I have A JBL 2205B pair rated at 47db. I was told these woofers are very efficient, yet I would expect them to be rated in the low 90 db range at the least. Am I wrong or is this rating from a different scale? Those of you familiar with this. Can you explain?
That rating is at 30ft which is what JBL used to use before the 1 m standard Works out to about 97 @ 1 M
Rob
Rob
I was under the impression spl dropped 6db for every distance doubled from source.
That would be roughly 83db @ 30’ and even if that was 30 meters it would stil be 71db.
Am I missing something?
Hmmm... I get approx. 66 dB at 1m.
47db at 30 feet
53 at 15
59 at 7.5
65 at 3.25
66 at 3.1 approx.
(yes, I just spotted the error in my ways 🙂 ) I will try again.
65 at 3.75
71 at 1.875
So how about split the diff at 68 or 69 at 1m?
Still doesn't work.
The 2205 is rated at 97dB.
47db at 30 feet
53 at 15
59 at 7.5
65 at 3.25
66 at 3.1 approx.
(yes, I just spotted the error in my ways 🙂 ) I will try again.
65 at 3.75
71 at 1.875
So how about split the diff at 68 or 69 at 1m?
Still doesn't work.
The 2205 is rated at 97dB.
Right, the original EIA rating was 30 ft @ 0.001W = 0 dB with 4 ft the near-field reference locally, so for 1 W/m:
47+20 log [30/~3.28084] + 10 log [1/.001] = ~96.22 dB
GM
edit: ~96.22 - 20 log [~3.28084/4] = ~94.5 dB/W/4 ft
47+20 log [30/~3.28084] + 10 log [1/.001] = ~96.22 dB
GM
edit: ~96.22 - 20 log [~3.28084/4] = ~94.5 dB/W/4 ft
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Cool....I knew something didn’t add up (even though my math wasn’t quite right!)
Learn something new every day! How long ago was that?
Edit....duh....1977!
What sort of enclosure are you planning? If vented, what tuning? And what is your peak SPL requirement? The reason I ask is because that driver has quite a limiting Xmax for deep bass (2.5mm). You're looking at 110dB tops at 40Hz with a port tuning of the same frequency. And that is at 1m w/o baffle step so perhaps 100dB at your listening position. Will you be using it with a subwoofer?
I'll be going with vented
I'm thinking the clarity of 42 Hz will work providing it rolls off gradual. I've not ever worked with a woofer this size and it appears well behaved for a vented box.
I'm thinking the clarity of 42 Hz will work providing it rolls off gradual. I've not ever worked with a woofer this size and it appears well behaved for a vented box.
Looks promising in spite of its inability to produce adequate bass below 40Hz. I'll have dust off my other project of making a subwoofer using 2/12s and a passive.
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