I have been working on trying to make sense of my subjective observations re the audible and visible discrepancy in AHB2's dynamic performance compared with other amps. Lots of great discussion on here, and interesting insights which have helped me get further with my understanding - and maybe closer to solving the problem. Thanks to all for the contributions - and patience with my sometimes painfully obvious gaps in knowledge.
It's an existential problem this hifi one - sounds good versus is good. I think measurements are a valuable starting point to compare, analyse, understand - but ultimately we listen to music through our ears at home in rooms of questionable acoustical quality. If you measure a difference but are unable to hear a difference it only matters in a subjective way. In other words if you cannot taste the difference between a 25 year old single malt and a blended 25 dollar scotch whiskey - drink and enjoy the 25 dollar one!! Unless your ego or pride dictate otherwise of course. Understanding seems the ideal result of hearing (experiencing) a difference and using measurements to observe the same difference (proving).
A day ago when picking up my 'new' Yamaha NS-2000 speakers I was able to spend some time comparing the rare Harman Kardon Citation XX amplifier with the Benchmark AHB2 x 2 (running in mono) and AHB2 x 1 (running in stereo). The Accuphase P300 from my previous posts was sold unfortunately so not possible to test again.
http://www.thevintageknob.org/harman_kardon-Citation_XX.html
The AHB2 is ground breaking, and this Harman Kardon is another ground breaking amp from a time when product design intent was more closely related to excellence in performance and less to budget and marketing (and warranty) IMO. Meaning that some of these old amps still out-perform many many modern amps designed with modern tools and components. Speakers for example - the Yamaha NS-2000 speakers measure roughly 10-15% less overall than the latest NS-5000 speakers despite almost 40 years separating them and $2.5k v $20k in price respectively.
So while I can somewhat agree to arguments about technological and material advances which have been achieved during the last 40 years, when it comes to open mindedly measuring and listening to different equipment and comparing - much modern equipment is not worth a fraction of the price paid/ asked.
The listening and measuring of the AHB2's with the NS-2000 speakers was very satisfying, the speakers have a reputation for revealing flaws in the audio chain due to their accuracy,clarity, and transparency. Despite the fact they are becoming harder to find, I think the effort was worth it because they seem to be a good match for the AHB2 due to it's exceptional abilities to keep the signal path clean and pure from source to speaker. The speakers have been well voiced to my ears, instruments and vocals are extremely realistic and accurate. Sound stage is out to almost 180 degrees horizontally - over the shoulders in other words. And they measure flat with a little mid range warmth. In summary, so far, my thinking has been supported by my measuring and listening - even a 40 year old pair of speakers can sound great with decent amplification.
One thorn continues to dig into my subjective well being (aka happiness) score however. The base response. Specifically the dynamic attack, or instantaneous peaks, leading edge. Unfortunately I did not take the laptop or microphone to the pick-up as I was merely intending to grab my speakers not spend 6 hours comparing amps. So what follows are subjective observations from a scientific/ engineering POV.
I focused on small sections of tracks, 10 seconds max, set levels of that portion of the track with an SPL meter. Play adjust play adjust then finally get levels the same then loop that portion of the track repeatedly until the brain and ears can identify the differences or lack of same. Many many different types of music but all with a consistent observable difference in the kick drum.
When you look at an audio spectrograph which has deep bass and kick drums, the kick drum frequency extends the total SPL above the continuous bass SPL. The kick drum attack is on top of the bass. It was absent from the AHB2 no matter how I tried different tracks and SPL combinations - turning up the power did not help, although running in mono was much much better (making me think power or current are part of the issue) . A kick drum has a fundamental around 40-100Hz but has mids and highs from 300-1200Hz. The AHB2 could not reproduce the leading edge 'kick' that other amps could. Different speakers, different amps - all managed to deliver some kind of leading edge punch. Even a small studio monitor running off each amp showed a clear difference despite the ease of driving the little speakers (therefore eliminating the amp power etc). Physical cone extension (mentioned in my original post) was much better with AHB2 x 2 in mono, no difference observable between the amps.
When I looked at the impedance curve of the NS-2000 it's dropping from +90 ohms @ 40Hz to 8 ohms @ 100Hz on the woofer. It seems like the speaker is being a little difficult to drive in that area, and the current demand of moving the cone might be beyond the amp. Meaning big magnet, big cone, dropping impedance requiring some decent headroom to deliver an accurate reproduction of the audio signal. As always a pair of headphones can clearly demonstrate what I am talking about compared with a live amp - particularly because it runs though the DAC/ preamp so therefore isolates the amp.
So help me understand and prove my observations. How can I best measure this phenomena? I am thinking REW, microphone 1000mm away from speaker centered on the woofer driver, and then overlay the amplified measurement with original digital audio sample to compare.
And I can also do the test with stereo AHB2 and 2 x mono AHB2's - because the latter is hands down better in this respect despite never clipping in either setup.
As always replicate the test before you comment because if a clueless novice like me can hear and experience the difference someone with professional experience and years of knowledge will probably experience things that I am unaware of...... which may be able to explain what I am experiencing.
Cheers.
P.S. - there are ongoing negotiations re acceptable room treatments - the succulents proved to be both reasonable diffusers and partner permitted additions. Just need to find something thicker on the floor in front of the speakers and something MUCH thicker bushier in the corners for bass traps.
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