Todd, I don't get it. Looking at this does tell you nothing??
Instead of oohing and aahing I would know that I have to do something against all those "anomalies I have, like "holes" and non-uniform decays". And after that a second waterfall would tell me if it was worth the $64k I spent.
An externally hosted image should be here but it was not working when we last tested it.
Instead of oohing and aahing I would know that I have to do something against all those "anomalies I have, like "holes" and non-uniform decays". And after that a second waterfall would tell me if it was worth the $64k I spent.
markus76 said:
Markus, this plot doesn't show those anomalies I mentioned, perhaps because the time resolution is too low, or perhaps just not in this room. however, I could have looked at the steady state before and after and shown that i reduced that resonance.
I'm not saying there's no information there, just not simple to characterize.
markus76 said:
Mr Markus,
Are you serious with this?
I thought this was a joke that was a bit poorly worded given the smiley face, and all - but it doesn't seem to be so with your followup. So forgive me if you were indeed joking, but I must say something...
This demand of yours is a bit obnoxious to me. Anybody who takes this much time and trouble to help others out should be appreciated, even if you think they are wrong about something. If thats the case feel free to disagree. But you are quite mean spirited in your behaviour and I think you owe an apology.
The guy shares the information of what he prefers, FREELY; posts chapters of his book on the web for FREE; tells everyone, in some detail, specifically how to build it for themselves for FREE (- in addition to all of the countless pages of posts sharing his knowledge and expertise in all matter of audio) and you have the nerve to say he has to PROVE something to you personally, and to do so in the time and manner of your choosing? He even explained why he wasn't interested in this. Why do you think you have the right to demand this?
Aren't you using his multiple subwoofer method that you touted at the start of this very thread!?
And which you quote him extensively here... http://www.mehlau.net/audio/multisub_geddes/
You should be a lot more grateful and humble, my friend.
'someone else' was correct in what he stated so it was obvious that john k. didn't feel the need to correct. In free space an unequalized dipole rolls off -6dB/oct and below the woofer resonance an extra -12dB/oct leads to -18dB/oct.
The ported enclosure falls with 24dB/oct due to another reason: the combination of the two mass spring systems (driver and helmholtz resonator) and the output of woofer and port which are more and more out of phase down below the BR tuning frequency.
It is not my intention to nitpick, nevertheless I do feel the need to correct statements which are not technically correct according to my knowledge.
Sorry if you feel I am picking on you, but you are representing yourself up as the expert and people read and listen to what you say. Thus it is more important for you to be correct, and not make brash statement like... no sound....
Also I have asked more than once in this thread (both recently and some time age) how a 3-woofer system should be set up in a hypothetical, ridged walled, sealed, rectangular room so I can post comparative simulations of the 3 woofer, 1/4 floor mounts 4 woofer, and DBA formats. I've gotten no guidance form you. My simulation attempts with 3 woofer have not been very successful.
I know, it's not real world but I still believe that such sims should define the fundamental physics of the problem. So excuse me for nit picking. It only because I know you know better.
Also I have asked more than once in this thread (both recently and some time age) how a 3-woofer system should be set up in a hypothetical, ridged walled, sealed, rectangular room so I can post comparative simulations of the 3 woofer, 1/4 floor mounts 4 woofer, and DBA formats. I've gotten no guidance form you. My simulation attempts with 3 woofer have not been very successful.
I know, it's not real world but I still believe that such sims should define the fundamental physics of the problem. So excuse me for nit picking. It only because I know you know better.
gedlee said:
Excuse me for picking this up again, but I had to dine. We have been discussing the effect of the room with little discussion of the source behavior. Trust me, and uneq'ed dipole response rolls off with a 6 dB slope. Now if you want to include the source make that 18dB below the sources resonance, as has been said, assuming the source rolls off at 12dB. So if the room is leaky the dipole rolls off at 18 and the monopole at 12. At some point they are both going to be down 12dB. Audible or not I won't argue.
If the point is that a dipole can not excite the DC mode in a sealed room and a monopole can, is that good or bad? It's a double edged sword. Below the 1st room mode the dipole response is unaffected by the room, sealed or other wise. Thus I can build a dipole with a 20 Hz cut off and be assured that it won't suffer from excessive "room boost" regardless of the room size. With a monopole, if the room is tight then I should start to consider how the DC mode affect the response. If the monopole has a 20 Hz cut off and is in a smaller room the bass can be over done due to the lift from the DC mode. This lift is dependent on room size. If I open a window or door the room boost for a monopole will change, and, potentially there could be a Helmholtz effect what an adjacent room making this worse. The dipole is void of that effect. So I don't see being able to excite the DC mood as necessarily a good thing. It might be a very bad thing in some situations. I would only caution that it is best to stay objective and look at the facts and not make judgments as to what is better or worse.
It's like the old joke about a guy in a Corvette pulling up to a guy in a WW II surplus Jeep and asking if the guy in the Jeep wants to race. The Jeep driver replies, "You pick the distance. I'll pick the course." Some times it better to just discuss the capabilities of each vehicle. Then, once the course is set the appropriate decision as to which vehicle is better suited for the task can be made.
jeroen_d said:
If you didn't notice, I didn't stand by the -12 dB / oct. I didn't check - it doesn't matter.
I have said time and time again that I really don't care what kind of sub one uses, I don't see it as making enough of a difference to worry about. I only state that multiple subs are a must; that they need to be setup correctly; and that three subs apears to be an "optimum" in the sense of lowest cost and complexity for the biggest improvement. Not that its "ideal" or "perfect", its just a very very effective bang for the buck.
This is why I'm not going to get into a numbers game with people on this topic.
How do you identify the cause of difference to be room, background noise, or speaker characteristic, etc. by just looking at these?markus76 said:
gedlee said:
I may be master of the obvious here, but sounds like one could make something analogous to a passive radiator, that works as a passive absorber instead. How about a construction consisting of a panel of a specific density (or adjustably weighted) with a soft foam backing (suspension), with a flexible membrane (surround) around the perimeter that seals the panel to the wall.
Seems the analogy could be extended to develop an equation that determines the needed panel weight and foam compliance, as a function of the area and wavelength of the panel. The panel stiffness and surface could be selected to reflect higher wavelengths or not, as required.
Sheldon
soongsc said:
I don't understand your question (as always). We're still talking about low frequencies, right? If you're able to do a waterfall measurement then you should be able to measure background noise or the near field frequency response of a woofer as well.
I encourage everybody to download REW and play around with it. It's free and you'll learn a lot.
Best, Markus
john k... said:
gedlee said:
Well, since john k seems to have the tools and willing to do some simulations, and you seem to have an exsiting room arrangement you use as a reference, why not just use your room and sub setup as a basis for simulation and see how things come out?
Yes, this is still talking about low frequency. How would you subtract noise from the waterfall. Does the REW do that (I assume you have used all it's features)? Then, how would the absorption factor spectrum be generated (assuming we are still on the low frequency absorption issue)?markus76 said:
Why would you want to substract the noise floor? Either your measurement signal is far enough away from the noise floor to generate meaningful data or it's not. A waterfall even let's you see the noise floor. Just play around with the settings in REW.
Don't understand the second part of your question at all. What is a "absorption factor spectrum"?
Don't understand the second part of your question at all. What is a "absorption factor spectrum"?
markus76 said:
Markus, I did download REW. It's like ETF on steroids. Very nice. I like that the eq seems to be geared towards just bringing peaks down, and not filling dips. I still have the same reservations about waterfalls, and of course just because a measurement program looks slick does not mean it is correcly executed. There's a lot under the hood. I know because we at Harman are developing our own measurement platform, so I ahve some familiarity with it. There's also a lot of possibilities for window choices (for example) which do affect the result, and there is often no clear choice for which window is "correct".
It would be interesting to compare it to mlssa or TEF or B&K pulse or one of the other programs that have been around a while.
Still, very promising, and free!
Todd
Absorption factors can be assigned to the room boundaries, so it's really not an issue.gedlee said:
I guess that you might not have measured the characteristics of background noise for enough cases to get a feeling how they effect measurements. Even if you may see the noise floor at a certain point in time, if it's mixed with what you really want, then there is no way you can look at what really is necessary with enought time resolution. Additionally, if you monitor noise spectrum in real time, you will find that the spectrum content is not stationary, and may vary quite significantly over 10db depending on environment, this may invalidates whatever interpretation of the waterfall data one might conclude.markus76 said:
Hi,
I am building a quartet of subs to try the approach being discussed her. I have a slightly OT question, but I'm sure you guys can help me out.
The subs are downfiring 12 inch Peerless XXL's in a cylindrical enclosure. How far should they be above the floor? The only info I have found is someone saying that the area of the opening (the height above floor * circumference of the enclosure) should be at least equal to the driver area. What do you think?
TIA,
Jan Didden
I am building a quartet of subs to try the approach being discussed her. I have a slightly OT question, but I'm sure you guys can help me out.
The subs are downfiring 12 inch Peerless XXL's in a cylindrical enclosure. How far should they be above the floor? The only info I have found is someone saying that the area of the opening (the height above floor * circumference of the enclosure) should be at least equal to the driver area. What do you think?
TIA,
Jan Didden
markus76 said:
Where was this recorded...in an empty warehouse? 430msec? Never seen anything like that.