in-room response (1 Viewer)

[GeorgeS]

Setting up new system - Adire Kit281 mains, LCC, Kit81 surround, & mid-Q sealed Tempest. I've been following and posting on a few forums hoping to better understand the issues and was hoping to get feedback on my measured response.

The 'room' is about 15x23. The viewing/listening area at one end and is setup transverse to the major axis of the room. Another room takes an 8x8 bite out of the corner of the room at the opposite end. The reciever (Denon 1803) is setup with all channels crossed over at 80hz. The sub amp (AVA250) low pass is disabled. Phase is set to 0. The sub is at the 5' mark along the 15' wall, a few feet closer to the listening position than the mains and a few feet to the side. Measurements were taken with the Radio Shack SPL meter (corrected using the values at http://www.danmarx.org/audioinnovation/rsmeter.html) playing the Stryker Audio test CD.

Response graph:
www.midcoast.com/~swanton/gs/ht/response1.jpg

I'm assuming the 16db peak around 36hz is a room mode and best corrected with EQ, and that the crater at 160hz is a room null and that I can't 'make this go away' electronically.

Theres a sharp 6.5db null at 80hz. With the sub amp low-pass disabled I'm assuming this isn't a crossover issue. I can experiment with the phase setting but where its an even multiple of the near-40hz peak is this also probably room related?.


Any feedback to verify or refute these assumptions and/or info on understanding in-room response is much appreciated.

Thanks

 

[Wayne A. Pflughaupt]

George,

First, welcome to the Forum!

To answer some of your questions:

The sub is at the 5' mark along the 15' wall, a few feet closer to the listening position than the mains and a few feet to the side.

Your placement may be causing some of the valleys you’re getting. It’s a well know fact that subs interact with boundaries at certain distance-related frequencies, and the more boundaries to interact with, the worse response is.

The way it works is the soundwave will bounce off a boundary – say a wall for this example – and reflect back toward the sound source – i.e., the sub. At a distance halfway between the sub and the boundary, the sound wave (delayed by time and distance) will meet the original soundwave from the sub. At this point there will be cancellation at a specific frequency; exactly what frequency is determined by the distance the sub is from the boundary.

So, if you have the sub 5’ in on a 15’ wall, like you do, there is reflection between the sub and left and right walls, the ceiling, and the wall across the room – a total of four boundaries and four cancelled frequencies.

If you put the sub in the corner the number of boundaries is reduced to three. In addition, the soundwave reflected off the two corner boundaries will be effectively in-phase and summed with the original signal, which will dramatically increase maximum output.

I suggest placing the sub in a corner and taking new readings. The result probably won’t be perfect response, but you should see a decrease in the number of those peaks and valleys. You should also see response below 40Hz improve noticeably

Regards,
Wayne A. Pflughaupt

 

[GeorgeS]

Wayne -

Thanks very much for the thorough response. I've read the suggested posts and several that they linked to. Things are much less mysterious now.

I have also moved the sub to the front right corner as suggested - nearly anyway, there's a heater that that needs clearance, but its much closer than it was.

I ran through most of the Stryke test cd (tones get progressively more annoying as they go higher) and took readings at the left, right, and center positions of the 'viewing position' (couch). Here's the new curve:



That's definitely a much better starting point.

[I should add that I took some more readings before the move and the 80hz 'null' was 'gone'. I guess I screwed something up when I took the initial readings.]

My BFD has arrived but I haven't unpacked it yet. I downloaded the software suggested in the link and it is a definite MUST HAVE in my opinion. Playing with the filters on-screen to match an inverse response curve is going to be MUCH easier than playing hunt and find with an SPL meter.

Things are kinda squirrely up higher. I'm assuming this is more of the same, reflections and what not. Any suggestions for taming this part of the spectrum are also much appreciated. These would have to be limited to surface treatments (suitable for a living room), etc. as a 'real' parametric EQ isn't in the budget, and I only have a modest receiver (Denon 1803) to work with.

Thanks very much for your help.

 

[GeorgeS]

Here's the EQ'd curve
(measurements taken at left, right, and center of couch, averaged, and SPL meter adjustments applied):



Filters
(freq +/- 1/60 octave adjustment, bandwidth in 60ths, db)
40+0 30 -27
63+0 18 -10
80+4 9 -6
32+0 6 -4
50+0 14 +2
40+2 6 +3
63+8 4 +2
32+6 5 -3
63+8 33 -7
25+5 9 +2

The second to last filter is the house curve. The final filter to fill in the small dip between 22 and 36 hz was applied after the graph was generated (I've taken enough spl meter readings for a little while).

I used the berringher software for a while and arrived at a decent set of filters that were an huge improvement, but I thought I could do better so I started over.

The current set was arrived at strictly from spreadsheet calculations (applying the knowledge gained from the first pass). I first applied a 'global' filter that was an approximation of the sub's overall response and took a new set of readings. This flattened much of the curve but didn't extend quite high enough so another was added at 63. At this point the response was enormously improved and if no other filters were available it would have been worth it just to apply these two.

The remaining filters were applied iteratively as repeated readings were taken and smaller and smaller bumps and dips were squashed or filled. This was more time consuming than approximating the overall curve with the software but the results were definitely superior.

Moving the sub to the corner was a major improvement. The change after applying the bfd filters is a transformation.

I've watched several scenes and listed to various musical selections (including organ music with 32' stops). Very nice!

Thanks again for the help.

 

[KyleGS]

How do you like the sound of the ruler flat reponse when listening to music (things like current pop and rock music)? If you don't mind me asking...

 

[Wayne A. Pflughaupt]

It’s not flat, Kyle. There is a 6dB slope from 100 to 22Hz.

Which brings me to what I was going to mention to George. That’s a pretty shallow house curve. Unless you have a huge space (significantly greater than 6000 cubic ft.) you probably need a steeper slope.

If you have some sine-wave test tones, play one at about 100Hz, and another at 32Hz. They should both sound (not measure) like they are at the same volume. If 32Hz sounds weaker, you might try increasing your slope.

Also, does this chart show response of just the sub, or with the L/R mains on? If the former, you should take final measurements and make final EQ adjustments with both operating.

Regards,
Wayne A. Pflughaupt

 

[Zack_R]

If you have some sine-wave test tones, play one at about 100Hz, and another at 32Hz. They should both sound (not measure) like they are at the same volume. If 32Hz sounds weaker, you might try increasing your slope

Is that really necessary?

Isn't a recording engineer mixing / recording the songs based on what he / she thinks sounds good? If they have a similiar low frequency hearing loss like everyone else, wouldn't this be compensated for by them boosting the bass when m,aking the recording so that it sounds good? It would seem that this could produce the best playback results when played on a flat system. If the recording engineer boosted the bass on the track so it sounds right to them then wouldn't it, in turn, sound about the same to someone playing it back on a fairly flat sounding system.
The song could actually be very dynamic and no "house curve " would need to be applied.

I really don't know that's why I'm asking the question.

 

[KyleGS]

Well that's pretty flat by *my* standards. I was just curious how such a response sounds on current popular music. I hear many people complain about relatively flat reponses sounding "sterile" with no personality.

 

[GeorgeS]

Wayne, Kyle, Zack -

The listening/viewing area is part of a larger space that opens to a loft via a very-nearby stairwell. For the purposes at hand the 'space' is probably on the order of 4800 cubic feet.

Yes, its a fairly shallow boost, but it was set deliberately. I used the process you suggested, comparing 100/56/32. It was a bit of a pain switching back and forth and I'll probably burn a cd that has alternating tones on it to facilitate the process. When we were comparing perceived tone levels my wife consistently reported stronger perceived levels on the low tones when I set them to what I thought sounded flat. Given the expenditures and 'redecorating' I've done with the system, I figured I would defer to her conservative assessment.

My feeling is that its a little flat for rock and pop, but I don't really listen to that much. Kick drum/slam fans would probably want a steeper curve, but I've been pleased with the sound for classical and some of the other music we listen to (e.g. Lorena Mckennitt, King's Choir around Christmas, ...), although this is the only system I've ever had of any quality. I thought we'd listen to it 'mild' for a while and boost it later for ht if we wanted a little more 'oomph'. A friend was over last night for 'show and tell'. He was very impressed. I'm not sure what changed her opinion but my wife now seems to agree with my original assessment that it could use a few more db boost.

This was one of the reasons I posted, but I didn't want to color the feedback by asking to have my own opinion validated - figured I'd see who said what unprompted. Thanks for the feedback.

That was the other reason I posted. I appreciate the support getting it set up and wanted to 'report back' with the results. Thanks again.

 

[GeorgeS]

BTW: the mains are operating above. I measured higher but didn't post that part of the graph as I haven't worked on anything but the sub.

BTWBTW: my test cd has 'warble tones' in addition to the 'regular' tones I've been using to take measurements. I surmise from their presence that they have value, but have to admit I don't know what it would be (variation reduces obnoxious standing waves??) Anyway, open to any enlightenment here as well.

Thanks

 

[Stephen Dodds]

Warble tones are supposed to reduce room effects, which makes them less than useful for checking room response .

Personally, I wouldn't touch that response. It might sound a tad light at low volume levels, but unless you want to a 'loudness' curve it seems very accurate.

Steve

 

[Wayne A. Pflughaupt]

Zack,

Isn't a recording engineer mixing / recording the songs based on what he / she thinks sounds good? If they have a similiar low frequency hearing loss like everyone else, wouldn't this be compensated for by them boosting the bass when m,aking the recording so that it sounds good?

This isn’t so “cut and dried” as it may seem.

There is no “universal” standard for this.

For instance – the size of the studio the engineer is listening in will affect his or her perceived bass response. As will the speakers he’s listening on. For instance, they might be naturally bright, in which case he would boost the bass. Or, they might be a little weak on the top end, which prompt him to reduce the bass. Perhaps you can see why it is that anyone who has more than one CD or DVD will testify that bass levels vary on one disc compared to another.

Not to mention – the engineer has no idea if you’re going to be playing his CD in a car, your living room, or a large dance hall (if you’re a DJ, for instance). The smaller the space, the more the slope of house curve needs to increase in order for the bass to sound natural.

Hope this helps.

Regards,
Wayne A. Pflughaupt

 

[BruceD]

George,

my test cd has 'warble tones' in addition to the 'regular' tones I've been using to take measurements. I surmise from their presence that they have value, but have to admit I don't know what it would be (variation reduces obnoxious standing waves??) Anyway, open to any enlightenment here as well.

warble tones are quite useful for checking equal SPL levels across the xover boundary between mains and sub. Since they are relatively unaffected by room modes, they give a more accurate SPL output reading when checking frequencies just below, right at, and just above the xover frequency.

 

[Zack_R]

Yes, I agree there's no universal standard for the way recordings are made. You would think, to a small degree, kick drums should sound fairly similar from band to band. I have a few CDs where all you here is the foot pedal striking the drum and no accompanying bass.

It would be interesting to note if George has calibrated his flat bass line with his main speakers (such as the avia 5.1 sub test). If the calibration is a little under it may account for why the bass seems anemic. If it is flat and the bass sounds anemic it may have something to do with the house curve effect.