Building new speakers!

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#23
Cheers moondog, looks like I will go with those drivers.

So for the XO's I should use 2nd order butterworth? Havent been able to find many designs for a 2.5 way, but is it basically a 2 way XO (at 3000Hz) but branched off the 5" (mid) I add another inductor and 8" to the circuit? Given I want my box's 350mm wide, should this rolloff frequency from the 8" be 115/0.35? = 330Hz (BSF)?
And if so what value inductor does this have to be? (Haven't been able to find an equation to calculate that one..) 🙂

Thanks!
 
#26
Ok, so using an online calculator for a 2nd order LR, crossing at 3000Hz, and given you think a 5mH inductor will drop the 8" woofer at around 250 Hz, would this design be suitable?

Also since these will most likely be sitting quite close to a wall should I avoid rear mounting the baffle step woofer and just have it facing fowards?

Thanks once again!
 

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#27
Well mounting them close to a wall means less baffle step is needed ( guess here ) so put them on the front, which is OK anyway.

That is a "Book" calculation for the XO, you have the idea correct but you need to use the actual values not the "ideal" 8R when doing the calculations.
The tweeter is very close to 8R at 3k but the woofer is closer to 11R, so either use 11R or add a Zobel ( conjugate network ) to the woofer to get the impedance closer to the desired ideal value, and I can't tell you whether or not the tweeter needs to be wired reverse polarity or not
 
#28
Oh ok, yeah well that makes sense actually! =),

At 11R Inductor = 1.17 mH and capacitor = 2.41uF.

With those changes should that design be fine?

Both inductors are availiable +- 0.03mH from those calculated, so that should be fine.

Ie this one? 1.20mH 15AWG Cored Inductor 0.11Ω DCR 5004 Induction Coil 15 AWG 1.2mH Cored [] - $12.50 : SpeakerBug, capacitors, inductors, resistors, crossover parts, speaker supplies

Which capacitors are the best to use also? would these be alright?
3.3uF Jantzen Audio CrossCap 3.3uF MKP Metallised polypropylene Capacitor 400V dc [] - $3.60 : SpeakerBug, capacitors, inductors, resistors, crossover parts, speaker supplies


Thanks!
 
#29
Near enough is good enough with components, +/- 5 or 10% as a first project.

For inductors in the signal path use air-cored coils if you can afford them.
My limited experience would go with a first order plus Zobel on the woofer, then manipulate the resistor value in the Zobel to achieve the desired end point; this is mainly because I am
1# Cheap
2# Resistors are very cheap compared to other components
 
#31
Ok looks like ill do that moondog!
For calculating the capacitor for the zobel I have found the formula ' Le/Rc^2

All very well except what value do I use for Le? (Jaycar website doesn't specify one)?

Chris thanks for that software advice, ill check it out!

Other than that I think I’m all set, I reckon I will order the parts tomorrow!

Thanks so much guys, hopefully I am done with questions for a while and can start proper work on them!
 
#32
Hi,

If you look at the links I provided hardly any drivers are zobelled,
only tweeters where not doing it causes a rise in treble response.

Passive Crossover Network Design

Is misleading. Its only useful for understanding and then best ignored.

Electrical c/o filter functions as above is simply not the way to do it.

What matters is the correct acoustic filter functions, and if your
dabbling with simple c/o's often series first order is a lot better
than parallel, simulation here is very much your friend.

Also use WinISDpro to model bass power handling, can be very useful.
You don't want a 2.5 way severely limited by one of the drivers.
(Or any other simulator that does that.)

rgds, sreten.
 
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#34
So Sreten you would reccomend not using a zobel on the mid? Isn't the idea to zobel my case because im using a 2.5 way, and doing so may help the midrange reach that 3k crossover to the tweeter?
Thanks for winISD pro, when I get time ill put those driver details into it (seems strange that standard winISD has them preloaded but Pro doesn't...).

Moondog, with a zobel (R= 7.5, C= 10.67) is this placed after the 2nd order LR and before the speaker? as shown in the diagram? Or is that wrong due to the bass driver/LR XO? (I haven't been able to find much information on how it should be... 🙂 ).

Thanks guys!
 

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#37
Pete, after using your values calculated for the 8" jaycar, and putting them through WinISD (Sorry but Unibox seemed a little complicated...) it calculated "optimal" box of 58.5L at 32Hz! That’s for a vented enclosure anyway, which it recommends...
Since it’s for the bass driver, 44L at 35Hz is looking pretty good (Am starting to understand a bit more about those graphs ) .

I’m guessing midrange would be better in a sealed box? So it can reach that 3k cut-off? (Website recommends a 9L sealed, or 20L vented... thoughts?)

I think I have finalised that crossover design..? 2nd Order LR (3k Hz) for tweeter, 1st order BW + Zobel for mid (3k Hz), and then 1st order BW for sub! (250Hz).

Thanks once again,

Felix
 

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#38
#40
Parts are ordered and En route! 🙂,

Thanks for all you’re help guys, really appreciated!

No doubt I will have some more questions when it comes to actually assembling them... speaking of which, when putting together the crossover do you generally put it onto Vero board? Or is it best to use a bit of ply and solder together the legs of components? College is over for the year so I don't have access to an etching tank... . Also I assume the inductors should be placed as far away as possible from each other?

Thanks again! ,

Felix
 
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