Cone Movement vs. Phase

[jobe_smith]

I restored a pair of bookshelf speakers (replaced the surrounds and refinished the cones), but when getting ready to reinstall the woofer baskets into the enclosure, I discovered that everything I had done to mark the positive and negative terminals both on the speaker and in the crossover had gone to pieces one way or another.

I can determine the points on the crossover network easily enough (it's just a two-way), but the cone has baffled me for the past year and a half.

Should a woofer that is in phase exhibit a cone that extends out (max. excursion) at higher frequencies and has less excursion at lower frequencies, or should the cone have more excursion with lower frequencies and less with higher frequencies? This is a bass/mid-bass driver.

Any ideas related to this topic or wavelength/frequency/excursion relationships would be greatly appreciated so I can know with confidence that my speakers are in phase.

[Klewless]

My goodness! Not quite sure just what you are asking but I can offer this. The woofer cone always has max excursion at the lower frequencies.

It has nothing to do with phase.

I believe you are asking whether or not you have the woofer correctly phased relative to the tweeter. When the woofer and tweeter are in phase, both move the same direction when given the same signal, which is what happens at the crossover point.

Here is a way to determine which way to connect the woofer leads.

1. Hook up one woofer to it's crossover

2. Hook up the other woofer with the leads REVERSED

3. Put the speakers right next to each other in the middle of the room away from walls

4. Listen to only ONE AT A TIME (use balance control on amp)

5. Play the hissing noise between FM stations

6. One will probably sound hollow (this one will be the wrong way)

7. The other will sound more natural (this one will be the right way)

Good luck!

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John P

St Paul, MN

[lynnm]

The safest way would be to play a brief passage of bass heavy music and then power everything down - reverse the wires for one speaker and replay the same passage. If position one has more bass than position two then position one is in phase - otherwise position two is the in-phase setup.

This works simply because out of phase bass signals will tend to cancel each other. The effects of out of phase midrange and tweeter are less obvious,(initially). Running speakers out of phase results in a less than satisfactory bottom end and a muddy mid/high end.

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It is meet to recall that the Great Green Heron rarely flies upside down in the moonlight - (Foo Ling ca. 1304 BCE)

[JohnA]

A woofer's excursion increases as the frequency goes deeper.

To test the phase of the woofer, use a 1.5 volt battery and connect it to the terminals. When the + terminal of the battery is connected to the + terminal of the driver, the cone will move forward. Normally the - terminal of the speaker wire connector is connected directly to the - terminal of the woofer and the active elements are on the positive side of the circuit. There is no reason for this, but it seems to be habit. Expect black wires from the crossover to be negative, but be sure to connect both speakers the same way.

John

[jobe_smith]

Thanks guys! I'll finally be able to get these woofers into phase and stop worrying about it! I've tried the usual ways mentioned, like playing FM static and deep bass passages, but I could never hear the difference. I'll try the 1.5 volt battery method and make sure that the cone has max excursion at lower frequencies. Thanks again!

[Klipschguy]

When indicated, I always check phase by placing each speaker face to face, about one to two inches apart. Play any tune with some bass content, reverse the leads on ONE of the speakers. When the speakers are in phase, there will be discernable bass and output. With the speakers out of phase, there will be ZERO bass, and the overall output will be greatly diminished. You do not need to be "Golden Ears" to hear the difference with this test, it's obvious. For individual driver phase testing, I like using the 1.5V battery trick John mentioned. Go easy with the DC voltage, voice coils don't like it.

Andy

[Klewless]

To clarify what has been said here,

1. I was addressing phasing between the woofer and tweeter within one cabinet. The other woofer/tweeter box should be made to be the same.

2. Using a battery helps you figure out which way the speaker cone moves when a voltage is applied to it's terminals. While this gives useful information, it does not help with the tweeter(which sometimes is actually wired out of phase with it's woofer). The battery method cannot be used with the tweeter.

3. Checking for bass response between both speakers is equivalent to the battery trick. It ensures that both woofers move the same direction when the same signal is sent to them. Also set your amp on MONO if you are not using the battery trick.

Another way I have seen people use, is to make the speaker move forward (toward you when facing the speaker from the front) when the + terminal of the battery is touched to the + (red) terminal of the cabinet. Then determine the correct polarity of the tweeter. A word of caution: do not leave the battery connected to the woofer very long. Touch, observe which way speaker moved, release.

If you can visually determine where the common wire of the circuit within the crossover, let it be the - (black) for the woofer. This would be the same as ground (common) on the amp.

Another way of looking at all this is + (red) on amp to + (red) on the speaker makes the woofer move away from the inside of the cabinet.

Good luck

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John P

St Paul, MN

[jobe_smith]

Thanks again! I've finally got these back in phase, and now I'm sure of it.