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Author Topic: Y Cable at the back of an amp  (Read 4498 times)

Ivan Beaver

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Re: Y Cable at the back of an amp
« Reply #10 on: February 13, 2017, 12:19:58 pm »

Ivan, I've encountered several speaker mfgs that quote nominal impedance as the standard impedance (2,4,6,8) closest to the LOWEST impedance they expect the speaker to present.  So if it's 5 Ohms, they will say 4 Ohms.

Now I don't know if this is the right way to do it, but it is important in calculating what to set the amp limiter to.  It gives that little extra "headroom."

John R.
Yes, the spec should be towards the bottom of the impedance curve.

If you set the limiter for the lower impedance-it will just limit a bit early-which is NOT a bad thing.

Also if you look closely at a lot of driver power ratings, you will see that they rate the wattage based on the MINIMUM impedance-NOT the rated impedance.

So if you figure a particular voltage with a lower impedance the "wattage" spec will be higher.

YES the "little number" DO mean something and ARE important.

Sadly, more and more manufacturers only give very simple numbers-if you can even get that.

It is amazing how many "basic specs" are missing on some highly respected products-such as wattage-sensitivity-real -3dB numbers etc.

But we won't go there
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Ivan Beaver
Danley Sound Labs

PHYSICS- NOT FADS!

Luke Geis

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Re: Y Cable at the back of an amp
« Reply #11 on: February 14, 2017, 02:26:34 pm »

Wait a minute.....

If you run a single speaker line out from the amp and connect it to a speaker that has a through connection, the connection is in parallel. It is the same thing as a Y from that point. The next speaker connected in line will then drop the impedance seen at the amp. Assuming a Y from the amp is used and each speakers is 8ohms, then there would be a 4ohm load on the amp. The individual speakers ohm rating will not change regardless of the way they are connected, but the load seen at the amp will change.

So the direct answer to the question as stated is yes the ohm ratings of the speakers will still be the same. However the load seen at the amp from the speaker will cut in half. So two 4 ohm speakers would present a 2 ohm load upon the amp.
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Mac Kerr

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Re: Y Cable at the back of an amp
« Reply #12 on: February 14, 2017, 03:17:40 pm »

Wait a minute.....

If you run a single speaker line out from the amp and connect it to a speaker that has a through connection, the connection is in parallel. It is the same thing as a Y from that point. The next speaker connected in line will then drop the impedance seen at the amp. Assuming a Y from the amp is used and each speakers is 8ohms, then there would be a 4ohm load on the amp. The individual speakers ohm rating will not change regardless of the way they are connected, but the load seen at the amp will change.

So the direct answer to the question as stated is yes the ohm ratings of the speakers will still be the same. However the load seen at the amp from the speaker will cut in half. So two 4 ohm speakers would present a 2 ohm load upon the amp.

Huh???

Two speakers plugged into a single amp channel will present the same load to the amp whether they are "daisy chained" via the "Through" connector or connected via a Y cable at the amp. The only difference might be slightly less loss in the cable because of more copper.

Mac
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Don T. Williams

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Re: Y Cable at the back of an amp
« Reply #13 on: February 14, 2017, 05:21:55 pm »

I think Mac and Luke are both correct in their thinking.  The problem is in the way the question is stated.  Two 8 ohm speakers stay 8 ohms each, and the amp "sees" a 4 ohm load.
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Stephen Kirby

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Re: Y Cable at the back of an amp
« Reply #14 on: February 14, 2017, 05:47:27 pm »

  Audio is AC and as such has another characteristic called reactance due to the presence of the voice coil (an inductor) in the speaker itself.  Since music is an ever changing, complex AC waveform the actual impedance the loudspeaker presents to the amplifier is a function of both the frequency and the level of the signal.  Impedance also changes due to other factors such as the construction of the cabinet (speaker has to work harder to overcome the backpressure of the air inside the enclosure) and heating of the actual voice coil as the speaker is utilized.
You may have been trying not to over complicate things but I would say that the reactance caused by the mechanical aspects (weight of cone, stiffness of suspension, back EMF of the cone once in motion, reactance of the cabinet's tuning) far outweigh the contribution of the coil's static inductance.

The upshot of which is that you really want an impedance curve of the speaker system (driver in cabinet and any associated passive crossovers) to know what load is being presented to the amp at any given frequency.  And as you mention about thermal effects, the voice coil and any coils in a crossover will change characteristic as they heat up from passing larger currents at higher SPLs.

Nothing is as simple as it sounds, even in sound.
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Re: Y Cable at the back of an amp
« Reply #14 on: February 14, 2017, 05:47:27 pm »


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