Mono amp, 1 - 2 ohm dvc, 2 - 4 ohm dvc sub...?

[EastoutWest]

Hey everyone,

I'm exploring the possibilities for my sound system and I thought I'd pose a question I've been pondering...

I've had a JL Audio 8w3 dual (2-ohm) voice coil powered by about 150 rms watts for years now. It has suited me pretty well (although my favorite sub was a 10" alpine type r powered by a bridged Rockford Fosgate Power 800a4 - never should have sold that amp).

Anyway, my old sony amp died so I just replaced it with an alpine class D mono amp that gives 200 rms watts at 4 ohms. I have had this JL wired in series to present a 4-ohm impedance.

It sounds good but I have found that I occasionally reach the sub's excursion limit before I reach my desired volume. In other words, I want it just a bit louder. Like a 10" sub I guess.

I have a few old Radio Shack 8" subs lying around. They are also dual voice coil but 4 ohms.

I may be wrong, and please correct me if so, but here is what I'm thinking: If I wire the JL in series, It's 4 ohms. If I wire the dvc's on each radio shack sub in series they will each show 8 ohms. So then If I parallel the two 8-ohm radio shacks they present 4 ohms. Now If I parallel the two radio shacks and the one JL, the final load to the (mono) amp will be 2 ohms... right?

In other words, what happens when you parallel-wire a 4 ohm load and two 8 ohm loads?

The next issue is that the JL sub is rated to handle 150 watts rms and the radio shack subs are rated to handle 50 watts rms, 100 watts peak.

The amp claims it will put out 500 watts into a 2 ohm load... will the power be distributed evenly?

I know this is a bit of a quandary, and I also know there are those of you out there who will say I'm crazy to even think about using radio shack subs. You are more than entitled to say that... I agree a little but the experiment would be free as I have the materials. I'm just trying to get an idea if its even worth building a box for these 3 subs. In normal circumstances, I think 3 (matched) 8's would probably sound really good, but will I start clipping or distorting the radio shacks before I get any volume out of the JL? Will it sound like &^@$?

- Ian

 

[EastoutWest]

P.S. Another option would be to use two subs - the JL in series (4 ohms) and one voice coil of one radio shack sub (4 ohms), the two subs wired in parallel to present the amp with a 2 ohm load. But 500 watts would be a whole lot for these two subs.

Thoughts?

 

[EastoutWest]

P.S.S.

What would happen to my JL if I wired just one 2 ohm voice coil to my amp and gave it 500 watts (over three times the suggested wattage)? Would it be louder? Would it distort higher or lower in volume? Would it blow on the first drum kick or bass line?

 

[EastoutWest]

well, I just discovered that my sealed box is almost twice as big as it should be...

so that's probably why I was maxing out the excursion so easily. Time to get out the saw!

I'm going to try shrinking my box to JL's recommended volume and see if I can go a little louder. But I'm still curious if anyone has thoughts about the impedance issue.

 

[toypaseo]

I am very rusty on this, but I think you are correct, if I am reading it correctly.

one JL sub wired at 4ohm
two Radio Shack subs wired at 8ohm each

You wire in series, the Radio Shack subs, for a 4ohm load

You wire in parallel, the JL, and the two Radio Shack subs, for a 2ohm load

Since the JL is one unit, and the Radio Shack subs are basically wired as one unit, power will be split 50/50. The Radio Shack subs will split their 50% evenly.

 

[toypaseo]

Not sure if this is right, but...

Wire the coils of each Radio Shack subs in parallel (which makes each speaker a 2ohm speaker) and then wire the two subs in parallel for a total of a 1ohm load.

The coils of the JL are wired in parallel for a 1ohm load.

Wire those in series for a 2ohm load.

 

[Jasonaudio317]

Never run one coil of a dvc subwoofer. . . it will cause problems down the road. Other option is to port the jl 8w3, it will limit the excursion, and gain spl. Sealed boxes almost always have more excursion than a ported. Plus, the box for one ported 8, will be smaller than a box for 3 8's sealed if built to spec.

 

[EastoutWest]

nice to know I'm not the only audio geek out here...

Interesting idea ToyPaseo, I hadn't thought of that (doing the coils and radioshacks in parallel then series-ing the JL to the two parallel radio shacks). I feel like that would be more likely to send half the wattage to the JL and the other half to the two radio shacks.

JasonAudio, I was under the impression that porting actually allowed for more excursion since it seems there would be less resistance pushing back against the cone. Or is it that a ported box allows a speaker to create more spl for a given amount of excursion?
I like your point and the suggestion is a good one but I have always favored the tone of a sealed sub. I listen to a wide variety of music but I turn down my sub when I listen to hip hop, and turn it up when I listen to rock or old country (I favor the kick and the toms over synthesized bass).

Regarding the idea of running 1 voice coil on a dvc sub, after further research I agree as the consensus seems to be that using only one voice coil of two reduces the safe power handling of the speaker... and with a sub looking for 125 watts rms on two coils, I don't dare give one coil 500 watts!

On sunday, I'm going to shrink my box, turn up the gain a little, and see how it goes.

How's Southport these days Jason? I love that area, my second favorite southeastern coastline besides Ocracoke. I bet it has been beautiful with this early spring we've had! I assume you drive your explorer around Ft. Fisher?

 

[Jasonaudio317]

Fort Fisher, Carolina beach. . .Yeah. I actually live in between Southport and Oak Island. Great weather, but brings tourist, sigh! Lived here my entire life, dont plan on leaving either. As for the excursion, all my charts on winisd show my excursion on my 12w7 dropping severely when ported, by over .75 of an inch. JL is a brand I have dealt with for years, and have owned almost every sub they have made at one point or another it seems.

 

[EastoutWest]

Well, I shrunk my box to JL's suggestion and guess what!

It sounds better than it ever has! I've only heard it distort once... when at high volume, the song changed from a quieter rock song to a louder hip hop song... much louder than I prefer to listen... My box is probably 35% smaller and the sound is 50% larger.

So within my dB range preference, it sounds amazing! Tight, punchy, and low enough for 95% of my music.

Thanks for humoring me on the impedance question but I'm happy to have ruled out the radio shack subs. By the way, I'm a big fan of re-surrounding speakers. This JL is around 12 years old and I paid $35 to have a professional replace the surround probably 4 years ago. It had become a little brittle and I accidentally poked a hole in it. I also had the surrounds on a free pair of Boston bookshelf speakers replaced and they sound amazing! Next time, I'm gonna try to do it myself.

 

[Crutchfield Vlad]

It looks like you have already gotten it taken care of. If you guys are more interested in the wiring, we have a ton of information on our web site just for the different wiring diagrams.

http://www.crutchfield.com/I-rFORc111/learn/learningcenter/car/subwoofers_wiring.html?g=500&tp=13