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Design Q's - advice sought
Hi,
I'd appreciate some input on a couple of ideas I'm noodling through.
Basic premise is an MTM based on Lou's LECBOS. I already own the drivers.
1. The woofer has a truncated frame, but the curved edge is beveled where as the truncated edge is not. I'm thinking these should be mounted with the curved beveled edge facing the tweeter. However the LECBOS has the truncated edge facing the tweeter. What should I expect for crossover adjustments?
2. Rather than a slot port on the bottom, I'm thinking of two smaller slot ports on either side of the tweeter, for aesthetic purposes. A commercial with slots like this is a Genelec HT206B. Any thoughts on spacing from the tweeter, location, or other means to manage diffraction?
Thanks and regards,
Rob
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Re: Design Q's - advice sought
The main thing that is going to happen with mounting the round sides adjacent to the tweeters is you're going to increase the CTC spacing. If the existing xo is low enough, that won't be a problem. If it isn't, you'll pretty much need a whole new xo, since Lou does all of his work based on in box measurements of the drivers, in their mounted positions.
I shudder at the thought of ports flanking tweeters
. I can't imagine what diffraction effects that would have, or how to model it in order to deal with it. I wouldn't do that.LECBOS sounds awesome just the way it is, I would use veneer, or other finishes to individualize your build.
But, maybe that's just me.
Mark
You know I'm born to lose, and gambling's for fools,
But that's the way I like it baby,
I don't wanna live forever,
And don't forget the joker!~Lemmy
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Re: Design Q's - advice sought
...1. The woofer has a truncated frame, but ...the LECBOS has the truncated edge facing the tweeter. ...
As Mark noted, these two work at crossed purposes. What's interesting is that you didn't see it...
2. Rather than a slot port on the bottom, I'm thinking of two smaller slot ports on either side of the tweeter... Any thoughts on spacing from the tweeter, location, or other means to manage diffraction?...Perhaps you're familiar with Zaph's test of the effect of driver flush mounting on frequency response? The key conclusion was to flush mount the tweeter, because the round flange caused all the diffraction in every direction to occur at the same frequency, resulting a large peak/dip. Woofer flush mounting had a very subtle effect as the distance from tweeter axis to driver edge varies with angle, spreading any diffraction effect out and resulting in very little FR shift. You're working the latter case here, with a low straight lip that will diffract over a range of frequencies and so not be audible.
The ports are kind of the opposite of a low straight lip. Ports are deep, so the diffract strongly. Frame a tweeter with a sharp-edge port and you're far worse off than any tweeter flange. There's a thread somewhere about modifications to Behringer B2030 speakers (ports on both sides of tweeter) to reduce port-induced distortion. It's a real effect....
HAve fun,
Frank -
Re: Design Q's - advice sought
On most of my designs, I would say OK, but the LECBOS crosses higher than most, I wouldn't mess with the CTC spacing. Ports can go in the back, out the sides, top or bottom. Tube port equivalents are spec'd on the page. I noted the crossover frequency, too. But, from the photo on your website it seems like it might be possible to rotate the driver 90 degrees without changing the CTC distance. If I flush mount the tweeter, I might be able to have the woofer overlap the tweeter a small amount. Sound OK, or am I out of space?
Thanks,
Rob
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Re: Design Q's - advice sought
I can also attest that the LECBOS sounds plenty good as designed, and paired with his sub they make a really phenomenal system in his garage. If I were going to do any "improvements" I would use a thicker front baffle maybe do a 3/4 inch round-over and MAYBE recess the tweeter, or put some of that super ugly felt surrounding the tweeter to deal with the edge refraction...I put improvements in quotes because while these seem like sane things to do from a theoretical standpoint, Lou's designs just kinda work...even without them (having a horn loaded tweeter helps too I think :P)
That's part of the plan. Flush mount the tweeter. If I can't rotate the woofers, then I might need some felt to soften the diffraction at that edge. At least I think I do. -
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Re: Design Q's - advice sought
I just took a look at mine and I don't think you can rotate the woofers w/o overlapping the tweeter flange, which would be the worst of the alternatives. You really should just build it as is. What little diffraction that may result from the surace mounted woofers is certainly not audible.
I actually don't think overlapping the tweeter flange is the worst option out there, and, as Frank noted, would actually improve the diffraction signature *OF THE RAW DRIVER RESPONSE*. Thing is, as I pointed out earlier, Lou designs his xo's based on in box and on baffle measurements, so the diffraction has already been accounted for in the xo. If you change the diffraction signature, you will change the sound. Whether that is unpleasant, or even audible, remains to be seen. If you can measure, you can build it the way you want to, measure, then tweak it to taste. But in the end, it might not be the LECBOS.But guess what? That's okay.
If the changes are significant enough, I would say that at that point it becomes "Rob's Design X, inspired by LouC's LECBOS". And nothing at all wrong with that, IMHO.
But I reiterate, the ports flanking the tweeter is probably a bad idea. How about a pair of side "wedge" ports, like Wolf's "Max"?
Mark
You know I'm born to lose, and gambling's for fools,
But that's the way I like it baby,
I don't wanna live forever,
And don't forget the joker!~Lemmy
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