Subwoofer Hookup Advice

Hi all,

I'm looking for some advice on the hookup of subwoofers.....

I want to hook up 2x 10" 4Ohm Dual voice coil subs to a 2 channel amplifier.  My head unit has L+R Subwoofer Pre outs...what would be the best way to hook this all up? 

Amp is a Phoenix Gold Ti600.2, subs are Boston Acoustics G510 4Ohm Dual Voice Coils and the head unit is an Alpine CDA-7998.
Maximum power from my amp is rated at a 2Ohm load stereo, or 4Ohm bridged.
Can I  run the L+R sub preouts into the L+R inputs on the amp, and bridge the outputs and still run 2 subs off a bridged output, or should I just run stereo subs?  Or should I get a monoblock amp such as the Ti800.1 and run my subs from that instead of a 2 Channel amp?

Also, when amp specs mention max power is at 2Ohm load, is that 2Ohm's per channel, or overall for the amp?

Any help much appreciated.

Cheers
Mark

https://photos.yahoo.com/hotvwnz

Yes, you are correct...run the RCA's into the amp imputs.  You then have the choice of running the subs one to a channel, or wiring the subs together (shown here) and bridging to the amp's bridged terminals.  The load on the amp and the power the subs get will be the same either way.  You just connect the best way for your setup:  e.g. the subs are in two separate enclosures, use the stereo hookup.  If they are sharing the same enclosure, you'll have less wiring by using the bridged method.

The only benefit you would have by using a mono amp would be less power needed from the car as it would be a more efficient amp.  But a two channel amp will work just fine for what you have and would have better specs, too.

The amp is rated at a minimum stereo load of 2 ohms, and 4 ohms bridged.  If you were going to hook one sub to each channel, the wiring for each sub would look like this:

You'll notice the difference in wiring of the voice coils in the two illustrations.  Decide how you are going to hook up to the amp, then wire the voice coils of the subs as needed.

Thanks stevdart, that is awesome info!

So are there any pro's/cons of running stereo subs over mono?  I plan on having two enclosures, so will need to go for the 2nd method...

Even though you will have two enclosures, it can still be wired in either method. I would still use method one myself, quite sure Stevdart would as well.

Thanks guys,

My amp is rated at the following;

150Wx 2 @ 4Ohm Stereo. 300W x 2 @ 2Ohm Stereo. 600W x 1 @ 4Ohms Bridged.

Rated Minimum Speaker Loads are Bridged = 2Ohms or Stereo = 1 Ohm. How do I know if this is stable or not?

So, for method one wiring, the 2 subs "present" a 4 Ohm load to the amp, and when running bridged at 4Ohms, the amp can generate 600W x 1 (so each sub will see 300W)...is this correct?   Forbidden, what are your reasons for choosing method one wiring (bridged) over method 2 (stereo subs).

Poetic got a little mixed up on the impedance of your subs.  You said they are DVC 4 ohm, which means that each voice coil is 4 ohm.  The illustrations are correct.  Now, look at the specs for the amp that you posted:  300W X 2 @ 2 ohm stereo.  That is what you get if each sub is wired as in figure 2 and each take a channel.  600W X 1 @ 4 ohm bridged:  that is the minimum ohm load the amp can take.  It is the same output, as you can see, as the output rating at 2 ohm stereo.  1 X 600 = 2 X 300.  Poetic, again, is under the impression that the act of bridging increases power from the amp...that is an old fable.  The amp ratings alone are proof, but Ohm's Law is better proof.  (There's your bash, poetic!) 

nzbug, your statement   "Rated Minimum Speaker Loads are Bridged = 2Ohms or Stereo = 1 Ohm.  How do I know if this is stable or not?"  is incorrect.  The minimum rating is exactly what you posted in last post.  2 ohm stereo or 4 ohm bridged.  You can't go to a lower ohm load than that.  With your equipment, you won't.

Your last statement is correct.  And when Rob speaks...I listen, and learn.  Let me see if I get this right, from reading the hundreds of posts that I have on the subject of mono vs. stereo with subs, particularly those from Rob: 

It's not the difference in power, which there isn't any.  And it's not a matter of what wiring looks best.  It's the impact you ultimately get when both subs are fed exactly the same signal, at exactly the same power.  While wiring in stereo will net you the same power to each, the signals will be different and the amp output will (most likely) be somewhat different from channel 1 to channel 2.  Even when both channels are set as precisely as possible with a meter when you're setting it up, a slight change can occur somewhere down the line. 

Wiring main speakers in stereo is necessary, of course, but not subwoofers.  You don't benefit from stereo separation when the frequencies are that low.  So, bridging the amp gives you the best and easiest power to two subs, separate enclosures or not. 

The subs will perform with more authority.

So Rob...did I get it?

Thanks again stevdart for clearing that up for me! 

Your thoughts, (and Robs) is great advice, and explains everything I wanted to know.....now all I have to do is wire it up ;)

Cheers guys...very much appreciated...

Mark

Stevdart, you missed a couple of things, one being more important than the other. This is the box. While in this case he may be using two separate boxes, quite a few boxes are designed as a coupled chamber design, for those that do not know what this means, it means two subs or more sharing the same enclosure. Thus it is viewed as a mono box and should be fed with a mono signal. A second thought just came to me, and that is most of the amplifiers used for subs are mono by design anyhow. (not in this case though) The wiring method may be more suited to the amp, than the subs. In this case his choice of amp and subs and box made the determining factor for me. Lastly, you use a little less speaker wire when wiring in method 1.

nzbug, as far as the wiring of the actual subs go, it may be easier than you think. More and more subs these days have multiple input terminals on them on the + and 1 inputs to each coil. This is done solely for ease of wiring in series or parallel circuits. Some of the drivers have spring loaded terminals where it is easy to insert a couple of wires into them. Look at the terminals to figure out what kind you have.

Thanks guys....some really good info coming out here...I am learning heaps!

One other question I have is about the bridging of the 2 channel amp....If my understanding is correct, the L+R inputs are "mixed" (don't know if this is correct term) into one amplified mono output....does this result in any lack of sound quality?  Is this the preferred way of running an amp, or is it "pushing" the amp too much?  My system is still sitting in boxes ready to go into the car, so I am open to any and all suggestions....I am not going for loud SPL, just a nice sounding, good SQ type setup.....

Yes, the channels are added one to the other, for a mono signal.  But if it affected sound quality in any way, you wouldn't have gotten a go-ahead to bridge the subs that way from us.  We already answered the questions here in previous posts.  Remember, the load on the amp is the same both ways, and the output to the subs is the same, too.

Now, what about your sub enclosures?  Are you going to build them? That would be preferred.

Thanks stevdart...

Ideally I would like to build the enclosures myself...I need to do some reading about the subject as I don't really know what the best design is and how best to build an enclosure...

The subs specs call for a 0.5cubic ft sealed enclosure, so that is what I will be aiming for.......I have seen some installs where the subs cone is facing and firing inside an enclosure and the back of the sub is open and exposed and I like the look of that.... so, would a 0.5cubic ft enclosure be OK for doing that type of install, or do you need a bigger/samller/different enclosure if installing the subs like that?   What are the pro's/cons of running subs like that as opposed to conventionally (with the back of the sub inside an enclosure)?

You can run the sub either way in this case. It is all determined by the net volume of the enclosure. If the box volume is .5 cu.ft. net internal volume, then you need to add the space that the driver takes up to this volume. (the driver occupies a volume of air) Let's say that the sub displaces .12 cu.ft of airspace, the gross volume of the box would now be .62 cu.ft. internal, less the sub mounted conventionally of .12 cu.ft, leaving a net volume of .5 cu.ft. internal.

You can choose to mount the sub either way, there is little to no sound difference that you will ever hear. One of the potential pitfalls to this type of mounting system is if you are going to carry objects in the trunk, if they are not secured they can hit against the sub and break of the speaker wires and or the speaker wire terminals.

If this is for a sealed box, you can be out by a country mile on air volume before it will adversly affect how the subwoofer is going to perform. A sealed box is very forgiving in how it operates. Try it both ways if you like to see if you can hear any difference. There is a great enclosure volume calculator on this site. Play around with it and see how changing the measurements change the overall volume.

When I see inverted subs I smell SPL.  Seeing the cone indicates SQ.  But that's just me.  Here's the sub manual.  Those are some nice subs, and I see they are rated at 450 watts RMS.  But should do fine with 300W each.  There is a model of a sealed enclosure in the manual.  It looks as though Boston is allowing for the displacement of the speaker when they indicate building a .5 ft^3 (internal dimensions) box.  They show  a box at 7.5" X 11" X 11", which comes out to 0.525 ft^3.  The dispacement of that sub must be close to .12, which is much more than the overage in the model indicates ( 0.025 ).  So the actual air volume after the sub is mounted will actually be less than 0.5.  I don't see anywhere in this manual where they provide the displacement of the sub.  I take that, along with their statement "Eclosure measurements are internal and include basket displacement" to mean that the box at 0.5 is what you build it at, not what's left after the sub is mounted.  If you have the right room, you might just build the boxes as shown in the model.  If they are going to be shaped differently, just design the box so that the volume of the inside come out the same as the model.

You have to know what the dispacement of the basket is, along with the volume of the cone area, to invert the sub and still have the proper air space.  The basket will be outside the box, as well as the area inside the cone.  So the remaining amount of air space has to be lessened to compensate.  As for sound quality, there should be no difference in the two mounting types as long as the air space in the box is proper for each way.

Cool, thanks for that....

I actually will have this install going into a 1969 beetle, (where the back seat used to be), so will have heaps of room to utilise.....

I want to do something a little different than just a square or wedge shaped box, so was thinking of doing a Fibreglass enclosure, building some MDF sub rings, and strectching some grill cloth into a nice contoured shape along the back firewall and sides of the back seat area...one sub either side....kinda hard to imagine without a pic if you are not familar with beetles :)  Keeping that in mind, is the internal shape of the enclosure super important?  eg; if I do build a FG enclosure with an irregular shaped internal airspace, and the intenal volume of the enclosure is 0.5cft, would that work OK?

I guess doing that, the only hard thing would actually be working out the internal volume of the enclosure.....