A HOLM starter guide

[rpb]

Re: A HOLM starter guide

Need to add a quick discussion on (or link to) measurement tips and how they effect the measurements and subsequent use in PCD or other software.

I'm still learning but something like...

Show curves measured at high and low volume to illustrate background noise level in room. Is 20dB above background enough? Perhaps not. Do you need 80dB? I don't think so.

Wear ear muffs. You need them for woodworking anyway.

Locate driver mid-way between floor and ceiling to minimize floor/ceiling bounce. Locate away from boundaries to minimize early reflections. Illustrate with curves from good and bad examples?

How to measure low frequency....mic at driver? Ground plane? Need to splice into full-range measurements.

Use consistent amp level (and input recording levels) when measuring a driver set. Tips for getting same level from analog level control (use reference driver/distance and adjust to same measured output?). Don't forget to defeat tone controls, DSP, subwoofer, and other active speaker channels. Flat is where it is at.

Use consistent mic and driver locations to get repeatable measurements. Measure mic location (horizontal and vertical) and driver locations to get horizontal and vertical offsets for use in PCD.

I'm trying to limit the scope of this guide to taking measurements with HOLM.

Information on measurement technics is already available. I will include some of that here, but mostly I want this to be a starter guide to get HOLM working. If anyone has some links to more information on measuring, I'll include them in the guide.

[50 watt head]

Re: A HOLM starter guide

RPB, this is a very helpful tuturial. You've done a great job organizing the information, esp. the screenshots.

[jeff_free69]

Re: A HOLM starter guide

If I have a mic(Shure PG48) and external sound card(Creative X-Fi) that work well together, will a mic preamp still be necessary? Or, does it need to be an OmniMic or something similar and a mic preamp

Any measurements are likely to be seriously flawed if you don't use a calibrated mic, especially when compared to a vocal mic (typically designed to boost above 1-2 k)

I can't see any reason not to mention something like this up front.

http://www.parts-express.com/pe/showdetl.cfm?Partnumber=390-801

That doesn't mean its expensive or of world-class quality; its just been measured and you load the supplied data so your program can compensate.

[donradick]

Re: A HOLM starter guide

Thanks RPB - looking good!
I appreciate the effort and thought this is taking, and it will be a great "idiot's guide" or "getting started" reference when done.

[rpb]

Re: A HOLM starter guide

Any measurements are likely to be seriously flawed if you don't use a calibrated mic, especially when compared to a vocal mic (typically designed to boost above 1-2 k)

I can't see any reason not to mention something like this up front.

http://www.parts-express.com/pe/showdetl.cfm?Partnumber=390-801

That doesn't mean its expensive or of world-class quality; its just been measured and you load the supplied data so your program can compensate.

I use an ECM8000, but it is not calibrated. I consider it accurate bassed on things I measure and listen to.

[jeff_free69]

Re: A HOLM starter guide

Hopefully you got one of the original ECMs.

I have / had one of those, before it died (behringer!). It was not one of the originals and by the time I got one they totally changed the performance. i had it calibrated by a third party and it was much more like a typical recording mic with several dbs of mid - hi boost; nowhere near the published spec / graph any more. Fortunately you can now buy the calibrated version from dayton for the same price.

[killa]

Re: A HOLM starter guide

Yay! holm to frd file is up:D thanks rpb and Ryan! Is there a way to put shorcuts in a thread? It would be cool if Tech talk allowed you to add something like that in the first post. also to the mods. Could you make this a sticky? Might help people to decide to get measurement equipment;)

[rpb]

Re: A HOLM starter guide

Yay! holm to frd file is up:D thanks rpb and Ryan! Is there a way to put shorcuts in a thread? It would be cool if Tech talk allowed you to add something like that in the first post. also to the mods. Could you make this a sticky? Might help people to decide to get measurement equipment;)

It's half way up, and out of order. Ryan sent me the files, but I have to figure out where the pictures go. So it's a little out of whack currently, but eventually, it will be right.

[ryanbouma]

Re: A HOLM starter guide

oh sorry. Thats my fault. Ive been a little busy and emailed rpb the files in a frenzy. Send me an email/pm if you need some clarification rpb.

[rpb]

Re: A HOLM starter guide

The process of uploading and posting would have got them out of order regardless. I need to actually make a FRD file a few times, then it will be easier.

[rpb]

Re: A HOLM starter guide

Yay! holm to frd file is up:D thanks rpb and Ryan! Is there a way to put shorcuts in a thread? It would be cool if Tech talk allowed you to add something like that in the first post. also to the mods. Could you make this a sticky? Might help people to decide to get measurement equipment;)

The guide is only one page. I can add a note to the first post saying that making a FRD file is included.

[ernperkins]

Re: A HOLM starter guide

I used to do the Excel conversion, but found an easier way. I just add an offset of 90 dB before I export the file. The trace will go off the screen, but will export correctly. I adjust my settings so I get a max of -5 dB in Holm which ends up to 85 dB with the offset. That level seems to work fine when the file is used in PCD. After the export is done I change the offset back to 0 dB and the plot re-appears in Holm.

Just my 2-cents,
Ed

[rpb]

Re: A HOLM starter guide

I used to do the Excel conversion, but found an easier way. I just add an offset of 90 dB before I export the file. The trace will go off the screen, but will export correctly. I adjust my settings so I get a max of -5 dB in Holm which ends up to 85 dB with the offset. That level seems to work fine when the file is used in PCD. After the export is done I change the offset back to 0 dB and the plot re-appears in Holm.

Just my 2-cents,
Ed

Like this?

[ryanbouma]

Re: A HOLM starter guide

I used to do the Excel conversion, but found an easier way. I just add an offset of 90 dB before I export the file. The trace will go off the screen, but will export correctly. I adjust my settings so I get a max of -5 dB in Holm which ends up to 85 dB with the offset. That level seems to work fine when the file is used in PCD. After the export is done I change the offset back to 0 dB and the plot re-appears in Holm.

Just my 2-cents,
Ed

This is a quick and easy way to do it, and is shown in short form in the tutorial. Most of the steps described are still required. Like exporting a txt and such. Depends on your measurements. If you have a horn tweeter or something, the excel way is likely necessary. If you don't care about total SPL, then this way cuts out a few steps.

Check out the very end of the PCD part of the tutorial where I explain that. Thanks for pointing it out.

[50 watt head]

Re: A HOLM starter guide

I haven't dived into all of the technical details yet, but -- it might be easier to use Response Modeler to adjust the overall SPL of an FRD once you've created it?