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Discussion Starter · #1 ·
So... I started building this a while back and progress has been real slow - and I've only had a chance to touch it here and there. I've definitely spent more time modeling it and thinking about it - than actually working on it. I bought a pair of Electrovoice EVX-180B drivers a while back (used) - and I've had this interest in high sensitivity drivers for the last few months - so I decided to try a build with them. The excursion is low (6.4mm xmax, 25mm xlim). Each driver is 8 ohms, so wired in parallel is 4 ohms. I have 2 EP4000s, one is driving a Tempest-X and one is driving a Maelstrom-X 18" -- so I need to decide what I want to do... maybe buy another EP4000.

I'll post some graphs tomorrow.

It's about 18cuft in total internal volume, when you subtract driver volume (about .4 cuft), bracing and the port volume, it's closer to 16cuft. Overall dimensions are big: 4ft wide, 2 ft tall and about 31.5" deep. Built entirely of 3/4" MDF. Port is 22.5" x 4". Tuning comes out to about 25hz (plus or minus a couple tenths of a hz depending on how well my internal volume calculations are - taking into account bracing). I'm mounting the drivers with 1/4" Hurricane nuts from Parts Express. They're actually already installed, I tried a little bit of superglue to help really seat them. I don't know if it helps or not.

I plan on rounding the port a little bit at some point - just need to shell out for some new router bits. Port velocities are VERY low. Probably lower than they need to be.

Tuning according to PDFs on commercial enclosures w/similar dimensions tuned to 25 yield a F3 of 24 hz. In the modeling that I've done in WinISD - it doesn't come out that pretty......but regardless you get substantial SPL levels for a fraction of the wattage needed for typical sub drivers. Edit: I remembered that the published F3 is WITH EQ. Electovoice recommends a HPF at 29hz and a 6db boost at 20hz. I've always read to be careful when boosting. 6db is a BIG boost. Anyone have any thoughts on that? Is 6db OK - if you have an overpowered amp?

The shell of it (no bracing or lining installed yet)


The slot port clamped and drying... with the 2 EV drivers sitting in there for scale..


I have a false wall in my HT room, with the speakers hidden behind it. I have a 8cuft sealed w/an 18" Tempest hiding back there... and I plan to hide this there too.

Going to coat in duratex eventually... likely when the weather gets WARMER.
 

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Discussion Starter · #2 ·
SPL w/high pass @29hz (Q of 2, I believe this is 2nd order) and 6db boost @ 20hz (Q of 2). Running with 300 watts.

SPL comparison of my dual EVX180 build (300 watts)- vs a Maelstrom-X 18" in a sealed 10cuft w/*2000* watts. Not bad!
Cone Excursion w/high pass @29hz and 6db boost @ 20hz
Port velocity in M/s.

Other interesting graphs:
Cone Excursion w/no EQ or filters - the need for a HPF is obvious.
SPL with no EQ. (Not realistic because of need for HPF)
 

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With a combination off room gain and Audyssey you may not need any boost. I find in my room my bottom end once I have run Audyssey boosts my bottom end up by 7db down low.

I would wait and see what you get when you get it up and running.

Also if you need to apply any extra EQ and depending on your room response you may find you have to apply cuts to remove peak which will help you apply some boost.

My dual sealed sub I applied 12db off boost on the bottom end and never had any clipping off my EP4000 amp which was bridged into 4 ohms. I did make a fair amount off cuts.

cheers

Graham
 

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Discussion Starter · #4 ·
I TOTALLY forgot about room gain when thinking about calculations.. I don't have any graphs handy, but for better or worse - I have a lot of room gain in my 10ftx20ft HT room. Didn't think to account for what Audyssey would do as well. It's been a little while since I've done REW sweeps.

I already remember having a couple nasty peaks in the room -- running a BFD1124 right now -- and makes a big difference.

Wow, 12db boost? that's substantial, good to know.

I like the EP4000 - because it always has more than enough power for my needs.

Thanks for your input.
 

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Me too but I wonder if it boosts the bottom end to flatten out the response. Dynamic EQ adds even more to my bottom. I did think that it was room gain alone but as there is more boost low down with Dynamic EQ over Multi-EQ it makes me wonder if Audyssey actually has some effect.

cheers

Graham
 

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Discussion Starter · #12 ·
I temporarily closed it up - just to play.

I kept having to turn it down... Have you ever heard pink noise at 90db?? haha. Yuck!
Hit 95 a couple times - while trying to keep it down..

Looking forward to getting the bracing in there and getting it closed up.

Need to grab one of my test DVDs and see how some sine waves sound.. Every time I listen to something - I underestimate how much content is above 80hz!

I have a Symetrix 551E with an adjustable low cut filter w/5band PEQ going to use as HPF for now.
 

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Discussion Starter · #13 ·
Whelp.

Bracing in: FIberglass in:

Forgot how mediocre my cell phone pictures are. 8MP of mediocrity! :)

I put the last panel on... and the glue is busy drying/curing..

I used insulation grade fiberglass. I got sick of reading all the wharrrrgarbl about the health risks. I wanted to see for myself if fiber shedding was in fact a problem. From what I understand, newer fiberglass is manufactured with a continuous strand manufacturing process - so pieces of it don't magically fly off. I guess I'll get to see for myself. It's going to sit behind a false wall covered with a screen and GOM fabric. I think that the errant MDF dust I have around is probably much more of a risk.

Lessons learned (or relearned):
1. It takes a little manhandling to work with a 120 lb box! It actually might be closer to 150lbs, since it's 2 sheets of 3/4" MDF - which I believe are around 90 lbs each. So, 180lbs minus driver cutouts and bracing cut outs, etc).......and drivers are another 60lbs!! So it'll be about 180lbs finished. OUCH!
2. Using R13 fiberglass isn't worth it. Too much effort to install (I stapled to install and compress). It's just a hassle to work with. In retrospect, I would have used proper rigid fiberglass - that holds it's shape and density.
3. Although polyurethane glue works great - it's also not that exciting to work with. I learned from a previous project that it can indeed stick to your hands for a week. :) I prefer it over wood glue for some joints because it expands a little to seal cracks.
4. I hate my bracing. I've always hated cutting bracing and I always overthink it - but I think if I could do it over, I'd do 1ftx1ft bracing. I'm not really worried about vibrations - as the thing is a tank... but if it was sealed, I'd likely have problems with walls flexing.
5. I wish I hate more clamps! And although Harbor Freight clamps are cheap - you get what you pay for. I knew that before - but seem to forget it.

So left to do:
1. Install and wire drivers. I'm planning on installing a Neutrick Speakon connector later - need to order more. If you haven't used Neutrik Speakon connectors - they're pretty sweet! Not pricey, rugged and convenient. PE carries them)
2. Probably in spring: Sand and primer box, cover with duratex or some other durable coating.

Things I feel I did right:
1. Getting better about getting accurate cuts with a circular saw. I have a table saw - but max with is 12" which basically makes it useless.
2. It's very square -- you'd be surprised how crooked you *could* make a 4'x8'x31" box.
3. Bought a plunge router and Jasper 200/400 jigs - I like my driver holes!
4. Based on initial testing - sounds excellent!
5. Despite the fact that they are pro-audio/cinema drivers - they model pretty well.
6. I bought a $30 planer from Harbor Freight - works well for tweaking fitment to get things fitting tight. Someday I'll have a real jointer...
7. Ran a box fan with a 24x24 air filter - does wonders for clearing the air of MDF dust.

Probably going to build a second cabinet - and take lessons learned... to make a better cabinet and "make it better" than this attempt.
Better bracing and using OC705 are definitely the 2 big issues I'd do differently.

Suggestions and constructive criticism are welcome!
 

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Hi there,

This is how i do my bracing but with two drivers I would have put 3 horizontal bracing and 1 vertical bracing.

I know what you mean about heavy boxes etc.. the dual sealed sub I mentioned yesterday with drivers weighed over 300lbs. Took 3 men to lift and was all out off 1" thick mdf. Didn't do that again.

Be interesting to see your results and how it sounds with music.

I modelled those drivers in a 24 cu ft box tuned to 25hz and it looked pretty good.

cheers

Graham
 

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Discussion Starter · #16 ·
Do you guys ever sleep??

Thanks for the pic Graham. I think that next time I'll do some more planning to come up with more elegant and functional bracing. Your bracing looks nice! In fact, whenever I look at others' bracing it always looks good... Heh.

Couple questions for you:
1. Where did you get the foam?
2. What are your thoughts about 1' MDF? Better than 3/4"? Or too heavy?

I chose not to recess the drivers on the front baffle - mostly due to weight. In retrospect, I would have recessed -- so that way I'd have the double-thick baffle -- and it would be more rigid. At least on the positive side, these are relatively light drivers. I just got a pair of AE TD12S that weigh almost as much!!

I'll see if I can play some music later today -- and do some REW sweeps. The glue should be in good shape by this afternoon, I think (I hope).

What's the vote for building a 24cuft box??? :neener::hsd:
 

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I live here in the UK so its 1.30pm in the afternoon at the moment.

There are different views on whether egg crate foam actually helps with resonances or not. I haven't tested it with and without. I haven't felt anything out off the ordinary with it in.

I wouldn't use 1" thick wood again unless it was for a smallish sealed sub. 3/4" mdf or BB all the way and with good enough bracing spread out evenly and not too wide apart you cant go wrong. Some people query whether you need that amount off bracing or not. For me I would rather have it in there than not as an extra brace won't effect internal volume at all.

Here's your comparison for the 16 cu ft tuned to 29hz and the 24 cu ft tuned to 25hz. Both have 2nd order hpf set without going over max excursion.

You may find that with room gain you might end up with the graph which is for the 24 cu ft box. In that case happy days. As you have already built one, I would run some graphs on that first. 24 cu ft is a big box.

Looking forward to the graphs.

cheers

Graham
 

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Discussion Starter · #18 ·
Not much time today - but got drivers installed.

Initial REW results are attached. Graph is with 1/3rd octave smoothing..

First run I forgot to bypass BFD DSP1124.... This is with a first order HPF close to 25. I have a Symetrix 551E - and unfortunately doesn't give as much flexibility as I like. I originally bought it because it could boost below 20hz - which I wanted to try.

The graph, unfortunately, still has Audyssey enabled. I forgot to bypass that and ran out of time to rerun sweeps.

Sub is not in final position, it was close to middle room - so I bet that results will be quite different when I have it tucked away.

I'll rerun REW and get some picture. Will probably be tomorrow..

Tried some music with it. I couldn't decide if I was happy with it or not. I thought maybe it sounded a little boomy - but could have also been the music I had. Since its a HT system in the basement, rarely play much music down there. I've read a number of posts that suggest that sealed systems "sound" better for music. I'm sure there's some explanation.. but my brain is turned off right now. :coocoo:
 

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