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#43866 - 10/23/04 08:25 AM Newest newbie has a question RE: Ohm's law and speakers.
OjLeno Offline
Junior Member

Registered: 10/23/04
Posts: 1
Loc: San Diego, USA
Hi, I have a quick question for anyone who might know this:

When I hook up more than one speaker to one channel of an amplifier (I'm thinking in series at the moment), do you actually get a "Change in the sound coming from the speaker"... and I don't mean change in the volume or SPL of the sound that comes from the speaker. So to rephrase the question another way:
Minus the change in "Loudness" (from a speaker) that has been hooked up in series... will the actual sound of music coming from that speaker be either more bassy/less bassy/ or have more/or less treble to it?


That was the question... if you already know the answer, I'd love to hear it. If you are wondering why I ask, here is what brought up the question.
I have two 450-watt (max) 4-ohm full sized speakers (3-way, including a 15-inch sub). I recently purchased a rack-mount amp for the speakers, but before I was using that I used the 120-watt/channel home stereo amp. The rack mount am (as stated per the user manual) is now sending about 750 watts per channel (at 4 ohms) to each speaker. Whereas I used to turn the highs up to match the lows (for music mixing) on my mixer, now the highs (coming from the speakers... with the rack-mount amp) are REALLY high, forcing me to cut the treble down to about 60-50% of normal. Thats fine and all I guess, but I was thinking maybe if I hook up my other 250-watt max each (at 8-ohm) tower speakers to this amp (and run the speakers in series), raising the total resistance to 12-ohms, maybe that would help solve my really high highs issue (by better matching the wattage from the amp to the wattage the speaker wants). What do you guys think. In advance, I'd like to thank you for your time .

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#43867 - 10/23/04 12:06 PM Re: Newest newbie has a question RE: Ohm's law and speakers.
hbiss Offline
Member

Registered: 12/16/03
Posts: 893
Loc: Hawthorne, NY USA
Well, for starters you never connect speakers in series. They do unpredictable things and the amp may do unpredictable things as you found out.

The correct way to connect multiple speakers is in parallel. Unfortunately this may result in a total impedance that is too low for the amplifier to drive. Remedy there is to use multiple amps and do your combining or crossovers on the inputs.

-Hal

[This message has been edited by hbiss (edited 10-23-2004).]
_________________________
www.myphonetechs.com

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#43868 - 10/23/04 04:31 PM Re: Newest newbie has a question RE: Ohm's law and speakers.
maintenanceguy Offline
Member

Registered: 12/02/01
Posts: 303
Loc: Southern NJ, USA
Lets assume it's just a speaker and not something more complicated with multiple speakers/crossovers/bandpass filters, etc. And if you just see two wires going to the speaker coil it probably is just a speaker.

That being the case, then the impedance of a speaker is mostly inductive instead of capacative. And an inductive coil (such as your speaker coils) tend to pass lower frequencies and block higher frequencies. Add two coils in series and the inductance increases so you'll block more of the highs.

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#43869 - 10/23/04 05:40 PM Re: Newest newbie has a question RE: Ohm's law and speakers.
hbiss Offline
Member

Registered: 12/16/03
Posts: 893
Loc: Hawthorne, NY USA
Add two coils in series and the inductance increases so you'll block more of the highs.

Maybe, but that's not what he is complaining about, it's the other way around.

Probably what is happening, because the speakers are in series, is that the power is being divided equally between the two assuming both are the same impedance. Now, keeping in mind that the low frequency drivers require most of the power, each is now only receiving half of the total. The high frequency drivers, being much more efficient work pretty much the same. The net effect is a weak low end.

This is theory of course, but like I said, never connect speakers in series.

-Hal

[This message has been edited by hbiss (edited 10-23-2004).]
_________________________
www.myphonetechs.com

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#43870 - 10/23/04 06:12 PM Re: Newest newbie has a question RE: Ohm's law and speakers.
Ron Offline
Member

Registered: 03/13/02
Posts: 577
Loc: White Plains, NY
Be sure you have not gone below the minimum equivalent impedance that your amplifier can drive, or above the generally accepted 16ohm max. http://www.termpro.com/articles/spkrz.html
As you change the load impedance (adding speakers), the amplifier has to provide power a bit differently, and depending on the quality of the amp, it may be better able to provide the rated power at a particular load impedance.
_________________________
Ron

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#43871 - 10/23/04 11:23 PM Re: Newest newbie has a question RE: Ohm's law and speakers.
pauluk Offline
Member

Registered: 08/11/01
Posts: 7693
Loc: Norfolk, England
The effect also depends very much upon the design of the output stage of the amplifier -- Whether transformer coupled or direct-coupled for example.

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#43872 - 10/24/04 07:56 PM Re: Newest newbie has a question RE: Ohm's law and speakers.
dereckbc Offline
Member

Registered: 10/08/03
Posts: 158
Loc: Tulsa, OK
Amplifier output ratings are dependant on the impedance of the speaker, and the amplifier design class of operation (A, AB, push-pull, etc.). So if your amplifier is rated 450 W @ 4 ohms, it should also list 225 @ 8 ohms, and 112 @ 16 ohms or something of that nature.

Speakers are not connected in series. The filters inside them would cause interactions and give undetermined results. However you can connect them in parallel. So in your case you could connect two-8 ohm speakers in parallel, or four-16 ohm. One speaker could be for the high range (mids and tweeter), while the other could be a woofer to get the tonal balance you are looking for.

Different amps of different power levels will sound different through the same set of speakers. It all has to do with the design of the amp and components used. I am old fashioned, I use three McIintosh tube amps which have a output matching transformer for 4, 8 and 16 ohms. This allows me to get full output power no matter the speaker impedance used. Not to mention it sounds a lot better than transistors when overdriven.

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