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How Bad Is It *Really* To Put A Resistor In Front Of Each Driver?

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  • kevintomb
    replied
    Originally posted by LewisH View Post
    Ok, thanks for all the help everyone 😁
    There is just SOO MUCH to explain, that I would wager, even most of us, would have a hard time knowing WHERE to start, as to explain how all of this works, and why it works and what all the factors are in designing a speaker.

    I think one needs to come into this hobby with a somewhat decent knowledge of how it all works first to at least some degree. As far as impedance/phase, driver sensitivity, measuring frequency response, and baffle step, crossover design, driver spacing, dispersion, bass reflex, and a few other key ideas and elements.

    Just knowing basic electronics will help a good bit, but there are many "Specialized" things that one must grasp when designing or even understanding how all elements of a multiway speaker work.

    Just when you think you got the basics, there is always more to learn or understand.

    Welcome to the hobby!

    Leave a comment:


  • DeZZar
    replied
    I also recommend in conjunction with reading books on speaker design, studying the designs and generously provided write ups from people like Troels Gravesen http://www.troelsgravesen.dk/Diy_Lou...r_Projects.htm

    This helps transfer the theoretical to real examples and Troels has more than most to learn from.

    Leave a comment:


  • JRT
    commented on 's reply
    You bring up a good point. The equal loudness contours illustrate the nonlinearity of human hearing perception with respect to both frequency and SPL. Relative to the reference monitor listening level at the listening position that was used in the mastering effort, listening at significantly reduced playback level imposes nonlinear distortion in hearing perception which cannot be well corrected with linear equalization, which conventional loudness compensation attempted to do. All that said, I do think those attempts at loudness compensation were better than nothing, especially for background music at very low playback levels.

  • LewisH
    replied
    Ok, thanks for all the help everyone 😁

    Leave a comment:


  • fpitas
    commented on 's reply
    And if you use a multipin connector like a Speakon you can swap crossovers fast ;)

  • JRT
    commented on 's reply
    A good way to learn is to build with two external crossovers, one of the original design and one of your own design, and develop the latter while trying to improve upon the former, swapping between the two for evaluation.

    Developing the crossover filters in the digital domain adds more flexibility and allows comparisons of more variations without the expense and bother of changing physical components.

  • fpitas
    commented on 's reply
    I agree with this 100%. It took me years to know what I'm doing at speaker design, and I'm an engineer. Lots of nice kits out there. Some have cabinets, some you supply your own.

  • billfitzmaurice
    replied
    Rather than trying to design your own speaker you should start by building a tested design, or a kit. There are those who'll tell you to just go for it, but it's not their time or money at risk. The knowledge required to design high quality speakers takes years to acquire, so at first you want to take advantage of someone else having done so. As quaint as it may seem the best way to learn about speaker design is still with a book, like those by Ray Alden or Vance Dickason.

    Leave a comment:


  • fpitas
    replied
    A Loudness button on some receivers and preamps accounts for the Fletcher-Munson curve. Otherwise you design the speaker for your preferred listening level, or have EQ handy.

    Leave a comment:


  • Steve Lee
    commented on 's reply
    Your 3rd question really opened a can of worms for me!

    Short answer on that is that no speaker design can nor will be able to handle all the variables that went into creating the mix that you play upon those speakers in your environment - you will be tweaking the sound in your space on you equipment forever if you have a critical ear.

    Good luck my friend.


  • LewisH
    replied
    Now we're really getting into the juice!

    Are you saying that the impedance varies as each drivers impedance changes depending on the frequency that it's playing and therefore the calculation isn't that simple, but on average will be ok?

    Im wondering if with 3x 4ohm drivers, only one of which playing a (say) 4khz tone would damage the amp because the resistance of the other drivers wouldn't be present, or is that just not how it works? (Thanks for your patience in explaining this to me!).

    On the SPL, are you referring to the Fletcher–Munson curves? I was wondering if i should be aiming for a flat SPL and let the amp take care of that or if i should attempt to deal with that in the speaker and the amp plays an unaltered mix... or if both the amp and speaker should be flat and the music producer takes care of that! (Maybe the answer depends on the music producer or amp manufacturer?)

    Leave a comment:


  • Chris Roemer
    replied
    If you've got a basic (beginner's) knowledge of Ohm's Law, then you might think that a 3-way using 4ohm drivers would end up as only a 1.3ohm load (as seen by the amp), but that's not the case.

    The 3 drivers don't all play the same freqs. (so they're not ALL in parallel - THAT way). A proper XO (crossover) keeps the drivers separate: the 4ohm woofer hands off to the 4ohm mid, then to the 4ohm tweeter. The amp sees three 4ohm drivers, but each only playing in its own band. The load is a nominal 4ohms throughout the entire freq. range, and your amp is safe.

    Your other idea about matching SPLs isn't really correct either. A woofer (typically) needs to play 3 to 6 dB louder than the mid or tweeter (Google "baffle-step loss"). The mid and tweeter will typically use resistors to quiet them down, but never a woofer. Also, the mid & tweeter don't have nearly as much power (heat) in their pass-bands as a woofer (you can probably "sense" that that's true).

    Leave a comment:


  • LewisH
    replied
    It should be apparent that I'm a novice (learning lots but still having lots to learn), so thanks for not berating me for my musings / uninformed questions, and thanks for the great information - hopefully I've understood things correctly. Here's what I think I've understood / interpreted:

    1. amps volume controls probably are changed before the amplfiication, so the resistors have low values, which prevents them heating up as much, I imagine.
    2. resistors affect the electrical Q rating of the driver. I don't really understand this, so I'll have to refresh my theory on T/S specs and model it with software to get my head around it.
    3. resistors in crossovers generate a lot of heat, so avoid this. Maybe I'll have to use another driver in series if I need to change resistance without affecting quality?
    4. I'm picking drivers based on the SPL graph, trying to match the SPL so the volume is the same throughout the frequencies and that it crosses over nicely. This might not be the correct way to pick drivers based on Bill's last comment.

    The reason I'm thinking 3 parallel 4ohm drivers might be a problem is because I want to cross them so they're handling part of the frequency each. Therefore I figure if there's some music that only the tweeter is playing, I've got the tweeter's resistance at that frequency, which might only be 3ohms divided by 3 because it's in parallel with 3 drivers. Have I got that terribly wrong?

    Thanks for all the learnings, by the way. This forum is very valuable for beginners like me, to help improve my understanding / interpretation of what I've read elsewhere

    Leave a comment:


  • billfitzmaurice
    replied
    Originally posted by LewisH View Post
    Amps probably use variable resistors in the audio line to control volume
    Yes, and they're typically only 1 watt or less
    so how bad is it *really* to have a 4ohm resistor slapped in front of all of your drivers to bump up the impedance to protect the amplifier across certain frequencies?
    Really bad, because they'll burn off half the applied power as heat.
    I want to use 3 drivers (3 way)
    If by 3 way you mean woofer, mid and tweeter the system impedance would be 4 ohms. Why would that be a problem? Besides, very few drivers are offered only in 4 ohms. I can't imagine not being able to find 8 ohm drivers for any application. I don't know what it is about these 4 ohm drivers that you like the look of, but I suspect it's not their T/S specs.

    Leave a comment:


  • fpitas
    replied
    Most amps have a very low output impedance, 0.1 ohms or less. If you insert a resistor, it will affect the electrical Q of the driver, cause the frequency response to follow the driver impedance, as well as waste power. However, you should be able to SIM the effect.

    Some people have claimed that series resistance reduces distortion. That's pretty rare with cone drivers, although it is very appreciable with some compression drivers.

    Leave a comment:

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