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SI 18 D4 Linkwitz!

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18 d4 linkwitz
31K views 72 replies 16 participants last post by  Quaddragon 
#1 ·
I jumped on the closeout deal for the Stereo Integrity 18", it was too good of a deal to pass up. I am going to use a D4 and an inuke NU3000DSP to implement a Linkwitz Transform (LT) to reach down low. The box is being aimed for 4cuft net, which will put it near Qtc of 0.7. Some fill will be added to lower it a hair from there. There will be enough amp power for if I ever want to add a second in the future.

Trying an f0 for the LT of 25Hz it looks like it will do really well, f3 of 26Hz, -6dB at 20Hz and -10db at 16Hz. Without the LT in place it will handle all the power of the NU3000 at 8Ω bridged.

The MDF is 3/4" and bracing will tie in all sides of the box. I decided to go for the third donut layer on the baffle so that the driver and surround will be almost completely protected. The alternative I wanted to try would have been rear mounting the driver, but it seemed like it would have too many complications.
 

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#3 ·
I don't have the time, space, or equipment to make the box myself so I hired a professional box builder to make it for me :bigsmile: Here are his pics, construction is mostly complete sans the driver cutout and finishing. The finish will be black Duratex, which has a nice texture to it. His techniques and attention to detail are impossible to beat for the price, I won't advertise his company name per forum rules but anyone in the area who's interested let me know in a PM.
 

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#7 ·
His start point was $200, with extras costing more from there. And yeah I am very happy so far based on the pictures! The driver should show up later this week, along with a speakon connector and some Acoustastuf. I have a quiet fan and heatsinks coming in as well to mod the NU3000 with. Can't wait!
 
#8 ·
I'm Watching closly to this thread, Very nice build. I'm doing a build very close to this. want to use the inuke NU3000DSP and also pair it with 18" sub, is that SI a nice sub? My box is much bigger started with almost 11ft^3 but will be much smaller inside after displacment, with big sloted port. keep posting stats and photos:T
 
#9 ·
Thanks.

Here are some more plots, with and without the Linkwitz Transform enabled and with power adjusted accordingly. It seems like 1000-1200W would be a good range to set the limiter on the inuke DSP.

The driver shows up tomorrow, I plan to run some break-in noise on it and then measure it's true T/S params with my WT3. The box is also almost finished. Amp, fan, and heatsinks show up next week :bigsmile:
 

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#10 ·
Here's a wacky approach using a wide PEQ band and the Linkwitz to flatten the overall response further, f3: 23Hz, -6dB at 17.5Hz and -10dB at 13Hz! :dumbcrazy: I don't know if I will try it or not, just an idea. The flexibility of the DSP makes it all too easy to whip up.
 

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#11 ·
looking good, let us know how the nu3000 powers that sub, I put in for a custom build quote on an 18" from PSI, should hear back soon. I may need to go with the nu6000 if i get that power hungry sub. but would rather stick with nu3000 if it can push it.
 
#13 ·
Please post pics of where you place the heatsinks if you can, I my have to do the same modification. I have a bunch of heatsinks of different size from computer Mod days. I even have water cooling stuff, BUT not going there. Plus it's just cool to know and learn.
PS: The sub is Nice:T
 
#14 ·
That PSI looks like a job for an iNuke 6000 at the minimum. The iNuke 3000 only lasted one day powering my B&C 21" sub. It only puts out about 2kW @ 4 ohms bridged anyway. The sub actually caused the amp to shut down. I will admit it was a 10Hz sine wave test but the fan was kicking into overdrive before I could get the sine high enough to measure peak SPL. This has never happened before, either with the 3x15" TC Sounds system or others. Class D just ain't my thing, and the iNuke 3000 will be my last experience with one. It's back to class H for me. YMMV.
 
#15 ·
The specs of the NU3000dsp are just right for the SI 18, or pair of SI 18s, especially considering confirmed bench test ratings. Killing an amp trying to get a max SPL rating with a 10Hz sine wave isn't really a representative test of HT or music use :duh: The price is right so hopefully it does me well!

Here are the T/S results of my 18 D4 using WT3/DATS after running a break-in tone all day, series and parallel. Didn't go to the trouble of measuring Vas.
 

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#16 · (Edited)
Well lets be honest, the iNuke 3000 puts out nowhere near 3000 Watts bridged and certainly a lot less between 10 and 20 Hz...Nope...does not happen. It will surely be fine for the SI's but as I mentioned in the post, the PSI subs mentioned above are a different story. I'm sorry but the iNuke is just not an amplifier that can be driven hard, at least compared to other more robust offerings. I do sine wave testing to find the limits of the driver and the amp and if the sub shuts it down under testing then its a no go, plain and simple. Yes, done long enough a sine will eventually shut down any amplifier but not after less than ten seconds. The ep2500 survived many sine tests without bother.

http://www.diyaudio.com/forums/class-d/213071-behringer-inuke-nu3000-measurements.html

For HT sub use it would be useful to know what it is at 20 or better yet, 10 Hz.
Out of curiosity, I tested voltage and continuous power output for 20hz & 10Hz.

With no load:
20Hz = 49Vrms
10Hz = 44Vrms

With 8 ohm load:
20Hz = 282 Wrms
10Hz = 230 Wrms

With 4 ohm load:
20Hz = 475 Wrms (< 10 seconds)

After about 10 seconds, the power output dropped back to 280Wrms.
Based on this, I skipped the 10Hz and 2ohm testing.
 
#20 ·
Sure a few dozen movies out of literally hundreds (otherwise known for good bass) have strong ULF content below 20Hz. Out of how many of those is it something sustained for more than 20ms to 3sec bursts? Probably zero, meaning high short-term power outputs are the most useful metric for a gauging an amplifier for that use! I've said it once and I'll say it again, the bench test results of the NU3000 is just right for proper HT or music use. I'm sorry you are dissatisfied with it and it didn't meet your needs but that doesn't mean hasn't worked well for many others. Most people watch movies and listen to music with their amplifiers, not try to debunk and verify manufacturer claims by testing extreme limits.
 
#22 ·
Russ, I'm very interested to see what happens here. I've wanted to do a nice powerful sealed LT'ed sub for a long time, and the SI was one I was specifically interested in. Can't wait to see the results.

And I have to say, that's a great way to use corner clamps! Your builder is a smart guy.
 
#23 ·
I agree, I've always been intrigued by high-power sealed subs with LTs. The extreme low price of the SI 18 at ~$200 shipped, along with the NU3000dsp for $280 shipped (normally $400), was too good of an opportunity to pass up.

I've been doing some playing around while I wait for the box. I also got the heat sinks and fan swapped into the amp. For the heatsinks I doubled them up on the mosfets in the outputs stage, putting one on the transistor itself and a second on the heatspreader. I had enough spares to also put some on the power supply heat spreaders and the other exposed transistors.
 

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#24 ·
More pics. I'd definitely recommend putting heatsinks on the two power supply transistor heat spreaders like I did (the two off to the side), they get pretty hot to the touch since they aren't in direct line of the fans airflow. The bare transistors between the transformer and output caps don't seem to get hot at all so I didn't bother putting anything on them. The pack of heatsinks was all of $12, plus $6 for the fan.

I'll definitely be running the amp bridged at 8Ω rather than a single channel at 2Ω in order to even out the load.
 

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#28 ·
Nice modding there. I have read of guys putting in the heatsinks, modding the hood and changing out the fan. Bridged at 8 ohms, I don't think you will have any problems. When I get a second 21SW, I'm going back to 8 ohms as well. Fewer problems really. Interesting and unusual design on the baffle...good woodworking!
 
#29 ·
The mdf is 3/4", the baffle is double layered, so the trim donut should make a total of 1.5" recess for the woofer. This should protect the surround so that none of it is exposed fully. I also wanted something unique on the cabinet since there are a lot of plain cubes out there. Picking up the cabinet tomorrow :jump:
 
#31 ·
Got it all buttoned up and ready to go yesterday. The craftsmanship on the cabinet is beyond A+, and better yet, the Duratex perfectly matches the textured satin black paint I used on my mains. I added 3lbs of Acousta Stuf and plan to verify the Qtc here shortly. For internal wiring I used some old 8AWG aluminum power wire I had laying around, and used ring lugs for a more positive connection. The alan head steel wood screws from PE fit the gasket great but are just barely big enough to not go through the holes in the driver flange, whew.

I haven't tried much music yet but needless to say it passed the HT test with the new Thor movie last night.
 

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#35 ·
Very nice looking sub. Your builder is to be commended...Well done. I would recommend Europa Report and Gravity. I watched both of them back-to-back yesterday and felt like my head was in a fish tank the whole time. LOTS of low frequency in both movies.:T
 
#32 ·
Here is the initial go with REW and Audyssey XT32, looks pretty good! I set a 9dB LS12 @ 25Hz in the inuke and then used the other 7 PEQ bands with REW, then used Audyssey. The room is open to most of the house and there's a vaulted ceiling. The crossover with Audyssey is 80Hz. Not bad at all :bigsmile:

No smoothing and this is with a UMM-6. Audyssey set to movie mode with +10dB reference.
 

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