[Letitroll98]

....it's baffling to me why there is any confusion about this.

doug s.

I understand your frustration, I think it's the age old confusion between efficiency and sensitivity.  But my point is that the argument while valid, is spurious at best because the numbers are simplified to free air conditions and cannot be directly applied to real world drivers in enclosures.  I would have much more sympathy to an argument that stated, "I achieved X increase in SPLs under in-room conditions by adding a second driver".  For example, in the PSB Image line you have the T6 and T5 speakers, nearly identical except for an additional driver and a modest increase in internal volume.  The in-room sensitivities are 91db and 90db respectively.  This is because of all of the other design considerations are put in play, there is not a 3db increase in sensitivity achieved by adding a second driver of the same type.

BTW, they are very "big" sounding speakers.   

[*Scotty*]

If we have two 70watt drivers and a maximum available power of 140 watts into 4ohms. The voltage is divided between the two drivers and the current is shared between them. Each driver always sees half the total available power. The 3 db gain due to the summing of output that occurs when two mid-range drivers operate covering the same frequency range can be lessened by placing them too far apart on the baffle,but it is not hard to get this right and realize the full 3dB gain,the 3dB gain from halving the load always happens.
 Maybe when Danny Ritchie gets back from RMAF he can be persuaded explain what happens in a more understandable form.
In the case of the PSB T5 and T6 I think the impression of a large sound is once again aided by the additional cone area devoted reproducing the to the mid-range. One key reason that you see so few MTM and WMTMW designs with higher than 90dB 1 watt per 1meter ratings is that there are very few dome tweeters with higher than 92 to 93db efficiencies. The mid-range has to be attenuated or the drivers basic electrical efficiency must be reduced by the drivers motor design to account for the difference in relative efficiencies.
Scotty

 

[*Scotty*]

What question of makes a large multi-way speaker or WMTMW design sound small or like a pair of boxes in the room with in you is at least as intriguing. Obviously multiple drivers and a complex crossover do not guarantee the creation of a large sound-stage or life-size images. Apparently something can go very wrong somewhere and the various designs that fail to justify their use of multiple drivers and the cost associated with them abound. I can identify the theoretical advantages of using multiple drivers covering the same range but exactly where it could all go wrong eludes me.
Scotty
 

[JohnR]

I understand your frustration, I think it's the age old confusion between efficiency and sensitivity.  But my point is that the argument while valid, is spurious at best because the numbers are simplified to free air conditions and cannot be directly applied to real world drivers in enclosures.

I don't believe it's really an ideal vs reality thing. The factor that determines whether or not the 3 dB gain in efficiency takes place is what Scotty referred to as "acoustic coupling" and I as "output from drivers in phase at all frequencies." This will tend to happen at low frequencies (with two identical drivers close together), and tend not to happen at high frequencies (because of the distance between the drivers and shorter wavelengths resulting in phase differences and thus cancellation between the output from the two drivers).

Somewhat back on topic, I prefer large drivers, they sound more natural to me.

[Edit: the efficiency increase is explained here: http://www.linkwitzlab.com/faq.htm#Q21]

[*Scotty*]

Good link John,that is a much more precise explanation of the 6dB efficiency increase I was trying to describe in my earlier posts.
Scotty

[doug s.]

Good link John,that is a much more precise explanation of the 6dB efficiency increase I was trying to describe in my earlier posts.
Scotty

the point i am making is fully consistent with the info on the linkwitz website. 

doug s.

[Letitroll98]

I can identify the theoretical advantages of using multiple drivers covering the same range but exactly where it could all go wrong eludes me.
Scotty

Thanks to all for getting more on topic, great posts.  Where it all goes wrong is all the other parameters of speaker design.  The great link John supplied is a wonderful resource, I hold with many of Dr. Linkwitz's ideas, but remember in this particular FAQ page he's describing dipole radiators in free space, not cones in boxes.  So crossover, enclosure size, damping, loading (acoustic suspension, transmission line, various mass loading and port loading strategies) Vas, Qms, Qes and Qts, etc. all mitigate and modify the end result output. 

[turkey]

In your opinion, what makes a speaker to sound large and what makes a speaker to sound small? Does a floostander always give you the impression of large speaker sounding over bookshelf? Do the numbers of drivers and size have any impact? Does midbass has any thing to do with it?

I'm not sure that I know what makes a given speaker sound large or small. I have definitely heard speakers that sounded that way all the time, but I don't think I can point to any one of more design feature that always caused this.

On the other hand, I have heard some speakers that sound large or small depending upon the recording being played through them. I would say that this is more correct behavior than many other speakers that make all or most recordings sound big (or all small).

[turkey]

I can identify the theoretical advantages of using multiple drivers covering the same range but exactly where it could all go wrong eludes me.

Above the bass frequencies, the ear is very sensitive to arrival times. Multiple drivers (or large drivers like panel speakers) cause a sound event to arrive at your ears multiple times.

This kind of thing could well be the reason that I've never found panel or line source speakers to have realistic treble. Also, I've found that speakers with bunches of drivers in a box tend to sound like bunches of drivers in a box. They never really gel for me into a single sound source.

[JLM]

I agree about the multiple drivers sounding like multiple drivers.

As others have mentioned, having the bass and mid/bass diverted to a sub or such should help a speaker sound bigger. 

Keep in mind that the cabinet should only help with frequencies below 300 Hz.

One of my audio epiphanies was in 1976 listening to Fried Model H (LS 3/5a type satellites with the "coffin" stereo transmission line bass cabinet).  The sound filled the room, yet I couldn't find which speakers that the sound was coming from (from the wall of small speakers).