MFW 15 sub help (amp died)

Steeve-O,

Its not the price of the enclosure that bugs me. Its the time to make it! Plus I don't trust myself. I was playing with WINISD and if I put in one parameter wrong I will screw up the whole thing. I was thinking about buying a pre-cut kit (the one where you glue it together) and throw in a amp & driver (kind of like you suggested). I want it ported but don't really want a huge box either though. My sub is 5.5 cubic feet (outer measurement) and that is big enough. If I do all this it may just be best to pay $800 for the turbo kit.

Pav26,

I will call the SI guys and see they have a 15 inch leftover because they don't sell them anymore (or look for a used one). Also, I am shocked by that graph in your link. When I bought my sub I saw graphs that showed my sub was flat to 20 HZ. I think it was at 90 or 95 DB though. Maybe the graph in your link is MAX SPL and so it has a huge drop off below 40 HZ. The sub drops 16 decibels between 40 HZ and 20 HZ! That sucks! But, it does the same thing with the other drivers (just at a higher volume).

Wow. So much to learn. You gave you been really helpful to me.

Mike's graph is a model of the subwoofer in an anechoic environment, and also does not include the effects of EQ the stock amp would have had on the response. The quoted performance figures for the MFW15 are 103dB at 20Hz, and 115dB from 35Hz and up (1M measurement)- see here: http://www.audioholics.com/subwoofer-reviews/av123-mfw-15

That matches up quite well with Mike's graph. The turbo package includes a Dayton 1000w rackmount amp - it is also mentioned by Kevin that the amp has modifications to best suit the specific enclosure airspace and driver. Most likely with the inuke, if you plan on that, you will have to use some EQ to get the flat response you must be used to.

5.6 cubes gross and 2.8 cubes net is perfectly realistic, as is the port length. with those dimensions, the specific tune is 21.4Hz. That makes sense, the port is folded in the enclosure. I cannot say if it is actually 44.5" since I don't own a MFW15, but I can assure you it is realistic.

The port, driver, and any bracing will take up a lot of space in the enclosure - not to mention the thickness of the cabinet walls itself. Let's see:

External dimensions: 18.125" x 23.25" x 22". This gives us 5.4 cubes.

Now, let's assume 3/4" walls all round. That reduces internal volume to 4.3 cubes.

Now for the port. The port is 16.5" wide, 2.25" in the enclosure (1.5"+0.75" MDF height) and 44.5" long (or so it seems). Including the port displacement, the volume is now 3.3 cubic feet.

Finally, including the driver displacement, amp displacement and bracing will bring us down to right around 3 cubic feet. As you can see, yes, the internal volume can really be as little as 2.8 cubic feet. I did not account for a double baffle - if the mfw15 does have one, then that reduces internal volume further.

Yeah it's mainly the port that always takes up the most room in the enclosure, it can take up quite a lot depending on overall box size.

imported_juiceblrc said:

I am surprised the sealed 18 has a many DB in 20 HZ to 30 HZ range as the ported 15. I guess the bigger driver helps out. More importantly if the 15 ported had a bigger box I think it would have many more DB in this range??

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Yes, the bigger driver does help out. You are also right - if the 15" SI HT was given a larger box (say 2x, so about 5-6 cubic feet) it would outperform the single sealed 18 in terms of SPL 20Hz and above. The MFW 15 is a very small enclosure, although it may not seem like it. It has to be though - it was a commercial subwoofer designed to meet the needs of most normal HT buffs, i.e not be the size of a giant coffin! There are always tradeoffs to be made. Since the box had to be made so small, the right driver was needed and the tailoring of EQ was needed to get the response flat to 20Hz. That's why the graph looks bad, in it's raw form without EQ and room gain that's more or less the response you'll get. When we built DIY subs, we model with the goal of using least EQ as possible, that's why graphs for builds on this forum will look "better". Because DIY subs don't need to be size restricted, we can get the most bang for the buck by using a large enclosure and as little EQ as possible. Ideally, for me at least, the only EQ used should be to tame room peaks/dips in the response of a subwoofer.

imported_juiceblrc said:

I wonder how many more DB I could get in this range by using an EQ? 5 DB? 10 DB? I guess I could try until the driver bottoms out & then back off a bit?

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The way to do it would be to first measure the raw response of your sub with the new amp with no EQ (and driver, if you get one) and go from there. The amount of EQ you can get away with depends on your room size as well as even personal preference. Some people prefer a response so flat you could set a beer on the graph of one. Others prefer what's called a "house-curve". See this very informative thread to learn some more about that: http://www.hometheatershack.com/forums/rew-forum/96-house-curve-what-why-you-need-how-do.html

You will be able to get equal, if not better response from an SI HT 15 and the inuke in that enclosure compared to stock for sure. (Once you EQ it, that is).

spareho said:

jman, im in a similar situation, one mfw smoked and another humming loudly. I am close to pulling the trigger on the turbo upgrades. after reading I came across your reviews. You are the only one I see that has heard the chane sub and the mfw turbos. It looks like for the money I have a choice between the 2. What do you think for running duals? Im in a sealed designated room designed by bryan pape, double layers of 3/4 suppress drywall and green glue etc etc... thanks for any input.

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Ironically, both the SBE-118 and MFW Turbo are within 5 feet of me as I type this message. How many people have ever been in a position to say that?

They're two completely different animals really, so it depends upon what you're looking to achieve. Since they both use the same SA-1000 amp that's essentially a draw, although the one supplied with the MFW Turbo has been modified specifically for their setup. But the core is the same, so we'll call that one a tie. For total output and "in your face" bass I would probably give the nod to the Turbo, while refinement and purity goes to the SBE-118. Neither lacks in too many areas though, so it comes down to what you're looking for really. Each has abilities beyond what it costs you to buy them, that's for sure.

Are your MFW cabinets from the 'good' batch? The one Mark Seaton gave me to evaluate is from the era where AV123 was supplying very nice woodwork, and as such this one is quite impressive - one of the better subwoofer cabinets I've seen to date actually. The MFW cabinet is taller and deeper than the SBE-118 is, but the latter is wider. For all intents and purposes they take up about the same amount of space though.

To be honest, I'm not certain either would be a bad choice. It's more along the lines of which would be better for your particular circumstances. I really enjoyed both of them. Not sure my house feels the same though...