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Mixing Speaker Impedances

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Posted on November 27, 2016 at 13:44:04
Cpwill
Audiophile

Posts: 1096
Location: DC
Joined: December 22, 2003
Contributor
  Since: October 24, 2008
 I hope this question is not as dumb as it sounds to me, the questioner. What are the ramifications of mixing different driver impedance in a multi-way system? More specifically, can one add an 8 Ohm woofer and/or super tweeter to a 16 Ohm full/wide-range driver to extend the frequency range? If so, would one simply plug in the respective impedance into a crossover calculator (to get started in the right ballpark), or would other adjustments be required? I have only designed/built single-driver speakers before, so I apologize for the rudimentary question, and thank you all in advance for tolerant answers.
"Anyone who understands jazz knows that you can't understand it. It's too complicated. That's what's so simple about it." - Yogi Berra.

Cpwill

 

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It's a good question, posted on November 27, 2016 at 14:32:32
Uncle Mike
 I don't know enough to give an answer but I have seen, in old Altec speakers, drivers of different impedance.

 

RE: Mixing Speaker Impedances , posted on November 27, 2016 at 16:54:14
Bill Fitzmaurice
Industry Professional

Posts: 5371
Location: New England
Joined: October 20, 2002
 You can do just what you said, but you have to pay attention to differing driver sensitivities with equal voltage input. Resistive padding of a tweeter is easy, of a woofer isn't.

 

RE: Mixing Speaker Impedances , posted on November 28, 2016 at 05:02:55
Cpwill
Audiophile

Posts: 1096
Location: DC
Joined: December 22, 2003
Contributor
  Since: October 24, 2008
 Thanks, Bill. Can you elaborate any? The drivers at hand are 98db sensitivity for both the woofer and wide-range and 108 for the super tweeter. Thanks in advance.
"Anyone who understands jazz knows that you can't understand it. It's too complicated. That's what's so simple about it." - Yogi Berra.

Cpwill

 

RE: Mixing Speaker Impedances , posted on November 28, 2016 at 12:40:22
Bill Fitzmaurice
Industry Professional

Posts: 5371
Location: New England
Joined: October 20, 2002
 Don't go by the 1m/1w sensitivity, you have to go by 1m/2.83v, as all the drivers will receive the same voltage. 98dB/1w is 2.83v into 8 ohms, but it's 4v into 16 ohms. So if they're both rated 98dB/1w then the 16 ohm driver will have 3dB lower sensitivity with equal voltage input. Padding down a tweeter with a resistor LPad is no biggy, but with a full range or woofer the resistor power requirements could be substantial. OTOH if the woofer has higher voltage sensitivity that would help offset the need for baffle step compensation.

 

you wouldn't be the first! :-) , posted on November 29, 2016 at 10:11:20
mhardy6647
Audiophile

Posts: 16019
Location: New England
Joined: October 12, 1999
Contributor
  Since: October 23, 2016
 Still fiddlin' with an admixture of 8, 16 and "8/16" ohm drivers here.

Altec called the 604E an "8 to 16 ohm" driver (or something like that).

You pays your money, you takes your chance.
Other than that, I can't help much.
DSC_6439

all the best,
mrh

 

RE: Mixing Speaker Impedances , posted on November 29, 2016 at 12:58:30
badman
Reviewer

Posts: 8801
Location: Tustin, CA (Orange County)
Joined: March 10, 2001
 You can absolutely mix them. Doing it right is relatively involved, but worth doing (a learning experience). Good acoustic measurement and impedance measurement can be utilized along with a good crossover designer- pcd win is pretty simple and flexible (as these, inherently complex, things go). Basic online calculators will get you in "the ballpark" but sometimes that means a college team trying to win the world series- things like Fs/Fc impedance spikes and inductive rise can really throw basic resistive calculations out the window. For high efficiency, generally, 2nd order is a minimum, usually 3rd and a notch or some other shaping is what I need to really get things singing. First can be done, with very well-behaved drivers (which are rare in higher efficiencies- the advantages of high efficiency are not in ease of use)

Not trying to scare you, just saying what it takes to do it right. A basic RTA and impedance sweep method is reasonably affordable (couple hundred) and can get you pretty darned close, but for high precision a proper calibrated mic etc etc can run into the thousands (or $5-600 with care, dayton makes a couple good and affordable easy-to-use products for this). You'll have to decide how deep you want to delve- there are entire forums and books on audio measurement so I suggest spending some serious time googling and putting down a plan on paper, if you want to design it yourself. Alternatively, there are people who can design a good XO for you based on the drivers etc, though it often requires shipping the system for proper testing.



Bass is supposed to sound big. 6.5" is not a woofer size.


 

Mark, Have I Shown You, posted on November 29, 2016 at 13:54:17
tubav
Audiophile

Posts: 549
Joined: March 21, 2009



My rebuilt Eico ST40? Seeing the two Eicos in your pic reminded me. Gary Dodd of Dodd Audio (sadly now deceased) took this one back to the chassis, transformers, and tube sockets. He eliminated tone controls and phono stage, added beefier power supply, and straight forward speaker hookup. It sounds wonderful. This is the stock faceplate just covered with zebrawood veneer. I always love seeing your room.

 

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