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How to accurately gauge speaker sensitivity to match with tube amp?

I'm in the process of matching speakers to my amplifier and need a bit of advice. Most recently, I'm trying Focal 936 towers with my Quicksilver Mono 60w amp. They were sounding pretty decent until I experimented by hooking up my old Adcom 535L amp. All of a sudden, there was a giant jump in control, tautness in the bass, quickness in transients. The QS stuff was doing quite decently, but the Adcom really snapped these towers to attention. The mids and high ends, not to mention the soundstage, were worse with the Adcom — no question. But there was quite a difference with the other qualities just mentioned.

My question becomes one of sensitivity. The Focals self-rated as 92 db. Stereophile rated them as 89.5db. I realize that these are average measurements and a much bigger picture is told by the impedance graph (and other factors).

As I continue to search for the right match of speaker (I have a couple contenders), I'm sure one piece of advice is to look for speakers with higher sensitivity averages. But what else should I look for to help make a guesstimate about whether the amp will drive the speakers with the kind of control they are capable of? [Specs for this amp are here: http://quicksilveraudio.com/products/sixty-watt-mono-amp/ ]

I realize I need to hear speakers, in my house, with my gear, etc. to get a sense of them. I’m working in exactly this way. Your advice can help me eliminate candidate speakers that would pose similar challenges to my amp as these Focals have.

And I just bought the amp, so I don't want to change it.

Thank you for any thoughts. 

P.S. Anyone who has has had great success with this amp or similar, please shout it out.


hilde45

Showing 7 responses by ieales

ieales's avatar
ieales
1,201 posts
 
Smaller mains and a pair of subs:

Relieving the amp of the necessity of driving the low end roller coaster effectively doubles its power, allowing less efficient unported mains. [I've never heard ported low end I liked].

Getting smaller mains up on [sand or shot filled] stands solves several problems.

Subs like the Martin Logan ML---x series have ARC built in which can do wonders for bottom end coherency. Subs must have multi-slope crossover, phase and polarity controls. Delay is icing on the cake. The MLs are quite light and will stroll, so be prepared to weight them.

Just don't get swarmed by Mr Carbon.
ieales's avatar
ieales
1,201 posts
 
driver tubes ... have more influence on the sound than power tubes 
Nonsense. Tubes are like fine wine. They vary bottle to bottle and with temperature, age and side dishes [system and programme].

@hilde45 - IMO, there are better options than a sh.tload of tweeters, unless you happen to love phasy sound fields. Tekton's patent is one of the funniest I ever read, right up there with Michael Jackson's moonwalk shoes.
ieales's avatar
ieales
1,201 posts
 
@atmasphere +1

An amplifier, cables and speakers form a system in which they interact.

Anyone who claims one thing in particular is a panacea for all ills is prevaricating.

To wit, from MBL Noble Line N11 line preamplifier @
https://www.stereophile.com/content/mbl-noble-line-n11-line-preamplifier
"Some of my work involved tuning the power supply. It may come as a surprise to learn that you can change tonality without even touching the signal path, because the signal originates from the power supply. The impedance curve of the N11’s power supply is absolutely homogenous from DC to 200kHz, which creates a very balanced sound. I also tuned the resistors for the voltage gain, using a mix of carbon and metal resistors to create a neutral balance. There are a lot of preamps that claim to be ’neutral’ or ’in balance,’ but there are different shades of ’neutral.’ If you have a tube preamp, for example, ’neutral’ is at a different level than solid-state; it’s not better or worse, but it is different. It took a lot of work to find the tonal balance I like a lot that measures well, with low noise, and fits very well in the Noble Line." [emphasis added]

One can only assemble a system in one’s locale with one’s components.
All else, especially idiot topics "What [insert device here]?", is pure folly.
ieales's avatar
ieales
1,201 posts
 
guitar cabinets typically don't have tweeters or crossovers
ieales's avatar
ieales
1,201 posts
 
@nakam
20wpc is good for 96db @ 3.5m w 91db 2.83V/8Ω/1m speakers
Plenty loud.

Speaker impedance may change the above somewhat
ieales's avatar
ieales
1,201 posts
 
@djones51

A square wave is an infinite series of odd harmonics above the fundamental. When an amp clips, the waveform stops at the power supply limit and creates an odd multiple series of the clipped fundamental. Below is an abreviated list of 200Hz odd harmonics to 20kHz. They continue forever. As you can see, they cover all driver ranges. Note that if only a portion of the wave is clipped, that period is the fundamental and the odd harmonic progression starts there. 1% clipping @ 200Hz starts @ 20kHz and continues upward. On a 200wpc amp, that’s 200w into the tweeter for a few µs. 200Hz 10% clipping starts @ 2kHz and supplies full power for a dozen plus full power harmonics continuing to the amplifier bandwidth.

H# Hz
003 600
005 1000
007 1400
009 1800
011 2200
...
091 18200
093 18600
095 19000
097 19400
099 19800
101 20200

Music has an approximately 50% power ratio per octave and acoustic instrument harmonics are only a fraction of the fundamental, so there is very little power actually sent to the HF driver. [Electronic instruments, buzz guitar and heavily Eq’d program can have a grossly skewed driver eating power spectrum.]

Hz   Pwr %
200 100%
400 50%
800 25%
1600 13%
3200 6%
6400 3%
12800 2%
25600 1%

When a tube amp distorts, there is a fair amount of lower even [2nd & 4th] harmonic distortion which is a good indication the amp is losing control and gives fair warning. A good SS amp with robust power supply gives no warning and dumps the full spectrum willingly. By the time user hears it, it can be too late for the HF driver.

Hence a low power SS amp into inefficient speakers is more of a risk.
ieales's avatar
ieales
1,201 posts
 
a look at Legacy impedance curves  https://www.stereophile.com/content/legacy-audio-focus-2020-loudspeaker-measurements and  https://www.stereophile.com/content/legacy-audio-studio-hd-loudspeaker-measurements clearly show they could be some transformer, AND a good many SS, unfriendly.


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