The reason is that the impedance spectrum across the frequency range of the new speakers represents an easier load to your tube amplifier in addition to the fact that the true sensitivity is only 1dB difference, as per @atmasphere.
Sensitivity 86 v 90
I am considering an upgrade from speakers with a sensitivity rating of 90 db, 4 ohms, to larger speakers rated at 86db, 8 ohms nominal. Same brand, PMC. My tube integrated amp is 80-112 watts triode/ultralinear, and it’s fine for my 90 db speakers. Although, it is sometimes at around 4 o’clock on the volume control, approaching the max at 6. I am aware of the “amp power must double for each 3db increase in volume” rule of thumb, but really have no practical experience with this. I do like having 90 db efficiency, always assumed that meant a less powerful amp would suffice.
My question is, would the decreased efficiency be a concern?
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I went ahead and bought the less sensitive speakers (PMC 25.26 @ 87db, replacing PMC FB1i Signature @ 90db sensitivity) and if anything, they seem to produce more volume at a given setting. I can only speculate as to why, but now I’m certain that speaker sensitivity has very little predictive value, given my level of (mis)understanding of these things. I suppose there are just too many variables involved. @ atmasphere Roger says the circuit is designed to use any 12a_7 in that spot. I don’t know how he does it. Apparently the 12au7 is the quietist (and lowest gain) and perhaps, the best sounding, but 12au7, 12ax7, and 12at7 all work fine in that spot.
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While a higher gain 12Axx tube can drop into the same socket without damage to the tube or the circuit, that's not the same as saying it will sound right. The various 12Axx tubes have different operating points; if the circuit is to bring out the best in them it will be optimized for a particular type. |
12AU7 is a low-gain tube. A 12AX7 will definitely provide more gain in a given configuration. Most listening takes place around 1 to 2 watts depending on speaker efficiency, distance from the speakers to the listening position, room size and a few other variables. Musical transients can exceed that.. If your preamp / phono stage gain is low, it will give a false "reading" of the amount of amp power you're using to just get to your typical 1 to 2 watts output, but shouldn't limit transients.. |
To answer the questions, I have been using PMC Fb1i Signature speakers. 2-way, 90 db sensitivity. Went ahead and bought PMC Twenty5.26, 3-way at 86 db sensitivity. Based on the cogent responses here, I am optimistic this will work out ok. thanks again for all the responses, this had been interesting and very informative. I will have to read it all again several times. |
@lloydc Efficiency is 1 Watt/1 meter. With this spec, the speaker is fed 1 Watt for the measurement.
With Sensitivity, the speaker is fed 2.83 Volts instead. 2.83 Volts into 8 Ohms is 1 Watt. Into 4 Ohms its 2 Watts. So subtract 3dB from the efficiency of the speaker you have now, and you'll see there's only a 1 dB difference. For tube amplifiers the Efficiency spec is more useful, since tube amplifier do not double power as the impedance is cut in half. But there is another issue here, which is the how the amplifier interacts with the impedance! Your amp uses an output transformer, and output transformers are always less efficient driving a lower impedance load! They also can lose as much as an octave of bass response between the 8 Ohm tap and the 4 Ohm tap. In addition, the amplifier will have lower distortion driving 8 Ohms. Since the difference between the two speakers is really only 1dB (if you do the math), you won’t have any trouble in that department. So the impedance is the far larger variable. I say go for it since the amplifier will be working better (if you measure the temperature of the output transformers before and after, assuming the same warmup time, you’ll find they are running cooler; that extra heat is caused by greater signal losses in the transformer). In short I don’t see a downside with this move. |
I have had various speakers and amps. Almost all amps I have had were tube of various wattages and speakers that varied from 86 db to 90db, 4 ohms, 8 ohms....you name it. Frankly in my modest sized rooms and listening to levels in the 85-90b range, I rarely found I lacked power. I might have found that were I to have used a 20 watt amp with the 86db speakers I would have had an issue but I would never have done such a mismatch. But 100 watts per channel is lots of tube power. That being said, some speakers do work better with lots of power and then you probably would want a beefy solid state amp. I completely agree with posters suggesting you are dealing with issues where there is not enough voltage coming from your source to drive your amp properly. You claim that you have much more output with your CD player and less with your phono preamp. Most CD players have a healthy output of about 2 Volts and most amps input sensitivities are such that they will deliver full output with about 2V input so you have likely a good match between your amp and CD player. The issue, I think exists within your phono preamp and cartridge. Most phono preamps have a fixed gain. They will put out a healthy voltage output if the phono cartridge has enough output. However, cartridge outputs vary a lot. For example, If your phono stage needs a cartridge that puts out 2 Millivolts for a full output into your amp, and the cartridge you have only puts out 1 Millivolt, then that is your problem. Perhaps you could post what cartridge and phono preamp you are using? I suspect that once you have that sorted out, you will find that the amp you have will be sufficient to drive those 86db speakers rather well. I think a change in your cartridge to one of higher output or a change in your phono preamp to one with more gain (some phono preamps have variable gain switches and are adjustable in fact) will probably improve the phono side of things irrespective of what you do at the speaker end of things Many in this hobby, piece their systems together, buying from various sources online. What that approach lacks, if you don’t have the experience, is the knowledge and expertise gained from a brick and mortar dealer who would guide you through the process to ensure component work well together. I am not a dealer, but knowledge and experience goes a long way towards helping avoid these mistakes. Forums are useful, but as you know, everyone has an opinion, and many times they are wrong. |
Look at the impedance dip. That is where things make a difference. I had Salk Songtowers...easy to drive at 6 ohms and 88db efficiency with 30 watts. And great sounding speakers in their cost range. BUT it dipped into the 3 ohm range momentarily. There are subtle things that come to the fore with 93db speakers that I didn't so much with 88db.
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How Is Speaker Sensitivity Measured?
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"would the decreased efficiency be a concern? " Short answer: "probably not". In fact, the possibility exists that the new speakers will play louder. Not knowing what the new (or existing) speakers are, I’m going to render a guess and predict the new speakers are larger -- i.e. bigger, and badder. This being the case(?): The existing speakers, by comparison, will have smaller and/or fewer drivers. All speakers have limited dynamic headroom via finite speaker piston area, travel, etc. Therefore, even though nothings sounds "wrong" with your current speakers, there is audible (and, measurable) dynamic compression which will improve when more and/or larger drivers are introduced into the equation (and, the listening room). Even IF the sensitivity of the new speakers is (somewhat) less, this could be more than made up for in gains in dynamic headroom because of more/larger drivers coupling with the air in the room. As others have suggested, pairing your exising rig (a lot of audiophiles like to refer to their stuff as a "rig") with the target speakers may be most "efficient" way to arrive at a conclusion.
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Agree. I am concerned you are already sometimes listening near the top of your amp's volume range. Running valve amps hard reduces tube life. You don't mention which PMC speakers you are thinking of buying. As you are using tubes it is worth looking at their impedence curve to check it is not near or below 4 ohms over too much of the frequency range. If it is, this will put more pressure on the amp even if it has a 4 ohm tap you can use. Some PMCs are a benign load - the fact.8 don't go much below 6 ohms. One other thing you need to watch out for is over-optimistic sensitivity values quoted by manufacturers. Whilst no two tests can produce identical results, in 40 years of reading John Atkinson's tests in Stereophile I have never found his sensitivity measure to be higher than the manufacturer's figure. His measure averages 2-3dB lower. I have seen manufacturer quotes up to 6dB higher. It pays them to publish the highest figures they can as we all want more sensitivity. |
A lot of variables. It is correct that sensitivity on 4 ohm is normally measured with 2 volts and 2.83 volts on 8 ohms. These past couple of years, I see more and more speaker manufacturers labeling 4 ohm sensitivity @ 2.83 volts. The amp is also a factor. Under normal conditions a good solid state amplifier can double its power output @ 4 ohms. With this scenario, you very well could hear a difference in a 4 ohm speaker vs 8.....(4db higher sensitivity plus 3db in power gain) However, as mentioned earlier many tube amplifiers perform better at higher impedances and have separate taps for 4 and 8 ohms. In a good tube amplifier with reasonable power output and using 8 ohm taps, it is not likely that you would hear any appreciable difference. I believe that if you are not a head banger and have 40 watts per channel or more, you should be just fine with a tube amplifier and 86db 8 ohm speakers. I hope this helps, Tim |
Look at the impedance dip. That is where things make a difference. I had Salk Songtowers...easy to drive at 6 ohms and 88db efficiency with 30 watts. And great sounding speakers in their cost range. BUT it dipped into the 3 ohm range momentarily. There are subtle things that come to the fore with 93db speakers that I didn't so much with 88db.
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If the ratings are reasonably accurate (a BIG “if”), the 8 ohm load of the lower efficiency speaker might make it a better match than the higher efficiency speaker. I generally find that an easy load is more important when it comes to tube amps. Not knowing the size of your room, how loud you listen to music, etc., it is hard to speculate on whether you have enough power. I generally expect 80 watts with 86 db/w speakers would be sufficient; at least I would not rule the amp out. |
Tube amps usually put out the same power into 4 or 8 ohms so that might not make any difference. But I am surprised that your tube amp has to work so hard to drive your 90db sensitivity speakers. I have a much lower-powered tube amp driving Vandersteens (sensitivity 86 db) in a moderately large space to volumes higher than I want to listen to. Perhaps the input level to your amp is too low? |
Yes it is a issue if you are pushing the volume now ,then you will be running the amplifier into its highest distortion which can damage yours speakers as well as your amp, find a speaker around 90 db there are plenty of them out there Even if you have to wait and save more Monies , we’ll worth the wait or get rid of the amp and get a bigger one. |
@lloydc Wrote:
That is a nice amp, you have plenty of gain. What phono preamp do you have? Mike
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Thanks for the explanations! My integrated amp (Rogers EHF 200 Mk 2) has 40 db of gain. The volume control is turned up much less with signal from the dac, than while using the phono preamp, which I presume means the dac has higher output; but (as I understand it) the gain from the phono preamp can be increased by switching the driver 12AU7 tubes for 12AX7's, if necessary. Which, maybe I should do anyway, as @Soix and @tomcarr imply. |
@lloydc Wrote:
I like having 2.7% efficiency and 96 dB sensitivity! 😎 Mike |
I went from JBL 4319 monitors rated at 92db efficiency, 6ohm nominal, 4.7ohm at lowest point to Atalante 3 monitors rated at 87db efficiency, 6ohm nominal, 4.4 ohm at lowest point and only have to increase volume 1- 1 1/2 db for the same results. Some reviewers are using 15 watt tube amps and getting wonderful results. Even at the old normal listening level, I’m hearing more than with the older speakers. Just the SPL is lower. Without the cabinet and crossover, the drivers in the Atalante 3 are rated at 91db efficiency on their own. Turning the wick up to get the same scale and impact requires just a db or so to get there and it sounds more convincing in some respects but can sound too loud. Go figure. I wished I had bookmarked a review where it was explained how efficiency is such a misunderstood measurement since no two speakers rated the same, perform the same and those that vary some will perform the same. All the best, |
"Overcoming misinformation One misleading piece of information with which our customers are often provided is sensitivity. This specification is commonly misrepresented as "efficiency" which it most certainly is not. Loudspeakers are terribly inefficient and it is likely that virtually no consumer has ever been given an actual efficiency specification. The most efficient loudspeaker designed to date was the Altec Lansing Voice of the Theater, which had an efficiency rating of approximately 3.6%. No loudspeaker manufacturer would ever publish an efficiency specification because it would discourage and mislead consumers. Be clear on one point: sensitivity and efficiency are not the same thing. Even when using a solid state amplifier, one cannot necessarily equate high sensitivity to high efficiency - the physics are simply more complex than many manufacturers, and sadly reviewers, lead us to believe. Instead of efficiency, loudspeaker manufacturers provide a sensitivity specification. This figure is supposed to indicate how loud a speaker will play when fed one watt of power, or 2.83 volts, listening from one meter away. The problem with this measurement is that the conditions under which it is to be recorded are not well defined and hence the figure does not provide a consistent "apples to apples" point of reference. For one thing, the input sensitivity (gain) of the amplifier used to measure the sensitivity is unknown and unspecified. More importantly, while the specification calls for measurement at one meter away, the conditions of the listening room are not defined. It is not clear whether measurement is to occur in an anechoic chamber, a concert hall, a coat closet, or a gymnasium. Each of these rooms will yield remarkably different sensitivity readings at one meter from the speaker. The most important lesson to learn from the above discussion is that for the purposes of determining tube-friendliness, sensitivity is essentially meaningless. Many tube gurus insist that one must use speakers with sensitivity ratings of 90 db or higher. This is simply not true. Many speakers with high sensitivity ratings are poor choices for tube amps, just as many speakers with low sensitivity ratings often work quite well. Why is this so? Read on…" https://www.dhtrob.com/overige/tubefriendly_lsp_en.php |
@lloydc Wrote:
No! The two speakers have the same efficiency. Changing the impedance of the speaker will change the voltage sensitivity, not the efficiency -- the 4Ohm speaker is getting 2 watts from the amp, the 8Ohm speaker is getting 1 watt from the amp. That’s why the 4Ohm speaker has a 3dB higher sensitivity. (Ohm’s law) Sensitivity and efficiency are not the same. See below: Paragraph C. Hope that helps. Also, what is the gain of the amp you have? Mike
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In my experience for most speakers, the relationship between sensitivity and amplifier watts is often an overblown consideration. Gain, however, is predictable. Like others have stated you may have a gain issue. I do not know your preamp but 4-6 o'clock seems quite high already and a lower sensitivity is sure to make that more challenging. |
What is your preferred listening volume in the room? Have you bought a sound level meter in order to get a real number to work with? Note that one person's "loud" is another's "medium" and so on. The size of the room is also a factor along with whether or not you use a subwoofer (deep bass takes the most power.) Finally, keep in mind that the position of the volume knob is not an indication of whether or not you are at or near the amp's max output. Here, the voltage output of the source and the input sensitivity of the peramp/amp play a big role. For example, a while back I tried using a unity-gain preamp with a low sensitivity power amp and having the volume knob turned to max only gave me moderate volume. I had to switch to a preamp with additional gain to get the sound I wanted, even though I did not change power amps. As you can see, lots of moving parts. But your first move is to figure out your desired listening level. |
Agree with @soix You can never have too much power, but you can sure have too little. |