Re: Ovoid gevalt!
Hi HK26147,
That's interesting that you have already made a couple of these enclosures. I have been looking on the Internet but really can't find anything on the DIY line for projects utilising spherical enclosures.
There are hundreds for the usual coffin type and I would of thought that if, as people say, spherical enclosures are the best, there would be plenty of projects available. Or, is it just a lot of balls!
to most people.
What construction method did you use and how did they sound? I would and I suspect many others would really like to know.
HK26147 said:
Hi HK26147,
That's interesting that you have already made a couple of these enclosures. I have been looking on the Internet but really can't find anything on the DIY line for projects utilising spherical enclosures.
There are hundreds for the usual coffin type and I would of thought that if, as people say, spherical enclosures are the best, there would be plenty of projects available. Or, is it just a lot of balls!
to most people. What construction method did you use and how did they sound? I would and I suspect many others would really like to know.
HK26147 said:
Well I can definately say that those are cool sims!!!
I have used a real ripple tank, with water, for decades. It can show some very interesting things and can do a lot that the sims don't do. Absorption is very difficult in sims like this, but easy in a water ripple tank. So the water ripple tank can tell you where to place absrption, etc. that can be very useful. I'm building a bigger one now using plexiglass as the tray. Then you mod a loudspeaker with a paddle as a source. Foam acts as a super absorber and wall of horns, etc, are just cut pieces of plexi.
But those sims can teach a lot of basics, but not really any detailed problems. But they ARE lots of fun!!
Re: Re: Ovoid gevalt!
Just taking plans for a "coffin type" and changing the enclosure to a sphere will not guarantee an overall improvement. While the sphere may improve diffraction issues and make for a rigid cabinet, the baffle loss frequency will be higher. Whether or not this is a negative or an improvement may depend on other issues, such as the enclosure's position relative to room boundaries that support loading at low frequencies, crossover design, etc.
cirrus18 said:
Hi HK26147,
That's interesting that you have already made a couple of these enclosures. I have been looking on the Internet but really can't find anything on the DIY line for projects utilising spherical enclosures.
There are hundreds for the usual coffin type and I would of thought that if, as people say, spherical enclosures are the best, there would be plenty of projects available. Or, is it just a lot of balls! javascript:smilie('
Just taking plans for a "coffin type" and changing the enclosure to a sphere will not guarantee an overall improvement. While the sphere may improve diffraction issues and make for a rigid cabinet, the baffle loss frequency will be higher. Whether or not this is a negative or an improvement may depend on other issues, such as the enclosure's position relative to room boundaries that support loading at low frequencies, crossover design, etc.
Re: Re: Re: Ovoid gevalt!
I'm not trying to just copy a "coffin type" but trying to get some fundamental design information pertaining to spherical enclosures. I was hoping that the knowledgeable people here would help.
From what I've read below at least a spherical enclosure is a step (no pun unintended) in the right direction.
Quote: from original article here, http://www.t-linespeakers.org/tech/bafflestep/index.html
Figure 1. Effects of baffle diffraction for 18" wide baffle
Please note that this diffraction loss curve is for an ideal loudspeaker mounted in a sphere, which exhibits a very smooth transition. Other shapes, such as the common rectangular enclosure, will introduce peaks and dips in the response, but the overall trend remains the same. Very little may be done to predict these response anomalies as they are predominantly spurious. The only reliable way to determine whether these peaks and dips are objectionable is with listening tests and acoustic measurements.
pooge said:
I'm not trying to just copy a "coffin type" but trying to get some fundamental design information pertaining to spherical enclosures. I was hoping that the knowledgeable people here would help.
From what I've read below at least a spherical enclosure is a step (no pun unintended) in the right direction.
Quote: from original article here, http://www.t-linespeakers.org/tech/bafflestep/index.html
Figure 1. Effects of baffle diffraction for 18" wide baffle
Please note that this diffraction loss curve is for an ideal loudspeaker mounted in a sphere, which exhibits a very smooth transition. Other shapes, such as the common rectangular enclosure, will introduce peaks and dips in the response, but the overall trend remains the same. Very little may be done to predict these response anomalies as they are predominantly spurious. The only reliable way to determine whether these peaks and dips are objectionable is with listening tests and acoustic measurements.
It is indeed true that the spherical shape will be smoother. I was just pointing out that by going spherical, the baffle loss frequency will be higher, and you may have to account for that.
I asked Roy Allison how he determined the "width" of an enclosure for calculating the baffle loss frequency, since most baffles are rectangular. He suggested using an average.
Regarding a sphere, where do you measure its width? If you measure it at its diagonal, you will find a higher baffle loss frequency than predicted. This is because the baffle is getting narrower way before this point. A good first assumption may be to take the average width between the front width and the maximum at the full diameter.
Also, the baffle step compensation at 6db is not ideal. This looks only at on-axis amplitude. As baffle loss is an acoustic loading phenomenon, you cannot just equalize the on-axis response and expect good results. If you do that, the POWER response in the room will be out of balance. I think this is why many settle on a 3db baffle step compensation.
I asked Roy Allison how he determined the "width" of an enclosure for calculating the baffle loss frequency, since most baffles are rectangular. He suggested using an average.
Regarding a sphere, where do you measure its width? If you measure it at its diagonal, you will find a higher baffle loss frequency than predicted. This is because the baffle is getting narrower way before this point. A good first assumption may be to take the average width between the front width and the maximum at the full diameter.
Also, the baffle step compensation at 6db is not ideal. This looks only at on-axis amplitude. As baffle loss is an acoustic loading phenomenon, you cannot just equalize the on-axis response and expect good results. If you do that, the POWER response in the room will be out of balance. I think this is why many settle on a 3db baffle step compensation.
pooge said:
To me the whole "baffle step" thing is oversimplified. Its really the entire enclosure diffraction and its going to be very complex. By simply measuing the loudspeaker in its enclosure this "step" is accounted for no matter how complex it is. To me any other way is just guessing.
I agree, but you measure power response. The average DIY would more than likely not be doing that. My point was that using the simple equation and correcting as advocated may not get you the correct results.
Moreover, bass accoustic loading is not just a function of the baffle size. It is also a function of distance to room boundaries, frequency, whether or not more than one driver in the same frequency range is used, etc. In other words, it MAY be a better approach, for a given baffle loss frequency, to design the speakers to be acoustically loaded with respect to room boundaries, or to use a pair of woofers optimally separated, etc., than equalizing (as these approaches will regain the acoustic LOADING lost by the baffle), because equalizing the on-axis amplitude (since a 6db increase in amplitude equalization will boost the power response up above flat, or overcompensate for the power loss due to baffle loss.)
In that sense, it may be better not to compensate, since room gain will certainly come into play at some point.
For a good simple tutorial on this, Roy Allison's patent is a good start.
Moreover, bass accoustic loading is not just a function of the baffle size. It is also a function of distance to room boundaries, frequency, whether or not more than one driver in the same frequency range is used, etc. In other words, it MAY be a better approach, for a given baffle loss frequency, to design the speakers to be acoustically loaded with respect to room boundaries, or to use a pair of woofers optimally separated, etc., than equalizing (as these approaches will regain the acoustic LOADING lost by the baffle), because equalizing the on-axis amplitude (since a 6db increase in amplitude equalization will boost the power response up above flat, or overcompensate for the power loss due to baffle loss.)
In that sense, it may be better not to compensate, since room gain will certainly come into play at some point.
For a good simple tutorial on this, Roy Allison's patent is a good start.
gedlee said:
This was one of the reasons that some of the pre-karmon infinities (think kappa) were so good- they had large-diameter roundovers (technically, kerfed bends) and felt-faced baffles. Not perfect by any means but very solid speakers that didn't goof around as you got off-axis, too much.
Did someone say bigger woofers?
Yes, this is a good way to address this. A larger (and thus typically more sensitive) woofer allows one to get better sensitivity within the bass and accordingly not have to pad down the frequencies above the baffle step, which to my thinking is throwing away power. This means a larger driver with bigger cabinet requirements and more expense. No free lunch. More sensitivity is better, but cabinet size is a problem for many users...
Even I run into cabinet size limitations sometimes, but thankfully I have a wife who is beautiful, can cook, and lets me get away with murder from a decor standpoint.
Yes, this is a good way to address this. A larger (and thus typically more sensitive) woofer allows one to get better sensitivity within the bass and accordingly not have to pad down the frequencies above the baffle step, which to my thinking is throwing away power. This means a larger driver with bigger cabinet requirements and more expense. No free lunch. More sensitivity is better, but cabinet size is a problem for many users...
Even I run into cabinet size limitations sometimes, but thankfully I have a wife who is beautiful, can cook, and lets me get away with murder from a decor standpoint.
cirrus18
I put an update to this thread I posted a while ago
http://www.diyaudio.com/forums/showthread.php?s=&postid=1739919#post1739919
Perhaps there is the best play to discuss, and let this thread be about theory and discussion(?)
( I'll answer there best I can, maybe brainstorm? )
Syd
I put an update to this thread I posted a while ago
http://www.diyaudio.com/forums/showthread.php?s=&postid=1739919#post1739919
Perhaps there is the best play to discuss, and let this thread be about theory and discussion(?)
( I'll answer there best I can, maybe brainstorm? )
Syd
gedlee said:
Earl,
Sorry I didn't communicate this well. I will try to clarify what I meant when I can get more time. But I meant to speak to the increase in power response of two drivers over one driver (for the SAME input power) due to mutual coupling at low frequencies. I haven't wrapped my head around the numbers for years, so I may not have this exactly right. Mutual coupling will raise the power response by 3db at low frequencies, while dropping it off faster at high frequencies. I was refering to use this as a tool to offset baffle loss instead of voltage equalization of the on-axis amplitude response, because, if I can recall correctly, amplitude equalization will raise the power 6db (you are equalizing drop in on-axis response in a changing acoustic load vs. frequency), where acoustic load loss due to baffle loss reduces power response 3db.
Again, I had that worked out at one time. My head is not totally into this right now as I focussed on other things. I'll have to check those numbers again, if you don't already corrent me on them. Of course, this opens a whole new can of worms, and would have to take room gain into consideration, as well as crossover point. But as you said, it is not as simple as the baffle loss step compensation scheme normally cited.
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