A question I've always wondered the answer to..Power vs load

[brodzowski]

Perhaps it's a silly question for someone who's been into car audio as long as I have, but does anyone have a definitive answer on bridging amplifiers and the power requirements for subs? Do they multiply? I have 4 RSDC102s on the way which are rated at 600 rms. They are dual 2 ohm voice coils and can be run at a 1ohm or 4 ohm load with my setup. If they are tethered together, does that effectively mean that they should be seeing 2400 rms? Peak they are 1200. 4800 watts for 4? Really? That just seems insane to me. I must be missing something or I'm really stuck in old school world.
The pinnacle of the MS career, the MS1000 was 1000 watts x 2 BRIDGED. Good lord. I remember thinking, who in the world could actually use that kind of power? And then came along "the one" albeit not for the real world. Regardless, I know that you don't double your power when you bridge, but if you DO double your power "needs" when you series/parallel, then I'm not going to have NEAR enough juice to run these guys. Planned on running my 2500 at 1 ohm or my 2125 at 4 and seeing which I preferred. If neither worked I was going to sell the 2125 and upgrade to the 2250. Any thoughts on this setup?

Also, do the 2125 and the 2250 have the same size sink? I looked in the literature and the 2250 had much bigger dimensions, but I wondered if that was because of the fan shroud.

Thanks for any help!

[stipud]

Peak wattage is a nonsense number, RMS is all that matters. It doesn't matter what the voicecoil configuration of the subwoofers are; if one is rated 600w RMS, two are rated 1200w.

Bridging is when you use two channels of a multi channel amplifier together to add their outputs together. Since the load is shared between channels, the load on the individual channels is actually half of the load connected. So if you have a 4 ohm bridged load, that is the same as 2 ohm stereo. "The One" is a mono amp, so it can't be "bridged". However, it is designed to be "strapped", which is essentially bridging two separate monoblock amplifiers, doubling their power output (at double the impedance)!

Power between your 2500 at 1 ohm and 2125 at 4 ohms is going to be pretty similar. I would personally use the 2500 at 1 ohm, since that frees up the 2125 to be used on the front stage. You shouldn't need a 2250... it's double the power, yes, but that only accounts for a 3 decibel increase in sound levels. Not a big deal.

[cyberpunky]

Subs use power and the 600wRMS rating is just the maximum RMS power they can take, so in theory you could feed them(combined) a total of 2400wRMS, but whether you need to or not is another question. BTW forget peak, as you cant measure it, adjust for it etc, it just a marketing exercise.

How much power you need depends on what you are trying to achieve. If you are building an SPL one note car, then it really matters how much you can throw at them and how much they can handle, but if it's for music then it's doubtful you will need that sort of power.

For music you are trying to get an overall (spectral)balance. You don't want too much treble or not enough midrange etc. If you were to run 4 subs getting 2400W then you would have a hard time building a front stage that could keep up. No doubt you would end up with the level of subs pulled down and not getting anywhere near the maximum output the sub system could produce.

Also remember that amps only put out full power at full volume(maximum level), and so even if you had 2400w on tap you may only be listening to 10W or 100w at more normal listening levels. You subs won't break if you don't feed them the max they can take. I had 2 900wRMS subs(so they could take 1800w total), but I only fed a total of 600RMS to them. They sounded great and were balanced with front stage nicely.

If you can run 1000w(or 10W) and get the level you need, then buying an amp that does more is really a waste.

hope that helps
peace
Cyberpunky

[00goobs]

I think the actual power of any amplifier would be the capability of its power supply. Each transistor is rated for a good amount of amperage, but the voltage starts to drop the more power you use. So doubling the wattage when you add more of a load/resistance only goes as far as the power supply can provide. I think recommended fuse size multiplied by actual voltage and efficiency gives a pretty good estimate of max power ability... Maybe...

Hello from my phone!

[NewOldStock]

its also a common misconception that a dual 2-ohm sub can only be run at 1 or 4 ohms. There is nothing wrong with running a single voice coil on a sub. Its actually not uncommon on some SQ setups to wire just a single VC to better tune the SQ of the subwoofer.

[Mr. Wild]

The amount of power you need depends on your subs and how loud you like it. I would imagine just 2 RSDC tens would play as loud as hell. Plus they could handle all the power your amp produces.

I'm running one JBL 1200GTI with about 100 watts, and I'm a bit worried about my hearing. Then I don't have the subwoofer cranked up. I listen to metal music, not my equipment.

Yes you can run a DVC sub with only one coil connected, but the T/S parameters are totally different. So you need to know what you are doing. No sub manufacturer I know of publishes T/S parameters with only one coil connected.

[gfunk_nz]

Yes you can run a DVC sub with only one coil connected, but the T/S parameters are totally different. So you need to know what you are doing. No sub manufacturer I know of publishes T/S parameters with only one coil connected.

and you would normally short out the unused coil to try to minimise the effects

[stipud]

Yes you can run a DVC sub with only one coil connected, but the T/S parameters are totally different. So you need to know what you are doing. No sub manufacturer I know of publishes T/S parameters with only one coil connected.

Not to mention the power handling is halved. Depending on how the coil is wound it might not work at all.

Generally not a good idea!

[ttocs]

its also a common misconception that a dual 2-ohm sub can only be run at 1 or 4 ohms. There is nothing wrong with running a single voice coil on a sub. Its actually not uncommon on some SQ setups to wire just a single VC to better tune the SQ of the subwoofer.

The only sub I have ever blown was hooked up in this manor. Sure you can disconnect 4 of your 8 cylinders but those remaing 4 will have to work harder to pull the same weight, and harder work will add up fairly quickly. I have heard since then to NEVER do just one coil.

[Eric D]

I have never heard of anyone using just one coil on a DVC sub for an SQ setup. If you use just one coil the sub will not sound right, as its frequency response will change from the additional weight of the second coil not helping the sub move. You end up with a speaker which does not sound as good, has half the power handling, and moves only a fraction of what it should. So you have nothing to gain.

If you short the "spare" coil, there is a good chance you will kill the sub. A shorted coil in a magnetic field is like an air break for the sub. This will highly restrict the motion of the sub, and generate even more heat in the voice coil assembly. You can short a coil and move the sub by hand to feel the difference it puts on the motion of the sub.

[gfunk_nz]

I remember seeing focal K2P I think woofers with a shorting ring included and instructions on using it, they were the only manufacturer I saw though do that, also just recently either Scott Atwell or Nick from Fi gave a good run down on what changes when you only run one coil. Some also use potentiometers to adjust Qts.

edit, found the bit I was looking for

"While we dont tell people its OK, you can fudge it a little by shorting the non-powered coil. Simple jumper across the + and - terminal and it will bring TS specs a little closer to original values. Otherwise, Qts is significantly higher. Power is a different story... and while not cut in half, it can have issues with higher current through a single set of leads over other wiring scenarios which can lead to issues.

Thanks,
Scott "

[00goobs]

I had a Pioneer home speaker system that used a dual VC 15" (dual 8 ohms). One VC was direct to the input and the other to a passive low-pass x-over. With the straight input removed, it was almost completely sub-bass and with the x-over disconnected, the bass was alright but playing full-range. Of course, the 15s sounded better in a truck and actually hit 130db with 320watts of Kenwood 921 power, hehehe.

Yes, this has almost nothing to do with the original post, but it has dual voice coils, hehehehe...

I do believe shorting a coil counter-acts the magnetic force and acts like a brake as it does with a DC motor. I THINK it is like a destructive eddy current or something...

[shawn k]

its also a common misconception that a dual 2-ohm sub can only be run at 1 or 4 ohms. There is nothing wrong with running a single voice coil on a sub. Its actually not uncommon on some SQ setups to wire just a single VC to better tune the SQ of the subwoofer.

I see NewOldStock is getting some flack for this statement, so I thought I'ld help him out a bit He's right guys, well for the most part. There are some SQ tuned systems that do this. Although I would not go as far as saying "There's nothing wrong with it" because there are certainly trade offs that won't work well with certain design goals.

If you use just one coil the sub will not sound right, as its frequency response will change from the additional weight of the second coil not helping the sub move

This is not true. The added weight of the unused coil will have an effect on TS parameters (mainly raising Qts) but in no way will it nor can it "change" the freq that the driver is being fed.

You end up with a speaker which does not sound as good, has half the power handling, and moves only a fraction of what it should. So you have nothing to gain.

Does not sound as good as what? This is a matter of opinion really. The higher Qts of this design allows for smaller enclosures still allowing for low F3, or moderately sized enclosures with even lower F3. True, power handling does drop as well as excursion. But this is why also why it's typically used for SQ systems. Here you don't need astronomical power handling nor extreme excursion (the more excursion the higher distortion anyway).

Back in the 90's, when car audio competitions were rampid, there were many competitors who would exploit this technique. For instance: you might see someone using two fifteen dvc's (seperate chambers) in his install. This would be great for high spl scores! Then he could engage a couple relays and run just one of the fifteens with just one coil in the same enclosure thereby raising Qtc and lowering F3 and now he's ready for SQ judging

[brodzowski]

Back in the 90's, when car audio competitions were rampid, there were many competitors who would exploit this technique. For instance: you might see someone using two fifteen dvc's (seperate chambers) in his install. This would be great for high spl scores! Then he could engage a couple relays and run just one of the fifteens with just one coil in the same enclosure thereby raising Qtc and lowering F3 and now he's ready for SQ judging

I find this incredibly interesting. Really has nothing to do with my original question, but thank you for this debate/lesson as it's very intriguing regardless.

[Eric D]

A shorting ring and shorting the voice coil are two similar things, but are not the same thing. Shorting rings are generally very few winds, and they are generally located at the ends of the voice coil former so they can act as "brakes" when the coil reaches extremes of excursion.

As for one coil not having the same frequency response as using two on a DVC, until proven otherwise, I still feel I am right. The reason I feel so is I have done it, and I have measured it with lab equipment. Now in all honestly, I can see it being theoretically true that the frequency response would not be affected, as you have the same moving mass, and are just reducing the flux generated in the coil, no different than reducing the input voltage to the speaker. So with that in mind, then why would it measure different?

Also, I am not talking about the speaker changing the frequency response of what it is being fed, I am talking about the frequency response of the drivers output changing. With a flat input and both coils used you get one frequency response, and with only one coil used, and a flat input (at a compensated voltage for the single coil), you get a different measurement than before.

[Eric D]

Well, from my internet research I just did since my last post I think I have this figured out...

1) Frequency response should be the same using one coil from a DVC woofer. Why I have had different results in the past was likely due to an error in my setup or something. Plus being 8 years ago when I did it, who knows.

2) Qts and F3 are exactly the same using one coil over using two. (this is assuming the second coil is not connected to anything)

3) Power handling is half (with only one coil, you have half the thermal power handling)

4) If you short the second coil you have problems, and it is a bad idea.

5) If you connect the second coil to a resistor, or a pot, you can change the Qts

6) Now, my assumption is is you connect the second coil to a resistive load, your speakers power handling will fall by even more than half. Reason being, if you run a shorted coil through a magnetic field the current generated becomes heat in both the coil and the resistive load on it. This is just my assumption, but I am pretty sure it is correct.

[gfunk_nz]

They Guy I quoted above knows his stuff when it comes to all things speakers, he designs and builds in Vegas for both his companies Fi and Ascendant Audio, along with other manufacturers, he also has a company that has designed noise reduction stuff. He was also the brains and one of the gusy that started RE Audio. He doesn't post up a great deal, but when he does I listen to what he says.

[shawn k]

They Guy I quoted above knows his stuff when it comes to all things speakers, he designs and builds in Vegas for both his companies Fi and Ascendant Audio, along with other manufacturers, he also has a company that has designed noise reduction stuff. He was also the brains and one of the gusy that started RE Audio. He doesn't post up a great deal, but when he does I listen to what he says.

Yes, I agree with him completely (not that he needs my approval ) but it does coincide with what I've been taught/researched over the years

Anyone with a dvc sub can easily test this. Disconnect one coil and listen to some music with some good low freq information and you should be able to hear that the sub drops a little lower. (Do this at moderate listening levels though. High output is not the goal here and power handling will drop! ) Of course some drivers will have a more significant difference than others, but it should be noticable. An analyzer would give you the opportunity to measure it as well.