splitz

Ok, I understand the principle, less resistance equals more power, but what does that mean to a dual voice coil sub?


MY THEORY:

Connecting an Infinity Kappa Perfect 12d in paralell for 2 ohms mono on a Sony 1002HX, 380 (max) to each voice coil and 760 watts (max) total ouput power to the sub.

MY QUESTIONS:

Is the theory correct?

The sub is listed at 350 watts (RMS) 1400 watts (peak), is this for BOTH voice coils or for EACH?

Will this be better than running a single voice coil at 4 ohms, and having it recive 630 (max) watts?

I also will take any suggestions instead of the Infinity sub, as long as it is under $170.

Thanks to all who have helped in the past, and to those who shall help in the future.

Splitz

Southbound

Your theory is only correct if the amplifier CAN SUPPLY the power.

Your statement of less ohms EQUALS more power should really be stated as... Less ohms REQUIRES more power. It's the amplifier NOT the speaker that determines the actual power involved.

If your amp can indeed drive a 2ohm load and remain stable, then this would provide twice the power or 3db more SPL to your system. I don't know how much major thump you are after... but you could blow your amp if it's not designed for the dual voicecoil 2ohm load. And since power is logarithmic, you will only gain another 3db in SPL.

I don't know anything about the particular woofer that you are speaking about, but perhaps some other members can give you better advice.

I can just advise you about simple power calculations. Just remember that it is the AMPLIFIER that creates the power and therefore ultimately determines how much power is actually delivered to your speaker system.

Ohms law is simple for easy calculations. (assuming rms sinewaves, which is good enough for these purposes, Some manufacturers do not truly use rms values in their product specs, and peak power can be very misleading)


OHMS LAW...

VOLTAGE (E) equals CURRENT (I) multiplied by RESISTANCE (R)

CURRENT (I) equals VOLTAGE (E) divided by RESISTANCE (R)

RESISTANCE (R) equals VOLTAGE (E) divided by CURRENT (I)

POWER IN WATTS (W) equals VOLTAGE (E) multiplied by CURRENT (I)

POWER IN WATTS (W) equals VOLTAGE (E) SQUARED and then divided by RESISTANCE (R)

POWER IN WATTS (W) equals CURRENT (I) SQUARED and then multiplied by RESISTANCE (R)

BASIC REMINDERS...
TWICE THE VOLTAGE equals FOUR TIMES THE POWER or 6db more SPL.

TWICE THE CURRENT equals FOUR TIMES THE POWER or 6db more SPL.

TWICE THE RESISTANCE equals HALF THE POWER or 3db less SPL.

HALF THE RESISTANCE equals TWICE THE POWER or 3db more SPL.

HALF OR TWICE the POWER equals a change of 3db in SPL. NO MATTER if you're talking about 1 milliwatt or 1 megawatt.

TEN TIMES POWER equals a change of 10db in SPL.

100 TIMES POWER equals a change of 20db in SPL.

1000 TIMES POWER equals a change of 30db in SPL. etc, etc.

HALF OR TWICE VOLTAGE OR CURRENT equals a change of 6db in SPL because Voltage and current are SQUARED in the equation for power. This means that HALF or TWICE the VOLTAGE OR CURRENT produces FOUR TIMES THE POWER. Double the power equals 3db plus doubling it again to achieve FOUR TIMES THE POWER adds another 3db for a total change of 6db in SPL.

I hope some of these basics help.

Good luck!
Southbound

splitz

Southy,

Thanks for the info; basically I am trying to get the max power therefore SPL out of the amp as I can. The amp is 2 ohm stable running mono, and reading your post I still have a few questions because the variables are NOT mutually exclusive:

If resistance is halved (from 4 to 2 ohms), then current is increased, voltage is decreased and there is a 3dB increase in SPL? (I would think that the decrease in voltage would have an adverse affect on power, therefore on SPL gained as well

If resistance is doubled (from 4 to 8 ohms), then the current is decreased, the voltage increased and there is a 6dB increase in SPL? (I would think that the increase in resistance and a decrease in current would have an adverse affect on power, therefore on SPL gained as well)

So which is best for the MAX power/SPL?

A single VC running at 4 ohms
A DVC running at 2 ohms
A DVC running at 8 ohms

Thanx,

Splitz

shawhite

in your equation the voltage sould remain pretty constant.. (+12v)... the only varibles that should change are current (I) and resistance (R)...as for which configuration would give you the max power.... i would say a dvc running @ 2ohms will give you the most power to that speaker... if you ran the dvc @ 8 ohms you would be getting approx 1/2 the power of the amps rating @ 4ohms.. and 1/4 the power of the amps rating @ 2ohms... so say the amp is rated @ 380 x 1 @ 4 ohms and 760 x1 @ 2ohms... @ 8 ohms you would get somewhere around 190w.....

oh also the kapa perfects are recommend for 175w rms to each vc... i could not find anything on that amp but i was wondering when you say 380 (max) does this mean peak... if so then your rms (root means square) value would be the max value x 0.707... either way this amp should push this sub just fine... to be honest this amp could push two of the single vc kappa perfects just fine...

splitz

shawwhite,

Rock on, so that is what RMS stands for! Yeah that is 380 peak output, so if what you are saying that means 268 watts rms will be sent to EACH voice coil?

peak @2 ohms bridged = 760
760/2 = 380
380 * .707 = 268 watts rms to each VC

So the amp might be a little TOO much if it is 175w rms to EACH VC.

The specs for this amp can be found at http://www.carsound.com/reviews/amps/xm1002hx.html

As for two of the single VC kappas, uh I have two issues with that, currently I have one Kappa Perfect 10 and I'm just looking for a little more umph so two 12's might be overkill (if there is such a thing) and DOLLAASSS (as in I dont wana spend alot of em).

thanks for your help (once again),

Splitz

Brewboy

The power rating per vc is NOT a power requirement. The power ratings for subs are per IEC268-5 (using a specific test signal). This does NOT mean you need the listed power rating to get full performance from your sub. What it means that your sub's vc can handle xxxW of power with the test signal. The max amount of power to your sub is dependent on your box type and box size. You should use the T/S parameters for your sub to determine the max power needed to reach full excursion in your specific box type/size, else you'll get a blown sub, especially when ported w/o a subsonic filter.

splitz

Brewboy,

I know the power rating is NOT a power requirement, but I want to get the most out of what I have (or will get). Infinity recommends a 1cuft sealed box for the sub, so I'm assuming that the max power that is listed is in reference to that.

All I am really looking for is what will sound the best:

A single VC running at 4 ohms
A DVC running at 2 ohms
A DVC running at 8 ohms

On a related note I've found a site with all kinds of info (too much for me, but I'm trying to digest it ALL). Anyway, here is the link to calculate the box size:

http://www.eatel.net/~amptech/elecdisc/spboxad2.htm

and here is the link to ALL of the calculators and info:

http://www.eatel.net/~amptech/elecdisc/caraudio.htm

Splitz

Southbound

splitz,
shawhite is right on with his response in that the Voltage does not typically change when the resistance is changed. It should remain constant and only the current will change. However, in TRUE practice the voltage will sag a bit depending upon how beefy the power supply feeding the amplifier is. SO FOR EXAMPLE, an amplifier rated for 200watts rms, into 4ohms should theoretically provide 400watts into 2ohms. But you will find in reality that it will probably only produce 300 and some watts because the power supply voltage has sagged in the amplifier's output stage or the power supply itself.

Power calculations and product specs can be VERY misleading! The only true rating to trust is the RMS power into a certain load resistance. Peak power can sometimes be overrated and really be refering to "Peak to Peak" power. If the amplifier company doesn't have enough balls to provide a TRUE RMS power rating into a referenced load impedance, then I wouldn't trust any of its specs....

"RMS" (root mean square) applies DIRECTLY to VOLTAGE, NOT POWER as stated above. You must use the RMS voltage (and rms current will follow) to calculate the actual RMS POWER.

"root mean square" means the square root of the sum of all the voltage amplitudes squared... throughout the sinewave's various phases. One cycle of a sinewave is made up of 360 degrees. The amplitude of the sinewave at any given point in its cycle, is simply the "sine of the phase in degrees" at the point measured. The sinewave starts out at ZERO degrees at the baseline of zero volts. At 90degrees into its cycle it is at the POSITIVE PEAK of its amplitude. At 180degrees into its cycle it is back at the baseline of zero volts. At 270degrees into its cycle it is at the NEGATIVE PEAK of its amplitude. At 360degrees, it is back at its Zero degree starting position, and another cycle starts out all over again.

You could take the sine of each degree within the cycle to determine the voltage amplitude at that point with respect to the PEAK voltage. If you did this for all 360 degrees, and then squared all of those values, and then added them all up, and then took the square root of that value, you would have the RMS (root mean square)value of a SINEWAVE. IT SO HAPPENS, that after going through all of that math, it comes out to be the SINE OF 45 DEGREES OR .707 TIMES THE PEAK VOLTAGE.

So back to your formula for RMS power verses PEAK power... it isn't simply .707 times the PEAK power to come up with the RMS power. You have to find the RMS voltage of the PEAK voltage and then use OHMS LAW. THE RMS VOLTAGE OF A SINEWAVE WILL ALWAYS BE .707 X THE PEAK VOLTAGE. This is significant because this is the value that produces the same current and heat characteristics as a continuous DC voltage. THAT IS WHY RMS SPECS ARE SO IMPORTANT! They give you the amplifier's TRUE continuous power capacity, or a speaker's true continuous power handling capability. So for example again, a PEAK voltage of 10volts would have an RMS value of 7.07volts. (10 X .707). This means that a true sinewave of 10volts peak would have the same power and heating characteristics of a DC voltage of 7.07volts applied to a load.

Sorry I drifted again, so back to the RMS power formula. As another EASY example, take an amplifier system that has a power supply of +10volts with respect to ground. This means that the amplifier has an available range in which the output stage can swing of zero to +10volts. In this case, one would typically bias the amplifier to have a no signal output voltage set to the midpoint of this power supply, or 5volts. Once a signal is applied, the output will swing from 5volts up to a max positive peak of ten volts at 90degrees in its cycle, and down to a negative max peak of zero volts at 270degrees into its cycle. If the gain or the input signal is excessive and tries to force the output signal above or below these two excursions... IT WILL CLIP THE SIGNAL. That's what amplifier clipping is. The amp has run out of available power supply rails in which to swing between, and all it can do is stay at the peak until it is further along in its cyle to where it would be below the 10volt or ground amplitude excursions. Then it will come out of clipping. The harder you drive an amp into clipping, the larger a portion of its cycle will stay up in the clipped region and can appear almost as a square wave.

SO, FOR THIS PARTICULAR EXAMPLE, the PEAK voltage would really be 5VOLTS, the PEAK TO PEAK voltage would be 10VOLTS, and the RMS voltage would be .707 times the PEAK of 5volts, or ONLY 3.535volts!

To find the RMS power into 4ohms, use the formula in my post above where current and resistance are known. 3.535 (squared) divided by 4, which equals 3.125 WATTS RMS...

The PEAK power would be 5 (squared) divided by 4, which equals 6.25 WATTS PEAK...

If a CHEAP amplifier company wants to overrate its specs, they sometimes use the PEAK TO PEAK voltage for their power ratings and still get away with calling it PEAK POWER. In this case PEAK TO PEAK power would be 10 (squared) divided by 4, which equals 25 WATTS PEAK TO PEAK! That is a BOGUS way to rate an amp, but some manufacturers do this to appear bigger and better than they really are.

Keep in mind that the example above is ONLY an example and did not use typical voltages or BRIDGE techniques involved in actual amplifier design. HOWEVER, the math is still accurate no matter what power supply is used or whether or not the amp is bridged.

You will notice that the difference between the TRUE RMS WATTS (3.125) and TRUE PEAK WATTS (6.25) is EXACTLY DOUBLED or 3db difference. SO again, the actual math becomes REAL EASY to calculate in your head. To find the RMS (DC equivalent) POWER rating from a PEAK power rating, SIMPLY DIVIDE BY HALF. This is the only area where shawhite was slightly mistaken. You can't simply take .707 times the PEAK POWER to find RMS POWER... You MUST break it down to the voltages involved, and then square that voltage using OHMS LAW to come up with the RMS Power value. However, after all of my rambling, it simply turns out to be 1/2 of the PEAK VALUE or 3db less. THAT ASSUMES THAT THE POWER SUPPLY REMAINS CONSTANT AND THE VOLTAGES DO NOT DROP AT THE PEAKS . IN A HIGH POWERED COMPETITION SUBWOOFER SYSTEM, the alternator voltage can sag during peaks and therefore, not make the PEAK rated power, which would also change the actual value of the RMS power as well. That's when guys start putting in giant caps across the power supply to hold up the voltage during these peaks, and/or adding a larger alternator and battery, etc.

So your analysis above is ALMOST correct. The 780 PEAK watts into a double voice coil load of 2ohms would equal 780 divided by 2, or 360Watts PEAK into each 4ohm voicecoil. The RMS power into EACH voicecoil would then simply be 1/2 of 360watts or 180watts RMS each. The total system RMS POWER into 2ohms would be... 1/2 of 780watts PEAK, or 360watts RMS TOTAL. This assumes that they didn't use PEAK TO PEAK values when calculating the PEAK power for the spec. sheet??? It would have to be a really cheesy amp for them to pull that trick, but I've seen it done...

In ANY CASE, your loudest SPL will come if you parallel the two voicecoils into a 2ohm load as long as the amplifier is stable and intended to drive that low of an impedance. As Shawhite explained, 4 or 8 ohm configurations would produce less power. Again REMEMBER it is the AMP that PRODUCES THE POWER. It is the ohms that determine how much power the amp will need to supply at full voltage. So your statement above where you mention that the amplifier may be a bit TOO much because it is rated at 175watts rms is incorrect. I don't know how you derived that conclusion? If a speaker is rated at a particular wattage, then any amp below that wattage can still drive it, just not to its full potential. And an amp that is rated HIGHER can still drive the speaker, but has the capability of destroying it if turned up too loud.

I hope things are starting to make sense to you now, as I have spent an hour and a half writing this novel. JUST REMEMBER TO COMPARE APPLES TO APPLES. Be sure that you are comparing RMS values to RMS values and PEAK values to Peak values. ALSO BE SURE THAT THE POWER COMPARISONS ARE INTO THE SAME OHMS! You can re-calculate any of the values using the different variations of OHMS LAW that I posted above...

For most suds, go the 2ohm route. I guess I could have just told you that, but then I'm here to try and help people better understand the whole story.

Good luck!!!
Southbound

splitz

Southbound,

Scarily I understand pretty much everything you said...I'm going cut and paste everything I've learned from you and publish a book!

No but seriously, thanks for the great info as always, I guess I just have to decide on a sub now.

Anyone have any thoughts?

$160 Infinity KAPPA PERFECT 12.1D
$145 Kicker 02S12L5 Solo-Baric L5
$140 Xtant A1244A
$135 Rockford Fosgate Punch HX2 RFD2212
$130 Eclipse SW-6122DVC
$115 Alpine SWR-1241D Type-R Series

Splitz

Brewboy

Splitz,
A much better program to use is winISD PRO. Can download free from
http://linearteam.dk/default.aspx?pageid=winisdpro
Has huge library and can add others, gives much more info like spl, excursion, phase, etc...
As for subs less than $150, I'm partial to the Adire Shiva at $125( I have two in my home audio sys). Also, as of a couple of days ago, a newer company, Elemental Designs, is offering a preorder for most of their subs at 15% off the direct price. Shipping to start June 1. They offer a few subs in your price range too. They have a flat cone and woven leads. I may even pick on up to play with. Search for their website.

splitz

Brew,

I took a look at Elemental Designs on sounddomain.com, there stuff looks pretty good, but I'm sketchy about getting something that is off brand (not that I have ruled it out yet). I'll do more research on them and try to get in contact with the people who have purchased from them. The same pretty much goes for Adire; not main stream, but thier products look pretty good so we'll see.

Splitz

shawhite

what about alumapro or boston acoustics... they are both excellent speakers..

splitz

Shaw,

Hey that's a great tool, but it said that the Infinity Kappa Perfect 12.1d required a box with 1.23 cu ft, vice the 1 cu ft Infinity has printed on thier spec sheet. So which one is right?

Splitz

Brewboy

Splitz,
The difference in box size is dependent on the user. Different box sizes will give you different alignments, Qtc. Mfg's will quote box sizes that are easy to live. Go back to the graph and change the box size from 1 to 1.23 to 2 and notice the Qtc number and fr will change . For sealed systems, the smaller the box, the higher the alignment. A higher alignment results in a bit more midbass punch(watch the fr graph) while a low alignment, ~.6, will give you a more realistist bass- best for the home set-up. For the car, it'll range from .707 to .9 depending on what the user likes for their particular install/vehicle due to cabin gain and such. If your not sure which alighment you'll like, it's best to build a box as large as you can live with giving you a lower alignment- then you can add wood block into your box to reduce internal volume thus raising your Qtc number till your happy. If you want to take the middle of the road(~.73-.77 Qtc), you can always add poly-fill inside the box to make it act like a larger box, thus lowering the Qtc a few points.
As for branding, well think about how much your paying for advertising, middlemen distribution of those name-brand equipment. Prob about 15% or so. IMO, you getting more bang for your buck with the smaller companies and usually better customer service. Visit SD and Termpro and such and do your research like you've been, maybe pose the same question with the addition of Adire and ED. IF so, to get the best responses, include as much info as you can.. amp, music tastes, max box size, SQ vs SPL, trunk mount, etc... Good luck.

splitz

Brew,

Thanks for the info as always.

I think I am going to go with the Infinity 12 for now but may order an ED...it looks pretty good and what the heck I'll try it. I was playing with the program and it looks like a ported box will sound better it has higher SPL and better transfer function magnitude(whatever that means). I've never built a ported enclosure before, so more questions for the audio gods:

Does the port placement matter?
Would porting it into the cabin be good?
Is a sub-sonic filter absolutly neccisary? I'm only running 280 rms and the chart says thats the max for around 20 Hz.
What should I tune the box to?
How much SQ will I loose with a ported box?
Should I even bother with it?

I finished creating the template this weekend and ordered my components for the doors...this weekend I'll make the template, run the wiring, do the eq bypass, install the speakers (if the come in), and finish the plans for the box & amp rack. We'll see what actually happens.

Brewboy

Port placement matters, usually 1 port diameter from all walls and driver.
I would try to port in the cabin. A few people here have done so. Maybe they'll chime in with their results. The port doesn't have to be in the box, it can extend outside the box up to/thru the rear deck.
At that power, I wouldn't think you'll need a filter, the sub can take it. Usually recommended for people pushing high watts or so. But double check your data to be sure.
I would start at mgf'ers numbers. Think about building the box and port so you can tweak it later. For instance, if the port extends outside the box, you can easily add or subtract length to change tune freq. I wouldn't glue the port in place until you've tweaked it to your liking. You can also tune a little higher for more spl bump when you want to and then plug the port, effectively turning it into a sealed box for daily driving. If you use pvc pipe, you can use a pipe plug or even a nerf football or such.
Most people would agree that a sealed box is better for SQ, but as with any type box, it's all in the install.
Try it, if you don't like it, just seal the port, add some volume to raise the alignment for a sealed box.
Don't be afraid to experiment, good luck.

BTW, just ordered the ED O12. Gonna play around with an IB install.