Microphone placement for speaker measurement?

[Fivetide]

Hi, need a bit of advice. I’m about to do an upgrade on my speakers. What I want to do is measure the sound using a microphone before and then after the upgrade. But I’m a bit confused about where I put the microphone, I don’t want to measure the room acoustics as such, just the quality of upgrade. I have a none calibrated ECM8000 Measuring Microphone, small stand and a laptop. I have run the audio out of the laptop into a RC cable into the amp. Seeing some articles they say do one speaker at a time and from your listening position? But I want to try and cut down any interference from my room so that its standard comparison. So should I place the microphone say a foot away between the mid and top? Or is there some well-defined way of achieving what I want ?

[audiomik]

Don't know which software you are using but using similar techniques to AP in this link AP High Performance Audio Analyzer & Audio Test Instruments : Loudspeakers might be useful
Mik

[Pano]

It all depends on what you want to measure, but the standard distance is 1 meter. Often 50 cm is used and the results interpolated to 1M.

50 cm might be a good option for you to exclude room effects - unless your speakers are large or open baffle.

[weltersys]

Originally Posted by Fivetide

Hi, need a bit of advice. I’m about to do an upgrade on my speakers. What I want to do is measure the sound using a microphone before and then after the upgrade. But I’m a bit confused about where I put the microphone, I don’t want to measure the room acoustics as such, just the quality of upgrade. I have a none calibrated ECM8000 Measuring Microphone, small stand and a laptop. I have run the audio out of the laptop into a RC cable into the amp. Seeing some articles they say do one speaker at a time and from your listening position? But I want to try and cut down any interference from my room so that its standard comparison. So should I place the microphone say a foot away between the mid and top? Or is there some well-defined way of achieving what I want ?

You need to define what you want.
"One speaker at a time and from your listening position" will measure the speaker and room.

"The microphone say a foot away between the mid and top on a small stand" will measure the on axis response, but still will introduce floor reflections if measured on the floor. At only one foot, very small differences in mic placement may make rather large FR differences.

To effectively measure "before and after", measure outdoors, speaker and mic away from any objects by a wavelength or so, and measured at a meter or two, so the angle difference between drivers is lessened.

Practically, you may find it difficult to get the speaker and mic up high enough to eliminate ground bounce, so you can do a second measurement with the speaker and the microphone on the ground (half space measurement). The microphone can be layed on a thin piece of foam or a towel, or a mic stand adjusted so the capsule is as close to the ground surface as possible.
Wind screens are advisable for outdoor measurements, and if there is wind, take several readings to average.

At any rate, do exact measurements of the speaker and mic placement so the experiment can be repeated exactly.

As an example of location difference, testing woofers outdoors about 2 meters from my shop, mic at one meter, reads 4 dB higher in the octave around 40 Hz than the same test done done 10 meters from any building.

Art

[Wavebourn]

Standard measure in decibels per 1W / 1M does not mean it is measured on 1M distance. Usually frequency patterns are measured on many different distances, in many places. Of course, in anechoic camera. For DIY it is too expensive, so some far from civilization field in quiet day can be used instead.

[Fivetide]

Originally Posted by Pano

It all depends on what you want to measure, but the standard distance is 1 meter. Often 50 cm is used and the results interpolated to 1M.

50 cm might be a good option for you to exclude room effects - unless your speakers are large or open baffle.

Thanks Pano, that’s really about the answer I need, I don’t think its practical to take one outside , this is England and winter, we pray for at least one day without rain ! lol My main room is not to large and fairly uncluttered so I think I will go with the 1 meter tests and basically just keep repeating them as I build the speakers, they are RTL TDL 2's and this is the list of replacement parts I bought from Falcon Acoustics

2 no. Scanspeak 18W 8545-00
2 no. Scanspeak D2905/970000
2 no. D2905/970000 version crossovers
Crossover Assembly ( 1 no) ClarityCap ESA250V caps
6 sheet Dead sheet 375 x 2m
BAF wadding (970mm width)
6m 079 cable
18 eggcrate acoustic tile
4 no. Prs Falcon GoldP Terminal Sets

Jerry at falcon has assembled one of the crossovers and I will get the other as a kit, I want to learn basic electronics so I can use his built one as a template for building the other and at the same time work out what everything is on the schematics.


This is the reason I want to measure them to see if it makes the almaighty difference to the sound and also to post the graphs on here to see if people can point out any more improvements I can make.


There will also be gluing and screwing involved.. or is that my other hobby !!?