REW Results - Analyzing HELP Needed For Optimum List. Postn.

[mrfye17]

Hi People,

After many months of researching, thread posting, reading, listening, building, measuring and analysing, I am now in the final stages of setting up my Home Studio. Primary usage will be MIXING and Recording Guitars, Bass and Vocals.

To re-cap, I have a 11.5'W x 18.5'L x 8'H room with 6" thick panels and 17" square soffit style Bass Traps all filled with Roxul Safe'n'Sound.

I have attached pictures of the Front Half and the Back Half of the room.

I used REW to take a whole bunch of measurements to establish a Speaker and Listening Position and need some SERIOUS HELP with analyzing my results in order to narrow down the Best positions.

I have 2 Krix speakers (HiFi but good) that are Front Ported and am not using any Subs.

There will be a Ceiling Cloud with four 6" thick Panels (24" x 48") with a 6" gap (I think) and will Install them and Secure the rest of the Panels after the Listening and Speaker Positioning is established.

Measurements Taken:

There are 4 listening positions -
62", 69", 74.5" and 83.75" (38%) from the Front Wall down the Middle of the room.

Using an Equalateral Triangle on each, I started from the Wall (W) and came into the room using increments of 3".
Just to be as detailed and Clear as possible, all the Measurements taken were.....

62" ........Wall, W+3", W+6", W+9", W+12", W+15", W+18" and W+21"
69" ........Wall, W+3", W+6", W+9", W+12", W+15", W+18" and W+21"
74.5"......Wall, W+3", W+6", W+9", W+12", W+15", W+18" and W+21"
83.75".....Wall, W+3", W+6", W+9", W+12", W+15", W+18" and W+21"

On the measurement notes, I also have the Distances from the Front Wall and Side Wall to the Front of the Speaker on each one, as well as the Distance between the Speakers (Center to Center).

Because the mdat files are too large to attach, here is the link to my Google Drive where they are situated:

https://drive.google.com/file/d/1y5ECOd ... sp=sharing

I know it's a LOT of information but I really do need some help (being an untrained analyzer) to help narrow-down the field and maybe shed some light on this bugger!


Thank You so much for your attention and help,

Chris (mrfye17)

p.s. If you need any more info or have any questions, please yell out!

[DanDan]

Here mrfye as requested. I am afraid the question is too big. Reminds me of my 2 Do list...... write an article describing my approach to finding optimal positions........ Not an easy task.
I believe the optimal listener position changes with speaker locations, and vice versa. If one is lucky, something will 'stick' or stay optimal over a range of other parameters. But so many...... Width, Height of Woofer......
I often use Real Time feedback to at least rule out No Fly zones.

But a potentially overriding question. Why are there thin traps behind your speakers?

[mrfye17]

Here mrfye as requested. I am afraid the question is too big. Reminds me of my 2 Do list...... write an article describing my approach to finding optimal positions........ Not an easy task.
I believe the optimal listener position changes with speaker locations, and vice versa. If one is lucky, something will 'stick' or stay optimal over a range of other parameters. But so many...... Width, Height of Woofer......
I often use Real Time feedback to at least rule out No Fly zones.

But a potentially overriding question. Why are there thin traps behind your speakers?

Hey Dan,
I hear you about the 17 million items on the 'to do list' lol!

I guess what I need is to eliminate the 'No Fly Zones' by looking at the REW results....please, please, please can you have a quick look?
(there's not many ppl I trust on these forums sometimes)

The front wall panels are 6" thick.
Initially, I didn't have any on the front wall but found that, although they didn't make that much of a difference, they did smooth out the Low Mids and Upper Bass regions just a bit.

Cheers,

Chris

[Gregwor]

Hi Chris,

Sorry it took me so long to get to your post.

If I had to choose, I would go with this one:

C_B+FWT 62" Wall

It yields the best results out of all of them except in the impulse response. You can see in the picture below that you have a strong reflection at ~3.98ms. Using the string trick, you should be able to find out where that reflection is coming from.

Chris IR.jpg

Greg

[mrfye17]

No problem Greg.

Happy that you had a chance to take a look.

C_B+FWT 62" Wall
It yields the best results out of all of them except in the impulse response. You can see in the picture below that you have a strong reflection at ~3.98ms. Using the string trick, you should be able to find out where that reflection is coming from.

Very Interesting....never noticed this.
So, by " The String Trick " do you mean 3.98m from the Measuring Mic or from the Speakers?


The 62" listening position puts me right up against the Desk....could be a bit awkward.

If you had to chose one from either the 69", and/or 74.5" and/or from the 83.75" Listening Position. which would you go for?

Thank you so much from your Input, it's helping me understand things a lot more

-Chris

[Gregwor]

So, by " The String Trick " do you mean 3.98m from the Measuring Mic or from the Speakers?

If you use this new position you don't need to worry about the string trick. I won't give the explanation here since you don't need to do it now.

If you had to chose one from either the 69", and/or 74.5" and/or from the 83.75" Listening Position. which would you go for?

There are always compromises. This position obviously isn't perfect but in my opinion, this is the next best position:

C_B+FWT 74.5" Wall

Greg

[mrfye17]

There are always compromises. This position obviously isn't perfect but in my opinion, this is the next best position:

C_B+FWT 74.5" Wall

Thanks Greg

Quote:
So, by " The String Trick " do you mean 3.98m from the Measuring Mic or from the Speakers?

If you use this new position you don't need to worry about the string trick. I won't give the explanation here since you don't need to do it now.

After a Listening test, if I were to use the original position you mentioned, could you give me a brief explanation of "the string trick" please?

Just a guess here but, is it when you take a string from speaker to mic and then use that same measurement from the mic to locate possible relection surfaces?


-Chris

[Waka]

Hi mrfye17,

Here's a short explainer on the string trick:

Get the length of your reflection's travel: Speed of sound is 343 m/s or 0.343 m/millisecond. Your sound wave traveled for 3.98ms. So 3.98 * 0.343 = 1.365m. Which is very short, almost certainly a desk reflection.

So cut your piece of string longer than 1.365m. Stick the string exactly on the acoustic axis of a monitor using a piece of tape. Measure 1.365m from the monitor tape and stick another piece of tape exactly there, on the tip of your measurement microphone. The string should droop in the middle, it won't be tight (if this really is a reflection issue)

Hold the center of the string between the monitor and your mic and gently pull it towards different areas of the desk and walls/ceiling/floor (if it reaches) There will (should) be only be one point where it just barely reaches the reflection point and it is in the correct trajectory between the monitor and microphone.

It might help to get a couple of people to help, by holding the string securely against the microphone and monitor, so it doesn't fall off.

Dan

[mrfye17]

Get the length of your reflection's travel: Speed of sound is 343 m/s or 0.343 m/millisecond. Your sound wave traveled for 3.98ms. So 3.98 * 0.343 = 1.365m. Which is very short, almost certainly a desk reflection.

So cut your piece of string longer than 1.365m. Stick the string exactly on the acoustic axis of a monitor using a piece of tape. Measure 1.365m from the monitor tape and stick another piece of tape exactly there, on the tip of your measurement microphone. The string should droop in the middle, it won't be tight (if this really is a reflection issue)

Hold the center of the string between the monitor and your mic and gently pull it towards different areas of the desk and walls/ceiling/floor (if it reaches) There will (should) be only be one point where it just barely reaches the reflection point and it is in the correct trajectory between the monitor and microphone.

That's Insane Waka, never heard of this method but makes sense...love it and will definitely try it.
Great way to accurately pinpoint reflections

How much longer should the string be so it can droop loose?
....OR it doesn't matter because the string will be marked at 1.365m, so whatever that mark (tape) touches when moved around, that is the reflection pt?
Have I got that right?


Thank you so much!

Cheers,
-Chris

[Waka]

How much longer should the string be so it can droop loose?
....OR it doesn't matter because the string will be marked at 1.365m, so whatever that mark (tape) touches when moved around, that is the reflection pt

The entire length of the string should be just over 1.365m. But that's just so there is enough string at each end to attach tape to. The droop is determined by the reflection. Your monitors must be quite close to the listening position, for a 3.98ms reflection.
The 1.365m mark represents the entire journey of the sound wave. Not just the reflection.
For example:
If the reflection was off a flat surface on the desk the reflection point will be exactly half way along the string (ie 0.6825m).
The 1.365m point is always at the tip of the microphone. The "droop" is directed towards possible reflection points, forming a point that barely reaches the location.

Is that a bit clearer?

Dan

[mrfye17]

The entire length of the string should be just over 1.365m. But that's just so there is enough string at each end to attach tape to. The droop is determined by the reflection. Your monitors must be quite close to the listening position, for a 3.98ms reflection.
The 1.365m mark represents the entire journey of the sound wave. Not just the reflection.
For example:
If the reflection was off a flat surface on the desk the reflection point will be exactly half way along the string (ie 0.6825m).
The 1.365m point is always at the tip of the microphone. The "droop" is directed towards possible reflection points, forming a point that barely reaches the location.

Is that a bit clearer?

Thanks heaps Dan, you explained it perfectly.
Yes, it's the beginning of the desk.
This is one of the positions that had a " flattish " response where the speakers are only 60" from that listening position (in a straight line).

Now I can look at a couple more that I had my eye on, where the speakers are slightly further apart (66" to 74") and get rid of a couple of reflections, have a listen (for depth, image etc.) and re-analize the REW results, thanks to you.

Cheers,
-Chris

[Gregwor]

Here is a screenshot from a little calculator I made to help with the string trick:

3.98ms distance travelled.png

If it helps, I'll give a quick instruction here.

Measure the distance from your speaker to the tip of your microphone. Add the length described in the image above to your measurement. I don't recommend cutting the string, but simply mark the length with tape or a marker. Tape one end of the string (at the mark you made of course) to the speaker and the other end of the string (the other mark of course) to the tip of your microphone. Like playing pool, find the surface that the sound would have bounced off of on its way to your mic. This could be a wall, a desk, a floor, a ceiling, etc.

Greg

[Waka]

Measure the distance from your speaker to the tip of your microphone. Add the length described in the image above to your measurement

I had forgotten about this. You're right you need to add it to the listening distance. I thought the length I gave was really short!
You add to the length because what we're seeing is a sound wave arriving 3.98ms after the initial sound, causing interference.

Mrfye17 hopefully you've not taken your measurements yet, but can do the string trick correctly now. You will add 1.37m to the distance from your monitor to the tip of your microphone and do the string trick with that length.

Dan

[mrfye17]

OK Gentlemen,

Let's see if I've got it correct! (I may be repeating what you boys just said...lol!)

Tape 1 on string for speaker
Tape 2 on string at tip of mic
Tape 3 on string 53 31/32" (in this case) past the mic.
then....
Tape 3 on string goes to tip of mic.
Hold Tape 2 (the droop) and whatever is close to touching it then that's the reflection point.

Is this right???

Thanks boys.

-Chris

[Gregwor]

Yes, but realize that the droop isn't really a droop. It's just extra string length. You use this extra string length to find out what surface the sound bounced off of on it's way to your microphone. The sound would obviously be a specular reflection, so it could be from any surface between the the speaker and the microphone.

Greg