[sprexumn]

I am looking for recommendations for subwoofer(s) to use two channels of 100w 2 ohm (75w 4 ohm) from my Jl Audio xd800 amp. I have audiofrog front stage (gb10, gb25, gb60) using 6 of the 8 channels so I cannot bridge the amp to get more power. Everything is controlled from a minidsp Dirac dsp.

I am currently using ZR800 8 inch infinite baffle drivers in the rear doors as subs. But the door rattles are just too much so I am going to build proper enclosure(s). I could just drop the two 8 inch 4 ohm zr800 drivers into the recommended .75 ft3 enclosures and call it a day. But since those are optimized for Infinite baffle, I am assuming there must be better drivers out there.

I have been toying with the idea of using a single 2 ohm dvc sub, probably 10 inch, as a way to get more power out of the amp. But I haven’t seen any 2 ohm dvc subs made for such low power. I have heard there could be issues with power mismatch between channels causing strain on the voice coil when using two amps on dvc drivers, but I am not sure how much to worry about that.

Using a pair of 2 ohm JL Audio 10w1v3 seems like a possibility as they suggest power as low as 75w. I think that would be better than the 2 ohm 10w3v3 which suggests minimum power of 150w.

This all raises the question for me of how to know which sub is going to produce the most output dBSPL per precious watt. I know the efficiency rating is not the way to tell this since that is measured at higher frequencies. Is there some sort of formula to wrangle the Thiele Small Parameters into a useful low freq efficiency number? That is just an aside.

So what sub drivers are best for a 100w 2 ohm amp? My main criteria is tight audiophile bass, but I think the marginal amp means I can’t waste power on overdamped subs.

 

[miniSQ]

you don't have enough power for any sub to keep up with the front stage. Add a second amp for the sub.

 

[sprexumn]

I should mention that this is a hybrid Toyota Prius where the 12v system is fed by an inverter that maxes out somewhere in the neighborhood of 400w. Another amp will just be another heat sink.

 

[420tabbycat]

I should mention that this is a hybrid Toyota Prius where the 12v system is fed by an inverter that maxes out somewhere in the neighborhood of 400w. Another amp will just be another heat sink.

Would you explain the 12v problem? There’s not a 12v battery and alternator that can be used in the normal wiring fashion of standard type cars?

 

[Holmz]

…
I am currently using ZR800 8 inch infinite baffle drivers in the rear doors as subs. But the door rattles are just too much so I am going to build proper enclosure(s). I could just drop the two 8 inch 4 ohm zr800 drivers into the recommended .75 ft3 enclosures and call it a day. But since those are optimized for Infinite baffle, I am assuming there must be better drivers out there.
…

Better drivers for what?
IB are the most efficient, so it may be more optimal to attempt to fix the door rattles?
Once you shove those into sealed boxes the SPL will go down at some fixed wattage.

…
This all raises the question for me of how to know which sub is going to produce the most output dBSPL per precious watt. I know the efficiency rating is not the way to tell this since that is measured at higher frequencies. Is there some sort of formula to wrangle the Thiele Small Parameters into a useful low freq efficiency number? That is just an aside.
…

The efficiency number is usually dB/W oR dB/2.8V, and somewhere in the 80-95 range.
So you have a spec to use.

The “As an aside” part: is to use the T/s numbers in WinSD and model them.

…
So what sub drivers are best for a 100w 2 ohm amp? My main criteria is tight audiophile bass, but I think the marginal amp means I can’t waste power on overdamped subs.

“toight bass” means you probably do not want an efficient bandpass box, maybe a transmission line would work?
So you would be more optimal with IB, and maybe on where the rear shelf is, but thathas no isolation between the boot and the cabin if it is like the Mrs last two Prii.

Rather than a single 100W 2-ohm, maybe four 8-ohm speakers in parallel?
(that would give more cone area)

 

[FAUEE]

You should sell me your zr800s, they're definitely your problem. I'll take them off your hands though...

Semi jokes aside, 100W isn't going to really power a sub.

 

[DaveG]

Several thoughts… do a trunk baffle/IB with a dvc 2 ohm sub that’ll work. It needs to be super efficient though. That would be channel 7 to one coil at 2 ohms and the same for channel 8 on the other coil.
But better yet bridge 5 & 6 to one GB60 for 150 watts at 4 ohms and 7 & 8 to the other GB60 and get a separate sub amp and open up your choices. XD1000/1 has the same footprint as your 800/8 and could be stacked easy enough. Buy once, cry once! Don’t eff up some nice equipment with a sh!tty low end! Keep us posted.

 

[sprexumn]

Would you explain the 12v problem?

There is no 12v alternator in the hybrid car. The 12v system running headlights and everything else is fed from the high voltage propulsion battery, which is fed by the motor generators in the hybrid system. The 12v battery is about a quarter the size of a normal battery, since it doesn’t start the engine, just starts the computers.
Takeaway is that we only have a few hundred watts of power to feed the amps.

 

[DaveG]

Forgot about the ev so scratch the xd1000. How about an XD400/4 bridged for 200 watts @ 4 ohm x 2? Fuses @ 40 amps. And still bridge the GB60s. They are incredible at 150 watts. There’s one in the classifieds if interested.

 

[sprexumn]

Better drivers for what?

For using in enclosures. I am done with the rear door IB speakers, have spent years trying to get rid of rattles.

The efficiency number is usually dB/W oR dB/2.8V, and somewhere in the 80-95 range.
So you have a spec to use.

A spec, but not a useful spec. According to threads like Sensitivity Spec in Car Audio : Hoffmans Iron Law Discussion , they measure efficiency at midrange not low freqs.
Since my original post I have done more reading on this topic and consensus seems to be that the answer I'm seeking can best be answered by using speaker simulators and seeing which can get loudest given my 100w input. Honestly, I'm not excited about learning a new program and entering lots of speaker data.

So you would be more optimal with IB, and maybe on where the rear shelf is, but that has no isolation between the boot and the cabin if it is like the Mrs last two Prii.

Good idea, but I have long ago thrown out the rear shelf that covers the hatchback area in my Prius. And it didn't seal so the air would shortcut through the edge cracks ruining the infinite baffle effect.

Rather than a single 100W 2-ohm, maybe four 8-ohm speakers in parallel?
(that would give more cone area)

Clever idea, but I don't think surface area is my limiting factor. I'd like to stick with 1 or 2 subs.

 

[sprexumn]

Several thoughts… do a trunk baffle/IB with a dvc 2 ohm sub that’ll work. It needs to be super efficient though. That would be channel 7 to one coil at 2 ohms and the same for channel 8 on the other coil.
But better yet bridge 5 & 6 to one GB60 for 150 watts at 4 ohms and 7 & 8 to the other GB60 and get a separate sub amp and open up your choices.

I have no trunk in this hatchback :-( Also I can't bridge just 5/6 and/or 7/8 on the XD800; doing so would also bridge 1/2 and 3/4 which I use for the other channels.

How about an XD400/4 bridged for 200 watts @ 4 ohm x 2? Fuses @ 40 amps. And still bridge the GB60s. They are incredible at 150 watts. There’s one in the classifieds if interested.

My current thinking is to biamp a single IDQ10 with dual 2 ohm voice coils, and because Andy W says that ported enclosures maximize efficiency, go that route. Build a ported enclosure that sits behind the driver seat. This squeezes the available 200W out of the current XD800 amp, and allows me the possibility of future expansion if I decide later that I need to add a sub amp.

The IDQ10 was chosen mostly just on the reputation of Image Dynamics for Sound Quality, and availability of dual 2 ohm. Their suggested power is 250W, the lowest I've seen for quality 10" subs.

 

[Holmz]

You can somewhat ignore their “suggested power” if:
1) you have a quiet Pruis
2) know you havE a Prius with limited power available
3) Prefer listening at lower levels of SPL

Basically look in the mirror and if you do not appear similar to their demographic, then you have a better chance of running them on your power.

Also some marketing has ambitious power levels for the demographic that like to run high power amplifiers.

If you know it is not an ear bleederbuild, then a modest ported does seem like a good option.

 

[sprexumn]

Well I am educated enough to know that doubling power only gives a few db more sound so I guess I am not the max power demographic. And the Prius is very quiet with dynamat in all the doors.

I have been reading the image dynamics manuals and they are pretty emphatic that sealed sounds best. Which gives me pause about going ported. But I suppose those manuals were written long before DSP was around so they are probably thinking about the uncorrected response.

 

[Anu2g]

Btw, the XD800/8 bridges @ 200w @ 4 ohms, so all this talk of DVCs isn't really necessary. I mean, you could use a DVC, but assuming you want to use 2 channels of your amp on a sub, you will have 200x1 @ 4 ohms bridged. So doesn't matter if it's a DVC 2ohm or just a SVC 4 ohm. It's going to be 200 total watts regardless, and you might as well bridge so that you aren't trying to gain match, etc.

Same 200w rule holds for bridging to the mid-bass, which I definitely recommend (I do the same on my XD800/8 to ML1650.3 mid-basses)

 

[sprexumn]

Btw, the XD800/8 bridges @ 200w @ 4 ohms, so all this talk of DVCs isn't really necessary.

If I had channels to spare, that would be the way to go. But alas I am already using 6 channels of the 8, and you can't bridge just two channels together without bridging the others.

You are the second person who has suggested this, so maybe there is something I'm missing about the XD800... Is there a super secret undocumented way to bridge just 7/8 without bridging the others?

 

[Anu2g]

If I had channels to spare, that would be the way to go. But alas I am already using 6 channels of the 8, and you can't bridge just two channels together without bridging the others.

You are the second person who has suggested this, so maybe there is something I'm missing about the XD800... Is there a super secret undocumented way to bridge just 7/8 without bridging the others?

Nothing super secret (it's in the manual). You can bridge any set of 2 channels by just using L+/R- on those 2 channels. You may be getting confused with the input switches, which is completely independent of any bridging.

 

[Anu2g]

Let me know if it still isn't clear, though; i'm glad to help.

As an example, in my current config, I'm using the amp to power a 3-way active; 75x2 to tweeters; 75x2 to mids; 200x2 (bridged) to mid-basses.

My input mode switch is set to 8 channel.

The two tweeter channel RCAs on the DSP go out to Channels 1/2 on amp.
The two mid channel RCAs on the DSP go out to Channels 3/4 on amp.
The left mid-bass channel RCA on the DSP uses a Y cable, to output to Channels 5/6 on amp. Speaker output uses 5's positive output and 6's negative output.
The right mid-bass channel RCA on the DSP uses a Y cable, to output to Channels 7/8 on amp. Speaker output uses 7's positive output and 8's negative output.

Does that make sense?

For your sub, you would essentially copy what I did for my right mid-bass

 

[sprexumn]

You may be getting confused with the input switches, which is completely independent of any bridging.

Yes! You are correct. I reread the manual and you are right that I can bridge just 7/8 without the others being bridged.

Thank you!

So now my issue is finding the best 4 ohm sub for 200w. And back to the question of which will get me the most SPL out of those 200w.

 

[Anu2g]

I second the person who mentioned a bandpass box. I used to have 2x100 from a PPI Sedona amp, powering 2 10w1s in a bandpass box. SPL wise, it was comparable to a ton of higher-powered boxes that I've owned. Obviously it will only play a narrower band, though

 

[sprexumn]

I chatted with a crutchfield rep and he recommended two subs:

JL Audio 10w1v3-4
Morel Primo 104

They both have power ratings in line with the 200w that I'm supplying and work with ported boxes in the 1.4 cu ft range which is my practical limit for the location I have in mind on the floor behind the driver seat.

I asked if the audiofrog GB10D2 would work, since it would be nice to match the fronts. He said, and I think I agree that would be too heavy for my use case. But it is tempting that they list sensitivity of 93db, higher than the Morel (90) and JL 10w1 (84). Even though I know I shouldn't trust that spec ;-)

I will read up on bandpass; I haven't really considered it but happy to learn new things!