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Discussion Starter #1
I posted this in my Fostex thread but figured the little drivers deserved their own thread. :)
I built a TL for the CHR 70's and they are INCREDIBLE!!! I was able to get a -3db point of 38hz using a transmission line enclosure!! It was amazing to listen to a 4 inch driver do 35hz!!!!!!!!!!!!! Of course I was using two per enclosure to get any kind of volume and will end up using 4 drivers per enclosure. I am going to order the alpair 6's next and give them a test run. THIS IS FUN.

Matt
 

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Re: Mark Audio Drivers!!!!!!!!!!!!!!!!!

Got any pics? That sounds pretty interesting. I wonder if you could do a combination line array/TL..
 

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Elite Shackster , HTS Moderator Emeritus
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Re: Mark Audio Drivers!!!!!!!!!!!!!!!!!

I have a buddy who did a little 3" TL build a while back and they ended up sounding great. Volume wasn't very good, but sound quality was excellent from a single driver.

Please post pics, if you get a chance.
 

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Re: Mark Audio Drivers!!!!!!!!!!!!!!!!!

Thanks guys for the positive feedback!! I was really excited to get the roll of so low!!!!!!!!
I will get a couple of pics of both the inside of the box and the freq response curve.

I am planning on doing 4 drivers per box so I guess that would qualify it as a line array of sorts. It is really everything I know slammed into one enclosure. It is kinda a TL/Line Array/Dipole/WMTMW lol.

The top end sounded pretty good to my ears but did not look so hot in REW. It tends to break up in the higher freq. I will post a screen shot. I am planning on crossing them over somewhere between 500hz and 1000hz so I am not to concerned about their top end. :)

If I make the baffle large enough I can avoid the baffle step compensation which will be a huge plus. If I cross everything over just right and build the baffles just right I might be able to avoid any notch filters as well but we will see. Each pair of alpairs will be in series which should bump up the efficiency by 3db and then all 4 will be compound loaded which should give me another 3db in theory, so they should be very efficient if all goes well.

I need to get some good software to measure these things with. :) Any recommendations? Thinking ether SoundEasy or LspCad.

Matt
 

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Re: Mark Audio Drivers!!!!!!!!!!!!!!!!!

I posted this in my Fostex thread but figured the little drivers deserved their own thread. :)
I built a TL for the CHR 70's and they are INCREDIBLE!!! I was able to get a -3db point of 38hz using a transmission line enclosure!! It was amazing to listen to a 4 inch driver do 35hz!!!!!!!!!!!!! Of course I was using two per enclosure to get any kind of volume and will end up using 4 drivers per enclosure. I am going to order the alpair 6's next and give them a test run. THIS IS FUN.

Matt
Tell us more... pics, plans?

I've just been listening to the 1st set of EnABLed CHR -- a reallygood driver, utterly transformed.

dave
 

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Discussion Starter #7
Re: Mark Audio Drivers!!!!!!!!!!!!!!!!!

What is an EnABLed CHR? The pics I have are of a really ugly box as it is just a test box. :) I am using a basic TL straight tunnel enclosure. Nothing special yet, except for the nice low-end.

Here is a screen shot of REW. Not sure why the top end is bad. Almost looks like REW was clipping. Any thoughts?
 

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Re: Mark Audio Drivers!!!!!!!!!!!!!!!!!

What is an EnABLed CHR?
So far one pair exist and they are in my living room. EnABL is a very specific cone treatment.

More here:
http://www.diyaudio.com/forums/showthread.php?s=&threadid=119676
http://www.diyaudio.com/forums/showthread.php?s=&threadid=100399
http://www.diyaudio.com/forums/showthread.php?s=&postid=1460032#post1460032


Is that an in-room response? It is far too flat to not have something wrong with it.

How long is the TL? Cross-section? Driver offset?

dave
 

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Discussion Starter #9
Re: Mark Audio Drivers!!!!!!!!!!!!!!!!!

Ya, the response looked funny to me as well. It is an in room response. I am going to wait for all for drivers to fill the enclosure and then take it out side and measure it as I don't have a chamber. I do have a very nice flat room though. :)

That EnABLed looks like a TON of work is really worth it?

Driver is offset from the beginning of the TL line by 3 inches and diameter of the line is twice the sd of one driver. Did not want to make the box to big. :)

THANKS for the links!!!!!!!!

Matt
 

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Re: Mark Audio Drivers!!!!!!!!!!!!!!!!!

That EnABLed looks like a TON of work is really worth it?
VERY much so.

Driver is offset from the beginning of the TL line by 3 inches and diameter of the line is twice the sd of one driver. Did not want to make the box to big. :)
Then i'm pretty sure the measure is screwy. Without taking advantage of offset (which for a straight line is somewhere near a 3rd of the way down the line) either you should have a fair bit of ripple from the 1st harmonic, or you have stuffed it until it is close to aperiodic and the rolloff should be similar to a sealed box of the same size (or maybe you have a small, solid room)

Such a small cross-section is also suspect. Did you use any of the available tools to design it, or is it a classic line (ie not likely optimal)

dave
 

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Discussion Starter #11
I have built many a TL but this is my first journey back into the world of TL in 15 years and there are now tons of resources on TL's. Back when I used to build them we did it with lots of math and trial and error but these new resources are making it easier to get right the first shoot out. Which saved me a ton of time, well maybe not a ton as I had to do a lot of reading. :)

I am not sure what you mean by offset? You can't use fancy words like that to a guy who comes from the old school TL world. :bigsmile: If you mean are the drivers mounted in the middle of the Line then the answer is a yes and no. :) Two are in the middle of the line and two are at the beginning of the line to try alleviate the ripple in both the 1st and 2nd harmonic, which looks like it worked up to 500hz. Which should be just below the fourth harmonic if my math is correct. :)

I do use a lot of stuffing both wool and standard pillow stuffing. I have also had good success with sound deadening foam. :)

Not sure why twice the sd of the line diameter would be suspect except for the fact that I am using a total of 4 eventually but during the measurements I used two which should be spot on. From my experience I learned and the reading I have done recently seemed to agree that line diameter should be sd for a straight line TL. Do you do something different? Is there a different way to do it now. 15 years has passed by. :)

Matt
 

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Discussion Starter #12
Going to have to do some reading on the EnABLed stuff. Did you measure the Theil parameters after you did the modification did it mess with the Mms? This sounds interesting to say the least.... :)

Matt
 

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I am not sure what you mean by offset? You can't use fancy words like that to a guy who comes from the old school TL world. :bigsmile: If you mean are the drivers mounted in the middle of the Line then the answer is a yes and no. :) Two are in the middle of the line and two are at the beginning of the line to try alleviate the ripple in both the 1st and 2nd harmonic, which looks like it worked up to 500hz. Which should be just below the fourth harmonic if my math is correct. :)

.... Not sure why twice the sd of the line diameter would be suspect except for the fact that I am using a total of 4 eventually but during the measurements I used two which should be spot on.
Offset is the distance of the driver from the closed end of the line. from memory 0.3411 gets you cancellation of the 1st undesirable harmonic.

Sd actually has no direct relationship to the required cross-section. This is determined by Vas & Qt. I've not time to run the numbers thru King's tables, butthat is always a good starting point.

How long is your line?

dave
 

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Discussion Starter #14
Sd actually has no direct relationship to the required cross-section. This is determined by Vas & Qt. I've not time to run the numbers thru King's tables, butthat is always a good starting point.
THANK YOU VERY MUCH for that info!! That is new to me. Do you have a copy of kings tables??? :)

So using 4 drivers then two of the drivers are very close to the .34111.

Wow, I had no idea TL's had come this far! This is very, very cool.

Line length is 48 inches based of a the 1/4 wave of 70hz. But the way the box is designed the second line length is would be 96 inches. Here is a drawing since the box is so UGLY. :)

 

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THANK YOU VERY MUCH for that info!! That is new to me. Do you have a copy of kings tables??? :)
My TL site: http://www.t-linespeakers.org/

The ReadMe 1st has links to Martin King's website & to Bob Brines. All 3 taken collectively are a wealth of TL info. Martin's tables are on his site. Somewhere on diyAudio.com someone has posted an Excel spreadsheet with the tables embedded.

Line length is 48 inches based of a the 1/4 wave of 70hz. But the way the box is designed the second line length is would be 96 inches.
So the actual line length is twice as long as it should be. You actually get less bass if you make the line too long.

If you are running the CHR full range, you are best to just build a square column and put a driver on each side to avoid combing. If they are all on the same face, you'll need to get fancy with an XO to rolloff the top of some of them.

dave
 

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All that measurement shows is that is was clipping the entire measurement. Try turning the volume down, or the meter level up.
 

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Discussion Starter #17
Martin's tables are the 30 pages I read. I just looked at the author.


So the actual line length is twice as long as it should be. You actually get less bass if you make the line too long.
Looking at my design do think the woofers are seeing the full 96 inches or are they just seeing the 48 inches of line length?

I was planning on crossing them over and letting a mid range and tweet take over the highs.

I have had issues with using more than one full range driver per baffle. So, I was not planning on going that route.

I will check out your site and THANKS for the info!!!
 

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Discussion Starter #18
It is funny with all the fancy math and table the basic fundamentals don't change much. :)

Any idea how to locate the pc parameter? I figured out everything after reading the document tons of times but can not find the pc parameter that is needed to finish the calcs. :(
His explanation of pc is "wave specific acoustic impedance" .. any idea how to find it? :gah:

Matt
 

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Looking at my design do think the woofers are seeing the full 96 inches or are they just seeing the 48 inches of line length?
Yes

I was planning on crossing them over and letting a mid range and tweet take over the highs.
Why would you get a CHR70 and then ruin it by adding a mid & a tweeter. I could see using it as a midtweeter with a bass driver.

I have had issues with using more than one full range driver per baffle. So, I was not planning on going that route.
I do as well, you have to get creative if you want to use more than 1. Here is a good way to use a pair...



dave
 

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Discussion Starter #20
Why would you get a CHR70 and then ruin it by adding a mid & a tweeter. I could see using it as a midtweeter with a bass driver.
Because I am nuts. :coocoo::dumbcrazy: No I am looking to build my own version of the ML's that hand on the wall. A thin speaker that still can go low without a sub but is designed to be used from 60hz up. That and I have always been partial to full range speakers especially were voices are concerned. Besides what other speaker is going to give this kind of sound quality for the money. :bigsmile:

I LIKE you creative design on overcoming the baffle issue with dual full rangers but what about of axis phase response. :)

Do you have any idea were I find the parameter pc that Martin King is referring to in his formulas? If I could get that one parameter I would know how far off my design is.

Just got the active crossover/loudspeaker management unit to go all active, no more coils or caps. :yay2:

If they are seeing all 96 inches thin it back to the drawing board. I will test and see.

THIS IS A FUN HOBBY!!!!!!

Matt
 
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