November 29, 2013

QRD Quadratic Residue Diffuser Kits now in the Loudspeaker Kit store!

QRD Quadratic Residue Diffuser Kits now in the Loudspeaker Kit store!

These are for those serious about treatment and getting diffusion into your room.

These are 500 Hz diffusers effective up to around 3.5k. They are quite a bit deeper than typical commercial options, meaning they work down lower into the midrange.

When I assembled a dry run with this kit, I was very pleased to discover how easy it was. All the parts slot together nicely.

Find them here:

October 24, 2013

Melbourne Hifi Show 2013

At the recent Hifi show, LSK & Red Spade Audio shared a room with Weston Acoutics.  Earle Weston builds valve pre, integrated and power amps.

HE2 on the right is an efficient speaker designed with these kinds of amps in mind. On the left, you can see the first appearnce of F47. This is a time aligned floorstander designed by SGR Audio, soon to be available as a kit.  

This photo was taken at the closing of the show. The rest of the time there were too many people in the room to take photos, and I was occupied much of the time with questions and talking with our visitors. 

An existing stock M4 on the left next to a new revamped M6 with new OEM drivers and a new crossover.

The rack in our show system:

 M4 boxes on display along with a demonstration video playing:

A nice collection of valves:


Topaz monoblock:

Timber samples:

Cine series prototype (Cine 8.1):

October 1, 2013

LSK kits due for release at the hifi show

At the upcoming hifi show in Melbourne, we have some kits due for release.

Starting from the left ...

M4: an entry level mini monitor.

M5 and M6: value-oriented compact stand mounts.

These are revamped kits with new crossovers and upgraded drivers. 

F47: Our flagship two channel speaker featuring a passive 3 way design with a 4" midrange and 7" midwoofers. In this design we are using high end OEM drivers which we have found to be superior to even the best regarded drivers available to DIYers.

Cine 8.1: Despite being no larger than a mid-sized stand mount, Cine 8.1 hits hard. The secret lies in using pro drivers and optimising senstivity over extension. The driver has such a low moving mass, that we had to use a port just to get to 80 Hz! This means we can achieve 93 dB sensitivity in a compact speaker. A compression driver is loaded into an elliptical aluminium anodized horn, yielding very good dispersion control.

Cine 8.2: This takes it up a notch with 96 dB sensitivity and higher power handling. This speaker is all aobut how much kick we can squeeze into a speaker that is slim enough to find a place in a living room.

HE2: This is designed to be a good all-rounder. It's a passive two way 10" floorstander with a horn loaded compression driver. Bass extension in-room will vary typically from 30 - 50 Hz.

Cine 12: This is the ideal choice for a home theatre speaker in a dedicated room. Features an elliptical oblate spheroidal waveguide with a compression driver, paired with a 12" pro midwoofer. 97 dB sensitivity.

Find us in room 342 at the show.

September 19, 2013

Australian Audio & AV Show 2013


Australian Audio & AV Show 2013 details

InterContinental Melbourne The Rialto

459 Collins St Melbourne 3000

Nearby Stations: Southern Cross

Telephone 03 8627 1400

Date 18-20 Oct

Open Fri 2-8pm Sat 10am-6pm Sun 10am-4pm

Have you booked your ticket yet? The Australian Audio & AV show this year is in Melbourne. I will be there representing LSK The Loudspeaker Kit and Red Spade Audio in a room also shared with Earle Weston of Weston Acoustics - visit us in room 342, which is located on the third level right at the end, opposite the elevators.

You can book tickets HERE
You can see a complete list of exhibitors HERE
For more information about the Australian Audio and AV Show, contact Chester Group.

September 17, 2013

Isn't it about time Australia had a home theatre forum?

I think it's about time!

Of course, we've had StereoNET for almost a decade, but it's focus is primarily two channel.

Now finally we have a home theatre oriented forum - AV life. I think it will be a good thing for Australian audio enthusiasts.

Facebook page

September 4, 2013

Ring Radiator waveguide tower

Shown during testing on an elevated turntable. This is a rear ported design, in which I compare both a Scan Speak and Vifa ring radiator.

The problem with this combination is that these drivers don't want to hold hands. The waveguide is used to lower distortion of the ring radiator and match dispersion whilst also allowing a reasonably simple crossover. Used incorrectly, these drivers very easily sound bright.

September 3, 2013

Cinem8 - a custom active waveguide speaker

Cinem8 is a custom designed active speaker. It is designed as a compact horn speaker that carefully treads the line between large horn speakers and compact conventional designs. It features a compression driver for extreme output and 8" midwoofers which achieve enough extension even in a sealed box to mate with a subwoofer.

Cine8 coming soon

August 7, 2013

Contact Red Spade Audio

We welcome enquiries regarding our consulting services or custom design:
  • room analysis
  • bass integration
  • treatment advice
  • custom designed speakers and subwoofers
Please contact us via the Red Spade Audio website >

July 24, 2013

Free speakers

Clearing out some speakers! Pickup from Melbourne. Send me a message via the contact link (top right column) if interested. 

Eminence Delta 12A 12" driver.


An old pair of 5" bookshelf speakers. Do you need a workshop speaker? 


These are better. Vifa C17 and D19 - quite decent budget drivers. This speaker was called Diva I believe. Wrapped in speaker cloth in decent condition. It sounds quite good. Sealed box with not much bass. 

July 19, 2013

Altec A7 Voice of the Theatre horns measured

How well do those old Altec Voice of the Theatre horns measure? Here I put some Altec A7 horns to the test. The passive crossover was not available for testing.


Compression driver: Altec 908-8A 8 ohm
Horn:  Altec 511B horn
Midbass driver:  Altec 416-8B
Cabinet: Altec A7

It should be noted that these are not the drivers used in the original Altec VOTT A7. The diaphragm on the compression drivers is most likely a replacement different to the original. 

First the A7 cabinet was tested for frequency response. This is a half space measurement in less than ideal conditions. The horn was sitting in front of the garage in which it had been stored. The mic was placed at the mouth.


The response apart from this peak, is +/- 4 dB below 500 Hz. This cabinet was used up to 800 Hz in the original A7. The peak at 200 Hz suggests a poor horn/driver combination. It could be related to the wrong driver being used, or one that has suffered deterioration. This problem may not be present in all of them. 

Bass extends to around 60 Hz. In its intended application, this speaker would have been placed against a wall in a commercial theatre, providing additional low frequency reinforcement.

The compression driver is intended to operate above 800 Hz. However, in the testing a cap was used that I had on hand. Its value was less than ideal and so the extension of this horn/driver combination isn't represented in these measurements. 

Compression driver/horn gated frequency response:

There is a major problem with the horn. The response is reasonable flat at +/- 3 dB below 4.3k but then there is a major dip that is 45 dB deep. This hole exists for almost an entire octave. The top end extends only to 12k. The frequency response is very problemmatic and we can see that it isn't really suitable for music reproduction. This particular combination should be considered a vocal PA system at best. 

This measurement most likely shows a problem with the driver.

The horn was elevated on my directivity turntable and measured from 0 to 90 degrees. 

The HF horn had a serious problem with ringing and required damping. Knocking on the horn caused it to ring like a bell for an extended period. A steel horn requires significant damping but none was used here.

Directivity sonogram:

Horizontal dispersion was measured. From 1k to 6k, constant directivity is achieved ~ 90 degrees. Above this point the pattern starts to narrow before severe beaming occurs above 8k. Below 1k pattern control beams due to the inadequate mouth termination. Since this plot has been normalised, we are simply looking at the dispersion behaviour. The major hole centred around 5.6k is not evident in this measurement as a result - it does not affect the dispersion.

This is a quick snapshot of one particular speaker that might be called the Altec A7 although this would be a little unfair, given the use of the wrong drivers. The results suggest problems with both drivers. This should serve as a warning to anyone considering buying them. These speakers are typically sold without any data to confirm their performance. The measurements don't represent all of them.

60L sealed 18" flat pack


Flat pack for 18" drivers - 60L. Designed for corner placement on an angle. Corners are chamfered off in order to avoid intrusion into the room.

Construction is made simple with pieces fitting into CNC machined trenches.

CNC machined MDF.

June 19, 2013

Curved sub prototype progress

The pieces fit together in a jigsaw-like way. The final version will use a combination of hardwood and MDF. MDF for bracing internals and hardwood for all exposed outer surfaces. This is to make it more suitable for a high gloss painted finish.

June 17, 2013

60L 18" flat pack

This is a section through a 60L sealed box designed for 18" drivers. This one makes allowance for Acoustic Elegance TD18 which has a very large magnet. It will fit most 18" drivers. Designed for corner mounting at an angle, it is ideal as a bass module for Unity horns. 

June 6, 2013

Curved sub - progress

This is the first run with CNC on a challenging project. The final sub will be machined with solid timber. I'm providing a design-only service in this case. This project has demonstrated how communication with the CNC machinist is required - understanding the process and how things work. The design originally led to elements which could not be done, so I had to modify the design in many ways. This probably won't be clear from the photos.

May 31, 2013

Introducing Cine12 - a HT speaker with extreme dynamics and constant directivity

Cine12 is currently in development for an LSK kit.

This is a speaker designed with home cinema in mind. As such, it doesn't need much extension, making a small box with high sensitivity possible. Max SPL is around 120 dB, 95 dB sensitivity, 60 Hz anechoic extension.

May 29, 2013

Room Treatment primer - part 2 - mid and high frequencies

Have you seen my previous article for StereoNET?

Room treatment primer - bass traps >

Now part 2 is out:

Room treatment primer - mid + high frequency treatment >

This is a practical get-started-now guide, for those who want to roll up their sleeves and get started. Not so much for the tech theory junkies.