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MultiWay Conventional loudspeakers with crossovers 

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29th November 2013, 09:59 PM  #21 
diyAudio Member
Join Date: Oct 2009

' I just knocked out a MLTQWT tuned for 47hz just to compare. .it came out 72" long 1.55 cu.ft took me les than an hour to build it out of scrap wood.

29th November 2013, 11:04 PM  #22 
diyAudio Member
Join Date: Feb 2009

I'll share more information in a little bit, but a tuning frequency of 47 Hz is too high IMO as I came up with an optimally flat response using just under 40 Hz in an MLTL. Have you been able to model accurately what you've ended up building?
Paul 
29th November 2013, 11:28 PM  #23 
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Join Date: Feb 2009

Here's what I modeled for an MLTL
I modeled a simple MLTL as a floorstander having internal dimensions of 7"W x 7"D x 38"H with the woofer's center located 8" below the internal top. I used a port having a diameter of 2.5" and a length of 4.75", with its center located 4" above the internal bottom. The top half of the cabinet is stuffed with polyester fiber at a density of 0.75 lb/ft3. I modeled with 0.5 ohms assumed in series with the woofer, like from a crossover inductor, which raises Qts to 0.37. The tuning frequency I found to give the flattest overall response was just under 40 Hz. The predicted F3 was 38 Hz. For a 35watt input I've attached 3 graphs. The first shows the overall system bass response (red line) with an output SPL of 105 dB. The red line in the second graph is the woofer's excursion in mm RMS (an Xmax of 11 mm Peak equals 7.8 mm RMS). The third graph shows the air velocity in the port as a percentage of the speed of sound (the port can be mounted on the baffle or back panel).
Paul 
29th November 2013, 11:49 PM  #24 
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Join Date: Feb 2009

I am assuming you literally mean an MLTQWT with a tapered, expanding area from closed end to open end, and with the woofer located at the approximate center of the line's length? I quickly modeled pretty much what you described, same length, a volume of 1.46 ft3, a zero crosssection area at the closed end of the line, and an area of 7" x 10" at the open end. The port had a diameter of 3" and a length of 1.85", with the port's center located 4" from the end of the line. The system tuning was 4647 Hz. The first 49" of the line were stuffed at 0.75 lb/ft3. I've attached the system bass response for a 2.83volt input. I obviously can't state this is exactly what your design will give, but it ought to be really close.
Paul Last edited by pkitt; 30th November 2013 at 12:12 AM. 
30th November 2013, 04:15 AM  #25 
diyAudio Member
Join Date: Oct 2009

I intend to run the 6.5" driver crossoverless with no inductor , please advise as to any changes. I'm ,sorry that I didn't tell you this before. I didn't anticipate you introducing this into the modeling. It't late and i will have more time tomorrow to digest the rest of your information. Thanks so much for your help.
The 47hz MLTQWT sounded exactly like the graph that you modeled of it. Sounded like *** compared to the B.R. 
30th November 2013, 01:47 PM  #26  
diyAudio Member
Join Date: Feb 2009

Unless there is no passive crossover involved I usually model with 0.5 ohms assumed in series with the driver. If I know what the exact resistance value will be, I'll use that, of course.
I hope you didn't waste your time with the MLTQWT you put together quickly. Of course it illustrated why it's so important to be able to model a design before you start making sawdust. I find some time to remodel the MLTL with zero resistance added in series. It will require tuning a bit higher due to the lower Qts. Paul Quote:


30th November 2013, 02:38 PM  #27 
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Join Date: Oct 2009

Thanks again Paul. How do you feel about a wider front baffle as long as the cross sectional are remains the same like 10" wide x 4.9" deep ?

30th November 2013, 03:05 PM  #28 
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Join Date: Feb 2009

You have to keep in mind the length of the port and make sure there's enough clearance between its internal end and the opposite panel. You can make the port smaller in diameter and that will allow it to also be shorter, but then the air velocity will be higher at resonance, which increases the likelihood of audible port noise. So, no, I would stick with an internal width of 7", making the external width at 81/2" if using 3/4"thick side panels.
Paul 
30th November 2013, 04:54 PM  #29 
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Join Date: Oct 2009

I picked up some 8" dia. tube to play around. I will make a couple enclosures out of it to your modeled specs.

30th November 2013, 05:31 PM  #30 
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Join Date: Oct 2009


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