The ask Tin about audio thread

[SuperCoupeMatt]

Any suggestions on an inexpensive center channel speaker? I have Klipsch KG4 mains.
The Cerwin Vega VE-5C is under $100, Polks are the next inexpensive centers starting at $130, besides bic, pyle, daytons and the such, which can be had super cheap.

[347convert]

There has been a pardigm center channel on cl for a while now.. I'm sure he would come down on the price. Next ti.e on on the laptop and not my phone ill link it to you.

[Marc@AutoLavish]

Can't wait for the coming questions from audio/car guru Dan...

[danox574]

Marc actually bumped this thread after I called him today to ask him this question as I'm staring to work to create a dedicated 2 channel system at home. I'm no guru of anything though.

How are tube amps rated? This is perhaps a discussion of paper specifications vs reality. I can't imagine that they are equivalent to solid state amps, because the ratings are so much lower but they seem to be able to drive some decent speakers. Browsing around for DIY plans and hardware, I'm finding amps that claim to be 2W or 3W -- and I know the speakers that they are driving would need much higher rated solid state amps. In fact, even when McIntosh back in the day was selling 1,000W Monoblocks in solid state, they were selling 25W tube amps driving sizable speakers and doing it well.

I realize that most modern equipment specifications are a little bit of nonsense depending on how thy are presented, but when looking at tube amp ratings, is there something else to consider or that helps explain why they are so low powered on paper yet able to sound as large as much higher rated solid state amps?

[Killjoy]

A Watt is a Watt. It doesn't matter if it was produced by a tube or solid state... they're identical in terms of power output & ability to drive a given set of speakers. Why then can an older, say 1970's era 25W speaker system sound as loud as a typical 100W system of today? Lots of possibilities, but I would suggest starting by looking at the efficiency ratings of the drivers in the cabinet. When it takes double the power to gain 3db, and 10db to roughly double the effective loudness... there's a huge difference in using a driver that has a sensitivity of say 96db 1W/1M vs. one that's 88db 1W/1M in terms of power amp output requirements. And since loudness is a logarithmic scale, it's diminishing returns as you go up.

The two most notable difference between solid state and tubes is 1) sound quality, or distortion, they add. Solid state, assuming no clipping is occurring, is normally very clean. Tubes generally have a more "warm" sound, more distortion. 2) The other side is that a tube's output is more pure since the signal is not going through all of the D/A conversions and other electronic circuitry that it does in a SS amp. Bottom line, personally, I would audition multiple amps on the same set of speakers and pick the amp based on your ear's preference... not whether it's a tube or SS. But know going in that the tube path can be painful and takes quite a bit of commitment - replacing blown tubes, changing tubes for different sound, letting them warm up, etc. And the $ difference is also night and day.

As retro and cool as tube amps are, you also need to make sure you're not just doing it to be cool. I would decide on what speakers you want to run (based on YOUR EARS), and then make the amp decision. As an example, the sub in my HT utilizes leading edge technology and produces probably the best sound quality you'll find anywhere. I had to have this driver... amp requirements be damned. The challenge? It's an 89db 1W/1M power hungry beast that needs 1-2 KW RMS, 6-8k peak. Good luck financing a tube amp that would drive this beast... and that's for a single driver. And I'm not sure why you'd even want to run a uber expensive amp on sub duty. Save it for the full range speakers...

Anyways - I do like tubes in some applications... but not HT/music. JMO.

[Tin]

Tube amps are a different animal from solid state amps, the main factor not even being the tubes themselves. Tube amps can hit up to +10dB peaks at full power output for very short periods of time. This has nothing to do with the output stage, but more-so in the power supply. The power supply of a tube amplifer is built to handle the voltage swing necessary for these peaks. A solid state amp on the other hand, will only handle +3dB to +5dB peaks. Watts are watts, but for dynamics, with the right speakers, tubes will put you right in the middle of the performance.

I run single-ended triodes, the simplest form of amplification, and also the best sounding...to my ears. Single-ended triodes are low wattage, but also the most linear amplifying device known to man. There is nothing out there, tube or solid state, that has as linear of a sound as a 45 tube, a 2A3, 6B4G, or a 300B. Single-ended triodes are a different kind of beast, being that they produce second order harmonics. On paper, my amp should sound like crap, as the second order harmonics drive the THD up to 4%. The flipside, Mother Natures Law of Physics rule here. Our ears are built for even order harmonic distortion. Harmonics are based on the fundamental note/pitch/tone. A second-order harmonic is two times the frequency of the fundamental, a fourth order harmonic is four times the fundamental, etc. Each even-order harmonic is one octave or multiples of one octave higher than the fundamental - so they are musically related to the fundamental, hence, they dont sound like distortion, and you get that fluid lifelike sound. Even order harmonics need to be ~10% or more to be detected by the human ear as distortion. Odd order harmonics, on the other hand, are offensive to the ear, and offensive to speakers. Large amounts of odd order harmonic distortion can damage a speaker in short order. All of that distortion will make quick work of a voice coil. Even though 10% THD even order harmonics isnt detectable, it only takes roughly .01% odd order harmonics to be detected. Odd order harmonics are just a side effect of higher amplifier power. As speakers got less efficient, bigger power was needed to drive them, and different amp topologies were designed accordingly.

As for low-watt friendly speakers, you need to look at 2 things. Efficiency and impedance curve. A 100dB 1W/m speaker in itself should theoretically be great for a low powered tube amp, but theres a catch. If there are large impedance dips, the amp has to work harder. Take a large Cerwin Vega for instance, normally rated at 100dB+, but with impedance dips down to 2 or 3 ohms. That in itself will tell one to stay away from tubes. The higher the impedance the better, as tube amps love resistive loads. An 8 ohm speaker that seldom dips below its rated 8 ohms will sound louder and fuller than one with impedance dips. A speaker rated at 90dB with a benign 8 ohm+ impedance curve will match up better than a speaker rated at 100dB with an impedance curve of the Rocky Mountains. Another factor is Hoffmans Iron Law....small, deep (bass), efficient...you can only pick 2. My sage advice, pick your speakers first, then pick the rest of the downstream components. Many speakers out there will work fine with a push-pull tube setup or solid state amps. Single-ended triode amps need a different type of speaker, like what I mentioned above. Generally, the larger the speaker, the better it will be for tubes. SE friendly speakers are usually much more difficult to find, and many are quite large, but truth be told, a very large percentage of audio folks look no further once they finally land on single-ended triodes. I used to change out amps multiple times per year...until I started using single-ended triodes. Ive been on the same amp for almost 4 years now. Marc really loved my system...in his words "It defies the laws of physics" Well, not really, it just defies modern conventions on amps and speakers

[jhilla68]

I'm certain Bob will chime in, but Killjoy hit the nail on the head. Instead of power, look for high efficiency/sensitivity speakers. I know Bob has already covered it earlier in the thread. But, depending on the speaker efficiency, you'll need to double your power output in order to get the same volume level as a higher efficiency/sensitivity speaker.

I picked up a set of Klipsch Chorus loudspeakers, and they're rated at 101db @ 1 watt/1 meter. That literally means, with merely 1 watt of power, they will produce 101 db of sound at 1 meter.

This is a great little blurb from Wikipedia:

A driver with a higher maximum power rating cannot necessarily be driven to louder levels than a lower-rated one, since sensitivity and power handling are largely independent properties. In the examples that follow, assume (for simplicity) that the drivers being compared have the same electrical impedance, are operated at the same frequency within both driver's respective pass bands, and that power compression and distortion are low. For the first example, a speaker 3 dB more sensitive than another produces double the sound power (or be 3 dB louder) for the same power input. Thus, a 100 W driver ("A") rated at 92 dB for 1 W @ 1 m sensitivity puts out twice as much acoustic power as a 200 W driver ("B") rated at 89 dB for 1 W @ 1 m when both are driven with 100 W of input power. In this particular example, when driven at 100 W, speaker A produces the same SPL, or loudness as speaker B would produce with 200 W input. Thus, a 3 dB increase in sensitivity of the speaker means that it needs half the amplifier power to achieve a given SPL. This translates into a smaller, less complex power amplifier—and often, to reduced overall system cost.

It is typically not possible to combine high efficiency (especially at low frequencies) with compact enclosure size and adequate low frequency response. One can, for the most part, choose only two of the three parameters when designing a speaker system. So, for example, if extended low-frequency performance and small box size are important, one must accept low efficiency.[35] This rule of thumb is sometimes called Hoffman's Iron Law (after J.A. Hoffman, the "H" in KLH)

[jhilla68]

As guessed, Bob chimed in while I was!

[Marc@AutoLavish]

Some good information from all parties here. Great discussion.

[suggtt48116]

This is a great little blurb from Wikipedia:

Hoffmans Iron law I thought was de-bunked? Sunfire's white paper tells of the way the "Tracking Downconverter" amp works. I have had my Sunfire True Sub Signature for 15 years and it is amazing.

Sunfire white paper http://www.vxm.com/21R.69.html