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Multi-Way Conventional loudspeakers with crossovers

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Old 12th July 2005, 05:39 AM   #11
pajazo is offline pajazo  Finland
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The email address is info at hifitalo dot fi. I'm quite sure they will understand emails written in english.
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Old 12th July 2005, 10:57 AM   #12
Zaph is offline Zaph  United States
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pajazo, do those wave guides come with a method to bolt the tweeters on the back? The kind we get here in the states has to be modified greatly before it can be used. If they have an actual mounting method such as screws, many of us would be willing to order from Finland.
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Old 12th July 2005, 12:41 PM   #13
AJinFLA is offline AJinFLA  United States
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I e-mailed them (in english) over a year ago and got no response.
Perhaps I should have been more persistent. Zaph, I believe they are screw on.

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Old 12th July 2005, 01:18 PM   #14
pajazo is offline pajazo  Finland
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The waveguides only have a flat surface on the back. They must be glued to the tweeters. It is quite easy to glue them but after that there's no way removing the waveguide from the tweeter. I had to pay ten euros per piece for the waveguides.
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Old 12th July 2005, 02:17 PM   #15
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I learn more about waveguides every day. From what I understand today, An "optimal" waveguide shape is specific to the crossover frequency for the driver it is mounted in front of AND the dispersion of the lower frequency driver it is paired with. An off-the-shelf waveguide may provide better response from a driver, though not as good if it were tailored to the system it is included in.
A waveguide also induces backpressure forces on the driver diaphragm. This may induce distortion. For this reason metal domes seem to be favored.
This is timely. I'm encouraged by the interest expressed here. I've copied some posts by Pooge and others from the AA forum that provide the formulas needed to plot "optimal" shapes. I plan to slash my way through Excel this week to see what I can come up with.

The following are excerpts from some of those posts and are shared to whet your appetite. For the “full” story, go to Audio Asylum and search “waveguide’

Waveguide shape
Pooge ( A ) on March 29, 2005 From "Sound Radiation in Acoustic Apertures" by Geddes, JAES, April 1993:
"A short waveguide may not yield the best directivity control at the low frequencies, while a long waveguide will yeild poor high-frequency results (on axis) due to the aperture diffraction since the first "hole" [in the axial frequency response] is found to be located at ..."

It was found that "diffraction limit" for a circular mouth is

kR = 15.0/sin^2(angle);
where R = the length of the horn
K is the wavenumber, or (2*pi*f)/c,
where c=the speed of sound

"This frequency will be called the aperture diffraction limit for a waveguide. Above this value the frequency response and the directivity will be strongly affected by the mouth diffraction. Below this limit the waveguide will behave as a directive point source. [The formula] can be used as a rule of thumb for deciding the correct length of a waveguide." Thus:

"kR" should be less than "15.0/sin^2(angle)".

What is clear,… is that a baffle and a radiused termination of the waveguide into the baffle will reduce the diffraction effect that causes the condition for which the hole in the freqency response was found. The final curve at the mouth is not part of the 'horn flare', which is what the waveguide equations determine. It's simply a radius to reduce diffraction (and probably reflections back down the horn) from the mouth. There probably is some theoretical basis for this, but I would guess that empirical is pretty good. I think Pooge is right that Geddes uses a ~2" radius - simply blend that into the curve for the flare as smoothly as possible and you should be in good shape.
For anyone that wants to play with other throat sizes and waveguide angles, here are the formulas:

[(y^2)/{((a/2)^2)*sin^2(ang)}] - [(x^2)/{((a/2)^2)*cos^2(ang)}] = 1
where a= 2r/sin(ang)
where r= the radius of the throat or y at x=0
and ang=the angle from the x-axis to one wall of the waveguide.
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Old 22nd November 2007, 11:41 AM   #16
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It's been a while now, I guess you've finished the speakers and had a year or two of listening, how do they sound?
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Old 22nd November 2007, 12:12 PM   #17
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Hi Pajazo,

God work, can you tell us how it handles sound pressure? HiFi Talo does not speak too good english.

You can take a look at www.dxt.dk and/or http://www.seas.no/index.php?option=...184&Itemid=179

"coming soon to a shop near you"


Jon
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Old 22nd November 2007, 04:05 PM   #18
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1) Great looking speaker, great choice of drivers, with resultant great sound I'm sure.

2) How did you finish the cabinets pajazo? Very nice woodwork!

3) Per Ed: "An 'optimal' waveguide shape is specific to the crossover frequency for the driver it is mounted in front of AND the dispersion of the lower frequency driver it is paired with. An off-the-shelf waveguide may provide better response from a driver, though not as good if it were tailored to the system it is included in."

In this case it would be nice to be able to fabricate one's own waveguide, specific to the application - I'm thinking with a block of wood cut on a lathe perhaps, although it would ideally be a programmable lathe. Would look nice too - would integrate well with the baffle.
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Old 23rd November 2007, 01:05 PM   #19
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sdclc126

Interesting to revisit this thread ~ 2 years later. A spreadsheet in excel is available for viewing/printing any variety of waveguide profile. JoshK may be doing some additional work to set the entry angle @ the throat. Send me your address if you are interested.

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Old 23rd November 2007, 09:06 PM   #20
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Didn't pay any attention to the age of the thread!

Ed - thanks for the offer but it's not something I'm planning on, and I don't have a lathe! Could always pay someone else though. Was really just thinking out loud on fabrication methods.
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