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Old 24th February 2009, 07:40 AM   #1
jm_kzo is offline jm_kzo  France
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Default How do you guys measure your subs ?

Hi all bass gurus,

I am currently working on a 5.1 kit using a Beyma 10G40 and a B&C DE250 compression driver in a RCF H100 horn.

As I am finalising the x-over, I thought it was good time to start thinking about the .1 (that might turn into a .2). The mains are _meant_ to go down to 80Hz (possibly lower), but I think measuring is required to define my "bass target" (in this case, how high does it have to go based on my mains measurement, this could impact the number of sub and possibly the technology).

Previously, I mostly paid attention to the measures for my X-Over, now that I look at the bass, something seems flawed in my measurement method and it seems that a roll off is "introduced".

I started describing my problem here but thought that this was a better place.

I have been using SpeakerWorkshop (Panasonic WM61A cap + "Wallin" pre-amp) with a 11.5ms window placing the mic at 1m from the baffle. In this set up, the bass started to drop at 330Hz. I tried putting the mic further away (3m) and had to increase the SW window to 17ms... The bass then started to drop at 700Hz... for the exact same speaker.

The method seems flawed for bass.

How do you guys measure your subs ?
Any pointer welcome, many thanks in advance.
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Old 24th February 2009, 07:42 AM   #2
jm_kzo is offline jm_kzo  France
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PS : I did some forum research and googling, but with no luck...
So if it was obvious, please accept my apologies and do not "fry" me .
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Old 24th February 2009, 09:58 AM   #3
SY is offline SY  United States
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Nearfield measurements (Soundeasy) to see if the sub response is at the target.

In-room measurements (REW) at and near the listening position to see if my target was the right one.
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Old 24th February 2009, 08:17 PM   #4
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G'day Jean-Michel

I guess you've stumbled across one of the problems with making low frequency measurements. I use an MLS based system called IMP/MLS that I can set up for a ~2 second window, giving me ~0.5Hz resolution. These low frequency measurements are only usable up to ~500Hz and I need to do a sample rate change to get me up to 20KHz. The two measurements can then be merged to give frequency response from ~1Hz to 20KHz. With this very long window, there is no way to to remove room reflections, except for taking measurements very close to the source, thus swamping the response from the room. Alternatively the measurements can be taken out doors and away from any reflective surfaces to get a far field response.

Cheers

William Cowan
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Old 24th February 2009, 08:45 PM   #5
jm_kzo is offline jm_kzo  France
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Good day William (well, evening here ),

I tried to Google IMP/MLS but did not find any usefull link (one going back to your site ).

Is it a discontinued or confidential product ?

I am only interested in measuring below 200Hz.

I use gated response with SpeakerWorkshop and it seems to be OK above 200Hz, just what happens below is crazzy.

I tried not gated far field measuremebnt (still with SW) tonight, but it does not look conclusive either (curve is "erratic", needs loads of smoothing and does look bad anyway).

Nearfield measurement could be an option, as it looks better, the issue is that my system is vented and I am not sure if I can measure the event, the loudspeaker (both nearfield) and sum them... They are quite far apart anyway (the loudspeaker is 6dB louder than the event)...

Thanks for your tips anyway.
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Old 24th February 2009, 08:55 PM   #6
HK26147 is offline HK26147  United States
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Quote:
I tried to Google IMP/MLS but did not find any usefull link (one going back to your site ).
Try
http://www.linearx.com/
from:
http://www.fesb.hr/~mateljan/arta/links.htm

I don't know how you are going to get measurements of the bass ( sans the room reflections ) short of outdoor measurements ( away from boundaries )
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Old 24th February 2009, 08:56 PM   #7
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G'day again Jean-Michel

IMP/MLS was developed back in '92 and has been my measurement platform ever since: http://www.libinst.com/discontinued.htm It has been superseded by many much smarter systems.

Far field you will always see the response of the room, which is often nasty. A bit of smoothing will make the plots a bit easier to view.

Cheers

William Cowan
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