Sealed subs distortion is much lower than ported below the port tuning. When subs are ported in things like an extended bass shelf, you tend to get higher distortion throughout that range, which means in many cases, really low tuning doesn't solve that issue. When used within their effective range, a sealed sub can have lower distortion than ported throughout their range (they will be the same above the tuning frequency). In many cases, the subs with really low distortion numbers on HT Shack are about the drivers rather than the enclosure. Certainly a port can give greater output, with lower distortion, at the given tuning frequency, but much below that the distortion will rise far above that of the sealed, and response drops like a stone. Often the difference is so small, and our hearing acuity for distortion at those frequencies so poor, I'm not sure it makes a difference.
I have two of Dr. Geddes bandpass subs for my main subs, I don't know their exact range, but they are the broadband type, and relatively small, about 2 cubic feet. I'm fairly sure they extend into the 100+hz range with no low pass on them. Their distortion measures very low between around 60hz and 100hz or so. I didn't measure much above that, so I can't say, and below that it started to rise, but I'm sure not in any audible way.
My ULF, so to speak, subs are a ported design in a 5 cubic foot box with a 12" TC Sounds TC3000 with a one-off motor design they were testing right before being bought out. Lower inductance, lower distortion, and optimization in larger boxes. The other uses dual dayton RSSH15HF subs in a push-pull sealed 2.5 cbft box (Previously I had these each in their own 2 cubic foot sealed boxes), and that sub has lower distortion below 25hz than the TC Sounds design. The difference is small, and the TC has much greater LF output abilities than the Dayton, but its all in the driver, not the enclosure. The TC has far more than 30mm of one way linear excursion and more than 3000 watts of power handling.
I have two of Dr. Geddes bandpass subs for my main subs, I don't know their exact range, but they are the broadband type, and relatively small, about 2 cubic feet. I'm fairly sure they extend into the 100+hz range with no low pass on them. Their distortion measures very low between around 60hz and 100hz or so. I didn't measure much above that, so I can't say, and below that it started to rise, but I'm sure not in any audible way.
My ULF, so to speak, subs are a ported design in a 5 cubic foot box with a 12" TC Sounds TC3000 with a one-off motor design they were testing right before being bought out. Lower inductance, lower distortion, and optimization in larger boxes. The other uses dual dayton RSSH15HF subs in a push-pull sealed 2.5 cbft box (Previously I had these each in their own 2 cubic foot sealed boxes), and that sub has lower distortion below 25hz than the TC Sounds design. The difference is small, and the TC has much greater LF output abilities than the Dayton, but its all in the driver, not the enclosure. The TC has far more than 30mm of one way linear excursion and more than 3000 watts of power handling.
On a completely separate note, Dr. Geddes I have a question? Do you think you would ever consider making a dedicated center channel which used two 12" drivers and a single 15" waveguide above the drivers. Using the setup to allow an enclosure that isn't as tall as the current setup, and also offering better on-axis response (not the driver setup, just crossover optimized for this and larger waveguide). It's probably wishful thinking, but I would love the ability to have a center that is about 4-6" shorter so I can mount my screen lower, and not use an acoustically transparent screen. I know you prefer them, from a sound standpoint, I do too, but I couldn't give up on the image quality difference in my non-dedicated room.
As you said, above freq around tuning, sealed and vented behave the same.
It's only below Fb that vented excursion increases over sealed, and this is true for EBS.
So I disagree that distortion is higher in EBS shelf freq range.
Why all the worry about distortion in a sub? It really isn't a factor. Flow noise in the ports is, because it's uncorrelated and goes higher in frequency, but THD type distortion in a sub is certainly not audible. At least this is true for a well designed sub. Some of the plate amp subs that I tested had incredibly high distortion due to the amp clipping at even reasonable levels. This is an issue. From my studies it was all about not overloading the design and having enough port area that didn't cause flow noise. Plate amps just do not seem to have the headroom that is claimed - they all seem to clip very early. I suspect its the amp, although with a plate amp installed in the system its hard to tell, but the distortion rises very quickly at some point, which is indicative of clipping, not a driver issue.
Matt - I'm not sure that I see the two 12's as being shorter. I do make a crossover modification for center channel use, write me if you want and I'll tell you what to do. I don't think that I was doing this when you bought yours. I would just turn the speakers on their side, which isn't ideal, but its not going to be a big issue either.
Matt - I'm not sure that I see the two 12's as being shorter. I do make a crossover modification for center channel use, write me if you want and I'll tell you what to do. I don't think that I was doing this when you bought yours. I would just turn the speakers on their side, which isn't ideal, but its not going to be a big issue either.
I think that is what I was getting at. Looking at THD at levels below clipping is meaningless and if the amp is clipping then thats simply a "use" issue - you are using it past its design intent (well not according to the marketing brochure!) At levels below the amp clipping, I have found that only port noise is an issue. Nothing else matters.
But nobody (except me, I guess) measures port noise, so that leaves you without much data.
Dr. Geddes, you previously sent me some sort of mod for using it as a center. It was a change in the trap values I believe, and a change in the cap value on the parallel wired cap and resistor in series with the tweeter.
I tried it on it's side, sounded terrible. Added a lot of harshness. I tried a lot of things to improve things, nothing worked as well as simply putting it back up right. On it's side everything sounded somewhat harsh and nasally. In my opinion, not a small difference either. I thought it might be reflections off the floor, so I placed 2" of rockwell on the floor all around it. It didn't solve the issue, so either it wasn't enough, or it wasn't the problem.
My thought was that two 12's would allow a shorter speaker than the Summa, but could still use the 15" waveguide that has less on-axis issues. The idea would be to place the 15" waveguide into the space or crevice made between the two 12's when next to each other. The two 12's would be together like a figure 8 on it's side, and then that v crevice would be where the waveguide is nested. The 12" waveguide would fit best, but then its just shorter, no better on-axis I would assume.
I tried it on it's side, sounded terrible. Added a lot of harshness. I tried a lot of things to improve things, nothing worked as well as simply putting it back up right. On it's side everything sounded somewhat harsh and nasally. In my opinion, not a small difference either. I thought it might be reflections off the floor, so I placed 2" of rockwell on the floor all around it. It didn't solve the issue, so either it wasn't enough, or it wasn't the problem.
My thought was that two 12's would allow a shorter speaker than the Summa, but could still use the 15" waveguide that has less on-axis issues. The idea would be to place the 15" waveguide into the space or crevice made between the two 12's when next to each other. The two 12's would be together like a figure 8 on it's side, and then that v crevice would be where the waveguide is nested. The 12" waveguide would fit best, but then its just shorter, no better on-axis I would assume.
Auditions are a great thing, but I think that they are a luxury that drives the price of speakers up well beyond the benefits that they offer. Just as when I design them, auditions should simply be a matter of confirmation and not a factor in a decision. Decisions should be made strictly on concrete data. To have dealers and the historical feature of auditions would double the price that I would have to charge. And that basically doubles the price for everybody! Far far better is too learn to read the data and to insist on being given that data by the manufacturer. That saves an awful lot of money for the consumer. This is precisely how I can sell speaker that costs a fraction of any else in its class.
But hey, if there is someone who is willing, then go for it. Try Duke Lejune just up Idaho, he may be willing - he has a set of Nathans at the moment. But I don't think that there are any Abbeys shorter than Denver.
But hey, if there is someone who is willing, then go for it. Try Duke Lejune just up Idaho, he may be willing - he has a set of Nathans at the moment. But I don't think that there are any Abbeys shorter than Denver.
Thanks for the quick comment. As a design engineer I agree with you in general. The data, especially if it is real, and not made up or tweaked, is a large part of the decision. I design pro and high end audio gear for a living, but have no experience in acoustics or speakers.
I do trust my ears, but always want to see the data as well.
There are speakers closer than I thought, so that is good news. I probably will have some income soon, through sale of some vintage tubed audio gear from the 60's. I probably will have only one chance to get the speakers I will live with for many years. I want to be sure before I plunk down the cash!
I am very impressed with what you are doing, and want to learn more!
Thanks,
-david BTW
I do trust my ears, but always want to see the data as well.
There are speakers closer than I thought, so that is good news. I probably will have some income soon, through sale of some vintage tubed audio gear from the 60's. I probably will have only one chance to get the speakers I will live with for many years. I want to be sure before I plunk down the cash!
I am very impressed with what you are doing, and want to learn more!
Thanks,
-david BTW
David,
If you don't have anybody to audition close by, I would strongly suggest you get on a flight and go directly to Geddes' chateau. It's well worth the trip to get the honest truth. It's a whole lot cheaper than getting speakers you may not be satisfied with - at least in the long run. However, if you can audition the Nathan's, they will give you an idea of what the Abbey sounds like. But it's only an idea. Imho, the Abbey is superior, having heard both, I would easily plunk down the small amount of extra cash to go with the Abbey instead of the Nathan.
And Earl is completely correct about *insisting* and then analyzing the data the loudspeaker manufacturer provides you. It's only then you can make an informed decision. If they don't provide you with that data then it's difficult to make that decision as it becomes an irresponsible and misinformed one.
Best of luck,
Anand.
Anand - a trip here is what I recommend as well. Few people have gone to the extremes that I have in my room and its worth it to see what these extremes get you. From that basis you CAN make an inform decision about what speakers to buy, how many subs to use, what to do with the room and most importantly why you should not spend a lot on electronics.
I don't know of anyone who has been disappointed by a visit - unless I was in a bad mood and didn't offer coffee or something like that!
I don't know of anyone who has been disappointed by a visit - unless I was in a bad mood and didn't offer coffee or something like that!
I think your setup is proof how much more important the room and speakers are than the things many of us spend much more on. I'm sure that amps and preamps will play a role in improved sound, but when given the choice of 1000 dollars for a receiver or pre/pro and amp, or 30,000 dollars, the improvements are probably incremental, possibly non-existent, and the 29,000 spent on room acoustics would sure make a lot more sense.
I've seen 100,000+ dollar stereo's stuck in the worst rooms and wondered why they even bother. Speakers stuck against the walls, often too far apart, with bookcases or tables between them, equipment setup in such a way to cause pretty poor wire dressing, which I'm sure is adding noise, hardwood floors, no carpet, hard walls, hard ceilings, no absorption, and terrible places to sit. Whats the point.
I've seen 100,000+ dollar stereo's stuck in the worst rooms and wondered why they even bother. Speakers stuck against the walls, often too far apart, with bookcases or tables between them, equipment setup in such a way to cause pretty poor wire dressing, which I'm sure is adding noise, hardwood floors, no carpet, hard walls, hard ceilings, no absorption, and terrible places to sit. Whats the point.
You forgot to offer me coffee you know. No problem. Next time, we'll go out or I'll bring my own powder to share!
Anand.
I'd hate to hear your response if it was something other than coffee, the other major export of Columbia.
So Dr. Geddes, I'm wondering if you have any thoughts/plans on upgrading your receiver at some point to handle the new audio codecs. I've completely gone head over heals for the new HD Audio formats on Bluray, they are miles ahead of the older DTS and DD. Even the newer refinements of DTS and DD are great, DD+ for instance sounds miles ahead of DD and DTS, even if it's not as good has True HD or DTS Master Audio. Anyway, I'm curious your opinion on the matter, and if in near time, you have plans to look at ways to add that capability to your system.
So Dr. Geddes, I'm wondering if you have any thoughts/plans on upgrading your receiver at some point to handle the new audio codecs. I've completely gone head over heals for the new HD Audio formats on Bluray, they are miles ahead of the older DTS and DD. Even the newer refinements of DTS and DD are great, DD+ for instance sounds miles ahead of DD and DTS, even if it's not as good has True HD or DTS Master Audio. Anyway, I'm curious your opinion on the matter, and if in near time, you have plans to look at ways to add that capability to your system.
ah good to know. What model do you have now?
If you have a new one, I'll assume you have MCACC. If its the top version of that, I'm wondering if you have tried it and what you think? You already do much of what the "room mode" portion if its correction does, but it has something they call like Full range phase correction, or something like that. I'm not sure what it is, but when first introduced it was indicated in an email to me that it corrected the phase response of each individual speaker across the full range. They wouldn't go into details on how they were doing this, but were very insistent this was not simply a phase control or phase flipper, it uses sophisticated filters to correct the phase, not just reverse it.
The 9 band graphic EQ is of no real interest to me, but even the room mode correction could be used to further improve the bass response, as it could add correction to the low end of the main speakers, which my setup can't do. If yours is setup like mine, I assume you can't either. The Room mode corrector is also not divulged in a good meaningful way, but I was told it uses filters that target the problem area's, not generic PEQ or worse yet, graphic EQ filters. All of this, including the phase correction, makes me wonder if its using a form of FIR filters, but then, I would think it would be silly not to use IIR filters for room mode correction, no?
If you have a new one, I'll assume you have MCACC. If its the top version of that, I'm wondering if you have tried it and what you think? You already do much of what the "room mode" portion if its correction does, but it has something they call like Full range phase correction, or something like that. I'm not sure what it is, but when first introduced it was indicated in an email to me that it corrected the phase response of each individual speaker across the full range. They wouldn't go into details on how they were doing this, but were very insistent this was not simply a phase control or phase flipper, it uses sophisticated filters to correct the phase, not just reverse it.
The 9 band graphic EQ is of no real interest to me, but even the room mode correction could be used to further improve the bass response, as it could add correction to the low end of the main speakers, which my setup can't do. If yours is setup like mine, I assume you can't either. The Room mode corrector is also not divulged in a good meaningful way, but I was told it uses filters that target the problem area's, not generic PEQ or worse yet, graphic EQ filters. All of this, including the phase correction, makes me wonder if its using a form of FIR filters, but then, I would think it would be silly not to use IIR filters for room mode correction, no?
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