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Old 30th August 2011, 03:22 AM   #531
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Quote:
Originally Posted by Pano View Post
Sweep or MLS will give you the same impulse, or close enough. Yes, they well respond differently because they are filtered high and low. Even without a crossover they still roll off top and bottom. If you lock the time in Holm you'll be able to see that.
Ok..it should be straight forward to "time align" the left and right speakers (same speaker size) to the desired listening position. However, what is the best approach to time align the sub, midbass, and midrange +tweeters? For staging, I would like the peaks to be aligned. Thanks Pano.
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Old 30th August 2011, 04:16 AM   #532
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You're welcome.

I would suggest running sweeps of all the section without crossovers first. Be careful of the tweeter, of course! (You can limit the sweeps in HOLM.) This will give you a good picture not only of each driver's raw FR, but the distortion as well. Seeing the distortion can help when picking crossover points.

Once you've done that, we can look at what you've got and proceed from there. Often it's not just aligning the impulse but flipping polarity as well.
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Old 30th August 2011, 04:39 PM   #533
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Default Is it possible to get absolute dB measurements?

I've noticed that everyone's F-R graphs have only negative values on the Y-axis. Is it possible, maybe by using an SPL meter to calibrate, to plot the actual SPL at the microphone location?
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Old 30th August 2011, 04:43 PM   #534
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HOLM does not do absolute SPL levels, there is no calibration. REW is pretty easy to use if you want SPL values.

Honestly there is no need to do SPL levels since they are all relative. We only need to know the difference in SPL levels between drivers.
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Old 31st August 2011, 07:21 PM   #535
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Default Plots to determine cross over points..

Ok, so taking Pano's suggestion, I measured frequency response plots from the drivers without xovers. These are right side drivers only.

The exception is the tweeter which has to be on a passive crossover to make a 4 way system. I only have a 6 channel amp w/ 6 channels from the processor. So, I plotted midrange w/ tweeter, but I don't have any control on that crossover point.

Here's the three plots:

1) Midrange to tweeter
Sine sweep starts at 100 Hz
Red curve - midrange
Blue curve - tweeter
2) Midbass and midrange
Sweep sweep starts at 20 Hz
Green curve - mid bass
Red curve midrange
3) Sub and midbass
Sine sweep starts at 10 hz
black curve - sub
green curve - midbass

Observations: To my novice eyes, I believe I am not far off from optimal xover points. Baseline from sub to midbass at ~80 hz and midbass to midrange ~300 Hz.

Would you suggest crossing over lower from 80hz? Maybe 70hz?
Is 400 Hz better than 300 Hz?
Any suggestions on best method to determine xover slopes? thx.
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Last edited by bginvestor; 31st August 2011 at 07:25 PM.
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Old 1st September 2011, 02:52 PM   #536
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I'm looking and thinking. Someone else will probably jump in. This might be worth it's own thread.
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Old 3rd September 2011, 06:07 AM   #537
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Default still can't export FRDs from HOLM

Quote:
Originally Posted by doug20 View Post
How do we export .FRD files from HOLM?

Nevermind, I just need to export the txt file and rename it FRD
I found this old post from March 2010, in which someone renamed a text file "FRD" file and SpeakerWorkshop imported it. I remember long ago file types were defined by the file extension. The modern versions of windows don't seem to use that system anymore. Files don't have extensions. Changing a text file, and adding ".FRD" on the end does not allow Speakerworkshop to import it. SW still recognizes it as a text file. Does anyone know how to get HOLM Impulse to export a FRD file with the modern versions of windows? HOLM Impulse is pretty worthless without this ability.
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Old 6th September 2011, 03:01 AM   #538
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Quote:
Originally Posted by Pano View Post
I'm looking and thinking. Someone else will probably jump in. This might be worth it's own thread.
In terms of choosing the x-over slopes, I decided to assess this empirically. My chosen x-over cut-off frequency is 400hz. In the attached graph, I measured the "right" channels using various db slopes..

I found that a 12db/oct slope provides a smooth transition.

I am very curious where the peak between 300 hz and 400 hz is coming from. Unfortunately, my processor cannot tame this peak using a parametric eq.
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Old 6th September 2011, 03:04 AM   #539
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I don't see a peak, I see a dip. Since it's mostly on the 4th order, it could be underlap or just a polarity reversal. Did you try a polarity swap on one driver?
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Old 6th September 2011, 07:08 PM   #540
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Oops, my comment on the peak is between 200 to 300 hz..

I'll check sensitivity on polarity. I don't have underlap, actually, its overlap, both LP & HP are set at 400hz. I increased the LP on the midbass since it really helped the sound stage. My midranges are known for not being the best w/ sound dispersion, however, the sound quality is excellent. thx.

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I don't see a peak, I see a dip. Since it's mostly on the 4th order, it could be underlap or just a polarity reversal. Did you try a polarity swap on one driver?
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