Crossover caps hard to get?

[Hayden]

Hey ya,
Just curious I have a 2way set that I’m trying to stop the top end from going lower than 100hz
I was thinking of a simple butterworth HPF probably a 12db cut or 18db just experimenting at the moment (bluetooth speaker)<--- says it all haha

560uF and about a 4.5mH coil sound about right?

My issue is how the heck do you get caps? They seem to jump value a ton I can’t even get close to the values needed. Went to a store today and they had 400uF NP then it jumped into the thousands
Am I missing something here? Do I need to recalculate to fit what value caps are made?
Any input would be greatly appreciated

 

[JonSnell Electronic]

Increase the value of the inductor and you can decrease the value of the capacitor.

 

[AllenB]

Just use two standard 1000uF back to back.

 

[Dave R]

If you put capacitors in parallel, just add the individual values to get the total. In parallel, Cequiv = C1 + C2 + . . .

As an example, you could combine in parallel a 400 uF, 100 uf, and 60 uF to get 560 uF.

Other combinations can get the same result.

You can combine capacitors in series also, but the math involves reciprocals. (not as easy to do in your head)

In series, 1/Cequiv = 1/C1 + 1/C2 + . . .

Hope this helps.

 

[TBTL]

Passive crossovers at these frequencies are ridiculously expensive and do not work, because loudspeakers have impedance peaks around these frequencies. Try using an active crossover. It goes between the bluetooth board and amplifier.

 

[waxx]

Check industrial sites like Mouser for Polypropylene or Polyester filmcaps that are in the region. I quickly checked mouser and found this 550uF filmcap:

DCP6N06550E100KS0M WIMA | Mouser Belgique

This kind of values won't be cheap, but 84€ is not a fortune neighter....

In the fancy "audio grade" brands you won't find this values, as most don't use those. But those fancy audio brands are a big part overpriced hyped brands. They won't make the difference with decent quality caps that is not branded as "audio quality". The difference is only the stamp they put on it. Wima is a good decent brand of caps, and their MKP caps are all over the place in audio devices, even in expensive hi-end ones...

 

[waxx]

Passive crossovers at these frequencies are ridiculously expensive and do not work, because loudspeakers have impedance peaks around these frequencies. Try using an active crossover. It goes between the bluetooth board and amplifier.

That is ********, not all drivers have resonance peaks at that point, and even if they have, you can still make a filter arround that point (but need to adapt the design to the resonance peak).

DSP has it's place, but this is about passive crossovers. This forum needs to stop to push everybody who has a question about this to DSP, it's extremely annoying for those who seek info about passive ones and don't want DSP for their project (whatever de reason is).

 

[18Hurts]

That is ********, not all drivers have resonance peaks at that point, and even if they have, you can still make a filter arround that point (but need to adapt the design to the resonance peak).

DSP has it's place, but this is about passive crossovers. This forum needs to stop to push everybody who has a question about this to DSP, it's extremely annoying for those who seek info about passive ones and don't want DSP for their project (whatever de reason is).

Why would bringing up DSP be a bad thing? Reading between the lines, the guy most likely wants to add a subwoofer but his amplifier does not have a 60 to 100 Hz high pass filter. He did not indicate what speaker he was using be it a true "full range" tower speaker or a 5" two-way small speaker--and that is a go/no go situation. Say he was using a 5" woofer that has an Fs of 60Hz and wants to make a passive filter at 80Hz--very, very complex way you can do it but it is within about a third of an octave of the peak--this makes it very tough to get any form of accuracy with passive filters. It is a good thing to bring that up! Not much of an issue if he was running a 12" three-way with the woofer Fs at 30Hz--not too hard to do but it depends on the speaker.

Back in my car audio days--I would get asked about "bass blocker" passive filters and my best advice was to look at the cost/size of such things, the complexity of the build to get any form of accuracy with small car speakers and so on. End result was to use "bass blocker" caps--not very accurate but would protect the small automotive speakers enough (if you held your mouth right) For most people, they then saw the wisdom of using active filters and these days very much so!

If the OP was not aware of changing the capacitor sizing by running additional caps in parallel--he might not know about resonant peaks with woofers as that tends to be in the more complex information. Since we don't personally know this person, I think it is always good advice to offer options to help them on their way. The OP did not define what he was doing (home, car, portable audio etc.) did not say what his main speaker were and never said if the filter was for subwoofer use. At that point, offering information about the major issues with passive filters at low frequencies IMHO is a GOOD thing.

So relax--getting a few options thrown in while getting the answer to the original question is normally how it is done. Sure, you can put a turbo charger on your riding lawnmower to increase the power to cut tall grass--but the option can be expanded to changing the 13 HP engine for a 20 HP and most likely would be less costly to perform, much easier to get it right so a higher chance at success than be stuck with a bunch of parts that won't work for the task at hand.

For the OP, if you are doing something like a chip amp 2.1 board thing that has no high pass for the main channels, look into basic electrolytics as they are much smaller, much less expensive and so on for the basic project. If you are using serious amplifiers be they high powered consumer grade or professional amplifiers--I would learn more about passive crossovers, how they are designed and the pitfalls with those designs. Once you get below 200 Hz, the part sizes get huge (very large at 8 ohms or higher) for polypro caps they look about the size of Coke cans if you go below 100Hz. That is the hobbies way of saying "Are you sure you want to do this?" You can do anything you want, just make sure you know all the details before jumping down that particular rabbit hole. If you tell us what you are doing, we can offer advice on several different ways to do it which would save you time, money and aggrivation during your quest. Good luck!

 

[Tweet]

Hey ya,
Just curious I have a 2way set that I’m trying to stop the top end from going lower than 100hz
I was thinking of a simple butterworth HPF probably a 12db cut or 18db just experimenting at the moment (bluetooth speaker)<--- says it all haha

560uF and about a 4.5mH coil sound about right?

My issue is how the heck do you get caps? They seem to jump value a ton I can’t even get close to the values needed. Went to a store today and they had 400uF NP then it jumped into the thousands
Am I missing something here? Do I need to recalculate to fit what value caps are made?
Any input would be greatly appreciated

Hayden,

Here is a site in Oz I often buy from, you can parallel up caps for the value you want.


Electrolytic Standard


You can get the inductance value you want here too.


P-Core


Absolute exact values are not necessary at that frequency to get the roll off you need.


C.M

 

[Moondog55]

Jaycar has NP and at a cost that is close to Speakerbugs, it's the cost of the copper in the coil that hurts most even with cored inductors, You need the biggest copper [ lowest DCR] you can afford to reduce SPL robbing resistance. Sometimes it makes sense to go active , but is doesn't have to be DSP. I have Behringer XOs that work fine at the low frequencies needed for woofers and subwoofers and S/H can be cheaper than passive components. Nothing wrong with passive either except the high cost