What Sensitivity with Tube Components?

   Whoever told you that was probably speaking of "single ended" tube amps, that have low power. There are lots of tube amps that will drive your speakers, I would recommend something in the 50 watt range for your speakers.
Good luck finding the right one and welcome to tube sound! Tish

I've been told that my 89db (sensitivity) B&W speakers will not work all that well with tubes and that at best, speakers should have at least a 90-91db sensitivity to used with tubes.

wcc10  - curious to know where you heard something like that ?  

It depends. you need to provide more info.
Which B&W speakers (model);  how big is your room and how are speakers placed in the room; How far away do you sit from them and how loud is it (average)  ?

Do you listen to all music genres or any specific ones ? 

If you can answer those questions I can make some suggestions. 

Cheers 



 
 

Thanks for the replies,
B&W CM6s speakers (for now)
Speakers situated on solid bookcase/cabinet about 7 feet apart right to left. Listening position about 7 feet from speaker position. I listen loud enough to hear it! (no distortion!!)
Room is about 24x24 feet with banks of windows on two sides.

Listen to a lot of Blues/Adult Rock, some Jazz and some Classical.

Look forward to any suggestions.

24 x 24 room - nice....
On a bookcase - against the wall ? 
are one or both speakers along one bank of windows ?
CM6s2 ?  like these 

http://www.u-audio.com/shopimages/gmosp156/0000000045302.jpg

what are you looking to improve upon and whats the current amp? 

About 6 inches from rear wall both speaker have clear field horizontally. Windows are about 3-5 feet from speakers.
Current Amp/Receiver is Yamaha R-S700.
Yes, speakers like those.
I have decent cables but system sound "bright" to me. Granted, there is room for improvement all the way around. Looking for more "warmth."
You can see, this is a "budget" system compared to many. I'm open to suggestions.

Those speakers are extra hard to drive - inefficient - due to the small box and B&W trying to make more bass with it.

B&W Manual
88dB spl (2.83V, 1m) its not a straight 88db spl (1.00v, 1m) comparison.
So they are actually worse.
Do the windows have curtains ? if so have you tried closing them.
The manual also says they need to be at least .5 meters 1.6 feet from the back wall and side walls.
A Big TV between them makes it worse too - not sure if that is the case. 

Your amp makes 100 watts at 8 ohms. and only 120 watts at 6 ohms. Your speakers go down to 3 ohms to make their bass.
The speakers are making your amp struggle imo with the bass. This throws off the tonal balance. Makes the speaker therefore sound bright.

If you buy a SS amp make sure the specs show doubling going down - 100 wpc 8 ohms, 200 wpc 4 ohms.
if you buy a tube amp makes sure it has 4 ohm connectors on the back.
I would go with as many watts as you can afford which ever way you decide to go.
important.
try to bring the amp home for trial. if you can't do that bring your speakers to the store and listen there set up as close as possible to your home.

my 2 cents.

All makes sense but you are saying that these speakers should be connected to a 4 ohm output? The Yamaha R-S700 has an impedance switch on the rear which allows for 4-8 ohm speaker set ups, bi-wire & not. (see page 13 manual)
I have not tried this setting in the "Low" (4 ohm) setting but maybe it would be worth a try?
Also, These speaker are at least 1.5 fee from the rear wall but I've always felt speaker stands would help. (The wife is not into this as much as I am) So on the built in book case the remain!
As for tube, you suggest as many watts as I could afford. You can buy a Jolida 100 watt Tube for under $2,500.00. So price does not always seem to dictate great sound.
Do I consider Class A, B, AB Tube amplification?
Thanks.

Nothing between speaker, yes one side has heavy curtains which I have closed. Other side does not.

briefly looked at the manual. So you are using pure direct mode, cd direct amp ?When I said the 4ohm setting earlier I was implying for the tube amp. but this is an interesting amp.  

I have not tried this setting in the "Low" (4 ohm) setting but maybe it would be worth a try?

I am not familiar with that amp but would say - Yes.
See the wording here.  

http://hometheaterhifi.com/reviews/receiver-processor/receivers/yamaha-r-s700-stereo-receiver/

the R-S700 is bi-wire ready. In this case, it uses both sets of internal amplifiers (Speakers A & B) for one pair of bi-wired speakers. This implies a true bi-wired scenario, where separate discrete amplifiers are used for the tweeter/mid-range and woofer section of your bi-wire-able speakers.
Note that if you do use this bi-wiring feature, it is important to select the proper impedance (high or low) setting for the receiver. The high setting allows bi-wiring speakers with 6 Ohm impedance or higher, while the low setting allows bi-wiring of speakers rated 4 Ohms and higher. Similarly, the high/low impedance switch needs to be properly set for standard wiring too.

As far as wattage - B&W benefit from more good wattage.   I would try the above settings first and see how you like it. I believe you will get more oomph - and it will be a warmer sound.    

Do I consider Class A, B, AB Tube amplification?

That can become a long discussion.  there are real amp experts here that can help you out more.
Push Pull a/b tube amp works well from my own experience with lower efficiency bass needs.  And yes stands would improve things alot - but thats a no due to your wife saying so.    

Indeed!
Thanks for the input.

Since you're not using stands, are you using some kind of acoustic footer so that the speaker is decoupled from the furniture? IOW, are the bottom of your speakers sitting on the bookcase or are they raised?

If brightness is your problem it is the B&W speakers. With the free-mounted  aluminum tweeter you can change your gear till the cows come home and they will always be bright. My friend had the 805’s and they would drive you right  out of the room! BTW, I had the original 802's many moons ago and they were also bright! Power is not the problem,the speakers are!

I agree with yogiboy - it's the speakers that are bright. As far as power I drove Dynaudio C1's with 40-70-110W Octave tube integreted's with no problem. BTW the C1's are rated at 85db. What I did notice is with each 'bump' up with power there was a hair more control in the music.

The room with glass walls on both sides contributes to the brightness.

Yes, the speakers are on the rubber feet supplied with speakers. I was afraid that the answer lay in the speakers themselves. It is unfortunate that today you can spend $2,000.00 on speakers and not be satisfied. Sure, in the total these are inexpensive speakers and maybe I expect too much?
I go back to 12 inch woofers in my old AR3a's. Apples to oranges I know.

I would not try to cure the brightness by going to a tube amp.  Somewhat counter-intuitively, it would stand a very good chance of worsening the brightness.  The reason is that relatively small speakers such as yours, that strive for good bass extension relative to their size, are often designed with a lower impedance in the bass region than at higher frequencies.  The idea being to capitalize on the fact that a solid state amp will deliver proportionately more power into low impedances than into higher impedances (assuming the amp is operated within its capabilities), thereby enhancing the speaker’s deep bass response.  A tube amp will not perform in that manner, and depending on a number of variables specific to the particular tube amp and speakers, and also on which output tap is used, will very often deliver even less power into a lower impedance than into a higher impedance, resulting in an overly bright sound with a speaker designed in that manner.

I couldn’t find an impedance vs. frequency curve for your particular speakers, but that is one of the reasons that many B&W speakers are not considered to be tube friendly.

Good luck.  Regards,
-- Al

It is unfortunate that today you can spend $2,000.00 on speakers and not be satisfied.

Sure, in the total these are inexpensive speakers and maybe I expect too much?

wcc010 - imo - Those are not inexpensive speakers. And they definitely will not replace what a 12" woofer will do.

I am curious to know what happened when you switched to the low impedance speaker setting on your amp ?  Did it change anything? 

Cheers

There are plenty of speakers in that price range that are outstanding. You should take a gander at Harbeth,Spendor,etc. I think a sealed two way monitor will give you a satisfying musical experience!

ct0517, yes when I did switch the impedance and switch there was a definitive change, and not for the better. Mid-range was more pronounced but almost to the point of distortion. (only way I can describe it) Otherwise I didn't notice much too much change. I didn't leave it there for too long as I was not happy with the change.
Currently I am using 12 ga cables with bi-wire at the speaker end only. Perhaps I will try a true bi-wire set up with the switch set to low. Worth a try.
I listened to these speakers at my local Mcintosh dealer, B&Ws & Mcintosh 275 amp. I was very disappointed with the sound, actually the Yamaha was more to my liking. So to say that B&W speakers may not be "Tube Friendly" sounds quite plausible.

I think almarg is giving you some good advice. I have been using low-medium powered tube amps for 40 years, and if you want to get into tube amps, I would not say anything to discourage it, they can provide a very satisfying listening experience. My advice is not to get too hung up on speaker sensitivity. The key is to mate them with speakers that have a fairly benign impedance in the 6-10 ohm category. For instance, the original Pro Ac Reponse 2 had a sensitivity of only about 85 db, but they worked nicely with a 50-watt Audio Research tube amp that I had at the time, because the Pro Ac impedance was perfect for the amplifier. On the other hand, there are speakers out there rated at 91 db sensitivity, but the impedance is 4 ohms or less and would not mate well with most tube amps. I'm not sure about the impedance rating of your current speakers, but that would be the place to start.

  Perhaps I will try a true bi-wire set up with the switch set to low. Worth a try.

Hi wcc10 according to yamaha amp manual this is what has to happen to test that feature setting.  Even Yamaha recognizes different speaker impedance's and it is the reason they included that feature in your SS amp. Give it a try - costs nothing.  

from that earlier link.

the R-S700 is bi-wire ready. In this case, it uses both sets of internal amplifiers (Speakers A & B) for one pair of bi-wired speakers. This implies a true bi-wired scenario, where separate discrete amplifiers are used for the tweeter/mid-range and woofer section of your bi-wire-able speakers.

 
So give it a try definitely. 

But and this is a big but..... someone that is used to a 12 inch woofer like yourself - it can be like mothers milk you know ...  if infants could talk when being switched from mothers milk to artificial I am sure they would say - ew ,  yucky, phewy.

If the above doesn't work I would switch speakers, or get your wife to approve a sub to bring balance to the music.Those speakers in a space surrounded by windows is a challenge.

Let us know how you make out - good luck 


     

Mother's milk! I love it! ;-)
All very good info. I'm glad I posted this question on this forum.
I have another set of 12 ga cables so I will give the bi-wire a try. As said, it cost's nothing! I'll let you all know how it works out.

Thank you all!

wcc10,
You have received some very good responses here. Al gave you the definitive answer,= your speaker is designed to be driven by a transistor amplifier. Small, inefficient and striving to produce bass(via low impedance). I'm a tube guy but tubes  usually won't match well with this type of speaker design. As has been said, tubes work better with higher impedances with a relatively flat impedance range. If you ever decide to try a tube power amplifier, get speakers with friendly  and flat  impedances. With your speakers, stick with solid state amplifiers.
Charles,

Yup, that is the message I'm getting. Makes total sense and I'm glad I posted before I took the plunge into tube amplification. I've had these B&W speakers for about 1 year and I always intended to "upgrade" at some point. This discussion has shown me that upgrading my speakers with a view toward going over to tube amplification requires serious homework before making that switch. It also shows me that where I buy is as important as what I buy. If the guy selling me the gear has no clue about what he is selling then chances are I will end up not being happy.
Mcintosh MC275 MK6 - B&W CM6 S2 don't match up very well as proved to me first hand.

An update; I did try the Bi-Wire set up with my speakers & Amp. With the Impedance switch set to Low and using two sets of 12 GA cables there was a bit more "oomph" but also seemed to be a bit of distortion again in mid-range. Switching back to impedance setting High cleaned up the distortion and sounded more like the cables single end at the amp and Bi-Wire at the speakers. I was using two different brand of cables so that must be taken into consideration but I could not justify using 2 cables as there was not a great deal of improvement. Speaker placement is highly important and I guess right now I'm going to have to be satisfied with what I have. Which is not all that bad considering.
Thanks to all for the help!

Also i would look for a front ported speaker if in enclosed bookshelf !

Good point.