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DIY HT sub/ use what I have or start over?


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8 replies to this topic

#1 of 9 OFFLINE   dragonetti

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Posted February 11 2009 - 12:55 AM

I will start by saying that most of my experience with subs and sub building has only been in a car. So I need some good HT advice.

My equipment, Denon 3808ci running my old Paradigm monitor 7's, cc350, and monitor 3's v3 rear. Had a ps1000 sub which I gave to my Dad because it wasn't doing it for the room. The room is large, 20' x 24' with a 15' ceiling.

Want to use what I already have plus the cost of wood. I have two Digital Designs 1010 woofers (which are not their massive spl woofers) and a Paradigm Ref. 1500w Ultra D class amplifier.

When I had the woofers in my car the box was designed for spl, both in the same space with a large port area and tuned to 35hz. Will designing a box with less port area reduce spl and increase SQ? Do the woofers need to be divided or can I pair in one enclosure? Does tuning to 25hz sound about right? I know the room needs more than I am willing to give it, but I also know if I build this box right it will be a lot better than it was.

#2 of 9 OFFLINE   Brent_S

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Posted February 11 2009 - 12:12 PM

Chances are you were better off with the PS1000.

I could only find specs on the 1010 by looking in the Wayback Machine. DD doesn't list Xmax, but says the magnet gap is 13mm. I'd generously model Xmax at 6.5mm, but it's likely a bit less.

Plugging what specs are available into WinISD, I get a decently flat curve with 1.242 ft^3 (net) tuned to 28 Hz. Using an Xmax of 6.5mm, power handling is limited to 114 watts @ 40hz with a bit more either side of the minima. Supposedly, it would be good for an f3 of 28Hz in this alignment. With 120 watts (again, with Xmax = 6.5mm), WinISD says 104dB-106dB at 1m groundplane from 30Hz - 100Hz.

That 1500 watt amp you have likely came out of one of Paradigm's sealed models meaning it likely has a fair amount of EQ to bring up the bottom end. A ported box, espeically with limited Xmax, needs a subsonic filter right around tuning to prevent the driver from being overdriven. It's highly probable the Paradigm amp will be applying a boost curve below 28Hz where you really need an agressive rolloff to be happening.

With such nice main speakers, you really need to match them with something better than the DD1010s appear to be. Consider ordering four of Jack's surplus npt-11-083-2 for $120 total. Put them in 2 - 2.5 ft^3 sealed each (8-10 ft^3 net total) wired in parallel and enjoy. They won't handle nearly all of the 1500 watts the sealed design should work better with the EQ that's probably in the amp.

-Brent

#3 of 9 OFFLINE   dragonetti

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Posted February 12 2009 - 04:27 PM

120 is not a bad price. I didn't see what ohm the voice coils are in the link. I don't even know what ohm load this Paradigm amp will run. Ultra D class car amps can normally handle 1 ohm load but that's a car amp. A guy at work has a Seismic 12 (same amp I have) but he won't let my crack it open to ohm the speaker and see if it is DVC or SVC Posted Image . I guess I'll ebay the DD's and give the npt's a go.

#4 of 9 OFFLINE   dragonetti

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Posted February 13 2009 - 01:02 PM

Wouldn't a ported design fill the room better?

#5 of 9 OFFLINE   Brent_S

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Posted February 13 2009 - 01:45 PM

Quote:
Originally Posted by dragonetti
Wouldn't a ported design fill the room better?

Yes, a ported solution could have more output below 40-50Hz, but I addressed that point.

Quote:

That 1500 watt amp you have likely came out of one of Paradigm's sealed models meaning it likely has a fair amount of EQ to bring up the bottom end. A ported box, espeically with limited Xmax, needs a subsonic filter right around tuning to prevent the driver from being overdriven. It's highly probable the Paradigm amp will be applying a boost curve below 28Hz where you really need an agressive rolloff to be happening.


Additionally, for a similarly smooth rolloff without exaggerated peaking, you'll need a 4.5 ft^3 or larger box per driver compared to the 2 - 2.5 ft^3 to run it sealed.

Ken Kantor, founder of NHT, and at least codesigner of the 1259 motor, strongly recommended against running the 12" 1259 in a ported cabinet due to its suspension. Not sure if that absolutely applies to these 10"s with the 1259's motor, but the T/S parms point to a sealed alignment being preferred.

-Brent


#6 of 9 OFFLINE   Brent_S

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Posted February 13 2009 - 02:04 PM

Quote:
Originally Posted by dragonetti
120 is not a bad price. I didn't see what ohm the voice coils are in the link. I don't even know what ohm load this Paradigm amp will run. Ultra D class car amps can normally handle 1 ohm load but that's a car amp. A guy at work has a Seismic 12 (same amp I have) but he won't let my crack it open to ohm the speaker and see if it is DVC or SVC Posted Image . I guess I'll ebay the DD's and give the npt's a go.

Most plate amps are rated at 4 ohms. That doesn't necessarily mean Paradigm used a 4 ohm driver. For marketing, they could truthfully list the sub as having a 1500 watt amp (into 4 ohms), but it might only be delivering 800 watts to an 8 ohm driver.

Amps are simply class D. Ultra-D is a trademark of Paradigm.

Jack's inventory spreadsheet also contains the T/S parameters. Re is spec'd at 9.5 ohms suggesting the driver's are probably 12 ohm nominal. In a 2.5 ft^3 sealed box, WinISD sims the lowest impedance below 80Hz to be 12 ohms rising to a peak of 64 ohms at 34Hz and dropping to 10.6 at 100Hz. I think a 4 ohm stable amp should easily handle four of the NHT's in parallel especially given how much reserve power you'll have with the Paradigm amp...the NHTs only need 100-180 watts to reach Xmax in the 30-40Hz range. You could always series 2 driver and parallel the pairs for a 5-6 ohm minimum load if four in parallel does cause a problem.

Bottom line, SPL is about displacement. Displacement = surface area * excursion. I don't think you'll find more displacement than those surplus NHTs for anywhere near the money. BTW, Jack's spreadsheet said there are only 13 left the last time I checked. Disclaimer: no personal dealings with Jack, not even a customer of the surplus deal, but I do have a pair of original 1994 vintage 12" NHT1259s.

Possibly the next best displacement/dollar driver currently is the Torrent XO12. Supposedly, this is as close to a SVS dB12.2 driver as NDAs will allow. While the driver is optimized for ported applications, you'll still have an amp that is likely setup for sealed alignments.

-Brent

#7 of 9 OFFLINE   Brent_S

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Posted February 14 2009 - 06:30 AM

You might be interested in reading through this thread at AVS. It's a project using *12* of the NHT 11-083 drivers in a sealed alignment. He's got some in room measurements of the frequency response, not output, near the end of the thread.

If you're familiar with RoomEQ Wizard (REW), available at HomeTheaterShack, you could use it and your DD1010s to get a rough idea of EQ built into the Paradigm amp. Measure the frequency sweep through the Paradigm amp. Maintain the same mic to speaker relationship and run a sweep using a channel of your receiver as the amp. Using the 5.1/7.1 analog input should remove any EQ, crossover, etc. so that you can see what the speaker does with a flat amp. Any difference in the shape of the curves will show the EQ, subsonic, and the fixed low pass filter that's usually present in plate amps up around 200Hz or so. If you are careful to match the calibration levels between tests, you'll have a fair idea of the amount of EQ and at what frequenices they're being applied in the Paradigm amp.

-Brent

#8 of 9 OFFLINE   dragonetti

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Posted February 14 2009 - 11:57 AM

This site will not let that link you posted work. I put an order in for the four 10's. If they don't give me what I want I can add something further down the road. Never had good luck with sealed enclosures and low frequencies. Wrong sub for it or not enough air space I guess. Now I need to figure out where to put them, hehe.

#9 of 9 OFFLINE   Brent_S

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Posted February 15 2009 - 03:09 AM

Quote:
Originally Posted by dragonetti
This site will not let that link you posted work. I put an order in for the four 10's. If they don't give me what I want I can add something further down the road. Never had good luck with sealed enclosures and low frequencies. Wrong sub for it or not enough air space I guess. Now I need to figure out where to put them, hehe.

Sorry, didn't realize the situation between AVS and HTF.

If you search the DIY forum at AVS for "NHT build" or something like that, you should be able to find it. Searching for "NHT 11-083" would probably do it as well.

-Brent


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