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    1. · Registered
      2005 Pontiac GTO
      Joined
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      527 Posts
      Discussion Starter · #16 · (Edited)
      The GTO system continues to progress ....

      As stated earlier, I really want to reclaim my trunk space, and with hopes of doing so, had installed 8" subs in the rear deck but have been waiting on the amp to be delivered to power them. Well, the amp was finally delivered a few weeks back, and I had some time this past weekend to work on it.

      The amp is an NVX XAD21, which is one of NVX's brand new X-Series line of amplifiers. These are 1-ohm stable amps, and the specs on it are impressive.

      RMS Power Ratings:
      • 4 ohms: 250 watts x 2 channels
      • 2 ohms: 550 watts x 2 channels
      • 1 ohm: 1000 watts x 2 channels
      • Bridged, 4 ohms: 900 watts x 1 channels
      • Bridged, 2 ohms: 1600 x 1 channel

      The 8" subs are Cerwin Vega V82DV2 "Vega" series:
      • 8" Dual 2 ohm Vega Series Subwoofer
      • Switchable between 1 or 4 Ohm
      • Power Handling:
        • Peak: 750 watts
        • RMS: 250 watts

      Finding a place to mount the amp was kind of a pain, as I want everything hidden, and there's not a lot of spaces behind the trunk panels for mounting. I finally settled on this location, on the driver's side of the trunk. You can see the Helix V8 on the far left, and then the NVX amp as well.



      I was able to fish the power cables through a channel which spans across the trunk area, which made it very convenient to keep the power cables separated from the signal cables.

      And here's a look at the other side of the trunk, where the power cabling is located. You can see the power and ground wires feeding up, and to the left, into the channel I mentioned above ... heading over to the NVX amp. I decided to leave the wiring for the RF 12" sealed sub in place as well, so I can do some A/B testing between the two 8's and the single 12.



      For connecting to the Helix, I decided to hook up both the 8's and the 12, and did so by taking advantage of the unused powered channel (Virtual Channel 'F') of the Helix. I moved the RCA preouts of the Helix from the RF 12" enclosure over to the NVX amp, and then connected the unused powered output of the helix to the RF 12" sub, and set it for High Level input.

      So here is the end result of the connections:



      And the power ....




      I should note that prior to moving the RCAs, I took some RTA readings of the 12" sub performance 1st. Then when I connected the high level input to the 12" sub, I then adjusted the channel config to match the same performance. I did this so I could do the A/B comparison later.

      To set the gain on the NVX amp, I disconnected the speaker leads from it, turned the HU up to 52, and played a 40Hz tone at -3dB ... then I used a DMM to set the gain to output 31.6v. So, 250w @ 4-ohm.

      Then I reconnected the speaker leads, and setup two configs in the Helix ... one with the RF 12" sub active and the 8s muted ... and a second one with the 8s active and the 12" sub muted. Now I can easily change between the two configs using the Conductor remote to do some critical listening comparison.

      I was running out of time by now but was able to take some initial readings.

      Here is the REW RTA result with the 12" sub activated and the 8's muted ... playing pink noise through the system ... i.e. My baseline:



      Here is the REW RTA result with the two 8's activated, and the 12" muted:



      And here are the two overlaid on each other, for easy comparison:



      I have to say, I am quite impressed with the result. I did not expect these Vega 8's to be able to match the performance of the sealed 12, but it's pretty darn close. Keep in mind, I did not do any EQ work after moving the RCA cables over to the NVX amp. It was late, and I was out of time to do any more ... so the EQ in the Helix on the sub channel, which I set up for the 12" sub, is what is feeding the 8's right now.

      Seeing as the 8s are in the cabin, instead of in the trunk, I believe a proper EQ session will greatly improve the curve even further.

      Before I finished for the night, I did listen to a bit of "Boston's Greatest Hits" CD, and it sounds really good! Like better than I expected. The 8s are much more musical than the 12 (which was completely expected), but they still dig down really low (the unexpected part).

      I'll say I'm really pleased with the result thus far, and have no doubts I can remove the 12" sealed enclosure from the trunk now and be satisfied with the balance of the system.

      That said, seeing how easy it is to create configs in the Helix, and recall them with the conductor ... I think I may try running both the 12" and the 8's at the same time, by configuring the 12" sub to handle say 30Hz and below and the 8's to handle 30Hz - 80Hz? It might be interesting to see how this does, just as an experiment. But in the end, I really want my trunk space back! :)
       

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    1. · Registered
      2005 Pontiac GTO
      Joined
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      527 Posts
      You can make this work with a 2 channel, 1-Ohm stable, amp.

      Wire the coils on each sub in parallel, so you get a 1-Ohm load on one and a 2-Ohm load on the other.

      Run a test tone through the system and dial the gain to produce 500w @ 2-Ohm (31.62vac). Then reduce the input signal on one of the channels (say channel 2), so the amp is outputting 500w @ 1-Ohm (22.36vac) for that channel.

      Hook the 1-Ohm wired sub to channel 2 and the 2-Ohm wired sub to channel 1. You should get 500w to each sub in this config.

      The NVX XAD21 2-channel amp is stable down to 1-Ohm, and is rated for 550w @ 2-Ohm and 1000w @ 1-Ohm.

      You can reduce the input to channel 2 from the headunit preout (if it has stereo sub outputs) or from a DSP (if you're using one). If neither of those are an option, you can attenuate it with other simple methods as well.


       
    1. · Registered
      2005 Pontiac GTO
      Joined
      ·
      527 Posts
      Discussion Starter · #1 ·
      I found this amp listed on Sonic Electronics, but I can't seem to find any additional information about these amps; not even on NVX's own website. Is this a new series which hasn't been released yet? Even a google searh doesn't find anything for the XAD21 ...

      NVX XAD21 | 2000W RMS X-Series Class D 2-Channel Amplifier

       
    1. · Registered
      2005 Pontiac GTO
      Joined
      ·
      527 Posts
      You’ll hear another members thoughts on these same 8’s in the same car when he gets the adapters i 3d printed for him. He’s in this thread and other ones. I’m anxious to hear what he thinks of them.
      The adapters arrived today, and look great! I ordered the V82DV2 subs yesterday, and also pre-ordered a NVX XAD21 amp; which probably won't arrive until mid to late November.

      Now I do have a Helix V-Eight DSP mk2, so I would expect I'll be able to dial them in a bit more ... but they'll also be replacing a Rockford Fosgate P300-12 (12", sealed, 300w all-in-one box) currently in my trunk, which I've been able to get dialed in very well over the past month or so .... So we'll see how I get along with the 8's :)

      [/URL]
       
    2. · Registered
      Joined
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      647 Posts
      Discussion Starter · #61 ·
      The adapters arrived today, and look great! I ordered the V82DV2 subs yesterday, and also pre-ordered a NVX XAD21 amp; which probably won't arrive until mid to late November.

      Now I do have a Helix V-Eight DSP mk2, so I would expect I'll be able to dial them in a bit more ... but they'll also be replacing a Rockford Fosgate P300-12 (12", sealed, 300w all-in-one box) currently in my trunk, which I've been able to get dialed in very well over the past month or so .... So we'll see how I get along with the 8's :)

      View attachment 314122 [/URL]

      Glad you like em. How do they feel, solid? pretty dense dont they? I did your infill either completely solid or 80%...Ive printed a bunch of other parts since then so i dont remember lol. pplaying with the dsp a little last night I was able to gain some volume at 25hz but thats as low as i could get them to produce sound. I dont have any music i can think of that goes lower. Theres a rap song that almost every sub I've had would not play it well, but these 8's actually do. I can't wait to get your feed back on how you think they sound. Cool thing is you have the same car. Make sure you put a decent amount of deadening on the back deck, seal all the holes and seal the chamber that the rear seat speakers are in. Pull the carpet trim back on the trunk side panels and you'll see theres a slot that leads to the rear seat speakers (the ones by your feet in the rear. seal that off with deadening.
       

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