SPL- rsd vs rsdc

capitolj80 · Post by **capitolj80** » Wed Aug 13, 2008 5:58 am

so how much louder do the rsdc's typically go than the reg rsd's on the same wattage, comparing them both in 1.3cu net sealed enclosures on the rsd1200.1? with a sensitivity diff of 6db, i imagine it's a pretty noticable difference

Post by **stipud** » Wed Aug 13, 2008 7:04 am

The RSDC woofers are rated at 2.83V, while the RSD woofers are rated at 1W/1M. As such you can't compare their efficiencies directly.

Using the formula...

voltage = square root ( impedance * wattage )

voltage^2 = impedance * wattage

voltage^2
----------- = wattage
impedance

Now let's look at the 2 ohm DVC sub in parallel...

2.83^2
-------- = 8 watts
1 ohm (2x2 ohms parallel)

And the 4 ohm DVC sub in parallel...

2.83^2
-------- = 4 watts
2 ohms

So the 2 ohm sub is actually getting double the wattage that the 4 ohm sub is. The rule of thumb is when you double wattage, you gain 3dB.... so this explains the ~3dB difference in efficiency between the D4 and D2 comp subs. So 2.83V efficiency is biased towards lower impedances, and in order to accurately compare two woofers, you have to subtract 3dB every time you halve the impedance.

1W/1M efficiency ratings are more accurate at comparing how loud woofers will be on the same wattage. This is because they only get 1 watt, regardless of their impedance.

Also note that on an 8 ohm subwoofer, 2.83v and 1W ratings are the same thing...

2.83^2
-------- = 1 watt
8 ohms

So we've got an RSD 12 D4, 84dB at 1 watt... and an RSDC 12D4, 91.7dB at 4 watts. Halve the wattage on the RSDC, and remove 3dB... now we've got 88.7dB at 2 watts. Halve it again.... 85.7dB at 1 watt. Now we're comparing watt to watt!

So, the RSD comp is APPROXIMATELY only 1.7 dB louder than the RSD on 1 watt. A noticable difference, but not as extreme as over 6dB.

HOWEVER... I did switch from 2xRSD 12's to a single RSDC woofer, and that single woofer is at least as loud, if not louder at some frequencies.... so the T/S parameters don't tell you everything.

Post by **kg1961** » Wed Aug 13, 2008 7:10 am

wholey crap! were do you get all this info!!

scorpio86 · Post by **scorpio86** » Wed Aug 13, 2008 7:12 am

no doubt.. damn nice write up though.. cuz i was kinda wondering the same thing.. and i always wondered how'd you compare the sens.. at 1w/1m to a 2.83V. good lookin' out stipud

Post by **stipud** » Wed Aug 13, 2008 7:44 am

I know this because I once asked the same question. I got the answer, and now I can share it with you. Hopefully it will stick, and you guys can help others in the future.

Elementary, my dear Watson.

capitolj80 · Post by **capitolj80** » Wed Aug 13, 2008 7:47 am

aahhh...i didnt even notice that they were rated on different terms...i know it makes no difference on the mathematical results because it's progressively proportional, but i was refering to 2 rsd's on a 2ohm final load compared with 2 rsdc's (dual 2ohm vc in series) on a 2ohm final load.

Post by **Bfowler** » Wed Aug 13, 2008 8:27 am

well done professor tom.

It's not MAGIC!

It's MATH!

denim · Post by **denim** » Wed Aug 13, 2008 8:38 am

stipud wrote:I know this because I once asked the same question. I got the answer, and now I can share it with you. Hopefully it will stick, and you guys can help others in the future.

Elementary, my dear Watson.

And that is the way audio forums should be.

capitolj80 · Post by **capitolj80** » Wed Aug 13, 2008 8:47 am

i just checked out the manuals for the rsd and rsdc subs and they're both rated @ 2.83v there, so it was easy to apply stipud's math and make it make sence...good stuff...here's another question a lil off topic...i just did some math (hope i was approaching it correctly!) and i concluded that one rsdc124 wired in parellel (2ohms) would make about 126db on 1228 watts...if that is correct, then what effect would adding adding a 2nd sub to the same wattage supply have on the db output?...this would be with 2 rsdc122's wired in series to maintain a 2ohm load.

Post by **stipud** » Wed Aug 13, 2008 8:53 am

Really? The RSD manual I checked (in the forum downloads) was rated 1W/1M. All four subs were rated 84dB, regardless of impedance.

Doubling cone area, just like doubling power, generally adds 3dB. Double both, and you get 6dB.

126dB will be a lot less than what you will actually get. Efficiency is supposedly measured in an anechoic chamber... it doesn't take environmental gains into account. In a car, there's a ~12dB/octave BOOST in lower frequencies. This is why car subs can get away with rolling off well above 20Hz, despite giving you flat response in the car. The environmental boost in the home is much less than a car, so you see many more ported and passive radiator subs for home purposes. This reinforces the bottom end a bit more, where it would not be necessary in a car.

capitolj80 · Post by **capitolj80** » Wed Aug 13, 2008 9:03 am

my bad..i was looking at the info on the Rodin-PG website, rodinaudio.com (you should check it out and see if their info is right)...there they have them both rated at 2.83v....so doubling cone area is the same as doubling wattage...that anwers my question perfectly...i knew that each variable related to the install i.e. cabin, enclosure, ect. will affect the final db outcome, i just wasnt sure how much...thnx stipud..you rock

SPL- rsd vs rsdc

SPL- rsd vs rsdc

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