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 Post subject: measuring sound levels
PostPosted: Tue Nov 25, 2008 6:04 am 
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Joined: Wed Nov 28, 2007 6:24 am
Posts: 3
Location: Brampton, ON, CA
Hello
I picked up a device to measure sound levels from The Source store (we don't have Radioshack anymore) and had a go at measuring my listening room...
Using some instructions from the ‘net’ and Stereophile test CD 2; I used the pink noise track to get 80 dB at my listening position and then set about recording the sound pressure values at various frequencies. The ‘net’ instructions said that I really wanted to get as close to 80 db at all frequencies and I was pleased to see that for the most part (give one or two db) I did. However there were certain frequencies where this was not the case these were:
20 Hz (85.4 db)
25 Hz (85.7 db)
40 Hz (70.7 db)
63 Hz (87.1 dB)
800 Hz (86.3 dB)
10 KHz (87 dB)
12.5 KHz (86 dB)
16 KHz (76 db) not that I could hear much at this point Â…
20 KHz (40 db)

IÂ’m assuming these differences are caused by how sound reacts to my room and I was wondering if these figures are still acceptable and if not anyone can suggest what I should try to improve things? My listening position is pretty much fixed (give or take a foot or two) but I could move the speakers (Dynaudio Focus 110s and a MJ 100 sub). The room is approx 10.5ft x17.5ft x 8ft and has some acoustic treatments.

Any suggestions would be most appreciated

Many thanks

Steve


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PostPosted: Tue Nov 25, 2008 10:03 am 
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Joined: Sun Feb 26, 2006 8:24 am
Posts: 478
Location: San Miguel de Allende, , MX
Hi Steve

That seems to be useful information. Your room dimensions are quite similar to mine, I'm curious about your speaker and listening chair positions. While it may vary with speaker design it would be interesting to compare to my own setup....Thanks

Rick


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PostPosted: Tue Nov 25, 2008 12:08 pm 
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Joined: Sun Jan 16, 2005 8:59 am
Posts: 2769
Location: Dundas, ON, CA
Vifferboy wrote:
Hello
I picked up a device to measure sound levels from The Source store (we don't have Radioshack anymore) and had a go at measuring my listening room...
Using some instructions from the ‘net’ and Stereophile test CD 2; I used the pink noise track to get 80 dB at my listening position and then set about recording the sound pressure values at various frequencies. The ‘net’ instructions said that I really wanted to get as close to 80 db at all frequencies and I was pleased to see that for the most part (give one or two db) I did. However there were certain frequencies where this was not the case these were:
20 Hz (85.4 db)
25 Hz (85.7 db)
40 Hz (70.7 db)
63 Hz (87.1 dB)
800 Hz (86.3 dB)
10 KHz (87 dB)
12.5 KHz (86 dB)
16 KHz (76 db) not that I could hear much at this point Â…
20 KHz (40 db)

IÂ’m assuming these differences are caused by how sound reacts to my room and I was wondering if these figures are still acceptable and if not anyone can suggest what I should try to improve things? My listening position is pretty much fixed (give or take a foot or two) but I could move the speakers (Dynaudio Focus 110s and a MJ 100 sub). The room is approx 10.5ft x17.5ft x 8ft and has some acoustic treatments.

Any suggestions would be most appreciated

Many thanks

Steve


Hi Steve,

Before ya get too concerned about the high frequency roll-off, you've gotta understand that inexpensive SPL meters use cheap microphone capsules and aren't calibrated for flat response. These cheap meters feature a response that droops significantly in the top and bottom octaves. A calibrated hand-held SPL meter capable of accurate 20hz-20khz measurement is waaay more dough than anything The Source or Radio Shack have to offer.

Now the RS SPL meter's drooping frequency response issues were sufficiently consistent, unit-to-unit, that reasonably accurate correction tables could be and were created for it. Here are the tables for the original analog RS Meter for example. These correction factors applied to your RS meter measurements were a much closer reflection of reality.

You need to do a little research to find out whether The Source is selling the same meters that RS was selling to determine whether the available RS Meter correction tables are applicable. If so and it is the currently common digital version 'o the meter, then do a Google search to locate the appropriate correction table.

Happy Trails!
Vince@Freewheelcycle.com

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"Live fast. Ride hard... and have a good looking bike!"


Last edited by MTB Vince on Tue Nov 25, 2008 2:26 pm, edited 1 time in total.

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PostPosted: Tue Nov 25, 2008 2:01 pm 
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Joined: Wed Nov 28, 2007 6:24 am
Posts: 3
Location: Brampton, ON, CA
ford07 wrote:
Hi Steve

That seems to be useful information. Your room dimensions are quite similar to mine, I'm curious about your speaker and listening chair positions. While it may vary with speaker design it would be interesting to compare to my own setup....Thanks

Rick


I'll get out my tape measure and let you know :)


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PostPosted: Tue Nov 25, 2008 2:05 pm 
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Joined: Wed Nov 28, 2007 6:24 am
Posts: 3
Location: Brampton, ON, CA
MTB Vince wrote:
Vifferboy wrote:
Hello
I picked up a device to measure sound levels from The Source store (we don't have Radioshack anymore) and had a go at measuring my listening room...
Using some instructions from the ‘net’ and Stereophile test CD 2; I used the pink noise track to get 80 dB at my listening position and then set about recording the sound pressure values at various frequencies. The ‘net’ instructions said that I really wanted to get as close to 80 db at all frequencies and I was pleased to see that for the most part (give one or two db) I did. However there were certain frequencies where this was not the case these were:
20 Hz (85.4 db)
25 Hz (85.7 db)
40 Hz (70.7 db)
63 Hz (87.1 dB)
800 Hz (86.3 dB)
10 KHz (87 dB)
12.5 KHz (86 dB)
16 KHz (76 db) not that I could hear much at this point Â…
20 KHz (40 db)

IÂ’m assuming these differences are caused by how sound reacts to my room and I was wondering if these figures are still acceptable and if not anyone can suggest what I should try to improve things? My listening position is pretty much fixed (give or take a foot or two) but I could move the speakers (Dynaudio Focus 110s and a MJ 100 sub). The room is approx 10.5ft x17.5ft x 8ft and has some acoustic treatments.

Any suggestions would be most appreciated

Many thanks

Steve


Hi Steve,

Before ya get to concerned about the high frequency roll-off, you've gotta understand that inexpensive SPL meters use cheap microphone capsules and aren't calibrated for flat response. These cheap meters feature a response that droops significantly in the top and bottom octaves. A calibrated hand-held SPL meter capable of accurate 20hz-20khz measurement is waaay more dough than anything The Source or Radio Shack have to offer.

Now the RS SPL meter's drooping frequency response issues were sufficiently consistent, unit-to-unit, that reasonably accurate correction tables could be and were created for it. Here are the tables for the original analog RS Meter for example. These correction factors applied to your RS meter measurements were a much closer reflection of reality.

You need to do a little research to find out whether The Source is selling the same meters that RS was selling to determine whether the available RS Meter correction tables are applicable. If so and it is the currently common digital version 'o the meter, then do a Google search to locate the appropriate correction table.

Happy Trails!
Vince@Freewheelcycle.com


Hi Vince

The one The Source sells is made by SCOSCHE and looks very different from the famous Radioshack one I'll do some digging and see what I can find out.

Thanks Steve :)
u


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PostPosted: Mon Apr 04, 2016 9:57 pm 
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Joined: Sun Aug 17, 2014 8:11 am
Posts: 73
Location: Rose dale, BC, CA
You do need bass traps,all 4 corners if possible floor to ceiling,try 38% rule, sweet spot where ears are 38% from front wall or rear wall what ever works in your room.speakers 2 to3 ft. off front wall 1 to 1.5 ft. from side walls,play around with placement and toe in as needed.Most important is first reflector/ absorbers and ceiling included,if you don't do this,you will not be able to have proper imaging and soundstage.After these things are done some diffusion on rear wall to breakup standing waves and smearing,Wulla all done, now start tweaking addiction,spin vinyl only,no DIGITAL!


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PostPosted: Tue Apr 05, 2016 8:06 am 
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Joined: Wed May 30, 2007 7:54 am
Posts: 3451
Location: Vernon, BC, CA
HF response is notoriously hard to measure accurately due to the highly directional nature of high-frequencies.
The size and shape of the microphone will influence the response as much (or more than) the room will.

With a basic mic and graphing system focus on overall freq balance, and low frequency (200Hz and below) response.

Can you measure 40Hz, 80Hz, 120Hz, 240Hz?

If so, and they are all lower than the other freq. you can try moving the speakers into the room a foot and remeasure.


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PostPosted: Tue Apr 05, 2016 8:22 am 
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Joined: Mon Sep 07, 2009 5:37 pm
Posts: 763
Location: Markham, ON, CA
I would consider acoustic treatment.

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