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Maelstrom 21" With 4 - 2100 Gram 18" Passive Radiators

57878 Views 180 Replies 23 Participants Last post by  Mike Cason
Here is my build thread for the Maelstrom 21. I'll try to provide enough quality pics during my build for you.

I'm using Kevin's Maelstrom 21"er with the passive radiator design. I normally don't like building a passive radiator sub with a Qts over .4, but it is so close, I won't have a problem.

Here's the deal....23" x 23" x 60"; 13 cubes and 15.5 hz box tuning. With the typical passive radiator design there is more of a roll off but at this already low box tuning, I'll have more than plenty of bass. I needed the height to match my main speaker's height and get the cabinet volume I need. Better WAF here.

I just picked up the pallet of materials from my mill. My construction material is 1.25" mdf. It looked like I had ten bags of concrete in my truck going down the road. In the roll of plastic, I've got two sheets of Pionite black slate laminate to match all of my other speakers.

Cabinet resonance with this thick material; I don't think so. Moving it? Now that's another challenge.

Just got back from Houston with the materials so here is the first build pic:

Read more: So where are the Maelstrom-X 21" Build Threads! - Home Theater Systems - Electronics and Forum - HomeTheaterShack http://www.hometheatershack.com/for...elstrom-x-21-build-threads.html#ixzz0XWvNWnLo


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All right now you've convinced me to use passives on my next build depending on what it is.
Actually, the M-21 could make an awesome Birthday gift as it is my 16th on the second of February! :bigsmile:
I just can't believe how big the M-21 looks compared to your 18" passives. I wonder if the subwoofer market will keep going with bigger subs? Or will this be about the biggest you will see?
Hi there SJ....I think a better way to para-phrase your comment would be to say "the biggest you would ever need"!

Watching more movie material last evening, again I had to open closet doors by the front door and in the hallway to keep them from ratteling in their strike plates from the low frequencies trying to bounce out of them. I'm talking at very low volume movie watching! Yea, any larger would be problematic throughout the home and even for a dedicated HT room, it is more than plenty of bass. That's not a phrase I thought I would ever be putting in the forums.......:whistling:
Raven....I've finished the grills now. I've just got to get creative with my gold nameplate to put on this one. I've named my speakers the "Cason II", which is engraved on the name plates on the rest of my builds, but this subwoofer warrants a more suitable title.

SJ...you are creative....help me out with a name.....

I was thinking of having the engraver put the Cason II; with the words "The Ultimate" under it. It's quite an accomplished subwoofer and keeps getting better with break in!

Here's a finished picture. It now has a better WAF.


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Cason II, and underneath that, Ultimate 1.1
Thanks Mike...."We'll make that dog hunt!" I like the 1.1.....It does leave room for change like software versions, though I don't envision ever needing to try to outbuild this one.

SJ.....Thanks....It certainly doesn't look like a garage made sub anymore.

You are also right about the 10,000 times better part. I was in a Frys store last fall and as usual strolled their HT display rooms. It is something I do every time I visit their store to hear the latest offerings. They had a Velodyne $800 sub that was so incredibly horrible sounding, it almost hurt my ears listening to it. The sales person was so proud of it and they have a certain degree of sound treatment in the room, unlike I do yet.

Three words are very fitting here....DIY & Passive Radiators....just my opinion...

You all have a fantastic year!
Souunds good Mike :T
Last night after I posted, I was thinking of something along the lines of 1.1 to. :rubeyes: Strange...

The only store bought sub I've seen that sounded half way decent was a Klipsch 12" or 15" at best buy. It was clean sounding, but when it was taken up to higher volumes, you could hear mechanical noises for some reason. Maybe it was just a defective model, but maybe not... The Klipsch sure wasn't worth what it had cost to build a Mal-X like I did.
That's why I DIY.....

Years ago when I decided I wanted a high end audio system, I browsed the premier audio stores only to find Mercedes Benz pricing on fair to decent sounding speakers. I was buying a name with a pretty wood or veneer speaker attached to it. I was determined to spend as much time on the web and reading materials to build my own, no matter how many builds it took to get them right.
Woops....I started another build. :heehee:

A premier center speaker....I have most of the materials except a couple of woofers which will be here today. I'll probably start a build thread for it....The initial cabinet is glued and clamped. I'll be using a pair of the Hi Vi D10G 10" Kevlar woofers, my Davis Kevlar midrange driver and my Hi Vi RT2II planer ribbon tweeter. I had all of the crossover parts in stock and it is almost finshed.

The new nameplate has been ordered for the sub....Ultimate 1.1

.....when does it all end......:blink:
You might want to start a new thread in the DIY Speakers section for your new build...
Hi Dyohn,

I made mention of doing that in my post....Thankx
Cool, looking forward to it!

BTW, I once built a center channel for a client that incorporated dual 10" powered subwoofers...
I hope they were pleased, or I should say, I know they were pleased.....That's much better...

Here is my new build thread:

A center channel with 10" woofers???? Are you crazy man?! :coocoo:
Mike P.

The Maelstrom 21" Ultimate 1.1 is finally completed.

You are leaving your ideas worldwide in and on all sorts of locations.

Thanks, :T


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Hi Mate,

Did you ever get to take any REW measurements of this beast ?
I'm not set up to take measurements. If I were selling a finished product line, then I would set up one of my computers with the software to do so. I have a lot of projects to do already. I can tell you that it re-produces anything you throw at it quite well and without distortion.

In an earlier post, Kevin has a very nice graph modeling some 15" passives (I think) instead of the 2100 gram 18s I'm using now. Projected output 120 dB at 20 hz? Mike P. has also done a nice graph which projects about 118 db at 20 hz. Sprinkle in some room gain with 9' ceilings and you end up with a whole lotta bass! :hsd: I'm driving it with 2719 watts of high current torrodial power.

Cheers my friend,
You can put 2700+ watts through will no problems? Even at the tuning requency, the passives won't have any distortion? That's impressive.
I hope I can experiment with some passives soon. But, the AntiMode offered a better improvement for my room (at least I hope...lol) so I went with that instead of the passives.
Each of the 4 passives have a 3" P to P excursion. I would never, nor have the need to drive the sub that hard, but it is nice to have the reserve power in the amp to hit the occasional slams and deep bass when it is needed. I always like to have more power than needed. It's kinda of automobile setups with the extra capacitors mounted in the trunks that are able to hit the drivers with more power when they are needed, or like a truck with a much larger engine than needed for normal use. It's there when you need it though. The amp doesn't work as hard which reduces or eliminates clipping and provides cleaner power.

No, I've never heard distortion with anything I've ever played through it yet. Sorry ya didn't win the contest... :foottap:


Either in one of my posts or pms, I asked you about the noise level of the Face 1200 amp vs the QSC or Crown. Two things to note here. After using the QSCs for several years, I find the Face Audio amplifier to be a much better sounding amplifier. #2, I don't hardly even hear it. It is inside my equipment rack with a glass front and unless I'm driving it hard, then stopping to listen for the fans, I may barely hear them only for a few seconds then they are quiet. During normal to reasonably loud playbacks of music and movies, I don't hear a thing. They are sooo much quieter. You told me you had nothing to compare them with, so I wanted to pass this good information along to you.

At tuning frequency, the driver looses its ability for cooling due to the reduced Xmax (or just plain overpowering the driver), which results in the said bad smoke. I've read it before, and I thank you for posting it :bigsmile: :T
SJ, You are correct.....

When I test my cabinet for the tuning frequency, I watch for the driver to stop, and the passives to move a lot. My test CD is the Linkwitz Riley frequency CD which has short bursts. I also have some other test CDs but this is my favorite so I don't put a load on the voice coil and the lack of cooling at box tuning. The short bursts provide that level of protection.
great project! compliments

Thanks....After a couple of months of break in time and listening to music and movies, I would venture to say that this subwoofer is as good or better than any subwoofer offered in the retail or high end markets, including the Wilsons and others. The musical quality of this subwoofer/passive radiator combination is extremely clean, smooth and low. Movies are absolutely stunning! I just don't know how it could possibly be any better....period......

My hat is off to Kevin for such a magnificent product and service.....:fireworks1:
Thank you.

This is an impressive subwoofer to listen to. The term "idle" fits this sub perfectly. With even the slightest input signal it receives, the sub and passives are working together to move a massive amount of air. This is a true, deep, and clean bass as one can only dream of. It does fall under the category of being a high quality audiophile grade subwoofer which is much different than the type you built for bands and stages which look at the higher SPL as their main goal.

Years ago, I was going to build a sub with a pair of the Aura NS18" (I beleive that is the model #). At $800 per driver and reports of their failures I read in the forums, I changed my mind.

When I heard that Dan Wiggins had his XBL^2 motor on a 21" woofer, I knew my search for the perfect subwoofer driver was over!

Kevin Haskins is so fortunate to have such a wonderful driver, the Maelstrom, in his line of products. Kevin is also fantastic to work with, ie cool fellow! :wave: I'm using Kevins Face Audio 1200 series amplifier bridged to mono.

I use the Reckhorn B-1 crossover available from CSS. Bob Reimer is also a very stand up guy and will take good care of you.

I have Denon's flagship model 5308CI(A) receiver and use the LFE output to the Reckhorn B-1 for total subwoofer control, high pass, bass boost, and subsonic frequency protection which is sent on to the Face Audio amplifier.

Good luck with any build you may have in store.....
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