Can speakers lose sensitivity over time?

[rsharp]

I just got the first two of five replacement speakers delivered today; one being the center channel.

A new B&W HTM71 S3 replaces an older B&W XTC. The XTC's senstivity is 87 dB and the HTM71 is 89 dB.

With all other variables equal (same Pioneer SC-91 receiver, same speaker cable, same placement/distance of the front baffle to the MLP), I ran the manual speaker level setup on the receiver. Oh and same exact app on my same iPhone to do the SPL measurement (C-weighted).

I was anticipating that I would need to lower the level for the center by 2 dB. However, I found that I needed to lower the value by 4.5 dB. Wow did it play loud initially. I repeated this a few times to ensure it wasn't a fluke.

So I'm assuming that other variables are at play here, and/or the older speaker lost sensitivity over time. It was 13 1/2 years old.

Just curious as to why I needed to lower the value by that amount.

Tomorrow I should get the second B&W 702 S3 (only one made it today). These will replace my Bose 601 Series IV speakers which have no published sensitivity values whatsoever. With the 702 S3 being 90 dB, I have a feeling that I may also need to lower the levels for them too. But who knows, maybe the 601s are actually more sensitive.

 

[TLS Guy]

I just got the first two of five replacement speakers delivered today; one being the center channel.

A new B&W HTM71 S3 replaces an older B&W XTC. The XTC's senstivity is 87 dB and the HTM71 is 89 dB.

With all other variables equal (same Pioneer SC-91 receiver, same speaker cable, same placement/distance of the front baffle to the MLP), I ran the manual speaker level setup on the receiver. Oh and same exact app on my same iPhone to do the SPL measurement (C-weighted).

I was anticipating that I would need to lower the level for the center by 2 dB. However, I found that I needed to lower the value by 4.5 dB. Wow did it play loud initially. I repeated this a few times to ensure it wasn't a fluke.

So I'm assuming that other variables are at play here, and/or the older speaker lost sensitivity over time. It was 13 1/2 years old.

Just curious as to why I needed to lower the value by that amount.

Tomorrow I should get the second B&W 702 S3 (only one made it today). These will replace my Bose 601 Series IV speakers which have no published sensitivity values whatsoever. With the 702 S3 being 90 dB, I have a feeling that I may also need to lower the levels for them too. But who knows, maybe the 601s are actually more sensitive.

Then sensitivity as measured is barely half the story. The sensitivity is measured on axis. If a speaker has poor dispersion, which your former speakers had, then more of the power will be on axis, and that will tend you to overestimate the power delivered to the room. I suspect your new speakers have much better dispersion. In addition your new speakers have a lower impedance. Their impedance has a minimum value, of 3.1 ohms. The best rule of thumb is that the impedance of a speaker is minimum impedance plus 10%, if the manufacturer does not publish an impedance curve, which they usually don't. So your speakers are likely 3.5 ohm speakers at best, and certainly NOT 8 ohm speakers as published. So these speakers will draw a bit more power from your amp than your old ones. So your db. ratings sound about right to me. I hope you have robust amplification, as B & W speakers are generally receiver busters, and these would seem to carry on the tradition.

Older speakers with ferrous magnets, could loose flux density over time and loose some sensitivity. Modern magnetic materials however do not, and maintain flux density well.

 

[rsharp]

I hope you have robust amplification, as B & W speakers are generally receiver busters, and these would seem to carry on the tradition.

I don't get this at all. Not you, specifically, but so many replies stating that B&W needs a massive amount of power. I've done my homework and ran calculations several times.

For our listening levels and distance from speakers, we'll only need around 8 watts if the impedance drops to 2 Ω (I rounded down below the 3.1 Ω minimum to keep math simplier and to be more conservative).

I also use a sub, and set all speakers to "small". The Pioneer SC-91 is rated to 130 watts (2 ch driven). No idea on 5 ch driven, but it would definitely be above 8 watts.

For the Marantz Cinema 40, that should give around 87 watts for 5 ch driven (70% guarantee applied to the 125 watt 2 ch rating). So a decent amount of headroom.

 

[rsharp]

Note that 80 db may also be a bit too loud (that was about the max we'd listen to stuff). If I set our listening level closer to 75 db, only 3 watts now needed if things drop to 2 Ω

 

[Verdinut]

I don't get this at all. Not you, specifically, but so many replies stating that B&W needs a massive amount of power. I've done my homework and ran calculations several times.

For our listening levels and distance from speakers, we'll only need around 8 watts if the impedance drops to 2 Ω (I rounded down below the 3.1 Ω minimum to keep math simplier and to be more conservative).

I also use a sub, and set all speakers to "small". The Pioneer SC-91 is rated to 130 watts (2 ch driven). No idea on 5 ch driven, but it would definitely be above 8 watts.

For the Marantz Cinema 40, that should give around 87 watts for 5 ch driven (70% guarantee applied to the 125 watt 2 ch rating). So a decent amount of headroom.

B & W speakers require amps with a solid power supply, not because they are not sensitive, but because their impedance dips down below 3 ohms at low frequencies. This requires more current from the power supply.

 

[TLS Guy]

I don't get this at all. Not you, specifically, but so many replies stating that B&W needs a massive amount of power. I've done my homework and ran calculations several times.

For our listening levels and distance from speakers, we'll only need around 8 watts if the impedance drops to 2 Ω (I rounded down below the 3.1 Ω minimum to keep math simplier and to be more conservative).

I also use a sub, and set all speakers to "small". The Pioneer SC-91 is rated to 130 watts (2 ch driven). No idea on 5 ch driven, but it would definitely be above 8 watts.

For the Marantz Cinema 40, that should give around 87 watts for 5 ch driven (70% guarantee applied to the 125 watt 2 ch rating). So a decent amount of headroom.

Unfortunately life is more complicated than that. We actually don't know what load those speakers represent, until someone actually takes some measurements. We do not know where that impedance minimum is in the frequency spectrum or its bandwidth. An even bigger issue is that we do not know the phase angles between voltage and current at various frequencies. The problem comes when the phase angles become strongly negative in conjunction with impedance minima. This creates a situation where there is a huge demand for current, which can be very damaging to output devices. In these situation the apparent power far exceeds the actual power, but the devices have to provide the current for the apparent power.

Unfortunately B & W have justly earned a reputation for creating this situation in many of their designs, but certainly not all, but in reality too many. When we see a B & W speaker with a minimal impedance well below four ohms, we have come to expect the worst, with significant justification.

The next issue is that few receivers have a four ohm spec. anymore. This creates a further level of uncertainty, as it becomes impossible to know how current limited the receiver is. So we end up with a vast number of unknowns, absent rigorous third party measurements of both speakers and receivers. We really are now at the point where it is becoming essential to only make purchases of speakers and receivers, that have extensive third party measurements.

The drive to more channels crammed into one box, powered by inadequate power supplies has made the situation worse. You can tell the power supplies are struggling as power output per channel significantly decreases as power is advanced to more and more of the channels.

A lot, if not all, of the problems on the speaker end, are created in the design of the crossover. All of this makes the case stronger and stronger for doing away with passive crossovers, especially in the lower octaves. Speaker drivers connected directly to their own amps, with active electronic crossovers, is the way forward. This gives the prospect of much improved performance and reliability. Firms like Sigberg Audio are leading the way forward.

AV rooms are now a very large investment, and I am certain that reliability, especially, and also performance are not where they should be, or need to be. That especially applies to reliability. Equipment failures lead to huge hassles, with warranty issues, getting service and worse parts being unavailable for extended periods.
The most difficult aspect of any installation design, is assessing its reliability and the designer of an installation is flying blind far more than needs to be. I do my utmost to avoid flying blind. I also have the advantage, as in the case of speakers, as I am also the designer, and for some of the electronics also.

 

[Kingnoob]

Unfortunately life is more complicated than that. We actually don't know what load those speakers represent, until someone actually takes some measurements. We do not know where that impedance minimum is in the frequency spectrum or its bandwidth. An even bigger issue is that we do not know the phase angles between voltage and current at various frequencies. The problem comes when the phase angles become strongly negative in conjunction with impedance minima. This creates a situation where there is a huge demand for current, which can be very damaging to output devices. In these situation the apparent power far exceeds the actual power, but the devices have to provide the current for the apparent power.

Unfortunately B & W have justly earned a reputation for creating this situation in many of their designs, but certainly not all, but in reality too many. When we see a B & W speaker with a minimal impedance well below four ohms, we have come to expect the worst, with significant justification.

The next issue is that few receivers have a four ohm spec. anymore. This creates a further level of uncertainty, as it becomes impossible to know how current limited the receiver is. So we end up with a vast number of unknowns, absent rigorous third party measurements of both speakers and receivers. We really are now at the point where it is becoming essential to only make purchases of speakers and receivers, that have extensive third party measurements.

The drive to more channels crammed into one box, powered by inadequate power supplies has made the situation worse. You can tell the power supplies are struggling as power output per channel significantly decreases as power is advanced to more and more of the channels.

A lot, if not all, of the problems on the speaker end, are created in the design of the crossover. All of this makes the case stronger and stronger for doing away with passive crossovers, especially in the lower octaves. Speaker drivers connected directly to their own amps, with active electronic crossovers, is the way forward. This gives the prospect of much improved performance and reliability. Firms like Sigberg Audio are leading the way forward.

AV rooms are now a very large investment, and I am certain that reliability, especially, and also performance are not where they should be, or need to be. That especially applies to reliability. Equipment failures lead to huge hassles, with warranty issues, getting service and worse parts being unavailable for extended periods.
The most difficult aspect of any installation design, is assessing its reliability and the designer of an installation is flying blind far more than needs to be. I do my utmost to avoid flying blind. I also have the advantage, as in the case of speakers, as I am also the designer, and for some of the electronics also.

Ouch yeah I’d definitely avoid that bRand unless I could afford some potent amps , avr seem to keep getting weaker as you said . More amps more channels less wpch.
Very great explanation!

 

[rsharp]

B & W speakers require amps with a solid power supply, not because they are not sensitive, but because their impedance dips down below 3 ohms at low frequencies. This requires more current from the power supply.

Worse-case is that if I run into any issues, will pick up say a Marantz MM7055 (5 ch power amp). Or, say an Emotiva 3 ch power amp for LCR and then the receiver would just be powering two surrounds. I think I'd lean though towards a 5 ch amp in that I think I could then completely shut off the power amps in the Cinema 40 (just to have that run cooler).

 

[rsharp]

Then sensitivity as measured is barely half the story. The sensitivity is measured on axis.

Forgot to comment on this yesterday. Thanks for this; it's a great point and most likely accounts for the extra loss with the original center.

The B&W XTC is a 2-way design (M-T-M) whereas the new center is a 3-way (W-TM-W). The dedicated midrange driver is now right on axis to the MLP.

 

[Swerd]

… So I'm assuming that other variables are at play here, and/or the older speaker lost sensitivity over time. It was 13 1/2 years old.

I think TLS Guy's response best addresses your question. But, I'd like to directly answer your original question. I've personally never encountered speakers that become less sensitive over time. I've never even heard of such a possibility before.

There is no widely accepted standard for measuring speaker sensitivity. Different manufacturers can & do measure sensitivity in different ways. The result is that you cannot compare speakers from different makers by their published sensitivity values.

To make matters worse, some speaker makers deliberately claim higher sensitivities simply because their marketing people know that potential buyers pay too much attention to sensitivity when shopping for speakers. Some makers are notorious for exaggerating their speakers' sensitivities, other makers are reliably honest about their products, and others fall somewhere in between.

B&W was a large independent British speaker company 13½ years ago. But they were notorious for designing speakers that were power hungry, and they were known for claiming rather high sensitivity values for their products. Despite that reputation, B&W speakers always sold well. Since you bought your first B&W speakers, that company has been bought & sold once or twice. I be more surprised if their manufacturing and marketing practices had not changed.

What you've now learned is that the sensitivity of your older B&W speaker seems to be lower, in your hands, than what B&W published years ago. Don't be too surprised by that.

I don't believe that you meant to make an issue over this – it was a simple observation that left you scratching your head. But as a matter of scientific validity, I would never conclude that a speaker could loose sensitivity over time unless I had measured its sensitivity, by the same method, over those 13½ years. How many people do that?

 

[highfigh]

Read the owner's manual- I haven't looked recently, but they usually had "Prices and specifications subject to change without notice".

In the words of Tom Waites, "The large print giveth and the small print taketh way".

 

[Swerd]

After attempting to address the OP's question in what I hope is taken as neutral response, I had a churlish thought .

If speakers really do loose sensitivity over time, I wonder how those who obsess over the silly but never ending debate over speaker break-in would explain this. Do new speakers break-in as they first get played? How long does this break-in take? Once done, do speakers continue to break-in for their lifetime?

Some people claim that no one can hear break-in because it isn't audible or it just doesn't exist. Other people claim that break-in takes as long as 200 hours of play. And still others admit break-in occurs, but it takes only a few seconds.

A few wags will ask why do speakers always sound better and never worse after break-in? And, if speakers really do break-in, could that same process also lead them to eventually wear out ?

Before that debate picks up in earnest, I think I'll make a quick exit.

 

[cpp]

interesting thread. I would say x-over components maybe, just my opinion of course, the componet material of the speakers themselves, I know my older Kef104ab, had deterioration of the foam outers of the woofer. But to really know would not measurements had to be made when new to know how much that speaker degraded over time. I never took measurements, had the "new" specs, just a thought.

 

[rsharp]

I don't believe that you meant to make an issue over this – it was a simple observation that left you scratching your head. But as a matter of scientific validity, I would never conclude that a speaker could loose sensitivity over time unless I had measured its sensitivity, by the same method, over those 13½ years. How many people do that?

Spot on; I was really just curious. And agreed that unless you make measurements over time (with the same exact variables), it's moot.

 

[shadyJ]

Supposedly, the old AlNiCo magnets that speakers used to have did tend to lose sensitivity over time, which, of course, would reduce sensitivity. This shouldn't be the case with modern ferrite or neodymium, unless they get really hot. High heat can demagnetize the magnets.

 

[Kingnoob]

Supposedly, the old AlNiCo magnets that speakers used to have did tend to lose sensitivity over time, which, of course, would reduce sensitivity. This shouldn't be the case with modern ferrite or neodymium, unless they get really hot. High heat can demagnetize the magnets.

Yeah I can’t figure out what type of magnet most speakers use or is the cheap shelf system speakers I made a post of. So today’s magnet are better for durability ???

 

[rsharp]

Yeah I can’t figure out what type of magnet most speakers use or is the cheap shelf system speakers I made a post of. So today’s magnet are better for durability ???

Not sure what the vast majority would be, but my guess would be ferrite. I know that B&W will use neodymium in their 800 series and recall them mentioning partially in the 700 series as well.

One of the reasons listed for the usage in the 700 series was to have them be less top-heavy. I believe it would thus only be used in the midrange driver and not the woofers.

 

[shadyJ]

Yeah I can’t figure out what type of magnet most speakers use or is the cheap shelf system speakers I made a post of. So today’s magnet are better for durability ???

Yes, today's magnets are much better. AlNiCo did have a couple advantages though, but not enough to outweigh the degrading flux.

Not sure what the vast majority would be, but my guess would be ferrite. I know that B&W will use neodymium in their 800 series and recall them mentioning partially in the 700 series as well.

One of the reasons listed for the usage in the 700 series was to have them be less top-heavy. I believe it would thus only be used in the midrange driver and not the woofers.

There is no way that B&W is going to be using AlNiCo so no need to worry.

The only way that drivers can lose sensitivity without being physically altered is by temperature extremes. High heat can demagnatize magnets, and very low cold temps can stiffen the suspension components.

 

[TLS Guy]

Yes, today's magnets are much better. AlNiCo did have a couple advantages though, but not enough to outweigh the degrading flux.

There is no way that B&W is going to be using AlNiCo so no need to worry.

The only way that drivers can lose sensitivity without being physically altered is by temperature extremes. High heat can demagnatize magnets, and very low cold temps can stiffen the suspension components.

Before sometime in the sixties speakers magnets were largely ferrous. Back in the fifties and prior, magnets loosing flux density was a definite problem. Prior to WW II and even to an extent after mains energized magnets were common. In many cases the electromagnet was also part of the power supply, acting as a smoothing choke (now known as an inductor). My fist electronic reproducer was a 1930 s HMV radiogram that had a mains energized speaker. It was an elliptical unit. It had no HF worth talking about.

This was the turntable it had 78 RPM. Steel or fiber needles.

Anyhow in the fifties speaker manufacturers did offer magnet refluxing services.

In the sixties huge strides were made in magnet technology and I have not seen this issue since personally.

There is another reason a speaker can loose sensitivity, and that is from overdriving and getting voice coil turns fusing, reducing the output, but not causing gap rub. The VC resistance goes down. The last time I encountered this was with the coaxial tweeter in my center speaker. The speaker seemed to be loosing HF and it was. The VC resistance was below spec. So I had to repair it. A post mortem showed burning marks on the VC. I had to do another iteration of the crossover and have not had the problem since.