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Old 10th January 2006, 04:54 PM   #121
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Greets!

No need to apologize, I was just surprised at your remark since several folks have shown off different designs for this driver on various forums over at least the last couple of years. The only reason there's not more is few are willing to spend this much on a 'fullrange' driver, much less a Fostex.

FWIW, here's my Vb = Vas, Fb = Fs ML-TL based on my way of calcing them:

L = 45.22"
CSA = 133.5"^2
zdriver = 17.81"
rp = 1.25"
lp = 2.13"
zport = near/at the bottom

Obviously, this puts the driver too low, so a mass loaded bottom chamber is required, which can do double duty as stabilizing stand. This long a pipe needs a massive top also, whether multiple layers of wood, or my fave, a marble, slate, or similar decorative top plate.

Since MJK's WS's adds the flexibility though of what's possible with increased stuffing that I wasn't willing to explore on an experimental basis decades ago, a longer pipe to shift the driver up to ear level can yield most of the smoothness without what I consider the excessive damping required when the driver is placed near/at the top and the vent near/at the bottom typical of BR 'tower' designs:

L = 55.38"
CSA = 133.5"
zdriver = 20.2"
rp = 1.5"
lp = 2.13"
zport = near/at the bottom

In each case ~2.35 ohms series R is required based on published specs for a T/S max flat alignment.

GM
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Old 10th January 2006, 05:56 PM   #122
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Quote:
Originally posted by Scottmoose
gif in preference to jpg in future you say?
Yes. Gif is a non-lossy format, so no artifacts. And if your software is powerful enuff (i recommend PhotoShop Elements to anyone doinfg casual raster file processing), you can force the gif to 2^n (n=<8) colors, in the case of the charts you are posting probably 8 colors, which makes picking out the red curve a 1 step process

dave
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Old 10th January 2006, 09:24 PM   #123
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Thanks for the advice Dave -I'll definitely shift to gif images in future posts & I'll look ino Photoshop Elements too.

GM -as always, I'm in your debt for suggeting new (to me) ideas to consider, with other observations too: the over-damping part of having a driver / port too near the top / bottom is particularly interesting to me -I'll start to look into that. Could you expand a bit on your views in this? Many thanks once again for the input and advice.

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Scott
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Old 10th January 2006, 10:19 PM   #124
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Well, it had to be done: I've just modelled GM's two MLTLs for the F200a in the latest MathCad sheet. Absolutely superb (as you'd expect). Here's the anechoic prediction for the shorter enclosure assuming just 0.25lbs ft^2 of stuffing (in gif format Dave!!!). As you can see, there's a slight decrease in the response just before cut-off which will likely make their in-room performance better ballanced than one with a peak or a completely flat anechoic response.
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File Type: gif gm short f200a mltl anechoic.gif (14.3 KB, 288 views)
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Old 10th January 2006, 10:24 PM   #125
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I didn't run the in-room response for this one however, as Greg appears to favour the second, longer enclosure. Here's the anechoic prediction of that one with the same stuffing density (there will, however, be quite a lot more of it, by virtue of the longer line-length). A fractional increase will clobber the tiny wriggle, but personally, I wouldn't exactly be loosing any sleep over that whatsoever.
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File Type: gif gm long f200a mltl anechoic 0.25lbs ft^3.gif (12.4 KB, 268 views)
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Old 10th January 2006, 10:29 PM   #126
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And here's the in-room prediction. Don't set much store by this, because it's dependent upon many factors, not least the HxW dimensions used, and is not going to be optimal. Carpeted room, front baffle 32" from the rear wall, front port, nearfield and on-axis. Very, very good indeed I would say.
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Old 10th January 2006, 11:27 PM   #127
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Greets!

You misunderstood, placing them at the ends causes peaking at Fb since this is where the pipe's max gain is, and too much comb filtering between driver/vent in any decent length pipe IMO, ergo much more stuffing is required to damp it all down. For limited BW apps, this isn't an issue, but in wide BW apps it 'sucks' too much 'life' out of them for my tastes.

BB OTOH builds to a height limit, sets the driver as low as practical, then raises the vent to smooth it out somewhat to ~split the difference, so to speak.

Trade-offs, always trade-offs, so 'optimum' is in the 'eye of the beholder'.

GM
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Old 11th January 2006, 07:13 AM   #128
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Ah, I see what you were getting at now -obviously not one of my brighter moments! I try not to have a driver mounted closer than 0.25 of the line length to So for similar reasons, as I refuse to go over 0.5lbs ft^3 of stuffing, and preferably no more than 0.35lbs ft^3 if possible. Unless it's an MTM design of course, when one driver will often be closer -I'll keep the taller options in mind now though as a way of avoiding that; good tip. As / when Martin gets his twin-driver additions going it'll be interesting to see the effects and if they need more stuffing than the current sheets predict.

Cheers
Scott
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Old 11th January 2006, 12:56 PM   #129
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DDF posted:
Quote:
Scott, the yellow compressed fiberglass is the fiber board I mentioned for my tests. If Bob is using this, then perhaps he's gunning for an attenuation tailored over frequency and location. Most of these materials have very high densities, and as my measurements show, will partially reflect if the angle isn't normal. The LDC corroborates this, with 4lb/ft3 fiberglass causing fo and f3 to increase vs 2lb/ft3.
I don't fully understand what is being said about "fiber board". The material I'm aware of is referred to a "duct board" and used in HVAC installations. It is available in thicknesses of 1/2, 3/4, and 1". I believe it is available in greater thicknesses.

What would be the likely result from using this material at each end of the line? Damping? Attenuation?
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Old 11th January 2006, 02:03 PM   #130
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I assume it should damp out the higher harmoics a bit like stuffing -after all, that's the point of stuffing or lining the enclosure in the first place. Or at least, that's my view. Have a look at BB's comments on his Mk2 FE167E MLTL -scroll down a bit to get there; the first half of the page is all his original Mk1 stuff. He observes that the lined cabinet is 'over-damped' with the bass rounded off, but F10 remains the same, which pleases him (as it should) because it means that with the room factored into the game, the speakers are unlikely to 'boom'. Interesting.

http://www.geocities.com/rbrines1/Pa...n_Details.html

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Scott
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