Unexpected results with Alpha Pro Diffusor/Absorbers

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brucew268

I’m getting some unexpected results in experimenting with Alpha Pro panels 1D (which I take to be BAD-type panels) and not clear how to interpret them.

My Hi-Fi is in my home office, 11’x12.4’, so not really any soft furnishings except carpeting. The speakers and listener make a 6’ equilateral triangle basically centred in the room with 4’x2’ absorption panels at the first reflection point.

When I replace the absorption panels with same size 1D Alpha Pro type, busy music becomes a bit more clear and can more easily keep track of various instruments in the mix, BUT I lose depth and dimensionality in the more centred voices and instruments. This has a negative impact on the realism of voices, etc.

When I keep absorption at the first reflection points and put the Alpha Pro’s on the wall behind the left and right of my shoulders, there is a noticeable increase of pressure in the room and everything feels a bit too in your face and crowded. So I assume that is a phase problem somehow introduced.

I’ve also played with Alpha Pro’s next to the absorption panels directly adjacent to the speakers, but also get that increased pressure and in your face presentation, just a little less so.

What should this be telling me and what might I try instead?

I was trying to introduce some diffusion because the room feels a little small acoustically in busy passages and I wanted to get some of the acoustic space back that I heard when it was set up in my main lounge – which I thought diffusors should do. Of course the room is small enough that I can only get 5ft between me & “true” diffusors if put at the first reflection points.


JWL.GIK

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Re: Unexpected results with Alpha Pro Diffusor/Absorbers
« Reply #1 on: 8 Feb 2023, 06:15 pm »
Hi Bruce,

A few comments. First thing is, when making changes like this in the room, make sure you give your ears enough time to adjust to the novelty. Ideally this should be weeks, not minutes or hours. Lots of interesting nervous system/perception/psychoacoustic stuff going on in this suggestion -- this article is a good place to dive a bit deeper into that if you are interested. Short version: most often our first impressions are negative whenever there's a change from something we've gotten used to. But once our ears have time to adapt to the sound we can often find it's actually better.

Second thing is, to better evaluate what's happening, you might consider getting some testing software going. This will give us more specific clues, and helps us put our subjective listening impressions into a more objective context. I have some idea what things like "realism of voices", "in your face and crowded", etc mean, but what you intend and what I interpret could be very different. The data helps eliminate confusions like this.

Lastly, I'd post more detail about your room and the setup, showing all the treatments in the room. Coverage area (surface area of all panels in the room, relative to room size) is the most important part of performance so having a better idea of what's going on in the room can help us better troubleshoot this. If you were working with a GIK designer, definitely email them directly, or if not you might consider using our Free Advice Form on the website to get that detail over to us and we can help you improve things.

brucew268

Re: Unexpected results with Alpha Pro Diffusor/Absorbers
« Reply #2 on: 8 Feb 2023, 10:09 pm »
Yes, I recognise the psychoacoustic phenomenon. Yet, I regularly try changes to see if it improves an aspect of the music presentation I find lacking. Usually, I find the effect is mixed. Tweaks often emphasize certain frequencies which make some aspects sound better but at the expense of other aspects and the overall balance. Not to imply acoustic treatment are tweaks, instead fundamental to sound.

In this case I’ve had the Hi-Fi in two different rooms and noticed that in the smaller one the music felt less relaxed and able to breathe, a bit more congested – slightly busy and muddy. In the larger room the effect was as though the sound wave had more room to expand and take shape before being reflected back.

My understanding is that when properly implemented diffusion should address exactly those aspects. With my attempts in my room with the Alpha Pros, I was expecting something moving that direction but found it moved most of that the opposite direction. It helped the slight clarity/muddiness issue but strangely made things busier and more congested, and made the room feel smaller and over pressurized -- and imaging lost depth. I'm not really willing to listen for days let alone weeks to sound like that – not being a masochist.

In this office, much of the walls are lined with cabinets and bookshelves, so the first reflection point has full size (4’x2’) acoustic panels leaned in front of them. The desk behind me has various bits that break up the sound but also a flat monitor and lfat wall behind it. I have a couple 4’x1’ panels placed elsewhere to address some specifics. I did try a couple extra 4’x2’ acoustic panels adjacent to the speakers and it might have given a very slight improvement -- I was surprised not more, but putting the 1D Alpha Pros there had the opposite effect. (No room for bass traps unfortunately, but judicious speaker placement seems to be balancing that OK, unlike the main lounge which needs and benefits from a few bass traps.)

Yes some analysis software and a calibrated mic would be good, but that puts any answers weeks out from now… and a technical learning curve. I was hoping the descriptions above would give clues. I guess not.
« Last Edit: 9 Feb 2023, 09:54 am by brucew268 »

ric

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Re: Unexpected results with Alpha Pro Diffusor/Absorbers
« Reply #3 on: 9 Feb 2023, 02:42 pm »
I have limited experience, but I do have a few cents worth.
I have tried some DIY bass traps and found I liked one in the corner--having one in each corner robbed soundstaging/imaging.
For years I have used DIY Shakti Hallographs and highly recommend trying them if you are semi-carpentry competent. You can PM me, if so.
It also sounds like with all the cabinets in the room the reflection points may be moot.
    Good luck!

Carl V

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Re: Unexpected results with Alpha Pro Diffusor/Absorbers
« Reply #4 on: 9 Feb 2023, 02:50 pm »
Not every recording/mastering engineer likes Phase altering Diffusion & scatter plates.

I like their Poly Diffussors.

Next your room may be too small to effectively place Diffussors.
 You need some distance between the speaker & the Diffussor.
And you need some space between you and the Diffussor.

Best of luck. 

brucew268

Re: Unexpected results with Alpha Pro Diffusor/Absorbers
« Reply #5 on: 9 Feb 2023, 09:58 pm »
Not every recording/mastering engineer likes Phase altering Diffusion & scatter plates.

I like their Poly Diffussors.

Next your room may be too small to effectively place Diffussors.
 You need some distance between the speaker & the Diffussor.
And you need some space between you and the Diffussor.

Best of luck.

Hmm. I thought scatter plates (Alphas) did not alter phase but QRD diffusors do. Did I get that wrong?

Too small? Maybe. I knew that QRD's require some space (at least 5') from the listener but was not aware they need significant space from the speaker as well. Is that true?

Carl V

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Re: Unexpected results with Alpha Pro Diffusor/Absorbers
« Reply #6 on: 9 Feb 2023, 10:39 pm »
Hmm. I thought scatter plates (Alphas) did not alter phase but QRD diffusors do. Did I get that wrong?

I don't know id Alphas alter phase as much as QRD or at all.

Too small? Maybe. I knew that QRD's require some space (at least 5') from the listener but was not aware they need significant space from the speaker as well. Is that true?

Again I don't know the exact answer to your queries. I'd like to hear from our Acoustic Specialists.