I am looking through a couple of box and crossover simulators and they ask for frd and zma files. I have WT3 and Omni-mic so that is not a problem, but I am wondering about the test set-up for generating the files.
Most speaker data is free air, but it seems to me the sims would work best if the curves were generated under actual working conditions - ideally, in the actual cabinet in a half or quarter space environment.
The question is would this give more accurate results, or do the simulators presume free-space measurements and try to modify the free space curves as part of the simulation??
I would assume it assumes free space measurements, but none of the programs I have looked at actually specify, and I would think it would be more accurate if one could import 'actual condition' curves - but again I can find no ready answers.
Can anybody sort this out??
Most speaker data is free air, but it seems to me the sims would work best if the curves were generated under actual working conditions - ideally, in the actual cabinet in a half or quarter space environment.
The question is would this give more accurate results, or do the simulators presume free-space measurements and try to modify the free space curves as part of the simulation??
I would assume it assumes free space measurements, but none of the programs I have looked at actually specify, and I would think it would be more accurate if one could import 'actual condition' curves - but again I can find no ready answers.
Can anybody sort this out??
Well, PDC asks for both frd and zma, so I should use actual cabinet curves for that...?
I ask because for one thing my tweet is a horn, so what you see is what you get (other than baffle step, which is actually below tweet in this project), so I have to think 'real' curves for the rest of the drivers (3-way design) would be called for as well... yes?
Hi LafeEric,
I build my cab (sometimes even finish it) and install the drivers. I then take my speaker outside and put it on a ladder at least 2m in the air. I then prop my microphone up there as well and take frequency response measurements. I use the bi-amp terminals on my boxes because it makes this part a lot easier, and testing cross overs easier also.
Doing it this way shows the baffle step and diffraction properly. I've done it inside many times and it works just fine as well. Just set your gate time carefully. I once measured about 4m above the ground and my raw measurements were nearly identical to my gated measurements. But inside that's never the case.
In short, yes, take the measurements in the cab. While you're at it, find the relative acoustic offset for setting up PCD properly if using a minimum phase approach. If not, then just import the measurements directly (if you haven't moved your microphone) and don't use the geometry functions in PCD.
I've used PCD a fair amount, so let me know if you have any questions regarding the setup. I have lots of screen shots. And pictures of my outdoor measurements too. Good luck.
I build my cab (sometimes even finish it) and install the drivers. I then take my speaker outside and put it on a ladder at least 2m in the air. I then prop my microphone up there as well and take frequency response measurements. I use the bi-amp terminals on my boxes because it makes this part a lot easier, and testing cross overs easier also.
Doing it this way shows the baffle step and diffraction properly. I've done it inside many times and it works just fine as well. Just set your gate time carefully. I once measured about 4m above the ground and my raw measurements were nearly identical to my gated measurements. But inside that's never the case.
In short, yes, take the measurements in the cab. While you're at it, find the relative acoustic offset for setting up PCD properly if using a minimum phase approach. If not, then just import the measurements directly (if you haven't moved your microphone) and don't use the geometry functions in PCD.
I've used PCD a fair amount, so let me know if you have any questions regarding the setup. I have lots of screen shots. And pictures of my outdoor measurements too. Good luck.
Ah! That sounds like my situation, pretty much. Not sure how I'm going to hoist a 220 liter cab up on a ladder, but I'm sure I'll figure out something.
I was thinking room modes perhaps should be figured in there too, but you're right, best to know what the speaker is doing, and each driver, and go from there.
I was looking at figuring out the acoustic offset by looking at the impulse response from the Omni-mic. I already have the mid and tweet horn baffle mounted, I just haven't run the test yet.
It's all first time for me, so I really appreciate the offer of help. I'm sure I'll have a few questions.
I was thinking room modes perhaps should be figured in there too, but you're right, best to know what the speaker is doing, and each driver, and go from there.
I was looking at figuring out the acoustic offset by looking at the impulse response from the Omni-mic. I already have the mid and tweet horn baffle mounted, I just haven't run the test yet.
It's all first time for me, so I really appreciate the offer of help. I'm sure I'll have a few questions.
Here is a good way to find relative offset: Finding Relative Acoustic Offsets Empirically
I think lots of people think it's best to measure in the room they'll be listening in to capture the room effects, but it's not the right approach. At least I haven't found a way to do it well. Unfortunately the room swamps the microphone with reflections and you end up with unworkable responses. A big speaker like that would be hard to measure indoors without high ceilings.
Best to get a helping hand hoist it onto your ladder and then gate the measurement with respect to the height. Most likely good response down to 100hz. A big speaker might need to be measured at 2m also.
Good luck.
I think lots of people think it's best to measure in the room they'll be listening in to capture the room effects, but it's not the right approach. At least I haven't found a way to do it well. Unfortunately the room swamps the microphone with reflections and you end up with unworkable responses. A big speaker like that would be hard to measure indoors without high ceilings.
Best to get a helping hand hoist it onto your ladder and then gate the measurement with respect to the height. Most likely good response down to 100hz. A big speaker might need to be measured at 2m also.
Good luck.
Definitely a helping hand if at all possible.
Put the cab in a rope sling that it sits in securely and stabley. Use strategically placed towels, bound round the rope with string, to protect anything that needs it. Have your hauling rope join the sling well above the centre of gravity of the cab.
Lead the rope up the ladder and take a turn around something solid. Then back down to ground level and another turn around something there. Be clear how you'll tie it off securely.
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