# Phase plugs on a speaker make it better



## geshat00 (Jun 1, 2016)

I just wanted some clarity on phase plugs... why they are used and maybe is there a specific frequency range it works better than others?

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## SkizeR (Apr 19, 2011)

they help reduce breakup on the upper end


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## ErinH (Feb 14, 2007)

phase plugs are used typically for one of two reasons: as a heatsink or to mitigate lobing (what happens when a driver is playing well beyond the beaming point; see below image).

most boutique brands don't use them for the former and in nearly every case (except for tweeters or wideband drivers) the latter is unnecessary because your crossover point will be well before the point where the phase plug does anything useful.


Lobing explained:
Kvart & Bølge | Audiophile Quarter-Wave Full-Range Speakers |


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## ErinH (Feb 14, 2007)

actually, I didn't read the above link, just sourced it for the image. that link is more in regards to two drivers' lobing.

this is a more acute example of the specific question:
http://www.bikerman.co.uk/images/ja...used in loudspeakers by Wave Interference.pdf


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## ErinH (Feb 14, 2007)

heck, even better... via google, yo!

ftp://ftp.veracomp.pl/pc/logitech/docs/.new/PR news/LOGITECH/Z-560/technologia/Phase Plug.pdf


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## Patrick Bateman (Sep 11, 2006)

In addition to what Erin said, a couple more points:

1) A phase plug can help you get a specific set of T/S parameters. For instance, a lot of drivers with aluminum cones have a high QTS value because the mass of the cone is high. By using a phase plug, you lower the MMS, and this lowers the QTS. (Because about a third of the cone is gone now.)

2) In compression drivers, a phase plug is there to get a specific wavefront shape. For instance, you don't want a converging wavefront; a phase plug can help you bend the wavefront so it's diverging as it enters the waveguide or horn.


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## geshat00 (Jun 1, 2016)

Now that about the material used. I see some use wood, plastic, metal etc.


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## Rybaudio (May 23, 2008)

For the purposes of reflecting sound, those materials are all very rigid and more or less function the same.

For heat sink purposes, metals are going to work better.

If the plug plays a role in the magnetics of the motor, which metal used can make a difference.

That being said, I would not discard or even evaluate a given driver based on the phase plug material or the existence of a phase plug at all. Look at the net performance and judge based on that. In my experience, phase plugs can have a positive benefit, but it is typically on the upper end of the driver's usable bandwidth and the acoustic improvement is fairly marginal. I am not really sure how much of a thermal benefit there is - maybe that is more significant, but I've never really heard or seen evidence to that effect.


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## Hillbilly SQ (Jan 26, 2007)

Two 6.5-7" drivers that got quite a bit of praise (and criticism from nonbelievers) for being able to play way higher than people thought they should have off axis without too much bad behavior were the HAT L6 and Audible Physics Arian. Never ran the HAT's myself but I had the Arian's and those things could go up to 5khz and beyond in a car door without too much worry for noticeable beaming. Both of these speakers came from a boutique company (well maybe not AP so much since Rishi goes well beyond the car audio side from what I understand) and both of them had phase plugs. One had an alloy cone and the other an unshiny paper cone or something along those lines. 

What I'm saying basically is to never scoff at something you don't have a clue about. I'm guilty of it. Some things you just have to take someone else's word for how they really perform or try it for yourself on a curiosity.


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## Frogsrule (Aug 25, 2016)

Arrrrrrrrrrrgh...

If you've tried a google search for the answer to this question, you've undoubtedly come up short. The high frequency improvement that is most often cited as the reason is a minuscule part of the improvement that a phase plug (the conical shaped thing in the center of the cone, not the phase plug in a compression driver) makes. 

The main use is much simpler.

1. Dustcaps often become an additional radiator at high frequencies and contribute a huge peak in the response. The directivity of this peak is much lower than the rest of the cone at high frequencies, so the giant peak persists in the off axis response. 

2. Removing the dustcap eliminates this problem at the expense of cone area. Removing cone area reduces sensitivity. 

3. Removing the dustcap also leaves a cavity in the center of the moving cone, which becomes a separate Helmholtz resonator when the cone moves. That resonance makes sound of its own and degrades the performance of the loudspeaker. 

4. Sticking something in the hole eliminates the resonance. 

5. If you're using a tweeter, none of this matters because you'll probably be crossing the tweeter in and the mid out before any of this has any effect. 

6. If you're using the mid as a full range driver, then removing the dustcap and replacing it with a plug improves the high frequency response, but the effect of the plug on high frequency directivity is minuscule. In fact, it's so miniscule that documentation of its effects is quite rare. 

7. The frequencies that are affected by the phase plug (the little conical thing in the middle of a cone shaped speaker) are determined by the dimensions of the phase plug. The waves have to be shorter than the dimensions of the plug to be blocked by the plug. Putting an obstruction in front of a tiny tweeter or a tiny cone does have an effect. On a 6" mid? Not so much. 

8. Dust cap design is a pain in the ass. Removing it relieves the pain, somewhat. If the dustcap is a small portion of the cone, then removing it can be a big improvement with relatively little compromise in sensitivity. Removing it from a small mid is a big compromise in sensitivity. Speakers designed for multiway use are often designed to move the dustcap problem to a frequency higher than the intended bandwidth of the speaker. Then, it can be eliminated with a crossover.


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## Kenneth M (Oct 14, 2014)

Frogsrule said:


> 7. The frequencies that are affected by the phase plug (the little conical thing in the middle of a cone shaped speaker) are determined by the dimensions of the phase plug. The waves have to be shorter than the dimensions of the plug to be blocked by the plug. Putting an obstruction in front of a tiny tweeter or a tiny cone does have an effect. On a 6" mid? Not so much.


Great post. 

This portion (#7) made me pull out some speakers to compare their phase plugs. Interestingly, not only is the midrange's phase plug wider, it also seems that there are either of a different wood, different lacquer, or both. Interesting stuff!


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