need help with TL calculations

jmillerdoc · 2nd March 2009, 11:37 PM

Can anybody tell me where to find a TL calculator that will allow for 2 drivers instead of one? For instance, there is a calculator link on Madisounds website... It seems to me the only variable that would need to be changed is the effective area of the driver...can you simply enter in twice the area for 2 drivers and keep all other variables constant? If this is the case where would you start the length measurement for the TL? Somewhere1/2 way between the 2 drivers? ( this is assuming the MTM axis is in line with the long axis of the TL)

Since nobody has been able to give me a proven design I have decided to try a MTM TL with the Vifa P17WJ00 and Morel MDT33 and let Madisound design the crossover for $30. I'll keep y'all informed when it's done!
Thanks to all,
Jeff
millerjeff@ccmhonline.com

MJK · 2nd March 2009, 11:44 PM

If you go to my site and look under the General Speaker Related Articles link, there is a short write-up about how to model two discrete drivers as a single equivalent driver. The equivalent driver model is different for drivers wired in series and parallel. You would then place the single equivalent driver half way between the two real drivers in the computer simullation model.

planet10 · 3rd March 2009, 12:45 AM

Quote:

Originally posted by MJK
General Speaker Related Articles link,

While you are their read as much as you can...

Is this the calculator linked from Madiosound? http://www.mh-audio.nl/Transmission%...udspeakers.asp

It is a classic line calculator and is very unlikely to generate anything near optimal. You'd be better off with Martin's tables.

dave

Scottmoose · 3rd March 2009, 08:34 AM

Just to point out Jeff, it's perfectly possible to take an existing, proven BR speaker kit (or just design) & come up with a TL cabinet for it. That's no big deal. Some are more suitable than others, naturally, but the vast majority should be fine. For e.g., I designed a TL cabinet for Zaph's BAMTM a few months back -not sure if anyone's built it, but it should be a great box.

To re-echo Dave's comments, avoid the older design calculators -they're usually way off the money WRT line-length and pipe volume. The more recent tables, such as Martin's, will give you a much greater chance of success.

jmillerdoc · 3rd March 2009, 10:58 AM

It's the tables I am having a hard time with now, UUUUGGGHHH. Im not sure I understand exactly how to use them. Study, study, study.

Henkjan · 3rd March 2009, 11:20 AM

I have made an excel sheet that automates Martin's allignment tables. it is not in english at the moment, if you have some patience I'll translate it and post it here.

Scottmoose · 3rd March 2009, 11:36 AM

It's not all that difficult. They look harder than in fact they are. Remember, Martin's done the spade-work for you.

1/ Select line length for a given tuning frequency & taper. Pretty self explanatory.
2/ Select the Dz value, again, based upon your selected tuning frequency & taper. Again, not difficult -just read the value off from the table.
3/ Select the appropriate Dr value for the driver Qt. There is some fudge factor here, as naturally, not all possible Qt numbers are given. Use the existing values to approximate for your own unit.
4/ Select the approriate driver offset ratio (not rocket-science; again, just read it off the table).
5/ Square the Bl value of the driver & write it down.
6/ Carefully work out the following:

1.21 x 342 x driver surface area in square metres x Dz x dr x driver Re. Then divide by Bl squared (which is why I said work it out in advance). That gives you the CSA for the throat (sealed end of the line) expressed as a multiple of the driver surface area. The terminus area will be a percentage of that based upon your selected taper, so divide by 2 if a 2:1 is selected & so on & so forth.

What Martin's tables don't really cover are the selection of an appropriate damping density. I believe he sets a general assumption of dacron (the material used does make a difference however) and 0.5lbs ft^3. So you'll have to experiment somewhat.

Remember, if you're using two drivers, if in parallel (which is usually the most common method), double Sd & Vas, & halve Re before entering any data into the equations / formula above. Alternatively, be a luddite, work it out for the single unit, then double the line cross-section.

pkitt · 3rd March 2009, 04:45 PM

Quote:

Originally posted by jmillerdoc
It's the tables I am having a hard time with now, UUUUGGGHHH. Im not sure I understand exactly how to use them. Study, study, study.

Jeff, I sent you an email yesterday and offered to model a TL for you using Martin's worksheets and I asked you some questions to guide my efforts. Did you not get that email? Or, do you just prefer to do this yourself?

Cambe · 3rd March 2009, 05:35 PM

I could use some help with a TL sub. Could someone model a TL for me using Martins worksheets? Something folded .
I plan on using the W0838R-8".
Thanks

Cambe · 3rd March 2009, 06:08 PM

Oops!

2nd March 2009, 11:37 PM	#1
jmillerdoc diyAudio Member Join Date: Mar 2009 Location: Lawton, OK, USA	need help with TL calculations Can anybody tell me where to find a TL calculator that will allow for 2 drivers instead of one? For instance, there is a calculator link on Madisounds website... It seems to me the only variable that would need to be changed is the effective area of the driver...can you simply enter in twice the area for 2 drivers and keep all other variables constant? If this is the case where would you start the length measurement for the TL? Somewhere1/2 way between the 2 drivers? ( this is assuming the MTM axis is in line with the long axis of the TL) Since nobody has been able to give me a proven design I have decided to try a MTM TL with the Vifa P17WJ00 and Morel MDT33 and let Madisound design the crossover for $30. I'll keep y'all informed when it's done! Thanks to all, Jeff millerjeff@ccmhonline.com

3rd March 2009, 10:58 AM	#5
jmillerdoc diyAudio Member Join Date: Mar 2009 Location: Lawton, OK, USA	Tables It's the tables I am having a hard time with now, UUUUGGGHHH. Im not sure I understand exactly how to use them. Study, study, study.

Thread Tools	Search this Thread
Show Printable Version Email this Page	Search this Thread: Advanced Search

Similar Threads
Thread	Thread Starter	Forum	Replies	Last Post
BIB Calculations	davidallancole	Full Range	44	11th March 2007 03:04 PM
Need help with calculations please.	Wynand	Solid State	6	27th June 2006 01:00 PM
x over calculations	bcycle	Subwoofers	10	8th February 2006 06:58 AM
calculations	lXxAndyxXl	Multi-Way	8	19th October 2004 04:53 PM

New To Site?	Need Help?
Register to Participate Search Privacy Statement Contact Us	Frequently Asked Questions Did you forget your password? Mark Forums Read


	Please consider donating to help us continue to serve you. Ads on/off / Custom Title / More PMs / More album space / Advanced printing & mass image saving

2nd March 2009, 11:44 PM	#2
MJK Account disabled at member's request Join Date: Feb 2002 Location: Clifton Park, NY	If you go to my site and look under the General Speaker Related Articles link, there is a short write-up about how to model two discrete drivers as a single equivalent driver. The equivalent driver model is different for drivers wired in series and parallel. You would then place the single equivalent driver half way between the two real drivers in the computer simullation model.

3rd March 2009, 08:34 AM	#4
Scottmoose diyAudio Member Join Date: Mar 2005 Location: UK	Just to point out Jeff, it's perfectly possible to take an existing, proven BR speaker kit (or just design) & come up with a TL cabinet for it. That's no big deal. Some are more suitable than others, naturally, but the vast majority should be fine. For e.g., I designed a TL cabinet for Zaph's BAMTM a few months back -not sure if anyone's built it, but it should be a great box. To re-echo Dave's comments, avoid the older design calculators -they're usually way off the money WRT line-length and pipe volume. The more recent tables, such as Martin's, will give you a much greater chance of success.

3rd March 2009, 11:20 AM	#6
Henkjan diyAudio Member Join Date: Jan 2006 Location: Berkel en Rodenrijs	I have made an excel sheet that automates Martin's allignment tables. it is not in english at the moment, if you have some patience I'll translate it and post it here.

3rd March 2009, 11:36 AM	#7
Scottmoose diyAudio Member Join Date: Mar 2005 Location: UK	It's not all that difficult. They look harder than in fact they are. Remember, Martin's done the spade-work for you. 1/ Select line length for a given tuning frequency & taper. Pretty self explanatory. 2/ Select the Dz value, again, based upon your selected tuning frequency & taper. Again, not difficult -just read the value off from the table. 3/ Select the appropriate Dr value for the driver Qt. There is some fudge factor here, as naturally, not all possible Qt numbers are given. Use the existing values to approximate for your own unit. 4/ Select the approriate driver offset ratio (not rocket-science; again, just read it off the table). 5/ Square the Bl value of the driver & write it down. 6/ Carefully work out the following: 1.21 x 342 x driver surface area in square metres x Dz x dr x driver Re. Then divide by Bl squared (which is why I said work it out in advance). That gives you the CSA for the throat (sealed end of the line) expressed as a multiple of the driver surface area. The terminus area will be a percentage of that based upon your selected taper, so divide by 2 if a 2:1 is selected & so on & so forth. What Martin's tables don't really cover are the selection of an appropriate damping density. I believe he sets a general assumption of dacron (the material used does make a difference however) and 0.5lbs ft^3. So you'll have to experiment somewhat. Remember, if you're using two drivers, if in parallel (which is usually the most common method), double Sd & Vas, & halve Re before entering any data into the equations / formula above. Alternatively, be a luddite, work it out for the single unit, then double the line cross-section.

3rd March 2009, 05:35 PM	#9
Cambe diyAudio Member Join Date: Aug 2001 Location: USA,NorthCarolina	I could use some help with a TL sub. Could someone model a TL for me using Martins worksheets? Something folded . I plan on using the W0838R-8". Thanks

3rd March 2009, 06:08 PM	#10
Cambe diyAudio Member Join Date: Aug 2001 Location: USA,NorthCarolina	Oops!

Currently Active Users Viewing This Thread: 1 (0 members and 1 guests)