Baffle step compensation, crossovers and overall efficiency, and more...

Discussion in 'Archived Threads 2001-2004' started by Jeff Meininger, Nov 7, 2002.

  1. Jeff Meininger

    Jeff Meininger Second Unit

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    Question #1: In a two-way design crossed over at ~2.2 kHz, can all of the baffle step compensation take place below the crossover slope to avoid having to pad the tweeter? I've been trying to model things and understand them, and it seems to me that with a 3rd (or higher) order crossover, you could keep BSC from interacting with the crossover summation (and be able to pick a less sensitive tweeter). I'm very unsure of this conclusion, though.

    Question #2: I notice that the GR AV3 uses a 90 dB sensitive tweeter, and the overall AV3 sensitivity is 91 dB. It uses two 87.5 dB sensitive GR165's in parallel (for 93.5 dB total sensitivity). I assume that around 3 dB of woofer sensitivity is consumed for BSC, which explains the overall sensitivity rating nicely, especially if the answer to my question #1 is correct. But the crossover here is 1st order... so isn't the tweeter still rolling off in the area affected by BSC? In other words, the tweeter's LF output would be reduced by the BSC. The GR165 seems to have a rise in the same region, so reducing the tweeter's input into the crossover summation could theoretically flatten out the woofer's response, right? It seems like it might be a very elegant/neat solution. Are any of these observations correct, or am I way off?

    (I might end up building some AV3s rather than trying to design my own towers, but I want to understand the theory regardless of whether the kit has already done the hard work or not. It's interesting to me.)

    Question #3: With a 2-way (one tweeter, one woofer) design starting with an 87 dB sensitive woofer, your maximum system sensitivity is 87-X where X is the amount of BSC you're using, right? If so, then why is the SCH tower kit that uses an 86.7 dB woofer rated at 88 dB sensitivity overall? In fact, how can that be possible even if you DON'T subtract X db for BSC? Can crossover components increase driver efficiency somehow?

    Question #4: is the "acoustic center" of a horn-loaded tweeter like the Morel MDT-37 further back than that of a normal tweeter since the dome itself is recessed?

    I have many more questions, and I'll add them to this thread as I run out of luck in trying to find their answers on my own.
     
  2. Hank Frankenberg

    Hank Frankenberg Cinematographer

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    Hi Jeff. If you want to study crossover design because it's interesting to you, I have a recommendation for you so you won't have to ask your questions on this thread. The questions will quickly involve more complexity and would require long answers from the few here qualified to provide reliable answers (I'm not one of them). I recommend you buy two books if you haven't already. Start with the little book, "Advanced Speaker Design", a paperback you can buy at Radio Shack. Then buy "Loudspeaker Design Cookbook" by Dickason. Then buy the GR Research AV/3 kit. You'll have a basic understanding of crossover design and you'll have a great price/performance value system.
     
  3. Jeff Meininger

    Jeff Meininger Second Unit

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    Cool, I'll give "Advanced Speaker Design" a read if my local RS has a copy. I've been trying to find "Loudspeaker Design Cookbook", but have struck out at Barnes and Noble and Half Price Books. I'll order a copy from somewhere on the internet.
     
  4. Jonathan M

    Jonathan M Second Unit

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    Hi Jeff,

    I'd suggest popping over to the Madisound Forum to ask these questions. There are folks here that could answer them, but most around here are kit builders. The suggestion of the books by Hank is also a good one. (Although I'm designing my own 2-ways without reading them)

    I'd recommend getting hold of Speaker Workshop, and doing a google search for "Speaker Workshop Tutorial". The first link that pops up shows you how to get manufacturers data into SW. I've played around for a while with SW, and it's quite easy to design and optimize good xovers with a bit of playing around. BSC can often be taken care of by optimizing the xover for a goal (such as LR4 at 2.2kHz) that is down around 3dB or so on the high-end of the woofer response. Remember that the majority of effect of BS is up to around 1.5kHz, so the tweeter generally is not that effected - you just have to pad down to the top end of the woofer's sensitivity.
     
  5. Patrick Sun

    Patrick Sun Moderator
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    BSC is used on the woofers, not the tweeters.

    Unless you were crossing down low, in the 300-500Hz range, to get a smooth speaker, you'll have to integrate BSC into the woofer's network to smooth out the rise in output over the 500Hz range. This will lower the woofer's output level. It is this smoothed over woofer output level that used for padding down the tweeter to match the woofer output level to the tweeter output level.

    That's about it in a nutshell. How you actually achieve the BSC and the level matching is a bit art, a bit science.
     
  6. Chris Carswell

    Chris Carswell Supporting Actor

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