Quote: "Hey swez this is steve. im researching more into car audio, and im just stuck. I understand the watts in a sub. but what i dont get is RMS. I dont know what it is. I also want to know how to match subs to amps. What do you look for when matching? I trust you, you know a lot, any advice for this would help a bunch." Thanks swez, Steve
Yes, I just spotted it... hehe. I don't get too may Clubmails and forget to look at times... Sorry... M I BADD or what?
I wanted to post this on the board as others often want to know the same things.
RMS POWER: This is often called "Continous Power" and can be expressed in Volts RMS, Amperes RMS or Power RMS. (Watts) RMS means Root Mean Square of a sine wave. (Trig functions here) In a nutshell, RMS power is the AC sine wave equivelent to a DC power source.
Technically speaking, if we have a 100 watt AC sine wave "Peak" voltage value, the RMS value is: 100 x 0.707 or 70.7 Volts AC. This has the same ability to do work, as a DC voltage source of 70.7 volts. (Got all that?) SMILE
OK, back to your other questions. We want to look at RMS power (Watts) ratings on amplifiers, speakers and subs as we choose a given combination.
1. Figure out how much power we want
2. Pick speakers that can handle the RMS power desired
3. Choose an amp that gives the same or a few watts more RMS power than the speakers/sub(s) are rated for
4. Make sure the amp is properly matched for optimum efficiency and power delivery to the ohmic load of the speakers or sub(s) we will use
Example: Say we want a sub amp that can deliver 600 watts RMS to a sub load of 2 ohms. How do we get there from here?
Let's use a Kicker amp for this application. Most know Kicker products are solid and do a very good job.
Amp: Kicker SX 650.1
It's a very good Class D amp choice. It will deliver 650 clean watts RMS into a 2 ohm load. At 4 ohms, it will deliver 325 watts RMS. (Amp supply voltage of 13.8 volts)
Obviously, we want a sub load of 2 ohms here. This load is safe for the amp and most efficient use of the amp too. To get this magic 2 ohms and handle that much power, we'll want either a single 4+4 DVC sub or a pair of 2+2 DVC subs.
1 strong DVC sub, such as an 12L5 or perhaps a 12L7, 4+4 DVC sub with both coils wired in parallel to amp. This nets a 2 ohm load and either sub will take that much power without breaking a big sweat.
Now, suppose we use a pair of subs. Here, we can look at the Comp VR series. These subs are rated at 400 watts RMS per sub, but we can still get good results from the amp mentioned earlier. Here, we'll use a pair of 2+2 DVC's. Each sub coils are wired in series for a 4 ohm per sub load. When both subs are wired in parallel to the amp, we get that magic net 2 ohms and each sub gets a clean 325 watts RMS. Not a bad fit eh?
OK, that's how things work in general. There are other options available too. It all depends on the amp and speaker combinations one chooses to use. Time and space do not permit a full run down of every possible amp/speaker/sub combination we have at our disposal.
Hope that helps you Steve, CLAP
Swez
Replies (17)
lilschtive on 08/15/2006 15:46:04
I think i get it..Tell me if im right/wrong here:
(I'll pick a random sub JLAduio.com for an example)
12W7 DRIVER SPECIFICATIONS
Free Air Resonance (Fs): 27.2 Hz
Electrical “Q” (Qes): 0.514
Mechanical “Q” (Qms): 7.807
Total Speaker “Q” (Qts): 0.482
Equivalent Compliance (Vas): 2.33 cu. ft. / 66.0 liters
One-Way, Linear Excursion (Xmax)*: 1.15 in. / 29 mm
Reference Efficiency (no): 0.249%
Efficiency (1W/1m)**: 86.2 dB SPL
Effective Piston Area (Sd): 84 sq. in. / 0.0542 sq. m.
DC Resistance (Re): 2.47 ohm
Nominal Impedance (Znom): 3 ohm
Thermal Power Handling (Pt): 750W
Driver Displacement: 0.14 cu. ft. / 4.0 liters
Net Weight: 45 lbs. / 20.4 kg
this sub is 3 ohm and 750 w...
that means i need an amp that can deliver 750 watts at 3ohm?
where can i find the RMS in this sub?
swez on 08/15/2006 18:18:54
The RMS power this sub can take, is actually up to about 1000 watts RMS. See power chart:
http://mobile.jlaudio.com/products_subs.php?series_id=9
Here, the JL 500/1 or 1000/1 would do a very good job. However, if you wanted a non-JL amp, It would need to produce about 1000 watts @ 2 ohms and 500+ @ 4 ohms. With a 3 ohm sub coil, that nets about 750 RMS @ 3 ohms.
This is a bit different animal than other choices out there as we have a 3 ohm SVC sub and a unique amp selection to match it. (A very regulated power supply and can deliver the same RMS power between 1.5 - 4.0 ohms)
====================================================
OK, I did that one. Now, you match this one OK?
Sub: Alpine SWR-1242D
12 -inch
Impedance 4 ohms
Cone Material Kevlar Reinforced Pulp
Surround Material Santoprene rubber
Sealed Box Volume (cubic feet) 0.57 - 1
Ported Box Volume (cubic feet) 0.75 - 2
Port diameter (inches) 3
Port length (inches) 9.9
Free-Air No
Dual Voice Coil Yes (4+4)
Sensitivity 85dB
Frequency Response 25 - 0.5k Hz
RMS Power Range (Watts) 500
Peak Power Handling (Watts) 1500
Top Mount Depth (inches) 7 9/16
Vas (liters) 45 32
Fs (Hz) 29 28
Qts 0.47 0.64
Xmax (millimeters) 18.2
OK, what amp is a solid choice for this sub? (Hint: The sub is rated at 500 RMS and each coil is 4 ohms, they take 250 RMS per coil)
Alrighty Lil, go find an amp to match and my budget is $200.00.
Swez
Victor on 08/15/2006 18:42:31
I like this... SMILE
lilschtive on 08/15/2006 19:36:04
500 @ 4.....if thats what i think is correct. i really want to nail this one too!
I'm comparing the JL to this one.. This sub is 500 watt, compared to the JL's 1000 watts. You say a 500/1 or as 1000/1 will work for the JL. The Alpine sub is 500 RMS @ 4 ohm..The JL is 750 @ 3 ohm..(according do both descriptions) What im thinking is i need a 500 watt amp @ 4 ohm.
With much thinking..I came up with this. Not sure of the brand, but it fits the price range AND what i think was right.
This is what made me reccomend this item to you:( Taken from the description off of the item)
4 ohms - 240 W Rms+ 240 W Rms
8 ohms - 180 W Rms + 180 W Rms
*-*-**-*-4 OHMS BRIDGED- 550 W RMS-*-*-*-*-*-*-*(Matches what i thought i needed)
8 ohms Bridged - 450 W Rms
http://cgi.ebay.com/FLECO-PA-1-POWER-AMP-550-WATTS-NEW-IN-BOX_W0QQitemZ150022912079QQihZ005QQcategoryZ23787QQssPageNameZWDVWQQrdZ1QQcmdZViewItem
SO, how did I spend YOUR money. And are you a satisfied costumer :P.
P.S-This is the big "test" for me ! HA!
Victor on 08/15/2006 19:47:56
reconsider, u got one more chance...
that is a PA amp it wont even blink on 12volt power supply...
lilschtive on 08/15/2006 19:55:50
Well, was i on the right path? I mean does the 4 ohms w 550 work? why doesn't that work?
lilschtive on 08/15/2006 20:04:21
Aha, i think i might have it....Hopefully
http://cgi.ebay.com/KENWOOD-KAC-9102D-1700-WATT-MONO-AMP-CLASS-D-NEW_W0QQitemZ180017535905QQihZ008QQcategoryZ79828QQssPageNameZWDVWQQrdZ1QQcmdZViewItem
This cuahgt my attention:
500 watts RMS @ 4 ohms (20-200Hz,0.5%THD)
lilschtive on 08/15/2006 20:05:52
If that amp ^^^ doesn't work. Then i need some more help. I like examples from Ebay.
swez on 08/15/2006 21:01:41
The KENWOOD KAC-9102D is an excellent choice for most any sub configuration that does not go below 2 ohms. Here, we can get 500 watts RMS @ 4 ohms and @ 2 ohms, 850 watts RMS.
If a guy knows what he is doing during the setup process, this Alpine sub, (SWR-1242D) will love the extra "clean" power. (+300 watts RMS) However, in the wrong hands, this sub will be toast in no time at all.
Uhmmm, you're getting warm Lil.... the Alpine sub is a 4+4 DVC sub. We get 2 or 8 ohms, depending on how the coils are set up. (series = 8 ohms; parallel = 2 ohms)
MISSED THE 4+4 DVC part about that sub... small blunder, but learning.
With the Kenwood amp, what should I do? (2 or 8 ohms?)
Is this a good amp?
Will my bass be loud as heck?
Will this sound good with my stock speakers and HU amps?
====================================================
SUMMARY:
Pros
1. Solid amp choice
2. Great price
3. Plenty of power
4. A good brand too
Cons
1. A bit strong on power for the Alpine sub noted (But in skilled hands, it can do a fabulous job feeding this sub)
2. In the wrong hands, the sub will be toast in short order, if gain settings are wrong
Not bad... not bad at all son. Now answer the other questions above.
Swez GRIN
PS The PA amp is not all bad for the price, but it's 120 volts AC. Did not pass on that part of this test. As for the Kenwood/Alpine sub combo, much better... a solid "B" for that one. (Forgot to note the sub is a 4+4 DVC is all) That would have made it an "A"+ answer otherwise.
lilschtive on 08/15/2006 21:09:32
What is a 4+4 DVC?
I didn't notice much on the first amp, i got too excited on the 500 @ 4 part heh
But for the alpine sub, it was 500 @ 4 OHM. Isn't that exactly what we needed?
swez on 08/15/2006 22:10:04
Actually, the Alpine SWR-1242D is a DVC sub. Each coil is 4 ohms and when combined, we get either 2 or 8 ohms, depending on how the coils are wired together. In short form, we call this a 4+4 DVC sub.
That Kenwood amp will deliver 500 RMS at 4 ohms. However, we have only 2 options here... 2 or 8 ohms. At 2 ohms, the Kenwood delivers about 850 RMS @ 2 ohms. Pretty strong for this Alpine sub. But, if one sets up the gain, bass boost and low end EQ well, the sub will love the extra clean power on short bass hits. The long, deep bass notes will strain this sub hard in a larger sealed or ported box.
Swez
cybersailor420 on 08/16/2006 09:39:46
An easier way to see this concept, might be to pretend you have 2 speakers, each one with a 4 ohm voice coil and handles 250 watts RMS. Thinking about it that way, now decide how you would wire these two together, and to what amp? Does that help clarify at all?
-Ian-
Victor on 08/16/2006 09:55:40
http://www.clubknowledge.com/Car_Audio_FAQ/?t33
see all the wiring diagrams in detail and you will find it much easier to derive to a sub-amp combination.
lilschtive on 08/16/2006 13:06:06
ok that diagram makes sense. Becuase the sub's specs said 4+4, does that mean tthe alpine sub is 8 ohm?
swez on 08/16/2006 19:10:13
The Alpine sub is actuall a 2 or 8 ohm sub.
Think of this sub as really being 2 subs in one speaker assy. There is 1 cone, 1 magnet, 1 motor system and 2 voice coils in one speaker. (sub)
I can see you are somewhat befuddled by DVC type speakers. You're not alone. I too struggled with that concept a few years ago, (1999) when the DVC's first came out. Now, some subs actually have 4 coils. How's that for a mind-boggler? ;-)
Swez
Victor on 08/16/2006 19:17:48
if you wire those 2 voice coils in series the impedence adds up R = R1 + R2
( Where R is the resistance/impedence of the voice coil) ,
hence 4+4 = 8ohms sub
, but if you wire them in parallel the Final impedence of the sub system turns out to be like this.. 1/R = 1/R1 + 1/R2
hence 1/R= 1/4+1/4 = 2/4 = 1/2, hence R= 2...
Having a DVC sub gives u a flexibility to wire the sub for variable impedences...
So you can wire the 4omhs DVC sub ( ie. dual voice coil where each voice coil is 4 ohms ) for 8 as well as 2 ohms....
Thats food for brain...IDEA... digested...???
Victor...
swez on 08/16/2006 20:10:02
That's for walking into my fishing hole and really mucking up the waters dude... Now, I have to move to a new fishing hole upstream, until the dust settles. If I fall in a get wet... it's YO FAULT.... GRIN
Swez
Yes, I just spotted it... hehe. I don't get too may Clubmails and forget to look at times... Sorry... M I BADD or what?
I wanted to post this on the board as others often want to know the same things.
RMS POWER: This is often called "Continous Power" and can be expressed in Volts RMS, Amperes RMS or Power RMS. (Watts) RMS means Root Mean Square of a sine wave. (Trig functions here) In a nutshell, RMS power is the AC sine wave equivelent to a DC power source.
Technically speaking, if we have a 100 watt AC sine wave "Peak" voltage value, the RMS value is: 100 x 0.707 or 70.7 Volts AC. This has the same ability to do work, as a DC voltage source of 70.7 volts. (Got all that?) SMILE
OK, back to your other questions. We want to look at RMS power (Watts) ratings on amplifiers, speakers and subs as we choose a given combination.
1. Figure out how much power we want
2. Pick speakers that can handle the RMS power desired
3. Choose an amp that gives the same or a few watts more RMS power than the speakers/sub(s) are rated for
4. Make sure the amp is properly matched for optimum efficiency and power delivery to the ohmic load of the speakers or sub(s) we will use
Example: Say we want a sub amp that can deliver 600 watts RMS to a sub load of 2 ohms. How do we get there from here?
Let's use a Kicker amp for this application. Most know Kicker products are solid and do a very good job.
Amp: Kicker SX 650.1
It's a very good Class D amp choice. It will deliver 650 clean watts RMS into a 2 ohm load. At 4 ohms, it will deliver 325 watts RMS. (Amp supply voltage of 13.8 volts)
Obviously, we want a sub load of 2 ohms here. This load is safe for the amp and most efficient use of the amp too. To get this magic 2 ohms and handle that much power, we'll want either a single 4+4 DVC sub or a pair of 2+2 DVC subs.
1 strong DVC sub, such as an 12L5 or perhaps a 12L7, 4+4 DVC sub with both coils wired in parallel to amp. This nets a 2 ohm load and either sub will take that much power without breaking a big sweat.
Now, suppose we use a pair of subs. Here, we can look at the Comp VR series. These subs are rated at 400 watts RMS per sub, but we can still get good results from the amp mentioned earlier. Here, we'll use a pair of 2+2 DVC's. Each sub coils are wired in series for a 4 ohm per sub load. When both subs are wired in parallel to the amp, we get that magic net 2 ohms and each sub gets a clean 325 watts RMS. Not a bad fit eh?
OK, that's how things work in general. There are other options available too. It all depends on the amp and speaker combinations one chooses to use. Time and space do not permit a full run down of every possible amp/speaker/sub combination we have at our disposal.
Hope that helps you Steve, CLAP
Swez
Replies (17)
lilschtive on 08/15/2006 15:46:04
I think i get it..Tell me if im right/wrong here:
(I'll pick a random sub JLAduio.com for an example)
12W7 DRIVER SPECIFICATIONS
Free Air Resonance (Fs): 27.2 Hz
Electrical “Q” (Qes): 0.514
Mechanical “Q” (Qms): 7.807
Total Speaker “Q” (Qts): 0.482
Equivalent Compliance (Vas): 2.33 cu. ft. / 66.0 liters
One-Way, Linear Excursion (Xmax)*: 1.15 in. / 29 mm
Reference Efficiency (no): 0.249%
Efficiency (1W/1m)**: 86.2 dB SPL
Effective Piston Area (Sd): 84 sq. in. / 0.0542 sq. m.
DC Resistance (Re): 2.47 ohm
Nominal Impedance (Znom): 3 ohm
Thermal Power Handling (Pt): 750W
Driver Displacement: 0.14 cu. ft. / 4.0 liters
Net Weight: 45 lbs. / 20.4 kg
this sub is 3 ohm and 750 w...
that means i need an amp that can deliver 750 watts at 3ohm?
where can i find the RMS in this sub?
swez on 08/15/2006 18:18:54
The RMS power this sub can take, is actually up to about 1000 watts RMS. See power chart:
http://mobile.jlaudio.com/products_subs.php?series_id=9
Here, the JL 500/1 or 1000/1 would do a very good job. However, if you wanted a non-JL amp, It would need to produce about 1000 watts @ 2 ohms and 500+ @ 4 ohms. With a 3 ohm sub coil, that nets about 750 RMS @ 3 ohms.
This is a bit different animal than other choices out there as we have a 3 ohm SVC sub and a unique amp selection to match it. (A very regulated power supply and can deliver the same RMS power between 1.5 - 4.0 ohms)
====================================================
OK, I did that one. Now, you match this one OK?
Sub: Alpine SWR-1242D
12 -inch
Impedance 4 ohms
Cone Material Kevlar Reinforced Pulp
Surround Material Santoprene rubber
Sealed Box Volume (cubic feet) 0.57 - 1
Ported Box Volume (cubic feet) 0.75 - 2
Port diameter (inches) 3
Port length (inches) 9.9
Free-Air No
Dual Voice Coil Yes (4+4)
Sensitivity 85dB
Frequency Response 25 - 0.5k Hz
RMS Power Range (Watts) 500
Peak Power Handling (Watts) 1500
Top Mount Depth (inches) 7 9/16
Vas (liters) 45 32
Fs (Hz) 29 28
Qts 0.47 0.64
Xmax (millimeters) 18.2
OK, what amp is a solid choice for this sub? (Hint: The sub is rated at 500 RMS and each coil is 4 ohms, they take 250 RMS per coil)
Alrighty Lil, go find an amp to match and my budget is $200.00.
Swez
Victor on 08/15/2006 18:42:31
I like this... SMILE
lilschtive on 08/15/2006 19:36:04
500 @ 4.....if thats what i think is correct. i really want to nail this one too!
I'm comparing the JL to this one.. This sub is 500 watt, compared to the JL's 1000 watts. You say a 500/1 or as 1000/1 will work for the JL. The Alpine sub is 500 RMS @ 4 ohm..The JL is 750 @ 3 ohm..(according do both descriptions) What im thinking is i need a 500 watt amp @ 4 ohm.
With much thinking..I came up with this. Not sure of the brand, but it fits the price range AND what i think was right.
This is what made me reccomend this item to you:( Taken from the description off of the item)
4 ohms - 240 W Rms+ 240 W Rms
8 ohms - 180 W Rms + 180 W Rms
*-*-**-*-4 OHMS BRIDGED- 550 W RMS-*-*-*-*-*-*-*(Matches what i thought i needed)
8 ohms Bridged - 450 W Rms
http://cgi.ebay.com/FLECO-PA-1-POWER-AMP-550-WATTS-NEW-IN-BOX_W0QQitemZ150022912079QQihZ005QQcategoryZ23787QQssPageNameZWDVWQQrdZ1QQcmdZViewItem
SO, how did I spend YOUR money. And are you a satisfied costumer :P.
P.S-This is the big "test" for me ! HA!
Victor on 08/15/2006 19:47:56
reconsider, u got one more chance...
that is a PA amp it wont even blink on 12volt power supply...
lilschtive on 08/15/2006 19:55:50
Well, was i on the right path? I mean does the 4 ohms w 550 work? why doesn't that work?
lilschtive on 08/15/2006 20:04:21
Aha, i think i might have it....Hopefully
http://cgi.ebay.com/KENWOOD-KAC-9102D-1700-WATT-MONO-AMP-CLASS-D-NEW_W0QQitemZ180017535905QQihZ008QQcategoryZ79828QQssPageNameZWDVWQQrdZ1QQcmdZViewItem
This cuahgt my attention:
500 watts RMS @ 4 ohms (20-200Hz,0.5%THD)
lilschtive on 08/15/2006 20:05:52
If that amp ^^^ doesn't work. Then i need some more help. I like examples from Ebay.
swez on 08/15/2006 21:01:41
The KENWOOD KAC-9102D is an excellent choice for most any sub configuration that does not go below 2 ohms. Here, we can get 500 watts RMS @ 4 ohms and @ 2 ohms, 850 watts RMS.
If a guy knows what he is doing during the setup process, this Alpine sub, (SWR-1242D) will love the extra "clean" power. (+300 watts RMS) However, in the wrong hands, this sub will be toast in no time at all.
Uhmmm, you're getting warm Lil.... the Alpine sub is a 4+4 DVC sub. We get 2 or 8 ohms, depending on how the coils are set up. (series = 8 ohms; parallel = 2 ohms)
MISSED THE 4+4 DVC part about that sub... small blunder, but learning.
With the Kenwood amp, what should I do? (2 or 8 ohms?)
Is this a good amp?
Will my bass be loud as heck?
Will this sound good with my stock speakers and HU amps?
====================================================
SUMMARY:
Pros
1. Solid amp choice
2. Great price
3. Plenty of power
4. A good brand too
Cons
1. A bit strong on power for the Alpine sub noted (But in skilled hands, it can do a fabulous job feeding this sub)
2. In the wrong hands, the sub will be toast in short order, if gain settings are wrong
Not bad... not bad at all son. Now answer the other questions above.
Swez GRIN
PS The PA amp is not all bad for the price, but it's 120 volts AC. Did not pass on that part of this test. As for the Kenwood/Alpine sub combo, much better... a solid "B" for that one. (Forgot to note the sub is a 4+4 DVC is all) That would have made it an "A"+ answer otherwise.
lilschtive on 08/15/2006 21:09:32
What is a 4+4 DVC?
I didn't notice much on the first amp, i got too excited on the 500 @ 4 part heh
But for the alpine sub, it was 500 @ 4 OHM. Isn't that exactly what we needed?
swez on 08/15/2006 22:10:04
Actually, the Alpine SWR-1242D is a DVC sub. Each coil is 4 ohms and when combined, we get either 2 or 8 ohms, depending on how the coils are wired together. In short form, we call this a 4+4 DVC sub.
That Kenwood amp will deliver 500 RMS at 4 ohms. However, we have only 2 options here... 2 or 8 ohms. At 2 ohms, the Kenwood delivers about 850 RMS @ 2 ohms. Pretty strong for this Alpine sub. But, if one sets up the gain, bass boost and low end EQ well, the sub will love the extra clean power on short bass hits. The long, deep bass notes will strain this sub hard in a larger sealed or ported box.
Swez
cybersailor420 on 08/16/2006 09:39:46
An easier way to see this concept, might be to pretend you have 2 speakers, each one with a 4 ohm voice coil and handles 250 watts RMS. Thinking about it that way, now decide how you would wire these two together, and to what amp? Does that help clarify at all?
-Ian-
Victor on 08/16/2006 09:55:40
http://www.clubknowledge.com/Car_Audio_FAQ/?t33
see all the wiring diagrams in detail and you will find it much easier to derive to a sub-amp combination.
lilschtive on 08/16/2006 13:06:06
ok that diagram makes sense. Becuase the sub's specs said 4+4, does that mean tthe alpine sub is 8 ohm?
swez on 08/16/2006 19:10:13
The Alpine sub is actuall a 2 or 8 ohm sub.
Think of this sub as really being 2 subs in one speaker assy. There is 1 cone, 1 magnet, 1 motor system and 2 voice coils in one speaker. (sub)
I can see you are somewhat befuddled by DVC type speakers. You're not alone. I too struggled with that concept a few years ago, (1999) when the DVC's first came out. Now, some subs actually have 4 coils. How's that for a mind-boggler? ;-)
Swez
Victor on 08/16/2006 19:17:48
if you wire those 2 voice coils in series the impedence adds up R = R1 + R2
( Where R is the resistance/impedence of the voice coil) ,
hence 4+4 = 8ohms sub
, but if you wire them in parallel the Final impedence of the sub system turns out to be like this.. 1/R = 1/R1 + 1/R2
hence 1/R= 1/4+1/4 = 2/4 = 1/2, hence R= 2...
Having a DVC sub gives u a flexibility to wire the sub for variable impedences...
So you can wire the 4omhs DVC sub ( ie. dual voice coil where each voice coil is 4 ohms ) for 8 as well as 2 ohms....
Thats food for brain...IDEA... digested...???
Victor...
swez on 08/16/2006 20:10:02
That's for walking into my fishing hole and really mucking up the waters dude... Now, I have to move to a new fishing hole upstream, until the dust settles. If I fall in a get wet... it's YO FAULT.... GRIN
Swez
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