Sensitive Bass Cabs

[jimmy23cricket]

Hi All,

There is a lot of talk about how sensitive a bass cab is. What exactly does this mean and how is it measured?

Apologies if this has been covered before or if its a daft question!

Thanks

 

[EBS_freak]

If you abuse it too much they cry.

Sensitivity is basically how efficient they are in terms of wattage in, decibels out. The more sensitive cabs are, the louder they are (in dB) for less watts (W).

So a cab with say a single 12, that is say a couple of dB louder than another cab with a single 12, you could say that the first cab is more sensitive than the latter.

In reality, the more sensitive the cabs are, the less you'll need to get to the target volume.

Edited September 2, 2019 by EBS_freak

[Bill Fitzmaurice]

1 hour ago, jimmy23cricket said:

how is it measured?

That's the key question. Some manufacturers play fast and loose with their sensitivity ratings, quoting, for instance, what it measures in the midrange, rather than in the lows where it really matters. For this reason ignore sensitivity ratings that aren't accompanied by a chart of sensitivity across the full frequency spectrum. SPL (sound pressure level) charts are common with better PA speakers, but they're totally unknown in the electric bass cab industry.

[wateroftyne]

Here's a couple of bonus questions - what makes one speaker more sensitive than another? And.. is there a reason you'd need a low sensitivity speaker rather than high? Is it purely down to construction cost?

[Bill Fitzmaurice]

The answer is complicated, because most of the Thiele/Small specs contribute to the driver sensitivity, as does the enclosure. There's no reason why you'd need a lower sensitivity speaker per se, but by and large what contributes to higher sensitivity also contributes to less low end extension, and vice-versa. For that reason if you see a single driver speaker rated at more than 98dB/1w it probably doesn't go very low. By the same token if a single driver speaker claims to be -3dB at 35Hz it can't have much more than 93dB sensitivity. And lastly, if a small speaker claims both low extension and high sensitivity they are, in a word, lying. It's all summed up by Hoffman's Iron Law.

[wateroftyne]

2 minutes ago, Bill Fitzmaurice said:

The answer is complicated, because most of the Thiele/Small specs contribute to the driver sensitivity, as does the enclosure. There's no reason why you'd need a lower sensitivity speaker per se, but by and large what contributes to higher sensitivity also contributes to less low end extension, and vice-versa. For that reason if you see a single driver speaker rated at more than 98dB/1w it probably doesn't go very low. By the same token if a single driver speaker claims to be -3dB at 35Hz it can't have much more than 93dB sensitivity. And lastly, if a small speaker claims both low extension and high sensitivity they are, in a word, lying. It's all summed up by Hoffman's Iron Law.

Understood - thanks as ever, Bill.

[itu]

The big difference is this:

1 W - 102 dB (this is the sensitivity number @ 1 m distance)
2 W - 105 dB
4 W - 108 dB
8 W - 111 dB
16 W - 114 dB
32 W - 117 dB
64 W - 120 dB (threshold of pain)

1 W - 90 dB (this is the sensitivity of another cab)
2 W - 93 dB
4 W - 96 dB
8 W - 99 dB
16 W - 102 dB
32 W - 105 dB
64 W - 108 dB
128 W - 111 dB
256 W - 114 dB
512 W - 117 dB
1 kW - 120 dB (beware!)

So you need an amp that has lots of headroom or a sensitive cab to reach loud voices. I do admit that the first cab example would have very, if not extreme sensitivity. But when comparing the wattage, you may get an idea, why watts are not very good measure of loudness. It is reasonable to have headroom, but amps are not something that you can compare one to one, except that wattage. The whole system - including preamp, power amp and cab - produces the loudness, not any single component.

[Dan Dare]

Bill, as usual, is spot on. A simple sensitivity figure, with no information about the range of frequencies reproduced, is meaningless. Tweeters/horns are much more sensitive than bass drivers, so if one measured the output from that alone (to use an extreme example), it would likely be very high. However, it wouldn't tell you anything about sensitivity where it counts for a bass cab - in the low frequencies.

[itu]

7 hours ago, Dan Dare said:

A simple sensitivity figure, with no information about the range of frequencies reproduced, is meaningless.

This is very important!

There are too many companies that use some marketing nonsense in their ads. If the measured charts would be available, the comparison of different units would be easier. But everybody is just talking about wattage and impedance that tells practically nothing about the sound or loudness or anything.

Every measurement should be normalized. Then at least few numbers would be comparable. Frequency response should be within +/- 6 dB. Then these ridiculous "18 Hz to 13 kHz with a 12" driver" responses would disappear completely.

But there is no such thing as an honest marketing manager when talking about comparable facts. It is so tempting to write 500 W / 4 ohms, when the amp can deliver 300 W / 8 ohms. Because 500 is just bigger number than 300. Then kids think that the cab should be 4 ohms "to deliver the most loudness" from that amp. Oh dear! The loudness difference between an 8 ohm and a 4 ohm cab would be nearly 2 dB that usually can not be heard. IF the cabs are similar - which they are not.

So sorry to announce: Too many numbers in the music industry are meaningless.

1) It is impossible to tell user how many dBs the system can produce within the frequency band, if the system is not tested and measured.

The reason for this is because some amps and cabs like each other while some do not. The cab may be hard for the amp.

2) It is impossible to tell what is the frequency range of the system if it is not tested and measured.

The frequency range may be limited somehow because of the amp or the cab.

3) It is impossible to tell the difference between two systems if they are not tested and measured.

Two sets of amps and cabs may give very different performance depending on the 1) and 2). When these two sets are mixed, you get a system #3 that again acts in a different way.

Without trying a complete set in vivo, you are unable to predict the way the set, a system works. Period. It would be possible to measure the parts and the set in an acoustics lab, but who would pay the costs? Just because the amp says ampeg and the cab says 8x10" has nothing to do with loudness. The specifications only tell you that the system is heavy. Does the system go to 32 Hz within that +/- 6 dB, no one knows.

[jimmy23cricket]

Thanks for all the responses.

I thought that sensitivity may have something to do with the minimum power required to start moving the speaker! anyway, live and learn...

So, say for example a cab is advertised as follows:

Frequency Response: 35Hz - 17kHz -3dB

-10dB LF Response: 25Hz

Which one is the claimed sensitivity?

 

[wateroftyne]

Is this format a reasonable / useful way to to denote sensitivity?

Sensitivity [average]: 102 dB SPL @ 1 W/1 m
Sensitivity [100Hz]: 100 dB SPL @ 1 W/1 m
Sensitivity [max]: 105 dB SPL @ 2,3 kHz, 1 W/1 m

[Sparky Mark]

What a fantastic thread. Perhaps this explains why many on here have experienced a difference in 'heft' (low frequency content?) between their lower sensitivity ceramic and higher sensitivity neodymium speaker cabs? I definitely heard this difference with my Bergantino AE (neo) and HT (cer) single twelve cabs. 

[Dan Dare]

4 hours ago, wateroftyne said:

Is this format a reasonable / useful way to to denote sensitivity?

Sensitivity [average]: 102 dB SPL @ 1 W/1 m
Sensitivity [100Hz]: 100 dB SPL @ 1 W/1 m
Sensitivity [max]: 105 dB SPL @ 2,3 kHz, 1 W/1 m

I'd say (and Bill will probably be along to give a more informed reply) that the second is of most help, as it is in the frequency range that is important to us. The last is meaningless for a bass player - 2.3k is well into higher harmonics. However, all such figures will be obtained in anechoic conditions, using a measurement mic' at a distance of just 1 metre, which tells you little about real-world use.

[Dan Dare]

4 hours ago, jimmy23cricket said:

Thanks for all the responses.

I thought that sensitivity may have something to do with the minimum power required to start moving the speaker! anyway, live and learn...

So, say for example a cab is advertised as follows:

Frequency Response: 35Hz - 17kHz -3dB

-10dB LF Response: 25Hz

Which one is the claimed sensitivity?

 

None of those. See wateroftyne's post. You need to see something like - Sensitivity [average]: 102 dB SPL @ 1 W/1 m.

[Bill Fitzmaurice]

4 hours ago, jimmy23cricket said:

So, say for example a cab is advertised as follows:

Frequency Response: 35Hz - 17kHz -3dB

-10dB LF Response: 25Hz

Which one is the claimed sensitivity?

None.

Perhaps this explains why many on here have experienced a difference in 'heft' (low frequency content?) between their lower sensitivity ceramic and higher sensitivity neodymium speaker cabs? I definitely heard this difference with my Bergantino AE (neo) and HT (cer) single twelve cabs.



There are many factors that influence both sensitivity and frequency response. The magnet material is not one of them. By no means are neo magnet drivers or newer design drivers more sensitive. One of the highest sensitivity drivers ever made at 101dB/1watt was the original JBL D-130. It had an AlNico magnet, it was created in 1947, and it wasn't a musical instrument or PA driver, it was originally intended for hi-fi. It also had poor low frequency response, with a 100Hz F3 and 45Hz F10, but in 1947 that was sufficient for the program material that was available. 

[Daz39]

My brain is over-sensitive just reading all this!

I, and many players, would probably just want to listen to a couple of cabs through the same amp to hear the difference in volume and tone at the range of volumes you're likely to use. (boring answer!)

I think the marketing and design is often the biggest factor in swaying preference on how 'good' a cab is: e.g. (3 random brands at 3 price ranges) - Vanderkley, Markbass, Bugera. - even though if you can bear it long enough, a detailed look at what specs are decipherable would probably leave them in that order of 'good' anyway.

 

[Sparky Mark]

3 hours ago, Bill Fitzmaurice said:

None.

 

There are many factors that influence both sensitivity and frequency response. The magnet material is not one of them. By no means are neo magnet drivers or newer design drivers more sensitive. One of the highest sensitivity drivers ever made at 101dB/1watt was the original JBL D-130. It had an AlNico magnet, it was created in 1947, and it wasn't a musical instrument or PA driver, it was originally intended for hi-fi. It also had poor low frequency response, with a 100Hz F3 and 45Hz F10, but in 1947 that was sufficient for the program material that was available. 

Thanks Bill. I understand that magnet material shouldn't be a factor; maybe it's that more recent designs (that a lot of us are demanding are lighter weight so are neo) have a more balanced presentation across the frequencies? I'm not sure I want my bass cab to be perfectly balanced from top to bottom and wonder if some some of the best bass cabs have coloration that suits bass guitar rather than transparency?

Edited September 3, 2019 by Sparky Mark

[Stub Mandrel]

32 minutes ago, Sparky Mark said:

I'm not sure I want my bass cab to be perfectly balanced from top to bottom and wonder if some some of the best bass cabs have coloration that suits bass guitar rather than transparency?

This.

Applying hifi standards to instrument amplification ignores the fact that amplifier and speaker are part of the instrument not just 'colouring the sound' but a fundamental part of it. This is why people who eschew a backline and use IEMs will almost always use an emulator.

Even with two different setups side by side one which one sounds the loudest may depend on the frequency mix being played through it as much as the actual sensitivity.

 

[Bill Fitzmaurice]

38 minutes ago, Sparky Mark said:

Thanks Bill. I understand that magnet material shouldn't be a factor; maybe it's that more recent designs (that a lot of us are demanding are lighter weight so are neo) have a more balanced presentation across the frequencies?

Not really. Most Eminence drivers have always had a rising sensitivity in the mids, peaking in the 2kHz-3kHz range. They have not changed that with their neos. The same is true of Celestion and Fane. What you are seeing is more use of European brands, like B&C and Faital Pro, which tend to have flatter response, with all their drivers. They're fairly common now, but were hardly ever used in electric bass cabs as recently as fifteen years ago.

[itu]

1 hour ago, Stub Mandrel said:

Applying hifi standards to instrument amplification ignores the fact that amplifier and speaker are part of the instrument not just 'colouring the sound' but a fundamental part of it.

Sounds a bit like you believe that hi-fi systems have linear response. That may be the ideal in some circles, but not everywhere.

A switch that overrides tone controls may have some hidden low end enhancer. Just an example.

As we have seen in this thread, simplifications do represent nothing. Usually one single number is, what it is: a single number. Like: all basses with 4 strings are equal, aren't they.

[Phil Starr]

Basically it's very simple. Sensitivity is about how much sound you get per watt. 1 watt at 1metre is the usual measurement. 

Of course your amp adds more power and makes more decibels. moving from 1W to 100W adds 20 decibels so if your speaker gives 96dB per watt at I metre it will give 116decibels at 1m with 100W. Theoretically all you need to know is the sensitivity of the speaker and the power of the amp and you'll know how loud your system will go. If you understand it then it's also useful as a myth buster. I've seen 12"  PA speakers saying they are 97db/W and can make 128dB, but that is nonsense. To get that extra 31dB would take over 1000W and a 12" driver can't handle 1000W

I'm less pessimistic than most commentators so far about sensitivity figures. Of course it depends upon the frequencies you use for the measurement but it's a measurement that is easily checked and made at low signal levels. Most speaker manufacturers also provide frequency plots too so it's easy enough to check what they've done.

 

 

 

 

 

If you look at the plot above the red line is the speakers response on axis it is pretty flat from 100hz up to 1000Hz. above that two things happen; the response off axis starts to roll off (blue line) and the cone stops moving as a piston and starts to flex in this case giving a bit of a dip and then a midrange peak. That's all pretty typical. I'd say this speaker is 100dB/W but you could argue there are more bumps above the 100 line than below and call it 101 dB. If you used this as a bass speaker then that mid bump would also make it sound louder. That all tells me that if the speaker handles 200W then it will go to 123dB at 1m and experience tells me that's enough to keep up with pretty much any drummer in most venues.

So sensitivity is a useful figure when combined with other data, it is susceptible to distortion by advertising but no more so than other figures and a lot less in practice than figures for power handling or output.

Edited September 3, 2019 by Phil Starr

[Bill Fitzmaurice]

9 minutes ago, Phil Starr said:

Most speaker manufacturers also provide frequency plots too so it's easy enough to check what they've done..

Driver manufacturers yes, speaker manufacturers, no. Your plot appears to be that of a raw driver mounted in a wall. What's seen will remain pretty much the same when mounted in an enclosure above roughly 200Hz, but below that where the enclosure is a much responsible for the result as the driver it will be completely different. That same driver in ten different enclosures will have ten different result in the lows. Even without the enclosure information one can tell that it won't do well in the lows, as the impedance plot shows a resonant frequency of 65Hz, which is at the upper end of useful for an electric bass driver. That's to be expected with a driver with that sensitivity.

[Phil Starr]

9 hours ago, Bill Fitzmaurice said:

Driver manufacturers yes, speaker manufacturers, no. Your plot appears to be that of a raw driver mounted in a wall. What's seen will remain pretty much the same when mounted in an enclosure above roughly 200Hz, but below that where the enclosure is a much responsible for the result as the driver it will be completely different. That same driver in ten different enclosures will have ten different result in the lows. Even without the enclosure information one can tell that it won't do well in the lows, as the impedance plot shows a resonant frequency of 65Hz, which is at the upper end of useful for an electric bass driver. That's to be expected with a driver with that sensitivity.

Thanks Bill that's all true, I was trying to go for simple and not one of my long ones so I left the box related low end out and I think you are spot on. It was just a nice clear plot which showed everything I wanted. 

[Phil Starr]

On 02/09/2019 at 18:02, wateroftyne said:

Here's a couple of bonus questions - what makes one speaker more sensitive than another? And.. is there a reason you'd need a low sensitivity speaker rather than high? Is it purely down to construction cost?

That's a great question, I'll see if I can give a non-technical answer.

A speaker is a fairly simple system, you have a cone to move the air, the cone is on a couple of springs that hold it in place and you have a motor that moves it backwards and forwards. That is made a little more complex by the air in the cab and the nature of the cab itself.

The motor is the coil moving in the magnet, the stronger the magnet and the more coil in the magnet field the stronger the force moving the cone. The heavier the cone and the stronger the suspension the less the cone will move for the same force. The same is true of trying to move a large mass of air, the more air you shift the greater the force needed.

Because the speaker has a weight (the cone and air) balanced on the spring of the air and speaker's suspension it has a resonant frequency. Below that frequency it won't work well and you'll get a lot less bass. Just like a bass string a bigger mass and a loose suspension means a lower frequency.

So for bass you need a large diameter of cone a long voice coil and a heavy cone. A big heavy cone is harder to move and a long voice coil means only part of the coil is working within the magnet gap at any one time so it's hard to make a super efficient bass speaker. Guitar speakers will have smaller thinner cones mostly and short voice coils so generally they will be more efficient/sensitive.

The only thing the speaker manufacturer can really do to increase efficiency without other costs is to increase the power of the motor, with a stronger magnet.  A shorter coil will reduce bass handling and a lighter cone raise the resonant frequency as well as making the cone a bit floppy Big magnets are expensive and really big ones mean reinforcing the speaker frame. Neo magnets being intrinsically lighter have allowed us to move the envelope of performance. At any one time there is usually a point where bang for your buck dictates which is the most economically sensible solution, it used to be lots of cheap 10's. Now we are at the point where single neo 12's and 15's make more sense but that is a mixture of cost, practicality and sound.

Hope that helps

 

[Stub Mandrel]

Has anyone got experience of cheap and cheerful sound level meters?

How accurate are they?

More importantly, not worrying too much about absolute accuracy, how consistent are they across frequencies and time - are they good enough to make comparative plots of a few amps/speakers matched with a signal generator and RMS voltmeter on the output*?

 

*I know that differences in speaker impedance may well be enough to make even such comparisons less than accurate, I suppose I could measure RMS current as well, at least for external cabs.