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Title: Y Cable at the back of an amp
Post by: John Luty on February 12, 2017, 09:56:22 pm
if I were to use a Y cable at the back of my amp instead of daisy chaining from the speaker would that still be a 4 ohm load to each speaker ?
Title: Re: Y Cable at the back of an amp
Post by: Ray Aberle on February 12, 2017, 09:58:31 pm
if I were to use a Y cable at the back of my amp instead of daisy chaining from the speaker would that still be a 4 ohm load to each speaker ?
So, you're saying both speakers are plugging directly into the amp, as opposed to amp --> speaker 1 --> speaker 2?

If so, then yes, the amp is seeing the same impedance either method.

-Ray
Title: Re: Y Cable at the back of an amp
Post by: Mac Kerr on February 12, 2017, 09:59:43 pm
if I were to use a Y cable at the back of my amp instead of daisy chaining from the speaker would that still be a 4 ohm load to each speaker ?

If you mean a Y cable that splits the output of the amp so a separate cable goes to each speaker, yes, the impedance will be the same. The advantage is that there may be less loss in the speaker cables since you will have more copper.

Mac
Title: Re: Y Cable at the back of an amp
Post by: John Luty on February 12, 2017, 11:11:27 pm
yes y cable plugs into the amp speaker "A" into one of the y's speaker "B" into the other . I as pretty sure the ohms would be the same just a brain fart . Doesn't hurt to reaffirm
Thanks
Title: Re: Y Cable at the back of an amp
Post by: Scott Holtzman on February 12, 2017, 11:54:22 pm
yes y cable plugs into the amp speaker "A" into one of the y's speaker "B" into the other . I as pretty sure the ohms would be the same just a brain fart . Doesn't hurt to reaffirm
Thanks


It's really incorrect to use the term "ohms" as a noun in the manner you did.


Since this is a forum with an educational mission let me try and help fill in your knowledge.


Thinking in terms of a constant value of an ohm does not help you understand the relationship of a speakers impedance and the relationship to the amplifier.


An OHM is a unit of electrical resistance.  It is used in both AC and DC electronics.  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.


This is why the impedance value of a loudspeaker is a nominal value.  It is a representation of the average impedance of the box over it's entire operational range.  The actual impedance of the loudspeaker could vary more than 50% of the total range of the loudspeaker.


When connecting speakers together it is very important to keep this relationship in mind as most amplifiers have trouble driving low impedance loads.  Once you start connecting speakers together you could be presenting a load to the amplifier that is too challenging for it and could lead to premature triggering of the protection circuit.  At least premature compared to where the protection would engage at a higher impedance.


Lower impedances cause the amplifier to produce higher voltages and you risk rapidly damaging the loudspeakers.


As Ivan always says "it depends" connecting a single 8 ohm speaker to an amplifier output gives you much margin for error.  Once you begin to connect multiple speakers you erode that buffer.  Parallel speaker connections is a very complex topic.


 
Title: Re: Y Cable at the back of an amp
Post by: Chris Grimshaw on February 13, 2017, 05:56:09 am


Lower impedances cause the amplifier to produce higher voltages and you risk rapidly damaging the loudspeakers.

 

Think you mean higher currents. Most amps are constant-voltage devices. Drop the impedance, and current goes up.
No added risk to the speakers, they're all seeing the same voltage.

Chris
Title: Re: Y Cable at the back of an amp
Post by: Ivan Beaver on February 13, 2017, 07:35:20 am



This is why the impedance value of a loudspeaker is a nominal value.  It is a representation of the average impedance of the box over it's entire operational range.  The actual impedance of the loudspeaker could vary more than 50% of the total range of the loudspeaker.



I will disagree a little bit.

The impedance ratings of speakers is often NOT any sort of average.

If you look at the ACTUAL impedance curves, in some cases the ratings are a good bit "off" of the actual impedance.

The "nominal" ratings given are the "closest standard" number.  2-4-8-16 ohms.

BELIEVE ME-anything other than that just causes lots of confusion.

Years ago I rated a full range loudspeaker at 6 ohms-since I felt that number was a "good average" and representative of the load it placed on the amp.

I got LOTS and LOTS of calls from people asking what amp to use-because they could find any amps with 6 ohm ratings.

I changed the impedance rating to 4 ohms on paper (nothing changed in the cabinet) and the calls stopped-except for a few asking why the impedance changed.

It is for that reason, that is IS important to look at the actual impedance CURVE-and not just a simple number.

At some freq, the actual impedance could be several times (much more than 50%) higher than the rated impedance.

The only real concern is when the impedance gets much lower (and for a wide range of freq) than the rated impedance.

So-as with most audio questions, you MUST ASK "At what freq?"
Title: Re: Y Cable at the back of an amp
Post by: Ivan Beaver on February 13, 2017, 07:38:46 am
Think you mean higher currents. Most amps are constant-voltage devices. Drop the impedance, and current goes up.
No added risk to the speakers, they're all seeing the same voltage.

Chris
Until the amp starts to run out of current-then the voltage going to the speakers will drop.

Which is actually less "power" going to the speakers.

As you say-amplifiers are constant voltage devices (they have a preset amount of gain that is not dependent on the output load), so they will produce the same voltage with no load and with a full load (up to the current capability) and will not change (at least enough to worry about)
Title: Re: Y Cable at the back of an amp
Post by: John Rutirasiri on February 13, 2017, 10:29:30 am
The "nominal" ratings given are the "closest standard" number.  2-4-8-16 ohms.

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.
Title: Re: Y Cable at the back of an amp
Post by: DavidTurner on February 13, 2017, 11:23:33 am
Customer: "I need a new speaker for my bass amp"
Me: 4 ohm or 8 ohm
Customer "no, I just need 1 of 'em"



The "nominal" ratings given are the "closest standard" number.  2-4-8-16 ohms.


Title: Re: Y Cable at the back of an amp
Post by: Ivan Beaver 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
Title: Re: Y Cable at the back of an amp
Post by: Luke Geis 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.
Title: Re: Y Cable at the back of an amp
Post by: Mac Kerr 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
Title: Re: Y Cable at the back of an amp
Post by: Don T. Williams 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.
Title: Re: Y Cable at the back of an amp
Post by: Stephen Kirby 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.