Yes it is possible. Desirable maybe not at least at 1ohm but possible. Would you like me to build you a loudspeaker with such specs? I have a loudspeaker in my office 92.5db 1 watt 4ohms. Sure many others available near this spec.
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50W SS or tube? SS might work,tubes would be pushed too hard to develop power into that load. My Air Tight ATM 3s drove the top-end of the VSAs,but were not enough to sufficeintly drive/control the woofers (same with Audio Physics Virgos).You could switch them into "ultra-linear",but the magic was gone. |
I think when you look at the sensitivity of a speaker, the amplifier's watts are important but when you factor in the speakers low impedance, it becomes equally important that the amplifier can deliver adequate current rather than just power. For example, the old Quad ELS 57s only required low power (around 25 - 40 watts) but caused big problems for many amps that couldn't meet their current demands into their very low dipping impedance. I had many amps with the correct power ouput pack it in because they couldn't deliver enough current. |
What you are saying initially is pretty common if you think about it... The more drivers, the lower the impedance usually resides. The BW speakers act closer to being a 4ohm speaker than the 8 ohms they say they are... ex the 802N... Focal speakers too have lows beneath 4 ohms. Tyler units in the past have delved low as well... Even my Silverline Sonata IIIs respond better on some amps 4 ohms taps than their 8's. Damping rate of the amp can indicate a better fit than mere topology... SS v. Hs. I refer to damping as 'control' of the loudspeakers drivers, preventing them from returning energy to the amp. Generally, lots of watts can overcome it too. Others here can explain this interaction between the amp and speakers far better than myself. I've noticed this relationship just by how much more low level impact and timberal truth there is, and/or how much more the vol knob gets tweaked upwards to get the same SPL or satisfying sounds. BTW I'm not keen on high levels of Sound pressure, or immense listening levels. So I like an amp which doesn't have to be turned way up to sound good. |
Sensitivity and Efficiency are two specs that try to express the same thing from different points of view. The different points of view are the Voltage Paradigm and the Power Paradigm, which are opposing concepts of how to design and test amplifiers and loudspeakers. For a complete explanation see http://www.atma-sphere.com/papers/paradigm_paper2.html Efficiency is 1 watt measured at 1 meter. Sensitivity is 2.83 volts measured at 1 meter. If you work the math, 2.83 volts is 1 watt into 8 ohms. Into 4 ohms it is 2 watts, IOW if you have a speaker that is 92 db 1 watt/1M, it will be 95 db 2.83V/1M, if it is also a 4 ohm device. The Voltage Paradigm, which mostly describes transistor amplifiers, has no use for the Efficiency measurement, which is a Power Paradigm specification. Amplifier power and impedance are not the same thing; if you have a low impedance speaker that is also high sensitivity, a low power tube amplifier will be able to drive it just fine as long as it is able to get a good match to the speaker. FWIW these days there is little argument for 4 ohm speakers in high end audio. This because regardless of the amplifier technology (transistor, tube or class D), the amplifier will sound better and perform better on higher impedances. Of course, if you are unconcerned about sound quality, and more interested in sound pressure, than 4 ohm speakers will be more attractive if you also own a solid state amplifier. The other argument against 4 ohms is the speaker cable- they are extremely critical for best results on 4 ohms, while at 16 ohms they are not nearly so. Making a speaker to be higher impedance, all other things being equal, is an easy way to make the speaker appear that it is smoother with greater detail, always a desirable combination. |
Atmasphere Regardless the rated impedance of the loudspeaker, doesn't the curve of it's impedance linearity play a more important role? I mean some speakers, my own included profess an impedance level of 8 ohms... but in practice, delve to far lower means in common usage. From merely the numbers/specs of an amp or a loudspeaker system, can one derive some methodology for pairing amps to speakers, or vice versa? For instance, with your amplifiers, do you forewarn anyone as to the speakers with which they are not at their best? ....or are there such speakers? About the only guidelines I've been able to hang my hat on are these... with 250wpc SS power, there aren't too many speakers such an amp won't drive well. ...and conversely, if a tube amp has 100+ wpc, speaker choices are pretty broad too. The difficulty I've run into has been matching amps and speakers when the power levels of the amps get below 40 or 50 wpc.... or the speakers have exceptionally tall impedance, and a SS amp is the power plant. The former interests me greatly, the latter not as much, though I thought to include it as the antithesis of the formers train of thought. Thanks... |
Atmasphere - If you can remember 70's it means you weren't there. I remember The Beatles playing on 30W VOX amps and people tossing LUXMAN tube amps to get beautiful and modern transistor amps. These SS amps often had rated unmeasurable THD and IMD distortions and had a lot of power but sounded like crap because of deep negative feedback and tons of TIM distortions. |
Yeah- those LUXMAN amps were pretty cool! Blindjim, Here is how it seems to work: regardless of the amplifier, there are speakers it will work with and others that it will not. In the case of an 8 ohm speaker that has dips, the dips are of no consequence to a tube amp as long as its a crossover we're dealing with. What **is** of consequence is when the impedance maintains a sustained drop, for example when there are dual woofers in parallel (like in the B&W 802). There is no tube amp in the world that can play a B&W 802 properly (there are some that do OK) on account of that issue. Here's why- if you use the 4 ohm tap, there will be ringing in the mids and highs because the output transformer is not loaded correctly. If you set for the 8 ohm tap, you won't be able to get enough power to the woofers- it will likely be a good 4-6 db down! The B&W was designed for an amplifier that can make constant voltage into any load (double is power when impedance is cut in half). Conversely a transistor amp of 250 watts cannot make bass on an ESL (Sound Lab for example) because the impedance of the speaker is a lot higher in the bass than it is in the mids and highs. That transistor amp might be limited to no more than 30-60 watts into that load! So matching is important, and yes, we do try to check and see what a potential customer is using on this account. Of course I like getting a sale, but it will do no-one any good if the amp won't work with the speaker, so I've had to steer sales away from us a number of times in the past on this account. After years of this, I realized that there was a bigger issue- that equipment matching, tubes vs transistors, objectivist vs subjectivist are all the same conversation- thus the link I dropped earlier. Making power with tubes has always been expensive, and I have really come to value efficiency in a loudspeaker as long as it does not impair detail and bandwidth. That is a sometimes a tall order, but the speakers exist, but probably a topic for a different thread. |
Well, thanks very very much, Atmasphere, indeed. I sort of figured you would go down that path of viability in conjuction with the use of your amps to anothers current speakerage and their intents. I noted on my own Silverline Snoata IIIs. I foudn better results using the 4 ohm taps off my Dodd 120 wpc mono blocks, than I did the 8 ohm taps. On the 8's the sound was very 'tipped up' with little bass and it sounded quite thin, but with immense resolution in the upper bandwidth. Switching to the 4s on a suggestion from another Dodd owner, brought everything into greater balance. More bass, more anturalness, and less accentuation of the upper mids and highs. I had a similar result with them on a BAT VK 60 using the 8 ohm taps, but never switched to any of the other taps, (4 or 6) as I simply didn't know any better. primarily too, the speakers were rated by the maker at 8 ohms.... SO WHY THEN SWITCH TO A LESSER IMP TAP? It seemed counter intuitive and perilous to try other taps. Would you think then, the Sonata IIIs are a 4 ohm spkr vs. 8, or merely less sensitive than the posted numbers suggest? reportedly, Alan uses first and seconds with this speaker system. |
Blindjim, if I understand correctly, the Sonata IIIs have a substantial 4 ohm region in the bass, and 8 ohms (nominally) across the rest of the range. A tube amp is going to struggle with that 4 ohm region unless there is some provision made for that. Even though most of the range of the speaker is in the 8 ohm region, 4 ohms is what I would consider this speaker to be because you have to accommodate that in order to make it work. |
Atmasphere Thanks much. I did find it odd that tube amps needed to be set to taps other than the intuitive 8 ohm ones. Which follows my thoughts here and elsewhere, manufacturers suggest numbers they alone are accounting for... unless of course some recognized 3rd party wishes to spec out their product via other testing methods. Therefore, with that in mind, it seems to me it's a fairly dicey proposition to select speakers and amps by manufacturers spec sheets alone. in other words, "THINGS LOOK GOOD ON PAPER, YET DIFFER IN PRACTICE A GOOD BIT OF THE TIME." It sure is a shame that makers of such loftly priced goods cant' be more square shooters on the specs of their porducts using real world measures. Alan had told me these speakers never dropped below 6-7 ohms across their bandwidth, making them easy to drive with nearly any amp of 10wpc or more. I've also since found out that if one takes the bother to contact the maker/distributer, more insights to actual impedances can be obtained.... and it's suprising considering the contrast between their posted numbers and those gained by a simple phone call. Are there so many differring sorts of measureing methods that can be used today, which account for makers offering uh, more attractive numbers than may be the actual case? An impedance curve is far more the better information than is what a speaker does at 1K Hz... and truly the more erstwhile information prospective buyers require. BTW B&W too said they test and measure their units differently than the majority of other loudspeaker makers do. In this day and age, especially with pricing being held above the median for exceptional performance producing components, one would think some standards would now be in place and surely adhered to by all the makers, that better correlate to the practical use thereof... and not simply as an aid, or an out for posting their "at best" specs instead. Not to mention the added light of honesty it would cast onto the industry at large... thereby further increasing it's attraction to the public in general. |