# Comb filtering solution?



## McCoy (Feb 12, 2011)

Hi guys -
I recently started using REW to analyze my HT (living) room. I ran tests of the left and right front speakers individually, and the results indicate significant comb filtering from roughly 1k on up.

On the left wall of the room there's a large window, so an absorber panel isn't an option in that location. However, the window has vertical plastic blinds, so it occurred to me that replacing them with fabric blinds might improve the situation by absorbing some of the higher frequencies. I imagine that the fabric would have to be a relatively coarse weave.

Your input would be appreciated.

Thanks!


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## Phillips (Aug 12, 2011)

Can you post some graphs or .mdat files.


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## McCoy (Feb 12, 2011)

Here you go -


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## Wayne A. Pflughaupt (Apr 13, 2006)

Measured comb filtering is normal in all but the most dampened rooms. Fortunately, it looks worse than it sounds. Any kind of absorptive material over the window can't hurt, but unless you have wood or tile floors and/or walls of glass on two or three sides of the room, you probably don’t have a significant problem. Apply 1/3- or 1/6-octave smoothing to your graph to get a better representation off what you’re actually hearing.

Regards, 
Wayne


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## McCoy (Feb 12, 2011)

Thanks Wayne. The room is carpeted. I have bass traps in the front 2 corners & overall it sounds pretty good. But I was curious if this idea would be worth trying. Appreciate your help.


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## Barleywater (Dec 11, 2011)

I've looked at "right with mic next to chair". Please provide more information on speaker placement relative to walls, chair placement relative to walls. Also note proximity of microphone to objects.

Inspection of impulse response/ETC and spectrogram indicate extremely strong reflection at 1.4ms and 1.76ms additional very strong reflection at 6ms. 1.4ms and 1.76ms are responsible for much of what you are seeing in measurements. These could be objects close to speaker, or close to microphone. Object can also be speaker itself as baffle reflections, internal reflections back through driver(s) or port, or very poorly managed driver selection, spacing, and crossover management.


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## McCoy (Feb 12, 2011)

Left & right speakers are Paradigm Studio 60's, 28" from the front of the speakers to the front wall, 42" from the side walls, and about 7' apart. Chair is 10' from the speakers. Mic was centered between side walls by chair. Left wall has big window as mentioned, fabric upholstered couch on right wall. 4' tall bass traps diagonally across the front corners.


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## Barleywater (Dec 11, 2011)

Wayne's comments on looks worse than it sounds is likely best approach.

What influenced decision to purchase these? How long have you owned them?

Welcome to world of acoustic measurements.


I read through Stereophile review

Specifications page shows crossover points of 500Hz and 2kHz.

Their measurements are 50" tweeter axis based. They show tweeter and mid/woofer acoustic slopes of about 12dB/octave. Very common slopes for passive crossovers. No details are given for slopes of woofers and mid/woofer. Very likely at best also 12dB/oct.

Two woofers and mid/woofer are 5.5" diameter, and including frames are likely about 6" between centers. For narrow baffle width and such drivers radiation is very omnidirectional below 1kHz. Response at measurement position is sum of each driver response and room reflections.

In Stereophile measurement a deep suckout of combined woofer/mid response as farfield at about 1.2kHz is commented on. 

So, at 10ft, and tweeter height of about 3ft, and using 3ft as listening/measurement height, a floor reflection occurs at roughly 5ft. Doing the geometry makes reflected path length of 11.7 ft for difference of 1.7 feet. Dividing this by 1126ft/sec speed of sound yields: 1.5ms. This is ballpark for previously mentioned early reflections. At frequencies of interest, carpet (unless very deep) doesn't do much absorbing, and roughly 31 degree angle of incidence makes absorption even less. 

Off axis vertical response of woofers and mid/woofer <2kHz is mess too, the nature of which is seen in Stereophile's vertical response family measurements. It is off axis response in floor reflections of drivers that combine with direct sound at measurement point that dominate measured response, followed by front wall contributions for response below 2kHz.

Similar analysis of tweeter and mid/woofer with spacing, crossover point, and intended listening distance will produce very good reasons for response measurements as seen.


Paradigm makes lots of choices in design for consumer appeal. Looks are driven by small footprint. Bass response by multiple drivers. Crossover design driven by cost and what consumers generally will accept. Lots of marketing, for instance "reference studio". Yuck.

Speaker meets design goal of efficiently getting lots of sound into room over wide horizontal dispersion with small footprint. It serves only as reference to what can be profitably marketed.


I've heard many similar speakers, including Paradigm tower types. General listening is quite acceptable, certainly for HT.

Room treatments will do next to nothing in improving look of response, but will shorten decay time of room.


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## McCoy (Feb 12, 2011)

Thank you for your response. I've had the 60's for a few months, but also own older Studio 20's & 40's that I use in other rooms. Bought all of them used at significant cost savings. The choice of this brand was based upon personal listening sessions, not marketing hype. I don't have the expertise or a workshop to build a design of my own.

I daresay your comments regarding Paradigm design economics equally apply to most, if not all manufacturers in this price range. Also, they are located in my living room, so size, appearance and WAF all come into play. 

I understand the logic of choosing 1/3 octave smoothing for higher frequencies. The smoothing applied to the files I posted was just what I happened to be looking at when I saved the files.


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