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Just spent $20 on an inductor to be used with a $12 speaker?

  1. Jan 13, 2016 #1
    I recently replaced the rear "sub-woofer" speakers as the originals had rotted away in my vehicle. And? And it sounded terrible. Now I was getting the whole spectrum -or at least close to & the break up on the top end was nasty.

    What I didn't realize is that Subaru had glued an inductor on the basket/frame of the original speaker so that's in the landfill already with the blown speakers. So there was no low pass filter. That's why my new speakers were playing full range & sounded terrible. Well, inductors aren't cheap, at least not ones that you need where you intend to low pass around 100 hz, 4 ohm. Someone told me I could have simply wired a capacitor in parallel with the speaker & the high frequencies would have shorted there so that'd work too.

    That would have been like $1.57. I feel like an idiot for putting together a $40 crossover on speakers that are $10 a pop. I was going to post this on an audio forum, but those guys are biased & they all claim to have "golden ears" or something.


    & btw, if you can parallel a cap to a speaker to act as a lpf, can you then parallel an inductor to lets say a tweeter to act as a hpf? I understand this isn't, uh, very economical, but can you?
  2. jcsd
  3. Jan 13, 2016 #2


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    wellllll ..... to be honestly blunt ( or is that bluntly honest?), don't expect too much quality or life out of $10 speakers :wink:

    here's a practical crossover network .....


    there are many other ideas out there :smile:
  4. Jan 14, 2016 #3
    It was still way cheaper than an electrical engineering degree. Think of the thousands of dollars you saved. :biggrin:

    Impedance matching networks for speakers with frequency varying impedances? You got off cheap.
  5. Jan 14, 2016 #4
    The retailer I purchased the speakers from carries many inexpensive drivers (including the tweeter in the schematic you posted) found in monitors ranging from a few hundred to well over a thousand. Components are cheap. Paying you to design a crossover is expensive. And I'm not even sure if it's possible to design a "bad" speaker. I'm not even sure what that would mean. There's only so much to it >> cone/diaphragm, voice coil, surround, basket, magnet, etc... How do/could you screw that up? Not align the voice coil properly? Forget to glue the surround to the basket?

    No? So, part quality?

    Using aluminum over paper for cone material, rubber over foam for surround, neo's over ferrites...?

    Sure, aluminum holds up better than paper, especially in a leaky car door, but now you have break up so have fun finding a small format tweeter will do 2.2khz 2nd order. Tweeters that can play that low are expensive. You have gained nothing.

    Until speaker manufacturers design a speaker that will play 20-20khz flat, it will always be a give & take. Speakers are all the same to me, regardless of the cost.


    I was just looking for an inexpensive replacement. And is that a 4th order crossover? 4th order crossover = 4th order diff equation? I'm not even close to being able to model that circuit on paper. If I have to rely on software, then I don't know what I'm doing. No software please.

    Can you indeed low pass a speaker by paralleling a capacitor to it?


    Electricity, by nature, will always take the path of least resistance.

    Since the two components, the inductor (speaker) & the capacitor are paralleled to the input signal, then the signal can pass through either of them.

    The capacitor offers less impedance at high-er frequencies, so those high-er frequencies should "pass" or short through the capacitor & not the inductor (the speaker). Remaining frequencies (the low-er ones) should pass through the inductor since it offers less-er impedance at low-er frequencies. This is how your low pass works.
    Is this correct? Go easy on me. I'm just trying to get an intuitive understanding.

    And if so, is shorting out my circuit (via cap) a bad idea since I'd be putting a great load on my amplifier? ...the cheap IC stuck in my stereo. No external amplifier here.
  6. Jan 14, 2016 #5

    The speaker I purchased was a buyout. The retailer does not include frequency response graphs for buyouts, which is another reason why I went with a 1st order circuit. I'm taking a stab in the dark. Why bother with a sharper slope when I don't know where I'm aiming in the first place? I figure if I could get around 80-150hz low pass, I'd be okay.


    Think of the thousands of dollars my whole generation could save if colleges/universities allowed students to challenge more courses. I am 23 & back in college. I took a placement exam & was placed into Calc II. Yes I did rely on power rules. I'll get around to it soon. I graduated high school from small town USA. We didn't have physics. We didn't have calculus. We did have trig, but it wasn't required. I stopped at Algebra II. Youtube, specifically Khan & PatrickJMT, saved me $$$ from having to take trig, precalc, college algebra, etc. If colleges/universities weren't so greedy, Youtube/the internet & all it's forums could save me a LOT more. Go to Youtube & do a search >> integrals, how to differentiate, RC circuits, matrices ...I'm not even going to bother going on. You know what kind of information we have access to, and all for a small fee from your local internet service provider. Unfortunately, if I walk into a speaker manufacturing company & ask if there are any engineering positions available that don't require a degree, I'll get laughed at. Ask me how I know. Colleges/universities know this & they use it to their advantage. The whole thing is messed up.

    You'd be upset too if you went to the grocery store for a loaf of bread & had to purchase the $20 loaf when there's a $2 loaf sitting next to it.

    Yeah, no one is forcing me to go to college, but this is an area I'm interested in & it's an area I believe I'll excel at. Not exercising your talents is a selfish act. Not only are you keeping yourself from the things you love, but you are also shorting society of what you have to offer, which in my opinion is even a more selfish act. If everyone placed or was given the opportunity to place their talents where they should be, the whole world would be a better place for all of us.

    So yeah, I bought a $12 speaker because I spent all my money on a loaf of bread. Priorities..

    I'm going to spend thousands of dollars for content that's free, but I'm doing what I have to do, just like the rest of my generation. Books have been around longer than universities. It's the support that matters. Why bother going into the tutor center for help on a circuit when I can hop online, find a relevant forum & talk directly to an experienced engineer? You couldn't do that 25 years ago. You can now. College is a thing of the past. I'll stop my rant.
    Last edited: Jan 14, 2016
  7. Jan 14, 2016 #6
    Ouch. I touched a nerve.

    If you want an engineering job without a degree, build something. Do the math and be prepared to show you did. Many employers are more interested in getting their engineering job done than in a degree. (Of course most, particularly government contractors, need the paper.) A complicated electronic gizmo that works is worth nearly as much as a piece of paper. (Nearly as much, don't expect a good salary.)

    BTW, document your design and building process on YouTube. Soon people will come beating at your door.
  8. Jan 15, 2016 #7


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    That would work, but it might damage the amp if the amp wasn't intended to drive a load that's a dead short at hf. I'd feel much more comfortable putting a series inductor with a bass driver and a series cap with a HF driver, rather than paralleling either.
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