ProSoundWeb Community

Please login or register.

Login with username, password and session length
Advanced search  
Pages: 1 2 [All]   Go Down

Author Topic: Lab Sub driver module and LF extension vs Versions 1-2-3  (Read 5767 times)

Steve Shafer

  • Full Member
  • ***
  • Offline Offline
  • Posts: 170
Lab Sub driver module and LF extension vs Versions 1-2-3
« on: November 26, 2004, 06:43:58 pm »

Hello all:

Looking for tips on building the driver module.  This seems to be a most crucial part of the project.  Secondly, conceptually why are the two drivers positioned facing each other at the angle that they are?  

I have read that this Sub represents a combination of a band pass and and exponential horn.  If this is true where conceptually is the bandpass portion and to what order is the band pass.  

I have been reading some of Tom Danley's original design discussion and targeted parameters.  It is my understanding that the Lab Sub operates as a direct radiator when producing frequencies below the tuning frequency of the horn.  If I remember correctly Tom had the horn cut of some where in the 3X's Hz range.  

Of the three "versions" which one has the lowest usable frequency responce-say -3db point.  

Also Brad if you get a chance to read this, what advantages/disadvantages did you find to using the type of plywood that you used.  It seems more affordable

Thanks in advance

Steves
Logged

Brad Litz

  • Jr. Member
  • **
  • Offline Offline
  • Posts: 96
Re: Lab Sub driver module and LF extension vs Versions 1-2-3
« Reply #1 on: November 30, 2004, 11:17:18 pm »

The V 1&2 front chamber is very large and acts as a low pass filter. Also the horn bends limit the upper response to under 300 hz.

All the designs have about the same -3db point (with no horn extension).

The Appleply I used is maple on the outside so it looks good and does not splinter as easily as birch when you cut it. Also it is a full 3/4 thick. It has plys of alder and birch so it is probably not quite as strong as all birch Russian or Baltic plywood. It was not cheap.

Logged
Brad Litz

Mark Seaton

  • Full Member
  • ***
  • Offline Offline
  • Posts: 142
Re: Lab Sub driver module and LF extension vs Versions 1-2-3
« Reply #2 on: December 01, 2004, 12:28:35 am »

It should also be noted that the V3 design in casual investigation looks to allow more excursion from the drivers at the same drive level.  Below cutoff, there is also increased excursion due to the larger rear enclosure.  There is an according increase in output at some frequencies, and we would have to do some more investigation as to what trade offs come into play realtive to power dissipation in the motor and excursion vs. output.  This is directly related to the acoustic loading on the driver.  For Brad's use in a home theater with an extension, these trade offs makea lot of sense.  If you want to beat on the subs in a concert or club situation used in only pairs, I'm not sure this would be my choice.  

Best Regards,

Mark Seaton
Logged
Mark Seaton
Seaton Sound, Inc.
"Make no little plans; they have no magic to stir men's blood..." - Daniel H. Burnham

Brad Litz

  • Jr. Member
  • **
  • Offline Offline
  • Posts: 96
Re: Lab Sub driver module and LF extension vs Versions 1-2-3
« Reply #3 on: December 01, 2004, 09:56:55 pm »

The goal of V3.0 was to extend the bandwidth a little at both ends and remove a slight dip in the frequency response at 45 Hz.

As Mark mentions, there is a little more cone excursion at a given drive level at some frequencies. The increased cone excurion also provides more output and flattens the frequency response.

In high power use, the LABsub should always be protected by a high pass filter to prevent excessive cone excursion below the horn cutoff frequency.

The horn extension lets me get by with two cabinets when otherwise 4 are needed for sufficient mouth area. The extension also lengthens the horn some which also helps to extend the low end.

Logged
Brad Litz

Steve Shafer

  • Full Member
  • ***
  • Offline Offline
  • Posts: 170
Which version for live sound and Dj work
« Reply #4 on: December 12, 2004, 04:19:09 pm »

Mark & Brad:

After reading Mark's last post it seems clear that th version three Lab Sub is not the best choice for Live/Club use.  Are there any advantages of going with version one rather than version two in these applications?

Also, as I do not have access to the proper tools, the screw together joints that Brad used are much more feasible for me at this time.  

Can anyone  comment as to how many sheets of birch ply they  are using per box and an average cost per sheet.  I live in a very rural area and I can not just go to a home depot or a wood distributor and buy the stuff

Thanks

Steve Shafer
Logged

Brad Litz

  • Jr. Member
  • **
  • Offline Offline
  • Posts: 96
Re: Which version for live sound and Dj work
« Reply #5 on: December 12, 2004, 06:03:16 pm »

If you EQ v1.0 or v2.0 to the same flat frequency response as v3.0, you will get about the same cone excursion and use a little more power.

It really just depends on whether that dip in response at 45 hz is an issue to you. The rear chamber volume in v3.0 is closer to the volume recommended by Tom Danley than v1.0 or 2.0.

v1.0 and 2.0 are easier to build as there are no compound miter cuts in the module. My table saw had no problem with them so it made no difference to me.

You can push the upper x-over frequency a little higher with v3.0 which may be an advantage depending on the the rest of your system.

I do not believe the 3 to 1 compression ratio in v3.0 is a problem as the LAB12 cones are very stiff. This may have been a problem in other horn designs using 15" cones which are much more difficult to get as rigid as a 12".
Logged
Brad Litz

Steve Shafer

  • Full Member
  • ***
  • Offline Offline
  • Posts: 170
What benefits come from rear chamber "tuning"
« Reply #6 on: December 12, 2004, 07:30:11 pm »

Brad, Mark, Tom, and anyone else:

What benefits are gained by having the rear chamber for the drivers being closer to the actual area suggested by Tom D in the intial discussion and prototypes?

As for the dip in the 45 Hz range, how evident is it, and would it be "fixable" with a good eq or at the BSS minidrive?

Thanks

Steve Shafer
Logged

Brad Litz

  • Jr. Member
  • **
  • Offline Offline
  • Posts: 96
Re: What benefits come from rear chamber "tuning"
« Reply #7 on: December 12, 2004, 07:57:30 pm »

Here's some filtered responses of v2.0

index.php/fa/828/0/
Logged
Brad Litz

Brad Litz

  • Jr. Member
  • **
  • Offline Offline
  • Posts: 96
Re: What benefits come from rear chamber "tuning"
« Reply #8 on: December 12, 2004, 08:02:09 pm »

Here is my measurement of v3.0 with no filters.
Two cabinets outdoors (no horn extension).

index.php/fa/829/0/
Logged
Brad Litz

Michael_Elliston¶

  • Sr. Member
  • ****
  • Offline Offline
  • Posts: 261
    • http://www.geocities.com/xobt
Re: What benefits come from rear chamber "tuning"
« Reply #9 on: December 13, 2004, 05:35:13 am »

Smaller rear chamber - less LF excursion below cutoff

Obviously if its too small a dip results,But this doesnt happen when the right amount of boxes are used.
Logged

Too Tall (Curtis H. List)

  • Hero Member
  • *****
  • Offline Offline
  • Posts: 1591
Re: What benefits come from rear chamber "tuning"
« Reply #10 on: December 14, 2004, 10:18:09 am »

Brad Litz wrote on Sun, 12 December 2004 20:02

Here is my measurement of v3.0 with no filters.
Two cabinets outdoors (no horn extension).

index.php/fa/829/0/



Hi Brad,

Supposedly I have someone bringing over some version 3 LAB subs for testing. Do you happen to have an impedance measurement of a v3 without the flare extension?

Otherwise next best would be the prediction from modeling program. I want something for a base line so I can tell the owner it is working correctly or not.
Logged
Too Tall
        Curtis H. List    
             Bridgeport, Mich.   
        I.A.T.S.E. Local # 274 (Gold Card)
        Lansing, Mich
Independent Live Sound Engineer (and I'm Tall Too!)

Too Tall (Curtis H. List)

  • Hero Member
  • *****
  • Offline Offline
  • Posts: 1591
Re: What benefits come from rear chamber "tuning"
« Reply #11 on: December 14, 2004, 10:31:28 am »


Stevesb65 wrote on Sun, 12 December 2004 19:30

Brad, Mark, Tom, and anyone else:

snip-

As for the dip in the 45 Hz range, how evident is it, and would it be "fixable" with a good eq or at the BSS minidrive?

Thanks

Steve Shafer



Look at the graph in the next post by Brad.

The blue line labeled "2" is the response with a typical 24dB/octave Link-Riley low pass xover and a single parametric filter that you could find in just about any digital speaker management device like DBX Driverack, XTA, BSS or even Behringer.

   The result of the filter is that instead of a peak at 90Hz and a dip around 45hz (magenta line of raw frequency response) you now have a peak at 35hz and flat response above it.

Logged
Too Tall
        Curtis H. List    
             Bridgeport, Mich.   
        I.A.T.S.E. Local # 274 (Gold Card)
        Lansing, Mich
Independent Live Sound Engineer (and I'm Tall Too!)

Brad Litz

  • Jr. Member
  • **
  • Offline Offline
  • Posts: 96
Re: What benefits come from rear chamber "tuning"
« Reply #12 on: December 15, 2004, 12:23:12 am »

Here's the predicted response. Sorry, I did not measure it.

index.php/fa/839/0/
Logged
Brad Litz

Too Tall (Curtis H. List)

  • Hero Member
  • *****
  • Offline Offline
  • Posts: 1591
Re: What benefits come from rear chamber "tuning"
« Reply #13 on: December 15, 2004, 09:46:13 am »

Brad Litz wrote on Wed, 15 December 2004 00:23

Here's the predicted response. Sorry, I did not measure it.

index.php/fa/839/0/





OK thanks.

If the modeling program can export this graph as a text file (three columns of freq, magnitude and phase angle) then I would like that too.
Logged
Too Tall
        Curtis H. List    
             Bridgeport, Mich.   
        I.A.T.S.E. Local # 274 (Gold Card)
        Lansing, Mich
Independent Live Sound Engineer (and I'm Tall Too!)

Brad Litz

  • Jr. Member
  • **
  • Offline Offline
  • Posts: 96
v3.0 Data File
« Reply #14 on: December 15, 2004, 06:42:55 pm »

Here is a data file assuming the two drivers in a cabinet are wired in parallel and 2.75 volts applied. The data is for 1 cabinet in 1/8 space, 2 in 1/4 space, 4 in 1/2 space, or 8 flown (no horn extension).
Logged
Brad Litz

Too Tall (Curtis H. List)

  • Hero Member
  • *****
  • Offline Offline
  • Posts: 1591
Re: v3.0 Data File
« Reply #15 on: December 16, 2004, 09:46:56 am »

Brad Litz wrote on Wed, 15 December 2004 18:42

Here is a data file assuming the two drivers in a cabinet are wired in parallel and 2.75 volts applied. The data is for 1 cabinet in 1/8 speace, 2 in 1/4 space, 4 in 1/2 space, or 8 flown (no horn extension).



Thanks Brad,
Too Tall
Logged
Too Tall
        Curtis H. List    
             Bridgeport, Mich.   
        I.A.T.S.E. Local # 274 (Gold Card)
        Lansing, Mich
Independent Live Sound Engineer (and I'm Tall Too!)
Pages: 1 2 [All]   Go Up
 

Page created in 0.052 seconds with 18 queries.