What can Hifi learn from PA? (Pt.4)

Intro

Thanks for visiting the CODE Acoustics blog! This is the fourth installment of our series ‘What can Hifi learn from PA?’.

Who we are

If this is the first time you’ve come across CODE, we’re a small high-end Hifi company, based in Woking, England. You can see one of our products, the SA1 system below:

And I’m the founder and chief designer, Ceri Thomas:

The series

This blog series started after I visited Glastonbury Festival in 2017. There were many average sounding PA systems, but one or two very good ones. So I wanted to ask the basic question … ‘What can Hifi learn from PA?’.

Part one of the series looked at a couple of the best (IMO) PA sound systems at the festival:

https://code-acoustics.blog/2017/06/30/glasto-2017-what-can-hifi-learn-from-pa-pt1/

Part two took a closer look at horn technology:

https://code-acoustics.blog/2017/07/23/glasto-2017-what-can-hifi-learn-from-pa-pt2/

Part three dived into the difference between Hifi and PA drive unit design:

https://code-acoustics.blog/2018/06/24/what-can-hifi-learn-from-pa-pt-3-its-in-the-drivers-dummy/

The proofs in the pudding

In this fourth installment, I thought it was about time we started answering the question!

To do this we wanted to see if we could create a speaker that merges all we know about making high end Hifi speakers, yet incorporating the very best bit of PA speakers.

Namely high efficiency drive units, which contribute a lot to the great PA sound; excitement, great dynamics, attack, physical presence etc.

The two big questions to answer were:

1. Could we create a true high-end speaker using PA drive units?
2. Would the speaker be accurate enough to be used as a reference studio monitor?

Inspiration

In terms of high output, high quality speakers, the Burmester C500 prototype displayed at Munich 2016 high end show is right up there:

https://www.whathifi.com/news/burmester-introduces-c500-concept-speaker-rotating-woofers

I’ve also been impressed by some of the high end cinema speakers like the JBL 5732 used behind the screen in Dolby Atmos set-ups:

http://www.jblpro.com/www/products/cinema-market/high-power-screen-array/5732#.W0SsaKdKjIU

Finally there is a pro audio speaker company in Japan called Rey Audio. They were originally a start-up offshoot of the world renowned TAD Laboratories.

Interestingly enough, Rey did the sound system install at what is considered to be one of the best nightclubs of all time, the now defunct Space Lab Yellow in Tokyo:

http://daily.redbullmusicacademy.com/2015/01/nightclubbing-yellow

Brief

The system was to be a 3-way, active, DSP speaker (as per our SYSTEM-1 below). If you’d like to understand why, check out the link below:

https://code-acoustics.blog/2017/05/27/why-dont-you-just-make-a-passive-bookshelf-speaker-like-everyone-else/

The main point of difference with the new system is we wanted to use high efficiency (PA) drive units and we weren’t constrained by creating a compact package for the every-man living room.

We also wanted to limit the use of DSP to keep the speaker as ‘pure’ as possible and that took us down the route of reflex bass loading*.

*We could have gone fully horn loaded, but to keep the dimensions sensible, the horns would have been a sub optimal design (in terms of sound quality).

Finally, SYSTEM-2 (below) taught us the importance of heavily radiused edges to give a nice crisp stereo image. So this would also be carried over.

https://code-acoustics.blog/2017/08/01/code-acoustics-system-2-how-to-create-an-award-winning-speaker-in-3-months/

BESS

So after months of research, design, assembly and testing we can now introduce our Big Evolving Sound System or BESS for short:

And here’s a quick video. Please note, this is just recorded on a mobile phone, so the sound quality is not really representative!

Specs

Drivers:

• Treble: 1 x BMS 4524 1″ Compression driver on an 18 Sound XT1086 constant coverage horn flare.
• Mid: 2 x 18 Sound 6NMB420 6″ drivers.
• Bass: 2 x Volt RV3813 15″ mid/bass drivers.

Crossover:

• 300Hz 4th order L-R, 2.5kHz 4th order L-R

DSP:

• Hypex DLCP 6 channel 24bit / 192kHz

Amplifiers:

• 6 x Hypex NC500 n-core modules 700 watts in 4 Ohms @ 1%THD
• 6 x SMPS1200A700 power supplies

Cabinet Loading:

• Treble is sealed / horn loaded, 80 deg / 60 deg constant coverage horn flare.
• Midrange drivers are run in parallel in their own enclosures, 4.8l (each) reflex loaded with 130Hz port tuning.
• Bass drivers are run in parallel, in their own enclosures, 113l (each) reflex loaded with 42Hz port tuning.

Design notes

The main aspect of this speaker build was to use PA drive units, and evaluating whether this could produce a truly high end speaker. Let’s take a look at these drive units first:

Tweeter

For the treble we chose a compression driver from the well renowned German based BMS. Within their line-up they have a lower power 1″ exit 1″ diaphragm unit, aimed for high end audio and studio use; the 4524.

http://www.bmsspeakers.com/index.php?id=bms_4524

Coincidentally I noticed the high end audio brand Avantgarde Audio use this compression driver in their well reviewed Zero (Also a 3-way active DSP speaker):

The plot below shows the drivers performance:

You can see the break-up node at 19kHz, and the gentle drop in output due to the Constant Directivity (CD) horn. Other than that, the driver looks well behaved.

DSP EQ was applied to notch out the resonant spike and bring up the high frequencies to give a flat frequency response.

We chose the 18 Sound XT1086 constant coverage horn flare to mate with the BMS unit:

http://www.eighteensound.com/Products/Articles/Detail/catid/4063/eid/3353/xt1086

This is a beautiful horn with wide dispersion and crucially, no sharp edges.

 Apologies for the slightly blurred graphic, but what it shows is the horn flare is very consistent and well controlled down to 1.6kHz. We chose a 2.5kHz crossover on the compression driver with a 4th order L-R filter, which means you’re only hearing the horn in it’s region of correct operation.

Midrange

The midrange unit we chose is the 6″ 18 Sound 6NMB420. I’ve used 18 sound drive units on a couple of previous project and the technology they’re putting into the drive units and build quality are superb.

http://www.18sound.it/Products/Articles/Detail/catid/4050/eid/3407/6nmb420

Highlights are a high sensitivity, flat frequency response (very impressive for an undamped cone) and massive power handling (200 watts!).

BESS would utilise a pair of the 6NMB420’s run in parallel to further increase efficiency, power handling and radiating area for increased ‘attack’.

We covered this drive unit extensively in part 3 of this series, so If you’d like to find out more here is the link:

https://code-acoustics.blog/2018/06/24/what-can-hifi-learn-from-pa-pt-3-its-in-the-drivers-dummy/

Woofer

The woofer was a no-brainer and the first thing we decided upon. It’s the Volt RV3813:

https://voltloudspeakers.co.uk/loudspeakers/rv3813-15/

I’ve used this driver previously and been mightily impressed, but I’ll avoid describing the sound until the end of the blog.

The highlights are a super-light cone (67g), high efficiency, dual suspension and fantastic heat management (due to it’s ‘radial’ chassis’).

The only negative for me is an x-max of only 4.5mm, which would preclude it from being used as a woofer in most PA systems. The limited x-max is part of the reason the drive unit is so efficient – you can’t beat the laws of physics! My answer to the limited x-max is simple – use more boxes*!

*I realise this is a luxury most PA speaker designers don’t have!

Amplifiers

The thing with using highly efficient drivers is they will brutally expose any flaws in the electronics up-stream. So we decided not to take any chances and go for Hypex’s top of the range n-core module, the NC500 (right) mated to the mighty SMPS1200A700 (left) power supply:

The distortion figures are ridiculous, staying below 0.001% Total Harmonic Distortion (THD) over the vast majority of it’s power range.

Construction

The speaker boxes were constructed of 24mm and 18mm thick baltic birch ply, and heavily braced. PVA wood glue was applied liberally on all joints to aid cabinet damping.

Then the external edges were heavily radiused to eliminate edge diffraction:

The Sound

It’s hard to know where to start without just throwing out lots of superlatives! The sound-stage is incredibly spacious and well defined, detail retrieval is excellent and the dynamics!

One of my favourite test tracks is ‘Private Investigations’ from Dire Straits Alchemy. Lots of live recordings sound awful, but not this one.

On a bad sound system, the clapping sounds like frying bacon, and you miss lots of the sound picked up from the crowd, but not with BESS.

The track starts off fairly softly, slowly building up to a crescendo as more musical elements are added. It’s also a highly dynamic track with drum beats and bass guitar shattering the silence.

The kick

Most dance music is geared around the ‘kick’. This is the chest pumping, punchy bass with the most impactful element around 90Hz. If you get this right, people will dance.

Although BESS isn’t strictly a PA speaker, I felt it vital we get this right. The combination of the efficient Volt bass driver, massively powerful and well controlled Hypex amplifiers, and large vented cabinets means all the building blocks are in place.

Bass is indeed punchy, tight and well defined. One thing that is noticeable above other systems is how textured the bass is and how well separated different bass elements are, as opposed to one mushy general bass sound.

Conclusion

The question posed by this build was ‘Can you build a high end Hifi speaker using PA drive units?’ and ‘Can a speaker built with PA drive units be accurate enough to use as a studio monitor?’.

I think BESS shows the answer to both questions is a resounded yes! BESS has exceeded all expectations and is probably my favourite CODE product to date.

This isn’t the end of the story as we already have a number of upgrades planned for BESS. Stay tuned …

As ever, thanks for reading, and if you have any comments or suggestions, please just send us an email:

info@code-acoustics.com

Ceri Thomas
Founder & Chief Designer
CODE Acoustics