Newbie questions on Troels G. designs


2011-11-12 10:30 pm
Hello all!

Thinking of making a sub 30 litre floorstander from Troels Gravensen's great site in a couple of months but have a few questions before deciding on what to make.

My idea was to make something cheaper and replace the drivers and crossover as funds allow while keeping the enclosure. So I was thinking of starting with something like the Vifa PL18WO+XT25TG and work my way up to the MAYA (CA18RNX+T25C003) and then to the CNO-T25 or even the mk.II or TJL-T25, using the TJL2W enclosure (960x190x280mm). Do you think this is possible?

So, the questions regarding his designs:

1. Can I use the TJL2W box and use the CNO-T25 drivers and crossover as long as I have the correct internal volume, or will I need a new box?
Or should I just stick to the CNO box (950x200x280) and use the Vifa speakers? How much difference is there in 1cm?

2. Can I use a floor/bottom ported system instead of a rear port and how can I do this?

3. Can I place the tweeter off centered as in the TJL?

4. What should be most important to upgrade first, woofer or tweeter?

5. Where should I place better premium capacitors and where can I use cheaper ones to reduce cost?

Other options to start of with would be CA18RLY+22TAF-G or Paul Carmody's Amiga using the dimensions of the box above, or if you know of a design using CA18RNX with a cheaper tweeter than the T25 on the MAYA, like a Vifa DX or XT.
1. Yes as long as volume, tuning and baffle geometry is close. 1cm is uncritical

2. Just move the port, the fundamental output of the port will be the same. However, the level of unwanted harmonics may be affected by moving the port.

3. Yes

4. Partial upgrades are tricky as drivers and crossovers are integrated systems. In some few cases one tweeter can be substituted with an other with no or minor tweeks of the crossover

5. Woofer section is less critical than tweeter section. I would rather spend my money on the cheapest plastic fim caps from Parts Express /Europe Audio and buy the best drivers I can afford, then spending a fortune on esoteric caps (promptly dons my asbestos dress to survive the flame war, smile)


2011-11-12 10:30 pm
Hi DrBoar, thank you for your reply.

I guess I will try building the MAYA and later replace the woofer first as it's cheaper to get a CNO-T25, and later maybe the tweeter to the CNO-mkII with a T29CF001, and probably live happily ever after as the last speaker I'll need in my life as my room can't afford any bigger speakers... The crossover will need a new build, so will have to build the enclosures with service in mind.

I can't leave the speakers far from the back wall and I dislike the look of a front port. Do you think I can try something like the down firing port on the Kudos C2 or ProAc D18?

My estimate is around €600 plus boxes. How much better will it be from my Rega RS3?
I think that this is a good idea. I would make sure that your cabinets are built exactly to the final and most costly design.

I did something similar (but the other way round). I had a Scanspeak Revelator Two way design, which I changed from a BR cabinet to a transmission line. I was left with a nice BR cabinet that I had spent a lot of time building. I found another BR design using cheap drivers that would fit the baffle holes ($300 inc crosover, I think (all components were less than the price of one SS Revelator driver)). These speakers live in my holiday house. Listening to them now. Nice :)


2010-11-22 11:24 pm
About the caps, one way you could do is buy a standard electrolytic with (goal -1) uF and then add a 1uF MKP cap in parallel, much much cheaper than buying fancy caps =)

But yes as DrBoar said the limitations are mainly in the drivers so if you want performance spend your money there.


2009-02-28 9:20 pm
I miss the point in moving from the CNO-T25 to the TJL-T25, they are on the same league. Having that in mind, choose your desired end point and move backward because the Maya has the same cabinet as the CNO and the PL18XT has the same cabinet as the TJL.

I'm sure Troels design a crossover using the actual enclosure and even 1 cm of difference in width plus offsetting/centering the tweeter does make a difference. After all they are all optimized non-textbook crossovers, I wouldn't risk to downgrade the performance of a speaker with expensive drivers non using the correct enclosure and crossover for which they were designed.

Another point to raise is that placing a speaker near the wall you will seriously degrade the its performance, and doing so IMHO don't justify spending a lot of money on expensive drivers. In this case only one of the projects you are looking is worth to pursue (the PL18XT).

Keep in mind that a port really needs only a few cm to operate correctly. Moving the port on the bottom is not possible for the Maya (check the cabinet), and for the PL18XT you risk to modify the tuning from a BR to a MLTL.

If you want to reduce costs on caps, buy at least standard MKP (10uF 400V Audyn Cap KP-QS cost me less than 4€).



2011-11-12 10:30 pm
Thank you all for your replies.

It would be either the CNO-T25 or the TJL, no point in doing both and I do prefer paper cones so I'll go for the CNO when funds allow. But given the lack of funds, the idea was to start with cheaper drivers and try to build it with as little as possible and latter upgrade.

The Maya seems a good place to start, or the Vifa combo, though for not much less. They won't be placed that close to the wall, but I can't leave them much further than 30 or 40cm. The room is not very big either, is 4x4.5 with a two extra spaces totaling around 22sqm.

Finally, will probably be using Mundorf MKP evo for larger capacitance values and maybe Mundorf Supreme in the tweeter.


2010-11-22 11:24 pm
Another thing about the caps, all parallel caps like the 33 uF impedance compensation cap can be of lower quality without any issues since they aren't in the signal path. 33 uF MKP is expensive. Additionally i'd personally rather buy MKP caps from a known industrial brand, say Wima rather than from an "audio" brand.