SET 45 Amp Driving Dynamic Speakers

Indeed, high efficiency and high impedance speakers are common factors when you read/hear someone is happy with a SET amp. Another factor is the SET should be driven "well below" its rated power, which is of course undefined how low is low enough.

I'm in the process of building an active system with SETs for treble and midrange and class-D for midbass and subwoofers. It's said power required below and above 350Hz is about the same, so by crossing around there (or higher) you relieve the SET from carrying half the load. If you further divide the upper range into two, then each amp will carry 1/4th of the load.

I have my eyes on Yamamoto's A-08S (45 SET), and while the speaker driver options aren't super wide, there seems to be enough. I guess demand pulls for drivers where high efficiency and impedance aren't as big a deal, the manufacturers follow suit. It is being a fun journey!

Hello Ralph (Atmasphere).

I've seen your comments before and I am keeping them in mind as I design/assemble my new system, a 4-way active. If using a 45 amp to only reproduce 350 to 2000Hz on a 100 dB/W driver in a 25m2 room and if average listening level is 85-90 dB SPL, would a 45 suffice or be driven to the point where 5th order harmonics become an issue?

Thank you!

Hi jsman.

I'm interested in learning more about your midrange horn. Is it circular? What are your xo points and what is the horn cutoff frequency? I'm also exploring tractrix midrange horns. Right now with a suitable cone driver but also considering compression drivers.

Ralph,

I thought 45s made 2W and one should run them at under 1W draw to keep distortion from growing much.

Is this what you mean by 0.75W?

@guf 

Let me try and help there.
One one hand different people are comfortable with different levels of SPL. My wife likes the music much lower than me in our same room, same system with same distortion.
Then there is how each of us reacts to distortion, I'm guessing.
The kind of music you use also has an impact. Recent pop/rock tends to be  compressed so smaller dynamic range in the record. Older records and some current don't use compressors so the dynamic range is much higher. Higher dynamic range means louder passages are more demanding on power delivery from the amp and therefore likelier to distort. Atmasphere has stated repeatedly SETs should be used conservatively to keep distortion very low, under 50% and preferably under 20% of rated power.

Let's take a shot at the math: the 45 is rated for 1W, so on your 99dB/W at 1m speakers they would deliver 99dB at rated power at 1 meter. At rated power distortion is high, per Atmasphere. At 20% it would be 0.2W, so your speakers would deliver 92dB SPL at 1m, per speaker. Add the second speaker (and some losses) and let's add 4.5dB at 1 meter. If you listen at 8' away (2.4m), SPL would drop to 88.9dB SPL at the listening position. Add room gain...say 4.5dB and you are at 93.4dB SP at the listening position.

What were your settings on the SPL meter? C weighting?
Then there is also the speaker rating...99dB depends on how the manufacturer measures and defines this. Oh well...everything seems to be "it depends"...

You mentioned above 87dB with the 45 it became uncomfortable. If that was with current pop/rock music maybe your speakers aren't really 99dB efficient? Or the phone app isn't calibrated. Or a number of variables out there...

Like other I'm happy with my 45 tube and what it does for me, I think.

This is the key part. Don't think you are happy. Be happy and enjoy your system!! Understanding all of the above helps in just that: understanding. The enjoyment shouldn't be affected by our understanding, in my view.

cheers!