Humble Optimo TL stuffing tuning: Please help.

[dublin78]

I have finally finished my Humble Homemade Optimo project: http://www.humblehomemadehifi.com/Optimo.html

The sound is not great - slightly closed in and none of the fantastic midrange that I had expected. I have realised that I need to tune the tramsmission line by changing the amount of stuffing. This appears to be quite a technical issue.

On Tony's website he says to completely fill the first half. In an email from Tony, he said to lighly fill the first half.

The line is 172cm2 x 190cm long.

Initially, I have put a piece of BAF in the first half of the line that is 1000mm x 500mm x 40mm. It weighs 6 Oz (170g).

I have read somewhere (Weems) that TL stuffing should be 8 Oz (227g) per cubic foot (28317 cm3).

Have I put far too much in?
Can you help explain my temporary dissapointment?

I will write a thread with some nice photos once I have got this right.

[sreten]

Hi,

http://www.quarter-wave.com/TLs/Alignment_Tables.pdf

See pages 37 onwards in particular.

FWIW I'd suggest lining the 1st 1/4 or so of the TL with high quality
acoustic foam, as you would with a vented box, and then adjusting
the stuffing denstity and length for bass response versus bass ripple.

(Possibly also foam line just the outside front, bottom
and back of the U shaped fold of the line, YMMV.)

IMF used to foam line what can be considered the "back" of the line.



/sreten.

[dublin78]

Thanks Sreten: I had obviously read a few of Martin's papers, but I had not come across this bit.

Prior to your post, I had just purchased some accoustic egg crate foam to try behind and above the drivers, though I was not planning on much more.

I am now playing the Optimos without any stuffing at all, and the closed in or dead sound has gone. I am now going to fill the first half of the line with torn chunks of BAF which will result in less density.

I will bear in mind your suggestion of placing further foam along the bottom of the U bend. What do you expect this to achieve?

[ABO]

I have optimo's and they sound great. Of course I used top quality components for the crossover.

I had problem with bass. After some discussion with Tony, he suggested I use sheep wool, IIRC. It was a long time ago, I don't remember what my problem was exactly.

It sounds super now. I can tell you that even with expensive (several kEUR) player and amps, the speakers are the best components in my system.

[dublin78]

ABO: That is good to hear.

I went for the "budget" crossover components, though they cost 200EUR in total: 2.0mm air core inductors, MOX10 resistors, and a mix of Mundorf MKP and MKP ZN caps.



What selection did you choose?

Back to stuffing ideas now...

[ABO]

You can see my crossover on Tony's site. I think I used Mundorfs supreme all over. For the series cap for the tweeter, I started with a mix of Mcaps/Mcap Zn and Supreme. Later I threw out the normal caps and replaced them with Mcap supreme silveroil.

This really was a real worthwhile improvement. The highs were muchg better after the change. Normal Mcaps should be avoided at all cost. They don't belong in speakers like optimo's.

I don't think that resistor make much of a difference although I didn't try in crossover (but I do use those expensive naked vishays everywhere else where they do make a difference, hmm). I used mox10 I believe.

The coils should be aircore. I think I used tritec and flatband. It would not explain your problem.

My advice is that you double and triple check your crossover. The optimo's excel in a very open and transperant midrange and of course super highs. The bass is on par with other systems, but should be deep, tight and punchy with good amps and possibly some experimentation with the stuffing.

Unless you use the best of amps and sources, this speaker should not hold your system back.
Unless you use it in a large space of course. There is only so much that a 18cm woofer can do. But it goes easily down to 35 Hz in my home.

BTW. did you use the scanspeak ring radiator?

[dublin78]

Hello ABO - Thanks for your reply.

I think that I will change the 10uf MCaps for MCap Supremes @ 36EUR each at some stage soon. This is what Tony's high-end version suggests. The Silver Oil ones are 93EUR each!

Yes, I did use the R2904/7000 ring radiator.



I will let you all know how the tuning goes when I had recieved the egg crate foam (I dont want to loosen the self tappers by too many changes).

[pkitt]

Take a look at the first attachment ("Optimo 1"). This is how the Optimo TL as designed models with Martin King's Mathcad-based TL worksheets. Those big dips and peaks sure look they would sound ugly. This SS 18W/4531G00 works (models) much better in an ML-TQWT and I modeled one of the same length that could fit within the same box dimensions. Its modeled response is shown in the second attachment ("Optimo 2"). It's obvious the overall respnse is very smooth and F3 is several Hz lower. You can also get a good result in a tapered TL with this driver but the box would need to be larger for the same F3.

[pkitt]

Here's the first attachment, the one showing the poor modeled performance of the Optimo design as published. The attachment shown in my previous post is that for the ML-TQWT.

[dublin78]

Oh my, that looks ugly.

It begs the question as to why a respected designer (and several very happy builders) have been highly satisfied with this formulae/design.

See thread: Humble homemade Optimo loudspeaker

As I said in the previopus thread, we must respect ear over modelling sometimes, and attempt to understand why there are differences.

I am open minded.