Requests and biamping

[smolder]

somewhat of a noob here… and this has been generally covered, but I have a couple of questions specific to my gear.

I’ve been driving my requests with a Mcintosh mc2100. It’s on the bench getting some fresh electrolytics so I slot an utilized Adcom GFA 585 over. It doesn't sound as good as the Mc. It occurred to me that with minimal effort I could passively biamp this rig… using the Adcom for bass and the Mc for mid/treble. There is a wattage discrepancy though. The Adcom at 200 wpc, and the Mc at 100 (scopes at 130-150) may be a mismatch.

Will this end up boomy with bass (no volume control on the Adcom). I have plans for either another 2200 or a 275 tube amp to use on the high end. Is there a recommended wattage ratio? Other thoughts?

thanks in advance

 

[JonFo]

Bimaping is generally a plus on the older line, like the reQuests, so you are on the right track.

The biggest challenge is generally gain-matching the amps. The best is identical amps, or the L & R channels of the same amp driving the HF and LF sections. Guaranteed gain match there.

Gain is how much amplification will be applied to a given input voltage, typically around 27 to 30dB for home amps.
So if the Adcom has 27dB gain and driving the woofers, and the McIntosh has 29dB gain, and is powering the panels, the tilt to the HF will be noticeable (not huge, but noticeable).

Now, you are in luck, as the Mac has gain controls that should allow you to gain-match what the Adcom and the woofers are doing.

The Adcom is indeed best for the woofers, as it has a decent rating for damping factor of 600. The Mac is a lousy 14 for that spec, reason enough to not ever use it full-range or for woofer duties.

Now, your question is about wattage power ratings, and that is orthogonal to the gain issue. Wattage is how much power will be delivered at max gain. So as long as the system is operated within the envelope of the least capable amp, you should be fine.
The 2100, at a paltry 105wpc in stereo mode is probably ok driving just the panel if you keep the volume levels below 92dB/1m, which is lively enough, but not what many would call very loud.
Keep in mind that an avg level of 90dB can have peaks significantly higher. And it is the power to deliver those peaks that is of concern, as the transients create short duration distortion if the amp is driven beyond rated output.

So if you were happy enough with the 2100 driving the entire speaker, you'll be more satisfied with the bi-amp setup.

 

[JonFo]

To gain match, I suggest using an SPL app on your smartphone (if you have an iPhone, then StudioSix Digital AudioTools is very accurate) to individually measure the output of the woofers and panels being driven by pink noise.

Since the Adcom has no gain controls, start by measuring the woofer alone, then the panel alone, and adjust the gain on the 2100 to balance them.

Since the reQuest is a single driver woofer system, you should measure the woofer output nearfield, at around 18" from the center of the cone. That will reduce the room-gain impacts.

Same for the panel, measure at 18 to 24" to set initial gains.

Then measure from the MLP, as you might wind up with overly hot bass if the room has significant room gain.
Look at the RTA measurements as well to see the impacts of the room on frequency response.

Adjust to taste. Again, the RTA is a good way to double-check what you are hearing.

 

[smolder]

Thanks for that detailed response Jonathon! While my room is 16x36 with a slanted ceiling, I don’t think it presents any serious acoustical problems. I don't typically rattle the walls, but I do often fill the room. My speaker cables are biwired, it should be pretty simple to set them up. I’ll give it a shot and see what it sounds like shortly. You’ve given me more hope of success than I had previously.

 

[Sotiris]

Hello,somewhat of a noob here too. Currently vertical biamping a pair of reQuests with a pair of Aragon 4004 power amps.Thinking of selling one and replacing it with a stereo tube power amp or a pair of tube mono blocks with horizontal biamping - tubes driving the panels. What kind of specs should be matched between the tube power amp and the Aragon?What I shall be looking for? Thanks in advance.