thursday,

I have one more ? for you that no one has asked yet...

what type/power/general specification of AV recevier do you have?

a lot of quality surround receivers these days will handle a 4 ohm load without any problems. Most are built as one processor and 5/6/7 seperate amplifier channels...so using two 8ohm speakers for the center channel will likely be fine...

it depends on the type of speaker being used too....

NOTE*** This is NOT a first choice or recommendation, but depending on the receiver, the speakers, and the level of use, it MAY be a satisfactory solution***

Thanks for all of your responses. I think I have a handle on this now

Thurs

Better yet - use four speakers. Wire two sets of two in parallel, each set having a 16 ohm impedance. Then wire those two sets in series. Voila - 8 ohms!

Gee, sometimes I even scare myself!

Larry,
in series in a 12db x-over, the signal path will flow through 2 coils, 2 caps, and the drivers. It just seems to me that there would be big changes in impedence happening here. Which would result in crossover point changes.
I'm curious now! Please shed more light on this.

Okay, let's use a simple two-way filter: a series inductor on the woofer and a series cap on the tweeter, with these two sections paralleled. Thus, we can look at the two speakers' high or low sections independently, as just two tweeters or just two woofers.

As you know. the effective crossover frequency depends on the driver impedances, so when you series the two caps and two tweeters (or the two inductors and the two woofers), you double the effective driver impedance, so the overall crossover frequency remains.

The point is that two identical loads in series (or parallel, for that matter) will each behave as it would alone, with the exception of requiring twice the voltage (for series) or twice the current (for parallel) from the driving (powering) device.

Now, dissimilar loads, which each vary impedance with changing frequency differently, will, indeed, behave in undesireable ways when in series, because the voltage across each load will vary as the impedance imbalance shifts back and forth as you traverse the frequency range.

Larry, You are correct sir!
I did a quick bench test. Results, Sound quality was (not or mildly) affected. I appreciate that you understood what I was talking about. When you look at it on paper, it would seem to affect the output.
Anyhow, Thanks for your explaination.

Now if we could just figure out light switches from afar.

any sonic changes due to a series configuration of two identicalt speakers will be minimal as Larry pointed out. I would be more concerned with factors of using two speakers in such close proximity not desigend for this purpose such as comb filtering and lobing. Even with this said, the biggest consideration will be how your reciever is going to handle it. Keep in mind that all of the channels in the front shuold be at a relatively similar level. This might present a problem at higher listening levels if the center component demands more power

OK Guys....two words ZOBEL NETWORK...just use the appropriate values to get the impedence you need.

Zobel Network.

Thanks Larry...I should have posted that for the masses...

Trey

p.s. Thanks for the tip about West Ave. it has been good to me.

Ok, guys, another two cents here....

First, Zobels are GREAT at stabilizing the impedance that a speaker presents to a crossover, thus linearizing the voltages fed to the speaker, but why were they brought up in this discussion? If it is to deal with impedances that are too low, note that a Zobel is a network that lowers impedance at particular frequencies, so, basically, huh?


In 1980 I worked in Loudspeaker Engineering Department at Marantz in Southern California, where there was really a fantastic speaker engineer (true to Marantz's policy of ignoring gold in their pocket, very little was done with his product), I realized that Marantz amps NEVER put speakers A and B in series, but lower-priced competition did. I did research on the results.

As Larry points out, two speakers with identical impedance curves will perform the same in series as in parallel, frequency-response wise. I was surprised at this, because I thought resonant peaks in one would mess up the other. But no.

Incidentally, mixing different speaker models in series craps up the response of both speakers, but the response of the better speaker, which usually has the lower bass resonance, is messed up more by the cheap speaker than vice versa.

I still have the Bruel & Kjaer testing equipment impedance and frequency response curves somewhere, the ones that I made doing this research.

As to 4 ohms, 8 ohms, etc: Speaker impedances can indeed go very low, but usually a 4 ohm speaker goes very little below 4 ohms at any frequency. The case is similar with 8 ohms. Don't worry about two eight ohm speakers in parallel being worse for an amp than a four ohm speaker.

How about power, though? An amp with a really beefy power supply will put out twice as much power into 4 ohms as into 8, so two speakers in parallel would be 3 dB louder than one with such an amp. Most amps don't quite do this, so the resulting volume would be less than 3 dB more.

In series, the combination of the two speakers, giving sixteen ohms, will draw half the power from the amp that an eight ohm speaker would. So the series combination WILL be 3 dB down from a single speaker. I say WILL because an amp can easily put out half the current of the rated 8 ohm load.

And don't all of our surround amps have AT LEAST 3 dB of adjustability on the center speaker?

Oh, yeah, when I did this with a pair of Sonance M200s, little speakers, they sounded GREAT and there was no problem with comb filtering, lobing, or beaming. nobody could jump around from left to right fast enough to hear the difference in frequency response.