
Home  Forums  Rules  Articles  diyAudio Store  Gallery  Wiki  Blogs  Register  Donations  FAQ  Calendar  Search  Today's Posts  Mark Forums Read  Search 
MultiWay Conventional loudspeakers with crossovers 

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 

Thread Tools  Search this Thread 
30th January 2005, 03:58 AM  #1 
diyAudio Moderator

new morel MTM project: rantings
OK I'm starting this thread to dump stuff in with regard to my new MTM project I'm working on. Prompted because I was discussing something with kelticwizard and pretty much starting to thread jack.
Keltic, here is the nearfield measurement of one of the woofers (with both being driven) I was expecting from the sim, that freq response would start to drop off at 200Hz and the 3db to be about 80Hz, but it's doing the opposite (and if I take 12db as the reference point 500Hz) the 3db point is about 64Hz.... now from memory the nearfield data probably isn't much use above about 500Hz, but even so, this is really not what I expected. Tony. edit: the big dip at about 2Khz is baffle diffraction..... need to do something about that!! it corresponds directly to the width of 175mm of the baffle.... Not so sure about the big peak, probably not to worry as this is nearfield and it's probably nonsensical anyway 
30th January 2005, 04:17 AM  #2 
diyAudio Moderator

Just for the heck of it, here is a picture of my test environment yesterday not ideal but not to bad either. The pc under the speaker was purely for elevation. gave me a bit longer gate time, but unfortunately I couldn't quite push it far enough to get more resolution in speaker workshop.
The front baffle is very rough and was never originally intended to be used. It was more to sus out driver mountings. One thing I learned from my testing yesterday was that my idea of resessing the tweeter back into the baffle with rounded over edges was a really bad one!!!! huge trough in response between about 4.5 and 5.5K due to diffraction! (unfortunately I didn't save the response graph) This is only a test box, final one will be different, but it has proven invaluable as a learning tool. Learn't quite a lot yesterday from my testing with the mic too. Tony. 
30th January 2005, 04:17 AM  #3 
Wizard of Kelts
diyAudio Moderator Emeritus

Okay, so the Vas of the woofers is 9.8 liters each, and the the volume of the box is 6.6 liters, that is the same as one speaker with the Vas of 19.6 liters. Do I have tha correct?
__________________
"A friend will help you move. A really good friend will help you move a body." Anonymous 
30th January 2005, 04:23 AM  #4 
diyAudio Moderator

Ahhhh one important fact that I didn't mention. There is only one driver in that 6.6L the drivers have separate cavities.
Note I learn't something very usefull with my very dodgy braces that can be seen in this pic. The one directly behind the driver caused nast reflections, which caused a very nasty irregularity in the FR at about 700Hz! I'm now thinking that dowel may be a better thing to use as bracing!!! The sealing foam is only for this test box, the final ones will be properly glued. Tony. 
30th January 2005, 04:30 AM  #5 
Wizard of Kelts
diyAudio Moderator Emeritus

I did the math, according to the formula below.
I used the following parmeters: Vas = 19.8 liters, (for the two together) Fs = 34 Hz Qts = 0.41 I don't need to sim when I have the formula. In fact, the sim is based on Small's formula, which this is.
__________________
"A friend will help you move. A really good friend will help you move a body." Anonymous 
30th January 2005, 04:33 AM  #6  
Wizard of Kelts
diyAudio Moderator Emeritus

Quote:
Let me recalc, back in a minute.
__________________
"A friend will help you move. A really good friend will help you move a body." Anonymous 

30th January 2005, 04:35 AM  #7 
diyAudio Moderator

Doh, all the sims I did were for a single driver since I was modelling them in separate box volumes. I guess I should do one with two drivers and just double the volume.
Tony. edit: just realised part of the problem, the drivers have quite different specs, I guess I should model based on the average specs of all the drivers and just double it. Actually I did do the average, that is how I came up with 6L (then added 10% as is the norm), what did I do with those average specs...... 
30th January 2005, 04:35 AM  #8 
Wizard of Kelts
diyAudio Moderator Emeritus

Know what? I messed up the calculations in that post. So it is just as well for me to recalculate anyway!
__________________
"A friend will help you move. A really good friend will help you move a body." Anonymous 
30th January 2005, 04:44 AM  #9 
Wizard of Kelts
diyAudio Moderator Emeritus

I get:
Fc=53.6 Hz Qtc=0.65 And since, according to the formula below, the output is 3.79 dB at resonance when Qtc = 0.65, then the 3 dB point is probably just above Fc, (53.6 Hz). Let's call it 56 Hz. F3 = 56 Hz.
__________________
"A friend will help you move. A really good friend will help you move a body." Anonymous 
30th January 2005, 04:50 AM  #10 
Wizard of Kelts
diyAudio Moderator Emeritus

From your Speaker Workshop graph, I think the midpoint is probably about +12 dB. So the 3 dB down point seems to be just under 70 Hz.
Looks like either the ThieleSmall parameters or my calculations are a little off.
__________________
"A friend will help you move. A really good friend will help you move a body." Anonymous 
Thread Tools  Search this Thread 


Similar Threads  
Thread  Thread Starter  Forum  Replies  Last Post 
Morel CAW 938 vs. Peerless Exclusive 8'' for MDM 55 and OW I Project  leifislive  MultiWay  17  3rd March 2009 07:07 AM 
Morel 3way triamped project  JoeAl  MultiWay  0  12th December 2005 05:20 PM 
Big project planning  MOREL MW114S 4" DPC WOOFER  Deagle50ae  MultiWay  4  4th May 2005 07:38 PM 
Active 3 way project  Morel 110/PHL1340/Peerless XLS  Branwell  MultiWay  13  20th July 2004 08:22 PM 
Help with Morel sub project  andrew  MultiWay  5  11th May 2002 03:29 AM 
New To Site?  Need Help? 