I bought one of the Cross Spectrum EMM-6 mics years ago and was surprised at how much correction was needed above 5K. I was also surprised that my original EMM-6 (serial #200) was actually pretty flat when compared to the calibrated mic. I think it's a crap shoot with the Dayton stuff - kind of like those DSP boxes.
And there will be another right over the red line with a tweeter in the top right corner.
Joey -
A few more questions for you:
- In the above picture you have the dimensions as
9 3/4" W X 6" H. In another
picture you show the box that the baffle fits into. Could you post the external dimensions (L,W,H) of the entire enclosure and the thickness of
the wood? If the baffle is thicker than
the rest of the box include that too.
- Do you plan on putting in a divider to separate
the woofer enclosures? I personally would
include it so the woofers don't interact. Think how a strong bass note in the left
channel would impact the right channel woofer.
YMMV. If you're running mono then
it's not important except for the extra bracing it gives.
- You also had a picture that included ports. Do you intend to go ported?
I did a few preliminary BS sims, but want to wait until I
get the exact dimensions from you.
Those dimensions are external, the baffle sits on that enclosure. Depth is 5.75". I'm forgetting thickness but will measure. 99% sure it's 3/8". Yes, there will be a divider for sure. I was going to do ported when I thought they were the bd01, but the bd02 didnt model well in the airspace for ported if I did winisd correctly.
Appreciate your help and time! Hopefully my mic gets here in the next day or two.
Hey, I have a Beringer mic and phantom power preamp I'm not using. If you wanna pay shipping I'll send it to ya. I will want it back eventually, but it'll get ya playing around till you decide if you want to get your own.
Those dimensions are external, the baffle sits on that enclosure. Depth is 5.75". I'm forgetting thickness but will measure. 99% sure it's 3/8". Yes, there will be a divider for sure. I was going to do ported when I thought they were the bd01, but the bd02 didnt model well in the airspace for ported if I did winisd correctly.
Appreciate your help and time! Hopefully my mic gets here in the next day or two.
So external L,W, H is 9.75 W X 6 H X 5.75 D. And if 3/8" wood, internal L, W H is 9 W X 5.25 H X 5 D. With the 3/8" divider each woofer gets about 113 in3 = 1.85 L gross. Now you have to subtract the space taken by the woofer, tweeter and anything else. The bulk of the space is taken by the woofer magnet and frame. Looking at the BD01 dimensions in the pdf you posted I come up with an estimate of about 0.2 L, leaving 1.65 L per woofer net.
I threw that information into WinISD along with the T/S parameters from the your posted pdf. The first attachment shows the response of a standard (Qtc = 0.707, cab = 5.7 L) alignment in blue and your alignment (Qtc = 1, cab = 1.65L) in red. You do lose some bass response, but that little hump around 150 Hz may give the effect of more bass that actually exists. Which is a good thing.
I then gave each alignment 10W (= 94 dB) and looked at the cone excursion. Same colors, blue for the standard alignment and red for your alignment. You can see a nice side effect of putting the BD01 in a smaller volume is that excursion is reduuced in the lower frequencies. 94 dB is quite loud and theoretically with two channels you'd be at 100 dB! So at lower (more sane) levels you have the option of judiciously using a bass control (if you have one) to bump up the bass a bit. I'd say the BD01 worked out quite well.
Next step is to run blender so we can calculate baffle step and create some decent input files for PCD.
Double Doh! The sims should be correct. Here's the T/S parameters I put into WinISD, entered parameters are green, blue parameters are calculated by WinISD. I enter MMS and BL and let WinISD calculate Fs and Vas. You can do it the other way around too. In any event, there's really a good match up between what WinISD calculates and the .pdf values. Which means Wavecor is doing a honest job.
though some manufacturers provide good numbers and parameters compared to others, and some brands and manufacturer have tighter tolerances and quality control, if you are not getting custom T/S specs and graphs and matched pieces (some manufacturers go to this step to provide the actual data of the price you are holding in your hand), you still need to run DATs or build a limp jig for the T/S specs.
even if you have the actual measurements, its always good to run a impedance sweep, especially for woofers as they might be sitting around for quite sometime and cone sag, break-in etc can change to the T/S specs - though they are related for eg. if the Fs goes down the Vas goes up, etc. Wavecor gives numbers before and after burn in, but your unit might vary a bit.
the Limp jig is very easy and cheap to build (requires a resistor and some wires) and the free Limp s/w. Haven't tried the new DATs, but is supposed to be easier (basically a fancier Limp jig with a nice UI).
that's pretty much all you need on the measurement side - T/S specs / impedance measurement - limp jig/DATs - FR measurement - microphone with Hols Response / REW / ARTA or Omni mic
- a lazy susan or a revolving stool also helps for off axis measurement - maybe a microphone stand - while you are at it, build a anechoic chamber in your basement - but i digress....!
100% correct Ani. I would definitely use my DATS to get the data. But since Joey was using IB files to do his simulations I assumed he didn't have any measurement gear, hence the use of the Wavecor T/S specs. Maybe I should just drop the simulation with IB files topic since he's going to order a mic and do measurements anyway. But free time is plenty these days so I'll continue my battles with windmills.
Anyhow, I have just come to the realization that good old Response Modeler is a better tool to use than Blender when modifying IB files for baffle step and diffraction effects. Here's what I found:
The Blender tool is more geared toward measurements and assumes the high frequency data (i.e. gated far field) has the baffle step data included. As a result, it limits the baffle step/diffraction data to modifications of the low frequency data only. 100% correct for near field measurements. But for IB files you need the baffle step/diffraction data applied to all the data, both the low (simulated cabinet response) and high (IB file). And this is how Response Modeler does it. You load the IB file into RM, calculate and splice in the low end cabinet response and apply the simulated baffle step to the whole works.
To be honest, I haven't used Blender until today. So if I'm missing something with it please correct me.
And Joey - let me know if you want to continue the simulation approach or just wait until you get measurement gear. Back to my windmills!
Response modeler doesn't include the tails so the phase can be off. Response modeler does a hard splice where the blender gives a smoother transition
I should have stated my previous post differently to make it more clear: "If simulating with IB files don't use Response Blender as it will give incorrect results, use Response Modeler instead." That's because Response Blender assumes the High Frequency data already has the baffle step and diffraction effects included, as it would with any gated far field measurement. But that assumption isn't true when IB files are used instead of measurements. Response Modeler just happens to apply the baffle step/diffraction differently (over the entire frequency range) which works with IB measurements.
You load the IB file to the LF tab to add the baffle. That creates the HF response if you want to go back and add the box.
I guess my unfamiliarity with Blender is showing. Too bad we're not at a get together discussing this over a couple of beers - we'd be done in a matter of minutes. And who knows how long it will be until the next get together?
I think I understand what you're saying, but I'm having trouble in the execution. I did something similar that worked: I loaded the IB file into RM, added just the baffle step and saved the file. I then used that as the HF data for blender and used the cabinet simulator and diffraction simulator for the LF. Finally I blended the two responses, added tails and created the minimum phase version. That gave me the identical frequency response as if I did everything in RM. The phase responses were somewhat different at higher frequencies and I assume the Blender phase is more accurate because of adding the tails.
So then I tried to do everything in Blender. First I loaded the IB file into the LF tab and then did the baffle diffraction tab. At that point I tried to save the file so I could load it into the HF tab which at this point is empty. I tried it two ways: 1. Do the minimum phase calculation and then save the file and 2. Just save the file. In both cases I get a VB run time error and the file just has the header comment lines.
So I should take the DATS, measure my drivers first? Then Blender, then PCD, then mount and measure?
First, use the DATS to create your impedance (.zma) files. The tweeter impedance can be measured either mounted in the cabinet or not. The woofer impedance should be done with the woofer mounted in the cabinet.
Then you take measurements, then Blender and finally PCD. You can then take more measurements with the crossover in place to verify everything. Jeff Bagby (RIP) explained everything better than I ever could in the attached paper. This is my copy where I highlighted what I thought were the most important points. If you find the highlights distracting I can post the original paper.
So then I tried to do everything in Blender. First I loaded the IB file into the LF tab and then did the baffle diffraction tab. At that point I tried to save the file so I could load it into the HF tab which at this point is empty. I tried it two ways: 1. Do the minimum phase calculation and then save the file and 2. Just save the file. In both cases I get a VB run time error and the file just has the header comment lines.
So what am I doing wrong? Thanks John!
Ed, see if the tails are actually showing before calculating min ph. You may have to adjust the low frequency tail tie-in point higher to get the low frequency tail to show. Same with the high frequency, you may need to adjust the high frequency tail tie-in point to 19,000 HZ to get the tail to show.
There is one item missing from Jeff's write up that I previously posted and that is how to measure acoustic offsets. He covered it this separate, much shorter article. Don't be shy posting any questions you have concerning the articles' content - we've all been through the learning curve.
Thanks Ed!! My mic just arrived and I'm eager to play. Hoping tonight to get some time in. I appreciate all your guys willingness. I feel comfortable, just need to get all the parts lined up and ready.
Some do and some don't. I like to clamp it in a vise so it's in a stable vertical position. Others go farther and put it in a panel (size doesn't mater) and clamp that in a vertical position. Yet others test it horizontally and just make sure that the vent hole in the magnet (if it exists) isn't blocked. You could try all three and see what differences come up.
Measuring a woofer in free air is step one for determining its Thiele/Small (T/S) parameters. It gives you basically all the parameters except Vas and SPL (IIRC). To calculate those you either build a small test box or add mass to the driver cone and retest. The basic idea is to shift Fs up enough (test box) or down enough (added mass) so DATS can calculate the missing parameters. AFAIK most people use the added mass method because it's easier to perform. In either case DATS requires that Fs moves a certain minimum percentage before it will accept the second test.
And of course there's the question of how best to break in the driver (or if it's even necessary) before testing it.
Ok. I have the enclosure basically done, but it is a sealed alignment. There is a hole in the bottom I can feed the leads through though. How sealed does it need to be? finished product tight or mostly?
Comments
I've gone back to the CSL calibrated EMM, no more USB for this boy - 2 channel is too useful.
Joey -
A few more questions for you:
- In the above picture you have the dimensions as 9 3/4" W X 6" H. In another picture you show the box that the baffle fits into. Could you post the external dimensions (L,W,H) of the entire enclosure and the thickness of the wood? If the baffle is thicker than the rest of the box include that too.
- Do you plan on putting in a divider to separate the woofer enclosures? I personally would include it so the woofers don't interact. Think how a strong bass note in the left channel would impact the right channel woofer. YMMV. If you're running mono then it's not important except for the extra bracing it gives.
- You also had a picture that included ports. Do you intend to go ported?
I did a few preliminary BS sims, but want to wait until I get the exact dimensions from you.
Yes, there will be a divider for sure. I was going to do ported when I thought they were the bd01, but the bd02 didnt model well in the airspace for ported if I did winisd correctly.
Appreciate your help and time! Hopefully my mic gets here in the next day or two.
I threw that information into WinISD along with the T/S parameters from the your posted pdf. The first attachment shows the response of a standard (Qtc = 0.707, cab = 5.7 L) alignment in blue and your alignment (Qtc = 1, cab = 1.65L) in red. You do lose some bass response, but that little hump around 150 Hz may give the effect of more bass that actually exists. Which is a good thing.
I then gave each alignment 10W (= 94 dB) and looked at the cone excursion. Same colors, blue for the standard alignment and red for your alignment. You can see a nice side effect of putting the BD01 in a smaller volume is that excursion is reduuced in the lower frequencies. 94 dB is quite loud and theoretically with two channels you'd be at 100 dB! So at lower (more sane) levels you have the option of judiciously using a bass control (if you have one) to bump up the bass a bit. I'd say the BD01 worked out quite well.
Next step is to run blender so we can calculate baffle step and create some decent input files for PCD.
even if you have the actual measurements, its always good to run a impedance sweep, especially for woofers as they might be sitting around for quite sometime and cone sag, break-in etc can change to the T/S specs - though they are related for eg. if the Fs goes down the Vas goes up, etc. Wavecor gives numbers before and after burn in, but your unit might vary a bit.
the Limp jig is very easy and cheap to build (requires a resistor and some wires) and the free Limp s/w. Haven't tried the new DATs, but is supposed to be easier (basically a fancier Limp jig with a nice UI).
that's pretty much all you need on the measurement side
- T/S specs / impedance measurement - limp jig/DATs
- FR measurement - microphone with Hols Response / REW / ARTA or Omni mic
- a lazy susan or a revolving stool also helps for off axis measurement
- maybe a microphone stand
- while you are at it, build a anechoic chamber in your basement - but i digress....!
Anyhow, I have just come to the realization that good old Response Modeler is a better tool to use than Blender when modifying IB files for baffle step and diffraction effects. Here's what I found:
The Blender tool is more geared toward measurements and assumes the high frequency data (i.e. gated far field) has the baffle step data included. As a result, it limits the baffle step/diffraction data to modifications of the low frequency data only. 100% correct for near field measurements. But for IB files you need the baffle step/diffraction data applied to all the data, both the low (simulated cabinet response) and high (IB file). And this is how Response Modeler does it. You load the IB file into RM, calculate and splice in the low end cabinet response and apply the simulated baffle step to the whole works.
To be honest, I haven't used Blender until today. So if I'm missing something with it please correct me.
And Joey - let me know if you want to continue the simulation approach or just wait until you get measurement gear. Back to my windmills!
I have a DATS that supposedly runs off V2. I need to try it today for another BT radio I've built for a one off nd105 (or 140....I always forget..)
Mic should be here today or tomorrow.
I've downloaded PCD and the Blender.
So I should take the DATS, measure my drivers first? Then Blender, then PCD, then mount and measure?
I think I understand what you're saying, but I'm having trouble in the execution. I did something similar that worked: I loaded the IB file into RM, added just the baffle step and saved the file. I then used that as the HF data for blender and used the cabinet simulator and diffraction simulator for the LF. Finally I blended the two responses, added tails and created the minimum phase version. That gave me the identical frequency response as if I did everything in RM. The phase responses were somewhat different at higher frequencies and I assume the Blender phase is more accurate because of adding the tails.
So then I tried to do everything in Blender. First I loaded the IB file into the LF tab and then did the baffle diffraction tab. At that point I tried to save the file so I could load it into the HF tab which at this point is empty. I tried it two ways: 1. Do the minimum phase calculation and then save the file and 2. Just save the file. In both cases I get a VB run time error and the file just has the header comment lines.
So what am I doing wrong? Thanks John!
First, use the DATS to create your impedance (.zma) files. The tweeter impedance can be measured either mounted in the cabinet or not. The woofer impedance should be done with the woofer mounted in the cabinet.
Then you take measurements, then Blender and finally PCD. You can then take more measurements with the crossover in place to verify everything. Jeff Bagby (RIP) explained everything better than I ever could in the attached paper. This is my copy where I highlighted what I thought were the most important points. If you find the highlights distracting I can post the original paper.
Bagby White Paper - Accurate In-Room Frequency Response to 10Hz.pdf
There is one item missing from Jeff's write up that I previously posted and that is how to measure acoustic offsets. He covered it this separate, much shorter article. Don't be shy posting any questions you have concerning the articles' content - we've all been through the learning curve.
Finding the Relative Acoustic Offset in PCD .pdf
I feel comfortable, just need to get all the parts lined up and ready.
Measuring a woofer in free air is step one for determining its Thiele/Small (T/S) parameters. It gives you basically all the parameters except Vas and SPL (IIRC). To calculate those you either build a small test box or add mass to the driver cone and retest. The basic idea is to shift Fs up enough (test box) or down enough (added mass) so DATS can calculate the missing parameters. AFAIK most people use the added mass method because it's easier to perform. In either case DATS requires that Fs moves a certain minimum percentage before it will accept the second test.
And of course there's the question of how best to break in the driver (or if it's even necessary) before testing it.