I want to build a diy speaker box and im going to use a Dayton Audio TCP115-4 (4 ohms) and a Dayton Audio DSN25F-4 (also 4 ohms) for each channel wired in series for an 8 ohm load. my question is should i use a 4 or 8 ohm crossover for the tweeter in this use case?
I will guess that you want to wire the tweeter & woofer in series to maintain a higher impedance.
The correct way to do that is to use a two way crossover that both the woofer and tweeter are connected.
Since you are using Dayton drivers you have a great resource in Parts Express tech support and their speaker builder forum on how to DIY the speakers. They may even have a specific crossover board you can use.
So you're building some great small 2-way speakers. Why do you need 8 ohms? Most amps can handle a minimum impedance of 4 ohms. You get more power by loading an amp near it's min. imp. rating, but it may operate warm. If there's no issue with the amp, I'd accept 4 ohms as your system impedance. You choose the crossover components for the impedance/ DCR of the drivers. So stick with values for a 4 ohm system in this case. You MUST also consider the sensitivity ratings of drivers you choose and may need to 'pad' the tweeter, because there's a big difference between the 86.8db (woofer) and 95 db (tweeter) 2.83V/1m values. You will not be happy without padding the tweeter down to match the woofer. Also, the tweeter's power rating is 30 watts. I'm not sure if that's tested with a 1st or 2nd order curve, but you may get better tweeter power handling and protection by shifting the crossover point higher, or using a sharper filter cut-off. You will anyway, by padding it.
The woofer has a nice, smooth curve up to the 2,500hz recommended lower end of the tweeter. I wouldn't go higher, because of a dip around 3.4KHz and a peak in the woofer's response around 4.6Khz, as the summed response may reveal them and be noticeable. Also, if the tweeter's power rating is tested for a 6db first order crossover @ 2.5KHz (ask PE tech), then you can go with a 12db 2nd order to protect the tweeter. Your system power rating may be around 40-50W per channel. Call the PE tech guys and they can point you in the right direction.
I honestly did not think about using a two way crossover but i will be using that instead for convenience purposes. Also at the time i thought about using the Sure Electronics AA-AB32165 2x25W but that ran down to 6 ohms and i was going to source battery and charging components from another place. It turns out its more cost effective to just go with the setup that dayton audio has on parts express so i believe the Dayton Audio KAB-230v3 2x30W (as it runs between 4 and 8 ohms) is the better choice for what i want to do BUT that also means i should probably change the speakers as well
I will be reading around the parts express forums and some other forums to learn a bit more on crossovers and other diy speaker builds in general any suggestions on specific posts here or on other forums?
Also thank you Americanaudiophile and Sonic Illusions for the replies, for some reason i didn't get notified when you replied so sorry for the delay
I recommend keeping it simple. When choosing smaller woofers (8" and smaller), they have great mid to upper extension (some can be used as midranges), but study the curves of both the tweeter and woofer and also the sensitivity. Smaller woofers can have nasty dips and peaks toward their upper ranges, so stay at least an octave away from those near the crossover point. If you get lucky, you can find drivers with closely matching sensitivities. If not, pad the tweeter to match (-1db for baffle-step). Once you find acceptable drivers with good curves (most important), choose a 6db first order filter to keep it simple and for minimum phase shift. You can chat with the experts to choose your crossovers. You may even find a suitable generic (pre-assembled) crossover and then pad the tweets. Good luck!