Speaker sensitivity....again, but different

[cym_city]

There is something that I have been pondering. I've been over all of the previous threads that I could find that deal with the sensitivity ratings but none of them answer the question of "why". I understand the idea of sensitivity ratings and how some speakers need more power but what exactly in the construction of the speaker influences a speakers sensitivity? Is it the materials used? Is it determined by the type of driver or crossover? I know some of you brains out there know the answer. Just curious.

 

[lsiberian]

There is something that I have been pondering. I've been over all of the previous threads that I could find that deal with the sensitivity ratings but none of them answer the question of "why". I understand the idea of sensitivity ratings and how some speakers need more power but what exactly in the construction of the speaker influences a speakers sensitivity? Is it the materials used? Is it determined by the type of driver or crossover? I know some of you brains out there know the answer. Just curious.

I think it is largely effected by the stiffness of the cone. But this is probably only one part of it.

 

[Joeteck]

My understanding is the coil in the speaker is capable if needing very little power to get an output. the 1watt 1 meter measurement. While sending 1watt, and measuring at 1 meter, the speaker puts out 95db or similar... I'm sure light gauge wire with multiple layers would make it more sensitive, which is also based on how much electro-magnetic energy is produced...

I think I just confused myself....lol

 

[Swerd]

For individual drivers, all these contribute to sensitivity:

• Weight of all the moving parts
• Force generated by the voice coil and magnet assembly (the power of the electromagnetic motor)
• The amount of air a speaker can move (the diameter of the cone times the distance it can travel)
• Heat dissipation and the amount of electrical power the voice coil can handle without thermal failure

For a complete speaker (drivers, cabinet and crossover) a given design may require different amounts of equalization by the crossover to produce the best frequency response. For any passive crossover, equalization can only result in less overall sensitivity. A good example of this is a speaker in a typically narrow cabinet will produce midrange sounds that are 3-6 dB louder than midbass and lower. To compensate for this, a crossover would lower that midrange to the same level of the lower frequencies. This will produce a smoother frequency response, but it will also make for a less sensitive speaker.

 

[j_garcia]

Yeah, what he said Basically, if you have a 2 way speaker, each driver is covering a portion of the audio spectrum that it is capable of, and each driver has its own sensitivity rating. Each of the drivers and whatever crossover tom-foolery was done to make the speaker sound correct (proper transition from driver to driver, etc...), as well as the overall design of the speaker (sealed vs vented) will all affect how much SPL that speaker is capable of producing with a given input.

When you add a second identical driver, like in an MTM design, where the two identical drivers are playing the exact same frequencies, you will get higher sensitivity in that range; and obviously that needs to be matched to the output level of the tweeter as well.

 

[Swerd]

When you add a second identical driver, like in an MTM design, where the two identical drivers are playing the exact same frequencies, you will get higher sensitivity in that range; and obviously that needs to be matched to the output level of the tweeter as well.

Good point. I own MTM speakers, and I completely forgot to mention that.

For most speakers, sensitivity is usually not one of the things the designer worries most about. But in the case of MTM speakers, the main reason for using two woofers is to get more volume.

 

[annunaki]

There are many factors that contribute to overall speaker sensitivity.

-Individual drivers, their efficiency, design & the number used

-Enclosure design & how it relates to the driver's T/S parameters

-Losses incurred with the crossover

-Overall goal of the loudspeaker as the designer intended

Typically it is the design of the driver & how it interacts with the designed enclosure that will most affect sensitivity.

A more efficient driver will not necessarily have a higher sensitivity depending upon how it interacts with the enclosure it is in.

Most vented systems will have a higher sensitivity as they offer about 3db more output overall vs. sealed counterparts due to the gain from the rear wave interacting with the front.

There are many compromises that come into play when designing a complete loudspeaker system (Woofer, mid, tweeter, in one enclosure, etc.). Sometimes it is sensitivity that suffers, sometimes it is fidelity, sometimes enclosure size, etc. It ultimately relies on the designer(s) on what areas he/she wants the speaker to excel at.

This is why it gets expensive to design a great speaker that does well in many if not all areas as it requires designing of your own drive units to achieve all aspects. Just ask B&W.


IMPORTANT TO REMEMBER:

Sensitivity is a measure of sound output with a given amount of input power.

Efficiency is a measure to determine how much input power is wasted, mostly in the form of heat.

A more efficient driver is not necessarily more sensitive.

 

[CraigV]

…and remember, if your speakers are really sensitive, buy them flowers once in a while & tell them you love them.

 

[lsiberian]

…and remember, if your speakers are really sensitive, buy them flowers once in a while & tell them you love them.

lol Just don't spill any water on them.

 

[j_garcia]

Good point. I own MTM speakers, and I completely forgot to mention that.

For most speakers, sensitivity is usually not one of the things the designer worries most about. But in the case of MTM speakers, the main reason for using two woofers is to get more volume.

My AV-2s are MTMs and my AV-1s are the 2-way siblings. There is a definite difference between them as the MTMs are noticeably higher in sensitivity than the 2-way models. They have essentially identical timbre, but there is noticeably more midrange from the MTMs. That was why I chose them

 

[highfigh]

There is something that I have been pondering. I've been over all of the previous threads that I could find that deal with the sensitivity ratings but none of them answer the question of "why". I understand the idea of sensitivity ratings and how some speakers need more power but what exactly in the construction of the speaker influences a speakers sensitivity? Is it the materials used? Is it determined by the type of driver or crossover? I know some of you brains out there know the answer. Just curious.

You mean, the reason for even stating the sensitivity? So people don't try to break concrete with a 5W amp and speakers that only put out 83dB/W/1M. It's mainly a system design, as far as why it's important but how they achieve a goven sensitivity is an engineering problem.

Before they had permanent speaker magnets, they used a field coil, which provided the magnetic field that caused the cone's movement with the incoming signal. They had lots of voltage available and it didn't draw much current. They could also vary the field's strength, depending on the size of the speaker, amplifier power and cabinet size. The next step was to come up with a magnet material that wouldn't lose its strength when it got hot and Alnico was a good one. They kept working with different configurations and materials and in the late '50s/early '60s, Alnico became hard to get.make because Cobalt was deemed a strategic material, which made it unavailable for non-military use. Ceramic magnets became the go-to and the sound of speakers changed because it has different properties. When a magnet's mass is varied, the strength varies, too. Using a lot of materials costs more, so they came up with different voice coil configurations to make up for the differences.

Basically, if a speaker needs to be capable of extreme output, as in PA use, it needs to be extremely sensitive because using enough power to light up a house is great but the speaker needs to be able to survive being used that way. The speakers need to cover a specific area and that's another consideration.

 

[TLS Guy]

There is something that I have been pondering. I've been over all of the previous threads that I could find that deal with the sensitivity ratings but none of them answer the question of "why". I understand the idea of sensitivity ratings and how some speakers need more power but what exactly in the construction of the speaker influences a speakers sensitivity? Is it the materials used? Is it determined by the type of driver or crossover? I know some of you brains out there know the answer. Just curious.

The sensitivity of a moving coil driver is largely a function of the cone weight and the strength of the magnet. (flux density).

Now a higher cone weight tends to a lower free air resonance, which sets the practical lower limit of the driver's frequency response. High flux densities tend to require stiffer suspensions, to prevent damage. So light cones and strong magnets which speak for high sensitivity limit bass response. That is why there is an inverse ratio of flux density to bass response, and a trend to better bass response with heavier cones.

Now if you put two drivers together like an MTM, with the drivers in parallel, you gain 3db in sensitivity with a 1 watt one meter specification and 6 db with a 2.83 volts 1 meter specification.

Now loading is important also. Horn loading a speaker increases sensitivity and efficiency greatly, which is why many enthusiasts have been so fascinated with them over the years.

The crossover also has an impact, usually you have an insertion loss of about 1 db per order of crossover slope. It can increase if additional driver Eq circuits are required.

One other thing to be aware of is that 2.83 volts will supply 1 watt to an 8 ohm load. So for an 8 ohm speaker the 1 watt, I meter and the 2.83 volts 1 watt one meter sensitivity will be the same. However a four ohm speaker will take twice the current and therefore twice the power with a 2.83 volt input.

A mechanically identical speaker, but with a four ohm voice coil, will therefore seem more sensitive (3db) with the 2.83 volts 1 meter rating, than the same speaker with an 8 ohm voice coil. However it is taking twice the power from the amplifier.