Budget Optimo?

[crapitecture]

I’m here to ask for some help in developing a speaker design. I have a few pre-cooked DIY speakers under my belt that have been successful, but now I want to try to develop a custom design. I've been trying to learn Speaker Workshop and I'm finding that is is far from intuitive to me, but I'll work through it.

The project I want to complete is a design for my new mains. My current system consists of 3 NHT SuperZero’s for the front channels, surrounds based on Zaph’s Hi-Vi B3S design, and a Rhythmik 12” Sub. I want to eventually replace all the channels with designs that use all of the same drivers, but I’m going to have to piecemeal it as I get the money and time.

Although I’ve been very pleased with the NHT’s, I’m ready to shift them into my office, and build something hopefully a bit better and perhaps a tad more exotic. While searching for designs I might be interested in, I was intrigued with the Optimo design at Humble HiFi. I really like the way it looks and so does my wife. I am also interested in the challenge of pulling off a transmission line speaker. The drawback for me was the cost of the drivers he uses. I just wouldn’t be able to justify the expense to my wife.

I’ve looked at utilizing the work done on other designs like the Modula MT and porting it over to the TL design, but the Modula crossovers seem pretty complex and expensive to tame the RS180. So I’ve done some preliminary homework on a design that would instead utilize a TB W6-1721 and the Seas 27TDFC. They seem like reasonable quality drivers for the price. Also I haven’t seen any projects using the W6-1721 yet so I thought this might be an opportunity to see what this driver can do.

I've taken the T&S data and traced the FR and Impedance graphs from Zaph's site and imported them into Speaker workshop and then hit a brick wall in designing the crossover.

I’ve used MJK’s tables and Zaph’s measurements to arrive at the basic parameters of a TL design. The basic design is pictured below.

Here are my questions:

> Is the W6-1721 the right driver for a TL design? Are there better, less expensive speakers that I should be considering.

> When you fold a TL line how do you measure the length accurately? I’ve not been counting the additional length (measured at the centerline) at the 180 degree turn, is that correct? What about at the opening at the end of the TL? Also, I am assuming that dimensions regarding the placement of speakers, openings, etc are measured at the center line.

> Considering my sub, is a 30hz tune the right direction to go? I like the idea of creating a full range speaker that I can use elsewhere as I continue to trade up speakers, but perhaps a different tuning might provide a much better midrange character. Thoughts on this?

> I’ve been reading on ML TL designs and there seems to be some advantages to using that kind of design as it reduces the length of the line. Would one of the MathCad MJK Sheets gurus be interested in running the numbers for an ML TL design.

> Has anyone had experience developing a crossover with the 1721? Any help in creating a good crossover for this design would be much appreciated.

Thanks in advance for your help!

[dublin78]

There is a XO mod for the Optimo that allows you to use the Vifa XT25TG30-04 Tweeter which is far cheaper.

Simply change R1 to 1 Ohm.

[crapitecture]

I've continued to work on this project. I am certainly stumbling blindly through this, but I'm trying to learn. Using FRD tools, Speaker Works, and Zaph's measurements, I've created a basic crossover. I still need baffle diffraction, etc. to do, but I still haven't locked down the enclosure yet, so the baffle stuff is still up in the air. There seems to be a bit of a lull between 300 and 1500 hz. I'm not sure if I should be concerned about this yet.


Dublin: Thanks for the info... Is there less expensive option for the woofer?

[sreten]

Hi,

There are some classic driver combinations here :

http://www.geocities.com/woove99/Spkrbldg/

/sreten.

[dublin78]

You may ask Tony Gee to suggest a cheaper midwoofer, but a different tweeter + a different midwoofer will most likely require a different crossover if you were to do things properley.

I would imagine that the only reason why Tony offered the vifa option, was that the two tweeters behaved in very similar ways.

Streten's approach (TLing an existing design) may work, but as Tony Gee discovered the TL affected the midrange a lot, so an existing XO design for a ported or sealed cabinet may not be optimum.

My Optimos are nearly finished. The sanding and treating of the cabinets is taking a very long time, as it is not much fun...

[sreten]

Hi,

http://www.geocities.com/woove99/Spk...esigningXO.htm

The tuning / tweaking process is part and parcel of doing it right.

FWIW TG measurements show differences in the output of the line,
which whilst significant would not change the basic design of a
2-way much, possibly affect BSC a little and some balance issues.

Some of TG's subjective observations / theory is dubious e.g. :

Placing the reflex ports symmetrically to the left and right of the
tweeter is a very wise thing to do. Seeing as it is a two-way
system a lot of midrange energy will be coming out of the ports.
If you place the ports in the rear panel then this energy will arrive
delayed compared to the midrange energy coming from the drivers.
This will result in some blurring of the stereo image.
As this would be a D' Appolito design there are two ports
placed centrally around the tweeter as the woofers are.

All seems to make sense except I do not agree with a word of it.

/sreten.