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Since you asked about not many questions I have one.

Will you be permanently gluing down the front baffle once you are satisfied with the performance?
I would figure the gasket tape will yield a very good seal but that 21" monster will test it's limits.

Glad to hear about the good HR experience.

Great sub, can't wait to hear how you like it.
 

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Discussion Starter #64
Since you asked about not many questions I have one.

Will you be permanently gluing down the front baffle once you are satisfied with the performance?
I would figure the gasket tape will yield a very good seal but that 21" monster will test it's limits.

Glad to hear about the good HR experience.

Great sub, can't wait to hear how you like it.
I've used this same rubber-foam tape on my folded horn, which is a complex build, and had great results.

Considering the the baffle is "stepped", and nearly press fits in, air would have several solid panels to snake around. I'm pretty confident the insulation tape will hold considering the physical loads I have on it. And if I do detect leaks (which I'm honestly not sure how to "detect" leaks on this), I have plenty of surface area to add a second line of insulation.

See the steps in the baffle. Two of those layers will sit flush on the box. I could easily add a second tape line.




All this is to insure I can "service" the box or driver should it need it. Granted, I have a 19.5" hole I could crawl into if I really had to, but it's been standard practice for me to be able to open up any boxes I build...even if it's just to try out different damping methods. (or to look at the drivers because it's been so long I couldn't remember what model they were! LOL)


 

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Discussion Starter #65
I should probably add, if I don't feel the 2.5" stainless deck screws I'm picking up today will do the job, or they pull through the wood (which I wouldn't be surprised considering this paneling), I'd rather upgrade to bolts and T-nuts on the baffle then glue it all down.

Once I'm sure I have everything sealed and working well, I'll be "finishing" the box by rounding over the corners, and either using a roll on bed-liner type coating, or wrapping the whole thing in leather. It would make a nice ottoman. :bigsmile:
 

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Discussion Starter #69
Mini-Update: Last night I had some frustration with the sub and amp. I came home from a bad day at work, ran out to buy some 2.5" screws to put the baffle on, got the whole beastly thing upstairs by myself (it's actually lighter in two pieces, then my folded horn was!). And when I set it up, the output was...well, not impressive at all. I figured I had done something wrong, because the old pair of 10" had easily double the output of this 21". I was heartbroken, and just too tired and frustrated to look at it anymore, so I went out to dinner. When I came home, I remembered that I had been running the old setup with two inputs and two outputs. So I crawled back behind the rack and pulled the 1/4" plug out of input two, and the whole system came to life. So basically, the sub was probably only seeing half the sign wave, and I was only getting about half it's output.

This morning I did a few sweep with REW. I haven't yet pulled my microphone and mixing board out of storage, nor have I run my Audyssey XT on the Onkyo 805. I just wanted to run some sweeps now that I had a good nights sleep and time away from the frustrations of yesterday. I ran REW from 5 to 120Hz, noticed my rear speakers had somehow got set way too low, made some quick adjustments, and....WOW! This beast turns electrical energy into physical energy!

Apparently my DIY projector screen wants to jump off the wall at 15Hz, so I'm going to have to damp the screen and probably velcro it in key places to keep it from walking off the wall.

Overall impression...I have to say, I miss the horn. It just couples with the air better then anything else. It seems to excite the whole room, airspace wise. While the M-21" seems to press more mechanical/physical energy into the room. I'm getting the feeling that I'm going to need to decouple the box from the floor somehow, because the feeling of energy passing through the floor overpowers what the box passes through the air...or maybe not overpowers so much as I feel it before I hear it? So I think making myself a giant sub decoupler might help out here, though that would make it taller yet again, and it's already a bit obtrusive.

Again, all of this is without tuning and without trying out different placement options nor measurements. These are just my first impressions. I have a movie night planned with my friends tonight, so I have to get the sub at least setup enough where Star Trek won't bottom it out or clip the amp. But over this weekend I'll work on re-learning REW and taking some proper measurements.
 

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A few posts back you said that sliding the baffle into place caused the cone to puff out slightly. You don't want that to happen. With a sealed sub, heat will build up inside the enclosure, and heat causes air to expand - now you will have even more pressure inside the enclosure pushing against the cone. That can mess up the suspension over time.

The trick a lot of people use to counteract this is to place a small pin hole somewhere near the top of the enclosure. This will prevent a buildup of pressure in the sub over time, but should be small enough as to not lose pressure from the backwave while the sub is in use. Someone who uses sealed subs and such a method may want to chime in to give him exact details, as I've never actually done it myself.

As for mechanically exciting the whole room, in my opinion, that the best part :D I used to have one of my subs in a 3rd floor apartment and it would cause my whole floor to bounce. Now I have two such subs in a one floor townhouse over a concrete foundation and the effect just isn't as good without feeling the ripples of bass run through the floor. The floor still imparts some bass energy, but not nearly to the same level as the wooden floating floor did. In real life, if there is a big explosion, you will feel it through the ground - therefore, a sub that mechanically excites the floor offers a more accurate respresentation of that explosion.
 

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Discussion Starter #71 (Edited)
A few posts back you said that sliding the baffle into place caused the cone to puff out slightly. You don't want that to happen. With a sealed sub, heat will build up inside the enclosure, and heat causes air to expand - now you will have even more pressure inside the enclosure pushing against the cone. That can mess up the suspension over time.

The trick a lot of people use to counteract this is to place a small pin hole somewhere near the top of the enclosure. This will prevent a buildup of pressure in the sub over time, but should be small enough as to not lose pressure from the backwave while the sub is in use. Someone who uses sealed subs and such a method may want to chime in to give him exact details, as I've never actually done it myself.

As for mechanically exciting the whole room, in my opinion, that the best part :D I used to have one of my subs in a 3rd floor apartment and it would cause my whole floor to bounce. Now I have two such subs in a one floor townhouse over a concrete foundation and the effect just isn't as good without feeling the ripples of bass run through the floor. The floor still imparts some bass energy, but not nearly to the same level as the wooden floating floor did. In real life, if there is a big explosion, you will feel it through the ground - therefore, a sub that mechanically excites the floor offers a more accurate respresentation of that explosion.

Wow Steve, I've never heard of that before! Great tip! Hopefully someone else can chime in with some specifics as to how that pinhole thing is done.


I do enjoy the floor vibrating, true, but the folded horn did it in such a way that blended with the sound. This sealed box seems...separate from the sound. I'm not sure how to describe it. My fiance noticed it as well, but she's not terribly articulate when it comes to describing audio. I'm hoping tuning everything with Audyssey will help this some. Maybe I'm just being oversensitive.
 

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Looking back at your first thread on the idea of a LLT to replace your horn, it struck me that you probably haven't been exposed to the reproduction of low frequencies. This was your FR at the seat:



Your new subwoofer will not die below 40hz like the horn. And what do you know, below 40hz is where things will start to transition from audible to tactile at most listening levels. Welcome to the new world.

Also, your horn subwoofer was being used pretty hot for the range that it coud play - the large peak ~45hz probably made the bass essentially one-noted. You may not have noticed it then, and you still may not notice it now, but live with your new sub for a couple months, then listen to a sub with a large peak like that horn again, and you will definitely notice it.
 

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Discussion Starter #75 (Edited)
Steve, I know your dead on. I worked on that big hump with a super-duper-chunk, and some smaller OC703 corner traps around the room. I think I knocked it down a few db, but I don't have those measurements anymore. I realized I've rebuilt the computer I ran this on and didn't save any of the measurements. So it wasn't quite one note, but I had heavy coverage from 30-50.

Playing with the Mal-21 I'm seeing some pretty solid response covering 30Hz down to 15Hz with a dip at 17Hz (at least so say my senses doing a slow sweep). As I said, I'll do some proper measurements later. I just finished running Audyssey which seems to have helped blend everything better.

I appreciate the second set of eyes looking at this and helping my perception.

EDIT: I was just listening/watching a video that has some sweeps and shows you what freq the sweep is at, and I think I still have a bump around 45Hz. I'll know more once I find where I stashed my Mic and Mixing Board.
 

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Discussion Starter #76
Funny thing about running Audyssey, since putting diffusers on my back wall, Audyssey went from thinking my surround speakers were 6.5 feet (which is accurate) to thinking they were 12' 13'!

I guess that means the diffusers are working some!
 

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Funny thing about running Audyssey, since putting diffusers on my back wall, Audyssey went from thinking my surround speakers were 6.5 feet (which is accurate) to thinking they were 12' 13'!

I guess that means the diffusers are working some!

Steve pretty much nailed it. The sealed sub is coupling to the air just fine, it is doing it significantly lower in frequency that your horn. What most people think of as bass is >40Hz, so your horn sub did fine and dandy for that kind of bandwidth. It won't reproduce 20Hz with any authority, but for music and the upper frequency stuff, a horn can be downright impressive. It just won't plumb the depths the same as a big sealed box driver.

This is my favorite subwoofer horn build.

http://www.royaldevice.com/custom.htm#THE REAL TOTAL HORN


Kevin Haskins
Exodus Audio
 

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Funny thing about running Audyssey, since putting diffusers on my back wall, Audyssey went from thinking my surround speakers were 6.5 feet (which is accurate) to thinking they were 12' 13'!

I guess that means the diffusers are working some!
It could be just because those algorithms seem to have a lot to be desired. I'd manually set it all up and not trust the auto-EQ or the delay & bandwidth choice either.

Kevin Haskins
Exodus Audio
 

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Yeah, I'm not a fan of those auto setup and EQ systems. They get it wrong more often than right, and they tend to roll off your highs and lows for some reason. Setting things up manually shouldn't take but a few minutes. Setting the subwoofer distance will take a bit longer, but you'll want RoomEQ up and running before you try to dial that in.
 

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Discussion Starter #80
Yeah, Audyssey did a good job of blending the timing of all the speakers, but it goofed up the crossover points and did something to the center channel that dropped the dialog a bit.

Everyone loved the sound with the new sub...the general comment after watching Star Trek tonight was that the impact made them feel like things were actually moving past them. The most notable was the scene where Nero drops the "Red Matter" down the hole drilled into Vulcan, and the device drops past Kirk and Sulu who are on the laser drill. The surround and sub combined really made it feel like something just flew through the room! AWESOME!

So yes, I think this setup is better for the investment of time and $$. It's making me reconsider my choice of main speakers, and reminding me that I need more sound treatments in the room...
 
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