I said "massive" and that's what it is. I store blocks of uncut foam and piles of cut scrapes behind my screen, and hence behind my speakers. Its size varies depending on if I am low on foam or just received a new bun.
In other rooms we used several layers of heavy curtains hung several feet away from the walls.
Yes, above about 1kHz the speakers are quite directional, but remember they are toed in so there is still some sound towards the back wall.
OK, and empty room - that's not really appropriate since it was not the room "as used". It's what happens once the room becomes "usable" that kills the RT. Carpeting, big plush sofas, wall hangings, people. All that absorption adds up. And let a woman "decorate it" and all of the RT is gone!
I'm talking about a common room, as used, with people in it, etc. These rooms tend towards being too dead in general and unless you pay attention to NOT having this happen, it will.
Well it's less of a change than treatment with OB speakers, for sure! But unless something radical is done, I always hear the wall. The wall limits the depth of the image.
Remove the wall or move it way back and the depth goes way back too. Heavy absorption as Geddes uses can effectively remove the wall - at least above some certain frequencies. It works well. Random diffused reflections from behind the speakers can sonically remove the wall image, too. I prefer that to a dead wall, but not everyone does.
Maybe different people hear this differently. I've sat before many a pair of speakers (even my own) and heard others exclaim the "vast depth" behind the speakers. I don't hear it unless there is heavy treatment or a true vast distance.
OK, got you. I was starting with an empty room and trying to improve it in a systematic way - that's different. I'm happy with the results so far. Probably need to measure again, now that the room is full of junk.
No they don't. Not at all.
Of course there is more to the problem. Does anyone here really doubt that?
Nobody said RT60 would completely describe what a room sounds like, just that it was one factor.
And as a matter of fact, the polar response of the speaker has changed - it's been rotated by 60 degrees. So relative to the room and listener, the polar pattern of the speaker has been dramatically changed.
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Maybe you should build something that's more directional at low frequencies 😀. You know it can be done!
Ah, well that would do it.
I've seen a lot of folks hang a 1/2" sheet of packing foam, egg crate or a curtain on the wall behind their speakers, thinking that would do something. They were trying to go for damping like you have with the massive piles, but a thin layer right on the boundary does nothing. I usually tell them a thin sheet like that doesn't do anything except be an eyesore.
That's true. It isn't an issue with constant directivity cornerhorns, since they are acoustically close to the boundaries, essentially flush with the adjacent walls. No reflections. They're actually directional down to the Schroeder frequency. But that isn't the case with traditional horn/waveguide speakers. As you've said, the toe-in directs the pattern more towards the back wall. So it isn't attenuated nearly as much.
I really do like the constant directivity cornerhorn approach. It just solves so many problems. But it has one of its own in that it can't be used in every room - Some don't have the right corners. It's a magical setup in rooms with suitable dimensions.
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No reflections? I'd think that having a boundary next to the horn mouth is detrimental.
Not if the wall is the horn. It's an integral part of the flare expansion. The source is at the apex, and the walls, themselves, form the flare. That's the basic idea behind the constant directivity cornerhorn.
Both the woofer and midhorn are acoustically close through the passband. The tweeter is only acoustically close at the low end, but not at the highest frequencies. I suppose you could make a version that's snuggled back in tighter, if desired. My thinking is directional control increases as frequencies go up, so it isn't as much an issue. It's also easy to damp high frequencies. Some people install absorbent foam cradling their tweeters, surrounding it on both sides, behind it and towards the wall. That works great at the higher frequencies.
Of course it CAN be done, but is it cost effective?
You DIY guys just don't deal with the same issues that I deal with. I know, I don't belong here.
Markus - its not - don't bother, I've had this argument a dozen times and it just doesn't sink in.
I was alluding to comments that seemed to imply that the very early reflection patterns don't matter. In your example it's precisely that pattern that changes and that's about all. The direct field at the listener is the same, the sources DI remains the same, the rooms T60 remains the same, all that really changes is the VER pattern. If the sound is different then this pattern is important.
I know that you don't find this surprising, but the comment was meant to address other posts.
I actually had proposed this exact test to Floyd Toole at one time - he was not very receptive. To me it proves a lot.
Explain what you think should "sink in" please.
In the meantime, let me tell you what I think should "sink in".
In a constant directivity cornerhorn, the tweeter's orientation is no different than a more conventional waveguide loudspeaker toed-in 45°. Whatever advantages or disadvantages I've gotten from this arrangement seem to not be lost on you, since that's what you do now too.
The midrange and woofer are what differ. In the case of a constant directivity cornerhorn, they're snuggled back into the apex of the corner, acoustically close to the walls on each side. Because of this, there is no self-interference ripple off the backwall in the midrange. That's not trivial.
Further, the walls themselves act as large waveguides. You can blend them to whatever degree suits you in terms of throat profile desired. Personally, I am happy with what I have done with pure conical flares from the diaphragm forward, but if you would rather have a catenary transition, that's entirely within the scope of the design.
So what you have is a device that provides true waveguide loading from the Schroeder frequency upwards. Let that "sink in".
In the meantime, let me tell you what I think should "sink in".
In a constant directivity cornerhorn, the tweeter's orientation is no different than a more conventional waveguide loudspeaker toed-in 45°. Whatever advantages or disadvantages I've gotten from this arrangement seem to not be lost on you, since that's what you do now too.
The midrange and woofer are what differ. In the case of a constant directivity cornerhorn, they're snuggled back into the apex of the corner, acoustically close to the walls on each side. Because of this, there is no self-interference ripple off the backwall in the midrange. That's not trivial.
Further, the walls themselves act as large waveguides. You can blend them to whatever degree suits you in terms of throat profile desired. Personally, I am happy with what I have done with pure conical flares from the diaphragm forward, but if you would rather have a catenary transition, that's entirely within the scope of the design.
So what you have is a device that provides true waveguide loading from the Schroeder frequency upwards. Let that "sink in".
Sorry, I don't know them. I know the Aercoustics crowd here in Toronto and some Cavanaugh Tocci people in Boston.
I know where they are coming from and had the same debate with my boss at Aercoustics. RT is considered old hat but it is hidden in many of the more currently popular factors.
Beranek in his 1996 paper offers the following factors and weighting based on analysis of hall ranking: IACC - 25%, Te - 25%, SDI - 15%, Gmid - 15%, ti - 10% and BR - 10%.
Te is early decay time: essentially the early slope of the RT curve. SDI is surface diffusivity. Gmid is hall level gain at 10 meters from an omni source on stage. The Gmid equation relies on RT60 and other factors. ti is the initial time delay gap. And BR is the ratio between LF and MF RT.
So RT is wrapped up in 3 of the 6 factors.
At Aercoustics the design emphasis was on getting G to the right level, then a lot of work on increasing early lateral reflections, but there was always an assumption that a target RT would have to be met. (Generally by raising roof height to increase RT.)
David S.
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BUT when is the sound better? is it considered more realistic by an average human listener interested in HiFi music reproduction at home - because this is the only meaningful measure of quality of such a technical device as a consumer market High Fidelity loudspeaker, isn't it?
I'm long past discussing the relevance of measurements like RT60. All that matters is the reflection pattern at the listening position. Unfortunately we still don't have a satisfying answer how to measure and assess it.
Classic room acoustics and good work.
My living room has nice dimensions and near 12 ft. ceilings. I have 4 absorptive panels on the right side (4 " fg about 2 ft x 3 ft). Left of the speakers I've hung an oriental rug on the wall as the left side wall is very near the speaker. The wall behind the speakers is all glass but we have thick velour "theatrical drapes" with a liner. When you pull those drapes you really notice a difference as you talk.
I do have balance issues between the two channels and sometimes wonder about the rug on the left side wall....
David S.
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