Speaker Design Study Using New Purifi 8" Woofer

Speaker Design Study Using New Purifi 8" Woofer

DIY Plans No.1736

Purifi is a high end driver manufacture located in Denmark. Purifi is in the process of releasing their new 8" woofer, model PTT8.0X04-NAB-02. Purifi reached out to me and asked me if I would be interested in developing new DIY speaker plans for this new driver. This plan would be intended for two channel music playback in a home setting. This speaker project will be No.1736. Once introduced, these plans will include all the assembly and detail drawings required to construct the complete speaker, including the crossover schematic and bill of materials.

I haven't received the drivers yet, but Purifi did send me the 3D CAD model to start on some preliminary design work. Shown below is the 3D CAD model sent to me from Purifi.

Erin's Audio Corner did a detailed test on the PTT8.0X04-NAB-02 which can be found here

I've come up with a preliminary speaker design that has the following design goals. Please feel free to comment or provide recommendations on my own overall objectives. 

  • Easy to construct using 18mm plywood 
  • Uses standard off-the-shelf components 
  • Large stand mount in 2-way configuration 
  • Exponential horn (Faital STH100)
  • 1" compression driver (model undetermined) 
  • Passive radiators (SB Acoustics SB15SFCR-00)

Solidworks Renders 

 

I decided not to rebate the drivers in the name of simplicity. I will likely provide additional detail in the drawings if one wants to add the rebates. I also avoided adding any bevels since it's not clear at this point how much the speaker would benefit from this added complexity. This area is still undetermined.  

Passive Radiators 

I've had good results with the SB Acoustics passive radiators. The racetrack shape is useful for fitting them where needed. The high mechanical compliance allows bass frequencies to emanate unhindered while filtering midbass and midrange frequencies much better than a regular port. 

The box size and tuning frequency is shown below. It's yet to be seen if the chosen passive radiators will achieve the desired tuning frequency. I've found that this is usually a case of trial and error since there are no software simulation options available for passive radiators. 

Compression Drivers 

There are a variety of compression drivers that would be suitable including the Faital HF108R and RCF ND-350. I've chosen a compression driver over AMT or regular dome due to the low distortion capability. There simply are no other substitutes if you need high output capability and low distortion. Even a dome tweeter mounted into a waveguide or horn will not perform as well as a good compression driver/horn combination in terms of openness and transparency. The Faital Horn STH100 horn features an exponential horn flare geometry which is rare to see. Nearly all plastic horn lenses are constant directivity type for use in pro-sound. The STH100 achieves constant directivity performance however as can be seen below. 

Cabinet Construction 

Due to the Russian war Baltic birch plywood is not longer available. For us here in Canada the only alternative is Chinese birch plywood and I suspect it is the same for other countries. The maximum material thickness that I've been able to source is 18mm thick. Normally I would use 24mm thick on an enclosure of this size. So to compensate I've added internal bracing in all directions.

 

The speaker stands are a variation of speaker stands No.1114 which can be found here

Purifi Application Notes 

In terms of crossover design I've been following Purifi's own technical notes on the subject which can be found at the link below. 

I will be following these articles to ensure I'm getting the most from these excellent drivers. 

Purifi's own blog has some interesting studies on distortion. 

 Stay tuned on further updates on this project. 

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8 comments

Hi Joseph

I have been interested reading your site and blog, Kudos on some beautiful work!

This project looks interesting. I plan to build a pair of speakers soon. I do plan to use purifi woofers for their low distortion and ability to deliver deeper bass in smaller box. Small overall size is a design consideration. This set of drivers and horn in a slim and short tower would fit my needs. ( Say 10” wide and 36” tall) How difficult is it to rework the crossover design to account for a narrower baffle?

Peter Thomson

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Eric Jones

Hey, this is Eric and I ran across josephcrowe.com a few minutes ago.

Looks great… but now what?

By that I mean, when someone like me finds your website – either through Search or just bouncing around – what happens next? Do you get a lot of leads from your site, or at least enough to make you happy?

Honestly, most business websites fall a bit short when it comes to generating paying customers. Studies show that 70% of a site’s visitors disappear and are gone forever after just a moment.

Here’s an idea…

How about making it really EASY for every visitor who shows up to get a personal phone call you as soon as they hit your site…

You can –

Talk With Web Visitor is a software widget that’s works on your site, ready to capture any visitor’s Name, Email address and Phone Number. It signals you the moment they let you know they’re interested – so that you can talk to that lead while they’re literally looking over your site.

CLICK HERE https://boostleadgeneration.com to try out a Live Demo with Talk With Web Visitor now to see exactly how it works.

You’ll be amazed – the difference between contacting someone within 5 minutes versus a half-hour or more later could increase your results 100-fold.

It gets even better… once you’ve captured their phone number, with our new SMS Text With Lead feature, you can automatically start a text (SMS) conversation.

That way, even if you don’t close a deal right away, you can follow up with text messages for new offers, content links, even just “how you doing?” notes to build a relationship.

Pretty sweet – AND effective.

CLICK HERE https://boostleadgeneration.com to discover what Talk With Web Visitor can do for your business.

You could be converting up to 100X more leads today!

Eric
PS: Talk With Web Visitor offers a FREE 14 days trial – and it even includes International Long Distance Calling.
You have customers waiting to talk with you right now… don’t keep them waiting.
CLICK HERE https://boostleadgeneration.com to try Talk With Web Visitor now.

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Eric Jones

@Tom: Constant Directivity horns have been all the fashion in recent years buy you need to understand that you can’t have a horn that provides excellent loading of the driver AND excellent CD – you have to pick your compromise. There are some horn experts who believe that in a domestic setting horn loading the driver is more important / beneficial than CD. I believe Bjorn Kolberg subscribes to this school of thought and I think I’m right in saying that Troy does too – perhaps he will comment . . .

Ian

Quote “I’ve chosen a compression driver over AMT or regular dome due to the low distortion capability. There simply are no other substitutes if you need high output capability and low distortion.”
Comparing to most AMTs and domes yes but, Mr Stavros from Aries Cerat would i guess, disagree, using RAAL ribbons. His Aurora model uses RAAL in small wooden horn/waveguide.
Its just that combining $400 purifi with $1k raal per side and 3 passive radiators would bring these monitors to sky high price…
On a side not, such configuration, namely: open baffle bass, high sensitivity mids and ribbon/planar highs, seems to be #1 currently among high end models. Not only Aries, but Danny from GR-research has similar concept, but with servo OB subs and dynamic driver line array mids. Tomasz from Lampizat0r also, but has gone from OB bass to aperiodic cabinet for bass with just single 18inch driver. For mids , cheap Dayton 8inch, 99dB and dipole RAAL on top. Thats why his speakers are $6k and Aurora go for $100k ;)

Pablo

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