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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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Any graphs?
Yes, see post #5. Kevin Haskins did a nice job. I expect a little lower tuning with my 4 18" 2100 gram prs, but it is close.

I may be forced to sell this one with grills completed and the amplifier due to finances. I've got an order of drivers coming in from China and money is tight. Both of our main jobs came to a standstill but the bills haven't. I'll make that decision soon.

Oh...I'll gladly try out four 21" subs in my 13x13 room for no charge :hsd: :D
Simply send them and a few of those super fancy Face Audio amps that you have there, and we have a deal :bigsmile:
lol just kidding.

It's good to hear that everything turned out awesome Mike. Excellent build to. I wish I could have a 21" to match my Mal-X :T But, I'm too poor...a 15 year old in this kind of audio stuff...you tend to run out of money pretty quick haha
I'm proud of you for taking up this hobby son. There are so many other 15 year old's out there taking on hobbies that lead them down the wrong road. You are in a forum with a bunch of great guys and we'll support you all that we can.

Any pics of the sub in house?
I thought about that yesterday. It looks so much nicer in the home than in the garage. I've been very sick but am better, so I'll get a couple posted later on when I've been up a while. I need to clean the camera lens first.

.....I watched Celtic Women on local antenna yesterday and the subwoofer hit lows I've never heard out of a sub, ever! I just happend to be in the back room when that particular song played. I walked into the LR and was extremely wowed by the low earth shattering bass it was producing at a low volume. It was simply incredible and unbeleivable! :hsd:
Here it is Mike....

I still had a spot or two on the camera lens. The grills I'm making won't be full length like the mains to break up the looks a bit. To get a prospective on the driver sizes; the mains have 12" Lambda woofers and 15" passive radiators; and the sub has 18" passives with the sweet 21.


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Looks good, the sub blends in nicely with the mains. I can imagine the output after the sub and PR's loosen up a bit. It should be an experience! :hsd:
Thank you Mike....:wave:

They are improving by each day.

I was going to run some pink noise through them for a couple of days while I was out, but decided to burn them in during normal playback. As you know, I was going to part out and sell the drivers out of my other two subs in my avatar, but I sold the pair to some Shacksters in Illinois. Here's the report I got back from them this morning about them. I can't stress enough the quality of the bass you get out of a good passive radiator design. I'm so glad they went to a good home instead of being parted out. I was able to step up to the 4 - 18" 2100 gram passives too:

That 21 is looking nice! I have been following it on the SHACK. Bravo on another amazing build. That 21 looks intimidating!

I have gotten the subs integrated as of last night. I updated the firmware on my Velodyne SMS-1 which allowed me to set my subsonic filter even lower than 15Hz. I have usable output to 12Hz! I have been listening to music at moderate levels and am loving it. I watched a blu-ray concert last night in Dolby True-HD and was all smiles!

I found that the subs have so much clean output that I continue to turn the volume up until the levels are insane. I recently had my neighbors complain of things shaking in their house. They are over 300 feet away from the subs! My house does not like the new found power, judging by the groans and oscillating walls, but that is too bad.

I am a movie buff too, and the LFE on my favorite movies is superb.

I just wanted to tell you how much I am enjoying the subs. They are excellent!
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Looks fantastic Mike!

So, I'm guessing you have some issues with those large reflective surfaces at the front of the room...and I'm not seeing any room treatment in there. How do you deal with all that? I can barely stand it in my theater/living room and I've got a huge super-chunk with more absorption on the way.
Well Raven, you know I build a much better speaker than you do! Mine don't need a doctor and special treatment!! :devil:

I really don't have any issues. I do have a lot of reflective walls for sure. The reason we don't have room treatment is now handed over to the wife for the blame. We built our new home ourselves. It was a 3 year project. She wouldn't make or buy the drapes until we got rid of our well used sofas. "Color co-ordination" she said. We do have very thick pile carpet and padding with throw large rugs that help.

Well, I made a grueling non stop trip to some remote spot in Alabama and bought the 6 Lazy Boy recliners from Sonnie and now she has the color she can use for the drapes. Any neutral color would have worked for me. So now, I'm waiting on the economy to pick up so we can work again and get the drapes up. That's all I'm going to do for treatment because we still want our living room and not a room with bass traps or foam panels stuck in the corners and on the walls. In a dedicated HT room, you betcha!

Check the reviews on the Houston DIY Group thread and you will hear rave reviews about the sound quality it has as it is.

The system sounds fantastic as it is and we can listen to it for hours at high levels withought fatigue, so that is the most important thing to us.
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Well, I was a bad dad because I didn't allow skateboarding.....He never had a head split open either.....
We did a lot of other things that made up for it.

No, I don't plan on making any vids. I've got too much else to do to this time of the year.

I hit the system with the 1812 Overture this morning after I was told the cannon shots were 10 hz and wouldn't play them and would probably destroy my driver. After I played it once, I replayed it again at high SPL and no strain on this ole sub. She performed well. :rofl2: I did look across the room for the cannon ball hole~~~~

I checked out your build. Lots of work and I bet you have great bass. Keep up the good work! :bigsmile:

My mains have a pair of the Lambda TD12s midwoofers paralleld that can handle 500 watts each and I've got them crossed over at 700 hz, so they can speak loudly when needed. The Lambdas have a great motor design and build. Many a fine artists have played their concerts through them and they seem to get sweeter by the day.

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If you have the Telarc recording of the 1812 it contains 3Hz fundamentals....
Woooo..got to get it....got to get it.....I saw it on Amazon but am not buying anything until work and business picks up. It was neet to hear it even at the 10 hz though. Thanks for the tip robbo266317 :bigsmile:
What's with you Mike... you only built one of these? You need a at least a pair in your room... :dontknow:

Very nice work!
Thanks but I just listed it for sale in the classifieds.

UPDATE: I can't let go of this one....I'm pulling it off the market. It gets better by the day!

Sonnie, thanks for the suggestion but one more will destroy my home!....:T

Ahhh, crumbs. I'm sorry to hear that.

I'm teetering on that same abyss as well. For this month at least.
As Dave Ramsey calls it, "beans & rice" time.....
Good luck to you Mike, in fact good luck to us all as these times are worse than I can ever remember.

What kind of passive radiators are you bringing in?
Peerless Tymphany quit building the 830880 5.25" truncated passives with an fs of 23 hz. I use them in my Bang and Olufsen Redline RL60 modification and one of the owners of their Redlines said they were no longer available. I spent two years and a lot of money buying up used Redline speakers to help folks rebuild their Redlines, and I designed a replacement passive radiator system for the failed ABR plates the engineers used. Without these passives, two years of my work would have been for nothing. I had to pay for re tooling from Tymphany and had to buy a mininum of 1000 of them to keep my Redline modifications availble to folks. They are an excellent product and I've got a lot of information on my website about both the Tymphany passives and the Bang and Olufsen Redlines with a pictorial step by step on "how to" rebuild their faild ABRs. I paid more money today to LA customs and they will be here by rail on the 29th, even though I have purchased almost two hundred of them already from other distrubtors who dropped them.

This is a tough business and it takes a lot of capital to keep it going. I only make a few bucks on each of them so it's going to take a couple of years or so to break even, if I can manage to even do that.

They are excellent for many other applications and you can build deeper sounding bass in smaller cabinets with smaller drivers. Their use is endless. Computer speakers, boomboxes, Ipod speakers, mains, surrounds, and so on.

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Mike, I'm sorry to hear that your having to sell your awesome sub. These are definitely hard times, although they could be handled better by the president.

Just out of curiosity, how much did you list your sub for on craigslist?
I had it for sale for $3,600 with the amp, but it's off the market now.
Oh, my bad. I could have sworn that you said that you listed it on craigslist haha.
Sorry for the confusion...
I did earlier after I read your post.....Thanks for the reminder....I sold my new NAD in 10 minutes there! [Houston's Craigslist]
Well, another challenge being undertaken at this time. I've been working on the grill frames but ran short on red oak 1 x 2 material. I bought more than I thought I needed but still need two more pieces.

I hope to get the last one built tomorrow, route all of the edges front and back, paint them with a flat black paint to hide them behind the porous audio grill cloth. I'll then upholster them sometime this week. I'll probably do it Christmas day. Last Christmas season, I spent 4 days re-upholstering 13 grills on all of my speakers so they would all match. How coincidental!

These builds take a great deal of work, a lot more than meets the eye.


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The passive radiators are 18" 1600 gram flat MDF. I did add another 500 grams to each of them by using a two part epoxy from Devcon and some large heavy flat washers. They don't have studs, but the epoxy works well.
Kevin has some 21" passives available now. You would only need two of them.

As far as the placement, I wanted to get the woofer as low as I could for some floor reflection. I needed to keep it high enough so both the upper and lower passives would work together. Pioneer recommended an offset from center woofer placement for my truck shallow mount sub behind the seat. Not being an engineer, I would say it is due to some kind of compression reason. I also built a nice large polyfil bag out of stretched audio grade grillcloth in the upper portion of the cabinet, and I didn't want any influence or interference from that being in the way of the free air to the back of the main driver to the the upper passives.

I haven"t posted in a while and have watched more concerts and movies since then, pushing the limits and breaking in this monster. It has improved with the break-in time.

We watched the Day After the other night and I finally broke the WAF bass barrier. She doesn't like it! It got so low with the LFE from this movie, I had to keep setting my eq gain lower because the entire home was shaking. I didn't want to break any more seals on my large insulated windows either. I had to educate her that the subwoofer was producing the sounds just like the movie director intended! I have a 5" concrete slab on piers too! She has already lost many items that have fallen off the shelves and broke from my earlier builds. I can't say enough good things about this subwoofer. I even bought another 21" Maelstrom for a spare.

It would do you good to Google "XBL^2 motor" and learn more about Dan Wiggin's patented motor structure. That was the selling ticket for me as I know him and his work from the old Adire Audio days. I still communicate with him with some other work.

Buy one of these and you certainly won't be disappointed. Be sure to prep the wife for a whole new listening experience. You may need an D attorney later.

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This demo vid is in free air without any cabinet suspension and appears to be reaching its suspension's travel capabilities due to excessive power. I noticed that the same test tone is also being played, unlike the real world use of the driver would see. I would never do that kind of testing with my drivers. Any driver would have issues being tested and treated this way with too much power.

I haven't had the need to push the limits of my 21" and it performs flawlessly at a high a SPL. All things in moderation and correct application applies to all drivers.

The suspension is very stiff and this design is capable of producing an enormous amount of bass without distortion with both of the 18" & 21" drivers utilizing the XBL2 motor and long throw suspension if used correctly.

My concert DVDs and movies are reproduced quite well and even as low as the impact scenes go, I've never bottomed out. I'm not selfish with my power either; just 2700 watts.

Hi Mike, as it itches me to build sthng better than what i already have, do you expect reaching the PR excursion limits, when lets say me only using one PR or maximum 2PRs with a 15inch tempest X2 for example running at 500W+ in a 250 Liters enclosure? Or in other words, is it better to choose a PR with lower Cms when using such a powerfull driver? I came across PRs with Cms from 0.2mm/N to 1mm/N (even though different, Xmax are comparable for all those passives) ?

Thanks, Veltinorian
I would use two prs that are of equal size per driver or larger. If you are looking at using 2 Tempests, I would use 4 passives. The Cms of 0.2mm/N to 1mm/N is very low, even though the Xmax is comparable or higher. If they have a similar Xmax, two passives per driver should work well. It would be hard to reach full xmax when using two passives per driver. I have 4 15" passive in each of my mains that have only two 12" drivers each.

I would get someone to do some modeling for you to compare the low Cms for your application. I don't have that modeling software. I think Mike P. can do that.

I think Dan Wiggins of the Adire Audio days sold the flat MDF passive radiators that Acoustic Elegance builds. They are low Cms. That's what I have in my sub. If my memory serves me correct, Adire sold the Tempests, Bramah, and another sub.

The Cms of my 18" 2100 gram passive is .9 and I have a 3" point to point excursion. I'll never reach those limits using the four passives I have with the Maelstrom 21".

Dayton has a sub driver with a matching pr; Peerless XLS drivers had their own XLS passives to mate with their driver. Peerless also had their small SDS line of 6.5 woofers that had the Peerless 830880 passives to mate with their driver. Kevin has some 21" prs to match his Maelstrom 21" driver.

The key is to model out your design before you build your enclosure to ensure you will get the response and box tuning you are trying to achieve. IMHO, a properly built PR sub can't be beat, even though I haven't listened to good transmission line sub yet.

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I sold my extra Mael 21" driver and pulled my new sub off of the market, but anything is possible. This beast gets so incredibly low, my wife doesn't like it. She has been ok with all my builds for the past 15 years, but the low end is just way too much for her. pm me or email me if you have any questions. Hope you are doing well....:)
I tried, but when I ran the subwoofer for testing, I had to hold onto the walls to keep from being knocked over. Couldn't keep the microphone steady. When I get some extra help, I'll try again......

Really, I'm not set up for in room testing.... I was able to check the box tuning with Linkwitz test cd, and I'm right at 15 hz.
Man...now your really making me want a Mal 21...I hope I can win the giveaway for the 21". That would make my year. Then my dad could have my Mal-X, and we can shake the neighborhood down while watching movies :bigsmile:
If I could be blessed enough to win the 21 (lol), I would definitely try passives with it. Sounds like it would be awesome as you wouldn't have to worry about port noise, chuffing, etc...
It is worth the extra money to use them. The passive radiator design has its deep and well respected bass of its own. With as much air as this driver moves, I would expect to hear something from the ports. Vance Dickason states in his Loudspeaker Cookbook that an improperly built or other unwanted noises from your loudspeaker can be amplified by as much as ten times through the ports. You also eliminate the port resonance as it can't exist. Hope you get it son.....:T
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