Waveguide for Seas 25TAC/GW tweeter - diyAudio
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Old 17th March 2004, 05:22 PM   #1
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Lightbulb Waveguide for Seas 25TAC/GW tweeter

Hi,

Because of my recent frequency response measurements, I have now concluded
that in my speakers the crossover for the tweeter is right
(despite it was fully tuned by ear without measurements) .
Therefore if someone wants
to have a very simple crossover for the tweeter and wants to build a similar
waveguide than in my speakers (look at my speaker forum for more details),
simply one 2.2 uF polypropylene capacitor (and depening on the other
drivers a resistor in seris) in series with the tweeter
will do the trick assuming that the circular waveguide is exactly the same shape than
mine. Waveguide simplifies the crossover a lot. The boost to the midrange
area with the waveguide is in other words quite exactly 6 dB / octave towards
lower frequencies and therefore the 6 dB/octave high pass will straighten the
response to flat.

So if you need a decent tweeter without ferrofluid and that can be crossed as low as
at 1.5 kHz without any problems (without sacrificing distortion, clarity etc.),
I think the Seas 25TAC/GW is a good choice if accompanied
with the waveguide. The width of the waveguide is 17 cm and depth is
about 5 cm. You can go to my loudspeaker forum to look the picture.
There must not be any gap between the waveguide and the tweeter, so
be sure to mount it tightly.

I wonder why only few DIY speaker projects utilize waveguide since
their benefits are quite evident once you hear how it sounds like.
After that you may not ever want to go back to a waveguideless speaker again...
The secret of the soundstage and accuracy in my speakers is the low
crossover point and the waveguide. Without them, they would be just yet
another speakers without anything really much impressive,
but with the waveguide, they are pretty damn good.

Best Wishes,
Karoliina
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Old 17th March 2004, 05:39 PM   #2
SY is offline SY  United States
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I see the pictures of the waveguides, but no details on dimensions or design. Can you guide me? This looks like an interesting approach- I've used drivers with this sort of loading (like the Dynaudio/SENlabs D-28 and D-75), but I'm intrigued with the idea of being able to customize this.
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Old 18th July 2005, 02:34 PM   #3
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Karoliina, I was hoping to see your link to your waveguides but it doesn't seem to work anymore ...
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Old 18th July 2005, 03:54 PM   #4
Zaph is offline Zaph  United States
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Karoliina,

I've also become a believer in Waveguides after a recent set of tests I've done. Very simple crossovers do indeed work well.

For someone looking for a full set of measurements and construction techniques, I have this available. It uses a Lexan horn converted into a waveguide. It's pretty easy to modify for waveguide use.

http://www.zaphaudio.com/hornconversion.html
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Old 18th July 2005, 05:05 PM   #5
Zaph is offline Zaph  United States
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Oops, I thought this was a new thread, but now I see that it was a year old and just brought to the top with a reply.

I need to check those original posting dates. I feel like a dork now. Karoliina is probably not even paying attention to this forum anymore.

Paul, you must have had to dig deep to find this one.
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Old 18th July 2005, 06:06 PM   #6
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John, yes I've been doing some searching on a number of different topics, I'm on a learning curve with some ideas I've been working on. I saw Karoliina's waveguides a long time ago, and then more recently yours. Some time ago I turned up some crude attemps at waveguides for my Vifa dome tweeter, but I didn't have the means to do any measuring and couldn't pick a difference that I liked. Its more recently I've learnt that it only works with some eq, where the waveguide reduces excursion at the low end, hence reducing distortion, increasing power handling and potential output in addition to directivity control. The advantages are so many that it makes me wonder why it is not done more often.
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Old 19th July 2005, 11:32 AM   #7
rcw is offline rcw  Australia
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Default waveguides

I have built a test waveguide driven by a 25mm. dome tweeter.
This is essentially a conical horn with a flared mouth. The mouth flare was as far as I know first mentioned by Keele in a AES preprint, and allows constant directivity down to a lower frequency with a given mouth diameter. The flare has the secondary effect of reducing finite apperture diffraction that occurs at the upper end of the frequency range.
Geddes has published a proposal for a mathematical method to calculate this flare, but from my crude calculations it seems that a simple radius that matches the wall angle at one end, and the baffle at the other is as good as anything.
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Old 19th July 2005, 03:13 PM   #8
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So how does one determine the dimensions to use and what relationship they have to what you want to achieve? (ie point at which directivity is controlled down to ...)

I don't follow your description of the radius ...

Baffle shown yellow ...

On the right the flare is basically a radius, and on the left it is stretched in the x dimension and the line shows the starting tangent of the curve which is 20degrees from the other line drawn ...

Perhaps you can clarify ...
Attached Images
File Type: gif waveguide flare.gif (2.0 KB, 496 views)
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Old 19th July 2005, 10:35 PM   #9
mac is offline mac  United States
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I did a design prior to all the recent interest. The raw measurements didn't look too good but the aberations were fixable by the transfer function of the crossover.

Code:
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Old 19th July 2005, 11:01 PM   #10
Salas is online now Salas  Greece
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Zaph, did you notice in your tests that the midrange sounds more substantial after cd horn loading of a dome tweeter in a system?
After the needed ironing of the inflated mids and the gains in simplicity of suitable crossover and distortion, I guess the best element is that the dispersion shows continuity with a cone at crosspoint. This eliminates the flare in off axis power response and sounds fuller to me.
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