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Discussion Starter · #1 ·
Hello Gentlemen

Wonderful place you have here. I just read 48 pages of "grahams" thread about his dual 18" opposed woofer project and didn’t hear one word of negativity uttered. A huge feat in the world of online forums. I figured this would be a good place to pose a query.

I am running four 21" woofers. I don't know many specs... They are 800w RMS, 4.5" voice coil, with a peak excursion of about 1.75". They run on a Crown MacroTech 5000. They are mounted dual opposed, vertically, in phase. Their enclosures are 3/4 Baltic birch laminated with 3/4 MDF sealed. They are H 36" x L 30" x W 30"...

I was talking with my friend, the chief designer of the HE line arrays and my crossover, about cutting the boxes in half and lining the woofers at the front wall of my room along the floor behind the mains. Mike noted that the air coupling of the woofers in their current state reduces mechanical noise, but decoupling them would likely produce a flatter response based on room size and proximity to the "S line" I think he said.

I thoroughly stand by Mike in theory, but I was curious if any of you have gone from coupled to decoupled with all other things remaining equal? If you have, what did you find?

Thanks Gentlemen
Pat
 

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Discussion Starter · #5 ·
Hi Mike. They are a Misco, or Minnesota Speaker Co. make. I don't know the model number. They were developed for PA/road applications. A friend of mine was kind enough to procure them for me. I think they are off the menu.

They have a paper cone and a good sized motor. Can't for the life of me remember how many ounces right now. I'll look later tonight when I get out of school. One thing I haven't tried yet is flipping a wooded per box and reversing the phase. They have such a deep basket that I'm sure that will add significant footage to the enclosures, and it's also supposed to break some kind of linear connection between the magnets...

We'll see.

Oh, also, thanks for the input on the seperate boxes.
 

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Discussion Starter · #7 ·
So I flipped one driver and made sure to reverse the phase. I'm not impressed. I notice a more detailed mid range but it's lost punch on the low end. Watching the cone move at the spider I can see the excursion is much less than I thought. Maybe 3/4".
 

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Discussion Starter · #10 · (Edited)
Graham, yeah, they move more than a quarter inch, but probably less than an inch total.

Mike, I don't think they sound boomy. What is Q .92? Bass guitar sounds like a bass guitar being played through an amp, kick drums are tight. I think they struggle a little with ULF but they can do them. Probably more a matter of the Crown making them. I didn't realize their excursion was so low. Mounted conventionally they "appear" to move well over an inch at times...

Here are some photos. I'm not much for presentation. One day it will all look clean.





 

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Discussion Starter · #11 ·
You are currently running a pair in 15.5 cu.ft for a Q of .92. Do they sound boomy at all?
Mike, while looking for some more robust 21"s I found the B&C 21SW150 21" Subwoofer 4 Ohm. Do you know anything about these drivers?
 

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Discussion Starter · #12 ·
Well, here's my plan. I'm going to get two very good 21s and modify my existing boxes to a precise volume, fortify the bracing, and go with two floor standing, front facing, woofers instead of 4 "okay" drivers in a heavily eq'd boxes. I think the benefits outway the cons.

The B & C drivers look sexy. I'd greatly appreciate any thoughts.
 

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Here's a simulation to show a 3 cu ft dual sealed with 3000 watts and a qtc off 0.7 and a 10 cu ft dual tuned to 30hz with 3000 watts input power. I used the winisd file which was from the downloadable winisd files area.

cheers

Graham
 

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Discussion Starter · #15 ·
The specs look good on the B & C. What volume will you put them in?
Mike, an interesting coincidence is that my existing boxes halved are approximately 6.9 cu ft minus bracing. The B&C's recommended enclosure volume is 6.73 cu ft. Considering how large an investment the material alone for my current boxes was it would be nice to lop them in half and place a cap on the back. BUT, in an experiment last night I tipped one enclosure on its side and AB’d the sound. On its side overall output dropped, the frequency response went from rolling planes to the Himalayas, distortion was far more evident at the listening position, and mechanical noise from my house practically doubled. After I tipped the cabinet back up, my girlfriend who has no experience with sound said: “It’s not just louder, it’s… tighter, you know what I mean?”

Now I know tipping one enclosure doesn’t tell me what will happen if I cut my boxes in half and line them along the front wall, but it is indicating that the down/up firing system I have now is working. Is it ideal? I don’t know, but cutting my boxes in half to find out doesn’t seem worth it.

I talked with a friend last about a couple options:

a. Try different 21”s in the same enclosures, as they are. He pointed me towards AVS Forums and a new 21” design being undertaken there. I was going to check that out today, but the bit I’ve seen on those is limited availability and delays.

b. Modify the enclosures to house Fi 18”s.

I don’t know what to do, Mike, but I appreciate your time.

Thank you
Pat
 

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Discussion Starter · #16 ·
Graham

Thank you so much for running the graph. I know I need to educate myself in the terminology and tools of the trade.

Is qtc the same as q? I don’t know exactly how to explain it, but my understanding is that q is derived by combining properties of the driver (driver only in IB) and the enclosure, and on paper a desirable q is between .5 and .7.
 

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Yes it is indeed. For HT 0.7 is the desired average Q for a sealed sub which leans towards an all round balanced sound. For a lower Qtc expect less mid bass punch and more low end and with a higher qtc expect more mid bass but a boomier sound. Although I have to say my first dual sealed sub had a qtc of 0.95 and once eq'd it sounded great with music and still good for movies although nothing in comparison to when I went ported. I like the port simulation with the B&C driver. I personally think the specs lean much more towards a ported alignment. The Aurosound 18's model really well in a sealed box, much better than the B&C.

http://www.madisoundspeakerstore.co...-ns18-992-4a-18-subwoofer-returning-feb-2012/

It is really expensive though but a cracking driver.

The new mach audio 21" driver could be an idea worth thinking about if they come out.

The other option would be a dual FI SP4 15 cu ft sealed with 4000 watts. Attached is a pic to show the FI and aurosound driver also in a 15 cu ft with 1600 watts.

What is your budget on this.

cheers
Graham
 

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Discussion Starter · #18 ·
The Fi certainly has garnered a lot of respect in the community. I'm not finding prices :/

I could modify my boxes to house 18s and run 4 of them… Is the Mach Audio 21” limited in availability? Four Fi 18s are starting to sound appealing.

I’d like to stay under $2000 for drivers if possible.

Thank you for the feedback, Graham
 
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