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Purifi-6661
Copyright 2022 © Troels Gravesen

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"Hello, I want to start building a loudspeaker. Can you point to a small floor-stander with deep dynamic bass, smooth midrange and silky treble. My budget is around 1000 EUR". I have these mails regularly. Well, don't we all want this? You have to realise you just do not get all this for a minimum budget. There is no such thing. You want it small and good - but you have to pay quite a bit more. Quite a lot more, but if you really want all this, then this speaker may be the answer. I shall not make any claims of high-WAF, although I think the cabinets are quite nice. One person's blessing is another's anathema. It can obviously be made in high-gloss piano lacquer or gorgeous veneers, etc. Choice is yours.

The construction of the Purifi-6R certainly called for some more from this company and with the arrival of the PTT6.5W08-NFA-01 drivers and not least the PTT6.5M08-NFA-01 midrange driver, the tools for making a significant larger speaker was at hand.
The PTT6.5W08-NFA-01 "only" has some Xmax of +/-5.9 mm compared to the +/- 10 mm of the X model. Having a twin-bass setup, this is more than enough. In addition to this a little higher impedance making it ideal for a double-driver set-up for bass. The W also features a little higher sensitivity compared to the X model. With a combined cone area of 266 cm^2 we have something similar to a 9" bass driver and we can tune the overall system sensitivity to around 90 dB. I like that! The M model, the midrange driver, is not just a "W" with a shorter voice coil, as is sometimes seen, when manufacturers have to make a midrange unit - and save some money. The M has a different basket requiring a larger mounting hole. I has different rubber surround and it has lost some weight, 8 grams, (Mms reduction) and possibly other things I don't know of. Point is, this driver is designed to be a midrange driver.
 
I started by setting up the bass drivers in some 34 litre test cabinets and the midrange driver in 16 liter test cabinets (what I had at hand) and tilted the top for proper time-alignment of the midrange and tweeter. I know some people don't like stepped baffles - and well, some people don't like sloped baffles either. Well, we have to arrange for some kind of time-alignment to allow shallow - and better sounding - crossovers.
For tweeter there was no doubt in my mind that I would use the SBAcoustics TW29BN-B-08 tweeter. This is a phenomenal tweeter and I urge you to erase any preconception of "metal domes" and what bad metal domes may sound like. One guy asked if a Be dome would give him more "sparkle" in the treble range. What he was asking for was probably more distortion or just simply more level. You don't get that from the SBA Be domes.  
Next I constructed my favourite crossover from a range of simulations, and sat down for a listen. Actually I had bring quite a few more LPs to my workshop, because this mockup just invited for more and more. You really can't explain what is happening when all of a sudden you hear more details in the midrange. When resolution goes up and when distortion goes down, you kind of expect a wow-effect. Not so, because what you all of a sudden realise is that you have started to become more relaxed. Listening has become easier, and you don't know it until you hear what lack of colouration means. I used a small value Amber-Z copper foil capacitor for the Be dome and an overall very shallow roll-off and it made a smooth and seamless integration with the midrange at a fairly high point of crossover. For sure I wasn't going to change this in the final crossover. In addition to this it measures very well.

I had some ideas for the cabinet design and hearing my mockup, I realised I had to go all in when it came to making a heavy, rock-solid, non-resonant cabinet to allow as little cabinet colouration as possible. These drivers deserves it. 20 mm Baltic birch will be laminated with 10 mm high-density fiber board, HDF, glued together with elastic vinyl glue.

Due to the twin bass drivers, the 2nd order crossover between bass and mid and the LCR circuit flattening the upper impedance peak, we can keep a modest 4 Ohms impedance in the bass region. No big deal for most amps. When bi-amping, the amp running the mid-tweeter will see an impedance of minimum 9 Ohms! Total yummy for a tube amp. This is what I'm doing.
There will be two basic versions, one fully passive and one having a Hypex FA251 running the bass drivers. The Hypex version obviously has all the advantages of room adaption due to the DSP and the one I'll be making. Should the Hypex programming be an obstacle to you, and you live in an EU country, ship them to me and I'll do the programming and tests - and I'll charge you 100 EUR + shipping forth and back. But only EU citizens!
I used my Hypex UcD amp for bi-amping and it all worked very well. And BTW, looking at the people behind the Purifi drivers, I should think they approve of the Hypex solution, although Hypex and Purifi are two things. My guess is that Purifi some day may come up with a plateamp.

 

Latest vinyl additions. Picking up Christmas presents at the local vinyl pusher, I came across the Wolfgang Haffner LP and took my chances. I wasn't disappointed and with Lars Danielsen and Ulf Wakenius on the team, I shouldn't be. Very good recording made in Gothenburg, Sweden, and cut in Berlin at Emil Berliner Studio. Visit their website - quite an interesting place with everything from advanced digital to 2" analog tape. I don't think the Purifis left anything on that recording I should have heard and with a wide range of acoustic instruments, a good recording testing your midrange and tweeter tunings.
Recently I went to hear Vestbo Trio at the local music hall and picked up a couple of LPs. I don't recall when I last time bought a 10" LP, but the FLOWMOTION is such a thing. Recorded in a rather small room with a small audience and my goodness, the dryness of sound and dynamics! A phenomenal recording - and some really good music too! I cherish this local Aarhus band.
I can't say the Purifi drivers sound like anything else I have used before. It was tempting to say the noise floor had lowered, but that's nonsense. Noise comes from the amps in front of any speaker, but it is clear the lack of smear pays off and leaves as clean a sound as the front-end and source material allows. And by clean I don't mean sterile - whatever that means. We add all sorts of superlatives to sound because describing sound is futile. If the music is "sterile", then the Purifis will tell you. If it is lush, it will tell you. If it is dynamic, it will certainly tell you. You can put anything in front of them - and they'll tell you what you have done. Even mp3 (Dec 8th) files sound better on these speakers!
Image to the right is not an LP cover - rather my cappuccino for the listening session - and I had a lot of these.

 

Basics:
3-driver speaker.
Dimensions: 25 x 38 x 100 cm, WxDxH. Height 105-107 cm with feet.
System sensitivity: 90 dB/2.8V/1 meter.
Impedance: 4-8 Ohms.
Power requirement: 50+ watts/channel.
Power handling: A lot!
Please also read: http://www.troelsgravesen.dk/power-handling.htm, and remember any burned driver is a misused driver.

Useful links (Please read before writing!):
http://www.troelsgravesen.dk/tips.htm
http://www.troelsgravesen.dk/crossovers.htm
http://www.troelsgravesen.dk/LCR-RC.htm
http://www.troelsgravesen.dk/Inverted-Polarity.htm

FAQ (Please read before writing!):
You cannot change cabinet front panel dimensions and drivers' placement without needing a new crossover - and I cannot help.
You cannot use any other drivers with the crossover specified.
http://www.troelsgravesen.dk/crossovers.htm
http://www.troelsgravesen.dk/choices.htm

 


DRIVERS
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Download specs here:  TW29BN-B-8  PTT6.5W08-NFA-01  PTT6.5M08-NFA-01

Please do not ask for alternative tweeters! There will only be this one. Nor 4 Ohms versions.
And you cannot use the PTT6.5X-04 or PTT6.5X-08 for this construction.


CROSSOVER
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CABINET
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Click image to view full scale.
Chamfering of the bass section is optional.
Chamfering of the mid-tweeter section, look here. Can be done by hand.
And again, please go through all of the tips page. Saves me a lot of mails.

 


Some angle details here. Sorry about the decimals, but if I leave them out, some number-nitpickers will tell me immediately.
Mind you, cabinet dimensions can vary, let's say +/- 2 mm and it won't matter.
Click image to view large.


Cabinet for the passive version.
No, the couple of extra litres derived from the Hypex box, does not change anything.
Cut the supplied straight tube for port to 200 mm length. Comes in 235 mm length.


Workshop pics
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Workshop total mockup to hear if all of this had a chance. It certainly did!
I thought I'd over the years heard most - from el cheapos to diamond drivers. It turned out I hadn't.
The bass from these two 6" drivers is phenomenal, deep and dynamic.
The midrange: I probably haven't heard better. Utterly transparent, dynamic, yet non-aggressive.
The Be dome - well, I knew that one - but silky smooth. OK, I used an Amber-Z in my mockup!


I wanted to be well prepared for this. Better measure twice - and cut once!
Starting out with the mid-tweeter cabinet tilt of 6 deg.
If you use 20 mm BB, cut a groove down to the last two layers of veneer, and they will bend beatifully.


Setting up a test framework to see if the 42o cuts would join nicely. They did.

 


Upper joints and the groove for bending the sides.


This is how you cut the sides.

 
Cutting the side panels and gluing the bottom panel and panel between bass and mid-tweeter.


Making the braces with cut-out for Hypex enclosure.


Left: My guide for flush mounting the Hypex module. Optional. Right: Gluing the Hypex housing.

 


Left: Brace for midrange cabinet.
Right: To figure out the upper front panel design I made a mockup from residues. I think this is what I want.

 

 
Testing driver routings for the first time.
Make sure to chamfer driver holes to prevent any acoustic resistance!
Please read here: http://www.troelsgravesen.dk/chamfer.htm

 


All felt in place. I left the rear panel behind the midrange driver free for the crossover.


Before final lacquer and feet, I wanted to do some more crossover fine-tuning.
Here with the fully passive set-up and the Hypex UcD running the bass drivers.
There were quite some changes from the first crossover for my mockup to the final cabinets.
Midrange depth and transparency was improved from the narrow chamfered midrange cabinets.


Left: Preparing for the base frame. Quite wide to give the speaker a solid foundation. Adjustable feet here.
Right: First lacquer coat.


Mounting the base panel onto the cabinets made me realise they really didn't look good. Looks like clown feet.
So, I cut up the base structure and made them fit cabinet dimensions:


Looks better, right? These cabs are heavy and don't need a wide base support.


I placed the mid and tweeter crossover in the upper compartment.
Fill mid-tweeter compartment with 200 grams of wool.

 


Hypex modules in place and connected to binding posts.



Hypex FUSION FA251

Setting up the FA251, please follow instruction here: http://www.troelsgravesen.dk/FUSION_FA251.htm

Download program here (zip file): Purifi-6661.zip
Insert file folder in FilterData folder in My Documents as created when installing HFD software.


Above the three preset profiles. I'm using preset 2 in my room with a little boost at 40 Hz.
Presets must be tried to find out what suits your room, speaker placement - and taste.


MEASUREMENTS
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A few comments on MEASUREMENTS before you start interpreting the readings below.
First of all, if we think measurements will tell us how a speaker sounds, we're wrong. The perception of sound is way too subjective to be reflected in any measurements we can perform. A loudspeaker system is meant to give us a satisfying idea of an acoustic event and for some people a pair of 5 USD ear-plugs are enough, others spend 200 kUSD on a truly full-range pair of speakers - and the latter may not be happier than the former.
Measurements may give us an idea of tonal balance of a system, i.e. too much or too little energy in certain areas, although dispersion characteristics play a vital role here. A two-way 7+1 and a three-way 7+4+1 may display similar horizontal dispersion, yet sound very different. Measurements may tell us about bass extension if far-field measurements are merged with near-field measurements. In addition to this, ports may contribute to bass extension. Most of we diy'ers do not have access to an anechoic room for full-range measurements from 20-20000 Hz.  
What cannot be seen is what kind of bass performance we get in a given room. Bass performance is highly dependent on in-room placement of your speaker and the same speaker can be boomy in one place and lean in another. Actual SPL level at 1 meter distance and 2.8V input is useful for en estimate of system sensitivity and combined with the impedance profile may give an idea of how powerful an amplifier is needed to drive the speaker to adequate levels.
What measurements do not tell is the very sound of the speaker unless displaying serious linear distortion. The level of transparency, the ability to resolve micro-details, the "speed" of the bass, etc., cannot be derived from these data. Distortion measurements rarely tell much unless seriously bad, and most modern drivers display low distortion within their specified operating range. 
Many people put way too much into these graphs and my comments here are only meant as warning against over-interpretation. There are more to good sound than what can be extracted from a few graphs. Every graph needs interpretation in terms of what it means sonically and how it impacts our choice of mating drivers, cabinet and crossover design.
What measurements certainly do not tell is the sonic signature of the speaker, because speaker cones made from polypropylene, aluminum, Kevlar, paper, glass fiber, carbon fiber, magnesium, ceramics or even diamonds all have their way of adding spices to the stew. Nor do measurements tell what impact the quality of the crossover components add to the sound, from state of the art components to the cheapest of coils and caps, they all measure the same if values are correct, yet sound very different.


What interested me the most was the frequency response of the new midrange drivers. Here on a 80 x 120 cm baffle.
Sensitivity very much around 90 dB/1m/2.8V.

 


Above the four PTT6.5W-08-01A drivers on a 20 x 120 cm baffle. Smooth response up to 4 kHz.
With two bass drivers in parallel we will reach some 93 dB sensitivity. From this we have to deduct bafflestep loss and add assumed room-gain. The latter is always a guess, but we may well end up with system sensitivity around 90 dB.

 


Above one of the PTT6.5W drivers on a 80 cm (red) and 25 cm (green) baffle width.

 


Impedance in free air of all six units. Green and red are the midrange drivers.

 


Above comparing the PTT6.5W and PTT6.5M driver from a 25 cm baffle width. Red = midrange driver.
Here we see the result of some 8 grams reduced Mms compared to the W driver. Extended frequency response up to 8 kHz.

 


Final system impedance for fully passive version.

 


Here the result of the passive filter for the two bass drivers, w/wo low-pass filter.

 

 


SPEAKER-KIT
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All kit and component prices may be subject to change and are always to be confirmed by Jantzen Audio Denmark.
Kits can be bought with/without drivers and Hypex module.

There will 6 options, passive and Hypex versions -
with either Alumen-Z or Amber-Z for tweeter, C1.


 

Download Complete Kit Sale Presentations:

All technical questions to troels.gravesen@hotmail.com

All questions regarding purchase of kits, please mail Jantzen Audio at contact@jantzen-audio.com


CROSSOVER-LAYOUT
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Please read these files:

http://www.troelsgravesen.dk/tips.htm#Glue

http://www.troelsgravesen.dk/tips.htm#CONSTRUCTION_OF_CROSSOVERS

http://www.troelsgravesen.dk/LCR-RC.htm

 


Tweeter layout


Disregard the loop on C1 capacitor lead. During development I like to keep long leads on these seriously expensive caps. You never know.

 

 


Midrange layout.


Click images to view large.
L2 can be upright or horizontal, no big deal.

 

 

 


Bass layout for fully passive version. C-Coil for L4 giving extremely low DCR.


My prototype bass crossovers. Just follow the drawing.

The passive bass crossover does not provide the same room adaption options as the Hypex version, but there are some possibilities in tuning of the LCR circuit. R8 determines the impact and default is 5 Ohms (2 x 10 Ohms in parallel). If speakers are placed in corners, I suggest starting here with R8 = 5 Ohms.
R8 = 15 ohms adds some weight to the lower bass if placed further away from corners. Out on the floor with very little room-gain, you may disconnect R8 and hear what happens. The difference is some 2 dB in level, but the price to pay for not using the LCR circuit is lower impedance, 2.7 Ohms, so make sure your amp can handle this. Minimum impedance with the LCR circuit in place is 3.5 Ohms, basically a 4 Ohms speaker.

 

Speaker wiring



Wiring Hypex version

 

 

 



Wiring fully passive version.