search the archives of the forums here at Audiogon. this topic has been discussed over & over again - plenty of info available for you to read....
Showing 6 responses by bombaywalla
B&W's are traditionally easy to drive 8 ohm speakers and watts are cheap!wow! that's a new one on me. B&Ws are easy to drive 8 ohms speakers? Really? I did not know this - from my experience & every time I've heard them they've been nothing short of a difficult load for the amp. I might be missing something here....... |
Tntate, i found these measurements for the next rev of your speakers - B&W 705: http://www.stereophile.com/content/bw-705-loudspeaker-measurements could not find any such measurements for your CDM-1NT speakers but my guess (from my personal experience & seeing B&W's other speakers) is that the CDM-1NT & the 705 models measure about the same. the impedance & phase plots are totally wild, IMO & this speaker will drive most amps crazy as it yo-yos from capacitative load (negative phase) to inductive load (positive phase). You see this happening in the 1KHz-3KHz region. As the amp deals with capacitive & inductive phase shifts, the impact is felt in the music as phase distortion which will appear as a brittleness or an unusual sharpness in the vocals - the 1KHz-3KHz is a sensitive region for the human ears. Also, due to the wild phase shifts of this speaker, your amp will be wasting a lot of power into the reactive components (capacitor & inductor) of the x-over. The effect of this will be that your amp's instantaneous power will be reduced by the phase angle at that particular freq. For example, look at the 100Hz freq. The phase angle is -45 degrees. Let's say that you are cranking 10W into the speaker for your desired volume. Due to the -45 deg (capacitative) phase shift, the real power is only 7.07W & an equal amount of power is burnt up in the reactive component of the x-over. So, your amp will be working hard but only half the power makes it to the speaker drivers. That's why B&W are traditionally very hard to drive & require big amps that are almost always high-current amps. Higher the current in the amp's output stage, the more current the amp has to piss away into the x-over reactive components and STILL have enough to create a large enough voltage signal in the speaker driver to create a sufficient pistonic action to create a sufficiently large SPL for your listening pleasure. Zd542 has already given you some examples of how we can make a 100W amp - 50V*2Amps OR 25V*4Amps, etc. The higher the current the better for B&W and at the same time you will need higher wattage to ensure signal headroom for better (music) dynamics. Driving a B&W speaker is generally an expensive option because finding a high(er) wattage amp with high current that sounds nice is more often than not puling from a very small pool of amplifiers. Yes, you can use many amps in the market but you will never realize the potential of your B&W & you will generally remain unsatisfied with a perpetual itch to upgrade. Maybe more than you wanted to know but to tame the B&W beast it helps to know what you are doing..... ;-) |
Thanks for your input Levinskih01 - good for you that you liked the (more expensive) MC275 over the Rotel 1080. :-) Your comparison is not exactly fair but those were the 2 amps you had on-hand, I understand. The RB1080 sold for $990 when it was new back in 2002 & it seems like a very capable amp - even had THX certification back then. But at $1000 selling price + made in China, this amp has to be considered a budget amp with serious compromises to make that $1000 selling price. The MC275 was & is a superior built amp from all that I have heard, read & listened (at shows). It currently sells for $4500. It's commemorative edition sold for $3500 & even it's 1st edition of 1961 in today's prices would be a $3500 amp. So, it's no wonder that it sounded better than the RB1080. All-the-same, all B&W speakers that i know of are voltage paradigm speakers (as opposed to power paradigm). So, they are most likely the best sounding with SS amps - that's been my experience so far be it floor standers or stand-mounts, friend's houses or shows. Not saying one cannot use tubes but choose one's tube amp carefully - not any tube amp will suffice..... |
Lewinskih01, thanks for clarifying - indeed, I did misread your post! :-0 well, we do agree to disagree w.r.t. SS being better for B&W. But I will agree with you that the huge tube power amps (like the VTLs you mentioned) will do much better than most other tube amps - but then these large tube amps are designed to supply a lot more current into a difficult load & their price reflects it. 12-25-14: Tntateyou'll never find the current specs for most (If I may be so bold as to say "any") amp. you'll have to do the math & find that out for yourself. Make sure that the amp has plenty of current capacity for example in the 5Amp-8Amp region while ensuring that you have sufficient watts. |