hochopeper

Yet another set of room tweak measurements

8 posts in this topic

I'm about to embark on doing some minor tweaks of my room setup and taking some measurements as I go. This is a bit of a log to show the progression and I have a few questions as well.

To start with I haven't finished off the feet for my subwoofers that will eventually be down firing. So the subs are laying flat firing forwards. Main speakers will eventually sit on top of the subs.

I am waiting on a parcel with some parts to finish off the feet and its been delayed pretty badly for some time now, I had time to do some measurements today so took the opportunity to try to get used to the software and take some measurements while I was at it. Earlier in the year I had hoped that I'd be building bass traps by now but a bad back has slowed me up a bit.

Speakers are B&W CM5 standmount speaker, not much deep bass output from these. Subs are diy sealed box peerless - similar to the linkwitz Thor. For practical room arrangement reasons the best place for these for now is at the same place as L/R speakers go.

Room is an open plan lounge/living space but with some basic dimensions I've put into a spreadsheet a while back (can't find the thing now though I did save a pdf of the results). Here is output of the room modes expected:

post-107696-0-88259200-1336391290_thumb.

The question I have is in time aligning the sub and main speaker output. How do I measure which needs to be delayed and by how much? Is REW the right software for that job?

Before any eq added - linkwitz transform on sub and crossover between sub mains at 80Hz with LR 48dB/oct slopes.

Unsmoothed

post-107696-0-93086600-1336388521_thumb.

Waterfall

post-107696-0-84827200-1336388470_thumb.

Decay

post-107696-0-74381800-1336388505_thumb.

No changes to room/speaker arrangement just added EQ for now taken from REW and also changed highpass to main speakers to a LR 12dB slope and shifted the crossover point for these down to 40Hz, this basically means that all the bass from these is getting let through, I'm not sure if this is ideal, need to play with that as time allows. Lowpass filter still with steep slope to reduce any chance of localisation since I'm pushing these to go a bit higher than I'd ideally like a sub to go. In REW I applied a target curve as well to boost bass region a touch, which was sort of happening naturally in my original setup thanks to the LT I guess.

From the below its pretty obvious that the 35Hz and 25Hz modes are the ones needing the most work.

Unsmoothed

post-107696-0-86970100-1336388340_thumb.

Waterfall

post-107696-0-63328100-1336388376_thumb.

Decay

post-107696-0-46995000-1336388411_thumb.

Nearfield measurement of one sub unsmoothed:

post-107696-0-96436900-1336390853_thumb.

Edit: I think I generally followed the scale advice from Paul in his blog, do these look right?

post-107696-0-29054300-1336388316_thumb.

Edited by zman

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So I've been doing some research this week, I'll do a more detailed post of my thoughts/plans later but I have an extra question.

To control room modes is it ideal to place any room treatment in the location of the dominant room modes? So in my case I am better off placing treatment on the walls that run perpendicular to the 35Hz room mode?

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The 35 Hz mode stands out the most. The lower 25 Hz mode is of much less concern. You need either some really big broadband traps that can be effective down to 30 Hz, or perhaps even targeting that region with tuned absorbers.

Interesting to see the effect of EQ here. Notice how at 35 Hz your EQ has provided response shaping, which leaves the ringing unmodified. It has no effect at all on the decay rate. However, the peak at 65 Hz had a fairly high Q. Your EQ has reduced the narrow Q peak and this is reflected in the decay plot.

If you want to experiment with bass traps, then it could be worth attempting a tuned pressure trap. That could tackle the 35 Hz region and from there you could then apply an overall broadband strategy, assuming you are planning to treat the room.

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I've been distracted and forgot to get back to this.

I've attached a rough not to scale floorplan of my room with locations where I have considered basstraps.

I tried a while back to calculate dimensions for a perforated membrane trap but had trouble getting the results to make sense. I was using the equations presented in the BBC articles, is there any other resources that build or continue the work presented in those? I'm thinking a membrane trap tuned to 30 - 35Hz would be the go to start with. The area I've highlighted in diagram for membrane trap has a split system aircon mounted in the wall so I can get 1800-1900 of height beneath that and there is a ~1900 long display cabinet under the aircon so I would likely sit the membrane trap behind that (photo attached to show shelving unit).

My preference for the membrane trap is that is sits on the same axis as the 35Hz mode that is seemingly dominating the measurements I've taken. Is my understanding correct that when treating a room mode it should be ideal to where possible place room treatments in the area where the room mode exists, or at least in the path taken by the standing wave that is causing trouble. Has anyone investigated (or got links to studies/experiments) the placement of room treatments to target a specific room mode?

The two lower baskets in that shelving unit could actually be filled with foam as well if I end up with some spare foam since they're not used for storage.

Another possible variation is that when I go to replace the B&W CM5 speakers that currently sit on top of my subs I *could* replace them with floorstanding speakers that have better LF extension and relocate the other pair of subs to the rear of the room and run them from the LFE output of the receiver rather than from front L/R as they are now in current arrangement, that could change the game entirely I guess.

Any thoughts appreciated!

[edit: no need to comment on speaker wire for that rear left speaker!]

post-107696-0-62892700-1338627660_thumb.

post-107696-0-31786900-1338627797_thumb.

Edited by zman

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