mikebse2a3 Posted September 2, 2005 Share Posted September 2, 2005 Mike, "Dean has this ability to make adjustments in 1 to 2Hz increments using the PEQ section of the Behringer at low frequencies as well as small as 1/10 octave bandwith" That isn't sharp enough. 1/10 octave bandwidth is 2hz in the first octave, 4hz in the second octave,8hz in the third....etc...etc. I mean the Q of the filter needs to be able to be set sharp enough to literally effect all of a single hz in width. That way when you target the tight room resonance issues you aren't effecting more then just the resonance. Not much offers filters this sharp. Shawn Interesting Shawn. Have you actually seen resonances that sharp in normal/average rooms in the home enviroment? What was the room construction/material like? I'm sure the more substantial construction of all room walls/floor/ceiling (Concrete for example)would setup sharper resonances than say wood studs and sheetrock type construction. I would be very interested to know what the situation was that exhibited this and how it was dealt with. I haven't really seen anything this sharp in any enviroment I've dealt with. I believe average construction methods and materials seem to have enough inherit damping to broaden most room mode resonances beyond 1 or 2 hz. I also read in F. Alton Everest (The Master Hanbook of acoustics that a typical studio room modes exhibited a bandwith of 5hz. A 1Hz wide resonance that you mention would be very difficult to deal with electronically or acoustically/which from my understanding would take extrodinary means to make a bass absorber/resonator with this sharp a Q. I have read of resonators being made of ceramic or concrete to acheive high Q values. mike[] Quote Link to comment Share on other sites More sharing options...
sfogg Posted September 2, 2005 Share Posted September 2, 2005 Mike, "A 1Hz wide resonance that you mention would be very difficult to deal with electronically or acoustically/which from my understanding would take extrodinary means to make a bass absorber/resonator with this sharp a Q." I think the filters in my Lexicn can get down to 0.7hz in width. The designer of the room correction system has posted quite a bit of info about it. Meridian and Lexicon both offer automatic room correction systems both of which set their filters based on resonance/decay time. I believe both have said resolution/treatment down to 1hz is needed to really effectively deal with resonances without causing other unwanted effects. Shawn Quote Link to comment Share on other sites More sharing options...
mikebse2a3 Posted September 2, 2005 Share Posted September 2, 2005 Thanks Shawn Who is the designer of the Lexicon(AND Model?) you mention and If not to much trouble can you direct me too a few sites? Can I assume these are pretty expensive units also? mike Edit: I did some Googling and found this site on the Lexicon http://www.lexicon.com/products/details.asp?ID=15 The Designer is Dr James Muller To quote part of the article: The too-slow decay of a resonance mode can be corrected only by applying the proper filter. The severity of a resonance mode is defined by its "Q" value. The higher the Q of a resonance, the bigger its amplitude and the slower its decay. The presence of a resonance with high Q is not a desirable condition in listening rooms. Proper treatment of a resonance requires a filter with not only the correct frequency and depth, but also the correct Q. Graphic equalizers offer neither a variety of Q values nor a fine enough frequency selection. In addition, the typical bandwidth of a graphic EQ is 1/3 octave, which is not precise enough to be effective. A good parametric equalizer might work, but you would first need to have the time, expertise and equipment to measure the room's resonances. Our analysis is capable of identifying problem frequencies to within 0.732Hz ñ 10 times more precise than a graphic EQ at the low frequencies under consideration. ------------------------------------ From what I've read so far it can get you within .732Hz of the problem frequency center but nothing is mentioned about how high the Q(Narrow The Bandwidth) capability is. Also from what I'm reading here they are using the decay rate to locate the most severe room modes for treatment but it appears to me by this information that it is basically acting as a very good auto analyzing Parametric EQ. What was most interesting to me in some of what I have read on the unit is how they mention by cleaning up these modes that clarity is improved at frequencies above the 250Hz limit of the EQ adjustments and that many listening positions will hear improvements when controlling these modes which corelates with the perception I have had with using the Behringer in Three very different Rooms/Systems that I've used it in. This has been very interesting Shawn and any more information/articles describing the design features of the Lexicon would be appreciated. mike[] Quote Link to comment Share on other sites More sharing options...
sfogg Posted September 3, 2005 Share Posted September 3, 2005 Mike, The Lexicon's room correction was done by David Griesinger and Jim Muller. Along with designing the logic behind the measuring/determing where to place the filters Jim actually did the coding of it in the MC-12 too. The room EQ is an option for the MC-12/MC-12B processor. It is in v4 of the software in the Lexicon and in the V5 EQ version of the latest software. There is some info on the Lexicon's room EQ in the MC-12 v4 users guide at: http://www.lexicon.com/products/download-details.asp?ID=1&FileID=117 David Grisinger's home page is at: http://world.std.com/~griesngr/ And it has *loads* of information on it. Check out: http://world.std.com/~griesngr/asa05.pdf For example as it covers a bunch of good topics including room EQ. Jim Muller was online at the Lexicon forum answering a lot of questions about the room EQ when it first came out. The Lexicon forum is forum three at: http://forums.smr-forums.com:8080/login Enter as a guest if you don't want to register for the site. If you search forum three for posts with Muller in them you will find the posts from Jim. Go back a years worth to when v4 was first released and work your way forward. He gives lots of details on the system and even posted a room response program he wrote in the early development of the room eq software. He wanted to verify if the calculated theory matched the actual measured response. In a nutshell the Lexicon system used four microphones to measure the decay times of every speaker in the room. In some manor it priorities the resonances it finds by some type of psychoacoustical weighting system and also with some sort of logic having to do with how the resonances appear in each of the mics. It then applies filters between 19hz and 250hz to knock down the resonances it finds in the room. The goal of the system is *not* simply to flatten amplitude response, Jim has flat out said that is the wrong way to approach room EQ. Its goal is to attack the long resonances that end up giving 'tubby' bass in the room which also masks/smears details higher up in frequency in the rest of the music. It can do 7 filters per speaker and it also applies a sort of shelving filter when the EQ is on to make up for a perceived loss of bass when the resonances are removed from the room. A resonance effects the entire room (excepting null points) so reducing their influence improves playback basically throughout the room. Shawn Quote Link to comment Share on other sites More sharing options...
mikebse2a3 Posted September 3, 2005 Share Posted September 3, 2005 Thanks Shawn I was editing my last post (figuring you might respond tomorrow) while you where replying to me. I will definitly check this other information out and thanks for taking the time to list it all for me. mike Quote Link to comment Share on other sites More sharing options...
sfogg Posted September 3, 2005 Share Posted September 3, 2005 Mike, I'll see if I can find the posts from Jim on the 0.7hz thing. They built the measurement and the filters to have the same level of precision. But Jim has said (and others agree) that measurement/treatment to 1hz is 'good enough.' "What was most interesting to me in some of what I have read on the unit is how they mention by cleaning up these modes that clarity is improved at frequencies above the 250Hz limit of the EQ adjustments and that many listening positions will hear improvements when controlling these modes which corelates with the perception I have had with using the Behringer in Three very different Rooms/Systems that I've used it in." And there is a very good reason for that. Contrary to somewhat popular opinion performing EQ in the room to treat bass does *NOT* automatically limit the correction to being proper where the microphone was placed. If you place the filters to treat the areas with very long decays (resonances) it really does improve performance throughout the room. Everybody knows rooms have 'room boom' which causes huge amplitude peaks/nulls at specific locations in the room. Those are symptoms of the underlying problem in the room... not the problem itself. The actual problem is the room is resonating at those specific frequencies. And because of the resonance (sticking around longer then it should) the room is getting standing waves which gives the amplitude problems at a few specific places. However if you think about it... what is a standing wave? It is basically a wave that keeps bouncing back and forth between your walls in a certain pattern so that it causes large amplitude shifts from constructive/destructive interference. When you realize that the wave is of course bouncing back and forth within the room for longer then it should you also realize that this problem is effecting the entire room. And you can see that in action if you measure the room in the time domain... not just the amplitude domain. Something like ETF will show you this in its waterfall plots pretty easily. And if you measure from multiple points in the room you will see the same resonances throughout the room excepting the null points. The amplitude of the resonance will vary but the decay time of it will be more consistent. Therefor if you place your filters by analyzing the decay time (resonances) improvements you make will improve the situation throughout the room. And the reason it makes improvements in clarity well above the range of where you are treating is easy to understand when you think of the correction as treating the room in time. Literally a resonance in the bass is a note that 'keeps playing' in your room for longer then it should. It literally is material that is playing that shouldn't be there at all... that is pretty much the definition of distortion. Though it isn't harmonic distortion... more like a distortion in time. That material that is playing that shouldn't be there at all is masking details and music the follows the original bass material which started the resonance going. When you cut down the resonance you reduce/remove that long decay which was masking details in your music throughout the range. So..... IOW.... EQing a room can work throughout the room. The key is how the filters are measured and placed though. Shawn Quote Link to comment Share on other sites More sharing options...
Deang Posted September 4, 2005 Author Share Posted September 4, 2005 You guys are amazing - my brain is completely fried. Shawn - I built some 300/5500 networks and I was using the RTA to evaluate the result. It was especially helpful in determing squawker polarity. If you compare the results to the ones I posted in the 'Trachorn 400' thread (now on page 3) - you can see the improvement I garnered by making just a few changes. However, tweeter output comparisons go out the window because of the Beyma. JC - I forgot to bring the camera home, so I can't take a digital pic of what I saw Friday while playing with the 100uF capacitor across the woofer terminals - I can tell you though: It does exactly what one would expect to happen - the response rolls off sightly faster, and there was a 3db reduction in output between 300 and 375Hz. I'll probably do this again tomorrow with the mic placed lower. Dee - I'm very happy with the Beymas. I talked to Bob a few days who suprised me by saying he couldn't hear much if any difference between the Beyma and K-77 if the attenuation levels were matched. I'm running them with a slightly modified AA tweeter filter sitting behind a separate autotransformer swamped with a 20 ohm resistor -- which runs them at 8 ohms and 3dB of attenuation. As for 'integration', it sounds great, and as you can see from the pics on the previous page -- the transition and attenuation with the squawker is spot on. The whole top sounds much more dynamic and open with good sparkle. Quote Link to comment Share on other sites More sharing options...
BEC Posted September 4, 2005 Share Posted September 4, 2005 Dean, Why not give this tweeter a try? Bob Quote Link to comment Share on other sites More sharing options...
Al Klappenberger Posted September 4, 2005 Share Posted September 4, 2005 Bob, The k79 tweeter is 3 dB less efficient than the K77. I don't think it will balance up in a Khorn. Al K. Quote Link to comment Share on other sites More sharing options...
BEC Posted September 4, 2005 Share Posted September 4, 2005 Al, I haven't measured sensitivity myself, but specs claim it is 101 db in the Cornwall II. In that crossover, they use two 1.5 uF caps in series feeding the K-79. A single 2 uF cap might bring it close to what is needed for a Khorn. Haven't tried it. Just a thought. The K-79 can also use a titanium diaphragm which may also add a bit. Bob Quote Link to comment Share on other sites More sharing options...
sfogg Posted September 4, 2005 Share Posted September 4, 2005 Al, "The k79 tweeter is 3 dB less efficient than the K77. I don't think it will balance up in a Khorn." What about using an autoformer in reverse? I think I read Klipsch did that in some model at some point. Shawn Quote Link to comment Share on other sites More sharing options...
sfogg Posted September 4, 2005 Share Posted September 4, 2005 Dean, " I built some 300/5500 networks and I was using the RTA to evaluate the result." You could likely measure their response directly without including the drivers response in the output. Connect the Behringer across the drivers terminals with maybe 10k resistor inline and you should be able to see what the network itself is doing while loaded up with the drivers.. Shawn Quote Link to comment Share on other sites More sharing options...
Al Klappenberger Posted September 5, 2005 Share Posted September 5, 2005 Shawn, Yes, you can use a transformer in reverse to set up the level to a tweeter, but the impedance seen by the network goes down rather than up. You can no longer use the swamping resistor to compensate. It really would require a complete crossover redesign. When you test a netwrok using instruments you need to terminate the output with a resistor equal to the impedance of the driver it is desinged to drive. That wouldusually be 8 Ohms for the tweeter, 13 Ohms for a K55 and 6 in sereis with a 1 mHy inductor for the K33 woofer. In that case you measure across the 6 Ohms resistor. Using 10K Ohms will casue the response to show peaks and dips that are not really there. Al K. Quote Link to comment Share on other sites More sharing options...
sfogg Posted September 5, 2005 Share Posted September 5, 2005 Al, "you need to terminate the output with a resistor equal to the impedance of the driver it is desinged to drive. That wouldusually be 8 Ohms for the tweeter, 13 Ohms for a K55 and 6 in sereis with a 1 mHy inductor for the K33 woofer. In that case you measure across the 6 Ohms resistor. Using 10K Ohms will casue the response to show peaks and dips that are not really there." I meant having it normally terminated to the drivers like always. Just that when he connects across whatever driver put 10k inline with the positive to the Behringer. It is a line level component that doesn't have the different voltage inputs available like in the spectrum analyzers. The 10k was just to protect the input to his instrument. Shawn Quote Link to comment Share on other sites More sharing options...
Al Klappenberger Posted September 5, 2005 Share Posted September 5, 2005 Shawn, Ok.. I get what you'r dong with the 10K resistor. I really doubt it's need for the line inputs though. I doubt you could do any damage to the instrument that way. Al K. Quote Link to comment Share on other sites More sharing options...
sfogg Posted September 5, 2005 Share Posted September 5, 2005 Al, I'm not doing it that way, just suggesting it for Dean because he is using the RTA function in his EQ for measuring. That has a lot less flexibility as to what it can handle on its line level inputs. Just extra safety to be sure he doesn't damage it as it isn't meant to be hooked up to speaker level connections. Shawn Quote Link to comment Share on other sites More sharing options...
Al Klappenberger Posted September 6, 2005 Share Posted September 6, 2005 Shawn, Yep.. I agree.. Al K. Quote Link to comment Share on other sites More sharing options...
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