placing the driver 1/3rd of the length down a TL

[Bill poster]

Sorry, I asked this question once before but I couldn't find the answer.

..does the overall length of the line stay the same if the driver is positioned along the line rather than at the beginning?

And if so, is the general bass extension the same?

Thanks

 

[Scottmoose]

Yes and yes, but depending on the damping you've added, you may get a little less gain at the pipe fundamental.

 

[Bill poster]

Fantastic. Thanks Scottmoose.
The other question is tuning- I read somewhere that you should tune the quarter wave length around 5 khz away from driver resonance..the prob is I can't remember if that is above or below the driver resonance! Mind you I doubt its easy to get it spot on anyway, too many factors involved..

 

[planet10]

Also keep in mind that the 1/3 number is only an approximation of the optimum Zd. Download Martin King's tables. One of the tables is of the ratios of offset depending on the geometry of the line.

dave

 

[Scottmoose]

There are no 'shoulds' in terms of Fp, though it's generally inadvisible to tune below 0.707 Fs. Martin's Alignment tables assume tuning to Fs for e.g., but there are a wide variety of alignments (technically infinite, although that doesn't mean they're any use) depending on what is desired.

 

[Bill poster]

Ah I see. I wanted to try the new chr 70 which has a 65 hz fs but has quite a high qt. I think it goes down to 45 hz pretty flat. In this case shd i still stick to just above Fs or take the quite high qts into consideration?

 

[Leonidas]

You can also sim it in "hornresp".
Put the driver between S1 and S2 , in "driver-arrangement"".
Take the "speakerwizard" and watch response changes.

 

[GM]

.........or take the quite high qts into consideration?

I do. Good rule-of-thumb in today's T/S centric 'society':

Up to a ~0.707 Qts after any series resistance is accounted for: sim a T/S max flat alignment and make Fp whatever Fb it calcs.

Above this point, it's generally better to use Fp = Fs/Qts and definitely if it's a >1.0 Qts or you want the TL equivalent of a T/S max flat [AKA max flat impedance] alignment.

Works for me anyway. Try it both ways plus ignoring Qts, calculate them using MJK's Classic Alignment Tables, sim them in his software and let us know what you think.

GM

 

[GM]

Put the driver between S1 and S2 , in "driver-arrangement"".

Hmm, you sure about this? My understanding is that the driver is centered at S2.

GM

 

[Leonidas]

GM : you'r right, I'm wrong :

Correction : Put driver between S1 and S3 = S2 .
(Was too fast in replying and didn't check ed what I said!!)

 

[Bill poster]

This is a sketch of the design. The rear chamber is effectively 1/3 of the line with the 'fins' or wings having a folded line inside exiting at the rear. The line is about 4.5 ft long. It's symmetrical but the lower part is extended down to the stand.
View attachment img043 (1).zip

sorry, the image doesnt seem to be showing for some reason.

 

[pinkmouse]

That's because it's a zip file. Try reposting as a GIF or PNG

 

[GM]

Looks like some stylized '50s era Cadillac tail fin/light assembly.

GM

 

[bjorno]

Looks like some stylized '50s era Cadillac tail fin/light assembly.

GM

....Is this a half-wave TL or an quarter-wave with the terminating opening
marked yellow in this picture copy?

 

[Scottmoose]

And another

Right out of Fireball XL5

 

[Bill poster]

....Is this a half-wave TL or an quarter-wave with the terminating opening
marked yellow in this picture copy?

My sketch wasnt great but you got it exactly (1/4)- I made a small model last year but I couldnt figure out the internals until now

Will it work in theory? I'm worried about lobing..

 

[bjorno]

..Will it work in theory? I'm worried about lobing..

I have no doubt that this wouldn't work but the lobing issue is another consideration to deal with:
I would at first hand add another smaller FR driver to cure this inevitable problem or place a small capacitor in parallel with the lower placed driver if and only if the drivers are hooked up in series.

b

 

[Bill poster]

I have no doubt that this wouldn't work but the lobing issue is another consideration to deal with:
I would at first hand add another smaller FR driver to cure this inevitable problem or place a small capacitor in parallel with the lower placed driver if and only if the drivers are hooked up in series.

b

Thanks Bjorno

No doubt it would or wouldnt work? would, I hope!
I thought about adding a tweet and or maybe a 3rd sealed driver enclosure and rolling the Hfs off the outside two.. but maybe its a bit overkill, looks wise.
I like the idea of rolling off the lower driver but don't I need an inductor? how does that work?

 

[bjorno]

Hi Bill,

Sorry for being late...

No doubt it would or wouldnt work? would, I hope!

It will work

I thought about adding a tweet and or maybe a 3rd sealed driver enclosure and rolling the Hfs off the outside two.. but maybe its a bit overkill, looks wise.

Good idea.

I like the idea of rolling off the lower driver but don't I need an inductor? how does that work?

Place a small capacitor in parallel with the lower placed driver if the drivers are hooked up in series but when using the drivers in parallel: You're right: An inductor would be the first to choose.

Example of capacitor use: The patented Logitec Fdd2 filter : See the submitted picture

b

 

[Bill poster]

Place a small capacitor in parallel with the lower placed driver if the drivers are hooked up in series but when using the drivers in parallel: You're right: An inductor would be the first to choose.

Example of capacitor use: The patented Logitec Fdd2 filter : See the submitted picture

b

Cheers dude! Tack sa mycket!

Ah, so Logitec figured out a way of not using an inductor and.. strictly speaking .. I could try this but not for commercial use.

I will probably go this route or I had an idea to put an omni type lens in front of one driver.