Vifa M30WO-49 as sub driver? - diyAudio
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Old 27th November 2002, 01:40 AM   #1
Andy G is offline Andy G  Australia
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Default Vifa M30WO-49 as sub driver?

I can currently get this at half rrp, ie about $87AUD.

Has anyone used one of these, and can confirm or correct my calcs of a vented 65L box tuned to about 30Hz?
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Old 29th November 2002, 10:49 AM   #2
navin is offline navin  India
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cant find specs.

used 25cm cousin in 60 liters sealed to good effect.

Vifa 25W, 10M and D27 in 3 way ccame close to a Dynaudio 24W100, D52af, D21af combo. in fact the mids in teh vifa were nicer. just that in those days Dynaudio's high power handling capability was more imporant to me. Along with my mind I dont know where I put these speakers.

the low loss Vifas are very good. great VFM.
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Old 29th November 2002, 02:29 PM   #3
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Haven't used Vifa. Both WinISD and the Danish Sound Technology website list the parameters for your speaker.

WinISD recommends a setup very close to what you are talking about. They recommend a box of 62.6 liters and 37 Hz tuning.

I ran both on WinISD. The results are below. Very, very close.

Your alignment is in red.
WinISD's suggested alignment is in blue.

As you can see, both boxes are 3 dB down at 50 Hz. However, since the woofer is a very sensitive 93 dB, that is equivalent bass output to a woofer which is rated 87 dB and is 3 dB down at 35 Hz.

I checked the Vifa website: www.peerless.dk Click "Enter a World...."

The M30W0-49 only has a 14 mm long voice coil winding, and an air gap of 6 mm. That means it's linear travel is only (+ or -) 4 mm! In the old days, "long throw" meant 6 mm. Now that we have superheavyweights on the market that go (+ or -) 37 mm or more, that number pales in comparison. But still, 6 mm seems to be reasonable to expect for a subwoofer, don't you agree?

One other thing. Near resonance, vented woofers tend to move out of the center of their travel and move to the extreme end, where they clip half the waveform. A mild way of describing this is "high second harmonic distortion".

It theoretically is supposed to happen in sealed boxes too. However, I have only personally witnessed this in vented boxes, not in sealed.

To counteract this, you need a symmetrical magnetic system, which is usually accomplished by either a shorting ring, (Faraday ring), or an extended pole piece to even up the magnetic material in front and in back of the voice coil.

I have looked at Vifa brochures, etc., over the years, and they hint at a symmetrical system, but never say so. The basket is cast magnesium because it is supposed to be better for the magnet system. This woofer has a double magnet. They say low distortion, and ideal for bass reflex. Their sister Danish Sound Technology companies, Scan Speak and Peerless, have symmetrical magnet systems on many, if not all, of their woofers. Yet Vifa, for all their hints, never flat out says they have a symmetrical magnetic system.

I would Email them to find out, but I Emailed Danish Sound Technology about another question once and never got an answer back.

Anyway, your box alignment would seem to be confirmed. Just thought I would give you my take on the pro's and cons of this woofer, whatever they're worth. Like I said, have not used this particular woofer. Good luck on whatever your decision is.
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Old 30th November 2002, 05:20 AM   #4
navin is offline navin  India
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one thing. i notice that drivers with high sens tend to have low x max. is this true?
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Old 30th November 2002, 06:14 AM   #5
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That seems to be a general rule, I think. PA speakers tend to have the highest sensitivities, but low Xmax's-frequently a big 15 incher has less than a quarter inch each way.

One PA spekaer that seems to break all the rules is the Volt RV4504. 18 incher. Made in England-they don't even list an American distributor, though they have them in other countries. 96 dB sensitivity, (+ or -) 10 mm linear Xmax-that is getting pretty close to some of the 12 mm high excursion heavyweights we have been seeing lately. Symmetrical magnetic field-not a common feature in PA speakers.

I don't know what this thing costs but if it lives up to it's specs, it sure looks like a winner.
http://www.voltloudspeakers.co.uk/Ab.../about_us.html Look for "Loudspeakers", then "Radial Chassis".

I just bring that up because this Volt speaker looks like "the exception that proves the rule".

Most times, Navin seems to be right. The higher the sensitivty, the smaller the Xmax. I think it has something to do with a shorter voice coil having a greater percentage of the winding in the magnetic gap, or something. Shorter voice coils mean smaller Xmax's.

Volt RV 4504 specs:

RV 4504

Fs 33Hz

Re 5.5 ohms

Qa 4.26

Qe 0.38

Qt 0.35

Vas 217 litres

Xmax + or - 10 mm

Sd 962 cm2

Vd 962 cm3

Le 2.9 mH
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Old 30th November 2002, 10:32 AM   #6
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I looked at the volt a while back as a project for a friend, very nice speaker but it is about 470!!!
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Old 30th November 2002, 01:47 PM   #7
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I would go with the alignment you have now, not what WinISD says. It didn't give me the best results with my only speaker project. I find Loudspeaker lab 2.0 better.

18" PA speakers have a higher sensativity and lower x-max cause they play higher frequencies then 18" home or car subs.

Simple logic would tell me if you want to have a speaker with a highest possible sensativity at 1 Watt you make the magnet system handle 1W of power. Maybe I'm wrong

Woofers with a large X-max have high power handling magnet systems, therefore not giving good sensativity at 1 Watt.

I don't understand the importance of sensativity ratings a lot of the time. Like when designing a x-over, you know what the sensativity of your speakers is at 1 Watt, but they won't be playing at 1 Watt. You can have a woofer that's got a 94 db sensativity and one 89 db sensativity, but at 500 watts the 89 db sensativity woofer is a lot louder. This happened to me, but the 94 db sensativity woofer wasn't meant to handle 500 watts.
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