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Old 24th July 2012, 05:12 PM   #81
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Quote:
Originally Posted by speaker dave View Post
Another myth busted.

Good results Andrew. Thank you for sharing.

Any chance we could see your on-axis curves for the various states?

David S.
Hi Dave.
I don't have the data available. I did it back in the days at KEF on the 2pi baffle.
I might be able to find some other 4pi measurements of recent drivers where I have been trying to investigate response peaks by pulling off the dustcaps. As you have been pointing out, this is often fruitless because the issues are mainly from the cone, not the dustcap!
I concluded that given this, it is often a good idea to use a small diameter rigid dustcap bonded directly to the voice coil former to help stiffen the former.
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Old 11th July 2013, 09:52 PM   #82
Legis is offline Legis  Finland
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My latest project, 4" aluminum phase plugs for BMS 18" woofers:

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The phase plug goes partly in the shorting ring that sits on top ot the pole piece and they form electrically and thermally one piece. Each plug weights ~2.8kg, they dissipate heat and act as a heat buffer.

BMS woofers have triple shorting ring motors, so the plug did not reduce inductance at the VC's resting point but I think it linearizes inductance (Le(X)) as the higher order harmonics (>H3, also H3 reduced here and there) reduced nicely in the middle and upper bass area.

On the right is the phase plugified woofer (look for ex. at the pink, blue and orange lines between 50hz and 200Hz). Measurement distance ~65cm, woofer was in 36cm deep U-frame baffle. The woofer is BMS 18N850, neodium motor (modified cone and damped basket).

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Couple of sine tone comparisons, the phase plugified is on the right again:

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Above pictures in numbers:

100Hz:

Without phase plug / With phase plug / Difference
H3: 0,153% (-56,3dB) / 0,100% (-60dB) / -3,7dB
H4: 0,0201% (-53,4dB) / 0,288% (-50,8dB) / + 2,6dB
H5: 0,166% (-55,6dB) / 0,0771% (-62,3dB) / -6,7dB
H6: 0,0155% (-76,2dB) / 0,0123% (-78,2dB) / -2dB
H7: 0,0702% (-63,1dB / 0,0207% (-73,7dB) / -10,6dB
H8: 0,0098% (-80,2dB) / 0,0096% (-80,4dB) / -0,2dB
H9: 0,0332% (-69,6dB) / 0,0123% (-78,2dB) / -8,6dB

130Hz:

Without phase plug / With phase plug / Difference
H3: 0,262% (-51.6dB) / 0,0970% (-60,3dB) / -8,7dB
H4: 0,0287% (-70.8dB) / 0,0111% (-79,1dB) / -8,3dB
H5: 0,284% (-50,9dB) / 0,125% (-58,1dB) / -7,2dB
H6: 0,0345% (-69,2dB) / 0,0191% (-74,4dB) / -5,2dB
H7: 0,0936% (-60,6dB) / 0,0360% (-68,9dB) / -8,3dB
H8: 0,0276% (-71,2dB) / 0,0067% (-83,5dB) / -12,3dB
H9: 0,0107% (-79,4dB) / 0,0037% (-88,6dB) / -9,2dB
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Old 11th July 2013, 10:32 PM   #83
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Old 12th July 2013, 03:55 PM   #84
Legis is offline Legis  Finland
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Heh Cal, thanks I quess!

Have not had time to measure the effects of the aluminum phase plug in the BMS 18S430v2 (ferrite motor, 8mm calculated xmax, real-life linear excursion 10-11mm) and BMS 18N860 (neodium motor, 19mm calculated xmax). I suspect that the phasing plug might effect them differently than 18N850. Ferrite motors are more suspectible to flux modulation than neodium, and the longer VC of 18N860 is more in the phasing plug's area in the resting point, so it might result in inductance reduction. This effect of phase plug (phase plug acting as a shorting ring) is not often discussed. The 18N850 has only ~0,65mH inductance at the resting point (due to the triple shorting ring motor) and Le(X) is top-notch linear according to Klippel measurements, yet it still benefitted quite greatly from the phase plug's inductrance linearization/flux modulation reduction (or whatever is that caused the higher order harmonics to go down especially in the middle/upper bass).

Last edited by Legis; 12th July 2013 at 03:59 PM.
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Old 12th July 2013, 07:04 PM   #85
gedlee is online now gedlee  United States
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Originally Posted by AndrewJ View Post
The conclusion is that a so-called phase plug has no real effect on driver directivity, especially so for a midrange driver that will be crossed over to a tweeter.
Excellent work - thanks. It does not surprise me in the least, but quite contrary to the loudspeaker dogma.
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Old 12th July 2013, 10:05 PM   #86
VaNarn is offline VaNarn  Australia
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Perhaps I have missed an entry,so excuse me for re-calling that the origin for fitting phalli to speaker cavities appears to originate with F.H.Brittain and the GEC BCS 1851 metal cone speaker.( Wireless World,Nov.1952 ).The purpose of the device, which was called a "bung",was to remove a severe dip in the response at 2.5 kHz caused by destructive interference from opposite sections of the cone. D.A. Barlow called this phenomenon,Interference at Cone Apex,and his cure to remove a dip at 1100 Hz resulted in fitting a large spherically curved dome to the cone.(AES Loudspeaker Anthology,Vol. 1-25 ).
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Old 12th July 2013, 11:46 PM   #87
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Holy carp. I hope you didn't bring those slugs up all the way from rough with that polishing compound. Fine steel wool with a little dish detergent and water works very fast and will bring it 90% of the way to mirror...
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Old 12th July 2013, 11:54 PM   #88
pos is offline pos  Europe
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Thanks Legis, very interesting!
Have you measured T/S before and after?
Have you tried this on a midbass driver?
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Old 13th July 2013, 12:45 AM   #89
Legis is offline Legis  Finland
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Quote:
Originally Posted by Andrew Eckhardt View Post
Holy carp. I hope you didn't bring those slugs up all the way from rough with that polishing compound. Fine steel wool with a little dish detergent and water works very fast and will bring it 90% of the way to mirror...
I polished them after they came from the machining, the surface was quite clean (like in the first picture). I polished them attached to a hand drill, it was quite quick operation. Thanks for the tip, I will try that on one plug to see what it does. I have some 000 steel wool somewhere. Wax is good for finishing and protection against oxidation.

Quote:
Originally Posted by pos View Post
Thanks Legis, very interesting!
Have you measured T/S before and after?
Have you tried this on a midbass driver?

To my understanding the phase plug does not alter t&s parametres besides possibly the inductance. In this case it did not affect the resting point inductance, but the motor got more linear, maybe Le(X), flux modulation or something else got better. I have not tried this on any midwoofers, they came with the phase plug. For fullrangers I made aluminum phase plugs, and noticed slight reduction in inductance and higher order harmonics reduction but the plug made the cone resonances somewhat worse in CSD. Good decay and time domain behaviour is more important in fullrangers imo. I get nice higher order harmonic reduction also from current driving the fullranger anyway.

Last edited by Legis; 13th July 2013 at 12:52 AM.
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Old 14th July 2013, 03:28 AM   #90
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Quote:
Originally Posted by Andrew Eckhardt View Post
Holy carp. I hope you didn't bring those slugs up all the way from rough with that polishing compound. Fine steel wool with a little dish detergent and water works very fast and will bring it 90% of the way to mirror...
If you do this, make sure to follow up with another polishing step, otherwise you may see rouge (iron contamination).
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