Are Waveguides Good? This Explains Why Some Speaker Designers Use Them (Ep:69)

[@dl6519]

I've been building speakers with waveguides for almost twenty years. I agree with everything you said. WELL DONE!!

[@soundstagenetwork]

Great to hear!

[@KravchenkoAudioPerth]

Nicely done Doug. Inherent in loudspeaker design problems are the rules we must all obey. Physics. A tweeter that will give you a reasonable high frequency response is generally made around 25 to 28mm in diameter. A terrible size to cross over to a woofer that has a narrowing directivity at about 1.2kilohertz. That is most 6.5 inch woofers. Tweeters in the size range that is common have a useful lower range starting about 2.4 kilohertz. Not a great match to a woofer that at that frequency is very directional as you mention. If a waveguide ( Earl Geddes is to blame for this radio frequency term being appropriated into audio) is only a controller of the directivity of the air pressure front of the tweeter I call it a wave guide. If it is designed to create a lift in the response, I call it a horn. (How do you determine the difference between a waveguide and a horn? Depth of the horn. The deeper the horn the greater ability to amplify a lower frequency.) Your explanation of the reasons why this is important are spot on! It is true that the diameter of a horns mouth is what controls the expansion of the air pressure front from the driver diaphragm to the surrounding air. What is missing is the need for the depth of the horn to create an amplification of that air pressure front. This example speaker is using a conic horn. Easy to manufacture. But has it's own problems with reflections that cause cancellations in the frequency response. You can usually see these cancellations in the three parameter graph of frequency, phase and impedance. All of these on one graph is a view into the frequency and time domain as phase is a term used to describe time and place of a pressure pulse generated by a loudspeaker. The graph is a side view representative of looking a a cork screw like signal if you could see it in 3 dimensions. The impedance is a reflection of the mechanical system as measured in the electrical domain. So the impedance is giving you two measurements for the price of one. If you have gain in a horn you trade away bandwidth of how the horn can interact and control the output of a loudspeaker. Or, another way to describe it is that you trade away top end efficiency. The frequency response falls in relation to the area that the horn has been designed to control. Generally you are really stretching a horn if you try to work over a span of three octaves. So 1kilohertz -2 kilohertz, 2-4, 4-8 kilohertz. After this region a horn will have less and less effect on the amplification and pattern control. Pattern control stops working when your driver diaphragm or the horn itself is smaller than a half wavelength of the frequency being reproduced. In this horn I'd guess right around 10 kilohertz from the driver diameter. The horn will stop being effective a little lower. Happily this can be a true plus in a well designed system like the loudspeaker that you showcase. Mark

[@gregmatula9749]

Very well explained!

[@dougschneider8243]

Thank you!

[@Earache.]

I’m into car audio & I was wondering about which waveguide shape/size I should use and why.

[@bradburnside7644]

Speaking of diffraction effects, wouldn’t a waveguide’s forward projection reduce a driver’s interaction with the surrounding cabinetry? The tops of my new quad-amped active speakers are narrow and curved, with less than an inch above and to the sides of a 4” steel waveguide around a beryllium tweeter, to minimize reflections. These Meridian DSP9 have fabulous dynamics and imaging.

[@gtrguyinaz]

Hello Doug…. Nice info…

[@dougschneider8243]

Happy to hear it was useful!

[@21thTek]

Excelent !! 🌟🌟🌟🌟🌟

[@TriAmpMyFi]

Wave Guides VS. Separated Housings................................. Wave Guides are, as was said, specifically tuned to make the tweeter get along nicely with the midrange (don't get picky). But, the designers aren't testing the frequency responses in someone's living room. Their testing or trying to test in some type of anechoic environment. Therefore, the final design is fixed non-variable. Right? They're all the same. Now consider the subwoofer. It is nothing more than the removal of the low frequency transducer (don't get picky) from a full-range loudspeaker into a separate housing. We all know there are some distinct advantages to that arrangement. If manufacturers separated their tweeters from mid-range or mid-bass' into separate housings, one could realize a couple other unique advantages. There are endless tuning adjustments to be made, without any DSP or electronics. From horizontal and vertical axis responses to wave cancellation, etc. Ya, gatta' kep 'em separated.... dat dat da dum. Interesting topic. Thanks SoundStage, Reggae, Funk & Brass 🔈🔉🔊

[@dougschneider8243]

It's an interesting point, but with loudspeakers, potential "fixes" for certain problems can result in other problems. For example, if you separate the tweeter, you might create ridges that result in diffraction effects. You might also force it too far away from the driver it's passing off to. Or something else. With a subwoofer, it's a bit of a different story. The reason the subwoofer is separate is because they make them as separate entities, to be sold separately. But there are some resulting benefits to that, such as moving the "shake" from that big subwoofer driver away from speaker cabinet. Also, you can optimize the subwoofer placement for the best bass performance and the speakers for the best imaging. I'm not convinced that separating, say, a tweeter will be that beneficial. Bowers & Wilkins kind of already does that with the Tweeter-on-Top technology.

[@shining31]

The point here to work on the DI and power response of the speaker, which give a really good estimation of in room response beyond the critical distance. The separate tweeter is not a good option because of diffraction, center to center distance etc etc ... The comparison with a subwoofer is noncense because of wavelenth involved.

[@TriAmpMyFi]

@@dougschneider8243 One need not be assaulted for not moving the relative position of the drivers as designed by the audio engineers. A consumer could choose to leave the tweeter right where it is from the factory. A hairline seam, since we are aware of such things, can be reasonably dealt with. It's flexibility for our unique spaces. Subwoofers? Yeah, as you said, there are advantages to separating the cabinets. And now there are separate amplifiers for those separate subwoofers because there are advantages to bi-amping. Now consider that when considering separating out the tweeter & tri-amping. 🔈🔉🔊

[@TriAmpMyFi]

@@shining31 What's a DI? What's a speaker's power response? What is a critical distance? Why would an engineer choose poor driver positioning? Subwoofers are separate cabinets that contribute only part of the music frequencies. Same as a separate tweeter would, regardless of the wavelength.

[@shining31]

@@TriAmpMyFi don't get picky but discussing this topic without knowing (or faking to don't know) that....

[@bingdong8571]

I like your "active" waveguide idea, or maybe it was just your hand moving.

[@Vindexi]

Would a waveguide on a single full range driver still make sense, to control the on axis performance of the whole frequency band?

[@dougschneider8243]

That's quite a bit more difficult than it sounds. First, you need a driver that reproduces the entire frequency range well, which basically don't exist. Would a 10" woofer that would be great for the bass be equally good for the highs? Likely not. Then the waveguide would have to fit around those limitations. Basically, no, it wouldn't work well.

[@Vindexi]

@@dougschneider8243 The question is not wether it makes sense to design a speaker with only one driver. There are many great speakers that only utilize one full range driver (f.e. Le petite). My thought was about if it may help to uniform the radiation pattern through out the frequency band coming from a single driver.

[@dougschneider8243]

@@Vindexi I would argue with the word "great" -- I have yet to hear a "great" single-driver speaker. All the ones I've heard are deeply flawed in part(s) of the frequency spectrum. That said, you might get uniform dispersion, but you're likely not going to get the correct output all around the speaker because of the size of driver you need to use. If you use a cone driver of any size beyond an inch or so, you're going to have severe restrictions in it's higher-frequency dispersion because the driver basically starts "interfering with itself" due to its size.

[@wally7856]

All waveguides are horns (not all horns are waveguides). Horns are bandpass devices. Bandpass means only work for part of the frequency band.