Stereo Sub Power Requirements Question

[cytokine]

I'm going to build a set of MTM bookshelf speakers that will start to tail off at about 70 Hz.

I want to build a pair of subwoofers to run in stereo as the third part of this design to fill in the bottom end.

I am thinking of using the Vifa MA26WR09-04 10" Aluminum Cone Subwoofer shown here.

The relevent specs are that it is 83.3 db at 2.83V/1m and power handling of 300W (I'm presuming that's max and not RMS). It supposedly has an F3 of 33 Hz in 1.5 ft3 sealed.

My question is this:

If I build two of them and run them in stereo, how much amplification do I really need? Should I go with a full 250W plate amp or could I get by with 100W?

The difference in cost is a semi-non-paltry $60.

The top part of this is an MTM design that is ~90 db 1W/1m efficient.

Opinions and suggestions are most welcome.

[simon5]

Always depend on how low and how loud do you want to go.

What's powering your MTMs?

[Cal Weldon]

Is there a specific reason you want two? It's a lot easier to integrate one. Then there are few cancellations, you can afford one good istead of two mediums and only one amp to buy.

Cal

[cytokine]

I should have specified that this is for a dedicated two channel rig. The pre-amp is a Bottlehead Foreplay and the amps are monoblock gainclones.

The "how low and how loud?" is a function of the kind of music I listen to. This rig is used for 90% small ensemble acoustic jazz, 5% classical and 5% evenly distributed between classic rock and world music. I want it to blend in seamlessly so I only want the low bass to be as loud as it is supposed to be relative to the music.

The reason I want two is because I was thinking in terms of stereo all the way up and down the frequency range. Am I not thinking right?

I was also thinking of two subs for the coolness factor as well as that they could be used as stands for the MTMs.

I have a most excellent sub for the 5.1 rig; an Adire Audio Rava, which is basically a sealed Shiva. Very sweet.

I have not wanted to use that sub because I would have to adjust it every time I switch from the home theater rig to the music rig and back, and then there's the issue of running two separate inputs into it at the same time and the liklihood of that damaging the plate amp.

Open to suggestions at this point.

It occurred to me in a free moment this afternoon that the 100W plate amp probably wouldn't work because of the sensitivity of the Vifa sub compared to the MTMs. The sub is 83.3 and the MTMs are ~90. Hence I think I would need the 250W plate amp and that driver still might not be optimal.

Comments?

[Chris8sirhC]

I'm in a similar situation. I'm making the jim griffin jordan/g2si mini monitors. I actually think what I'm going to end up doing is to have 4 dayton reference 10's per side in a 5 cubic foot enclosure for stands and use some eq to get the lowest frequencys up.

[simon5]

I don't know how much power your monoblocks gainclones can give.

Let say 40W so each of your speaker will play at 106 dB.

To match that 106 dB, you'll need about 200W per subwoofer.

If your gainclones are more powerful, then you'll need even more power.

[RobWells]

The driver you've chosen seems to have a small x-max for a sub. (11.6mm peak) . Also in the pdf for it they show the freq response from 300Hz upwards A sub is generally used from ~100Hz downwards.

Personally I'd be looking at different drivers. The peerless xls 10" seems a good choice, but there are plenty of others.

Cheers,

Rob.

[Cal Weldon]

Originally posted by cytokine
I should have specified that this is for a dedicated two channel rig. The pre-amp is a Bottlehead Foreplay and the amps are monoblock gainclones.

Nice

[i]The reason I want two is because I was thinking in terms of stereo all the way up and down the frequency range. Am I not thinking right?[/B]

Not necessary as the lower you go, the less "stereo" there is.

[i]I was also thinking of two subs for the coolness factor as well as that they could be used as stands for the MTMs.[/B]

As you wish. Cool hasn't entered into my designs before. (mind you some do turn out pretty cool)

[i]I have not wanted to use that sub because I would have to adjust it every time I switch from the home theater rig to the music rig and back, and then there's the issue of running two separate inputs into it at the same time and the liklihood of that damaging the plate amp.[/B]

I agree, different woofers for different systems

[i]It occurred to me in a free moment this afternoon that the 100W plate amp probably wouldn't work because of the sensitivity of the Vifa sub compared to the MTMs. The sub is 83.3 and the MTMs are ~90. Hence I think I would need the 250W plate amp and that driver still might not be optimal.

Unless you're room is small, 250 is the way to go, if not more.

Comments? [/B]

I have had much less trouble integrating a single sub into systems than I have two. That's not to say you can't do it and do it well, just to say that my experience says go buy one nice big woofer and one good plate amp.

My main system is two 15" coax and one 15" woofer.

Cal

[cytokine]

Chris;

That seems like an interesting choice but perhaps not the most economical. That's a handsome driver though. I like the concept but it's not where I'm heading.

Simon;

I think the gainclones do 56 W but I know nothing. It's just something I think I might have read somewhere. Yeah, 100W with that driver won't get me there.

Rob;

Yeah, perhaps it's not the best choice. I'm taking the reference for this from Zaph, whose MTMs I am going to build. I respect his opinions but am open to those of others since I know nothing myself.

Cal;

OK, I'm convinced. A single big *** subwoofer.

Which one?

Or perhaps I should build something to replace the Rava for the home theater rig and move the Rava over for music duty.

More opinions? You guys are really helping me focus my thinking on this. I appreciate your time and efforts.

[RobWells]

Hi cytokine,

I have no listening experience of your vifa driver - I was just a bit wary of the x-max. My maths puts each of the sub's excursions at x-max (at 30Hz in a sealed box) when your mains hit ~8W.. However, I have been known to make fundamental errors when doing quick calculations.

If my maths is correct then a 100W amp will be plenty, but make sure its a 100W into 4 ohm amp.

If Zaph says they'll work fine then I'm sure they will.

Rob.