3way XO help greatly appreciated!

[tinitus]

Grant, I have to clarify on when a crossover is 6db, or something else, and I have written about it before, but you might have missed it


It must be very clear that the slopes that counts is MEASURED ACOUSTICAL SLOPES, and not how many components that are used

This means that a single inductor(6db electrical) can give a 12db acoustical rolloff......if placed closer to drivers natural rolloff
Likewise can a electrical 12db give a acoustical 24db
The reason for this is drivers own rolloff, which always must be taken into calculations when working with low order slopes...

This offcourse is true for both lowpass and highpass

As an excample we can look at you mids low crosspoint
THAT single series C is most likely to give a 12db rolloff
AND that means that your box calculations can play a very important role

AND that is one reason why it might work better with a higher crosspoint than 2.7khz ... to have a 12db slope with a single inductor

FR rolloff is an unpredictable "player" as well as is the impedance



About zobels...
Ofcourse wrong adjusted zobels are worse than no zobel

[grantnsw]

Hi Omni, re: midrange enclosure (- a reply to your previous one)
I read Vance again on your suggestion, and it seems that my existing 1.5Litre sealed and fibre-
filled mid-boxes may just be ok for the CA15's at HP 270Hz. As you say the driver will be
(partially?) operating in its piston range, so (from Vance) a 'sealed enclosure is required when
the Fb>=XO/2 to minimize phase disturbance', that is, from 135 to say possibly 150Hz.
I assume this applies to 1st order filters. But what is the Fb for the CA in 1.5L?

For closed box systems, the Fb is evidently dependent on the driver T/S parameters.
(I'll use Zaphs figures for the CA, ie Qts=.411, Fs~56Hz, Vas=8.78 L).
Also because Qts>0.4 it seems ok to use a closed box.
So for the 'Chebychev Qtc=1.1 alignment', Fb=(1.1 * 56) / .411 = 150Hz ...bingo!

To check this, alpha=5.85, so reading from the Qtc=1.1 table for Qts=.41,
Fb=56 * multiplier(2.68) = 150Hz. Does this appear correct to you?

If not, apparently an infinite baffle for tweet/mid sitting on top of woofer box has many
advantages but I have no idea what dimensions are required for response down to 270Hz?
The existing baffle could be easily removed and replaced with one for woofer and port only.
I think Troels G's site has some examples. thanks omni....grant
thanks for latest comments - reading now, will reply soon.

[grantnsw]

Thanks very much Tinitus!
Yes I see! total rolloff depends on measured acoustical slopes, as well as drivers own rolloff,
(quote) "....if placed closer to drivers natural rolloff". I'm not sure that I understand how close is close!!! I've been trying to 'fathom' summation response for a while by studying Vance's examples.

The CA15's 60deg off-axis rolloff is about 10dB/Oct from 2Khz and about 15dB/Oct from 4Khz, wheres the on-axis goes all the way to 9Khz! I chose 2700 only because I wanted to retain as much off-axis as possible, but I'm certainly very open to advise from people wiser than me!

I'll have to think about and work through your comments on changing C and L till I fully understand the outcomes and get back to you if thats OK?
"Wrongly adjusted Zobels are worse than no Zobels" - understood! Many,many thanks Tinitus

[grantnsw]

Thanks again Omni!
Yes, I have a fear that my amp might be blown up again, and also considering Tinitus comment:
"a wrongly configured Zobel is worse than no Zobel !" just about seals the argument for me!
I will go into Troels site again to look at infinite baffles and also to find what Sreten was referring to.
If I ever do get the drivers, I may experiment with Zobels at low power.

Our posts crossed, I did read Vance again re the midrange cavity size. Maybe 1.5L is not big enough as you suggest and my calculations are flawed, my other post refers (which I tried to squeeze down to the bare minimum - difficult for me not to get overly verbose, lol)

Yes I am enjoying this, especially all the wonderful help you kind folk generously provide.

TINITUS, I forget to mention that I do like to experiment a little. My crossovers are in plastic boxes on the back of cabs, and still only jumper-wired with alligator clips (strong ones so no chance of
losing a connection) I never bothered to solder them up, and if I want to modify something, its so easy.

[grantnsw]

hello again, Tinitus,
You and Omni have already helped me a lot, and I'm worried that I might be too bothersome or annoying because I have asked lots of questions (but my appreciation is immense, as you know,
and I think I'm slowly learning - new concepts can be a bit difficult, I'm not as 'sharp' as I used to be! lol)

So with a little trepidation, may I ask these dumb questions:

1) I now know a reversed-tweeter 2nd Butterworth will work with 1st (also Butterworth!) on mid and
woofer, but, WILL a LR2 (2nd order Linkwitz-Riley) also work for tweeter in this case? Untill now I had just assumed that an LR2 network had to be applied to each driver, don't know why, maybe
I'm wrong. If the answer is yes, then it would greatly simplify component values, and eliminate 'fudging' the capacitor value in my first tweeter circuit.

2) If this is indeed possible, and considering your comments re the Mid C and L values, which I'm still trying to understand, I'm looking at ways to implement your advice. I have been playing in Lalena and it seems very possible that I can reduce (as you suggest) the Mid inductor (to 0.39mH) by increasing the XO to 2950Hz and still use standard-sized inductors elsewhere. Which was my initial design goal.

3) the revised XO for 295/2950 (LR2 tweeter) attached may be more suitable? And I would only lose several dB of off-axis. Presumably, at this new XO-point, 'summed response' for the Mid will decay at around 16dB/Oct (10dB for the CA15 and 6dB for the filter).

4) If the mid chamber is appropriate; baffle-step and the previously mentioned woofer response is ok or able to be tamed, then I'm well on my way!
Thanks very much Tinitus and Omni for all of your time, grant
(I do realise that 3way's are very difficult to design, especially for a beginner, but it seems feasible,
and I would learn a lot more than building a published design!)
...new XO attached...

[grantnsw]

new XO....

[omni]

Grant, The issue of the cabinet size for the CA15RLY was one which I agonized for a long time during the initial design phase, as well as the overall cabinet size for my woofer. During that point I was discussing with Tinitus the virtues of what I thought would be a good volume for my woofer and he and a few others offered that I was thinking too small. I ultimately changed my box size from 2 cubic feet to 4 cubic feet for my woofer, which is sealed. I come from the school of sealed enclosures. The next step brought me to the midbass. Based on the fact that I was going with a sealed enclosure, which was simpler for me, and from what I have read and researched, I designed the midbass enclosure volume to critically damp its performance, ie, a Qtc in the range of .5. Also, since my crossover point is in the 300 Hz range, I wanted to optimize the box to tune to at least 2 octaves below the crossover point of 300 Hz. This is essentially 75 Hz. Using the downloadable programs: WinISD alpha, WinISD beta, I modelled many scenarios which rendered a workable enclosure size of around 15-18 Litres for the CA. The final enclosure size ended up being 15 Litres net after I deducted volume for the braces and magnet structures. Box tuning is in the area of about 65-75 Hz, which was my target. This renders a Qtc of about .517-.53, so the end result will be a midbass which will perform in the frequency range where pistonic motion will be there, however, it will be "tamed", thereby maintaining good lower midbass performance, along with the desired smoothness as it goes up in frequency......................I hope!..........You mention the difficulty not to get overly verbose, and as you can see from my posts, I suffer from that affliction as well...............Oh well, rather be more verbose than clear as mud....................Regards, .................Omni

[grantnsw]

tinitus, its me again! lol
re: (quote) "As an excample we can look at you mids low crosspoint
THAT single series C is most likely to give a 12db rolloff
AND that means that your box calculations can play a very important role AND that is one reason why it might work better with a higher crosspoint than 2.7khz ... to have a 12db slope with a single inductor "

hmm, I'm still struggling with these concepts, could you please elaborate (for a beginner?) I really need to understand this.
(risking 'wearing out my welcome' here!) ...grant

[grantnsw]

Omni,
It seems that I am completely 'way-off-target' WRT the CA mid chamber! (EVEN IF you are targetting
a Qtc ~ 0.5!) My calc. for 1.5 Litres @ Qtc=1.1 alignment(much? smaller sealed box) seems by
comparison horribly inaccurate and wrong! Where did I go wrong? - no idea, I thought I reasonably
followed Vance. Could my understanding be that poor?

My ported cabinet is supposedly optimised @ 72 Litres, woofer Vas=178 Litres but your 300HzXO
mid chamber (tuned to 75Hz) @ 15 Litres is a huge proprtion of that. I thought that 1.5 Litres may
be too small, but 15 Litres is an order of magnitude greater, even considering Qtc~0.5. Whoa, lol.

I've got some work to do! Are the WINISD programs free?, if so, I will download.
I can understand that your sealed cabinets are largish - but 4 cubic feet seems huge! (Litres?) for the
Peerless 830669: Vas~172 Litre, is less than my P25 (Vas=178 Litre!) I must have been misinformed
in the original design, unless a sealed box makes such a HUGE difference?

Btw, 'old school' sealed seems good (I'm old school in most things!), supposedly better transient
response.

Unless there is a way around this, it seems that I may need a seperate Tweet/Mid enclosure on top
of the woofer boxes OR maybe an infinite baffle similarly for Tweet/Mid also on top, but difficult
(Troels has a section on that) grant....pondering.....

[omni]

Grant, your math is not that wrong as you may feel. I ran a model in the WinISD alpha and beta for the CA with the driver database parameters and the parameters I inserted from Zaphs measurements. At 1.5 litres I got Qtc of 1.025 with a Fs of 152 Hz and in another I got Qtc of 1.061 with Fs of 146 Hz. so don't despair, your calculations seem to be right in the ballpark..............However, with that high of a Qtc for the midbass, the small 1.5 cabinet is NOT providing much damping to the driver. This is a problem for smooth midbass/midrange performance. I also checked out your woofer in the WinISD, but not thoroughly, however it seems that the EBP of 80 something suggests the driver is better suited to a ported enclosure. The 4 mm Xmax also suggests that as well. There are differences in optimized cabinet volumes when you compare sealed vs. vented, so my 4 cubic feet sealed enclosure with a 12 inch woofer compared to your vented enclosure with a 10 inch woofer is like comparing apples to oranges................But, as far as the CA15RLY is concerned, you can take a variety of approaches. SEAS, on their website recommends a box size of 6-9 liters vented box, I believe, but not certain, and these are only guesses from memory, so you may want to check their website. I am also of the thought that these alignments are based on a 2 way system, using the CA as the primary woofer. But Vance Dickason suggests that we are tuning the midbass enclosure to optimize it similar to a bass enclosure. It describes the alignments but I am not certain if it goes into port diameters and lengths........... Again, I chose to go sealed to eliminate hassles or problems in dealing with a port, not to mention my lack of working knowledge of vented systems, in addition to my research, but also, I believe the sealed midbass cabinet will provide for a more robust midrange performance..........Your idea of building a seperate cabinet for the midbass and tweeter may likely prove to be a good choice that you wouldn't regret. I was originally going to use my old cabinets which were only 2 cubic ft, but when I started dialoguing with some people on this forum and met Tinitus, They convinced me to rethink my design. I knew from the start that it would be a pain in the *** to do completely new cabinets, but now I believe it was the right choice to make, not to mention the joy that has come from this endeavor, albeit fraught with delays and a few cost overruns............As far as my bass cabinets being huge, here are a few considerations I had to face:....SPL sensitivity of the CA15RLY is around 86dB. My Peerless woofer is reported to be around 92dB. So, there exists a disparity in the drivers. As suggested by Tinitus, a larger enclosure will make my woofer less boomy........Have you ever heard a car drive by, blasting its' subwoofers, booming down the road, shaking the entire car and the windows in your house ? This is a result of the driver who obviously does NOT seek MUSICALITY, ....... but primarily from a high Qtc woofer system, generally in small boxes. My larger boxes will transform LOUD boominess into DEEP, TIGHT bass which will not drown out the CA15RLY, which has a lower SPL to start with. As Tinitus expressed to me, it is a way to "extract" more midrange sound. I am already risking the possibility af a laidback midrange, which I don't want, so making the bass cabinet was a start to improving the quality of the bass AND bringing out the midbass more, and I am very grateful he was almost somewhat insistant on this matter...........The WinISD alpha, and WinISD beta are free downloads, but I don't have the website address, as I am sure you can Google it, or someone here may be able to provide the link. Download both, as they have different driver databasses,ie, some drivers listed in one but not the other. You can also enter data from your drivers into the applications....................sorry so long......Respectfully.........Omni