Thiele-Small parameters

[Vivekphadnis]

Hi all,
I just wonder why no one ever talks of T/S parameters for 6x9 speakers. After all, it does produce bass down to about 50Hz. Any comments, anyone?

Cheers,
Vivek

[Vivekphadnis]

Anyone any ideas? Sam, Navin tell me something. I need to get the correct boxes for my GTO936.

Cheers,
Vivek

[Sam Kapasi]

Hi!
You are absolutely correct, however please remember that 6X9s are commercially sold car audio free-air speakers.
The designers do not make them so you can create enclosures for them. T/S parameters are a must when designing enclosures. We do provide all parameters with Subwoofers for enclosure design.
Let me see what i can dig up for you on the 936e

[Vivekphadnis]

Great! I am eagerly waiting for your inputs. Thanks a million.

Vivek

[navin]

you'll be surprised by what they can do in boxes though. A 6x9 has about the Sd of a 8" round speaker. the speaker was developed for the narrow rear deck motor-city cars in the 70s (along with the 4x6 and 5x7). I would try them in a box that is say 15" x 13"x 10". The 9" lenght along the 15" length of the box.

[Vivekphadnis]

I wonder what box sizes are available in the market. If something similar to the one you suggested is not available, I will have to make new boxes.
Also, do we have to worry about box proportions and standing waves?

[Sam Kapasi]

Standing waves will not be such a large problem. Your box will have uneven sides to make it fit perfectly in your car and that itself will solve most resonance and standing wave problems.
What Navin suggests is ideal, but i do not think you will be able to buy this off a shelf.

There are many installers who will make a box for you, or you could make one yourself. Use 12 or 16mm MDF, commercially available and you can line it with glasswool or wastewool, like the kind they line cars with under the carpet. Big colourful mass of threads, what is it called Navin?

[Vivekphadnis]

I have plenty of 18mm MDF left over from my Vifa floorstander project. So I am thinking of making it myself. And I assume we are talking about a sealed box for the 936.
For the lining, I have some polyfibre sheets left over from my Vifa project. That should do nicely, don't you think?

[navin]

I think you are refering to what is commonly called carpet liner in the US. dont know local names. if you want to make a nice box do this....

first take 6mm marine ply (not mdf) and the ply must be void free (hence the use of marine ply) this is the thickest marine ply that can be bent into a parabola. If you cant make 6mm bend use 4mm. You will need a frame to bend it over.

then line the inside of the parabola with fiberglass mat and pour resin on this mat. The total thickness now is about 9mm but the box is now very rigid.

If you want to make the box more inert layer the outside of the box with another layer of either the 3mm fiber-resin mat or 6mm of marine ply. for small boxes this is not really required.

Now line the inside fiber-resin wall with 1.5mm lead sheet. The lead sheet not only adds weight to tbe box but also lean being soft it does not allow the resonances to ring. the decay time for what resonances does increase but we will tackle that later. Lead sheet is available opposite pydhonie police station.

now layer the lead sheet with 12mm open cell foam, polyfill, dacron, or glasswool. this depends on your taste as each material will voice the box slightly differently. open cell foam is available near Tardeo AC market. for polyfill i raid one of those reliance (or is it vimal) pilllows. Dacron I dont like and glasswool i get from Telcabs in Charkop Kandivilli.

your box will be 12-18mm thick but have the inertness of a box many time thicker. Also using different materials with different densities impeds the tranmission or sound.

Vivek, You built an Vifa floor stander? using what drivers? Did you get the drivers from Corrson?

[Sam Kapasi]

Arrey Superb!!

I just got totally turned on reading that. Navin I am totally impressed. You are truly a criminal after my own heart. Oh that was excellent.
Make no mistake here Vivek, we are in the presence of a man who knows his sh*t!

[navin]

I build my home speakers this way incl. Vifa floor standers. The Vifa floorstanders weigh 60kgs each. The reason to build them was to take completely ordinary components (Vifa TC series 6" woofer and Vifa 1" tweeter) and extract the most out of them.

Otherwise anyone can take ScanSpeak Revelators or Skanning or Seas Exel or Focal Pro drivers and make a nice speaker. Well almost anyone! :-)

And Vivek, if you are a fan of discrete amps try layign your hands on B&K ST140 circuit. I used to have it somewhere but cant find it now or I'd have mailed that to you. The Hitachi Metal can MOSFETS they sued are quite nice. I reworked this circuit (in my younger days) to use 3 pairs (instead of 2) and slightly different driver transistor and quiescent current to get 200W/ch/8ohms/20-20kHz (1200VA R core Torodial tranny, 60,000uf filer caps) oh no I'm rambling again.

[Vivekphadnis]

You bet Sam, he is the leader.

Navin,
I used the Vifa TC18WG49-08 and the D27TG05-06 in an MTM configuration. Yes, I got the drivers from Corrson.
I have just put the whole thing together using an XO suggested by a friend. I want to do some simulation using Speaker Workshop but I have not done it so far. I have to first build the speaker measurement jig (which is half complete). I am very lazy you see.
I use the speakers with a bipolar amp I built out of an EFY magazine. The problem is that the TC18 does not have a very high Xmax and I do not drive the speakers too hard.

Cheers,
Vivek

[navin]

Sam, Vivek, I'm no leader. he is....http://www.korea-dpr.com/pmenu.htm

I used LSP Cad for XO simulation. but given the nice gentle roll offs of the TC18 I used a series filter instead of a parallel filter. Andy Graddon is the guru here. I used a variation of his scheme to prevent driver blow out. Series filters traditionnaly have very little driver protection (see AndyG's site use google to find it). Caps were polys from CTR and coils were air core 14SWG (12AWG) with DCR less than 0.2ohms.

another nutty idea was to isolate the XO in a cavity on top of the loudspeaker. the cavity has a smoked glass top so one can actually see the XO components but not enough details to see the dirty wiring. This allows me to tinker with the XO while standing up.

Another nie idea is to use locakable T-nuts instead of screws to bolt teh woofer to the baffle. The baffle will have to be made of one solid block. I used 30mm MDF. and braces should be spread out unevenly to break up any residual panel resonances and to move them out of the critical vocal range.

[Vivekphadnis]

I used a parallel filter. I did not get CTR caps but some other brand which is also yellow in colour. I wind the coils myself using 22SWG enamelled wire. I buy these rectangular transformer bobbins and wind the coil by hand. After a rough estimation, I scrape off the enamel and measure L using a meter. Painful process but no other option. My uncle has a coil winding machine but I could not find round bobbins.
I searched high and low for T nuts but no hardware storekeepers seem to have heard about it in Bangalore. This would be useful especially when building the speaker. In some cases, the grooves in the MDF got messed up.

[navin]

if the woofer is not vented you can bolt the rear of the woofer (pole piece) to the back of the cabinet.