[rramraj]

I recently got my Linkwitz Pluto's with subwoofers going. These are active speakers with the midbass firing at the ceiling. With these kind of speakers would the usual treaments , first reflections etc still apply? What basic treatments should I be looking at? I have a large thick carpet covering 2/3 of the room . My concern is the 8 ft ceiling. Should a diffusor be mounted there?

There seems to be a spike at the 31.5hz using test tones disc, where the whole room seems to be energised. Any advice is greatly appreciated.   

[lonewolfny42]

rramraj....Just curious....is this the speaker ? Thanks....

[rramraj]

Hi lonewolf,
Yup. Got a dear friend to build them for me.

Ram

[JLM]

Ram,


The 31.5 Hz spike is probably poorly characterized (seems like you're using the Stereophile test CD 1) as that disc only samples a few frequencies.  How did you measure?  If you used a Radio Shack spl meter, did you apply the correction factors (roughly 2 dB for 30 - 100 Hz and 6 dB for 20 - 30 Hz) for bass frequencies?

First, turn the sub off, then measure to determine a subwoofer crossover frequency (a bit below where bass response drops off).  BTW, the midbass can't be contributing at 30 Hz.  Then repeat starting with the sub turned down very low and bring it up to reach the desired response.  Most will say that the ideal amount of volume from the sub is just below the point where you can hear its contribution.


Regarding first point reflections, I'd treat side/front walls like any other speaker.  An 8 foot high ceiling is a standard and probably needed to make the design work the way its supposed to.  I've heard such speakers (upfiring mid/woofer with forward facing tweeter).  The presentation is quite unique (I heard a large soundstage that floated above the speakers).  You might try diffusion on the ceiling, but frankly thats why you bought that speaker, so why would you want to defeat one of the design principals? 

[rramraj]

Hi JLM,

I used Stereophile test CD 2 not the 1. There were more frequency samples. When it hit the 31.5hz, the whole room was energised. Im not tech inclined and based on the number of post, I deemed myself a newbie, trying to learn from the post of the more experienced audiophiles. I was wondering if bass traps might help. I was not using a sound meter at that time. Will try that out soon as per your recommendation.

You might try diffusion on the ceiling, but frankly thats why you bought that speaker, so why would you want to defeat one of the design principals? 

With regards to the above, when I heard these speakers at my friends place, the soundstage was more palpable. His room was bigger than mine with a more higher ceiling. I agree with u on the characteristics of the speaker design but wondered if difussors at the ceiling could help create the illusion of a higher ceiling. Appreciate your comments. Regards

[Ethan Winer]

I was wondering if bass traps might help.

Bass traps always help in every room. Probably not so much at 31 Hz, but as JLM explained that's not representative of your real problems.

--Ethan

[ooheadsoo]

Ram,


The 31.5 Hz spike is probably poorly characterized (seems like you're using the Stereophile test CD 1) as that disc only samples a few frequencies.  How did you measure?  If you used a Radio Shack spl meter, did you apply the correction factors (roughly 2 dB for 30 - 100 Hz and 6 dB for 20 - 30 Hz) for bass frequencies?

First, turn the sub off, then measure to determine a subwoofer crossover frequency (a bit below where bass response drops off).  BTW, the midbass can't be contributing at 30 Hz.  Then repeat starting with the sub turned down very low and bring it up to reach the desired response.  Most will say that the ideal amount of volume from the sub is just below the point where you can hear its contribution.


Regarding first point reflections, I'd treat side/front walls like any other speaker.  An 8 foot high ceiling is a standard and probably needed to make the design work the way its supposed to.  I've heard such speakers (upfiring mid/woofer with forward facing tweeter).  The presentation is quite unique (I heard a large soundstage that floated above the speakers).  You might try diffusion on the ceiling, but frankly thats why you bought that speaker, so why would you want to defeat one of the design principals? 

Unlike other speakers using this design, I think most of the midrange energy is actually coming from the 2" tweeter, and the midwoof doesn't play all that high.  The big tweeter helps, as does the active xover design.  I think the midwoof is playing in a range where the sound dispersion is mostly omnidirectional.

[rramraj]

Ethan,

Bass traps always help in every room. Probably not so much at 31 Hz, but as JLM explained that's not representative of your real problems.

Im getting worried. What are my main problems?

[Glenn K]

I recently got my Linkwitz Pluto's with subwoofers going. These are active speakers with the midbass firing at the ceiling. With these kind of speakers would the usual treaments , first reflections etc still apply? What basic treatments should I be looking at? I have a large thick carpet covering 2/3 of the room . My concern is the 8 ft ceiling. Should a diffusor be mounted there?

There seems to be a spike at the 31.5hz using test tones disc, where the whole room seems to be energised. Any advice is greatly appreciated.   

Any way you could post pictures and or room layout? I don't think you want diffusion in the early reflection point on the ceiling, but it would work fine behind you. The following is a layout of acoustics to give you a hand. But I would need to know more about your room to get more specific about your room.


 

Glenn

[youngho]

Did you read Linkwitz's own website? http://www.linkwitzlab.com/rooms.htm#D and http://www.linkwitzlab.com/stereo%20reproduction.htm

In the first link, he suggests that "sidewall reflections should be difused if treated at all" and advocates against absorption, since "lateral reflections are important for sound scene recognition." He also gives positioning suggestions. In the second link, he implies that rear wall absorption may be beneficial. Elsewhere in his website, he talks about the importance of lateral reflections, and there are even pictures of his own setup.

As for the ceiling, someone asked a similar question in the Pluto users' forum at http://orion.quicksytes.com/viewtopic.php?f=12&t=667

[Ethan Winer]

Im getting worried. What are my main problems?

Well, earlier you asked:

What basic treatments should I be looking at?

This is a deep subject, and a complete answer requires far more than will fit into a single reply here. So here's the short version. All rooms need:

* Broadband (not tuned) bass traps straddling as many corners as you can manage, including the wall-ceiling corners. More bass traps on the rear wall behind helps even further. You simply cannot have too much bass trapping. Real bass trapping, that is - thin foam and thin fiberglass don't work to a low enough frequency.

* Mid/high frequency absorption at the first reflection points on the side walls and ceiling.

* Some additional amount of mid/high absorption and/or diffusion on any large areas of bare parallel surfaces, such as opposing walls or the ceiling if the floor is reflective. Diffusion on the rear wall behind you is also useful in a room as large as yours.

For the complete story see my Acoustics FAQ.

There's a lot of additional non-sales technical information on my company's site - articles, videos, test tones and other downloads - linked under my name below.

--Ethan

[TRADERXFAN]

Please share your room dimensions, placement of the speakers in relation to nearby walls, and to other objects which sound could be reflecting from. Linkwitz recommended 3 feet from any large surfaces.

Also how far away are you listening? Linkwitz recommends nearfield with speakers spread further apart than an equilateral triangle, unlike most setups.   And not to sit close to the rear wall...

If you listen to actual music, does it overload the room?  Linkwitz discusses the problem of listening to test tones to judge room characteristics because its rare for music to have a prolonged notes that builds up pressure over time, most music tend to be impulsive. 

Also due to the active crossover network, if you can pin down an overload area then you may be able to makes some adjustments on the w-asp board and notch it out.  This is one of the benefits of the active crossover design.

I would hate for you to spend money on additional treatments until ruling out the considerations above first.  This design shouldn't be as problematic as traditional box speaker designs.

Good luck.

[rramraj]

Room dimensions - 16.5 ft (L) x 10(W) x 8.5(H). Based on the width of the room , speakers are about 2 ft from side wall and not 3ft as recommended. Speakers are 6ft apart and 10ft from listening position.  If I put them 3ft from sidewall, then they would be only 4ft apart.       

 :oops:I drew layout of room but dont know how to paste it here. sorry (damned newbie)

I get what Ethan is saying, treat it like any other room using standard speakers. I initially thought that these rules would need to be modified for omnidirectional speakers. 

[JLM]

Two issues here:  the 31 Hz resonance and imaging


Many homes with wooden floors and shallow crawl spaces have been known to resonant like crazy.  Even then I seriously doubt that the Pluto can overload a room at 31 Hz. 

Do you hear this effect with music?  Regardless of the tone source you can adjust the sub by ear as I described above.  Again I'd turn the sub way down and bring it back up to just below the point where you can hear it.


Absorption on the ceiling should help create the audible effect of a taller ceiling.  I haven't read about the Pluto for quite some time, but would guess (like ooheadsoo above) that the crossover frequency between mid/woofer and tweeter is about 1000 Hz (which is unusually low due to the unusually large tweeter).  Below that frequency (where the mid/woofer takes over) effective diffusion panels get very deep (2 inches at 1100 Hz, 4 inches at 550 Hz, 8 inches at 275 Hz, etc.).

Your room (other than the resonant floor issue I raised above) would seem to be a reasonably good space.  My only quibble would be that the length of the room is very nearly double the height, which would lead to the echo between floor/ceiling and front/back to reinforce each other.  But this is a quibble compared to so many other rooms people around here describe and can be easily dealt with if a problem.

Before I bought too many panels, I'd play around with speaker/listening locations, and try acclamating to the presentation.  I've bought six panels from these guys and have a dedicated room, but their pictures/standard advice (showing dozens of panels) scares me a bit.   

[bpape]

The rules can be slightly different for omni's - Just like it's a bit different for dipoles. 

An omni by definition is not going to provide pinpoint imaging but more of a large, encompassing image.  That said, diffusion in the front may be a better option.  Boundary related bass issues can still be there (SBIR) but need to be dealt with low at the wall/floor intersection with the diffusion up higher. 

In a room that's a bit more narrow like that, I'd recommend the broadband bass absorbtion in the rear wall/wall corners of the room.

Bryan

[youngho]

According to the information on Linkwitz's own site, you should consider two options for loudspeaker and listener:

1. Sitting MUCH closer to the speakers. In the specifications page for Pluto (http://www.linkwitzlab.com/Pluto/specs.htm)), he suggests sitting closer to the speakers than they are far apart. This would have the advantage of increasing soundstage, giving you much more of the direct sound, and moving you away from the rear wall, which would incidentally put you closer to the node for the first-order mode related to the length of the room, which might possibly help with that peak you're noting. I assume you have the speakers 3' from the wall behind them, so try pulling your chair forward about 5'. This link (http://www.linkwitzlab.com/rooms.htm) even has a diagram for you.

2. Turning the room sideways, since Linkwitz discusses Joachim Gerhard's (formerly of Audio Physic) approach to loudspeaker setup under the links page (http://www.linkwitzlab.com/links.htm). Unconventionally, Gerhard places the listener extremely close to the center of the rear wall, with the loudspeakers pulled forward about halfway what is now the length of the room (previously the width) and positioned along a very wide arc (70-90 degrees). I believe that Gerhard argues that the reflections from the rear wall will be so slightly delayed relative to the direct sound that they will not be perceived by the listener as problematic. By his own report, Linkwitz doesn't seem to have tried this but does seem to think that it's a reasonable approach.

Linkwitz's approach to room acoustics is significantly different than the approach espoused by Real Traps and GiK Acoustics above. The same rules for box loudspeakers do not apply, due in part to the mostly omnidirectional nature of the Plutos and the uniformity of the polar response. For example, in the acoustics link (http://www.linkwitzlab.com/rooms.htm) and an upcoming presentation (http://www.linkwitzlab.com/stereo%20reproduction.htm), he discusses acoustic treatments and the psychoacoustics of hearing. I would suggest taking the time to read Linkwitz's website carefully, trying to optimize the speaker and room setup (symmetry is critical, you should measure reverberation time before addressing absorption, diffusion or absorption should be broadband, etc) in a way consistent with his design philosophy because he is the one who also designed the speakers, and then finally addressing acoustic treatments like the rear wall absorption suggested above.

Best of luck, and happy listening,

Young-Ho

[rramraj]

To All,
Guys, I really appreciate the inputs and advice that you have shared with me. Seems like my system is in dire need of some tweaking. Bottom line, with guys like you around a newbie like me can avoid some of the pitfalls of going in blind. Regards

[el`Ol]

I listen with fullrangers facing the ceiling and I like the 3-dimensional imaging. Recently I found out that the delay of the ceiling reflection vs. direct sound is very close to the 4ms border of the human perceptional system that decides whether a sound is part of the source or just an echo. My room has exactly the height as yours. Can it be possible that you sit too far away from the speakers? Your friend with his higher room would have to sit further away to get the same delay.
http://img49.imageshack.us/img49/218/klotzpr6.jpg