Help with port size. JV60 Upgrade.

[insnamehere]

So a friend was looking at getting a DIY speaker kit the other day so that turned my attention to my own speaker kit i bought a few years back (Jaycar JV60 Kit). Now there was nothing wrong with them, but i decided maybe i could do some upgrading. First thoughts turned to replacing crossovers with quality parts, then remake the boxes to more exacting standards (my first effort wasn't exactly of great build quality).

Now this brings me to my dilemma, the original kit required inserting the adjustable ports into the box then glueing the adjustment piece to the back, so now their never coming out. which is fine they were ugly anyways. My problem now is i will need to use a different dia. PVC pipe for my new ports (either 65 or 80dia. OD).

Now i thought it should be easy enough to calculate the tuning of the original ports and just adjust to suit my new dia. However, no calculation i do comes any where near the 197mm length the original design used. On top of that the original ports, due to their adjust-ability, are made up of 2 different diameters, how does that work?

So can anyone help me calculate the correct port dia and length for my speakers?

System specifics;
Vifa P17WJ-00-08 woofers (x2 one Xovered to 200Hz and below only)
Cabinet dimensions: 863x227x253 (HxWxD internally)
Calculated volume: 49.56L (minus internal brace)
Original ports: 66mm dia. Jaycar adjustable 197mm in length.
I think from memory it said the boxes are tuned for 35Hz.

Thanks in advance for any help.

[dabbler]

I'm not sure if youve already started, but have you thought about rebuilding the cabinets as transmission lines?

Red Spade Audio: DIY Transmission Line Speakers

[insnamehere]

Nope, have not yet started. Ordered new crossover parts and cable, thats all so far. Have not even got the MDF yet so even that can be changed at this point (aiming for 25mm depending on affordability). I did consider and even looked at that exact page, i'm not convinced however of that design with 2 drivers in the one transmission space, it just doesnt look right to me. happy to give it a go if other would recommend it though.

[MellowFellow]

I've built the Red Spade TLs and they sound fine, although different to the original JV60. There's 3 main differences I notice with mine compared to standard JV60's

1 - the bass is quite different. JV60s have quite punchy bass while mine have a more relaxed bass. I couldn't say which speaker has 'deeper' bass but the delivery suits different styles of music.
2 - my speakers are able to 'image'.
3 - generally, the TLs are more relaxed. This is related in part to the bass, but there's more to it. If the JV60s were the speakers you built when young for party music, the TLs are the ones you relax with after work.

[paulspencer]

Funny you mention those ports. I never used them until recently, hacked one of them in half to make two ports!

Based on 49.5L and two ports 66mm dia x 197mm long, the tuning is 41 Hz. A quick WinISD model suggests that should work fine.

[insnamehere]

Thanks for the input guys.

Mellow, I do like my tight punchy bass.

Spencer, are you able to tell me if a port made up say 100mm of 66dia. and 97mm of 70dia. will still equal 41Hz? I have dug up the jaycar booklet thing, and it quotes a cabinet corner freq. of 35Hz, should this be what the port is tuned to?

Here's another side question, If I'm planning to build a subwoofer to add to the system should I consider a sealed enclosure for the jv60's? Am I right to assume porting is only for extended bass response?

Thanks again guys.