I am working on building a couple pair of 2 way bookshelf speakers based on the Purifi 6.5 https://www.madisoundspeakerstore.c...rifi-audio-ptt6.5x04-nfa-01-6.5-woofer-4-ohm/ and a Satori beryllium tweeter with waveguide https://www.madisoundspeakerstore.c...bnwg-4-beryllium-dome-tweeter-with-waveguide/. I am basing it on a Jantzen audio discontinued kit http://www.troelsgravesen.dk/Purifi-6R.htm. I am planning initially anyway to biamp them with a Minidsp DDRC 24. Probably going to put a cap with the tweeter as protection since it is expensive. Madisound recommended a 50 microfarad as I recall. At any rate the port in the TG design is hard to find in the USA so went looking around and found a Chinese sight that had 65mm by 180mm which is close to the 68mm by 160 that TG specifies. The TG/Jantzen has a larger flare at the opening as well. I am wondering if the pictured ports will provide close to the response of the Jantzen? Thanks for any insight.
Attachments
https://www.parts-express.com/Port-Tube-2-1-2-ID-x-8-1-2-L-Flared-260-478?quantity=1
This looks extremely close. The 2 1/2" number is an average size estimation because the tube tapers in diameter down the length like the Jantzen does. Converting the numbers it appears to have almost identical OD at the flange end. It tapers down to a little smaller diameter at the other end, but it is also longer, so it likely will be the same diameter as the jantzen when it is cut down to the same length.
If it is slightly different the tune isn't likely to change much in a negative way.. To the point it would be probably hard to tell which one is "correct" even if you were able to directly compare to the spec port.
This looks extremely close. The 2 1/2" number is an average size estimation because the tube tapers in diameter down the length like the Jantzen does. Converting the numbers it appears to have almost identical OD at the flange end. It tapers down to a little smaller diameter at the other end, but it is also longer, so it likely will be the same diameter as the jantzen when it is cut down to the same length.
If it is slightly different the tune isn't likely to change much in a negative way.. To the point it would be probably hard to tell which one is "correct" even if you were able to directly compare to the spec port.
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I am not a fan of those cheap commercial ports. A piece of PVC pipe works netter IMO.
And it is fairly straight forward changed vent size: http://p10hifi.net/FAL/downloads/Changing-Port-Size.pdf
dave
And it is fairly straight forward changed vent size: http://p10hifi.net/FAL/downloads/Changing-Port-Size.pdf
dave
You ideally want a well designed flare section at each end of a port to promote laminar flow as much as possible and delay the onset of flow-separation (turbulence aka chuffing). A good to have feature is adjustable length to permit tuning. PVC pipe allows the latter by trimming, but I don't see how you get a flare on both ends easily...
I've seen/used a commercial design that was tapered (not useful in itself), allowing the internal end to be flared and still fit through the mounting hole. Better would be a two-section design with detachable inner flare allowing trimming.
I've seen/used a commercial design that was tapered (not useful in itself), allowing the internal end to be flared and still fit through the mounting hole. Better would be a two-section design with detachable inner flare allowing trimming.
Considering the expense of your drivers I would absolutely not cut costs or construction efforts for the port. You may even consider a passive radiator: no chuffing, no port resonances, eventually less compression.
Here are my suggestions:
If you want to read more, here is my thread about ports:
https://www.diyaudio.com/community/threads/investigating-port-resonance-absorbers.388264/
(Scroll down to newer posts regarding flanges, chuffing etc.)
Here are my suggestions:
- you need big rounded flanges on exterior and interior end. Sharp interior edge will create lots of chuffing and resulting compression (less bass output). Bigger flange is better. Rounded flanges will slightly shorten the effective port length (or increase the effective cross section), so you need to consider eventual port length corrections.
- you might consider an even bigger diameter, given the huge xmax of the purify woofer (but of course also keep in mind longitudinal port resonance!). Once the port air speed gets high you loose output, increase distorsion and (worst of all) get chuffing noise.
If you want to read more, here is my thread about ports:
https://www.diyaudio.com/community/threads/investigating-port-resonance-absorbers.388264/
(Scroll down to newer posts regarding flanges, chuffing etc.)
Idealy the port has a “baffle" at both ends. Make them thick and use a router. Makes for a very pretty port.
But i use slots now. And often break the “rules”.
dave