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Old 7th October 2007, 03:34 AM   #1
nina is offline nina  United Kingdom
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Default Which drivers can be used in Hemp's Apra Grande canbinet

Hi,

I like bass reflex floor sand cabinet. Could any one tell me which driver below can be best used with Hemp's "Apra Grande" cabinet ? Thanks!

Hemp Floor stand
http://www.hempacoustics.com/ApraGra...FloorStand.pdf

Fostex
FE166e
http://www.madisound.com/catalog/PDF...ers/FE166E.pdf

FE167e
http://www.madisound.com/catalog/PDF...ers/FE167E.pdf

FE206E
http://www.madisound.com/catalog/PDF...ers/FE206E.pdf

FE207E
http://www.madisound.com/catalog/PDF...ers/FE207E.pdf

Peerless 850136 8" CSC-X woofer (bass unit for bi-amp)
http://www.madisound.com/catalog/PDF...ess/850136.pdf
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Old 7th October 2007, 04:18 AM   #2
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FE167, FE297 (and 296) will fit in similar cabinets (Scott has an ML-TL for the 167 and Martin for the 296/207

This caninet is a non-optimum ML-TL.

dave
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Old 7th October 2007, 09:22 AM   #3
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Logic would suggest that the Hemp FR8c might be a good place to start, given that this cabinet is notionally designed for that unit. Problem is, as Dave says, it's a pretty mediocre MLTL (rather than a BR box) even with the Hemp driver that's supposedly intended for it. Generally, you design a cabinet specifically for a driver, rather than aquiring a cabinet & then searching for something to go into it.

I'd suggest Martin's Project 5 MLTL, which is properly designed and optimised for the Fostex FE206/7E: http://www.quarter-wave.com/Project05/Project05.html

Alternatively, Bob Brines sells plans for some super-refined MLTLs for the same units, and one for the FE167E too: http://www.geocities.com/rbrines1/

FWIW, I've attached the plans of my own MLTL for the 167. It isn't as refined as Bob's equivalent, but I was aiming for as dynamic a sound as I could get from this sort of enclosure rather than perfect smoothness.

Re the drivers, the 166 needs correction to work well in box like these, so I'd forget that unit. The 206 does too, but being larger, it's more sensitive, so you've greater flexibility. 167 is fine. 207 is good too, but needs a tweeter.
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File Type: gif fe167e mltl.gif (71.5 KB, 193 views)
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Old 8th October 2007, 05:32 AM   #4
Nanook is offline Nanook  Canada
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Default ok folks, how is this an MLTL?

guess I'm missing the point. It appears to be a BR, and 70 litres is a suitable choice for this driver.

Help me out here dave, et al. What am I missing? As long as the internal baffles do not create a restriction and are not stuffed, how is this a Mass Loaded Transmission Line? Am i just missing the point?

certainly a less complex internal bracing arrangement can be made.

I've also considered the use of a 3.5 ft^3 enclosure with the FR8s, similar to a Kef TL.

back to sleep.....
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Old 8th October 2007, 06:22 AM   #5
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Default Re: ok folks, how is this an MLTL?

Quote:
Originally posted by Nanook
guess I'm missing the point. It appears to be a BR, and 70 litres is a suitable choice for this driver.
One of the dimensions is significantly longer than the others (and long enuff to support a significant quarter wave resonance)... the port is at one end, the driver at the other. Pretty much the definition of an ML-TL. That there is no driver offset to help smooth out ripple is one of the non-optimum choices in the design (or that the TL nature of the box was ignored)

dave
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Old 8th October 2007, 10:17 AM   #6
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Bass reflex assumes there is a uniform particle density throughout the cabinet & no standing waves. As Dave mentions, any tall, relatively thin enclosure like this one, with driver near one end, and the vent at the other, has considerable resonance action (i.e. standing waves). These can be used to advantage: that's what a Mass Loaded Transmission Line (or Mass Loaded Quarter Wave Resonantor if you prefer) is: a tuned QW line, loaded by a vent. If you ignore these resonances (i.e. it's a badly designed MLTL), then a) the tuning is not always what you might expect, and b) you'll get higher harmonic resonances that should be damped out.
This was a common issue a few years back (& to a considerable extent still is), when fashion started to dictate tall, slim floorstanders. Designers took a mathematical BR volume, made it tall & slim, and then discovered that they were getting a rather different response to what the box tuning formula said. It's often claimed that you can make a BR box any shape you like, which is, bluntly, nonsense. Well, you can, but you can't expect the tuning to remain the same.
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