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HiVi TN25 Fabric Dome Tweeter
If I'm using the HiVi TN25 and a HiVi M4N 4" Aluminum/Magnesium Midbass in a small boombox, about the size of a lunch box, is a crossover recommended? Thx.
The other posts here are correct. A crossover both protect the tweeter from burnout and keeps the woofers high frequency output from spurious out of phase pollution of what should be cleaner, sweeter output from the tweeter.So, you should use a crossover--on both the woofer and the tweeter. This is despite the fact that many supposedly quality manufactures of speakers (PE's Dayton B652's are a current good example) do not spend the money on the coil/inductor necessary for the woofer, trying to cut corners by hoping the voice coil of the woofer has inherent inductance does the trick. But it doesn't sound very good.Still, the drivers you selected are both very good quality. If you put a zobel (impedance flattening circuit) on the woofer, you can use a simple first order crossover. This could be any kind of inductor (air or cored) with a value of 0.4mH to 0.5 mH in series with the positive lead. Since the Re of the woofer is 6.5 Ohm, you could use PE's standard 10W 8.2 Ohm ceramic resistor married to about a 15 uF cap to achieve this. Although less expensive than PE's "audio grade" non-inductive resistors, I have measured these side by side with the audio grade resistors to confirm that they actually have less induction than the more pricey audio grade "boutique" resistors. So I recommend the cheaper ones as superior and more affordable (and I have use literally hundreds upon hundreds of these).The tweeter is nominally 5 Ohms and is about 5 dB's brighter than the woofer. Despite the theoretical ideal of getting them to be the same efficiency (in dB's of SPL) for most male listeners over 25 years of age, a difference of up to about 2-3 dBs (with the tweeter being brighter) is more desirable. So putting a 2-3 Ohm resistor is better and also give you a simple 8 Ohm tweeter to crossover. You can then put a second order crossover on the tweeter, using something like a cap at 4.5 uF to 5 uF in series and 0.4 mH in shunt (parallel). No need to reverse the polarity, as is common with 12 dB xovers--but you are welcome to check this yourself.As long as you use film capacitance in the high pass (tweeter) section you will be happy with the result. You need not agonize about what kind of film cap you use (polypropylene or polyester/Mylar). It is not likely you could hear any difference between the different film dielectric materials anyhow. But using a NP electrolytic cap(s) would be a mistake that will be audible. I say this from having measured the DF (dissipation factor) in many, many caps and from having built and sold thousands of crossover upgrades.
Date published: 2014-04-05