Speaker Sensitivity Question

All else being equal, is a higher sensitivity speaker easier to drive? I have in mind the notion that larger drivers in larger boxes are generally more sensitive than smaller drivers in smaller boxes, all else being equal.

Justin

 

Yes, higher sensitivity speaker easier to drive. If I remember right, 87 and up is good

 

Generally you are correct on both - usually speakers with bigger woofers are easier to drive than smaller speakers with smaller drivers because a big woofer doesn't need to move very far to create a large amount of bass while a small driver has far more excursion needed to move the air.

This is why you see these massive horn speakers with 110dB sensitivity that only need 1 watt to pelt the room with sound - while you can feed 1000 watts into a small speaker wiith a 4 inch woofer and get piddly ass bass and dynamics.

But you still need to check the sensitivity because some big speakers with big woofers are tough to drive.

A 6dB difference in SPL is twice the volume (though what the ear perceives is higher).

So if you plan to buy a SET amplifier of say 8 watts a High Sensitivity speaker is a must. To gain a 3dB increase in Sound Pressure Level (SPL) you need to double the power

87dB speaker with 1 watt makes 87dB
90dB = 2 watts
93dB = 4 watts
96dB = 8 watts - you are at your maximum volume level with 8 watt amp.
99dB = 16 watts
102dB = 32 watts
105db = 64 watts
108dB = 128 watts (But on the back of most speakers it will give a Maximum watt number - small speakers are typically between 50-125 watts). So there is no point in buying a bigger watt amp.
111dB = 256 watts
114dB - 512 watts
117dB = 1024 watts

With a 96dB speaker
96dB = 1 watt
99dB = 2 watts
102dB = 4 watts
105dB = 8 watts
108dB = 16watts
111dB = 32watts
114dB = 64 watts
117db = 128watts
120dB = 256 watts My Wharfedale Vanguard 3 way speakers are 95-96dB sensitive and have a max SPL of 119dB - this is very high. Still sound good too.

110dB speaker

110dB = 1 watts (to equal this from the 87dB speaker (any 87dB speaker - you would need about 200 watts! This is why watts in isolation is meaningless.
113dB = 2 watts
116dB = 4 watts
119dB = 8 watts. The typical 300B 8 watt SET will put out 119dB into these speakers - for the 87dB (any size or price) you would need over 1000 watts to get the same level!

And the SET amp will, in all liklihood, sound a lot better than the Solid State amp as well.

So all else being equal ALWAYS buy the highest sensitivity speaker you can. But all else is not always equal unfortunately.

 

Further to the above, speaker efficiency is more properly referred to an input of 2.83 V rather than 1 Watt. Why? Because an input of 2.83 V to an 8 ohm load dissipates 1 W. So, if your speaker has a nominal 8 ohm impedance, the specifications are the same. This is not the case for a 4 ohm nominal speaker, where 2.83 V equates to 2 W.

A famous example of a large speaker (15" woofer) with better than 90 db/W @ 1m efficiency that was difficult to drive (properly) was the B&W 801N/801D which had impedance dips to just over 2 ohms. That is why it was always coupled to high-power solid-state amplification. It could also suck up a 1,000W (if you could handle the volume!).

It is generally accepted that you need a 10 dB increase in SPL to perceive something as twice as loud (or 10x the power for each doubling).

Rather than use Watts, it is much better to use dBW, since you can then add the dBW figure to the efficiency (using a few fudge factors, like adding a second speaker overcomes the loss due to sitting more than 1m from the speakers, etc.) to get an idea of maximum volume level.

 

This all makes sense to me, and yet, yet, something niggles in the back of my mind.

I have a 15 watt tube amp (el-84) and medium sized Tannoys (as these things go), which are rated at 91db per watt at 1 meter. My amp goes plenty loud, but does seem to run out of steam when pushed. I am seriously considering two options - bigger amp, or . . . The next speaker up in size. Tannoy makes essentially the same speaker with a bigger driver in a bigger box. It’s rated at 93db.

With my amp, this will be more efficient . . . Louder at a particular setting. But I can’t wrap my head around the idea that the amplifier will have an easier time driving the larger cone. Which, btw, has 50% more surface area (and, therefore, 50% more mass). 12 inches versus a whopping 15 inches.

Justin

 

A 2 dB difference in SPL is not much.

You either need a more powerful amp for your current speakers to generate higher SPLs (cleanly with ease), or you need to switch to 100+ dB/W @ 1m speakers like Richard suggested.

 

Bigger drivers deliver more realistic sounding harmonics but can't be played too loud due to the physics of the excursion required to move large amounts of surface area of the cone. This is why speaking through a blow horn is quite loud but very small in size but the harmonics don't deliver a very realistic sounding voice.

Louder and large for better harmonics at higher volumes means more than one driver needs to be employed. (2) 10 in. drivers should be minimum for each enclosure. As an example if one wants both loud and realistic sounding look to the size of the drivers used at rock concerts. Now scale that down to get the same sound quality to fit your living room. Same physics are involved.

Small drivers like 6 in. aren't an efficient way to get loud and realistic sounding. Speaker sensitivity in db numbers isn't much to go on in determining whether you will get loud and realistic sounding. When I installed my own sound system in my car sensitivity db numbers didn't tell me anything on how it would sound loud. Too much upstream and in the cabin of my car to make that number pointless.

 

I DO think there is something else at play other than just sensitivity. If the bigger speaker plays louder at a given position on the dial, it has to be giving something back to the the gods of the laws of thermodynamics. But I’m not sure what it is.

 

My Klipsch have very high sensitivity and can be driven hard with 10 watts but OTOH they absolutely come alive with 200 watts.

 

Yes that is why it's important to read Black Elk's post # 4 - my post is a general - all else being equal sort of thing.

But for specific usage the impedance of the speakers is critical - the room size and listening distance and even recordings are critical - most pop and rock are quite compressed yielding less than a 10dB difference between the quiet part of the music and the loudest - classical music can be well over 20dB.

When the impedance drops from 8 ohms to 4 ohms - the speaker like a bucket is asking the amplifier for twice the power (the amplifier is like a well).

So if you are playing your 15 watt amplifier loudly and using 14 watts and there is a big bass line and the speaker drops from 8 ohms to 4ohms - the speaker will be asking for 28 watts not 14 watts (and if it dips to 2 ohms the speakers will be requesting 56 watts) - but your amp can't deliver. So distortion aplenty - and possibly damaging to your speakers.

Few speakers drop below 3 ohms and the ones that do I would avoid - there are plenty of great sounding speakers on the market - and there is ZERO sonic reason to buy a difficult to drive speaker. Virtually all of the best sounding loudspeakers are high efficiency loudspeakers if you value thinks like dynamics and a live sensation. Low efficiency speakers are fine on a budget or you need a really small speaker like the KEF LS-50 or Totem Model 1 or LS 3/5a - but none of these are "great sounding" they are merely good due to compromises you need to make.

I tell you - I just connected up my old Wharfedales in Canada from back in 1991 and boy do they pack a wallop and quite excellent sound - they were $2200US back in 1991 which was a lot - I doubt they would sell for less than $6000 in today's market given they were hand made and use 40lb cast iron woofer magnets. They could be found used for $300 and sound vastly better than my KEF LS-50 or enter any tiny ass speaker like it.

Tannoy is a funny company - some of their speakers are low power amp friendly while others are absolutely NOT. You need to know the min impedance, and make sure their numbers are correct. And not every tube amp is created equally - parts quality matters especially with regards to frequency response - some tube amps will produce 15 watts at 1khz but may not come anywhere close to that at 30hz - so some tube amps sound completely gutless while another will have tremendous bass. I compared the Audio Note Kit One 8 watt 300b- huge bass - to a Cary 300b 8 watts (completely gutless). The Cary cost twice as much too.

 

Hi, genuine question about this - other than just the volume, what are the perceived differences in the sound when driven by the the different amps? I know it’s not all about watts, but the difference between 10 watts and 200 watts is quite large! Thanks

 

Very good question with several answers at play.

You will need to look into the various classes of amplifier design Class A, Class A/B, Class B and Class D. Class A amplifiers typically have the least power and run the hottest but have no crossover distortion. Most audiophiles who have actually had all these at home feel class A sounds the best - All SET amplifiers are class A. Some push pull tube amps are class A and some (usually low powered) Solid State amplifiers are also Class A. Examples would be Nelson Pass Aleph and Sugden A21a. Typically Single Ended Class A amplifiers win blind level matched tests.

An additional observation I make is that almost all tube amplifiers use EI Transformers instead of torroid transformers. Torroids are chosen because they offer huge amounts of watts and low noise floors - BUT they tend to sound poor IME when comparing in the same general price band. But again this may not be about the transformer exactly as it may just be a tube versus SS thing and the few tube amps that use torroids like those from BAT (Balanced Audio Technologies) and Prima Luna I don't much like.

Lastly, As UHF magazine wrote in one of their books - high watt amps typically have high damping factors which also means more negative feedback - more and more SS amplifier designers have been finding that this sounds bad. Lower negative feedback sounds better - tube or SS and so when I see an amplifier with 200+ watts - chances are it's not going to sound very good. Nelson Pass of Pass Labs also made Threshold and sold all these 200 watt monstrosities - none of which sound any good and cost a lot of money - now he is making 5-15 watt low/no feeback amplifiers under the First Watt name badge - this is where his passion is and this is the "good sounding" stuff.

 

All else being equal, yes. But all else is never equal.

Two different loudspeakers rarely have anything close to the same impedance curve, or the same phase angle over frequency.

And the impedance curves can vary wildly: it's not uncommon to have a speaker have an impedance near 3 ohms at some frequencies and near 3o ohms at others, with a a phase angle that turns 20 or 30 degrees inductive at some frequencies or 20 and 30 degrees capacitive at others.

Those electrical characteristics are going to be as or more important to determining how easy a speaker is to drive, especially with a tube amp, as a speaker's efficiency or sensitivity rating.

Looking at speaker sensitivity/efficiency and seeing one nominal eight ohm speaker with an 87 dB at 1 meter with 2.83 volt input; and another with a 90 dB rating at 1 meter: The first speaker might have an impedance that never drops below 6 ohms, never rises above 16 ohms, has a phase angle that never gets more than 10 or 15 degrees inductive or capcitive; the second speaker might drop to 3.8 ohms across the 100-300 Hz range, and the phase angle might turn steeply inductive in the high frequencies and capactive in the low frequencies. That second speaker, despite its 90 dB efficiency/sensitivity rating is going to be "harder to drive" -- ie, more demanding of the amp, more demanding of current -- than the first speaker and, in fact, is going to be more like a 4 ohm speaker, and more like an 87 dB speaker than like an 8 ohm, 90 dB speaker.

Looking at efficiency without looking at a speaker's impedance curve isn't going to tell you much about how easy a speaker is to drive.

 

A tube amp will produce maximum power into a load that matches the reflected impedance the amp "expects" to see. So, say you connect to an 8 ohm tap on a tube amp. As long as the speaker stays 8 ohms and purely resistive, the amp will deliver full power. But speaker probably has something far from a flat 8 ohms impedance and certainly isn't just like connecting to a resistor, so as it drops to 4 ohms at some frequencies, or up to 30 ohms at others, your tube amp can't produces as much power as it can at 8 ohms. Furthermore, your tube am maybe has an output impedance of around 1 ohm, and as the speaker load varies in impedance you may see modifications in the frequency response from the speaker/amp interactions. Solid state amps work differently. They tend to have very low output impedances (like 0.2 ohms), and they tend to deliver more power and current as the load lessens.

Also, as to the two speakers you mention, changing the volume of the enclosure, changing the nature of whether it's sealed or ported, etc. these things are going to have big impacts on efficiency differences, unrelated to the sized of the driver.

 

Interesting. My Tannoy Turnberry speakers are rated 8 ohm nominal with a minimum of 5 ohms. Recommended amp power is 20 to 200 watts rms. I have them on a McIntosh MC275 VI, which is rated at 75 watts, but said to be at around 100. Should I hook up to the 4 ohm taps because the minimum is 5 ohms? They are now connected to the 8 ohm amp taps.

I know I can try it and see but I am curious what the technical recommendation would be based on this scenario of ratings.

 

It is impossible to determine, just by numbers, how difficult a speaker will be to drive. The impedance of the speaker is a complex curve that changes with frequency, and the phase relationship between voltage and current at any given frequency matters too. The nominal impedance, typically reported by the manufacturer as 4 ohms or 8 ohms, does not really tell you enough about how difficult a speaker will be to drive. A very rough guide people use is to add or subtract 3 db for differences between a 4 ohm rating and an 8 ohm rating. For example, if a speaker is 91 db and has a nominal impedance of 8 ohms, it is roughly the equivalent of a speaker with a rating of 94 db at 4 ohms. But, even this is a very rough guide to how speakers will really behave when working with tube amps. For example, one of the older Wilson Watt-Puppy combinations was rated as 96 db/w efficient with a nominal impedance of 4 ohms. These numbers sound reasonably tube friendly, but, these speakers only worked well with quite high-powered tube amps.

Some extremely low efficient speakers actually worked reasonably well with low and medium powered amps. An example would be the 15 ohm version of the Rogers LS3/5a speaker which had an efficiency rating of only 81 db/w.

It is hard to say if your EL84 amp running out of gas is the source of your issue with your current Tannoy speaker setup. Any number of factors could be involved with why they don't please you quite as much when playing at higher volume levels. If you can try them with a more powerful amp, that would at least give you a better idea as to whether power is an issue. The larger Tannoys rated only 2 db/w more efficient might be the answer even though, on paper, that efficiency jump does not appear to be that significant. That would be the case, for example, if the speaker were distorting while the larger driver is less likely to be driven into distortion.

Larger drivers are often more efficient and easier to drive even if they are more massive. A large reason why speakers are relatively inefficient in converting electrical energy to the energy embodied in moving air (sound), is because it is hard to couple the mass of moving speaker to moving air--air does not push back enough (low impedance) to make the transfer efficient. Try throwing a golf ball and then a ping pong ball. Although the golf ball is slightly larger and therefore suffers from more drag from the air, and although it also weighs far more than the ping pong ball, that weight pushing back against the arm trying to accelerate it, makes for a more efficient transfer of energy. The difference in mass between the speaker and the air it is trying to move is even greater than your arm and a ping pong ball. The larger cone would be pushing against more air, so it can more efficiently transfer energy to the air. Horn speakers, particularly compression drivers, are much more efficient because a large column of air is trapped by the horn and it pushes back against the movement of the diaphragm (i.e., the air compresses and pushes back against the diaphragm) to allow for a better transfer of energy.

 

I’m hijacking my own thread - but what other speakers did you try when you decided on your Turnberrys? Did you hear the Ardens? I am leaning towards either Ardens or Turnberrys. Same price.

 

Agreed, it was decades before I knew what to listen for when a speaker was driven beyond what the amp could deliver. Clipping? What does that sound like? Harmonic distortion? What does that sound like?

All the performance numbers mentioned in this thread from sensitivity to ohm rating to wattage max could not tell me.

Clipping sounds like sparks are coming from your speakers. Harmonic distortion turns a lead singer's haaaaa's into eeeee's, turns a drum's tim tom hits into sounding like the drummer is hitting a cardboard box with plastic sticks only VERY LOUD!

 

Hard do know, but 5 is not that low for a minimum, and if the phase angle isn't too severe, and or the frequency at which the impedance drops isn't full of too much musical energy, I doubt the 8 ohm tap will have much of a notable problem with the speaker, especially given the 75 watts of power and 0.57 ohm output impedance, at least I think that's what the old MC275 design was.

 

Well, I wouldn't go by just the nominal impedance, that's pretty much meaningless. Or, frankly, by the sensitivity/efficiency numbers. But if you can look at a third party measurement of the impedance curve and phase angle, as published by some reviewers, you can have a decent ballpark sense of how relatively hard or easy one speaker might be to drive vs. another. But without the full charts over the whole frequency range, then, yeah, I agree, it's impossible to know.

 

Have you or anyone here in this thread heard spark sounds at any time coming from your speakers?

 

Sure:

 

Sparks sounds that were caused by over driving your speakers that created its own electromagnetic interference within the voice coils. From your authoritative tone in your previous posts I thought I wouldn't had to have to explain, but now I know.

 

Didn’t try any other Tannoy speaker.

 

No. Other than guitar amps I haven't really overdriven an amp/speaker system since my college days many, many years ago.