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-   -   Discussion arising from Geddes loudspeaker (http://www.diyaudio.com/forums/multi-way/121614-discussion-arising-geddes-loudspeaker.html)

MaVo 18th April 2008 10:07 PM

(this thread split off from here http://www.diyaudio.com/forums/showt...0&pagenumber=1 :cop: )

Quote:

Originally posted by planet10
That is certainly the myth that has been perpetraited on us all...
Hi planet10, could you point me to the data, which led you to this knowledge?

planet10 18th April 2008 11:16 PM

Quote:

Originally posted by MaVo
Hi planet10, could you point me to the data, which led you to this knowledge?
You can start here... http://www.diyaudio.com/forums/showt...834&highlight= ... althou there may be data elsewhere as well.

dave

MJL21193 18th April 2008 11:24 PM

Quote:

Originally posted by planet10


You can start here... http://www.diyaudio.com/forums/showt...834&highlight= ... althou there may be data elsewhere as well.

dave

The majority of the data in that thread is counter to your assertion about the inferiority of MDF as a speaker building material.

Or did I miss something?

tinitus 18th April 2008 11:29 PM

I can relate to a horn sounding different with different "wood", sure that will be the case...but I think its a quite different matter with 2- or 3-way box
Well, in that acoustic respect(also) a closed box may even be better than BR

planet10 18th April 2008 11:40 PM

Quote:

Originally posted by MJL21193
Or did I miss something?
Sorry John, but i think you missed a whole lot :)

dave

planet10 18th April 2008 11:42 PM

Quote:

Originally posted by tinitus
I can relate to a horn sounding different with different "wood", sure that will be the case...but I think its a quite different matter with 2- or 3-way box
Well, in that acoustic respect(also) a closed box may even be better than BR
Everything matters... the idea is to not get the box to sound... and the low level stuff that oozes out of most MDF boxes does a lot to kill low level detail.

dave

MJL21193 19th April 2008 12:24 AM

Quote:

Originally posted by planet10


Sorry John, but i think you missed a whole lot :)

dave



Oh, and here I thought the only real "data" in thread was the results of my testing.

Personal preference, listening impressions and learned opinions are not data.

MDF is just fine for building speakers. You don't need to feel you have lowered your standards when you use it, as it is just as good, if not better than the other choice's.

ronc 19th April 2008 12:34 AM

From the FR tech archives:

Absorbation of energy in a given medium:

I keep on seeing the debates on what constitutes a good build material. Well like anything there are positives and neagtives to any material selection and application.Its covered in engineering materials.

Absorbtion of mechanical energy depends on density and elasticity of a medium given that the medium is a near constant in mass. This is more like MDF. It has a reflective index based on mass and impedance value and an abosrbation based on thickness. Many do not like the sound of MDF but that is due to the lower resonance frequency of the material for a given wavelength. In a strictly BR or TL alingment it will perform in an adequate manner as even a TL may be a totally resonante device, its dependant primarly on a given pressure and phase point and not on harmonics at a given frequency.

Horns are different as they depend primarly on harmonics to blend in with different actions. A good material for BLHs is a multi layered composit as the harmonic range is greater than a constant mass/density material which is more monocromatic in resonance. On the opposite side is the fact that a composit material can abosrbe more energy due to the fact that as any energy that traveles thru the mass is faced with different impedance values and the energy loss is greater due to the many interfaces of different impedance values.
ron

MJL21193 19th April 2008 12:45 AM

Quote:

Originally posted by ronc
A good material for BLHs is a multi layered composit as the harmonic range is greater than a constant mass/density material

Hi Ron,
What is a horn? Isn't a horn the interface between the driver and the rest of the world? Isn't the purpose of the horn to provide a low impedance transition for the loudspeakers energy?
How does the building material relate to this process, unless it is allowed to resonate without control?

tinitus 19th April 2008 12:52 AM

Quote:

Originally posted by ronc
On the opposite side is the fact that a composit material can abosrbe more energy due to the fact that as any energy that traveles thru the mass is faced with different impedance values and the energy loss is greater due to the many interfaces of different impedance values.
ron


You lost me there...I obviously dont understand english good enough:D


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