Megawoofer vs. original Polycone+efficiency

BC Dave · « **on:** 18 Apr 2006, 07:31 pm »

Hi,

I have ordered a 12-inch Megawoofer and new passive radiator for my VMPS original sub. Is the efficiency of the Megawoofer noticeably lower? My owner's manual states 95dB/1watt/1 meter for the older version and VMPS's website says 90 dB/1 watt/1 meter for the new one. I am concerned that I might not have enough power in my Adcom GFA-535 II. It works fine now because the original driver is a dual voice coil design and is being powered by both sides of the Adcom. The dual voicecoil driver option is no longer available. I understand the Adcom is not bridgeable for use as a monoblock. I don't think my wife would be too thrilled to see me purchase a bigger amp after buying this sub and updating the drivers a few weeks later. The room is very large, but I don't listen at superloud levels. Any help will be greatly appreciated.
THX.

John Casler · « **Reply #1 on:** 18 Apr 2006, 07:47 pm »

Quote from: BC Dave

Hi,

I have ordered a 12-inch Megawoofer and new passive radiator for my VMPS original sub. Is the efficiency of the Megawoofer noticeably lower? My owner's manual states 95dB/1watt/1 meter for the older version and VMPS's website says 90 dB/1 watt/1 meter for the new one. I am concerned that I might not have enough power in my Adcom GFA-535 II. It works fine now because the original driver is a dual voice coil design and is being powered by both sides of the Adcom. The dual voicecoil driver option is no ...

Hi Dave,

You'll have to wait for B, to get back from the Opera

for more specific answers, but I would guess that one is a misprint and that the MegaWoofers are "more" efficient than their standard counterparts, not less.

BC Dave · « **Reply #2 on:** 21 Apr 2006, 03:49 am »

Anybody else made the switch to a Megawoofer from a polycone? There must be someone? More, equally or less efficient? Punchier? Deeper? Enquiring minds want to know!
Thanks.

Brian Cheney · « **Reply #3 on:** 21 Apr 2006, 03:58 am »

It's a little more complex than that.

The MW has an 80oz magnet that is about 75% magnetized. If we magnetized 100% the Qt would be around .1. So we go for a Qt of around .4. The Fs of the MW is lower (about 24Hz) than the poly. However, the PR is tuned higher with lower moving mass for more output.
Result: F3 of 22Hz for the MW and new PR vs. F3 of 19Hz for the old poly with the heavier PR.

The big improvement with the MW is improved clarity. So, while bass quantity is about the same (3-4dB sensitivity increase is barely audible), bass quality is much improved with the Megawoofer.

Try the upgrade and hear for yourself.

BC Dave · « **Reply #4 on:** 12 May 2006, 08:37 pm »

And the verdict is:

I have installed my 12-inch Megawoofer and new 15-inch PR and seem to notice that the bass is a little clearer now, even though I had no complaints before. The megawoofer can sound lean with certain material, but leaves no doubt to its capabilities when listening to material with a lot of deep bass. I put on War of the Worlds and even though the walls were shaking, I didn't see that nasty little clipping indicator lighting up. Still, I think I will replace the amp with something a little more powerful, like the Behringer A500, bridgeable to 500 watts in mono. That Megawoofer is a hefty little mother. The magnet is most impressive.

Brian Cheney · « **Reply #5 on:** 12 May 2006, 09:03 pm »

Try tuning the PR by moving about a small pea size mass of putty from its center. Bass will go lower with higher output.

BC Dave · « **Reply #6 on:** 12 May 2006, 09:23 pm »

Thanks Brian. I will do that tonight. Just to clarify something from your previous post, are you saying that the Megawoofer modification has made my original subwoofer 3-4 dB MORE efficient than the old polycone and passive? If that's the case I haven't lost anything by powering the sub with one side of the Adcom.

John Casler · « **Reply #7 on:** 12 May 2006, 11:18 pm »

Also, the woofer and PR still have to get some "break in" time on them.

Brian Cheney · « **Reply #8 on:** 13 May 2006, 01:01 am »

You are correct, by sacrificing a few Hz at the bottom end of the range you gain about 3dB sensitivity.