Monitor Impedance

High output and wide dispersion without feedback.
Post Reply
Message
Author
JLX
Posts: 2
Joined: Sun Jan 06, 2019 9:36 pm

Monitor Impedance

#1 Post by JLX » Sun Jan 06, 2019 10:32 pm

I'm planning on building a set of Wedgehorn monitors, and would like to finish up with four 16-ohm cabinets that can be connected daisy-chain style (all parallel--to keep life simple). My system specifies minimum amp load of 4 ohms.
How do the plans specify wiring of the single 6" (or 8") plus the tweeters to come up with a total impedance load for each cabinet?
Thanks to all you builders who have already made these monitors.
Joe

Grant Bunter
Posts: 6015
Joined: Mon Nov 28, 2011 11:12 am
Location: Ilfracombe Queensland Australia
Contact:

Re: Monitor Impedance

#2 Post by Grant Bunter » Mon Jan 07, 2019 2:55 am

Hi and welcome to the forum :)

The plans show 8 ohm filters, using 8 ohm drivers, and you don't need to worry about the piezo's, that's covered with the filters in the plans too.

I don't think you can get the recommended drivers from eminence in 16 ohms nominal impedance.

edit: yes you can;
https://www.eminence.com/faqconc/do-you ... m-version/
See that word custom? That means retail price + 13%

You can get there another way, series/parallel wiring.
2 x 8 ohm cabs wired in series = 16 ohms. Parallel another pair also series wired, for an overall impedance of 8 ohms.
Better than running your amp at 4 ohms.

You can do this by building a simple break out box.
You could also wire up the cabs like that, but you would need to mark the appropriate speakons for their purpose.
You would also need some specially made and marked leads, but it's all doable.

If you're prepared to use the other amp channel, you could just parallel wire 2 x 8 ohm cabs together for a 4 ohm load per channel, and feed both channels the same signal...
Built:
DR 250: x 2 (melded array) with March 2012 plans. 2 more under way with CD horn
T39's: 4 x 20" BP102 , 2 x 28" 3012lf.
WH8: x 3 with melded array.
Bunter's Audio and Lighting "like"s would be most appreciated...

User avatar
BrentEvans
Posts: 3013
Joined: Thu Oct 09, 2008 10:38 am
Location: Salisbury, NC

Re: Monitor Impedance

#3 Post by BrentEvans » Mon Jan 07, 2019 5:16 pm

Impedance between woofers and tweeters (when used properly, i.e. with a crossover) does not sum or cancel. Impedance is variable with frequency. If you use an 8 ohm woofer and a 16 ohm tweeter with a properly designed crossover at 2.5khz, for instance, the cab will be 8 ohms nominally below 2.5khz and 16 ohms nominally above that frequency. For the purposes of daisy chaining cabs, you want to look at MINIMUM impedance, not nominal impedance or DCR. Since piezo tweeters don't have an impedance per se, you dont have to worry about that. For most purposes, with a cab using piezo tweeters, using the rated impedance of the woofer is sufficient as a rule of thumb. There are other issues with amps and piezos, though, which present a capacitive load rather than a resistive load, and can induce oscillations in some amps. BF cabs with the filters properly installed shouldn't have this problem, as the filter includes a "protection resistor" turning the capacitive tweeter into a resistive load (more or less).

We really need an impedance sticky. Not that anyone reads the stickies but it would be nice to point people to.
99% of the time, things that aren't already being done aren't being done because they don't work. The other 1% is split evenly between fools and geniuses.

JLX
Posts: 2
Joined: Sun Jan 06, 2019 9:36 pm

Re: Monitor Impedance

#4 Post by JLX » Sat Jan 12, 2019 8:40 pm

Thanks for the prompt reply to my post.
The breakout box seems like a really foolproof method for making series-parallel connections correctly while setting up on stage, and not ending up with too low a load for the amp, or too many speakers in series and crap for output.
But an extra 13% for custom speaker impedence from Eminence isn't bad and makes hookup even simpler.
The small size and light weight of these cabinets is really attractive.

Grant Bunter
Posts: 6015
Joined: Mon Nov 28, 2011 11:12 am
Location: Ilfracombe Queensland Australia
Contact:

Re: Monitor Impedance

#5 Post by Grant Bunter » Sun Jan 13, 2019 2:46 pm

JLX wrote:
Sat Jan 12, 2019 8:40 pm
But an extra 13% for custom speaker impedence from Eminence isn't bad and makes hookup even simpler.
Have a really good discussion with Eminence before proceeding.
Cost is cost, it is what it is.

The main issue is an potential altering of TS specs.
If you study a number of drivers made by Eminence that are already commercially available, the same model number driver, but in different impedances, can have different TS specs.
eg lab 12 and lab 12c. In the case of the lab12c, the TS specs fall outside those required for the cabs they can be used in in Bill's designs.

You wouldn't want to custom order drivers, and then find they don't meet the criteria for the WH's in terms of TS specs...
Built:
DR 250: x 2 (melded array) with March 2012 plans. 2 more under way with CD horn
T39's: 4 x 20" BP102 , 2 x 28" 3012lf.
WH8: x 3 with melded array.
Bunter's Audio and Lighting "like"s would be most appreciated...

Post Reply