Think OB makes the room irrelevant? Think again.

Tyson · « **on:** 27 Jun 2011, 07:25 am »

OK, I admit that OB bass is a godsend in difficult rooms like mine. And that OB's have an airy, open presentation that box speakers have difficulty matching. But, does that make the room (and by extension, room treatments) irrelevant?

NO! In fact, in some ways I think that room treatments are more important with OB than with box speakers - after all, box speakers are mostly front radiators, and have a longer time cycle before interacting with rear walls (side walls are another story).

I had a head-slapping moment today that brought this home. I've been trying to get better soundstage depth in my setup, something OB's are supposed to excel at. But I think the hard, flat, reflective surfaces on the rear wall kinda killed that, even with my speakers pulled 4 feet into the room. I have twin windows roughly behind each speaker. I leave them bare, usually, because we live in downtown Denver and the view out of these windows is spectacular.

Today I dropped down my hexcomb window blinds on a lark. Holy crap, the sound improved more from this than several weeks of tweaking crossover and eq settings in my active crossover!!!

But, here's the really awesome news - my wife has agreed to let me put up acoustic treatments in corners of the front wall! Tomorrow I sally forth to find some Owens Corning 703 compressed fiberglass to build some "real" treatments for the room. I'm stoked!

JohnR · « **Reply #1 on:** 27 Jun 2011, 07:53 am »

What's hexcomb?

Tyson · « **Reply #2 on:** 27 Jun 2011, 08:05 am »

I have the blackout honeycomb shades -

Tyson · « **Reply #3 on:** 27 Jun 2011, 08:17 am »

Here's a pic of my actual setup (speakers are much further into the room now) -

JohnR · « **Reply #4 on:** 27 Jun 2011, 09:04 am »

Can't quite tell what they are but that's interesting to read anyway

Rudolf · « **Reply #5 on:** 27 Jun 2011, 09:15 am »

Quote from: Tyson on 27 Jun 2011, 07:25 am

NO! In fact, in some ways I think that room treatments are more important with OB than with box speakers - after all, box speakers are mostly front radiators, and have a longer time cycle before interacting with rear walls (side walls are another story) ...

Think about it. What you really want to say is, that dipoles need room treatment at OTHER places than box speakers. Right? MORE Treatment? I don't see any proof of that in what you are writing.

Quote

Today I dropped down my hexcomb window blinds on a lark. Holy crap, the sound improved more from this than several weeks of tweaking crossover and eq settings in my active crossover!!!

Did you ever try this very same "tuning" with conventional monopole speakers? What difference did that make?

ebag4 · « **Reply #6 on:** 27 Jun 2011, 12:36 pm »

Quote from: Tyson on 27 Jun 2011, 07:25 am

Today I dropped down my hexcomb window blinds on a lark. Holy crap, the sound improved more from this than several weeks of tweaking crossover and eq settings in my active crossover!!!

This is in line with my findings. In my space diffusion is what was needed on the front wall. Absorption between the speakers on the front wall killed the sound somewhat, of course I did have a considerable amount of absorption. In my case a poly-cylindrical diffuser made of thin plywood improved the sound stage considerably, additional absorption in the gap created by the diffuser and wall seemed to help the bass response as well. I already had corner traps in place.

Best,
Ed

BPT · « **Reply #7 on:** 27 Jun 2011, 01:15 pm »

What Tyson and ebag4 may be doing is reducing the amount of direct reflected out of phase sound (from the rear of the OB) that they hear at the listening position. This will allow you to hear a little more of the in phase sound coming from the front of the speaker which will improve perceived imaging and depth of soundfield. It will take some trial and error to find the most absorption and/or diffusion to use before you start messing up the speakers overall power response.
Chris H.

PDR · « **Reply #8 on:** 27 Jun 2011, 02:13 pm »

Timely thread for me.....

I have the V-1s and just last weekend started to treat my dedicated room.
I have been in it since Dec, but my work is out of town and I am only home 4 days out of
14 so it goes slowly. I built 4 absorbers, one for 1st reflection on sides and ceilng, and one to cover
up a window that is located on the rear wall.....bass traps are next weekend.

I was surprised at the results as well. The room was quite lively before treatments, they tamed
them but what was really impressive was the improvement in tone(?) of the voices and instruments.
they are a bit more focused as well. The soundstage seems to of narrowed a bit but I was expecting that.
The panel sitting below the rear wall is for the ceiling, and I wonder what that will do.
There is a gap below and above the rear absorber to let heat escape from between it and the window
I'll have to address the daylight that shines through the gap.
The equipment sits on an old coffee table for now, I will build a low stand for it and bring it out
from the rear wall and hope to get some type of diffusor
below the rear panel....perhaps like what Ed has done.
I am driving the speaks with my Sunfire HT gear for now as my tube amp is in need of repair so I am looking forward to get it back in the chain.
The time and effort has been well worth the improvement.

ebag4 · « **Reply #9 on:** 27 Jun 2011, 02:21 pm »

Quote from: PDR on 27 Jun 2011, 02:13 pm

Timely thread for me.....

I have the V-1s and just last weekend started to treat my dedicated room.
I have been in it since Dec, but my work is out of town and I am only home 4 days out of
14 so it goes slowly. I built 4 absorbers, one for 1st reflection on sides and ceilng, and one to cover
up a window that is located on the rear wall.....bass traps are next weekend.

I was surprised at the results as well. The room was quite lively before treatments, they tamed
them but what was really impressive was the improvement in tone(?) of the voices and instruments.
they are a bit more focused as well. The soundstage seems to of narrowed a bit but I was expecting that.
The panel sitting below the rear wall is for the ceiling, and I wonder what that will do.
There is a gap below and above the rear absorber to let heat escape from between it and the window
I'll have to address the daylight that shines through the gap.
The equipment sits on an old coffee table for now, I will build a low stand for it and bring it out
from the rear wall and hope to get some type of diffusor
below the rear panel....perhaps like what Ed has done.
I am driving the speaks with my Sunfire HT gear for now as my tube amp is in need of repair so I am looking forward to get it back in the chain.
The time and effort has been well worth the improvement.

Your room is looking great Perry, nice space.

Best,
Ed

Pez · « **Reply #10 on:** 27 Jun 2011, 04:57 pm »

One of the big things I said to Tyson last time I was at his house was that I really notice the difference between my system and his when it comes to room sound. A lot of echoey liviness and I don't mean that in a good way. IMO open box speakers need room treatment behind the speakers. There is just a lot of issues with uneven rear wave issues with them. In fact I think they probably need more treatment and better diffusion than conventional speakers.

jtwrace · « **Reply #11 on:** 27 Jun 2011, 05:16 pm »

Quote from: Pez on 27 Jun 2011, 04:57 pm

I think they probably need more treatment and better diffusion than conventional speakers.

From my experience, with the exception of a CD controlled speaker, I completely agree.

JohnR · « **Reply #12 on:** 27 Jun 2011, 05:24 pm »

Geddes plug alert. Relevance: zero. Move on. Beep Beep.

jtwrace · « **Reply #13 on:** 27 Jun 2011, 05:29 pm »

Quote from: JohnR on 27 Jun 2011, 05:24 pm

Geddes plug alert. Relevance: zero. Move on. Beep Beep.

Actually not. That's my experience.

PDR · « **Reply #14 on:** 27 Jun 2011, 06:22 pm »

Thanks Ed....

Nyal Mellor · « **Reply #15 on:** 27 Jun 2011, 07:07 pm »

Ah, OBs and room treatment. Really it's quite simple - OBs just have different radiation characteristics than conventional forward radiating and CD speakers. In some regards this means they interact with the room nicer (e.g. less modal excitation), in other ways worse (e.g. the back wave reflection). All speaker designs need room treatment, it's just they need it in different places...IMO dealing the back wave is very critical to realizing best SQ from OBs.

jimdgoulding · « **Reply #16 on:** 27 Jun 2011, 07:26 pm »

I had electrostatic speakers four feet out from the back wall and it seemed to work well BUT I listened only six feet away from the speakers in very nearly an equilateral triangle. Didn't seem to interfere with imaging and yielded a large and spacious soundscape at that distance tho depth of field might have been better. Listened to some Magnepan speakers at a dealer that were nearly a foot closer to the front wall and they sounded bright and harsh. Then the dealer put some round Acoustic traps behind them that could be rotated for absorbtion or diffusion and they became much more pleasant sounding. Diffusion easily worked best. Absorbtion dumbed them down too much.

Nyal Mellor · « **Reply #17 on:** 28 Jun 2011, 01:10 am »

Jeff Hedback and I are currently working on a white paper on the acoustical standards for two channel / stereo that will include a section on dipoles. Our basic take on dipoles wrt the reflection from the wall behind the speakers:

----begin excerpt----
Dipoles radiate equally forwards and backwards. This makes placement of the dipole relative to the front wall (behind the speakers) particularly critical. ~15ft path length difference is required to reduce the level of reflection from the front wall to -15dB (our standard for the level of reflections relative to the direct sound). This calculation is correct for a point source. For a true line source (floor-to-ceiling) the distance is much larger since SPL falls off 3dB per doubling of distance as opposed to 6dB for a point source. 15ft path length difference requires the dipoles to be placed around 7-8ft from the front wall, which in most living situations is not practicable. Placing a dipole closer to the wall requires that wall to be acoustically treated. The difficulty is that this selfsame acoustical treatment can distort the dipole radiation pattern resulting in unwanted changes elsewhere.

Rocket_Ronny · « **Reply #18 on:** 28 Jun 2011, 01:35 am »

My take is that if the back wall is not treated you need to have the speakers at least 6 feet out. 8, 10, or 12 feet is even better.

Or. spread them wide with a hard toe in, so the back wave is sent to the sides.

Or, dampen that back wall.

Best solution sonically is to get a big room and pull your speakers out farther than you dare. I knew an audio dealer in the 80s who had Tympani 1Ds and had 20 feet behind them. WindChaser had Acoustat Model IIs and had at least 12' to 14' behind them. The audio store owner who set up the Acoustats and owned the Typanies said it was the best system he had heard. It was riveting. I was not so lucky and only had 5' behind my Acoustat Model IIIs.

Rocket_Ronny

jimdgoulding · « **Reply #19 on:** 28 Jun 2011, 01:40 am »

Hi, Nyal. I wound up with closer to five feet off the front wall and adjusted my seat to maintain a six foot triangle. The room is 15' long. Behind my seat the room was 50% open to a foyer with a diagonal staircase and a shallow secretary in the enclosed corner the doors of which were removed for diffusion. I think, and this is based on nothing scientific only my experience, that where you sit in relation to your speakers and room boundaries matters a great deal. I listen with direct radiators today in nearly the same config tho I have replaced the secretary with large open backed record cabinets for better diffusion and storage and everything seems independent of my enclosures and space. My recordings live and breath. That make sense? I look forward to your publication only about direct radiators these days. Best

Ronny, mine were Acoustat Three's, also.