some random thoughts while awaiting for a delivery of the geddes 15" OSWGs.
at the moment i'm concerned with a bass driver choice for the project.
do any of you, who had a chance to hear summas in better surrounding than geddes' panasonic AVRs, think that the bass driver choice (B&C 15TBX100) might be a weak point of the design.
i was looking into critical parameters and a number of things there is really not up to my taste - i'm appalled with the cone mass of over 160g for a driver aimed to play so high. can such a driver really match speed of the sound coming from the waveguide? however i'm ready to accept that this is all irrelevant and i'm being too picky with data on paper while in reality it just works different in a given design - never heard summas so i can't have an opinion here. this is a fun project for me but i want to make the most out of it.
my choices are now narrowed either to
a) cheaper options from B&C or other european manufacturers of the similar level (beyma)
b) lot more expensive contenders: BD15 or AE TD15M (with or without Apollo mod).
obviously the main argument for B&C driver is leads a project to rather safe ending - some kind of summa clone.
one of the main reasons why i really like TD15M was extremely low Mms and L which makes it ideal for driving it with low powered amps and that's my goal - to drive it passive with a very low power SET amp (like A2 biased 801A or similar). BD15 has even lower Mms but its inductance is not so low as with the AE driver, although it has a nominal 16ohm impedance (instead of 6ohm AE) which gives another advantage and and makes it an easy load - AFAIK DE250 is also a 16ohm version.
B&C would cost me around $500 a pair and i can source it locally. beyma alternatives are the same.
BD15 will be at least $1200. apollo version of TD15M will be in the same range delivered to me - $1100-1200. both would have to be imported.
i'm really fine with paying more if there's a clear guarantee it will yield sonic benefit in given design - which i really don't know.
any thoughts? what would you do?
at the moment i'm concerned with a bass driver choice for the project.
do any of you, who had a chance to hear summas in better surrounding than geddes' panasonic AVRs, think that the bass driver choice (B&C 15TBX100) might be a weak point of the design.
i was looking into critical parameters and a number of things there is really not up to my taste - i'm appalled with the cone mass of over 160g for a driver aimed to play so high. can such a driver really match speed of the sound coming from the waveguide? however i'm ready to accept that this is all irrelevant and i'm being too picky with data on paper while in reality it just works different in a given design - never heard summas so i can't have an opinion here. this is a fun project for me but i want to make the most out of it.
my choices are now narrowed either to
a) cheaper options from B&C or other european manufacturers of the similar level (beyma)
b) lot more expensive contenders: BD15 or AE TD15M (with or without Apollo mod).
obviously the main argument for B&C driver is leads a project to rather safe ending - some kind of summa clone.
one of the main reasons why i really like TD15M was extremely low Mms and L which makes it ideal for driving it with low powered amps and that's my goal - to drive it passive with a very low power SET amp (like A2 biased 801A or similar). BD15 has even lower Mms but its inductance is not so low as with the AE driver, although it has a nominal 16ohm impedance (instead of 6ohm AE) which gives another advantage and and makes it an easy load - AFAIK DE250 is also a 16ohm version.
B&C would cost me around $500 a pair and i can source it locally. beyma alternatives are the same.
BD15 will be at least $1200. apollo version of TD15M will be in the same range delivered to me - $1100-1200. both would have to be imported.
i'm really fine with paying more if there's a clear guarantee it will yield sonic benefit in given design - which i really don't know.
any thoughts? what would you do?
Low Fs, medium Qts, and still light coned
if you can live with the short Xmax 
FaitalPRO - Neodymium Professional Drivers
BD15 is NICE, but that's a lot of cash. Still, I'm a very large fan of underhung coils.
I wouldn't change a thing in the Summa.
You should be clear that you are NOT getting "Geddes" OSWGs. I think that claim is misleading.
And I think that your slam on my AVR is uncalled for. Have you measured it? I have.
Low Fs, medium Qts, and still light coned
and shorter voice coil - but wow, looks great for 170E!
thanks but if i'm misleading here, i'm doing it to myself only - i'm not selling anything.
if things start to look bad with the passive crossover i will certainly look what to do with a DEX or similar, either for simulation of a optimal passive crossover or as a final solution. actually i'm a bit worried that considering i don't want to give up on my 10Y/801A SET the only way to have it used would be within an active 2-way system.... but let's see
I understanhd that, but it sounds like you are getting those from me and thats not the case. I don't sell them either.
Reading through the "by-play" here.. it does indeed sound like he is "getting those" from you. Not directly, but by way of 3rd party resale. Correct or not?
He has also expressly stated that he isn't trying to make Summa's so why brusque defensive reply?
i think this is an official price list
http://www.showtek.it/files/faitalpro_listinoprezzi.pdf
just to clarify any confusion - i didn't buy this from geddes. i've got them from someone who bought it from earl long time ago when it was still possible.
i believe it's clear for quite some time that summa kits and 15" WGs are not available from the manufacturer due to his business policy.
thanks.
Thanks, that's clear now. I was wondering were they came from. I have no idea what's being sold on the resell market, but I do know that frauds are being passed off.
Summa kits are not available not because of business policies, but because it is not possible the way its designed now. That's why the system was redesigned - to allow for kits. There may be a kit with the same functionality as the Summa one day, but I really do not think that it would be a major product because of its size, weight and cost. The Abbey is a sweet spot in those terms and further development of it seems like the most viable approach.
I would go with the TD15M if you can. If you are using it in a home environment, you don't need the apollo upgrade and can save the money. B&C states that the 15TBX100 is more for sub-woofer and woofer use, but not as much for mid-woofer or midrange.
Tom
That's because that's what people tend to use them for. I've measured dozens of 15" woofers looking for good ones - particularly at the very top end - and the 15TBX100 is as good as any. I won't say its the best, at the top end of the list they are all about the same, but its as good as any that you will find. It has it's problems, they all do. PM me and I can get them for you cheaper than you can buy them anywhere else. But I won't quote them, I just tell you that you can't get them any cheaper than I sell them at.
direct radiator, cone-heavy driver vs hornloaded compression driver.
would you expect a perfect match of speed?
me not. unless you are talking literally.
maybe the terms are being used loosely and I'm just harping here, but I'm a bit confused by this discussion of the "speed of sound" mentioned above. The speed of sound is constant in a given medium, no? In terms of the speed of modulation, i.e. frequency, this too will not be different, and if it is, thats distortion, no? I mean, I've heard this argument before that heavy cones can't reproduce midrange well because it's too heavy, but I don't get the speed argument, makes no sense to me.
I think the more important argument is the directivity of each at the crossover point. If we consider the 15" waveguide and 15" woofers, this implies a crossover point in the area of say 600-1000hz range to properly match directivity. If you look at the response of any of these woofers mentioned, most if not all are quite comfortable in that range, no?
It seems like the biggest problems at these low crossover points is the resonances in the driver itself. This is typically well enough below the breakup point that the response peaking is easily dealt with. However, I know there is a dip in the response around 800hz in every 12" and 15" woofer I've looked at, which Dr. Geddes says is due to a common design element, is correctable, but that no driver has this right. The guys at AE claim its from dustcap resonances, and their woofers don't show thus, but that isn't true either. Their drivers also show this same resonance in roughly the same place (as do all other drivers I have ever looked at of this size).
In my Abbey's, the one problem in the response curve that I would most like fixed is this depression in the response as a result of the resonance, but I've been told by multiple sources, including Dr. Geddes, that this isn't reasonably possible. Admittedly, I really have no reason to believe that the its audible, as I've never heard these without it, so its mostly an aesthetic desire at this point.
I think the more important argument is the directivity of each at the crossover point. If we consider the 15" waveguide and 15" woofers, this implies a crossover point in the area of say 600-1000hz range to properly match directivity. If you look at the response of any of these woofers mentioned, most if not all are quite comfortable in that range, no?
It seems like the biggest problems at these low crossover points is the resonances in the driver itself. This is typically well enough below the breakup point that the response peaking is easily dealt with. However, I know there is a dip in the response around 800hz in every 12" and 15" woofer I've looked at, which Dr. Geddes says is due to a common design element, is correctable, but that no driver has this right. The guys at AE claim its from dustcap resonances, and their woofers don't show thus, but that isn't true either. Their drivers also show this same resonance in roughly the same place (as do all other drivers I have ever looked at of this size).
In my Abbey's, the one problem in the response curve that I would most like fixed is this depression in the response as a result of the resonance, but I've been told by multiple sources, including Dr. Geddes, that this isn't reasonably possible. Admittedly, I really have no reason to believe that the its audible, as I've never heard these without it, so its mostly an aesthetic desire at this point.
The resonance at arround 800 Hz. or so is due to the spider, not the dust cap. And yes I see this in every woofer that I test.
And yes, all the discussion of speed is kind of off base. The "speed" of the two drivers, the woofer and the tweeter are the same, just as all drivers are the same. The speed of sound does not change.
The point that I think is trying to be made is "How can a very heavy cone move as fast as a light one?" - its because the velocity depends on the mass AND the force. Did you ever see the magnet size on a 15TBX100? Or the voice coil? There is a lot of force there and this force CAN move that mass that fast.
And yes, all the discussion of speed is kind of off base. The "speed" of the two drivers, the woofer and the tweeter are the same, just as all drivers are the same. The speed of sound does not change.
The point that I think is trying to be made is "How can a very heavy cone move as fast as a light one?" - its because the velocity depends on the mass AND the force. Did you ever see the magnet size on a 15TBX100? Or the voice coil? There is a lot of force there and this force CAN move that mass that fast.