Third Order Topo Question.

I'm currently designing a two way bookshelf in which I have copied the original manufacturer HP Filter design wholly. I figure someone else has already taken the time to tame this driver and I'm using separate boards for the LP/HP filters.

My question is in regard to the third order Butterworth topology.
Specifically the order of the Caps in serial.

The original design specifies as follows:
C1 = 33uF
L2 = .33mH
C3 = 20uF

The only hesitation I have with this design is that every manual formula and every computer modeling program for Crossover design, always show the Smaller Capacitor first in series with the Larger Capacitor.

So I am curious why the original mfg has this reversed.
Since Capacitors in series always Sum the same regardless of size/order...
??? Does it matter the order in which the two caps are placed in series on the board???
 
Generally I regard filters with the large capacitor at the input as design error. However Zaph did it as well in the ZRT and I still wonder why. These circuits cause a very low impedance at the crossover frequency and work only with a large resistor in series.
 

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eriksquires

Member
2013-05-10 4:11 pm
So I took my own advice and simulated this. I am seeing a minimum impedance of half an ohm around 1.5kHz for the crossover alone. With the theoretically 8 ohm driver I get 1.5 Ohms. Is the coil in the filter very high DCR or is there a missing resistor?

Best,

Erik
 
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I should provide specifics. :)
The Driver is an ESS AMT5 Power Ring (Mid '70's vintage) rated for 4 ohms.
Please take a look at page 8 in the PDF provided by them...

Downloads – ESS Labs., LLC

I purchased a pair of these used in 1986.
They were in excellent condition and have served me well.
However, one weekend trip to the coast without the teenagers proved to be disastrous to my Receiver and speakers. That combined with the eventual decay of the original woofer surrounds lead me to this project.

Please have a look at the AMT5 schematic.
Is this a 1st. order LP with a 3rd. order HP?
Or is this a 2nd. order on both?
It could be I am interpreting the schematic incorrectly.

Perhaps my real question then might be...
Can the order of the components in series and in parallel be switched?
Usually you see the series first followed by the parallel.
Can this be reversed with no ill effect?
Thanks all.
 
I should provide specifics. :)
The Driver is an ESS AMT5 Power Ring (Mid '70's vintage) rated for 4 ohms.
Please take a look at page 8 in the PDF provided by them...

Downloads – ESS Labs., LLC

I purchased a pair of these used in 1986.
They were in excellent condition and have served me well.
However, one weekend trip to the coast without the teenagers proved to be disastrous to my Receiver and speakers. That combined with the eventual decay of the original woofer surrounds lead me to this project.

Please have a look at the AMT5 schematic.
Is this a 1st. order LP with a 3rd. order HP?
Or is this a 2nd. order on both?
It could be I am interpreting the schematic incorrectly.

Perhaps my real question then might be...
Can the order of the components in series and in parallel be switched?
Usually you see the series first followed by the parallel.
Can this be reversed with no ill effect?
Thanks all.

Please take a look at page 8 in the PDF.
 
Talk about a homework question! :rolleyes:

OK, An ESS AMT 5 speaker with 12" bass and a Heil Air Motion Transformer tweeter. Must be a lowish crossover with a 12" bass. Maybe 2kHz.

I'm looking at Page 8 and seeing a second order filter with attenuator. Below.

Page 13, also below, has a complete schematic that looks like a series filter, but I'd have to redraw it to make it look sensible.

I'll post the images and have a think about it.
 

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Oh, I must be bored to be doing this, but I am a crossover fanatic, so anything new is interesting. :eek:

I don't know anything about Heil Air Motion Transformers, so I just stuck in an 8 ohm tweeter. Here's how it's looking. Fairly regular second order series filter with 1.5kHz crossover. Downward slope on tweeter due to the little 0.08mH coil.

I've added the impedance plot for an 8 ohm tweeter. Goes a bit low, doesn't it?

Now what was the question again? :D
 

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Thanks Steve,
I think you've cleared it up for me.
I was looking for someone who knows what they are reading to confirm the topology.
I believe where I was getting confused was what I would guess is the Common Circuit trace path. Turning the schematic sideway gives the impression of a 3rd. order topo.
That combined with someone else telling me the HP was a 3rd. order Butterworth.
It is very common to combine a 1st. order LP with a 3rd. order HP. So that was tricking me.

I'll need to go back to the drawing board now that I know it is 2nd. order.

Now imagine this... I'm cutting my teeth on this project.
Tweeter: ESS Heil AMT5 Power Ring, Re: 3.7, Z: 4, SPL 93-95 Db.
Woofer: Focal 8W 5411, Re: 5.7, Z: 6, SPL 91 Db.
Box: Vented 23L 9Wx14Hx11.25D.
Shooting for a Nominal 6 ohm load.

When the tweaking is done and the project finished, I'll move onto an AMT1 (Large Original Heil Air Motion Transformer) combined with an ESS 12" Woofer.

This is fun and interesting for sure.
Thanks to all for helping. I'll be back I'm sure.
 
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It's a second order SERIES filter, to be exact! :D

529037d1454524799-third-order-topo-question-s7-ess-amt-5-crossover-deconstructed.png


Very fussy little things where a change HERE causes an unexpected change THERE. You definitely need to sim them.
Downloads

If your AMT tweeter is 4 ohms and reasonably flat impedance, it should be doable. But you also need the frequency response too. I looked up the Focal 8W5411 woofer. Le of 0.69mH. Should work, but I couldn't guess the filter without more thought.
 

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I actually started this project about 5 years ago, then put it to rest due to Crossover design issues. I must see it through though.

I used WinISD to design and tune the box.
HarrisTech XOP v3 on the filters.
One more modeling program can't hurt. After all it's free.
Maybe they will have the Param's and Response data for the AMT's in their database.
Cheers!
 
Originally a 1st. Order with EQ, rolling off at 1500Hz.
L1: .62mH ERSE 16Ga AC
Ce: 22uF ERSE 400V MP
Rc: 6 ohm 12W Mills

I suppose this might be OK, but will want to see the Response and Phase.
It's recommended is it not that with 2nd. order filters the HP/LP Topologies be the same?
Back to the board. :)
 
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You can't use 1st order (Single Coil) on a bass like that without it ending up a 3.5kHz crossover, just from looking at the slope of the Focal. You can do more with second order bass. And I am quite sure you'll need third order on the tweeter filter at least, and an attenuator.

I was thinking back to some Decca Kelly ribbon designs:
Ribbon Tweeter Horn Loudspeaker: Decca London/Stanley Kelly - Efficiency, Size, Filter and Frequency Response.

A little taste below. The Decca wasn't a very flat load, but near 8 ohms nominal.
 

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