# Build: DC Gold N7R Steel Enclosure



## Chester (Feb 19, 2007)

Hey, this is a project I started on ... well ever since I was 12 years old and really got into sound... I am 20 now so along the way I have learned tons. I actually began buying things for this project around 2 months ago however this is the culmination of 8 years of research. There is a reason behind nearly every feature of these speakers (and my entire system for that matter).








Here are the pictures of the build! http://picasaweb.google.com/Chesteta/N7RBuild#
-more pictures will be coming soon, I have misplaced the pre-plasma cutting and pre-Line-X photos, the pictures in the thread are some of the pictures from the Picasa web album.

The speakers are DC Gold Audio N7R's, ~93db/w/m, full range speakers; what I believe are some of the best full-range speakers out there, Neodymium magnets, ferro-fluid, no spider, aluminum and beryllium cone (with a coating), the grills also act as phase plugs. If you have heard of "Babb" speakers, these are made by the guy who bought out Babb... http://www.dcgoldaudio.com/

















The encosures are steel Flotec well pressure tanks, model FP7105 (6 gallons per tank), pressure tested to 100 psi http://www.flotecpump.com/

The tanks are coated with Line-X (polyurethane) http://www.linex.com/









The insides are coated with 3M Undercoating (to dampen the steel)









Then I added 2" thick rock-wool 'tightly' which REALLY deadens the steel, knocking on them sounds like hitting on a board of MDF but with a bit higher resonance frequency.









I used microfiber cloths to keep any rock-wool 'dust' out of the ferro-fluid used by the speakers.









8 AWG wire with soldered connections, and my 'signature' bolt terminals.

















The speakers are decoupled from the enclosures with silicone 'gaskets' (Mounted from the back)

















I'd love to hear your thoughts


----------



## StereoClarity (Apr 22, 2008)

What exactly is going on in this picture? What is that on the back of the speaker?



>


----------



## Chester (Feb 19, 2007)

It is a bracket... I don't think it is shown, but in the finished speaker, there is a hole drilled in the center of the back of the enclosure, a bolt and washer then go on the rod that is sticking up. Basically it pulls the speaker onto the front from the back, part of the decoupling system. 

EDIT: the 'frame' is made of aluminum and superglue (for magnetic reasons), the 'rod' is just steel rod... check out the picasa web album for some better pics of that stuff http://picasaweb.google.com/Chesteta/N7RBuild#


----------



## Ricci (May 23, 2007)

Interesting. I'm not so sure about the effects of the rod mounting system decoupling it from the enclosure, but who knows. How do you like the sound? I assume that you'll be building a pair of stands for them, or maybe already did since the enclosures are round?


----------



## Chester (Feb 19, 2007)

Thanks for the feedback, the rod system is loosely modeled after B&W speakers' decoupling system: the sound is incredible, they are very clear even at loud volumes  I am currently using cinder blocks as stands with rags (soon to be nice towels) help hold them centered on the blocks, I'll get some more pics up soon to show you...

EDIT/ADDITION: I have been considering using green glue instead of silicone as the decoupling material, it is a viscoelastic material which converts energy into heat, the only 'issue' is that it never completely sets, stays in a sticky tacky consistency, so I am not sure if I can keep it from oozing out around the speaker... in any case, the green glue company uses a thickness of .5 mm in their tests so it may be possible... Probably going to order a tube and test the consistency out 
http://www.greengluecompany.com/

EDIT2: looking around a bit more, I may use a product called "sorbothane", it appears to be a better option because I can get a gasket made to a spec instead of trying to mold one  I would definitely appreciate any advice/experience regarding sorbothane
http://www.sorbothane.com/


----------



## Owen Bartley (Oct 18, 2006)

Looks like a very unique project Matt, and I bet they would look really nice on some custom stands. Are you just building the pair, or do you have any plans for a surround setup? A sonosub would seem to go nicely with these too.


----------



## Chester (Feb 19, 2007)

Thanks OJ, I may go the 'custom stand' route someday but for now the cinder blocks are working quite nicely, they make good shelves also  I also am just rockin' a pair of speakers... It is my belief that a pair of *properly positioned* speakers is all you really need... I have things set up quite well where I can hear sounds to my sides and 'behind' me (if they were recorded to produce that effect). Maybe someday I will run 5.1 but right now this is all in my bedroom so 2 channels is just fine. I am currently running a JL 13w7 sub with dual passive radiators: the -3db mark is at ~14 hz  I built the sub a while ago however I will probably post some of my build pics soon. Everything is powered by (2) crown K2 amps running through a USM-810 processor/mixer; the amps are 'separated' on a per channel basis, so one amp does all the left channel (bass and high) and the other does the same; this seems to run much cooler temperature wise and also alleviates issues with the power saving feature (it can take a 1/10 of a sec for the amp to engage so if there is no bass for a while there is a delay before the sub kicks in if the amps are separated by highs and lows)

EDIT/addition: I also run all the audio 'balanced' from my computer to the speakers, even with the amp gains all the way up there is just a slight hiss with your ear near the speaker 
-this is all hooked up to my computer btw; using an audigy 2 zs with kx drivers to get a balanced output; i have 2 + weeks of music on my network drive


----------



## harleyhualer-sc02 (May 25, 2008)

Nice build. I thought I was the only one who knew about DC Gold on here. I plan to build a 7.1 system withe the n7r's soon,have to get my subs done 1st.


----------



## Chester (Feb 19, 2007)

just got the sorbothane  cutting it now (to replace the silicone)


----------



## Chester (Feb 19, 2007)

*Updated Pics*

I redesigned the rear mounting system; I could not 'wrench' down on the sorbothane as much as I wanted without the silicone failing around the magnet so I decided to do a steel approach using what the home depot calls clothing line hooks:








The black ring around the magnet is a vacuum belt cut in half (half the width) which helps keep the clothing line hooks aligned and also aids in aligning the aluminum ring; I used electrical tape to cover the hooks so there would not be metal on metal with the basket, also to keep from shorting anything around the electrical terminals.
















One change I may make would be a better decoupling on the back side; since there is so much more sorbothane surface area on the front of the speakers, the back side 'squashes' quite a bit (not shown well in this pic, I have since tightened them more)








































My computer and USM-810 processor in the closet, the only moving part on this system is the one fan on the computer, soon to be changed to a better solution; the buzzing of the cold cathode tube on my screen is all I can hear at my desk though  I hope to get an LED backlit LCD TV which should produce no noise...
















Here is the cut sorbothane sheet I used; since this project I have used the sorbothane to decouple my RTA-M mic from a stand I made out of a broken clothing rack... thats for another post though 









Sometime soon I will post the near-field measurements of the speakers...


----------



## Yad (Oct 19, 2009)

Bravo! Good job! Original construction!


----------



## tcarcio (Jun 27, 2007)

Very Cool, I love out of the norm builds...:T


----------



## evilskillit (Oct 7, 2008)

Looks pretty cool. Very interesting idea for an enclosure.


----------



## yourgrandma (Oct 29, 2007)

Nice work.


----------



## Yad (Oct 19, 2009)

Matt, why did you choose such unusual type of the driver's mount ?


----------



## Chester (Feb 19, 2007)

I used the unusual mounting system in an attempt to decouple the vibrations in the basket and mounting flange from the enclosure; according to basic physics, f=ma, if the speaker cone is moved out 1 mm, the basket, magnet, etc will be moved in the opposite direction at (1mm)*(speakers's Mms)/(mass of basket+magnet+etc.); to keep the vibrations isolated from the walls of the enclosure I used sorbothane (a visco-elastic polyurethane rubber)

http://www.linkwitzlab.com/Driver Decoupling.doc
This document should both explain the concept a bit better and also show some measurements done (not my work there, that document just inspired me to decouple my speaker)


----------



## Yad (Oct 19, 2009)

wow! reasonable choice! 
by the same reason i usually make very heavy boxes (closely to 1000 times harder than mooving mass of driver) e.g. for 50 grams of Mms (LF scanspaek) i make 50 Kg enclosure. 

Matt, i'm sure that you really enjoy with your construction! I would like to try that too' cause i've never heard such unusual boxes. :thumb: 
oh, i did not understand your drivers. A re they wide-range, or 2 way ?


----------



## Chester (Feb 19, 2007)

Yes; they sound amazing 

They are full-range speakers; so there is one voice coil per channel (not including the sub), crossed over at 80 hz; the speaker cone is an aluminum/beryllium hybrid *(not an Al/Be alloy, the aluminum is a piece, and the beryllium is also a piece) coated with a special epoxy coating (on the cone) that is a sort of closed cell foam. Check out http://www.dcgold.com, they are the N7r model.

EDIT/addition: The speaker transducers are quite efficient (~93db/w), they use a neodymium magnet, have a 'shorting ring' to reduce the inductance (helping the high frequency response), there is also no spider in the transducers; they are centered using ferro-fluid, which also aids in cooling the voice coil. Lastly, the grills are engineered to be phase plugs, they 'dip' into the center of the speaker (so the center of the grill is near the 'dust-cap' area, theses speakers do not have traditional dust-caps due to the foamed epoxy coating, there is no way to remove the dust cap without destroying the cone)


----------



## Chester (Feb 19, 2007)

*A few new ideas/updates*

I have made a few changes to the speakers; a new sorbothane system in the back utilizing larger diameter (2" dia.) washers, I drilled out the area where the rod comes through in the back more so there is a 1/2" diameter hole for the 1/4" diameter rod to go through (this is to ensure that the rod does not touch the steel enclosure, transferring vibration). I have also done a little more calculation regarding the amount of compression/torque put on the whole sorbothane system. Lastly, I put some guides on the top of the speakers to help with alignment for different seating positions. Using a laser level to aim the speakers at the listening position only takes ~30 sec, and with the guides on the top I am sure they are aimed exactly where I want them now 

The three marks are the three points I measured (and averaged) to find the thickness of the initial and compressed sorbothane states (using a digital calipers) to measure the thicknesses (calipers accurate to .01 mm however I got the average for the 3 points within ~.01 mm also). Using the sorbothane design calculator, I found that the difference of .01mm in the rear disc is equivalent to approximately 0.3 lbs difference in force (when near 20% displacement since it is a non-linear material). The overall force pulling the speaker into the enclosure is 392 lbs of force. The resonant frequency of the rear disc should be 24 hz, given a 100 hz signal (the maximum the sorbothane calculator allows, could use their equations to go higher) there is ~83% isolation (17% signal energy is transmitted), which corrisponds to around a 15 db reduction (used the calculator here:http://www.sengpielaudio.com/calculator-thd.htm) from the isolated speaker side to the enclosure, at 80 hz (x-over frequency) there is a 12 db reduction. The higher the frequency (the further from the resonant frequency of the sorbothane) the greater the isolation.








According to the sorbothane company, it dampens vibrations best under 10-20% compression so I shot for 20% on the rear, the front is a bit more difficult because of the shape of the speaker baffle (the metal rim that is visible on the front) and also the shape of the speaker enclosure (there is a 'high point' where it meets the speaker and then it tapers off to the sides of the enclosure) so I am not quite sure how much surface area is being compressed; a 'worst case scenario' (the entire ring is compressed evenly) given the already calculated force of 392 lbs gives a 12.58% deflection (within range!) and a resonant frequency of 34 hz, at 80 hz, there is a 6.6 db reduction in signal transfer from the speaker to the enclosure (remember, this is the worst case scenario), at 100 hz it is 10 db down... the best case scenario (to which I presume is closer to reality) was determined by slideing a sheet of paper into the gap between the curved speaker enclosure and the sorbothane; I determined that an outer diameter of 6.7" is actually in contact with the enclosure, the inner diameter is 6.23", presuming this number is correct, the deflection becomes 85 percent with the given amount of pressure (which seems unlikely since I have disassembled the system and the sorbothane rings return to normal shape, I would not think 85% deflection would be 'recoverable'). Anyways, it is probably somewhere inbetween, however even with a worst case model, a 10 db reduction in signal transfer at 100 hz is pretty good 








Here is the laser leveler that I use to aim the speakers, this picture was taken before I put the guide tape on the top 
















I have also put a blanket on my desk for the time being, till I find a better solution, to help reduce the reflection off the desk when sitting at it and listening to tunes  it is also nice for resting my arms on when typing rather than the glass edge which left marks on my arms...








Here is my method for creating an alignment system, I used a drywall square mounted flush against the frame of the speaker (the outer metal ring of the speaker). Then I laid a strip of masking tape along the edge; against that masking tape (which does not stick well to the Line-X) I placed pieces of electrical tape, the center line (between the two pieces) is the line the laser is pointed down. using the welded seam as a reference, I determined that the right speaker is 0.995 degrees offset from being perfectly aligned and the left is off 1.55 degrees... however since the square should find what is on axis for the speaker, the angle 'correction' is built into the line of electrical tape.

















Ideas or suggestions for improvements are more than welcome  I want to do some 'knock on the side of the enclosure' tests to show how acousticly dead they are but other than that I am not sure what else will help others with their projects. I should note that the sorbothane calculations were done using the "Sorbothane Design Guide" software available free at www.sorbothane.com


----------



## critofur (Aug 25, 2009)

Chester said:


> ...I would definitely appreciate any advice/experience regarding sorbothane
> http://www.sorbothane.com/


Sorbothane gaskets will be good for your application.

Have you taken measurements yet? 

I think it would be better to mount the speakers off-center, unless you're using a DSP or other type of filter to correct the frequency response effect that mounting a driver in the center of a circle will have (all equi-distant edges...)

If you could, do me a favor, and listen to the speakers mounted "backwards" so that you see the back of the cone from the side ( 90 degree angle ) - that is, if you are curious, and it would be something you're willing to try. In case you do that, they should be about at ear height, or slightly below.

Oh - I see you have an SGI VW monitor, cool, I worked at SGI when those came out.


----------



## Chester (Feb 19, 2007)

I wish I could have had your input before I got the sorbothane  It's all good though; I have taken measurements, however I need to take some new ones now that I have a better system figured out for compressing the sorbothane.

I see what you mean about offsetting the speaker in the enclosure; do you have any system or specific way you would have gone about doing so? (they are steel and pretty much 'finished' so I am not going to re-do them but I am interested to hear what you would have done differently, and the reasoning behind it)

I am using DSP filters though, up to 64 parametric eq's per channel... so I think I am covered 

I did (before I built the speakers) listen to the 'rear' pressure wave of the speakers; it sounds pretty much exactly like the sound coming from the front  I played them without enclosures (just sitting on the cinder blocks) till I made the 'tanks'.

I love the 1600 SW  I may sometime move to an LED backlit tv (40") but the 1600 SW has been running strong for 7+ years I believe (it has been a long time...)


----------



## Synthsayer (Dec 19, 2007)

Hey Chester, 
This is a really impressive project.

I first heard about people using full range speakers on a visit to Santa Cruz, CA about 10 years ago. A friend took me to a local shop that was a JBL Pro dealer. We listened to a pair of 8" full range drivers that may have had a 'whizer' cone. I couldn't believe a single driver could sound so good.

I love the idea of using the metal cylinders. I looked and looked for 12" PVC but could never find anybody locally that I could get just a couple of short pieces from.

It seems we think alike as far as damping the enclosure. The 3M material should do very well. The Sorbothane material is great. I used to have a record mat made from it on my old Linn Sondek LP12 turntable.

I can't see anything I would do differently. They look great and I bet they sound just as good.

I'm going to upload a few photos so you can see the systems I have been working on.


----------



## Chester (Feb 19, 2007)

Hey thanks, I actually made a different set of speakers out of PVC, they are an older project but I will probably get around to posting the pics sometime soon. They were made out of PVC sewer pipe, so any new building installations or city construction work may have some scraps you could get for free; I got my pipe from construction workers after they were done doing some work at my school... it was new pipe, I wouldn't use the old stuff  I got my pieces of pipe for free to later find out that the stuff is actually wicked expensive (like near $1k for a 20 foot section of it if i remember correctly)

I am interested to see your projects


----------



## Chester (Feb 19, 2007)

Some updates:
-The transducers were rebuilt a year or two ago by DC Gold, updated with new voice coil former (kapton instead of aluminum), and some other improvements to the transducers I am told 
-I am now using a piece of 28 awg enameled wire and two neodymium magnets to hold the grilles on.
-New speaker stands, minimal diffraction from stands now, and more floor space!


----------

