x-over confusion about driver loads

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Hi all,

I thought I knew what I was doing, but then I started to second guess myself about how to calculate driver loads in order to select crossover components.

I am trying to present a 2ohm load to the amp.
I will be using 1 tweeter and 2 mid woofers per channel, with a total of 2 channels.
The tweeter is 4 ohms and each mid is 4 ohms.
I wanted to run the woofers in parallel to get a 2ohm load.

In going for a Linkwitz–Riley 2nd order design I used an online calc to figure cap and inductor values based upon wanting a 4 ohm high pass and a 2 ohm low pass x-over, both with a target frequency of 3khz.

Now I am wondering if I am thinking correctly in the way that the stacked ohm values will be totaled as the amp and x-over will see it.

These are the drivers I am using:
https://www.madisoundspeakerstore.c...sxdSEfL1GBpP8UjUnbwtY8vysVNPQwbVKixoC1QLw_wcB


https://www.madisoundspeakerstore.c.../silver-flute-w17rc38-04-ohm-6-1/2-wool-cone/


Can anyone provide some thoughts please?
Thanks in advance!
 
You`re about right but not exactly. The 4 ohms you describe are usually the nominal impedance of the loudspeaker quoted by the manufacturer where the impedance is a reactive parameter and changes with frequency. The rate of change depends on the inductance of the driver. When you open an impedance plot, look for the region where the crossover would be targeted, in this case 3Khz. While the nominal impedance may be 4 ohms, the driver actual impedance at 3Khz may be much higher. To understand it better - have a look at the graph for this driver:
H1216-08 CA15RLY
It is given as a 8 ohm nominal impedance driver by its manufacturer but the actual DC resistance is 5.6 ohms. However, what you need is not the DC resistance but the impedance around the crossover region. That being said, if we look at 3Khz, it is about 12 ohms. This is the one you need and here come two ways to choose from:
1. Use a Zobel network to equalize the impedance of the driver - then you can input 5.6 ohms in your crossover calculator.
2. Discard the use of Zobel - this is in my own opinion the better approach as any parallel network will eat up some of the sound. In this case the value you need for the crossover is not fixed and means you need to take it into account. In the example with the driver above, you can use a value of about 14 ohms which is in between the 12 ohms at the crossover frequency and the value at 6Khz which is an octave above.

Something to seriously consider - while you state the drivers` resistance at 4 ohms, as you can see from the graph it may fall under it. In your case, if minimum impedance reaches, let`s say 3 ohms, you`d present a load of 1.5 ohms to your amp. You`ll use an inductor in the signal path so you could add 0.3-0.4ohms for the inductor resistance to your calculations ( thus if the speakers present a load of 1.5ohms, the amp will see 1.5ohms + 0.3ohms + speaker cables resistance ). There are car audio amplifiers that can take it down to 1 ohm but for a home amp - that would nearly kill it. Indeed, the nominal impedance (usually given as either 4 or 8 ohms ) is rather useless in loudspeaker design. Hope this help.
 
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Thank you both for the input!

This is just for a car so keeping it simple is a main goal and I am transferring components from another car so all I needed to buy was these speakers and get the crossovers made for them. It will be situated in a way that the tweeters will provide enough high end from what I can tell, and I have some much higher sensitivity vifa tweeters I can use if these are lacking. I don't plan to do a zobel for these as it's a non critical listening environment in my econobox daily driver.

I totally forgot about driver inductance at the x-over point though. I knew that something was being overlooked but couldn't put my finger on it. It's been a long time since I put a system together and I am a bit rusty. I should have some amp headroom as I will have 200-250 w rms depending on available system voltage. I seem to remember it being a regulated power supply below 12v, but unregulated above to provide greater output for those competing with 16v systems.

The tweeter is going to be 3.7ohms at 3khz and the mid is on a smooth gradual rise in impedance but I don't know what the figure is based on the info provided.

Could anyone take a guess what the impedance value could be based on the graph at the bottom of the page?

https://www.madisoundspeakerstore.c.../silver-flute-w17rc38-04-ohm-6-1/2-wool-cone/
 
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You may need to biamp the tweeter then, it is way too low in output otherwise.

With a delta of 0.5db is no bid deal, and this, like I stated above, is just for my econo-box ride anyway, so the stock non-whizzer cone drivers are sub-par from the start and adding any high end will be an improvement which I will be utilizing via the blank tweeter plates in the stock location, hence the need for 46mm drivers..

The impedance spec issue is still at hand here for the Silver Flute's and the mV given in the graph is useless to me as I know not how to make sence of it as if it were an impedance plot.

Anyone have a thought about how I should correlate the given data as how to determine the impedance of around 3kHz for the Silver Flute's?
 
Why the desire for a 2ohm load? That tweeter with a single woofer should work well enough. If you really want dual woofers then consider low-passing the 2nd down low (i.e. 70Hz 1st order, give or take after some listening with a single) to squeeze a little more bass out of them.

The woofers will not be collocated so for the driver (me), I will mainly be hearing sound coming from a single tweeter and a single mid up front on each side of the car. The other speakers will be for rear fill and passenger listening, but from what I have tested in the car so far, are placed in a way that the front seats don't really hear them. I have thought about running them with a little 1st order like you mentioned and most likely have the parts to do so, but will wait to see how things sound after all is installed.
 
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