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Discussion Starter · #1 ·
OK, I know I've seen this discussed but a search just turned up way too much stuff for me to get what I needed.

Initial questions

1. Is sensitivity rating on subwoofer a reasonable prediction of output.
a. If my subs sensitivity of 87.7 do say 148db at 2KW, would a sub rated sensitivity of 90.7 do the same output at 1KW?

2. Next question, it is my understanding that there's usually a tradeoff IE. excursion and low extension, or needing unreasonably large box. Is this true and to what extent?

3. How accurate are sensitivity ratings from manufacturers anyway? I'd hate to plan around a new driver(s) and piss away money to find out that they are less efficient than what I have now.

Really what's happening is I'd like to keep the same output I have now, low extension is important as I play a lot of movies and <30hz sound effects are important.

I am also up against the wall with space and power draw from my electrical system. I'd like to do the same with half the power and take a couple amps out of the mix to save space, but I'm not sure if this is feasible. I know there's no such thing as a free lunch, so what do you guys think?

Equipment: 2 TC2K 15", 4X Lanzar Opti 500.2 (Also have a pair of USX 1000F's that are a little stronger that I'd probalby use if I could get by with half power)

Max space appx 8 to 9 ft^3 gross for box. Budget would be whatever I could sell unused gear for plus a few hundred if necessary.

Any thoughts?
 

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1. Is sensitivity rating on subwoofer a reasonable prediction of output.
No. It loosely correlates to efficiency. Output should consider efficiency, linear displacement (Sd * 2(Xmax)), power handling, alignment of the enclosure, and, most importantly, the environment.

a. If my subs sensitivity of 87.7 do say 148db at 2KW, would a sub rated sensitivity of 90.7 do the same output at 1KW?
Not necessarily. At the very least, we must consider losses in output due to power compression. Essentially that is when the coil gets warm enough that the resistance of the coil increases; after a certain point, you quit gaining ~3 dB when you double power.

2. Next question, it is my understanding that there's usually a tradeoff IE. excursion and low extension, or needing unreasonably large box. Is this true and to what extent?
There are two different points here. First, we have Hoffman's Iron Law, named after J. Anton Hoffman, who identified that, of the following three, you may choose any two:

1) Efficiency
2) Enclosure size
3) Low frequency extension

Simply put, if you want an efficient driver that plays flat down to 20 Hz, you'll need to have a large enclosure. Or you can have the large enclosure, but you'll have to be either inefficient or soft on the bottom.

The second point was the tradeoff between excursion and efficiency. There is a trade-off between the two. I can describe the physical reasons behind that if you'd like.

3. How accurate are sensitivity ratings from manufacturers anyway? I'd hate to plan around a new driver(s) and piss away money to find out that they are less efficient than what I have now.
Not very.

Really what's happening is I'd like to keep the same output I have now, low extension is important as I play a lot of movies and <30hz sound effects are important.

I am also up against the wall with space and power draw from my electrical system. I'd like to do the same with half the power and take a couple amps out of the mix to save space, but I'm not sure if this is feasible. I know there's no such thing as a free lunch, so what do you guys think?

Equipment: 2 TC2K 15", 4X Lanzar Opti 500.2 (Also have a pair of USX 1000F's that are a little stronger that I'd probalby use if I could get by with half power)

Max space appx 8 to 9 ft^3 gross for box. Budget would be whatever I could sell unused gear for plus a few hundred if necessary.

Any thoughts?
The one way to get around the problems of Hoffman's Iron Law is to use EQ and boost the bottom end. The problem here is usually that your coil will see quite a bit more power and may lack both the thermal and mechanical abilities to compensate.
 

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Can you do an IB setup? Preferably with pair of 15 or quad 12s (like I have) minimum. I don't know about db but they go pretty loud and can hit 20Hz. You will not need much amp. I run 400rms on four 12s, they could take a little more (600rms, 150/ea) but I can't use it all now anyway because the 4x70rms on highs is pitiful in comparison. All that cone area hits the thunder nicely. I swapped temp to a 4x50rms/1x150 old alpine mrv 5ch...with the subs at 8 ohms it is pretty balanced. Does not go as loud but not far off on highs. The subs will not blow off the highs like before of course but plays pretty nice for normal listening of music. The 400rms on subs will shake the car, I'm eventually going to pair of 15 for more amp room and figure I will not lose much.
 

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Discussion Starter · #4 ·
Thanks guys. That confirmed most of my suspicions about the matter of "sensitivity" As I recall LEAP/LMS used to measure true efficiency (electrical energy in and accoustic energy out) and it was on the order of a couple % .

I had seen people oohing and aahing over 94db/w/m speakers on this forum and thought I'd double check (perhaps it's more important on mids/highs?).

I do have a rough understanding of how a speaker system works as a circuit and the effects of mass, compliance, and such, and yes, I'm positive I get all kinds of compression....can't really be helped if you want realistic explosions and dinosaurs in your movies.

My trunk is really crap and honestly if I had a better car I could get what I want with half the power (or area) anyway. I might be able to do IB with my 15's with some cutting of metal, no way in hell could I do 18 IB, my fear is it's rather permanent and it's been over a decade since I've seen it done. Wish there was some IB setups around here to check out.
 
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