ReQuests… harsh high end

[smolder]

I recently purchased a set of reQuests from a reputable person. As I improve components around them, there is a high frequency harshness that is more noticeable as the get loud and fill the room. The room is a carpeted 18x36, vaulted slant ceiling, adjacent to kitchen & dining room. Speakers point toward the longer dimension.

The panels were replaced by the original owner, but I don’t know when, or how old the speakers are.

I was reading about a capacitor upgrade for the crossovers that sounded like it improves what I’m hearing, but describing sound with words isn’t always precise. It’s a simple upgrade to me.

thoughts?

system: going either digital or vinyl to an NAD 106… vertically bi-amping… McIntosh mc2100 on the high end at 70% gain, Adcom 585 (200 wpc) on the low end. I’m wondering if the NAD is the weak link.

 

[Spike]

there is a high frequency harshness that is more noticeable as the get loud and fill the room

A quick glance at the specs yields the input sensitivity of 0.5V for MC-2100, and 2V for Adcom 585. That means the MC-2100 will be overdriven much earlier than the Adcom, and this matches your description. Given that the input sensitivity for the MC is 1/4 of the Adcom, I'd venture to say that it's being overdriven into clipping even at 70% gain. You might want to try reducing the gain further on the MAC.

 

[ttocs]

To test Spike's theory, which seems like it's a good one to me, is to remove the bi-amp wiring and go to single wire from one amp. If problem remains, then it's something else. Simple.

If you do this, then maybe also compare one amp vs the other.

 

[smolder]

Thank you both for the input! very helpful.

I double checked and the Mc was closer to 80-85%, but it’s a guess as pots aren’t the most precise operator. I dropped it to 50% and of course had booming bass, but compensated with the preamps tone controls as best I could.

I’d previously had the pre volume at about a third. With this reconfiguration I pushed it up to half for similar room volume. Sure enough, the ‘sizzle‘ distortion was gone. It seems to still lack some clarity and separation at the top end, but that might be an inexpensive turntable and cartridge (Sony PS-LX55II with a LP ATN3472SA).

I do wish the Adcom had a gain control.

will try the single amp test this weekend.

 

[JonFo]

there is a high frequency harshness that is more noticeable as the get loud and fill the room

Besides the gear-related suggestions above, I'd also say that even with the best amp / preamp pairing, what you are partially experiencing is room ringing.

Large panel speakers can over-energize a room at mid to high frequencies, and produce fatiguing and annoying resonances/ringing as reflective surfaces cause peaks at specific frequencies when they sum with the direct sound.

I went through several years in my custom HT where I just could not turn up the Monoliths to high levels for any length of time, as they would cause ringing. Once I acoustically treated the room, they are much clearer and without the room resonances, much less fatiguing at high levels over extended periods.

It took a ton (literally) of acoustic treatments to tame the surround setup, but a 2ch system can be done with fewer elements, just placed strategically.
Start by dampening the reflections from the rear wave of the panels with treatments on the walls directly behind them, and then on the lateral walls beside them, that is generally enough to cut the levels of the reflected sound and minimize two things A) comb-filtering and room ringing, B) dipole cancellation (ticker treatments will go down to 250Hz or so), restoring frequency balance to the lower midrange / upper bass.

 

[JohnA]

I've found that instead of stabbing in the dark, it is preferable to stick a microphone on the listening position and use REW to measure each speaker (or both).

Then you can change distance from side/back walls, tow, rake, drapes, what have you.
You may even find that a slightly assymetrical positioning works best if the room acoustics are assymetrical (dining room etc)

As for level matching power amps, a well-made passive preamp like this one might be worth having

 

[JonFo]

it is preferable to stick a microphone on the listening position and use REW to measure each speaker (or both).

What he said ^^^

Even if you don't know how to interpret the results, you can post them here (post the original measurement files, not just images, as that way we can pull them down and look at all the elements in detail).
Between a picture of your setup and a couple of measurements, I can generally tell if there are room acoustics issues and suggest options.