Power amp delemma

[rgpit]

My Harbeth C7es3 loudspeaker's rated efficiency is 86db 1W @ 1meter and rated at handling 150W program. I'm currently using a Benchmark AHB2 power amp which I really like. I've been thinking about adding a second AHB2 and running the two as mono blocks. I don't want to waste money if there isn't going to be an improvement in the speaker's performance. I'd really like to hear opinions from some folks on this forum on what to expect. Thanks.

 

[direstraitsfan98]

Short answer. No, adding a second amp to monoblock the system will not improve your sound. If you hear any difference it’s placebo. Harbeths start falling apart playing musical content above 95dB SPL. I remember trying to play the track Tom Sawyer at 90dB average with 95dB peaks and my Harbeth 30.2 40th Anniversary Editions sounded distorted. They literally cannot handle more power.

I was powering mine with a Pass Labs XA30.5, capable of well over 200W in class AB bias. I also had them hooked up to a very high gain class AB integrated amplifier (Kinki Studio EX-M1, 350WPC into 4ohms) and ran into the same issues.

 

[mjwin]

With a sensitivity of 86dB/W plus the Benchmark, I would have thought you'd get 100dB+ SPL out of them. Though whatever "150W program" means is anyone's guess. So the Harbeths might indeed begin to distort earlier. Can you find any measurements of this anywhere?

But you didn't say what music you're listening to or what specific improvement you're seeking in your current system. That Benchmark amp is second to none in terms of of its spec. Switching to bridged mode would give you twice the voltage swing, but that would only ever effect & benefit the very loudest peaks of the music, and make absolutely no difference elsewhere. So is the problem only when you play music loud, or is there some other aspect of the sound that you're not happy with?

And, dsf98, I'd agree: Harbeths + Heavy Rock. Hmmm... Probably not the best combo

As for that Rush album (moving Pictures?) Seemed as if Tom Sawyer was specially designed to give your audio system a good workout. I think it was my last year at school ('81) & everyone was playing it. Everywhere, and LOUD! "Hey, it sounds so clean, crank it up..." Then, of course came that ominous crushing noise, or whatever sound it was our cheap speakers & 20W amps made back then when driven hard into clipping... I'm not much into heavy rock, but Rush stand out, and that album particularly at the time because (iirc) it had very little distortion baked it, so it didn't sound "loud" in the conventional sense. Packed with energy though and Geddy's vocals occupy a little carved out space amongst the enormity of it all. This recalled all from memory, btw, as I haven't herd it in years. Don't think I have the album even; maybe the single somewhere...

 

[30 Ounce]

Considering that would be 460 watts into your Harbeth's 6 ohm load from your now 130 watts, I think it would be overkill. I think you should have more power than you need and never run your amp into clipping but once you get past 100 watts with mini monitors you probably need to look elsewhere for improvement. A sub woofer can relieve your Harbeth's from the power hungry bass and add a little more dynamic range.

 

[rgpit]

With a sensitivity of 86dB/W plus the Benchmark, I would have thought you'd get 100dB+ SPL out of them. Though whatever "150W program" means is anyone's guess. So the Harbeths might indeed begin to distort earlier. Can you find any measurements of this anywhere?

But you didn't say what music you're listening to or what specific improvement you're seeking in your current system. That Benchmark amp is second to none in terms of of its spec. Switching to bridged mode would give you twice the voltage swing, but that would only ever effect & benefit the very loudest peaks of the music, and make absolutely no difference elsewhere. So is the problem only when you play music loud, or is there some other aspect of the sound that you're not happy with?

And, dsf98, I'd agree: Harbeths + Heavy Rock. Hmmm... Probably not the best combo

As for that Rush album (moving Pictures?) Seemed as if Tom Sawyer was specially designed to give your audio system a good workout. I think it was my last year at school ('81) & everyone was playing it. Everywhere, and LOUD! "Hey, it sounds so clean, crank it up..." Then, of course came that ominous crushing noise, or whatever sound it was our cheap speakers & 20W amps made back then when driven hard into clipping... I'm not much into heavy rock, but Rush stand out, and that album particularly at the time because (iirc) it had very little distortion baked it, so it didn't sound "loud" in the conventional sense. Packed with energy though and Geddy's vocals occupy a little carved out space amongst the enormity of it all. This recalled all from memory, btw, as I haven't herd it in years. Don't think I have the album even; maybe the single somewhere...

I listen to a lot of different music, but mainly jazz, classical, and classic rock. I have only seen my AHB2 clip once, very briefly during a very loud passage. I was wondering if there are any sonic benefits in using two AHB2's other than the maximum loudness level. If it helps, I like to listen to live jazz at levels you'd hear during a live performance.

 

[wje]

I believe when they reference "Program Power" with respect to watts, it's another way of referencing RMS.

 

[rgpit]

Considering that would be 460 watts into your Harbeth's 6 ohm load from your now 130 watts, I think it would be overkill. I think you should have more power than you need and never run your amp into clipping but once you get past 100 watts with mini monitors you probably need to look elsewhere for improvement. A sub woofer can relieve your Harbeth's from the power hungry bass and add a little more dynamic range.

I wouldn't consider the Harbeth C7es3 as a mini monitor and I already have them paired with two subs I built using SB Acoustics SW26DAC76-8 and their matching passive radiators. I have the Harbeths running full range and the subs are crossed over using a minidsp 2X4HD at 48db/oct around 55Hz.

 

[MediumRare]

Here's a hopefully science-y answer, based on this review: https://www.audiosciencereview.com/...-and-measurements-of-benchmark-ahb2-amp.7628/

The Benchmark has similar THD and IMD at 20 W as it does at 150 W, so unless you're clipping regularly (over 200 W) there is no benefit, even an inaudible one.

So for better sound, IMO, you might look at your source or, as suggested above, adding a sub or two.

 

[mjwin]

I listen to a lot of different music, but mainly jazz, classical, and classic rock. I have only seen my AHB2 clip once, very briefly during a very loud passage. I was wondering if there are any sonic benefits in using two AHB2's other than the maximum loudness level. If it helps, I like to listen to live jazz at levels you'd hear during a live performance.

Aside from the max power available, I can't think of any mechanism which would result in improved performance when the amps are run in bridged mode. If anything, measured performance might be slightly worse due to the increased output impedance (& lower damping factor) of the amps when run effectively in series. Not that I would worry about this aspect, as I'm sure it would be inaudible!

I hadn't realized you used subs here. They will make a huge difference when playing loud as they'll handle a lot of the heavy power duty. It's worth experimenting with the crossover frequency though, but it's a juggling act to achieve a smooth transition. Maybe try slightly higher. Most folks go for around 80Hz. Sub positioning is also an issue. Potentially another juggling act; this time between sonics and domestic harmony!

 

[wje]

I hadn't realized you used subs here. They will make a huge difference when playing loud as they'll handle a lot of the heavy power duty. It's worth experimenting with the crossover frequency though, but it's a juggling act to achieve a smooth transition. Maybe try slightly higher. Most folks go for around 80Hz. Sub positioning is also an issue. Potentially another juggling act; this time between sonics and domestic harmony!

With my JBL 530 speakers, I'm running them at their full range. Also, I have a MiniDSP implemented, as the OP does, but have my pair of subs receiving a frequency of 70 Hz and below. There's a little bass overlap between the subs and the main speakers, but I'm fine with that. I've tried higher frequencies on the MiniDSP for the subwoofers (e.g. 90Hz and 80Hz), but realized for me, the bass was a bit too potent, so 70Hz is where it is for the moment. Though, that could change at any time depending if I want to play around with the settings again.

 

[LTig]

I hadn't realized you used subs here. They will make a huge difference when playing loud as they'll handle a lot of the heavy power duty.

Not in @rgpit's case. He runs the sats full range so they still must handle the same amount of power as without subs. To get the full performance lift of a 2.1 setup the sats must be high pass filtered. Only then the setup can play louder and cleaner.