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John, I disagree.

No one deny the importance of harmonics and you are right saying that “If a speaker does not reproduce the harmonics correctly, then the tone is not reproduced correctly.” However you are talking about a complete speaker, not about the narrow operating midbass channel. Yes, the relationship between midbass and upperbass channels will be tricky to set properly. People do not know but people do not use the midbass horns properly. You see typically people having midbass run it all the way up unto lower MF and in THAT case you would be correct. In my case my midbass will be running in very narrow band-path and then I will have a full blown upperbass horn that has no phase plug but it has very HF-able driver, not to mention that two octave above it I have a dedicated Fundamentals channel the takes over… So, the harmonics are not problem to handle properly. In case the people run midbass too wide and particularly in case of improperly folded horns the harmonics become screwed, I would agree but not in case of narrow midbass.

I do not plan to do phase plug on my midbass. Here is for you another reason why. Midbass horn is not upperbass horn. When the upperbass horn that you made for me outputs les say 120Hz then it sends out 8.2 feet wave.  This wave is comparable with listing distance and perfectly “matured” when I reach ears. That is why you upperbass is very much direct-firing type of horn and it does wonderful. Did you try to listen your upperbass from 1-2 feet?  It has completely different upperbass sound that I do not like. In my past I have build a small setup for the position right next to my upperbass mouth. The balance was right but the upperbass was totally wrong.

Not pretend that that my midbass horn shot his 50Hz. It will be 19 feet wave or 6 Meters; the 40Hz will do 25 feet. I do plan to keep my listening distance shorter then this, probably 10-12 feet as max. So, in this scenario I will be in the zone of immature midbass. Bruce Edgar looks like fight the problem with floor firing his 35Hz refrigerator midbass. I am planning to turn off my midbass horns from the listening position to get first bounce of midbass from boundary. For instance if I hang the horn at ceiling then the will be shoring to the back wall near-parallel to ceiling or to the side of the listening position. If I in this situation will do phase plug on my midbass then the sound of the horn from EQ perspective will become directional. I do not what it and I will intentionally use it as non-directional transducer. My idea to use midbass is to load the room, this why I do not want to have overly large room – I will burn the midbass excursion and midbass amp power. The directivity, HF harmonics and the sense of acoustic bass direction with respect to a listening position I anticipate overriding with the upperbass horn.  I would not even mention that a phase plug on midbass would require high order low-pass filtration with more complex phase spin at crossover point.

So, I do not see a phase plug in my midbass. I might remotely agree with it what people use midbass in context of 2-3 ways system but in 6-ways I do not see a need for it.  Also, a phase plug adds compression to the driver.  A 15” driver loaded to 8” throat without a phase plug would have the similar completion (I think) as the same driver loaded to 10” throat with phase plug. If I would be OK with higher compression for my paper-base driver then I would rather go do smaller throat, let say 6” throat. I do not as I feel that it might make my cone too stiff and to over-dumped with compression and with consequential tone diminishing. I am not convinced that it not going to happen even with 8” throat….

Anyhow, they were just a few my own arguments that I have against the phase plug on midbass horn. I have a few more but you the picture… Warn you that I never had a properly made midbass horn and evrything that I expressed is hypothetics and extrapolations form my other experiments. But this position of mine does make sense to me, at least now.

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