated.
 

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