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Multi-Way Conventional loudspeakers with crossovers

Why do HOMs Suck?
Why do HOMs Suck?
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Old 14th July 2019, 10:42 PM   #11
charlie2 is offline charlie2  England
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Still waiting for Patrick to reply...
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Old 14th July 2019, 11:04 PM   #12
Duke58 is offline Duke58  United States
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What is HOM?
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Old 15th July 2019, 12:29 AM   #13
Patrick Bateman is offline Patrick Bateman  United States
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Quote:
Originally Posted by Duke58 View Post
What is HOM?
A higher order mode is simply a wavefront that doesn't go directly from the loudspeaker to your ear.

Click the image to open in full size.


For instance, conventional horns have a sharp discontinuity at the moth of the horn. A fraction of the energy radiated by the loudspeaker won't make it to your ear. Some of it will be diffracted by the edge of the horn mouth. Some of it will be reflected back down the throat.

All of these "higher order modes" will have a negative contribution on the sound. They'll introduce peaks and dips in the overall response, because HOMs are delayed in time. They'll screw up the polar response; for instance a HOM off the edge of the waveguide will cause the off-axis response and impulse response to be sup-optimum. They'll confuse the location of the loudspeaker, because they contribute to secondary radiation due to diffraction. For instance, I once measured a loudspeaker and found that the *reflection* of the loudpseaker was nearly as strong as the "real" loudspeaker itself.
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Old 15th July 2019, 01:40 AM   #14
Duke58 is offline Duke58  United States
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Thanks for the info!
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Old 15th July 2019, 01:59 AM   #15
gabdx is offline gabdx  Canada
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waveguides amplify certain sounds, helping driver get more sensitivity, I see the problem with them when the driver retracts, it has to suck air in the horn which is far from linear, so it sounds like a cavern. Same way transmission line boosts bass... it is distorted bass, it helps produce noise with drivers that normally cannot produce any unloaded.
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Old 15th July 2019, 02:18 AM   #16
ScottG is offline ScottG  United States
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-and what seems to always be missing from this is HOM's at domestic levels.

(..even in my HT setup I don't reproduce sound that loud that would generate HOM's either at all or of significance).

Of course if you are trying for some extreme spl loudspeakers or are wanting a sound-reinforcement/public address/commercial theater/etc.. - then sure address the issue as best you can.


For 95% of us though: HOM's are a red herring.
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Old 15th July 2019, 12:14 PM   #17
phivates is offline phivates  United States
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Can't have a decent mystery without red herrings...I have thought that "higher" referred to interference corresponding to third and higher harmonics, as in the amplifier debates. Diffraction for example would likely be more random. Carry on, experts!
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Old 15th July 2019, 01:06 PM   #18
phase_accurate is offline phase_accurate
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HOMs are not a non-linear effect and therefore they are also generated at lower levels. They cause temporal distortion and also errors in the frequency domain. I would say they are not only waves bouncing back and forth due to the abrupt impedance change at the mouth they can also be waves bouncing between the walls on their way towards the mouth.
They might probably be below perception levels at lower SPLs. But they would still be there.

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Charles
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Old 15th July 2019, 02:07 PM   #19
mark100 is offline mark100  United States
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HOMs to me, has a specific definition as quoted below, that has been around a long time. (and in line with what Charles said)

I think if we call diffraction a type of HOM, we lose the value of the term HOM.

The snips came from an AudioXpress reprint....https://www.grc.com/acoustics/an-int...orn-theory.pdf
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File Type: jpg HOM 1.JPG (63.5 KB, 346 views)
File Type: jpg HOM2.JPG (130.1 KB, 348 views)
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Old 15th July 2019, 02:23 PM   #20
Soldermizer is offline Soldermizer  United States
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There can be the distortion called mouth reflection due to a poor impedance match at mouth of horn. This is well explained in other threads unlike HOM It can be minimized by mouth rounded or by the effective but visually apalling "towel trick." In contrast, as I (mis-)understand it, the HOM is prmarily caused by discontinuity anywhere in the horn, causing what I think of as a riccochet down the horn. These would not be caught by the towel mod, but would need a foam plug.


The foam plug is not necessarily cheap -- I think some people spend $100-200 for a piece of the correct foam, and must carve it to the correct shape. There are less expensive, and perhaps less effective, means to stuff the horn.
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