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Old 19th October 2006, 04:18 PM   #1
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Default 3way XO help greatly appreciated!

Hi. I'm STILL trying to upgrade my old Vifa 3-way because I never liked the D75 dome mids!
I think I may have finally found 'beginner friendly' drivers to replace them, ie the Seas 5" CA15RLY.
(At this price point I'm not after ultra-hifi, (54yo ears!,LOL) I just want to still use my other drivers).
The D25AG-35-06 1" domes still sound good and the P25WO-00-08 10" woofers have ample 'tight'
(for want of a better word) bass and are housed in nice homemade 72 Litre 1" MDF boxes.

The new XO at 2700 (and 270Hz) would seem (to me) to suit the Seas 60deg off-axis response.
The tweeter section is a slightly modified (to 2700Hz) copy of Mr John Krutke's L15/TFFC design ,
which I think may just work for the D25, because the specs seem similar (albeit higher IMD?);
while the mid and woofer are 1st order with values similar to those from the 'Lalena calculator'.

So, before I take the plunge (and possibly waste my money!) I'd like to politely ask for some help.

As I am not absolutely sure about the component values, and ignoring advanced issues like baffle
step (although the drivers will be spaced within 1/2" and flush mounted) I am wondering if an
expert would mind viewing the attached rough! circuit and briefly commenting on its usefulness and
suitability to these well known drivers? I hope my attempt is not too laughable! I'd be extremely
pleased to receive any comments and also hope that I'm not asking too much! Some thoughts:

1) I would prefer to use 'off the shelf' inductors, ie lowest DCR dependent on price! (Solen $75AU!)

2) the combined impedance of the tweeter(@2700) and voltage divider is close to 6.3 Ohms I think.
I would like to use a 0.56mH choke here, so the LC-product for 2700 yields 6.2uF for the Cap.
But I'm not sure if the resulting impedance @ 2700 matches the 6.3 Ohms mentioned above?
Is 6.2uF the correct value (in conjunction with 0.56mH) please?

3) the P25 woofer crosses at 270Hz where Z= almost 8Ohms and 90dB SPL; thereafter 6dB/Oct
attenuation. Do I need to Zobel it then? P25: Le=2.2mH and Re=5.7 (from specs).
So, again from Lalena for Zobel, C=43uF and R=7 Ohms. Are these values correct? Also, the
CA15RLY impedance rises sharply after 2700, do I need to Zobel it too? ---->C=16.7uF,R=7?

4) the bandpass values I have calculated also slightly differ from Lalena?

5) and lastly, should the Seas mid connection be reversed? I guess I could try it!
Thanks very much for reading all this, and very best wishes, Grant
(I am aware that s'ware calculators have big limitations but these drivers are very well known I
think and I have no test equipment). Maybe later I'll replace the D25's with Seas 27TDFC's.
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Old 19th October 2006, 05:35 PM   #2
tinitus is offline tinitus  Europe
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Filter look fine

If values are correct is difficult to say ... you might need adjustments ... over time

If mid is up to it I would try even smaller inductor .... and it may need RC

You should try reversed polarity on mid
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Old 19th October 2006, 08:14 PM   #3
omni is offline omni  United States
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Location: Rossford, Ohio
Grant, I read your post here, and was quite intrigued because I am working on a 3 way design using the SEAS CA15RLY midbass crossed over in the range of 250-300 Hz low end and 2500-3000 Hz high end. Also I am using the SEAS 27TDFC tweeter, so naturally, your post caught my eye. Let me preface this also by the fact that I am NOT an expert or guru!....... At any rate I am Zobeling both midbass and tweeter and am not gonna Zobel the woofer which is a Peerless SLS 830669. For my Zobels I used the calculation procedure Rod Elliot describes in his manuscript on passive crossover design on his website : sound.westhost.com aka Elliot Sound Products. The reason I am using this procedure is because it uses actual parameters from my drivers a little more in depth to calculate values. Also, I researched on this forum extensively and the overwhelming consensous appears to be that it is the preferred method. It gives values for the capacitors a bit higher than the Lalena calculator, and again, from extensive research, reports are that the C=Le/Rc squared, Rc=1.25xRe formulas provide the minimal values for components, which probably need to be adjusted upwards. However, Zobel networks are reported to be forgiving in their nature, so the design method one employs may simply be based on personal preference.........I am not sure...........At any rate the values for my Zobels for the CA15RLY are: C=22 microfarads and R=7.25 ohm, for which I will probably use an 8 ohm Mills resistor. For the 27TDFC C=2.1 microfarads and R=6.1 ohms for which I will use a 6 ohm Mills..........Without test equipment, where did you get your impedance measurements? I would like to compare, if possible. I am using 12dB per octave throughout, and will be reversing polarity of midbass, I am not certain about the 6dB network polarity, however, TINITUS recommends reversing it, so I probably would follow his suggestions, as I have grown to respect his input on these matters.........I have made many changes to my system based upon his input. Your questions pertaining to component values may be answered by someone more experienced, however, it is my understanding that the impedance of the particular driver, mounted in the cabinet, at crossover frequency will dictate the component values via your formulas. I am measuring mine with an old frequency generator using the voltage divider method, recalibrating the voltages to a reference resistor for each frequency/impedance measurement. Also am comparing the measurements to impedence charts from the manufacturer and the impedance charts available on Zaphs' site. Hopefully will get a respectable outcome. I look forward to reading of your results since we have similar projects going on here..........Respectfully....Omni
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Old 19th October 2006, 09:32 PM   #4
tinitus is offline tinitus  Europe
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Omni, good to hear you have progress

I like your approach with the "zobels" and it looks like reasonable values .... along the way you could try and "finetune" the zobels by ear .... at the moment I cannot live without double zobels/RC

Edit... remember that what seems to be 6db ... on paper....will rarely be excactly 6db ... nor will a 12db be excactly 12db ... sometimes less, other times more

I think of it as a modified smooth and soft 12db rolloff .... some say it is actually more like 10db ... but getting steeper at the end of the slope
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Old 20th October 2006, 03:07 AM   #5
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Default Re: 3way XO help greatly appreciated!

Quote:
Originally posted by grantnsw
1) I would prefer to use 'off the shelf' inductors, ie lowest DCR dependent on price! (Solen $75AU!)

2) the combined impedance of the tweeter(@2700) and voltage divider is close to 6.3 Ohms I think.
I would like to use a 0.56mH choke here, so the LC-product for 2700 yields 6.2uF for the Cap.
But I'm not sure if the resulting impedance @ 2700 matches the 6.3 Ohms mentioned above?
Is 6.2uF the correct value (in conjunction with 0.56mH) please?

3) the P25 woofer crosses at 270Hz where Z= almost 8Ohms and 90dB SPL; thereafter 6dB/Oct
attenuation. Do I need to Zobel it then? P25: Le=2.2mH and Re=5.7 (from specs).
So, again from Lalena for Zobel, C=43uF and R=7 Ohms. Are these values correct? Also, the
CA15RLY impedance rises sharply after 2700, do I need to Zobel it too? ---->C=16.7uF,R=7?

4) the bandpass values I have calculated also slightly differ from Lalena?

5) and lastly, should the Seas mid connection be reversed? I guess I could try it!
Thanks very much for reading all this, and very best wishes, Grant
(I am aware that s'ware calculators have big limitations but these drivers are very well known I
think and I have no test equipment). Maybe later I'll replace the D25's with Seas 27TDFC's.
Omni mentions Elliot Sound in his post above, I think the info published on that site can provide clear answers to most of your questions, in particular with issues regarding impedance behavior at crossover points. Unlike many such sites this one is written in plain English and is accessible to anyone interested in DIY crossover design, not just engineers and techies.

Here's the link:


http://sound.westhost.com/lr-passive.htm

I don't suggest going as far as winding your own inductors though
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Old 20th October 2006, 11:56 AM   #6
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I'm 'gobsmacked'! You guys (and this site) are amazing - 4 replies within 12hours!
Thank you so very much. I was almost too embarrassed to write that post but I'm glad I did.
I'm very encouraged and will buy the Seas mids when funds permit.

Hi Tinitus:
I'm reassured that the filter looks viable in principle for these drivers. The next 'stock' sized down inductor here is 0.39mH which would raise the mids LP (of bandpass) by 17% to 3264Hz (correct me if I'm wrong). The Seas could certainly handle it I think, its on-axis goes all the way to 9Khz. But at 3264Hz the 60deg-off-axis is about 9dB down whereas at 2700Hz its about 3dB down. (I guess I was trying to maximise both the off-axis response and xo frequency in a compromise). I assume I would also accordingly raise the tweeter xo.
And I need to Zobel the mid too. (Interestingly, Zaphs L15 design has a notch but I can't see that its Zobeled - its impedance rises very rapidly after 1Khz and its Zres=50 Ohm!)
I will certainly try Zobel on mid and woofer as your 2nd message suggests.

many thanks tinitus...replies to omni and willitwork to follow...
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Old 20th October 2006, 01:22 PM   #7
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Hello again Omni (you helped me before), what a coincidence re similar projects.

I didn't realise that tweeters need Zobel too, if the impedance is fairly flat within
5 ohms? I'm not aware that many manufacturers specify Le for tweeters, needs
to be measured, I guess.

Thanks for Rod Elliot link - the 'preferred method', I will read, also many thanks
for the CA15RLY/27TDFC Zobel values - great stuff!

The only reliable source I have for driver(T/S) values/reviews is (for the CA15RLY)
Mr John Krutke's "5"mid review" and for the 27TDFC the "Tweeter Mishmash'
section of his site. Otherwise, only manufacturers specs which I realise in some
cases could be very dubious. So, the best I could do 'on my own' would be
'ballpark values', unless people familiar with the driver(s) kindly offer to help.
BTW, I 'discovered' these drivers in that site.

As Zaph pointed out regarding the Vifa P17's and D25's, there may be significant
'batch inconsistencies', so much so, that he cautioned about using them. This is
why I probably will upgrade to the 27TDFC's eventually (like the CA15's good
consistency, smoothish response and value). I would have considered Dayton but
they are not available in AU.

Your 2nd order network is undoubtedly a good idea, but my P25 10" and new Seas
mid seem to have enough overlap to allow 1st order for the mid bandpass and LP on
woofer. ( Tinitus seems to think it might work). I'm also assuming the rolloff slopes
allow this, it seems OK from graphs.

Just remembered, there is a 'CAOW' design using these drivers and also a version
called 'Calypso', but they both use series xo's, which I know nothing about.

I would be greatly interested in the driver measurements you are doing, and if you
are inclined to share your observations, that would be fantastic! My project may take
some months due to limited finances. Very best wishes for your design too!
Thanks Omni, keep in touch!
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Old 20th October 2006, 01:26 PM   #8
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Many thanks willitwork,
that site is a treasure-trove of good information!
best wishes, grant
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Old 20th October 2006, 02:07 PM   #9
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Omni,
I just looked up the Peerless SLS 830669....
a question please? its impedance at 300Hz looks close to 8 ohms,
(very similar to P25 there) is that why you are not Zobeling it?

Also, please could you or tinitus explain ('please explain' is a funny 'in-joke' in Australia, lol- nevermind) why a tweeter needs it? I'm not
sure that a few ohms variance would make that much difference?
But of course, I really don't know till I read Rod Elliots site!

Also, the circuit I posted had a woofer inductor with a DCR of 1.4 ohms. Where a much more expensive Solen inductor has a DCR of
~6 ohms - difference 0.8 ohms. Will this difference cause significant attenuation of woofer response? I have a formula somewhere, but
I haven't used logarithms in decades.

thanks again, grant
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Old 20th October 2006, 02:44 PM   #10
tinitus is offline tinitus  Europe
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Hi,

"Why tweeter needs zobel..."?
I cant say it does .... though from my listening test I have found that high frequencies sound more smooth, might be phase related

"Zobel on bass..."
Actually you do have zobel on bass already .... what I suggest is to ad another zobel with smaller C .... BUT, two zobels wont follow "textbook" values
I do have a notch/ tilt curcuit on bass too.... outside its passband

You can steal a bit here and there, but that is not likely to work with the excact same values ..... because different drivers interacts differently with each others ... but ofcourse it gives a clew about where to start

I do like the KISS method, but it is also important to have some "tools" of adjustments

I would say a inductor/R in parallel with mids lowend crosspoint is needed to get it perfect .... but very difficult to get right ... and it might work without

Same thing with tweeter... parallel inductor/R is VERY difficult to get right

Thats why I need to say ... DO NOT just assemble your crossover and mount it inside your speaker .... I am sure you will enjoy making small adjustments from time to time... part of the fun
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