December 7, 2014

HE3 - an elegent valve friendly speaker

Here's a dilemma. How do you create a speakerthat meets all these goals:
  • easy for a valve amplifier to drive (benign impedance load and high sensitivity)
  • a slim and elegant design (tall and slender rather than wide and chunky)
  • pleasing tonal balance with full bass and no emphasised regions to get a high sensitivity rating
  • strong bass extension
Based on the questions I'm often asked, it's much harder than people realise. Often people don't realise the implications of each decision. If you want a slender box that isn't very big, with good bass extension, generally it's going to mean it won't achieve high sensitivity.Something has to give. 


HE3 is my answer. First we start with a conventional dome tweeter with fairly high sensitivity and an exceptional midbass driver - Acoustic Elegance TD6M. Here we achieve 93 dB sensitivity which is quite reasonable. Many speakers claiming higher don't actually deliver it. This is a spec that is often inflated excessively. Even individual drivers rated at 99 dB in reality may only have 93 dB of useful sensitivity.

Now the key in this design is that the bass is active, with a side firing 10" woofer. Here we dispense with high sensitivity and use brute force with a built in amp that also features DSP. The added bonus is that we can use EQ in the room.

Prototype coming soon.

Sonus Faber Cremona Auditor active crossover conversion

 The Sonus Faber Cremona Auditor is a fairly well known speaker using good quality drivers in a beautiful box. A client brought in a pair that he was not happy with, requesting an active crossover design. This is a speaker that measures quite well in terms of dispersion but it's not a speaker that handles higher levels very well. At moderately loud levels it sounds strained, most likely due to the use of a first order crossover with a ring radiator tweeter which is not ideally suited for a situation such as this which places heavy demands.

Raw response with the tweeter response raised for clarity: In reality they overlap each other.

No obvious breakup peaks are evident here.

The raw response of the woofer (green) shows a rise in the region from 700 Hz - 2.5k. This is eliminated with EQ (blue) and then a low pass filter is added.

 The same approach is used with the tweeter, first applying EQ and then a high pass filter.

Summed crossover.

This isn't shown here but I use a shelving filter to adjust the treble balance. This allows for a lot of adjustment later without messing up the crossover. 

This is just a quick snapshot and not the entire battery of measurements that were taken and analysed. 

Even a brief listen reveals an obvious improvement in the sound. The speaker is now entirely free of problems with a forward and strained sound.

December 6, 2014

HS215 - a horn sub with dual 15" drivers

Introducing HS-215. This is a custom job for a client and it's designed to sit behind a couch in place of a shelving unit. Designed as a flat pack where panels lock together such that large clamps can be avoided.

November 26, 2014

Speakers coming up at Red Spade Audio

I recently posted some speaker concepts I'm considering. 

The plan is now to develop all of them!

A: HE3 in slightly modified form with a single 10" active woofer
B: AV8 is already in my range
C: HE2 is already in my range
D + E: coming soon
F: coming soon

Out of the surround speaker options:

The two dipole surrounds are shelved, the third is AV8 already in my range and the one on the right side is currently in progress - it's a Coax 8" driver.

Articles coming up ...

Two article series coming up:

Acoustic measurement

There will soon be a series of articles coming together on the topic of measurement. A particular focus will be on helping people get started.

Active vs passive crossovers

A holistic look at passive vs active considering many aspects that are often forgotten.

Any ideas on articles you'd like to see?

November 24, 2014

PSE-144 - about using other drivers

A question we get asked often from those inquiring about PSE-144 is this:

'Can I use my own drivers?'

Often it's put this way:

'What is the price of PSE-144 if I supply my own drivers?'

This post is my answer to that question that keeps coming up.

About the drivers used

The drivers included in the kit are not available for separate purchase. They are included in the product as they perform better than the alternatives that people are likely to have in mind. They are purchased in large quantities and attract a better price than a single customer could purchase off the shelf. It's more than likely that if you are considering DIY favourites like B&C, BMS, JBL that we have actually tested the driver you are considering or something similar.


CD: CD144-08K

The high frequency compression driver matches a 44mm diaphragm to a 25mm exit. The kapton diaphragm achieves an ideal combination of damping and high frequency extension. This driver is carefully matched to the horn.

The vast majority of compression drivers fail to meet out standards and requirements. Setting aside specific requirements to match our horn, many of them cause listener fatigue and lack treble extension and detail. This speaker is designed to perform well with good quality solid state or valve amplification. There is no requirement to tame the sound with a mellow sounding amplifier.


Midrange: M425-08P

The mounting holes on this driver are machined into the horn baffles. For this reason alone, it's a problem to use other drivers as they are not likely to fit. The horn also has a mounting ring that precisely fits the driver.

The small matter of the crossover

Assuming that you are actually able to find drivers that will fit, an even bigger problem emerges - the crossover. Using your own drivers means that you are paying for a set of parts and developing your own crossover. Most DIY enthusiasts intending to "whip up their own crossover" have no idea about the size of the challenge they are taking on. It's an advanced design challenge and it's unlikely that most who are considering taking it on will actually appreciate all that they need to know in order to do it right. 

When you buy PSE-144, you aren't getting a series of parts. You are getting a well resolved product with years of development behind it. We understand the horn itself is a highly desirable one and many want to take this on as a DIY project but we don't recommend changing the drivers.


"Can you redesign the crossover for my drivers?"

If you have drivers that have the potential to work in this horn, we may consider this on a case by case basis. This would firstly involve a fee to test your drivers to ensure they have a chance of working. If they pass initial testing there would be a design fee to develop a crossover for your specific drivers. You would need to be ready to pay significantly more than the normal price, without promise of better performance.


"Can I buy the horn without the drivers?"

Yes, but you will need more than just the horn shell. PSE-144 includes a custom machined CD mounting plate, without which you will not be able to mount the tweeter. The plate is machined to keep the throat smooth. It also includes fixing points for the custom machined aluminium stand. 

The horn itself is a work of art, nothing like other horn shells available. It has a smooth durable gel coat finish on all sides - including the rear. Where the mids mount to the horn, it is filled with foam that provides mechanical damping. Where the CD plate mounts to the throat, cap screws fix it into metal inserts that have been embedded into the horn. 

The price without drivers is not much less than buying complete.

November 9, 2014

Scan Speak Revelator Tower

This loudspeaker is a custom design that features Scan Speak drivers. The tweeter is loaded into a waveguide which allows a lower crossover point.