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Zilch's AK Design Collaborative - Econowave Speaker

Wayne Parham said:
Not to be a contrarian, but I would always use a Zobel on a woofer fed from a passive low-pass filter of second-order or higher. There are some weird exceptions, like when using one of those AE woofers that are nearly resistive. Or maybe if the woofer doesn't reach high enough and you're trying to eek out some top end from a driver that is sagging up high using filter peaking (not recommended). But in general, you'll want a Zobel. Without one, the low-pass filter usually "sees" too high an impedance because of voice coil inductance. This causes it to be underdamped around crossover, resulting in a peak, sometimes a pretty big one.

I know it sounds somewhat counterintuitive, but the truth is the higher frequency crossovers usually suffer this problem more than lower frequency ones do. It seems like if you crossover real high, you're moving out of the passband, like you said "keeping out of trouble." But in reality what is happening is the voice coil inductance is rising higher and higher as frequency goes up. Each woofer is different, but a typical woofer may be 8Ω at 200Hz, at 500Hz it is probably closer to 10Ω and by the crossover frequency, it has risen to probably 16Ω. So the low-pass filter is probably underdamped without a Zobel. You could design the woofer crossover for a 16Ω load, I suppose, but that will alter the transfer function (amplitude and phase) in other ways. The point is that the load impedance changes with frequency, so an impedance conjugate filter (Zobel) makes sense.

Check out the handouts from the "Crossover Electronics 101" seminar, which is like a condensed form of the Speaker Crossover Document. The handouts and the crossover document both show various passive networks along with Spice models and their associated transfer functions. At the seminar I do each year, we discuss these and then connect a speaker through an actual physical circuit for each network shown. You can really hear the peaking shown in the Spice models, making it possible to identify what various response curve features actually sound like.
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Thanks. Although the posted impedance curve looks pretty smooth in the crossover region, there is a minor rise until it hits 4Khz...the Zobel should help the LP crossover a bit. Should not have any negative effects, I hope.
 
rlee777 said:
Although the posted impedance curve looks pretty smooth in the crossover region, there is a minor rise until it hits 4Khz...the Zobel should help the LP crossover a bit. Should not have any negative effects, I hope.
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How flat is the impedance curve? I ask because if it's flat enough, it's one of those rare cases where you don't need a Zobel. In those cases, the Zobel would have such small capacitance it's pretty much just an open circuit (and better not to even use one). But that's rare, I've only seen it with one particular woofer, from a company that makes inductance linearity a high priority on its list of design criteria.

If your woofer is 8Ω at 100Hz - 200Hz and only 8.5Ω at crossover, then don't use a Zobel. If it's 12Ω at crossover, then you'll probably want one. You could probably work with a rule of thumb, if there's more than about 30% rise in impedance at crossover, you'll probably benefit from using a Zobel.

One last thing about Zobels - I almost never find the textbook values provide the best response. Zobels tend to have a very wide tolerance, meaning you can use values within about 30% of textbook values and get the desired result. In fact, the Zobel is one of many things that can be used to set crossover phase, which is what sets the position of the forward lobe and vertical nulls. You can play around with the core low-pass and high-pass values too. In this case, the end justifies the means - Do whatever is necessary to get the in-pattern response flat, the forward lobe centered and the vertical nulls separated by a useful distance above and below the speaker.

 
C - C distance

It does appear to be 8ohms around 100hz rising to 12ohms at 2khz. Though the Econowave X-over is at 1.2khz, I might try the Zobel anyway -- it appears that the Zobel online calculators call for a 10uf cap, so a good value.

Another design question: center to center distance. I quickly searched through the thread and the only guideline for waveguide and woofer c-c distance is as "close as possible". Any technical guidelines to minimize vertical lobing issues with the std Econowave crossover? I will be using the 12" Selenium 12pw3.
 
I think that with 8 rising to 12 ohms at 2KHz, a Zobel would be warranted, for sure. That's a pretty substantial inductance... causing a 50% increase in impedance, less than 1 octave from the crossover point. That would definitely upset the lowpass function, I would think, unless a Zobel is put in place.

With a 12" woofer, you should have very little problematic lobing issues. Since this is smaller than most of the calculations were based around (14" and 15" woofers are the "norm", for the most part, for the lobing calculations), you shouldn't really have anything to worry about. Just, as they say place them "close as possible", and you should maximize the center lobe width... which is what you want to do. As Wayne mentioned, you can use the Zobel to help shape the response and position the lobe, to an extent... I'd start with the 10uf cap, but maybe experiment with slightly smaller and larger caps as well...

Regards,
Gordon.
 
I agree, Gordon. Rlee's woofer is pretty typical, and would probably benefit from a Zobel. Without one, there will be a peak around the crossover frequency. If there is a hole there, say because the woofer doesn't reach that high, then one could possibly make use of some peaking in that area. But generally, you don't want the peak and a Zobel is warranted.

About the CTC spacing and the nulls, here are three threads that show:

1. A description of the issues related to vertical and fore-aft driver spacing
2. A simple way to find the relation of fore-aft acoustic centers of the drivers
3. How to calculate the position of the nulls, knowing crossover frequency, vertical spacing and fore-aft offset
4. How to find the nulls with measurements, and
5. How to design the speaker, to center the forward lobe and set the nulls outside the pattern
 
Rapidroy said:
Made the box, sounds sweet, just need to sand and veneer.
872A Altec Madrid's, I like the minimus look the best.
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I have a 872A identical, 420y Biflex currently working alone without any croosover for high frequency use an EV-T35 connected to EV-C35 crossover at 3500Hz. Zilch several talks with whom I thank for their patience and support for project D220 Selenium EWG with PT Ti 12 "X 6" and the crossover design by EWG on 95db.Gracias Zilch to everyone for your comments,Martin
 
At last, one box done !

Yes !
It took a while because it was a first for me but it is done and it sounds just great.
A side by side comparison shows that these were due for a rejuvenation.
The result is remarkable.

Thanks for putting this project on the web via Wired. :tresbon:
 

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Well' I finally figured how to post the pics (new computer) These are my Infinity SM-100 e-waves with dayton classic 10's. Made my own pc boards back in the winter. In the garage I powered them with a yamaha 610 integrated amp and they were smokin! In the basement with it being more of a speaker warehouse the bass isn't as good. I need to thin the herd!
 

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BongoPJ said:
Thanks to you AKers ! :banana:

I wonder if the we will get to 100.
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I am sure we are over 100 already, if we count the total pairs made. Many EconoWave builders have built several pairs already. I have made more than one, with more on the way. Zilch only counts the builders, not the number of pairs built.

Is this a neat thread, or what? Anybody can build a set of KEEPERS for just a little bit of money, and brag to his friends that "I built them myself." And the EconoWave is just the beginning for most builders. Heady stuff, indeed! :yes:
 
Here they are...
 

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