Lets say I was looking at both a popular tower with MTMWW design thats 89 sensitive vs a popular TMM with larger drivers on the bottom end that was 84db. I was looking to amping the lower end speaker vs powering the higher sensitivity speaker with my receiver. Some people told me that it was "not worth it" to push the lower sensitivity speaker because its designed to sound relaxed. Others said that amping is the norm and it should sound perfect without issue. It seems that people who supported amping always included "ear damage" in the reasoning which appeared to be a way to side step the facts. I dont expect anyone to listen at 100db constant for hours per day and honestly I'm not even thinking of that. Ive DJ'd for 10+yrs (even in clubs) back in my 20's. Personally my hearing is just fine. I guess everyone's mileage may vary. I normally listen around 85db but my concern is that i'll clip if the listening position is 15feet (medium room)
Anyway thanks to this thread I have learned a few things that I didn't consider before:
1. The maximum power handling capabilities, continuous and peak.
2. The maximum SPL output.
3. Room size
4. Average spl listening levels
All will be considered and my search will continue on. Thanks.
You have asked a difficult question, that opens up a huge set of issues.
It goes to the heart of the matter, as to why speakers should be very large and the very high cost of making high performance speakers.
The sensitivity/efficiency/power handling equation is one that always calls for compromise to meet design goals.
On the one hand is the desire for speakers of practical size, even before you get to WAF.
So what makes a highly sensitive speakers.
1). First and foremost is the flux density in the gap. So you achieve this by having a powerful, magnet, with a voice coil entirely within the gap. (Under slung). Also you need to get the coil in very close proximity to the pole piece. This calls for expensive precision engineering. This also helps greatly in heat transfer to the pole piece and significantly reduces thermal compression and voice coil burn out. This also increases power handling greatly. The poles may or may not be vented and require copper shorting rings to focus the magnetic flux. This all adds up to a very expensive motor.
2). Next is moving mass, especially the weight of the cone being the major contributor. A heavy cone, lowers Fs and therefore how low the speaker can play. However a light cone will be more sensitive.
3). The stiffness of the suspension. This obviously is a factor. If you make a light cone, with high flux density and a very compliant suspension. The speaker will be sensitive and efficient, but have limited power handling, as the motor system will easily be driven beyond its mechanical limits..
Now lets look at how all these issues work against each other.
Now every speaker has a resonance, which is a combination of the electrical resonance (Qes) and mechanical resonance (Qms)
The relationship between the total Q Qts of a speaker and Qes and Qms is: - 1/Qts = 1/Qes + 1/Qms.
Now a moving coil driver does not exist in isolation. There is the relationship of the speakers and its loading. The total system Q, Qtlc, can never be lower then the Qts of the driver and it is always a bit higher.
Now Q really is a measure of damping. (acoustic over hang if you like).
The higher the number, the more uncontrolled and sloppy the bass.
It has been traditional to believe that system Qs of 0.7 are optimal. Many systems are higher than this. However as tastes become more refined, there is a marked shift to 0.5. I personally believe that total system Q needs to be 0.5 or even a little less. I am convinced now, that accurate bass reproduction is impossible, with total system Q greater than 0.5.
So how does this fit together.
As you increase gap flux density and sensitivity, you increase electrical damping and therefore lower Qes and therefore Qts.
If the suspension is loose, the driver will not handle much power. So the mechanical damping has to increase, so we have a driver with low Qes and Qms and therefore low Qts.
At first sight this seems like just what we want. However, when you try to align the driver with a low Qts, you find a bass cut off well above f3.
So you have poor bass, unless you make the cone very heavy to lower Fs. Then you loose sensitivity.
The only way round this is a large horn enclosure. That way you can get deep bass and very high sensitivity and efficiency.
If you load a low Qts driver in a sealed enclosure, the F3 is very high and it takes far too much power to equalize it.
So you end up having a lot of trade offs. In the end you end up with a driver in with a Qts in the 0.3 to 0.35 and porting the enclosure. The result is you get an speaker with sensitivity in the +/- 90 db range, and resonant reproduction with Qtc too high and blame the room for the bass bloom, which is sometimes true, but by no means always.
If you make a sealed alignment, then you end up selecting a higher Qts driver with a soft (poorly damped) suspension. F3 will then be in the range where Eq is possible, as long as the motor design can handle the heat and there is sufficient linear travel (xmax) allowed for. However you can still end up with a design with a tight bass and Qtc in the 0.5 range, as long as you select a driver with a Qts not far north of 0.4. Very high Qts drivers, quite common in even expensive subs always sound lousy.
As far as a TL is concerned again the sweet spot is a driver Qts 0.3 to O.35, with a low Fs. Because of the nature of the loading sensitivities of 93 db I watt 1 meter even down to 20 Hz are achievable, and with a Qtc no higher than 0.5. So you can have deep bass without resonance or bloom with relatively high sensitivity down to 20 Hz. However the enclosure will be large, but not as large as a horn.
So in summary low efficiency and sensitivity, in addition to wasting energy and amp power is not a good thing. It generally implies poor electrical and or mechanical damping. It also can imply high order passive crossover networks, which can aid in producing a speaker with excellent frequency response, but never results in a first class overall result, mainly due to horrendous time and phase shifts, which really do preclude excellent results.
The exception to the above is very small sealed enclosures where driver parameters can be set to achieve an F3 in the 80 to 90 Hz range.
Sensitivity then ends up being in the 84 db 1 watt 1 meter range. In order to get high spl, extraordinary design and manufacture techniques have to be brought to bear on motor design. You end up with an expensive small package. The classic example is the little ATC SCM 7 at $1000 per pair and worth every penny, where WAF is an overriding issue.
I hope this has explained the close cluster in in the spread is speaker sensitivities and bass extensions.
