Axiom Home Page Forums General Discussion Stereo Active LFRs and room treatment question

This post is aimed at Ian and Andrew but others are welcome.

I’m building a combo HT and 2ch listening room. My thinking on the ALFRs is that they need a untreated front wall from behind the speaker to the side wall and untreated side wall from a few feet in front of the speaker to the front wall but I’d like to verify that.

What I like to know is if putting diffusion between them (behind the screen) is Ok.
Same goes for the absorption at the first reflection.

Guess the discussion I want to start is about treating rooms with active LFRs …

I did find this article, particularly pages 22-24:

https://www.harman.com/documents/LoudspeakersandRoomsPt2_0.pdf

My interpretation is don't mess up an average room by buying acoustic treatments for an imaginary problem. haha

I think wall-to-wall carpeting and drapery will probably do more for a room than any acoustic paneling or diffuser ever will.

Floor carpet and maybe a 5 foot thick mattress along the back wall and you're golden. The more homogenous all room boundary acoustic properties are the better.

Hi Hambrabi,

I'm not one to over treat but I do experiment listen and measure ...
Trevor mentioned adding diffusion behind the screen (it's acoustically transparent ... well almost ... ~3db loss)
So I thought I'd try it but then got to thinking about how LFRs work and had this question and thought I'd see what people had to say.

Guess you replaced your back wall treatment with a 5' thick mattress since your suggesting it ... I'm sure that must of been a upgrade from the furnace filters and fabric stuffing you had there previously ... anyway most of the stuff I read on back wall treatment suggest that diffusion works well in most cases ... an experiment for sure ...

Actually Mojo, I'm looking for carpet ... any suggestions on what type I should look at ...

I have 3/8" thick, 10 lbs density underpad with high quality berber. It's 15 yrs old and still looks brand new even though I've dragged speakers and subs all over it. Back in 2007, I paid 5 grand Can for stairs and 680 sq ft for removal and disposal of the old carpet and underpad, and installation and material of the new. It's warm and sounds fruity compared to the nutty sound of the old carpet.

Don't knock the furnace filters and stuffing until you try it. You may want to include a couple of in-line, galvanized aluminum humidifier evaporator pads halfway in between the furnace filters and the wall. I found improved separation of details with the M100s. With the actives, I don't need the pads.

Ahhh, you still have the filters … and your giving away your valuable hard earned secrets telling people about the evaporator pads

Was thinking about berber … but also was wondering if what they use in theaters would be better. In the past I’ve had issues with rugs and carpets especially at high traffic points like doorways

My doorways don't drag on the carpet. I also forbid shoes indoors. Such a filthy habit!

How much room will you have behind your screen? I cant remember what CC you went with in the end. Vert OW180?

I would leave wall behind and beside LFRs open a few feet all around. The LCRs in my room have open back “Mid tunnels”. I had to remove absorbent SBIR traps. They sounded lifeless and dull. Smaller.

The neat thing about front wall diffusers is they work with lower frequencies and late reflections. Huge clarity benefit. I always say it deletes your impression of a fixed boundry, great for a huge screen with a diorama effect. A QRD is a great choice in this spot as you can make it deep with no penalty to room footprint if behind screen.

Pair that with the pop of a calibrated LX-NZ3….. just stupid good.

Haven’t bought one yet. Still have my VP180HP which I’ll sell or trade … planning on getting a VP180ow … was going to hang it as intended to keep the tweeters in line. If I wasn’t planning for masking I would have gone with a M180ow and made the area below screen also AT.
Have you heard the VP!80 vertically?

how deep do I need for a QRD? Currently I have 6” …

The projector should arrive sometime in June … it a LS12000

How much of the front wall surface should be QRDd?

The area a PJ screen would occupy. Pretty much area between speakers in entirety.

Dont need floor to ceiling or anything, but likely wouldnt hurt.

Similar to this in this ridiculous video.

https://youtu.be/Tyt3lselVm0

Geez those two are so full of shite.

yup, manage to listen to them for a little over a minute then needed to disengage
But I saw what you sent us there for ... the QRD between the speakers .. never saw one that big before
How deep is your QRD Trevor?

(If I did know the meaning of them meaning of the last few lines ... I'd be flagging the mod about some pervert ... Mojo, that's your Q)

You have a lot more room behind your screen ... think it was what... 3 feet?

Yeah close to 40” or so to work with behind theater screen wall. QRD is 8” deep. In my other 2ch room I have Arqen’s fractal “diffusers” up front. Same idea just a gentler effect about 4” deep. I would go QRD vs any other type if you arent going to see them or have enough depth. They can be gorgeous if made from wood, but weigh a ton. Mine are both EPS foam based and painted solid color.

This guy copied their rooms front wall after his Sonus Faber visit. He still hasnt reviewed the M5s properly after his Axiom factory tour…. I guess he would vote for QRDs. Although his look shallow?

He is ridiculous too though….

https://youtu.be/raBihcmADDg

Maybe I’m ridiculous? Dunno.

One would need 1.5 foot deep QRD to get down to 200Hz?

A QRD may not do me any good with a 55" LCD smack dab in the center of the 12 foot speaker width.

I can see the M5s wouldn't interest him unless they wore a leather dress.

I'd love to take part or see a double blind test with some of these high dollar speakers and other brands that are less $$$$. Not just to be like " look at Axiom" but to really see if these technlogy atually work to makethe sound more enjoyable or real. The doulble blind test would sure make leather clad front baffles seem a bit frivolous. I cant say i'd pck axiom for sure in that test, i really dont know until i tried a test. That would be incredibly fun to see the results, especially with songs and music that I was familiar with. I guess in the it's all pretty subjective, but removing the visual out of the test to limit a speaker to how it actually sounds is the real test. His review of the Sonus Faber was interesting but revolved alot arounfd how they looked and a bit about how they sound. If all there was was the sound to talk about than I think reviews would be believable. I bet most manufacturers are not keen on particiapting in a double blind test bc they aren't sure how they would fair.

Wouldn't it have been sweet if those two pooftas had shown listening window and sound power curves to justify the use of the leather?

Yeah, exactly. Wheres the proof eh? Like sure they're beautiful to look at but dam you better hope they ound as great as they look. Agreed though, where are the graphs to back it up. Maybe on the website? I haven't looked to be honest. If i was a purchaser id be sceptical if the graphs were not available. There's not a ton of speaker builders that present graphs.

They don't publish any graphs. They never said the leather made any audible difference. They likely have no idea if they didn't characterize the speaker with and without the leather apron.

What makes leather acoustically better than ostrich feathers?

I'm sure the ostriches of north America will have a say in that ... cows not ostriches!!

I was thinking Asian ostriches. Their feathers are reported to be acoustically superior.

that's just discrimination ... ostrich miss-information

You're probably right. A lot of that going on. Like ostriches burying their heads in the sand.

Actually ostriches don't do that ... it's a myth ... but in todays world there seems to be a lot of people who do

Yeah...that's what I said. You read it wrong because you're older than me.

Trevor, how to you incorporate your on-walls with-in the QRD?

I’ve heard other Sonus Fabers in person and many others in Calgary high end shops. They do sound really good in my experience.

RRlev was any of this helpful?

To mount the OW center speaker I would use two seperate QRDs and leave a gap between them. Notch the QRD where it joins at center to accomodate your CC. Leave small gap around the speaker all around. Build depth same as mounted speaker. 4.5” or so. Ports should be unobscured.

This is something you can add down the road. Use foam. Way lighter.

I was thinking about how much space the on wall needs to be given so it doesn’t sound like it’s at the back of a bookcase.
If I made the QRD 8” deep that puts the VP180 drivers at 4” … so my first guess would be to give it at least 6” of space all the way around.

I’m assuming your thinking of the QRDs made of blocks and not the slat kind … also
This might be another use for Axiom’s packing foam … I’ll have to add that one to the packaging reuse thread

Just block the speaker off the wall to suit your build depth. You are thinking a 2D skyline. Didnt do one of those. More of a ceiling thing.

I used EPS for my Arqen fractal upstairs. Built a hot wire foam cutter and worked well. Pretty accurate cuts and was a fun project.

For the Big QRD downstairs I used 1/8” wall panelling cut into strips for well dividers and 3” wide rigid packing foam. It is over 6’ wide and 48” tall or so.

Gotta be a rigid product whatever you use. The arqen is way lighter than a true QRD. Sections can be held in place with 3M command strips… but not a true diffuser like a QRD.

Here's an interesting DIY QRD build concept ... might add a bit of weight but it reduces depth allowing one to diffuse lower frequencies ... Folded Well QRD

on blocking out the center ... it might still need space around it but it does not have ports so ... have to ask Axiom about that.

Do yourself a solid and don't ever listen to the virtual centre the active LFRs holographize during a movie. You may then want to move to the LFR 180.

Have you tried the LFR180 Mojo?

BTW I listened quite a bit to the ALFR with a virtual center … that’s how I determined that it was not going to work for my space.
It’s fantastic if you never plan to have more then two possible 3 people if you sit close.

I’ll try it again when I get the seating in but I fully expect to end up with a 180ow behind the screen.

I agree with you.

Never tried it. One fellow came on the board and raved about it. He bought 100 grand of gear. A 1500 for each set of drivers in each of his actives.

Bet he never uses more than a 10th of that …

Be interesting to ask what voltage each input of the active speaker tops out at.
That along with max power it can dissipate will tell you when you have maxed out amp wise.
Bet a 1500 per woofer and a 1250 for everything else would be close (that is if you needed more than a 1500 alone/ALFR)

Given the nature of the LFR to send sound off the backwall, i've not put any thought into adding anything for sound purposes in those locations. Am close to getting a diffuser for the side wall opposite our curtained wall though (an acoustic felt product). Hopefully will have time to finally tune all the system in and measure it in the coming weeks, though a channel in our Axiom amp went dead so i have to get that resolved.

Some neat QRD ideas
https://www.soundtreating.com/qrd-diffusor/

The triple woofers are 800W, each mid is 75W for a total of 300W and each tweeter is 25W for a total of 100W. Hence 1200W.

Where did you get that info?

Mojo’s lab.

Trevor,
Really like the folded QRD designs. Think I might try a building a folded design using foam/board the way you did. Just have to figure out how to stiffen and support the fold … probably a combo of ply/foam held by standoffs. If I put the screen out 8” I can apparently get some effectiveness down to 125Hz … not sure how he’s calculating that … as he gives a theoretical number of 250Hz.

On the speaker blocking … I’d like to have some space between the screen and the front of the speaker … so no blocking behind. Just need enough space around it.

Sounds great to me. Cant wait for pics!

Might be a while as the plan was to have the screen, carpet, and seating, to get baseline measurements, before starting any treatment projects. The screen and projector are supposed to be here this month. The seats hopefully by August. The carpet I haven’t ordered yet. I might have to come up with an alternate plan as once the projector and screen are in … Im not gonna be able to wait!

I’ll try and post an update to the HT thread soon.

Mojo, Kind of looking back and had some questions …
Is that for max excursion? Heat dissipation? or something else …
Was it measure at a frequency or broadband (noise or other)?

Guess I want to know how you measured it … I.e. what does this wattage actually mean
and if instantaneous power above that is useful. I’m assuming it is …

It’s been a while since I’ve taken my electromagnetic courses … almost want to bone up on it again … but
Can’t even remember how to do differential equations no less Maxwells anymore …

Ok…I’ll bite … you managed to separate the cone, voice coil, surround, and spider from the magnet and basket …
btw that spider looks like you chewed it off with you teeth.

Ok Mojo … use your words ….
Whatever your trying to tell me I’m obviously not getting it …