NWCgrad's Sealed Subwoofer System - Design and Build Thread - AVS Forum
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post #1 of 19 Old 06-30-2013, 03:12 AM - Thread Starter
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I have been studying the different online forums for the past two years, since I am currently located in SE Asia I really cannot build much so I had plenty of time to ponder. However, my sentence is almost over. Wife and daughter flew out last week, I fly back to Maryland on 1 August!biggrin.gifbiggrin.gifbiggrin.gifbiggrin.gifbiggrin.gifbiggrin.gifbiggrin.gifbiggrin.gif

Decided to go with a sealed system, Linkwitz Transform enhanced low end. There have been lots of inspiring builds, but Gorilla's thread really fired up my desire to go crazy!

I've tried to embed images, but apparently this site doesn't like my ISP today, keeps freezing.

Enclosure: 20" w x 26" H x 18.75" D, made with genuine 13 ply Baltic Birch from hardwoods, Inc (Frederick, MD)

Drivers: (2) Dayton Audio 18" [Made in Taiwan, still trying to find drivers Made in US/North America that will be as good, TC Sounds and Funk Audio drovers are to pricey], will do stepwise increase until reach a total of 8.

Amp: QSC PL340. Plenty of power, -3 dB point specified as 3 Hz, Made in US. Yes, its pricey, but "buy once cry once" is my motto on amps.

EQ: miniDSP (2 x 4, unbalanced version)

Space: 5,000 cu ft, open floorplane basement, subs located on screen wall, eventually behind AT screen.

System Requirements:

1). Must meet or exceed THX reference in WinISD modeling (I am hopeful that the 2 Pi calculation will result in decent representation of listening position volume in a 1 Pi space). Main L/C/Rs (upgraded 4 Pi) can easily do the 105 dB requirement (110 dB listening to Black Sabbath, Pink Floyd, Porcupine Tree, Avenged Sevenfold, Rush, or Dead Can Dance is awesome); subs must be able to hit 115 dB without strain (125 dB if run them "hot").

2) Must excel at both music (70%), HT (20%) and sports (10%).

3) Single digit frequency response greater than 100 dB.

4) No mainland China products (difficult at best, but seeing how they treat countries up close eek.gif is enough to prevent me from supporting their economy).

A man who has nothing which he is willing to fight for, nothing which he cares more about than he does about his personal safety, is a miserable creature who has no chance of being free.

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post #2 of 19 Old 06-30-2013, 04:22 AM - Thread Starter
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Enclosure.JPG 92k .JPG file

Transfer Function Magnitude.JPG 119k .JPG file

SPL.JPG 100k .JPG file

Amplifier Apparant Load.JPG 135k .JPG file

I assume when using Linkwitz Transform, the amplifier must be sufficient to provide the apparent power vice the lower power used in the model.
Attached Images
File Type: jpg Enclosure.JPG (92.0 KB, 35 views)
File Type: jpg Transfer Function Magnitude.JPG (119.3 KB, 15 views)
File Type: jpg SPL.JPG (99.5 KB, 10 views)
File Type: jpg Amplifier Apparant Load.JPG (135.4 KB, 5 views)

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post #3 of 19 Old 06-30-2013, 06:05 AM
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Quote:
Originally Posted by NWCgrad View Post

I assume when using Linkwitz Transform, the amplifier must be sufficient to provide the apparent power vice the lower power used in the model.
That, and the driver must have sufficient Pe and xmax to handle the power.

Bill Fitzmaurice Loudspeaker Design

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post #4 of 19 Old 06-30-2013, 06:34 AM - Thread Starter
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^^^Thanks Bill, per Parts Express the PE is listed at 900 and Ricci determined the Xmax to be around 20 mm, both should be good. Realistically I do not forsee hitting 125 dB in a house, I want the capacity so the system is never stressed which tends to make distortion become audible. I wish I knew the T/S parameters for Nathan Funk's in house built driver, I REALLY like the subs he produces but they are rather pricey. I "think" based on reading the AES papers and online forums that multiple subs is the best approach, but I've not heard a good system so I lack first hand experience.

I really expected the UXL 18 to model much better than it did. My 18" Maelstrom X models very well, but I only have one and since Exodus Audio pulled stakes I am looking to sell it at some point. Seems best to start over with matching drivers. I should be able to get up to 4 in the next year or so. When I retire from navy and settle into normal life, ie not moving all over the world, I will build a dedicated HT and add the next 4. With amplification, 8 will run around 5 grand.

I am not even close to an expert, I just have had a lot of time to play on the computer now that it is monsoon season. I'm so sick of rain...

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post #5 of 19 Old 06-30-2013, 07:30 AM
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Quote:
Originally Posted by NWCgrad View Post

Amp: QSC PL340. Plenty of power, -3 dB point specified as 3 Hz, Made in US. Yes, its pricey, but "buy once cry once" is my motto on amps.

EQ: miniDSP (2 x 4, unbalanced version)

The unbalanced version of the miniDSP only puts out a maximum output voltage of 0.9 Volts RMS. The QSC PL340 (PDF link to specification) has an input sensitivity (input voltage required for full output power) of 1.96 Volts RMS when set to the 32 dB gain setting.

I think you're going to need the balanced miniDSP.
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post #6 of 19 Old 06-30-2013, 08:04 AM - Thread Starter
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Originally Posted by andyc56 View Post

The unbalanced version of the miniDSP only puts out a maximum output voltage of 0.9 Volts RMS. The QSC PL340 (PDF link to specification) has an input sensitivity (input voltage required for full output power) of 1.96 Volts RMS when set to the 32 dB gain setting.

I think you're going to need the balanced miniDSP.

Yeah, wish I had went that route when I ordered. Right now I am looking at either a Radial Engineering J+4 Stereo Line Driver -10dB to +4dB Interface (its hard to find specs on these types of interfaces, this one is rated 10Hz - 20 kHz +/- 1 dB) -OR- the miniDSP OpenDRC-AN (http://www.minidsp.com/products/opendrc-series/opendrc-an) as its only $100 more than the interface. The OpenDRC has XLR input/output and can hold 4 separate DSP settings. I need to read more on the unit to ensure it will do LT. I hate the phoenix terminals on the balanced version of the miniDSP and will pay more for XLR.

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post #7 of 19 Old 06-30-2013, 08:39 AM
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There is also the ART Cleanbox Pro, which looks to be a lot less expensive than the Radial Engineering unit.
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post #8 of 19 Old 06-30-2013, 08:51 AM - Thread Starter
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^^^I seem to recall it has a fairly high HPF, but maybe they have changed the device since I last looked at it.

Thanks, I will look it up. I do have an Adom GFP preamp that doing anything, I could use it to amplify the low signal coming out of the miniDSP.

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post #9 of 19 Old 06-30-2013, 05:24 PM - Thread Starter
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Has anyone used the Rolls MB15B Promatch? It does the conversion from consumer RCA (-10) to professional XLR (+4). It is pretty inexpensive at the online retailers. Would be a lot cheaper than a new balanced miniDSP and its Made in the USA.

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post #10 of 19 Old 07-01-2013, 07:33 AM
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Never tried the Rolls. I like my Henry Engineering MatchBox II. It is quite literally flatter than my measurement gear.

I measured no rolloff at 2 Hz. It's also made in the USA, and used ones are readily available on Ebay at ~$50 or less shipped.
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post #11 of 19 Old 07-01-2013, 05:21 PM - Thread Starter
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lilmike, I looked up Henry Engineering last night. They do look like a great option, most boxes only say 20-20 +/-XdB, Henry is rated down to the DC +/-1dB.

Thanks, I added this to my list of equipment to purchase.

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post #12 of 19 Old 08-14-2013, 07:09 AM - Thread Starter
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BACK IN AMERICA! Electrician is here running a dedicated 20 amp line for the sub amp. Still unpacking ling term storage items and my main stereo equipment is on a boat headed to America (packed out back in June so the slow boat should be here in about a month...gotta love customs).

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post #13 of 19 Old 09-06-2013, 02:03 PM - Thread Starter
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Quote:
Originally Posted by lilmike View Post

Never tried the Rolls. I like my Henry Engineering MatchBox II. It is quite literally flatter than my measurement gear.

I measured no rolloff at 2 Hz. It's also made in the USA, and used ones are readily available on Ebay at ~$50 or less shipped.

Matchbox II - ordered
Amp - QSC purchased used locally from music store (made in china but price was to good to pass up).
Drivers - On hold, sold wifes car before moving out of country. Had to spend big bucks to atone for making wife live in the bottom of the developing world for 24 months.

Will use the Mal-X with the QSC 1850HD amp (1800 w/4 ohms bridged) and support with two LAB 12 subs (sealed 1.6 ft^3 each; HPF @ 30 Hz for maximal SPL). The LAB 12 drivers seem to reach Xmax rapidly below 30 Hz in sealed boxes and would not be able to keep up with the Mal-X in SPL output without the HPF at 30 Hz.

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post #14 of 19 Old 09-16-2013, 02:11 AM
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The newer henry engineering matchbox hd has a higher signal to noise at 100 db vs the matchbox two at 85 db. Way better off getting the newer units but hey it is ordered LOL. I got a couple for 59.00 each off ebay, and they show up often. The aphex 124a will also get you very close to this performance.

A Good amplifier requires a adequate power supply, It does not matter what the amplifier is capable of if the power supply will not provide the power required. Most amplifiers have under rated power supplies. It is up to you to make sure you get the ones that are
least under rated if at all.
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post #15 of 19 Old 09-16-2013, 01:32 PM - Thread Starter
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The newer henry engineering matchbox hd has a higher signal to noise at 100 db vs the matchbox two at 85 db. Way better off getting the newer units but hey it is ordered LOL. I got a couple for 59.00 each off ebay, and they show up often. The aphex 124a will also get you very close to this performance.

I get no noise from the unit, I don't see the value in the newer unit for sub usage - perhaps for full range it could be an issue. Matchbox is flat to DC, Made in the USA, inexpensive and recommended by lilmike - what's not to love.

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post #16 of 19 Old 10-23-2013, 12:15 PM - Thread Starter
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My stuff shipped over from Cambodia arrived today! Everything looks okay, one of my 4 Pi speakers received cosmetic damage when one of the movers carrying it tripped. They are dang heavy.

Hope to have my system put back together soon. My two Cambodian built sub boxes arrived intact. They were made from solid wood instead of plywood which is hard to get there. They are 16" cubes and house Eminence Lab12 drivers. I plan to use them with my sealed Mal-X by using them only above 30 Hz so they can have equal output, below 30 they exceed come excursion at to low of SPL.

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post #17 of 19 Old 01-12-2014, 07:59 PM
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Does the Matchbox II boost signal voltage or is it just a converter. I do not see a adjuster knob on the unit. Trying to decide between it or a Rolls MB15 for full range use.
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post #18 of 19 Old 01-13-2014, 08:11 AM
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Does the Matchbox II boost signal voltage or is it just a converter. I do not see a adjuster knob on the unit. Trying to decide between it or a Rolls MB15 for full range use.

Anyone?
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post #19 of 19 Old 01-13-2014, 12:54 PM - Thread Starter
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Sorry I was away from my computer and phone today. I see that Beast answered the q on another thread. The matchbox is a dang fine unit.

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