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Purifi’s PTT6.5W04-01A woofer group buy

Purifi's PTT6.5W04-01A woofer group buy

You are invited to join a North American group buy of the Purifi’s groundbreaking long-stroke ultra-low-distortion PTT6.5W04-01A woofer, and optionally the matching PTT6.5PR-01A Passive Radiator. Owing to Purifi’s policy requiring orders go to a single address this gets complex, thus the long post.

Announcing the Purifi group buy will close January 31, 2020. At that point we will aggregate our funds and place the order with Purifi. Logistics require we place a single order so we will not be able to accommodate stragglers after the cutoff on the 31st. Sorry about that, I am a procrastinator myself but in this case we are early adopters and a decision is required.


Many of us have taken note of Purifi (Purifi Audio), a new research focused company in Denmark founded and staffed by a distinguished group of Hi-Fi industry heavyweights. The team at Purifi (for the roster see About - PURIFI) has extensive experience in the electronics, loudspeaker, and business sides of Hi-Fi. A following post to this thread will include links to both Purifi’s technology white papers and independent testing and listening reviews.

On the loudspeaker side Purifi’s initial offering is the PTT6.5W04-01A 6.5 inch woofer, a design that reduces distortion by tens of dBs while remaining linear to extreme excursion levels. This promises to allow bass depth with low midrange distortion that is normally the providence of large speakers using 12 and 15 inch woofers in jumbo multi-cubic foot boxes to be had from a ½ cubic foot / 15 liter enclosure 2-way system.

Purifi’s PTT6.5W04-01A is manufactured in Denmark. That is a good news bad news situation. Good news is for decades Denmark and Scandinavia have been a primary source of state of the art loudspeaker drivers and with European manufacturing by this team quality is a given. The downside is price, it does cost to manufacture in Europe, in this case $250 to $350 per driver depending on where one falls on the price breaks. So let us band together and save some dollars.

Purifi conducts all of their business in Danish krone, 1 Danish Krone equaling approximately 0.15 United States Dollar. As of this posting date cost in Danish krone and US dollars are as follows. These prices do not include shipping.

PTT6.5W04-01A Woofer Quantity based pricing table

Min__Max__Unit Price DKK__Unit Price USD

PTT6.5PR-01A Passive Radiator Quantity based pricing table

Min__Max__Unit Price DKK__Unit Price USD

Obviously if four or more of us commit to a pair of woofers each we can access the 8 pieces and above price break saving $150 to $200US on a pair. The exact savings depending on shipping costs, which I intend to pass on at cost. There will be no markup on this effort, I am donating my time to encourage fellow early adopters. That time will primarily be breaking the big shipment from Denmark into individual pairs, re-packing, and shipping onto the group members. Alas, to access the 8 and above price the shipment must be to a single address so a second shipment within N. America is required. I do have a commercial shipping address, which gets us a discount from Purifi’s shipping service DHL and avoids porch pirate worries.

Thanks to Purifi’s web store we can see exact cost to land a group buy to USA. The following tables show those costs as of January 2020 with shipping to Oklahoma. The first table for a group order for four of us to get one pair of PTT6.5W04-01A woofers each, eight drivers total. The second table shows the cost to buy a single pair of drivers as a comparison.

PTT6.5W04-01A Web Costing Group Buy

Item_____Quantity___Unit Price DKK__Unit Price USD___Order Price DKK__Order Price USD

Unit cost group buy landed in USA $274.05
Pair cost group buy landed in USA $548.10

PTT6.5W04-01A Web Costing Individual Buy

Item_____Quantity___Unit Price DKK__Unit Price USD___Order Price DKK__Order Price USD

Unit cost individual’s buy landed in USA $396.00
Pair cost individual’s buy landed in USA $792.00

Bottom line is buying individually a pair cost $792 vs. as a group $548 + Oklahoma to you shipping.

If you want to join this group buy reply to this thread and send me a personal message with contact info. I plan the process to proceed as follows:

1. Recruit enough participants to qualify for quantity 8+ pricing.
2. Close participation in initial group buy.
3. Check costs to buy woofers (and passive radiators if anyone orders those) and shipping costs Denmark to Oklahoma, communicate each individual’s total to participants.
4. Participants pay using PayPal to group buy organizer. Your PayPal receipt will state “Expected delivery time 6 – 8 weeks”, I will try to beat that, most of that will be determined by Purifi’s build time and shipping including clearing USA customs.
5. When all funds arrive order is placed with Purifi. Be aware Purifi states “Note that this product is made-to-order. Expect approximately 4 weeks delivery time.”
6. While Purifi builds and ship woofers group organizer will prepare boxes and packing for shipping leg within North America.
7. When shipment arrives in Oklahoma group organizer will break down into shipments to individual participants, determine cost, and communicate to each participant their North American final leg shipping cost.
8. After participant pays their individual within N. America cost group organizer ships their order.
9. Woofers arrive individual participants’ workshops where they are installed in boxes. Jaws drop, sonic bliss ensues.

Obviously at this level of cost to entry we have a classic case of it is expensive to participate at the cutting edge of technology. I expect the cost to entry will surface individuals with the commitment and means to participate. Given that one should not need to say, yet out of an abundance of caution I will; do not be a wimp! Once you commit do not try and back out! This is not Amazon with free returns, you buy via this group buy and they are yours. If ultimately the sound is not to your liking it is on you to store, scrap, or sell them on. I do not intend to allow that reality to give Purifi a pass on their quality obligation to deliver product as specified to us. What I will not allow is audiophile wimp buyer’s remorse with excuses like “I don’t like how it looks”, “I’ve decided to go a different route and want a refund to help fund that project”, or “upon audition they lack a certain air and “je ne sais quoi” my incredibly refined hearing cannot do without”.

I am excited the Purifi PTT6.5W04-01A is a true breakthrough, something rare in such a mature century old technology. I hope you will join me as one of the first to explore it.
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A collection of links to information about Purifi Audio and their initial products. A good place to start is the Purifi technology and application notes followed by the HiFiCompass Purifi PTT6.5 Woofer Review, and Audiophile Style review by Mitch “Mitchco” Barnett.

Purifi Audio
PTT6.5W04-01A 6.5″ Ultra Low Distortion Long Stroke Driver https://purifi-audio.com/vare/ptt6-5w04-01a/
Purifi technology and application notes https://purifi-audio.com/tech/

Purifi PTT6.5 Woofer Review Purifi Audio PTT6.5W04-01A midwoofer | HiFiCompass

Audiophile Style
Purifi PTT6.5 Woofer and 1ET400A Amplifier Technology Review by Mitch “Mitchco” Barnett. Purifi PTT6.5 Woofer and 1ET400A Amplifier Technology Review - Reviews - Audiophile Style

“Bruno Putzeys...He did it again” thread Bruno Putzeys...He did it again - AudioAficionado.org

diyAudio thread Purifi Audio by Bruno Putzeys and friends.
Founder of XSA-Labs
Joined 2012
Paid Member
You can count me in for a pair of the drivers.
Thanks for organizing this.

From the Purifi website - Here’s the technical specs for reference:
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-- I have question , I've been wanting to build a Synergy, Trynergy or maybe a K402 MEH Horn for long a while ... just haven't found the right one yet.... But my first thought when I read about these was their small package & low frequencies ... does anyone see an advantage in using these in one of the above horns.. or is it not really worth it When 10 or 12 inch bass drivers can do the job?...... My thought was keeping the horns shape as slim and compact as possible without compromising the sound.

Best Regards,
Founder of XSA-Labs
Joined 2012
Paid Member
These have a long linear motion with low distortion. You could use them as woofer drivers in a compact synergy like the Bookshelf point source horn. It will allow smaller waveguides to be used. We were using 8in woofers with the current waveguide, but these would allow smaller ones. But I think their design was primarily to make them high output compact stand mounts.

A Bookshelf Multi-Way Point-Source Horn

You could use them as front loaded horn midbass woofer. That would push an incredible amount of air and get +10dB sensitivity gain.
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January 31, 2020 is the deadline to signup, February 1 I will compute costs and communicate each individual’s total to participants.

This GB is getting great traction, as I write this 8 participants are signed up for 22 drivers and 2 passive radiators.

Some questions and comments….

Jmpsmash asked “Any info on the passive radiator? pros/cons of using PR vs ported for this particular driver.” The Purifi PR’s info is here: PTT6.5PR - PURIFI

As to the pros/cons ported vs passive radiator, with the PTT6.5W04 optimized for such a small (~1/2 cu. ft. 15 liters) vented enclosure, possessing a 30 Hz Fs, and featuring high air moving capacity fitting the port can be tricky. Say we want to tune the box to between 30 to 40 Hz. Looking at the Purifi SPK5 application note they use a 57mm ID port that appears to be about 360mm 14.25 inches long. I write ‘appears to be’ because to fit it in a box with a maximum dimension of 340mm avoiding the woofer and angled shelf brace it has to be bent twice so I am guesstimating the center line dimension. Modeling it I get tuning 37-38 Hz (ok) with port air speeds 47 m/s (ouch) at 200 watts. No wonder in SPK5 they use flairs on both ends of the port. Really cranking it my WAG (Wild A__ Guess) is some port noise will happen. Then again at the 200 watts of input the model shows 108 dB(!) of output at 50 Hz and 100 dB at 30 Hz so a little port noise may go unnoticed. Nevertheless let’s double up use two 5.7 cm ports, same tuning, and 37 Hz F3, with port air speed dropping to ~23 m/s. All good, except now the two port tubes each need to be 766 mm 30 inches long and I need to fit two of them in that 340 x 315 x 240mm box. At this point I start to visualize solutions like a dedicated speaker stand with uprights acting a port tubes or a petite tower with the lower 2/3 housing port tubes.

In contrast use the PTT6.5PR-01A and it’s as easy as build the box and cut holes for the woofer on the front and PR on the back. The PRs also attenuate any midrange noise from inside the box escaping out. Note as is typical the PTT6.5PR has a threaded location for attaching added mass to change tuning frequency. This makes final tuning as easy as listening &/or measuring while adding/removing mass. From the industrial design styling point of view our personal preferences may like what appears to be a second woofer on the box. I find it appears more ‘powerful’ with the second cone. As designer’s let us also check the BOM (Bill of Materials) cost effect. Assuming two of use get PRs on this GB they are $114 each. If I make the vents out of the MDF or plywood I am building the box from or a piece of PVC pipe from the hardware store vent cost is some sweat equity and a few dollars for the MDF/PVC. Personally if it’s a $500 pair of woofers I’m looking for something a bit nicer. I go to Parts Express for that and the Precision Port 2" flared port tube kit is $9.79 each. While on PE a quick check shows non-Purifi brand PRs in the 6 ½ to 10 inch sizes ranging from $11 to $196 each. Interesting to see the cost of a nice flared vent almost the same as entry level PRs.

So two long paragraphs that can be summarized the passive radiator is easier, likely sounds better, and looks better but its 11x the cost of a vent.

Xrk971 asked “Are you guys going to build the reference design (bass reflex with Mundorf AMT) or is anyone considering a more interesting alignment? Perhaps a tapered PMC style TL?” From the verbose answer above I think you can guess I am referencing the SPK5 reference design but going my own way. I lust after the Mundorf AMT but for now will use one of the tweeters from my stock. The TL is an interesting idea. I look forward to seeing, and in some cases I hope hearing, what everyone comes up with. I’m just having too much fun with this.
Founder of XSA-Labs
Joined 2012
Paid Member
That’s an interesting thought SkipPack! It also crossed my mind more than once. :)

This woofer does have a very flat and wide bandwidth that might make it possible to use with a 1st order transient perfect XO. I just got the XO boards made so the timing is great. The most compact box is indeed the PR. The volume of a 57mm x 360mm long vent is about 3.7L, a significant amount of that 15L box, which now needs to be an 18L box.


By comparison here is RS225-8:

I am ok with a TL of its overall volume is of order 24L. That’s about the same as my 10F/RS225 FAST.


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Announcing the Purifi group buy will close January 31, 2020. At that point we will aggregate our funds and place the order with Purifi. Logistics require we place a single order so we will not be able to accommodate stragglers after the cutoff on the 31st. Sorry about that, I am a procrastinator myself but in this case we are early adopters and a decision is required.