Re: Re: Re: Re: Re: Sealed Enclosures
You also mentioned port noise, which I took from your comments to mean turbulence noise from the port. I never design or implement this inadequately, even in my PA gear where size and weight are significant issues. I meant that ported systems with no acoustic stuffing damping inside the enclosure and front ports, you can hear mid and lower mid rear wave energy (which I call port singing). Once identified. I find it incredibly annoying, like someone singing along to a song slightly off key and out of time. A sealed box suffers none of these issues, and because a sealed box is trypically stuffed to some degree, rar wave reflected energy is much better controlled, and less returns out through the diaphram.
Cone motion: I ensure that there is sufficient cone area and therefore volume displacement and efficiency that even at very high SPL peaks there is < 1mm displacement, even in a sealed box (assumes>100Hz or so).
The majordrawback with ported boxes is their time domain performance; even the worst sealed is better than the best ported, a compromise I'm not willing to take. I'd rather have bigger speakers, or if forced by size restrictions or WAF, make a smaller nearfield system that still has fewer drawbacks than trying to do it what I've found to be the wrong way.
Let's take the last bit first: 80-1500Hz. I generally agree. But I would never bother with a ported box with an F3 of 80Hz, so I can do that sealed, open back or horn, and have no port issues and better time domain response. Below 80Hz I would use a driver system suited specifically to this task. I don't bother trying to do 2 ways any more as they've far to many compromises. Hell, between 80 and 1k5 I'd typically have two drivers.Hezz said:
You also mentioned port noise, which I took from your comments to mean turbulence noise from the port. I never design or implement this inadequately, even in my PA gear where size and weight are significant issues. I meant that ported systems with no acoustic stuffing damping inside the enclosure and front ports, you can hear mid and lower mid rear wave energy (which I call port singing). Once identified. I find it incredibly annoying, like someone singing along to a song slightly off key and out of time. A sealed box suffers none of these issues, and because a sealed box is trypically stuffed to some degree, rar wave reflected energy is much better controlled, and less returns out through the diaphram.
Cone motion: I ensure that there is sufficient cone area and therefore volume displacement and efficiency that even at very high SPL peaks there is < 1mm displacement, even in a sealed box (assumes>100Hz or so).
The majordrawback with ported boxes is their time domain performance; even the worst sealed is better than the best ported, a compromise I'm not willing to take. I'd rather have bigger speakers, or if forced by size restrictions or WAF, make a smaller nearfield system that still has fewer drawbacks than trying to do it what I've found to be the wrong way.
Really interesting discussion on sealed vs ported design. It just goes to show how different people hear things differently, even people who are attuned to the sound reproduction industry.
By the way, I have been corresponding with the person I bought the drivers from and the suggestion has been made to move up to the focal 120 series tweeter to help the lack of upper mid clairity. He has confirmed the box design as being correct, therefore the problem. Sounds promising, albiet more work on re-cutting the tweeter opennings in the baffle to accomodate the larger tweeters.
By the way, I have been corresponding with the person I bought the drivers from and the suggestion has been made to move up to the focal 120 series tweeter to help the lack of upper mid clairity. He has confirmed the box design as being correct, therefore the problem. Sounds promising, albiet more work on re-cutting the tweeter opennings in the baffle to accomodate the larger tweeters.
Depending upon your intentions, sometimes it can work well.phase_accurate said:
By bass guitar cab uses an 18 for LF. In the same box ported it's a QB3 at 40Hz. Block the port and it's Q=0.6 (roughly) at 65Hz so I can use the deep LF or not depending upon the stage.
I've seen similar done with music?HT systems with ported used for music, and sealed (socks in port) + sub for HT.
Re: Re: Re: Re: Re: Sealed Enclosures
Properly designed with the specific room in mind a sealed box will actually go lower than a bass reflex . This is because a selaed box has 2nd order roll-off and a BR 4th order. Even thou a BR may have a lower f3, it is quite possible that the sealed has lower f10 so when room gain is added in the BR has peaky bass and the sealed goes lower, flatter.
Further, since T/S parameters change with level a BR will often become mis-tuned just by moving the volume control. Further a BR can become mistuned by just a change in the weather.
I'm not a big fan of acoustic suspension enclosures, preferring a lower pressure enclosure. So if sealed it needs to be on the largish side (ie pushing towards unfinite baffle or critical Q)
dave
Hezz said:
Properly designed with the specific room in mind a sealed box will actually go lower than a bass reflex . This is because a selaed box has 2nd order roll-off and a BR 4th order. Even thou a BR may have a lower f3, it is quite possible that the sealed has lower f10 so when room gain is added in the BR has peaky bass and the sealed goes lower, flatter.
Further, since T/S parameters change with level a BR will often become mis-tuned just by moving the volume control. Further a BR can become mistuned by just a change in the weather.
I'm not a big fan of acoustic suspension enclosures, preferring a lower pressure enclosure. So if sealed it needs to be on the largish side (ie pushing towards unfinite baffle or critical Q)
dave
Brett said:
Thanks for the answer. I hope my question doesnt count as thread stealing. Here is a quote from Siegried Linkwitz, which is on topic again
(about his choice of a sealed sub)
"I did not consider alternate approaches to subwoofer design as acceptable for meeting my goal of accurate sub-bass reproduction. This includes vented, passive radiator and acoustic bandpass woofers. They all rely on resonant energy storage to increase efficiency and to reduce size."
So, according to Linkwitz and at least for subwoofers below the lowest room mode, closed is the best enclosure type.
"For music reproduction high accuracy and resolution of bass is most desirable. Unfortunately, this is often degraded by low frequency room resonances. To reduce their effect I have chosen open baffle woofers for the PHOENIX system."
Again, resonances are the thing which Linkwitz fears the most and he choose the open baffle speaker for reducing them. So, if we have good room treatment in the modal range, a closed box would be superior to other designs (in the sound quality aspect) as well.
MaVo said:
Thanks for the answer. I hope my question doesnt count as thread stealing. Here is a quote from Siegried Linkwitz, which is on topic again
(about his choice of a sealed sub)
"I did not consider alternate approaches to subwoofer design as acceptable for meeting my goal of accurate sub-bass reproduction. This includes vented, passive radiator and acoustic bandpass woofers. They all rely on resonant energy storage to increase efficiency and to reduce size."
So, according to Linkwitz and at least for subwoofers below the lowest room mode, closed is the best enclosure type.
"For music reproduction high accuracy and resolution of bass is most desirable. Unfortunately, this is often degraded by low frequency room resonances. To reduce their effect I have chosen open baffle woofers for the PHOENIX system."
Again, resonances are the thing which Linkwitz fears the most and he choose the open baffle speaker for reducing them. So, if we have good room treatment in the modal range, a closed box would be superior to other designs (in the sound quality aspect) as well.
you correctly state that outside of the frequency range with room modes a sealed box could be more musical because of less energy storage, resonance, group delay and all that
problem is - what makes you think such a frequency range exists ? for a room 20ft by 12fb by 10ft (high) the lowest mode is at 22hz
http://arts.ucsc.edu/ems/music/tech_background/TE-02/modes/Modes.html
and for a larger room the lowest modes will be even lower.
so while there is clear advantage for dipoles in terms of reducing energy storage in room modes ... im not sure if the advantage of sealed vs ported in terms of energy storage is significant in light of the room modes
you have to understand that Linkwitz had to push his Linkwitz transform technology which applies only to sealed subs enclosures, so that was probably the real reason he simply dismissed vented boxes which are good enough for say dynaudio or genelec.
Linkwitz is the guy who is big on building active filters and he has to find applications for them. i respect Linkwitz but i also respect Genelec which use vented enclosures exclusively.
i think that a resonant port is acceptable if its tuned to low frequency (say 30hz) because down there timing errors arent likely to mess with your stereo image. on the other hand to use small satellites with ports tuned to 60hz or so would probably not be a good idea.
I must say that I have had mid level receiver/amp setups from Harmon, Yamaha, Pioneer Elite etc and while they do each have their own sound, if you had an eq you could make them sound alike. With that in mind, my listenning room is 12 X 22 and I haven't had to push any of those amps beyond their means to fill the room with loud music or HT sound. So I'm not quite sure what the need would be to focus on a really expensive series of power amps with way more power then you would ever have the call to use. I am a musician so I do understand the need for power amps that kick out enough power to deal with rooms that need that kind of sound. But for a music listening room in a house that is not castle sized..........I don't get it.
Ok, to fantfool.
What you are hearing is the difference in gain of amplifiers, not their acoustical personalities, because there’s none. Match the levels with SPL meter and listen with switchbox.
The problem that you are having may be caused by a few different things.
1) Most of the Japanese receivers don’t like a low impedance speakers. It probably says on the back of the receiver “minimum impedance of 8 ohms”. Unless we find out driver parameters and crossover schematics, we will not be able to distinguish if it’s true, however it is my suspicion that your MTM deeps close to 2 ohms and your receiver simply can’t drive impedance that low at high level.
2) Your speaker came out extremely inefficient. Again, most likely it’s a mistake in the crossover design.
I wouldn’t look in to the amps at all until you find out what’s going on with your drivers and crossovers. I have same size room and Marantz 6001 receiver 100 wt./channel and I can’t crank it up all the way, without my wify screaming in horror. I mean, it gets f…g loud!
To Brett:
Hey, bud I am not distress at all, I am more like having fun about it.
I believe that a concept and preferences in the sound should be a beginning of the design. If I like the sound of magnetic planar (which I do), it is the most important thing that will keep me happy and later on if I need a 300wpch stable in 2 ohms amp to drive them, oh well. If a 100db efficient horn is the preference, 15w amp will be enough. I haven’t seen HT with efficient speakers and the problem that Fatfool is having aren’t caused by bad choice in the amp. The suggestion that was made by Planet 10 was entirely wrong in this case IMO and that’s why I started this whole thing. Let’s get back to his problem.
What you are hearing is the difference in gain of amplifiers, not their acoustical personalities, because there’s none. Match the levels with SPL meter and listen with switchbox.
The problem that you are having may be caused by a few different things.
1) Most of the Japanese receivers don’t like a low impedance speakers. It probably says on the back of the receiver “minimum impedance of 8 ohms”. Unless we find out driver parameters and crossover schematics, we will not be able to distinguish if it’s true, however it is my suspicion that your MTM deeps close to 2 ohms and your receiver simply can’t drive impedance that low at high level.
2) Your speaker came out extremely inefficient. Again, most likely it’s a mistake in the crossover design.
I wouldn’t look in to the amps at all until you find out what’s going on with your drivers and crossovers. I have same size room and Marantz 6001 receiver 100 wt./channel and I can’t crank it up all the way, without my wify screaming in horror. I mean, it gets f…g loud!
To Brett:
Hey, bud I am not distress at all, I am more like having fun about it.
I believe that a concept and preferences in the sound should be a beginning of the design. If I like the sound of magnetic planar (which I do), it is the most important thing that will keep me happy and later on if I need a 300wpch stable in 2 ohms amp to drive them, oh well. If a 100db efficient horn is the preference, 15w amp will be enough. I haven’t seen HT with efficient speakers and the problem that Fatfool is having aren’t caused by bad choice in the amp. The suggestion that was made by Planet 10 was entirely wrong in this case IMO and that’s why I started this whole thing. Let’s get back to his problem.
I totally agree!!
I was saying that I agree that the choice of amp is definately not related to my speaker sound problem. I echo what you said about being able to crank out plenty of volume with the 90 or 100 watt amps that I have used. The inefiency of my focal TC90 tweeters compared to the 2-6 1/2" Zetag mid-woofers is more likely the problem with the mains lacking that detail in the upper-mid frequencies. I should have measured the Zetags before I started since I don't have enough T/S information on them to begin with. I will be trying to swap out the TC-90s with TC-120s which are 2-3 db more efficient. This may be a better balance, besides, I would much rather damp a tweeter then woofers anyday.
91.5 db is quite good actually. What are the crossovers?
http://www.speakercity.com/Merchant2/pdfs/TC90TD5.pdf
http://www.speakercity.com/Merchant2/pdfs/TC90TD5.pdf
I'm not sure exactly what the crossover points are but they are an emulation of the wilson cub crossovers. That speaker uses the 2 - 6 1/2" mid-woofers and a focal TC120 tweeter. The woofers that wilson uses are very good quality seas I think. But in talking to one of the designers of the Zetags he compared the Hi G1 woofers to those.
fantfool said:
Ok, so my understanding is that you’ve build the boxes that were designed by someone else, made the crossovers without knowing exactly what and how they are and used the drivers that were suggested. I wander why the results are bad.
I would definitely start with measuring the woofers. If you use 120 tweeter without modifications to the crossover, you will get bad results. 120 have different efficiency, also much lower fs and different frequency response. You can’t just take one tweeter out, shove in a different model and expect to get to heaven. It’s not going to work.
My opinion is this.
1) Measure the woofers. If you have put lots of labor in to this project, it’s a good idea to get Woofer Tester from PE. After all Focal tweeters are expensive.
2) Try to figure out crossover the best you can. Take it out of the speaker and at list post a picture of it here.
3) Your closed center channel MTM should have a different crossover from ported main speakers.
4) Stuffing and changing the boxes or swapping out tweeters is not going to help unless you know woofer parameters
5) You will probably end up making new crossovers. Focal 90 is not a bad or inefficient tweeter at all. It does have a high Fs which makes it more suitable for a 3 way design. It could be used in the MTM but model 120 with Fs of 800 is a better choice. Again, can’t swap them without working with crossover.
R-Carpenter said:
Not entirely true. I did have some information on the woofer just not quite exact, if I remember correctly, this is what I had: fs 40-45 qts .4-.5 vas 1.2. The boxes were designed based on the information from one of the engineers of those woofers. They had used the Hi G1 woofers, a bookshelf 2 way design, in prototypes that were a 2 1/2 way design in a modified cabined of the HI G3 models with their tweeter which was a silk dome, I think vifa made product, using an entirely different x-over. My initial plan was to build that design but the x-overs were real bad. This is where my fishing started so to speak. I talked to the person I bought the drivers from because he had told me that he thought these drivers were the closest to the wilson cub woofers he had seen and he was using them for testing on a crossover emulation. I think the problem was I used the TC90s instead of the TC120s which is what he was using for the crossover design. Does this make more sense? Ok probably not.
Re: Re: Re: Re: Re: Sealed Enclosures
Then you may find a modern transmission line to your liking.Hezz said:
At higher frequencies, box loading becomes insignificant with either style of box. Also WRT box loading, looking at both closed and vented plots versus infinite baffle, closed and vented boxes both lift the response over a wide range.
Not that this isn't true, but the Xmax of a driver that can reproduce 1500Hz is significantly smaller than the 9" wavelength at 1500Hz.
Side discussion has been split off to here
http://www.diyaudio.com/forums/showthread.php?s=&threadid=114651
dave
http://www.diyaudio.com/forums/showthread.php?s=&threadid=114651
dave
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