108 DB with a Single 10" sub?

I just used a hand held meter, a test tone CD, and an SPL VS HZ chart that I printed from Polk's sub performance page for my Polk MM2104 10 inch sub as seen here
in an attempt to see how my system would perform. When I built my sealed enclosure I assumed that my sub would perform as indicated in Polk's DB vs HZ chart. According to that chart, the sub should hit a max of 85 DB at 50 HZ. My test showed 105 DB at 50 HZ and a max of 108 DB at 60 HZ. My graph that I made looks nothing like the graph on Polk's page and their graph is for the same sub I am using as measured inside a car (actual performance data).

With all that said, here are my questions:

(1) Does 108 DB for a single 10" sub sound correct?
(2) Can I attribute this differnce to a better in car gain in my vehicle?
(3) I have no idea what volume level was used in the test performed by Polk. I just turned mine to about "14" which was loud without distortion and performed my test at that volume level. Is this the correct method?

Any advice will be appreciated.

Mike


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2000 F150 Supercab Lariat, Alpine CDA-9831, Polk MMC570 in Doors, One Polk MM2104 Sub, One Polk Carbon C400.4 Amp.

John 3:16

They used 1 volt for the measurement, as you can read at the bottom of the linked page.  Their testing is done as a standard of measurement that they use for several drivers and the comparisons should be used amongst those drivers tested in that manner.  Any test you perform will show different results.

Otherwise, a woofer with a reference efficiency of 87 db at 1 watt would reach 108 db with only 128 watts applied.  And that doesn't consider the additional db's from cabin gain.

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Build the box so that it performs well in the worst case scenario and, in return, it will reward you at all times.

1 volt? So let me get this straight - the performance curve that they show is the results of a sub hooked to 1 volts with a sinusoidal tone? I wonder why they did not use 12 volts or even 14 volts? I took their data to be an actual in car performance in which I assumed that they are pusing the sub to its limits in order to get the highest SPL. Why would they publish data that seems "weak" in comparision to real world scenarios?

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2000 F150 Supercab Lariat, Alpine CDA-9831, Polk MMC570 in Doors, One Polk MM2104 Sub, One Polk Carbon C400.4 Amp.

John 3:16

Those specs they use are to show the effiiciency of the sub, not how much SPL it will produce. This is the standard for subwoofer efficiency ratings.

Jazzy

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Well, that makes since then.

Alright - then answer this, does 108 DB seem good/bad/great for a single 10" sub?

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2000 F150 Supercab Lariat, Alpine CDA-9831, Polk MMC570 in Doors, One Polk MM2104 Sub, One Polk Carbon C400.4 Amp.

John 3:16

stevdart wrote:

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Otherwise, a woofer with a reference efficiency of 87 db at 1 watt would reach 108 db with only 128 watts applied.  And that doesn't consider the additional db's from cabin gain.

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Build the box so that it performs well in the worst case scenario and, in return, it will reward you at all times.

Don't you mean 87 DB at 1 "Volt" instead of 1 Watt? The graph is in volts not watts. Am I missing the point?



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2000 F150 Supercab Lariat, Alpine CDA-9831, Polk MMC570 in Doors, One Polk MM2104 Sub, One Polk Carbon C400.4 Amp.

John 3:16

Yeah.  You asked,  "does 108 DB seem good/bad/great for a single 10" sub?"  I said earlier, and then again quoted, that a sub with an (average) efficiency of 87 will only take 128 watts to reach 108 db's.  That's anechoic...no additional db's from cabin gain included.  That's just doubling power for each 3 db's.

Too answer you question more bluntly..."bad"...with it being at '14' and all.

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Build the box so that it performs well in the worst case scenario and, in return, it will reward you at all times.

I believe my volume goes up to 25 on my Alpine CDA-9831. I've had it up to "21" which was really loud. I used "14" because it just sounded about right.

Can you help me with the math >> How did you determine that 128 watts yields 108 DBs?

Thanks,

Mike



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2000 F150 Supercab Lariat, Alpine CDA-9831, Polk MMC570 in Doors, One Polk MM2104 Sub, One Polk Carbon C400.4 Amp.

John 3:16

With a reference of 1 watt / meter, the sub's (in my example) rated efficient is 87 db.  (Some references use 2.83 volts, and some use 1 watt.  The reference you posted used 1 volt.)  But to compare apples with apples we'll use the common watt.  The sub will play 87 db loud with 1 watt of applied power.

The rule of adding 3 decibels for every doubling of the power is really a simplified form of a logarithmic equation (I quoted it in a post here) but I understand the simplified method much better.  If you start with 87 db's with 1 watt, then 2 watts will yield 90...4 is 93...8 is 96...16 is 99...32 is 102...64 is 105...and 128 watts will yield 108 decibels.

(I used 87 db as the reference efficiency of this example because you asked about 108 decibels and the numbers come out right.  If I'd used a sub rated 86 db, or 89, or any other number, I wouldn't have arrived on 108 db's for this illustration.)

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Build the box so that it performs well in the worst case scenario and, in return, it will reward you at all times.

I think I am catching on but let me continue - the "sensitivity" of my sub is 86 db. If I assume that was measured at 1 watt then the power/db numbers would be something like this: 1 watt = 86 db, 2 watts = 89 db, 4 watts = 92 db, 8 watts = 95 db, 16 watts = 98 db, 32 watts = 101 db, 64 watts = 103 db, 128 watts = 106 db, 256 watts = 109 db. I stopped at 256 watts because my amp, bridged, is pumping out about 250 watts into my single sub. Let's say for simplicity that my amp is delivering exactly 256 watts. Does that mean that my max DB (sub) is 109 DB? If so, then a sub with a sensitivity of 90 db (at 1 watt) would have 120 DB at 256 watts? Is this correct?

And what about the volume level I used during the test? Should I have maxed out the volume regardless of distortion just to get higher DBs or should I have found the highest volume that sounded good without distortion (which changed with the frequency of the test tone).



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2000 F150 Supercab Lariat, Alpine CDA-9831, Polk MMC570 in Doors, One Polk MM2104 Sub, One Polk Carbon C400.4 Amp.

John 3:16

Basically, correct, although the 90 db sub should be 114 db's at 256 watts.  When installed and measured in-car there should be another approximately 12 db's cabin gain added, mostly in the sub range of about 50 Hz.

And I see your point.  I take back my "bad" and upgrade to "normal"!

As far as your testing goes, you have to decide exactly what it is you are trying to find out.  If you're testing for SPL, then you need to power it up to the max but not at the point of clipping (sound of distortion).  If you're trying to get a response curve that matches a controlled test by the manufacturer, it's not going to happen.

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Build the box so that it performs well in the worst case scenario and, in return, it will reward you at all times.

Now I understand and thanks for the math correction (I ran out of fingers).

Just one more bit of info for all of you SPL hunters out there - I'm an SQ guy. SPL means little to me if it sounds like crap and even great sounding high SPL (140 and up ) can be too much for someone like me. After I measured my system's performance with test tones (which is where I got 108 Db) I then popped in Maroon Five's "Songs About Jane" album and turned it to track 12. It has a great bass line and funky guitar that I like. I cranked it up to the point where I just could not stand it anymore yet the music was not distorted. The meter read about 105 db.

There is no possible way that I can ride around listening to music at that level. It was loud. Clean but very loud. And yes - in my younger years - I had two kicker competitions behind the seat of my truck with an old school punch 150 on both. It was terribly loud but not very clean.

I'm very happy with clean sound at 90 db. That's all a person who wants to keep their hearing really needs - in my opinion.

Thanks for the continued help Stevdart.

Mike

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2000 F150 Supercab Lariat, Alpine CDA-9831, Polk MMC570 in Doors, One Polk MM2104 Sub, One Polk Carbon C400.4 Amp.

John 3:16