Effect of the room is always interesting....

[ThomasW]

I'm working on a "Introductory Guide to Subwoofers" and as such have been making plots to post for that guide. Here's a nearfield vs listening position comparison for my small IB (4-12"s). The blue plot is of course nearfield (mic inside the manifold). The magenta plot is 13' away from the manifold outlet and approx 3' off the floor.



Below I've added a 3rd plot taken from the actual listening position (green) this is 3' further back and 1' higher than the farfield (magenta) measurement. The amplitude of the 3rd plot is intentionally lower than the farfield plot to keep them separate on the graph



I hope this makes it clear why obtaining an 'perfect' plot in one specific room position isn't a particularly good idea

[carl]

Does this mean that you are not a proponent of EQing, or just pointing out how screwed up some rooms (like mine) are?

[ThomasW]

I certainly am an advocate of using EQ. If possible one should use EQ in conjunction with passive room treatments.

The best way to approach the situation is first use passive treatments to tame as many of the room issues as possible. Then fine tune with EQ.

If the SAF/WAF issues don't allow passive room treatments then EQ is the only available option.

What most people miss is they EQ for a single listening position. As seen by the plots above this can be a mistake. It's best to take measurements from several locations and average those measurements. Then create an EQ scheme based on the averages. Most websites that talk about EQ don't advocate this approach and have "galleries" for people to post their plots. This fails to take into consideration that optimal EQ in one position usually mean less than optimal perform ace in other seating positions.

I'm also working on a guide for designing building and installing bass traps. Part of that guide is done, but it's still a work in progress...

home.comcast.net/~thomasw_2/SubwooferSetupandEQpage9.html

[ThomasW]

For IB users I created a Excel spreadsheet that has the ability to make 5 separate plots, and contains frequencies lower than those in the standard spreadsheets.

home.comcast.net/~thomasw_2/IBmultiplots.xls

Here's a chart that will automatically average 3 plots taken from different room locations. People can use that averaged plot to generate their EQ. Note the forum software can't deal with the + sign, so copy and past the entire URL in your browser.

home.comcast.net/~thomasw_2/IB-3plots+average.xls

[jonfo]

As Thomas notes, EQ’ing for a single (or even a few closely spaced) location is not a great idea.

Here is a tool that will really help you measure, find and correct the room mode induced problems without being tied to a specific location.

The software is R+D from Acoustisoft, the makers of ETF.

I used it to measure 28 points in my HT and used its averaging and EQ targeting functions to clearly identify the dozen points of EQ (in the bass) that would improve the overall sound.

Sure enough, it works great. The bass is much smoother overall. I still have room induced nulls mind you, can’t get around physics, but the balance is so much better now.
It takes some effort to learn and then measuring that many locations is a bear. But what you wind up with is a measure once type solution.

Also, it will soon allow Midi control of the BFD2496 as well.