Please help me spec an amplifier, or two.

[Lucid_AV]

If you're driving both sets of speakers as you say you are then yes, you're sharing the power from the amp. Two sets of speakers connected to the A and B terminals will reduce the impedance that the amp sees. Two pairs of 8 Ohm speakers creates a 4 Ohm load. This is because there's only one set of output transistors and not two sets. Any speakers eventually connect back to the single set.

It's a quirk of the maths that amps often quote higher wattage figures for a lower Ohm connection, but if I can use a car analogy, what's missing is the fact that you're emptying the gas tank twice as fast and the oil and air temps are doubled too.

The Harman amp specs don't quote more power into 4 Ohms. They quote higher distortion. You can read that as reduced headroom. In other words, you'll hit the red line sooner at 4 Ohms than at 8. 'Red line' is appropriate because what we're really interested in doing is keeping the transistors cool. The harder they work then the hotter they get. Once they get too hot then like an engine with insufficient cooling something will break. This is how you blow up an amp.

Regarding sound level, a bigger amp won't magically transform the volume level. Our hearing isn't that sensitive to amplifier wattage or sound 'volume'.
To get something that most people would agree is twice as loud requires a 10X increase in wattage. What you'll buy with a more powerful amp is a small increase in volume but also more or a lot more headroom.

Another way (a better way) to increase the sound level is to buy speakers with higher sensitivity. However, both your Yamaha and JBL speakers are 90+dB, so unless you changed to some large horn-loaded PA speakers with a sensitivity of 100+dB then that's not a route you're likely to take. That 10dB increase from 90 to 100dB would produce double the perceived volume from the same wattage though. Food for thought.

Yes, you could do with a more powerful amp. If anything, you should think about either two amps or one commercial amp that is rated down to 2 Ohm. A good Crown amp would be a natural fit.

You might also want to have a look into the condition of the ferrofluid if used in the tweeters and maybe the bass drivers too. We're about 40 years on from when manufacturers started to use it in domestic gear to help with voice coil cooling. Mid-'80s to mid-'90s speakers are gettingto a point where the fluid is getting thick and restricting voice coil movement. That's not good for the driver.

[Deranged Rover]

If you're not trying to run at ear-bleeding levels or regularity experiencing audible distortion, then the setup you have will be absolutely fine. Both speakers are robust designs and the Harman Kardon amp is a decent, sturdy thing.

Unless you're particularly looking for more volume or bass, I'd stick with what you have.

[Lucid_AV]

You've added some new info which changes things. It turns out now that you're not running both sets of speakers together, so the amp isn't sharing out power.

Also, you're not running flat out. That means you're getting nowhere near the speaker's max RMS figures.

Amp power is like the top speed of your car. The volume dial is the gas pedal.

IME HK used to be be very conservative with amp power ratings. 0.003%THD or whatever it was at 70W into 8 Ohms is a tiny figure, even by Hi-Fi amp standards. There's a lot more power in reserve, and with the volume dial at 10 or 12-o'clock you're nowhere close to 70W output. For this reason I wouldn’t bother with that '70s 80W amp. You'd be swapping out a known good amp for something no more powerful but possibly a lot less reliable.

The Fostex looks good. If you want more power then that has to be a contender. Right now though you're not close to maxing out the HK

[Deranged Rover]

nuyorican said:

That's reassuring to hear. No, well, I do like it loud... but they're about six feet maximum from my listening position so never crazy loud. I don't think the volume pot has ever been past 12 o clock. Usually at 10, Whatever that means. Not much probably as it depends on how hot the signal it's being fed is I guess. Talking to myself now.

I'll carry on as normal but keep my eyes peeled for suitable amps with more power. I love vintage HiFi anyway. The best amp I ever had for sound quality was a 70's Sansui. God knows what the wattage was but it was one of those with a radio (integrated)?

An amplifier with a tuner built in is called a receiver, and there were some monsters in the 1970s!

See here: https://classicreceivers.com/

[TonyRPH]

nuyorican said:

<snip>

Here is my current setup:

Amplifier - Harman Kardon PM650 VXI. 70w per channel.

https://hifi-wiki.com/index.php/Harman/kardon_PM65...

Current delivery (the ability for the amplifier to provide sustained power output and not just peaks) is just as important (if not more important) as power output.

The HK gear generally has good current delivery (this is facilitated by a good power supply design with plenty of available current).

nuyorican said:

Speaker pair one - Yamaha NS10 Studio. 60w Program / 120w peak. (what does this mean in the real world? Guessing this is where I need a beefier amp to handle those peaks...)

https://www.manualslib.com/manual/340763/Yamaha-Ns...

The peak power is the absolute maximum power that the speaker can handle in short bursts - in other words, you generally don't want to be running your 60w speaker at anything more than 60watts constantly. The '60w Program' will be referring to the RMS rating. RMS is constant power.

nuyorican said:

Speaker pair two - JBL 4311 Control Monitors. 75w per channel.

https://www.hifiengine.com/manual_library/jbl/4311...

Thoughts? Thanks

As per above - these are rated at 75* watts RMS, or 150W peak (the peak power rating is usually (but not always!) double the RMS power rating.

• the JBL manual states "75 watts continuous program" which will be referring to RMS power.

The sound level (SPL - sound pressure level) is determined by speaker efficiency - the ability to turn that power into audible sound - and this is usually presented as x dB at x meter(s) for 1 watt input in the speaker specifications.

The JBLs are rated at 81dB at 10 feet with 1 watt input. (another manual I found states - 91 dB, 1 W, 1 m (3.3 ft) - )

The Yamaha speakers are specified as 90dB at 1 meter with 1 watt input.

These measurements will be on a logarithmic scale.

The JBLs are marginally more efficient than the Yamaha's - you wouldn't hear a 1dB difference in loudness.

With the amount of power you have on hand, unless you are playing this system in a concert hall, it will be more than loud enough without causing any damage to the speakers - and if in an average room (12ft x 12ft) you are likely to cause damage to your hearing before damaging the speakers or amp.

In other words - you don't need anything more powerful if using this in a medium (average) sized room.

[Panamax]

nuyorican said:

Amplifier - Harman Kardon PM650 VXI. 70w per channel.

At this point that seems a pretty ancient amplifier.

I'd be tempted to look for something more modern with more "grunt". Headline wattage figures are all very entertaining but, like a car, once you've got "enough power" the real question becomes how it's delivered.