The "W" word

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JohnR

The "W" word
« on: 13 Feb 2018, 07:29 am »
I've put this in Enclosures rather than the Lab because I'd interested in hearing of people's experiences with waveguides in commercial speakers (as well as DIY). In particular, I'm wondering about your experiences with smaller waveguides say up to 8" size.

In the DIY realm, this looks like a nice option for a small waveguide for compresssion drivers: Faital Pro STH100. For add-ons to a dome tweeter, there is the DIYSoundGroup SEOS-8 (but for me the shipping costs make it infeasible, also the tweeter that it was originally designed for is discontinued).

Folsom

Re: The "W" word
« Reply #1 on: 13 Feb 2018, 07:36 am »
A great many have the purpose to increase the efficiency in the lower frequency range, to lower the crossover point. 

JLM

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Re: The "W" word
« Reply #2 on: 13 Feb 2018, 12:46 pm »
Don't confuse waveguides with horns.  Roughly speaking horns affect impedance loading/efficiency while waveguides (a subset of horns) control directivity (and thus allows the driver to maintain output at lower frequencies).  Note that most front loaded horns are used in conjunction with compression drivers.  Here's a quick look into the issue of horns versus waveguides:

http://www.gedlee.com/Papers/What%20is%20a%20Waveguide.pdf

It would be hard to do a direct comparison with and without waveguides without building two speakers using the same drivers, one using a waveguide and the other not and adjusting the crossover for the waveguide effect.  The directivity crowd use horns and waveguides to achieve their design goals.  I'm not aware of such a comparison ever being made.

My experience with formal waveguides is limited to the JBL LSR305, which I find to be killer value.  Not highly 'musical' (like a studio monitor which it is) but does little really wrong either.  I do have varied experiences with extended range (single) driver speakers (without whizzer cones like the smaller Omega speakers) in which the cone acts as a waveguide at higher frequencies (similar coaxial drivers like found in the KEF LS50 would behave in the same way).  But again, not an apples to apples comparison.

JohnR

Re: The "W" word
« Reply #3 on: 13 Feb 2018, 01:02 pm »
Oh good point, I had actually forgotten about the low-cost JBLs, which do qualify as having small waveguides.

Not looking for direct comparisons per se, just experiences from people who have built and/or listened  :thumb:

neekomax

Re: The "W" word
« Reply #4 on: 13 Feb 2018, 02:58 pm »
Nice link, JLM.

Just a beginner question. Geddes says:

"With the “waveguide” approach, one can find that precise contour that allows the wavefront to progress to the shape that is required at the mouth to achieve the desired directivity. This is done with minimal diffraction and the resulting sound quality is distinctly improved. To me this is a waveguide – when there is a minimum of diffraction used to achieve the end result of directivity control. "

In this context, what is diffraction exactly? I always hear it discussed, but I've not been able to infer an understanding of the term, and it seems to be central to Geddes' own definition of a waveguide.

neekomax

Re: The "W" word
« Reply #5 on: 13 Feb 2018, 03:09 pm »
To try and answer my own question, I read this article about diffraction in general: http://audiojudgement.com/speaker-baffle-design-and-diffraction/

So now I have a better understanding of edge, phase, and baffle step diffraction. But which of these (are they all different?) is Geddes referring to in his waveguide definition (quoted above)?

poseidonsvoice

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Re: The "W" word
« Reply #6 on: 13 Feb 2018, 03:26 pm »
Geddes is a proponent of minimizing diffractions [which are  secondary sources of the original sound itself, and hence directly affect the frequency response curve]. He does that by:

1) choosing the right shape of waveguide [in his design, it is the oblate spheroidal type],
2) making sure that the internal aspect of the waveguide is very smooth,
3) making sure the coupling between the compression driver in the throat to the waveguide is smooth and that
4) that the coupling from the waveguide edge (or mouth) is smooth with respect to the front baffle.

He then minimizes diffraction on the baffle itself, and minimizes higher order modes as well by using his patented foam plug. Notice the alarmingly large round overs and such (which minimize baffle edge diffraction). This isn't by accident, and wasn't done for "looks."

In fact, he will further state that any furniture/stand/etc... that is near the main loudspeakers should not have rectangular edges etc... to minimize any reflections from them to the listener. That is something I have tried hard to do in my room, although it is difficult to do from an aesthetic standpoint.

There are other waveguide shapes out there that are not the oblate spheroidal type. Although they may reach the required amount of directivity control, in Geddes' opinion, they do have more diffraction as a result. As such they are not what Geddes would prefer to use. There are also horn shapes that not only increase the efficiency of the tweeter on the low end but also have some directivity control. However, the problem with many of them is the diffraction. It can be alarmingly high and can cause that 'horn honk' that many enthusiasts complain about. Subjectively, I find that these deleterious sonic consequences increases non linearly at higher spl. It doesn't sound twice as bad, it starts to sound ten times as bad!

I don't have much to say about smaller waveguides, although I do own (4) of Gedlee's Harper speakers, which serve as surround speakers in my theater. They have 8 inch OS waveguides. I also own the JBL LSR 305 in the family room which I am tickled pink with.

Best,
Anand.
« Last Edit: 17 Feb 2018, 11:53 am by poseidonsvoice »

jtwrace

Re: The "W" word
« Reply #7 on: 13 Feb 2018, 03:28 pm »
I have large and small WG.  Even more interesting it's the same speaker just on a small scale. 


http://www.audiocircle.com/index.php?topic=149780.msg1660520#msg1660520

DaveC113

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Re: The "W" word
« Reply #8 on: 13 Feb 2018, 03:43 pm »
I have 2 versions of the same driver, one is for flat baffles, the other is for a horn. The one for the horn has a rising response the horn corrects for and increases it's efficiency by 6 dB or so. However, it's only 6" deep so it is used up as high as the driver will go, around 15 kHz.

I greatly prefer the version in the horn. The sound is clearer which results in a much-improved soundstage that is capable of recreating the recording venue, it is very 3-D and immersive. Fine details of vocals and acoustic instruments are more apparent and make the images sound more realistic, and the are better focused and defined in space.

I believe this is a result of experiencing more direct vs reflected sound, eliminating 1st reflection issues and eliminating baffle step diffraction. The polar plots are of course very different, much more ideal with the horn.

In my testing, the 3-D immersive soundsatge is what everyone comments on. Other comments are far more random, but IMO the spatial presentation of the system that lends an immersive, "you are there" feeling to the music is what drives preference.