Hi To All,
I finally took the plunge and bought a measurement mic (Umik1) and after some setup headaches, I was finally able to capture my very first measurement. Everything is set up using Room EQ Wizard. My lack of understanding is where do I gate the IR given the attached screenshots. All the examples I have seen, there is a logical spot to gate the measurement around 4-5 ms. Any explanations will help in understanding what I'm looking at or what I should be looking for.
Best Regards,
Rich
I measure rightly or wrongly -12db frequency sweeps at upon check levels (REW)
If signal is distorted a pop up box tells you distortion detected pressing ok and then looking at frequency response graph can show a nice flat response
Click on to distortion and it is terrible
Thanks Charlie,
I'm starting to gain somewhat of an understanding of taking measurements and working in REW. Draki, had some great pointers in setting up in REW that was very helpful. Still much to learn but its been a fun pursuit while laid off work for the winter. That all comes to an end in about 3 weeks so I better get busy and finish the projects I've started.
Best,
Rich
I'm starting to gain somewhat of an understanding of taking measurements and working in REW. Draki, had some great pointers in setting up in REW that was very helpful. Still much to learn but its been a fun pursuit while laid off work for the winter. That all comes to an end in about 3 weeks so I better get busy and finish the projects I've started.
Best,
Rich
Smoothing and gating are used for completely different purposes. If you want measurements without room effects you have to set your gate time so that the first reflection is not in the measurement. You can calculate this based on speed of sound and minimum path length. It is preferable for me to just look for the obvious reflection as the first large bump following the impulse response. I've designed quite a few speakers and always get better results the first time by measuring at about 6 feet when I can get the speaker far enough away from everything. You should be far enough away that all drivers have summed. 6 feet for most two ways is sufficient. So the accuracy of anything below 300hz or so is not usable using this method. I have tried splicing near field several times but the rigor required to get reliable phase data is hard to pull off. Instead I do a ground plane measurement just to see how 20hz to 300hz relates to the rest of the response. I do NOT splice the ground plane measurement but just look at it while designing crossover in simulation. Some people might have luck with spliced near field but it's not for me. I'm not alone in this...
All that said, there are valid reasons to measure room reflections and consider them in the design of loudspeakers. That is a complex topic that could likely spin off lots of debate
Smoothing is just what it sounds like. If memory serves, psychoacoustics studies say it's hard for humans to detect frequency response peaks and nulls that cover less than 1/3 octave. I usually try to hit my target response at 1/3 octave first and then optimize at 1/12 octave. Any finer smoothing isn't really telling you anything useful toward a goal of a well designed speaker.
All that said, there are valid reasons to measure room reflections and consider them in the design of loudspeakers. That is a complex topic that could likely spin off lots of debate
Smoothing is just what it sounds like. If memory serves, psychoacoustics studies say it's hard for humans to detect frequency response peaks and nulls that cover less than 1/3 octave. I usually try to hit my target response at 1/3 octave first and then optimize at 1/12 octave. Any finer smoothing isn't really telling you anything useful toward a goal of a well designed speaker.
I take measurements with a mic height half way between the tweeter and woofer acoustic centers so that path length is equivalent. In this way you don't need to worry about offset. You can't always do this bit for 2 ways with a single woofer it is easier. This may go without saying but, you should never move the speaker or mic between the tweeter and woofer measurements.^Here is the beginning of xover design from measurements above. I used PCD7 to find correct offsets then imported summed response into Xsim and adjusted delay until lines overlayed perfect (1.71 in.). Hope I'm going about this the proper way. I welcome any comments that will help me learn at little more about measurements and xover design.
Best,
Rich
One last point, take a look at the response plots on Troels Gravesen's site. You will notice most of his speakers have a slight downward slope. Flat frequency response or a rising high frequency response is not the goal for me. While Harman group studies by Floyd Toole say users prefer flat response, I can't say crowds favorite speakers at audio shows have linear frequency response....
Post #19 first impulse. Just after and starting just before 2.5ms there appears to be a blip. I assume your speakers are not 2m wide, maybe it is something to try taking out.
R1 should be parallel to the tweeter, after the HP filter. Or, complete L-pad (R3 and R1) should be between the HP filter and the tweeter.
Hi Ralf,
I'm getting a couple small blips prior to 8ms but the first large reflection is right at that exact spot you figured. Should I worry about very small blips that do not seem to effect FR once gated? Also, can a person test HP and LP filters to see if the xover design done by simulation matches up in real world (dumb newbie question)? The reason for this question is I tried a LP filter to compare with my raw measurement of SS 18W/8434G mid woofer and there was no differences in the 2 graphs using overlays in REW.
Thanks So Much,
Rich
I'm getting a couple small blips prior to 8ms but the first large reflection is right at that exact spot you figured. Should I worry about very small blips that do not seem to effect FR once gated? Also, can a person test HP and LP filters to see if the xover design done by simulation matches up in real world (dumb newbie question)? The reason for this question is I tried a LP filter to compare with my raw measurement of SS 18W/8434G mid woofer and there was no differences in the 2 graphs using overlays in REW.
Thanks So Much,
Rich
Absolutly you can (and should) do measurements to compare the real world implementation of the crossover with the simulation of the same. If you get a close match then you can be sure that your measurements are good.
What I do.
Set everything up ready to measure. Once you have levels set and mic position don't change anything.
Measure the tweeter. Once I have the tweeter measurement I lock time zero in Holm (not sure if there is an equivalent in REW) so that the driver offset is part of the measurements.
Measure the woofer.
Measure with the crossover.
Now you run the woofer and tweeter measurements through your sim and compare to the measurement of the crossover.
You can also compare measured crossover to previous measurements in the sim but since any differences in setup will likely cause small differences doing it as above (ie all measurements done at the same time) is the best way to sanity check
Tony.
What I do.
Set everything up ready to measure. Once you have levels set and mic position don't change anything.
Measure the tweeter. Once I have the tweeter measurement I lock time zero in Holm (not sure if there is an equivalent in REW) so that the driver offset is part of the measurements.
Measure the woofer.
Measure with the crossover.
Now you run the woofer and tweeter measurements through your sim and compare to the measurement of the crossover.
You can also compare measured crossover to previous measurements in the sim but since any differences in setup will likely cause small differences doing it as above (ie all measurements done at the same time) is the best way to sanity check
Tony.
Thanks Tony,
Your method makes perfect sense. I will give it a try. I'm still at a loss trying to figure out why there was no evidence of woofer roll off with LP filter in place. I must be missing a step somewhere. Well, maybe I'll stumble upon the answer as I get more familiar with REW.
Best Regards,
Rich
Your method makes perfect sense. I will give it a try. I'm still at a loss trying to figure out why there was no evidence of woofer roll off with LP filter in place. I must be missing a step somewhere.
Well, maybe I'll stumble upon the answer as I get more familiar with REW.Best Regards,
Rich
Was the filter the one you showed earlier in the sim, with approx 2.3Khz crossover frequency?
Even with only the first coil you should be seeing quite a difference between with and without measurements.
Are you sure you didn't mix up the measurements and actually have overlayed two measurements of the raw woofer?
I'd start out simple, just put one coil on the woofer and compare, and see what you get.
Tony.
Even with only the first coil you should be seeing quite a difference between with and without measurements.
Are you sure you didn't mix up the measurements and actually have overlayed two measurements of the raw woofer?
I'd start out simple, just put one coil on the woofer and compare, and see what you get.
Tony.
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