Review and Measurements of Benchmark AHB2 Amp

[misterdog]

I think I could *just* detect a difference between them, but certainly not to the extent that any one sounded better than the others...

I guess it all depends upon how much distortion your loudspeakers are adding to that of your amplifiers.
Or how much distortion your source is feeding to your amplifiers.
Or how much your room is distorting the resultant sound.

The problem with audio is that there are few night and day, eureka moments.

It's all about the weakest link in the chain, and chiseling down the imperfections.

Some kit now has laboratory standards of perfection, whether people appreciate this lacks of distortion from the 'truth' is a matter of debate.

Unless you have stood next to a drum kit, grand piano or cello played acoustically, how would you know how it should sound.

If I measured my kit against the sound from a band playing 'live' using their choice of amplifiers and loudspeakers, I would have little concept.

 

[Guddu]

Dayton Audio UMM-6:

View attachment 26865

Hi Amir, FMs, @amirm
May be a novice question but does it mean that Dayton UMM-6 isn't a good calibrated microphone for basic measurements, like for room correction, etc. ?
Comparable to minidsp UMIK-1?

 

[Angsty]

We did some real world blind audition amp testing on Sunday with this amp and a few others. Here's a link for anyone interested.
https://www.avsforum.com/threads/ka...e-night-events.1496367/page-450#post-60198218
post 8989.

Have you done a comparison like this of DACs? It would be interesting to see results of those, as well.

 

[misterdog]

Comparable to minidsp UMIK-1?

UMIK -2 now available.

 

[Guddu]

UMIK -2 now available.

Thanks misterdog, but I was tying to get opinions on UMM6 because of its low price.
Its available for 76$ (including shipping and taxes), while UMIK-1 is around 105$ (including taxes).
Is it worth using for basic measurements?

 

[DonH56]

Thanks misterdog, but I was tying to get opinions on UMM6 because of its low price.
Its available for 76$ (including shipping and taxes), while UMIK-1 is around 105$ (including taxes).
Is it worth using for basic measurements?

The biggest issue with the UMM-6 is its noise floor is much higher IIRC. May be fine for you, but given the investment in everything else in my system, the UMIK-1 calibrated by Cross-Spectrum Labs (CSL) was my choice.

 

[Guddu]

The biggest issue with the UMM-6 is it's noise floor is much higher IIRC. May be fine for you, but given the investment in everything else in my system, the UMIK-1 calibrated by Cross-Spectrum Labs (CSL) was my choice.

Thank you for sharing this information.

 

[Archaea]

Have you done a comparison like this of DACs? It would be interesting to see results of those, as well.

We’ve not yet.

 

[Guddu]

The biggest issue with the UMM-6 is its noise floor is much higher IIRC. May be fine for you, but given the investment in everything else in my system, the UMIK-1 calibrated by Cross-Spectrum Labs (CSL) was my choice.

Just wondering role of noise floor in room measurements for calibration purpose!!!

 

[Vasr]

Just wondering role of noise floor in room measurements for calibration purpose!!!

A non-issue. You just keep the measurement signal at least 25-30db above whatever noise floor there is in the measurement room. Typically the room noise floor is far above whatever inherent noise exists in the microphone itself.

The calibration of the mic is more important if the microphone has a really weird frequency response but even this is a bit overstated. It is good if you have it, will still work if you don't. It is not going to change the nature of the target curve much in practice in my experience. The deviations are much more pronounced at the far ends of the spectrum where you are unlikely to do much correction in any case.

 

[DonH56]

Just wondering role of noise floor in room measurements for calibration purpose!!!

Depends upon what you are doing/measuring. IIRC the Dayton's noise floor was around -50 dB or so compared to the UMIK-1's -70 dB'ish (both higher than my Earthworks M30 through a good preamp). For simple frequency response it doesn't really matter since you'll be using higher signal levels well above the noise floor. For noise and distortion measurements you'd like the lowest noise floor you can get.

For me the calibration cost was not a significant adder and I like having accurate extended frequency response, especially on the low end, since I am moving subs around and tweaking for the best response. My in-room response is -3 dB at about 7 Hz. FWIWFM the CSL-calibrated UMIK-1's FR curve essentially overlies that of my Earthworks M30 from 5 Hz to 20+ kHz based upon an in-room measurement comparison.

 

[Guddu]

Depends upon what you are doing/measuring. IIRC the Dayton's noise floor was around -50 dB or so compared to the UMIK-1's -70 dB'ish (both higher than my Earthworks M30 through a good preamp). For simple frequency response it doesn't really matter since you'll be using higher signal levels well above the noise floor. For noise and distortion measurements you'd like the lowest noise floor you can get.

For me the calibration cost was not a significant adder and I like having accurate extended frequency response, especially on the low end, since I am moving subs around and tweaking for the best response. My in-room response is -3 dB at about 7 Hz. FWIWFM the CSL-calibrated UMIK-1's FR curve essentially overlies that of my Earthworks M30 from 5 Hz to 20+ kHz based upon an in-room measurement comparison.

Appreciate you responding with quite a lot of details, it was a bit too technical for my understanding though .

 

[DonH56]

Appreciate you responding with quite a lot of details, it was a bit too technical for my understanding though .

Higher noise floor does not usually matter for basic frequency response measurements when you can turn up the volume.
If you want to look at low-level (small, quiet) signals like distortion the higher noise floor may hide the details.

HTH - Don

 

[Guddu]

Higher noise floor does not usually matter for basic frequency response measurements when you can turn up the volume.
If you want to look at low-level (small, quiet) signals like distortion the higher noise floor may hide the details.

HTH - Don

This time it's perfect for me, noted and THANK YOU .

 

[yyzsb]

I have been using the UMIK-1 with REW to work with AccouticSounds.ca (remotely) to create CONVOLUTION files to run on ROON. Today, Mitch Barnett from AccousticSounds.ca, created the first file for me and it is brilliant. It has made my Thiel CS3.7 + all Benchmark gear + small room = incredible sound. The UMIK-1 seems to have done a good job gathering the initial data since the end result is such a tremendous success.

 

[yyzsb]

I am curious about the sound differences between 2 mono AHB2's vs a single AHB2. Do 2 mono's have louder SPL's at the same premp volume setting compared to a single AHB2?

 

[AudioExplorer]

Your assumptions are well thought out but incorrect. The AHB2 power supply is tightly regulated. The transients are not regulated.

If the clip lights on the AHB2 are not turning on, the transients are not being clipped, attenuated, or distorted. The clip lights have a timer that keeps them on for at least 1/4 second so that every clip event is always visible. If the lights are not turning on, the output is following the input exactly. Remember that the AHB2 also has a 200 kHz bandwidth, so it also follows high-frequency transients with precision and with phase accuracy.

What I failed to point out in my prior post is that a poor damping factor can have and audible impact on the frequency response of the amplifier. The Accuphase has a relatively low damping factor (60) and the variations in speaker impedance at low frequencies can have a big impact on the frequency response of the Accuphase amplifier. A damping factor of 60 means that that output impedance of the Accuphase is 8Ohms/60=0.13 Ohms. If your speakers dip to 1 Ohm at low frequencies (not uncommon), this would create a 1 dB error in the frequency response of the Accuphase and this would be accompanied by a significant change in the phase response. Difficult speaker phase angles will have a similar effect on the response.

The published frequency response of the Accuphase is flat but this measurement was made using an ideal resistive load. Speakers are not an ideal load.

Regarding the cone excursion: A non-linear phase response at low frequencies can have a significant impact on the excursion of the speaker cone. This is essentially a low-frequency ringing caused by a non-linear phase response. The cone is overshooting beyond the desired movement. This will cause an emphasis of resonant frequencies and a suppression of other frequencies.

Is the above problem describing low frequency ringing and loss of control of the cone at low frequencies due to low damping factor not a problem also at high frequencies? The AHB2 and many other amps, if I understand correctly, have lower damping factors at higher frequencies. Are these ringing problems not a factor at high frequencies for some reason? Apologies if this was already answered elsewhere.

 

[RichB]

My rear Salon2s are driven by a single AHB2 and that seems fine since the clip lights have not illuminated when I play movies very loud (for my family).

The rears are wired with 30 foot Belden 10 gauge cable from BlueJeans.
I have an extra set of runs available.
What if any are the advantages and disadvantages to combining the cables to create a even lower gauge wire for the rears.
At some point, does really low gauge wire have negative impact?

- Rich

 

[bigguyca]

As I'm sure you realize Revel provides guidance on minimum wire gauge vs. distance. Wires with a loop resistance of over .07 ohm will affect the crossover networks since the wire resistance becomes part of the crossover network. For 10 gauge wire the guidance is a maximum of 34 feet so you are good to go.

Cutting the resistance of your run from about .06 ohm to .03 ohm by using a double cable would slightly increase the damping factor. Revel thinks .07 ohm is OK and they must have thought of damping factor in addition to effects on the crossover.

While it likely doesn't make any difference, I run balanced signal cables to AHB2's that are located close to my speakers around the room. I do that because I can, and because I like to screw around with my system, not because it likely makes any difference. In the past I used the same speaker cable you use to make the runs with perfectly acceptable results. Belden ST00UP is nice twisted wire and not very expensive.

As you do, I've gone back to bi-amping Salon2's with the AHB2's. I've never seen the clipping lights. Even without watching the lights it's clear the system isn't going to come close to clipping looking at the gain structure of the system and the output levels I use. No rocket science required. 0dBFS is a hard limit, talk of transients and the like ignores the reality of the situation.

 

[RichB]

As I'm sure you realize Revel provides guidance on minimum wire gauge vs. distance. Wires with a loop resistance of over .07 ohm will affect the crossover networks since the wire resistance becomes part of the crossover network. For 10 gauge wire the guidance is a maximum of 34 feet so you are good to go.

Cutting the resistance of your run from about .06 ohm to .03 ohm by using a double cable would slightly increase the damping factor. Revel thinks .07 ohm is OK and they must have thought of damping factor in addition to effects on the crossover.

While it likely doesn't make any difference, I run balanced signal cables to AHB2's that are located close to my speakers around the room. I do that because I can, and because I like to screw around with my system, not because it likely makes any difference. In the past I used the same speaker cable you use to make the runs with perfectly acceptable results. Belden ST00UP is nice twisted wire and not very expensive.

As you do, I've gone back to bi-amping Salon2's with the AHB2's. I've never seen the clipping lights. Even without watching the lights it's clear the system isn't going to come close to clipping looking at the gain structure of the system and the output levels I use. No rocket science required. 0dBFS is a hard limit, talk of transients and the like ignores the reality of the situation.

That's a cool thought but moving the amps closer does not work in my living room.
I am not a EE so I don't know if the benefits of reducing resistance at some point become overshadowed but adding capacitance or inductance?

- Rich