REW and my towers

**v1rtu0s1ty** · **03-20-08, 01:04 AM**

Hi folks,

I would like to get some readings to find out how my Polk Audio towers perform using REW. I'm actually more concerned about the highs from the tweeter. I would like to test if the tweeter mod will actually do good to my tweeters. Someone sent me a cap and is claiming that it will make the sound better. So I would like to get a reading of the tweeter before the mod and after the mod.

How should I do it?

Any help would be greatly appreciated.

EDIT: Or is it the same process like when taking a reading from a subwoofer? Don't I need to change the frequency?

Thanks.

Neil

**Bob_99** · **03-20-08, 07:43 AM**

Neil,

I don't have an answer for you but if I may ask, what model of Polk are you modifying? Has this mod been tested before?

Bob

**brucek** · **03-20-08, 08:23 AM**

Quote:

is it the same process like when taking a reading from a subwoofer? Don't I need to change the frequency?

Of course. You would sweep the frequency area of interest. The measure routine allows any start/stop range. You will require a full range microphone and preamp to measure tweeters.

brucek

**thewire** · **03-20-08, 08:32 AM**

Sounds really complicated to me.

There are allot of different test.

There is a method of bypassing the influences of the room by adjusting the time gate, to say 200ms or so where the loudspeaker can be examined on it's own from 1 meter or 3 meters. I would try different time slices (varying the time gate in the impulse response window) and look for spikes that are the same looking on each of these readings. Once you establish which has least influence on your room, you can can create more accurate test results. This shows what is noise from the speaker itself, and what is caused by the room. When you have set the time gate , I think maybe following the instructions on the thread linked bellow will give you the best measurement so that you may bypass the influences of sound that are in your system. After you have basically established your test setup, you can begin running sweeps. This would work better in a large room. Pro's use a large reflective room with absorption behind the speaker I think to examine the room interactions from various locations.

You could sit the speaker near where you intend to use it and take a measurement before and after.

You may want to check Response + Harmonic Distortion.

It's been soooo long since I saw this done so this is merely my guess as to what to do. I would also like to know the correct way to do it. It would be very interesting to examine my own speakers if I get new ones very soon.

http://www.hometheatershack.com/foru...a-feature.html

**v1rtu0s1ty** · **03-20-08, 08:58 AM**

Quote:

brucek wrote:

Of course. You would sweep the frequency area of interest. The measure routine allows any start/stop range. You will require a full range microphone and preamp to measure tweeters.

brucek

Is my radioshack analog spl meter considered a full range microphone? I don't have a preamp. Or are you saying a/v receiver?

**v1rtu0s1ty** · **03-20-08, 09:03 AM**

Quote:

Bob_99 wrote:

Neil,

I don't have an answer for you but if I may ask, what model of Polk are you modifying? Has this mod been tested before?

Bob

It's an RTA 11T. This mod was tested by only one person.

I am actually going to upgrade the SL2000 tweeters to RDO194 something this year as recommended by Polk Audio. However, before I upgrade, I want to test the solution this guy has been pushing. This way, I can help put an end to that debate on that thread there.

**Bob_99** · **03-20-08, 09:03 AM**

Also, I would be cautious when measuring at the extremities of the frequency range (very low/very high) as this is where most instruments will vary quite a bit.

Bob

Thanks for the response regarding the model type. It sounds like an interesting mod.

**v1rtu0s1ty** · **03-20-08, 12:02 PM**

Quote:

Bob_99 wrote:

Also, I would be cautious when measuring at the extremities of the frequency range (very low/very high) as this is where most instruments will vary quite a bit.

Bob

Thanks for the response regarding the model type. It sounds like an interesting mod.

Looks interesting too. But other Polk Gurus on that forum are bashing on this mod. That's why I want to test it. They've been swearing at each other, hehehe

So I would be the second guy to hear what the mod does. I will keep you posted once the cap arrives. The guy sent it to me. Should be here by tomorrow or Monday.

**brucek** · **03-20-08, 02:15 PM**

Quote:

Is my radioshack analog spl meter considered a full range microphone? I don't have a preamp. Or are you saying a/v receiver?

No, the Radio Shack meter is not acceptable. It's only good for subwoofer measures. The microphone and preamp I speak of would be an Behringer ECM8000 and XENYX 802 preamp.

brucek

**v1rtu0s1ty** · **03-20-08, 02:56 PM**

Quote:

brucek wrote:

No, the Radio Shack meter is not acceptable. It's only good for subwoofer measures. The microphone and preamp I speak of would be an Behringer ECM8000 and XENYX 802 preamp.

brucek

Ok. For now, I will have to depend on my ears.

Thanks for the heads-up.

**JohnM** · **03-20-08, 05:46 PM**

You could use the RS meter to take relative measurements, comparing before and after. Just remember it is only the change that is valid, not the absolute shape of either response. Move the speakers well away from walls and put the meter about 3 feet away. Use a very short impulse response window to gate out room effects, around 5ms or so. Check the impulse response graph page to make sure the window is capturing the main peak.

**v1rtu0s1ty** · **03-20-08, 06:22 PM**

Quote:

JohnM wrote:

Use a very short impulse response window to gate out room effects, around 5ms or so.

Where do I set that value?

And also, is this setting correct? Slow, and C waiting on my RS meter?
I will also turn off my subwoofer. Do I set my fronts to LARGE?

Thanks.

**JohnM** · **03-20-08, 11:29 PM**

The windowing is set by pressing the button in the top right

C weighted and slow is correct (although fast and slow only affect the meter reading, not the analog output)

**v1rtu0s1ty** · **03-21-08, 01:10 AM**

I see 3 variables. Are you referring to the Window Ref Time(ms)? And should I increase the ending hz? The last tone is 200hz. And I'm starting at 40hz rather than 0hz. This is for my mains reading.

**JohnM** · **03-21-08, 08:33 AM**

Yes, you need to increase the end frequency or you will only be measuring low frequencies. To measure any effect on your tweeters set the end frequency to 20,000Hz. The settings to adjust are the left and right windows, left to 1ms and right to 5ms.

**v1rtu0s1ty** · **03-23-08, 03:23 AM**

The verdict. The tweeter with caps didn't sound properly anymore. The tambourine which was very lively before sounded as if there was a thick cloth that is covering the tweeter.

So, the mod is not good. I'll just save money on the tweeter upgrade as mentioned to me by Polk technical support.

Here are the 2 graphs.

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