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Discussion Starter #1
Hi,

I have been trying to decide if REW can help me or not; I am trying to set up a small room (12 feet by 10 feet) for 2 channel hi fi playback. So far the room has not been working out and to date I have tried about 40% wall treatment paying particular attention to first reflection zones, with a little success but I'm not yet enjoying the result.

Before I hit fleabay for a mike, preamp etc, does anyone think REW can really guide me to a better result? Any specific advice?

Many thanks

Tim
 

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does anyone think REW can really guide me to a better result? Any specific advice?
REW can definitely help you with a two channel room.

You can use it to select the best placement for your two mains, so as to obtain the smoothest response and the least cancellations at the bottom end - using either static response plots or real time analyzer.

You can use the Energy Time plots (ETC) to establish reflection points. See here on how to use the measurement tool. It would be very difficult to install that treatment for reflections without REW's ETC.

Be sure to get the ECM8000 mic (or a calibrated mic) - as we have a generic calibration for it that is suitable for home use.

brucek
 

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Thank you Bruce,

That was my gut feeling; having an engineering background I lean towards 'empirical evidence'.

Hopefully I can carefully time some purchases on a well known auction site and I may well be posting once I'm up and running,

thanks again

Tim
 

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So far the room has not been working out and to date I have tried about 40% wall treatment paying particular attention to first reflection zones, with a little success but I'm not yet enjoying the result.
What exactly are you unhappy with? A small room is usually pretty easy unless it has hard surfaces everywhere. With 40% treatment I would think you'd be sitting pretty... :huh:

Regards,
Wayne
 

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Discussion Starter #6
Wayne,

The room is what I think you would call drywall (we would call plasterboard) over breezeblock (cinderblock?). It is really hard to describe in words, it's like part of the sound is missing. Male vocals are ok but female vocals are harsh and in line with that lower mid sounds good but upper mid drives me crazy - it's tinny. Bass like kick drums are great but low bass is boomy which I reckon is a 50Hz mode problem. It seems to me that there is a poor balance issue as I have used the speakers in a larger room and they sound really natural, apart from the bass which is pretty shy I have to admit in a bigger room.

So the small room augments the bass the kills the mids somehow. I hope to find out why!

regards

Tim
 

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You might want to take a look at Part 2 of my house curve article (full-range). You can find the link in my signature. Placement can have an effect on the bass boom and lower midrange, but I doubt it's going to have any effect on the harshness problem. If you are sitting closer to the speakers than you were in the big room, that could make a difference.

Regards.
Wayne
 

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Discussion Starter #8
1st go.jpg

OK,

A sanity check would be most useful here, please..

I obtained a RS Digital SPL, Xenyx 802 and ECM8000 as per recommendations. I first hooked up the SPL and checked levels to 73db. Then I unhooked that and connected the ECM8000 using the .cal file. I didn't calibrate the soundcard cause I didn't have a 3.5 to 3.5 lead, but presumably it's a known quantity.

I then did a full range measurement (remember this is a 2.0 system) with the room in its current part-treated state and got the attached graph.

The 50Hz peak is a known room mode, I must calculate some of the others out (the room is 12x10). What does look rather suspicious are the rather deep looking nulls further up and down the range. Any comments?

many thanks

Tim
 

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That is normal comb filtering, to see the underlying response at higher frequencies apply some smoothing, e.g. 1/3 or 1/6 octave.
 

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First of all, be sure and post all your graphs using our standard 45-105 dB vertical axis and 15 Hz to whatever upper limit you want to examine for horizontal axis.

The deep, narrow nulls are comb filtering, which is caused by reflections in the room. It's standard stuff and not especially audible - nothing to worry about. If you want to see the overall trend up upper frequency response, use 1/3-octave smoothing.

Regards,
Wayne

 

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Discussion Starter #11
OK,

Here's a 1/3 octave smoothed version; kind of explains why males voices sound forward but almost everything else is a bit 'thin'? Any suggestions as to how to modify this?

Isn't it desirable to suppress comb filtering? Doesn't that cause 'ringing'?

cheers

Tim

1st go smoothed.jpg
 

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Ringing is not comb filtering. Ringing refers to the time it takes bass signals to fully decay (i.e. fade away). The way to minimize comb filtering is treatments that absorb the upper frequencies, to minimize their reflections from boundaries. Typically, though, it's not a big issue unless your room has a noticeable echo, and that's usually only present in rooms with hard floors and minimal furnishings. Some HT buffs who are really into acoustics like to "severely" treat the room (for lack of a better word) to make it fairly "dead" something along the lines of a recording studio. Personally I find that to be an unnatural approach, as even the best performance venues exhibit at least some reflections or "liveness."

Regards,
Wayne
 

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Here's a 1/3 octave smoothed version; kind of explains why males voices sound forward but almost everything else is a bit 'thin'? Any suggestions as to how to modify this?
If your receiver had a midrange control, you might reduce it a bit. If it has an adjustable frequency center, set it for about 600 Hz. Other than that, the best way to deal with the 50 Hz peak will be to get a subwoofer and use a parametric equalizer to eliminate it. After that you can turn the sub's level up to make everything sound "full."

Regards,
Wayne
 

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Discussion Starter #14
Wayne,

This is a two channel stereo setup, there's no receiver and no tone controls!

If I added a sub and used a aparametric equalizer to tame the sub at 50Hz wouldn't that still leave the same amount of 50Hz energy generated from the mains that I already have?

cheers

Tim
 

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Discussion Starter #16
OK,

Well the plan is to empty the room and start optimising from there beginning with placement; the speakers are reflex loaded so I have a couple of ideas to tackle the 50Hz peak.

Wish me luck!
 
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