8ft long SUB w/ 4-18" Obsidian/SI drivers

16hz lover

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Aug 2, 2013
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I wanted to show my new 8 foot long subwoofer I recently built using 4 of the Obsidian 18" drivers for my Great room system. I have a 110" diagonal projection screen that is 8 foot wide so I designed the subwoofer to fit under the screen and look like a piece of furniture and have a high WAF factor. This is what it looked like with just the screen on the 20 foot wide wall.


I built it in two pieces in case I needed to break it down in the future to move it.



I used a 8 foot long and 25" deep walnut butcher block top and used those dimensions as the basis for the rest of the cabinet, going with a ported design tuned to 20hz for each 4 foot long cabinet
I went with the Watco Danish Oil to end up with a low sheen to prevent reflections under the screen. I used matching walnut corner pieces and then thought the ends would look nice with black mirrored plexiglas. I wanted to have a one piece front grille and used some c-shaped aluminum channel for the grille frame.




I'll use a second post for more pictures
 

16hz lover

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Aug 2, 2013
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Here are the drivers installed


And in it's final resting spot with the grille in place which is held on by two support bars under it, and neo magnets to hold it to the main cabinet.



The Clements RT-7 speakers are ready for their new grilles so they are naked in this picture. I have two pairs of them and usually have them stacked, but will be moving them into the bedroom system soon as I will be getting bigger speakers to keep up with the sub in the near future.


I have large amounts of deep tight accurate bass now, and even at 120db peaks, the drivers are only moving about 3/4" so far. They are capable of 3" of travel. I also will be swapping them out with the Stereo Integrity 18" Home Theatre drivers to see what the difference is in SQ and SPL. I've tried many subs through the years and the Obsidian and SI drivers are the best sounding and best value out there. Let me know what you think about it. My wife loves the looks of it. I'm working on buying my Magneplanar Tympani IVa speakers back from the guy I sold them to as she also likes the looks of those the best of all the speakers I've owned through the years. That setup with the sub should give me the huge front soundstage with prodigous deep tight bass. I didn't have a powerful amp when I owned the Maggies before but now have a Cinepro 6 channel amp that will really make the Maggies sing.
 

LL21

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Dec 26, 2010
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WOW...fun toy! Curious as to the interaction between such a massive sub and your wooden floor. is it wood cabinet on wood floor, or are their isolation/cones/dampers in between?
 

cjfrbw

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Apr 20, 2010
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AwRite! Wall of Sound!
 

16hz lover

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Aug 2, 2013
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Wow, can I come to your place and watch few Blu-ray flicks; 'Tron Legacy' 3D among them? :b

Where are you by the way?

I'm in North Carolina, near Charlotte
 

16hz lover

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Aug 2, 2013
234
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WOW...fun toy! Curious as to the interaction between such a massive sub and your wooden floor. is it wood cabinet on wood floor, or are their isolation/cones/dampers in between?

well....I had a gray flannel moving blanket under it to get it into place and not mark up the floor. We tried initially to lift the sub on one end to get the blanket out and couldn't....haha, so it is what the sub is on. The sub is so well built and heavy that there is no real vibration problem on the floor or the cabinet, and the drivers barely move even when cranked way up since the signal is distributed amongst the 4 drivers.
 

16hz lover

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Aug 2, 2013
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Nice looking build. What are you using to crossover/eq that beast with the main speakers?

I just sold the Dynacord L2400 amp (3000 watts) that I was using to power the subs, so I was using the subwoofer crossover in the HT receiver and going straight to the amp. I'm going to be buying a new amp which will have DSP processing and crossovers in it and will use those functions to cross the sub over at 60 hz with a 48db slope. The big Tympani IVa speakers have great response and lots of surface area to handle all the midbass down to the 60hz crossover in the preamp section as well, and be well protected from doing any damaging duty below that frequency. The overlap should give me lots of slam in the important percussion range( I'm a former drummer so I want that "on the throne" feel). And as a backup, I have some horn loaded cabinets with (2) 15" drivers in them per side that are 105db efficient in case the Maggies don't cut it when I audition them before buying them.;)
 

LL21

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Dec 26, 2010
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well....I had a gray flannel moving blanket under it to get it into place and not mark up the floor. We tried initially to lift the sub on one end to get the blanket out and couldn't....haha, so it is what the sub is on. The sub is so well built and heavy that there is no real vibration problem on the floor or the cabinet, and the drivers barely move even when cranked way up since the signal is distributed amongst the 4 drivers.

Interesting. Do you think the bass is transferring to the floor?
 

JonFo

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Jun 11, 2010
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Nice build!

Are you looking at the Crown XTi's for the sub amp? they seem to have a nice range of power choices and good DSP implementations on-board.
I've been considering getting one for my IB sub.
 

mep

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Apr 20, 2010
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Interesting. Do you think the bass is transferring to the floor?

I bet it is. I think he needs at least 50 Stillpoints Ultra 5 isolation devices at $700 each in order to decouple the massive woofer enclosure(s) from the floor.
 

16hz lover

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Aug 2, 2013
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No transfer of vibration to the floor that you can feel. It is a laminate floor with a hard foam backing for noise isolation which is eventually over a crawl space. I actually wanted the floor to shake and vibrate my feet, but no such luck..lol. I'm not going to put any type of feet under it with the laminate flooring, as it's still basic mdf based material. Right now the weight is distributed over a large area under the box. Again, I've got shitloads of bass output already so there's no concern with coupling or decoupling factors.

So far I'm leaning towards the Behringer iNuke series, the 6000 watt model with DSP for 399.00. Been reading up on them on the other forums and they are slightly over rated on their power ratings, but I am not that critical whether or not they are off 10% when I've got that much wattage on tap anyway. I'm going to be swapping out the Obsidian drivers soon with the Stereo Integrity HT woofers and will have a nice even 4 ohm load per side for the amp, which will put about 1200 watts per woofer even with a 20% factor of loss for the Behringer amp original rating. I had the gain on the Dynacord amp set at 1/2.
 
Last edited:

zztop7

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SMART, Intelligent, common sense

"I built it in two pieces in case I needed to break it down in the future to move it."

SMART, Intelligent, common sense being.

Question: are you an Earthling or a visitor from an advanced culture?

zz
 

DonH50

Member Sponsor & WBF Technical Expert
Jun 22, 2010
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That is an awesome project! Curious, why 20 Hz and not lower? Drivers wouldn't support it, or just drew the line there?

Integrating with the Maggies (or any other speaker) requires careful phase-matching at the crossover point, which I am sure you know but bringing it up in case someone thinks just a crossover is enough (well, ok, depends on the crossover and preamp/AVR, but you need to be able to adjust phase someplace in the system).
 

NorthStar

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mojave

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Oct 29, 2010
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That is an awesome project! Curious, why 20 Hz and not lower? Drivers wouldn't support it, or just drew the line there?
I just modeled it and changing the tune from 20 Hz to 15 Hz with the Stereo Integrity drivers requires a cabinet about twice as big to maintain the same transfer function. If trying to keep a smaller size box and lower the tune frequency, then it involves a much more complicated slot vent since the vent length increases.
 

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