Speakers on Headphone Amplifiers

What's the difference between a headphone amplifier and a speaker amplifier? Mostly just power delivery and expected impedance.

But the lines are blurring..

Headphones on speaker amps is a thing. Low impedance headphones like LCD-R (2 ohms) and low efficiency headphones like HE-6 are commonly used with speaker amps.


Similarly, we can consider speakers on headphone amps. For the past week, I've been running a set of speakers off a Schiit Vali 2. The sound is a delight -- I'm hearing subtleties between tubes that were never seemed so clear on headphones.

AFAIK, commercial speakers don't cover this use case. So I'll showcase my simple DIY build.


Simple DIY Build

The key components are the speaker drivers: I used 16 ohm drivers which are at the lower end of most headphone amp impedance specs. Directly connecting lower impedance drivers might draw too much current, triggering amp protection circuitry or worse. I've found only a handful of options of speaker drivers at 16 ohms, and only a single one at 32 ohms.

Because I wanted a very simple desktop build, I went for small full-range drivers - FaitalPRO 3FE22. These have a decent frequency response down to 150Hz.



To bolster the bass below 150Hz, I examined a few 3D-printable ported enclosures. There's a technically excellent design for the 3FE22. I recommend viewing the linked videos if you're interested in the logic.



Having built and trialled this design and a few others, I ultimately preferred a similar and less technical backhorn design. The backhorn is effective at bringing up the lower-bass and sub-bass response. I'm very happy using these without a sub-woofer.



Most of the discussion on speaker cabinet design focusses on material properties - leading to a preference for heavy wood. I decided to try and get similar acoustic dampening from META-material design, meaning the structure of the material matters greatly (edit: this is the loose, but increasingly common use of 'meta-material' that makes Armaegis wince). Rather than dampening with mass (ie a 1-inch thick shell of plastic), my enclosures dampen via weakly connected concentric spheres. It's a design impossible to produce through traditional means, but which can be implemented by tuning infill settings.



How well does this setup it work?

It works surprisingly well! The speakers are good enough to bring out subtleties in the source and respond to tube rolling. Frequency response seems even other than the low frequency rolloff.

Despite worries about the limited power output of a headphone amp, there's enough for a desktop or small room. From the Vali 2, there is 20db to 14db headroom above comfortable listening volume at my desk. I've been leaving the Vali 2 pot at maximum and using the headroom to experiment with DSP.



I definitely prefer these to my powered class-D studio monitors. The payoff is using a known quality audio setup with a single change of transducers - a much more controlled and incremental step than adding pre-amps, power amps etc.

 

Yes, I have done this many times. I actually think that most headphone amps pay more attention to a lower noise floor so it would not be surprising that you are hearing details and nuances not previously appreciated. I made a set of speaker cables with a 4-pin XLR and have tried various amps with speakers over time. I think Marv might use his headphone amp to drive speakers - and am sure there are others too ..dB

 

Has your experience given any insights about what pairings work well?

 

It mostly has to do with sensitivity, inefficient speakers just need more power but good amps play well.

 

I still wince a bit at using the term metamaterials in this fashion, but I applaud the innovation. You may find this port/venting interesting from the Pioneer RM-05/RM-07. It has the reflex port with a dingle dangle hanging off of it.

Some info about that here:
https://www.soundonsound.com/reviews/pioneer-rm-07

 

Thanks! Great article,which showcases just how complex the issues around speaker design can get.

I didn't want to dwell on the speaker design aspect because it's a rabbithole to a deep and branching warren. The reason DIY became important for this project was because of impedance matching : you can get 16 and 32 ohm drivers, but apparently not pre-made 16 and 32 ohm speakers. With a Vali 2, output impedance is specced at 5.8ohms. A low output impedance amp is more likely to work well with standard 8 ohm speakers.

With regard to metamaterials, I agree. But I watched and read a bunch of comparisons of speaker materials, and there's a typical assumption that plastic means solid plastic like injection molded items. The potential to damp by structure is missed and has great potential with a small build like this one.

 

From the perspective of tube amps, headphone amps and speaker amps seem to be pretty much the same. The difference is the impedance of the output transformer.

 

I agree!

Here are two (headphone) amps I built during lock down. For near-field listening, I think they work fine driving sensibly efficient speakers.


PSE6SN7 (~ 720 mWpc) driving Altec 755As in Silbatone cabinets. The 755A is nominally 4 ohm but present a resistive load.


Same amp driving Snell Type JIIIs - least efficient speakers in my stash


JLH Class A headphone amp (~ 500 mWpc) from eBay > Altec 755A/Silbatone

The Snell JIII is rated 90dB/1W/1M but has a relatively complex crossover network and the woofer is 4 ohms. It's not such an easy load compared to the 755A which I guesstimate is between 92-94dB if the old specs are translated to modern terms.

In the real world, we listen to less than 1W per channel on the average. It's the dynamic peaks from complex musical scoring that demand power if the speakers lack efficiency. With efficient speakers, it's the first watt that counts!

 

I used a Stax amp with output transformers for years. Sounded better than it looked, even with inefficient speakers.

Your full-range speaker is a great opportunity to challenge this. Nelson Pass has a great article on current drive for full rangers, with passive eq.

https://www.passdiy.com/project/amp...e-amplifiers-and-sensitive-full-range-drivers

I'm using amps with a >200R Zout into 8 ohm drivers and am really pleased with the results after some eq.

Only if they're built right. Lots of tube headphone amps still use speaker OPTs with 4/8 ohm secondaries.

 

Maybe a better way to pose the question..

When does a headphone amp outperform a cheap amp designed for speakers? Like the ones built into powered studio monitors.

 

I absolutely love the look of that little DIY speaker! What a cool project.

 

Since @purrin2022 is otherwise engaged / banned.... here's @purrin2013 on his MJ1 to speaker config:

"I initially had the Mjolnir has a pre-amp feeding the Crest CA-2. After I confirmed with Jason that the Mjolnir wouldn't melt with a 8+ ohm load (the Fostex drivers), I wanted to give it a shot. Naturally, it sounds much better straight out of the Molnir than the Crest - less crap in the way. Plenty of juice and sufficient gain considering the speakers are 93-94db efficient."



"The Mjolnir sounds way better than the Crest. The CA-2 maybe has a hair bit more apparent bass extension and control, but we are splitting hairs - talking about 2-3%. (For reference, the EC Super 7 with the BK-16 kit had wooly bass. Too much so for my tastes.) The CA-2 output is rather dead and lifeless, even though it's got gobs of power, compared to the Mjolnir. It's all about microdynamics and plankton for me which keeps things involving. I did think the CA-2 sounded pretty good - that is until I got the crazy idea to run the speakers from the headphone jacks of the Mjolnir. The Mjolnir hasn't blown up yet and it doesn't seem too hot either."

 

The Ragnarok 1 is basically a more powerful and more firmware controlled (mostly keeping it from it going into thermal meltdown) Mjolnir 1. I think Mjolnir would have about 2 watts at 8 ohms at given spec.

I would not doubt the magic. It is that circolotron thing about the bass extension and control. The Rag has this in droves and as a speaker amp is stupendous. It almost is a better speaker amp than a headphone amp as far as performance goes. As a headphone amp sounds open and airy and super detailed. Highest gain (because it has 3 levels of gain) has more authority and weight.

 

We are typically referring to the headphone amplifiers that are essentially mini power amplifiers. Not all headphone amps will be able to run speakers but most amps that have beefy power supplies and decent heatsinking would fall into this category.

The experience will be highly variable depending on the efficiency of the speakers ( and impedance curve ) . I would not advocate buying a headphone amp with the intent of powering speakers but if you have a headphone amp that you absolutely love , adapting this experience to speakers makes common sense.

To do this there are 2 options.
1. use speakers that need flea watts to produce an enjoyable sound
2. add a neutral current buffer ( such as the Pass F4 ) which enables your headphone amp to drive anything, including maggies ( this is what I now do - my Liquid Glass drives the F4 which makes the Maggies sing and I get the same sound experience from the glass with my speakers that I get from it driving my headphones )

..dB

 

I intended my speakers for the Mjolnir 2, which AFAIK has the same output stage as the Mjolnir 1. It's been a surprise that they work with plenty of headroom as desktop speakers on the Vali 2.

Interpolation the MJ spec 8 Watts @ 32 Ohms and your guesstimate of 2 Watts @ 8 Ohms, maybe I'll get 4 Watts @ 16 Ohms.

 

Any views on whether this is a "don't eat those apples, although they sure look delicous" goading, "don't do stuff that might void your warranty" MOT advice, or a serious recommendation from his own experience?

 

Those look super sweet for a desktop rig. Any measurements with them inside that back horn design? how improved do you think the bass below 200hz gets?

 

I don't have a measurement mic here, so have been testing bass response using this test track. Also some bass heavy tracks like Lorde / Royals.

With the enclosure, I don't notice much rolloff until around 50hz. So ok on bass, weak on sub-bass like a pair of open backed headphones. I had a powered sub-woofer attached with an earlier set of drivers, but it doesn't seem necessary for the FaitalPros.

Also remember I'm running these off a Vali 2, which isn't going to showcase the bass so well. I'll have a better sense when testing them with other amps.

 

Sorry, my calculations were way of. I went the wrong way. (I am surprised nobody called me out on it.)

MJ1/MJ2 would be 32 watts @ 8 ohms.

It is also microprocessor controlled to keep it from thermal runaway/meltdown.

 

Trying the same speakers on the MJ2:

* 1pm on low gain is plenty for a listening room. Turning up the volume in high gain, speakers sound overloaded way before the MJ2 works up a sweat.

* Switching from desktop/near field the bass has become lacking and a powered subwoofer running off the pre-amp outputs has become essential. Vocals maybe improved a little. Leonard Cohen sounds hauntingly real.

* While decent, I don't think this setup has the same magical synergy as the Vali 2 / desktop speaker arrangement.