More volume from 1 sub @ 300W or 2 @ 150W each?

[drpeeb 10+ year member]

its not black magic or anything. alpine, jbl, jl, and a few others have amps that do the same power at any ohm. actually the jbl bpx1100.1 did more power at 4 ohm than 1.

I'm just saying I don't understand how they do it? Do you? I'd like to know.

In my head, normal electrical math: (All else being equal) Reduced impedance (ohms) = increased power (watts)

What part of the formula are they adjusting, and how?

 

[drpeeb 10+ year member]

No, meaning I disagree. I've done higher numbers on my own setup with half the power, and half the cone area.
90% of a decent setup is in the install.

Good lord! Now that's what I'm talking about! 1/2 the power and 1/2 the cone area. Can you elaborate??

I have very limited space in my extended cab truck ... and no need to waste power. How did you do it??

 

[Nicky Pass 10+ year member]

I'm in the same situation. I'm buying the PDX 5 this weekend and I've seen people post birth sheets that say the sub channel is well over 300...I've seen 321-371 watts. I am debating the same thing...thinking one sub or two....but I'm going with JL Audio W1s I think. I know that you gain 6dbs if you double your set up. Is 6dbs really audible?

 

[Safe_Cracker 10+ year member]

I'm just saying I don't understand how they do it? Do you? I'd like to know.
In my head, normal electrical math: (All else being equal) Reduced impedance (ohms) = increased power (watts)

What part of the formula are they adjusting, and how?

Not if there is a circuit controlling the load the amp sees no matter of the actual load at the terminals. You have to remember the voltage is there 100% all the time all it takes is for it to be switched on/off in a uniform wave pattern +/- voltages really doesn't need a load to produce the desired output.

Polo..

 

[drpeeb 10+ year member]

I'm in the same situation. I'm buying the PDX 5 this weekend and I've seen people post birth sheets that say the sub channel is well over 300...I've seen 321-371 watts. I am debating the same thing...thinking one sub or two....but I'm going with JL Audio W1s I think. I know that you gain 6dbs if you double your set up. Is 6dbs really audible?

Sorry, I had this wrong the first time

In math, a 3 dB gain is equal to 100% more, or double your original value (10W -> 20W is a 3 dB increase):

Original value + 3 dB = double your original value (example 10W -> 20W)

Original value + 4.8 dB = triple your original value (example 10W -> 30W)

Original value + 6 dB = quadruple your original value (example 10W -> 40W)

... so again if your 6 dB increase is accurate, I don't know how you couldn't hear it!

Oh, and one of the beauties of the PDX-5, with 300W RMS at either 2ohms or 4ohms ... you should be able to put in two 4ohm DVC subs at 150W each, and just yank one out when needed (if they're in separate enclosures that is).

The Alpine SWS-1043D (~$70) is a 4ohm DVC sub that can handle 300W RMS/ 900W max. I ordered two of them.

Kinda wanted the Alpine SWR-1042D "Type R" (~$105) (4ohm DVC) sub, but too darn deep and I'm not sure the PDX-5 has enough power for one, especially two of them.

 

[drpeeb 10+ year member]

Not if there is a circuit controlling the load the amp sees no matter of the actual load at the terminals. You have to remember the voltage is there 100% all the time all it takes is for it to be switched on/off in a uniform wave pattern +/- voltages really doesn't need a load to produce the desired output.

Polo..

I guess the PDX-5 must have resistors inside it, so that if you show it a 2ohm load, it can switch the resistors on to limit the power to 300W, instead of letting the power increase beyond 300W.

Maybe anything above 300W doesn't meet their other specs (distortion, etc.).

Is that right?

 

[Propimp 10+ year member]

I'm in the same situation. I'm buying the PDX 5 this weekend and I've seen people post birth sheets that say the sub channel is well over 300...I've seen 321-371 watts. I am debating the same thing...thinking one sub or two....but I'm going with JL Audio W1s I think. I know that you gain 6dbs if you double your set up. Is 6dbs really audible?

Yes put in this instance you are doing 1 of 2 things... Doubling the cone area and cutting power in half.... or doubling the power and cutting the cone area in half..

 

[drpeeb 10+ year member]

Yes put in this instance you are doing 1 of 2 things... Doubling the cone area and cutting power in half.... or doubling the power and cutting the cone area in half..

Is there any gain to be heard or felt from having a 2nd sub coming from a slightly different location? ... i.e. 1 under each rear seat? ... even though the power to each would be half ...

 

[drpeeb 10+ year member]

I'm in the same situation. I'm buying the PDX 5 this weekend and I've seen people post birth sheets that say the sub channel is well over 300...I've seen 321-371 watts. I am debating the same thing...thinking one sub or two....but I'm going with JL Audio W1s I think. I know that you gain 6dbs if you double your set up. Is 6dbs really audible?

The birth sheet that came with the new PDX-5 I just got says:

Specification is 75W RMS (Full-range), but Actual is 121W

Specification is 300W RMS (Sub-woofer), but Actual is 424W

I assume this is accurate ... Wow

 

[GMCJimmyslt2000 10+ year member]

I would get one sub and give it rated rms, to me, it would be better than getting 2 and giving them 1/2 rated power.

 

[drpeeb 10+ year member]

I would get one sub and give it rated rms, to me, it would be better than getting 2 and giving them 1/2 rated power.

Well .. I got a two-fer deal on the subs on eBay, and I still have more than 2/3 sheet of MDF ... so I will probably go ahead and try it with 1 and 2.

Just got the 1 in tonight ... Awesome!

 

[squeak9798 5,000+ posts]

I guess the PDX-5 must have resistors inside it, so that if you show it a 2ohm load, it can switch the resistors on to limit the power to 300W, instead of letting the power increase beyond 300W.

No.

The amplifier likely adjusts it's rail voltage based on the load to maintain equivalent output with differing loads. It doesn't "change" the load.

 

[Nicky Pass 10+ year member]

The birth sheet that came with the new PDX-5 I just got says:
Specification is 75W RMS (Full-range), but Actual is 121W

Specification is 300W RMS (Sub-woofer), but Actual is 424W

I assume this is accurate ... Wow

I picked mine up last weekend...

Specification is 75W RMS (Full-range), but Actual is 124W

Specification is 300W RMS (Sub-woofer), but Actual is 421W

I guess these things are underrated!

 

[cotjones 10+ year member]

I'm just saying I don't understand how they do it? Do you? I'd like to know.
In my head, normal electrical math: (All else being equal) Reduced impedance (ohms) = increased power (watts)

What part of the formula are they adjusting, and how?

Rail Voltage. The the Amp Detects the current load being delivered to the subs and adjusts the rail voltage accordingly to maintain the same output over a range of ohm loads and amp input voltages.

 

[cotjones 10+ year member]

Sorry, I had this wrong the first time
In math, a 3 dB gain is equal to 100% more, or double your original value (10W -> 20W is a 3 dB increase):

Original value + 3 dB = double your original value (example 10W -> 20W)

Original value + 4.8 dB = triple your original value (example 10W -> 30W)

Original value + 6 dB = quadruple your original value (example 10W -> 40W)

... so again if your 6 dB increase is accurate, I don't know how you couldn't hear it!

Oh, and one of the beauties of the PDX-5, with 300W RMS at either 2ohms or 4ohms ... you should be able to put in two 4ohm DVC subs at 150W each, and just yank one out when needed (if they're in separate enclosures that is).

The Alpine SWS-1043D (~$70) is a 4ohm DVC sub that can handle 300W RMS/ 900W max. I ordered two of them.

Kinda wanted the Alpine SWR-1042D "Type R" (~$105) (4ohm DVC) sub, but too darn deep and I'm not sure the PDX-5 has enough power for one, especially two of them.

This is incorrect. There is a difference in sound level intensity and perceived loudness.

Percieved loudness varies as the cube root of intensity.

So theoretically to double your percieved loudness with 10watts you would need 80 watts.