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Old 24th March 2007, 08:27 PM   #31
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Can of worms. Abby is an ML TQWT -like Dave, personally I'd use more mass-loading with the port, but they've a good reputation.

Conversely, the Lowther Club of Norway Voigt pipe has a duff reputation. Usually this is blamed on it being an So=0 design. Actually, it's not that that causes all it's problems, but a mismatch between length, Vb and vent dimensions. Abby, although it looks like an So=0 design externally, actually isn't. That's as far as I can go on-line though re it's internal dimensions, as they're a current production model for the company.
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Old 24th March 2007, 09:01 PM   #32
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I've never been a fan of the tall obilisk shaped speakers, either flat topped or one-side leaning.
>So< must be so close to 0, it might as well be 0.It wouldn't be hard to model with MJK's mathcad models anyhow. Using that, the best results are always obtained with the taper going the oher way, reducing cross-section toward the port.
Increase mass loading by making the port smaller, right?
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Old 24th March 2007, 09:23 PM   #33
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As i mentioned when i suggested the pine over the MDF, i did say that you needed to know what you were doing... building with solid is challenging. I have alerted Scott Dunn to this part of the thread -- he is the foremost expert i know on the subject. opefully he will check in on Monday (he only gets email at work) and comment.

dave

Well, I prefer to build with solid wood or chipboard. In my occupation I have to have some general knowledge in all of the mentioned materials.

The issue with MDF is as always, the sand dust from MDF is not so good for your lungs.
Also there's problems with the edges that tends to crack if the bonding in production of the MDF is not 100%.
Manufacturers of MDF do not keep the mixture of fibers constant due to availability of raw material =You could have a board with totally different properties from batch to batch.
This is hard earned experiences from my profession but maybe not an issue for the DIY community.
All in all, it's your choice that matters in the end

Cheers
Peter
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Old 24th March 2007, 09:42 PM   #34
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I'd paint the mdf if that ends up being that which I use. Still waiting to see what kind of Ply I can get and at what cost.


Pine is going to be expensive relative to the quality of the wood itself and price of MDF, and I'd only end up using it on the side panels. But I am familiar with it's tendency to warp, so it is likely a no-go, I had a look at the stock and its not as good as I'd want for the risks. I can only get HDF at 1/2".
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Old 24th March 2007, 10:23 PM   #35
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It's trunkated a fair way down the pipe. CSA of So still isn't vast, but it's significant. That's as far as I can go.

Yes, decreasing port CSA and / or increasing port length will increase the mass loading on the pipe. I've modelled Abby in Martin's worksheets -it's easy enough to do. I can't post the plots though for obvious reasons. Nelson Pass has some measurements of his own pair on his First Watt site.

Re a negative taper always giving better results, not really, no. It's application dependant. A positive taper QWR will always need to be longer than a straight or negative taper line as the resonant frequency of a pipe is a function of both length and taper, not just length. Conversely, you get more pipe-gain from an expanding line, which, for example, a low Q driver (or a fairly high Q one come to that) would find beneficial. Swings & roundabouts really.
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Old 24th March 2007, 10:40 PM   #36
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peterbrorsson: True, about there being a difference in MDF from sheet to sheet, manufacturer to manufacturer. One thing though, is the consistantcy of the material in each sheet is uniform, unlike solid wood.

scottmoose: I should hve qualified it by saying " better results for reasonable sized boxes" My master won't let me play with FR drivers, so I only have experience with real ones where high Q = less than ideal for a mass loaded system.
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Old 24th March 2007, 11:40 PM   #37
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peterbrorsson: True, about there being a difference in MDF from sheet to sheet, manufacturer to manufacturer. One thing though, is the consistantcy of the material in each sheet is uniform, unlike solid wood.

Hi MJL21193!
Consistancy of MDF in the same sheet is not the same. How do I know that? I have to be precise in application of stains and lacquers when testing for industrial use. Everything is measured in g/sqm. What I do is take a sheet and cut it in the same dimensions in order to make it easier to measure applied amounts. Each piece weighs different so I have to tare the scale every time a new piece is used. Ergo, density varies, consistancy not so good.
Truth is that I have not compared density differencies in percentages between solid wood and MDF. My bet is that hardwood is very close to MDF in this case. Pine and spruce are different animals.
In reality I don't think it makes any difference concerning "normal' sized speakers. What matters is price!!

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Peter
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Old 25th March 2007, 12:19 AM   #38
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Hello Peter! How much difference are we talking about here? In solid wood you can actually see the difference - growth rings, winter growth is slower and denser than summer growth. My own personal perspective is that the differnces between all of these materials is small, be it MDF or plywood or particleboard or solid. The difference between these only detectable by a Golden Ear type.
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Old 25th March 2007, 03:23 AM   #39
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Quote:
Originally posted by MJL21193
My own personal perspective is that the differnces between all of these materials is small, be it MDF or plywood or particleboard or solid. The difference between these only detectable by a Golden Ear type.
2 VI diyFests ago we built otherwie identical MDF & plywood bipolar ML-TLs for the FR125. Everyone could hear the difference.

dave
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Old 25th March 2007, 03:44 AM   #40
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Quote:
Originally posted by ruerose
I can only get HDF at 1/2".
I'd use 1/2" HDF (medite) over 3/4" HDF any day (i used to build everything out of 1/2" medite until i started listening to boxes in BB)

dave
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