Matt's Gedlee Summa Abbey Kit Build

[pjpoes]

Originally Posted by gedlee

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 if it didn't have enough force to move the cone at this frequency, would it not show up in the measurements?

[poptart]

Originally Posted by pjpoes

And if it didn't have enough force to move the cone at this frequency, would it not show up in the measurements?

Exactly. The cone can move back and forth one thousand times a second no problem, that fact is staring at you in every plot. I thought this was maybe referring to the audiophile voodoo that there are fast and slow bass drivers. I have no idea what that is supposed to mean but I suspect someone might have heard some room mode droning on or whatever and somehow come up with the idea they were hearing a "slow" woofer flopping around.

[anubisgrau]

no i didn't mean a speed of high mass cone driver vs low mass membrane driver (as in woofer vs compression driver) but rather direct radiator vs horn loaded. you simply have two different principles or air-coupling and one of these is dealing with air impedance in a much more efficient manner. i would expect this to be somehow audible - sorry for coming here to a subjective ground but i keep on hearing this in different designs and there's a clear reason why there's a horn loaded bass or mid-bass systems.

unless geddes' waveguides don't behave here like a usual horns - i know he was insisting that the main role of his WG is about directivity not the usual functions of the horns as we know them. maybe this is tackling the issue, i don't know.

i've found this to be a main problem of many speakers whose design is mixing horns and direct radiators (of a kind) - like avantgarde etc - a subjective feeling that bass is somehow lagging behind. i can even slightly hear that in my (small) room with much better design than avantgarde duo.

[gedlee]

Originally Posted by hornperfect

there's a clear reason why there's a horn loaded bass or mid-bass systems.

And that would be?

When I listen to Avantgardes, I dislike the bass as well, but its not because "its lagging behind", this is something your mind is telling you, not your ears. My room does not exhibit this problem, but its not because of Waveguides or anything like that. Its the use of multiple subs which creates a much better sense of bass that couples very well with the waveguides.

[anubisgrau]

why such a steep (24 db/oct) filter on bass in summa?

[pjpoes]

It's 3rd order, not 4th order.

[gedlee]

Yes, its 3rd order, not fourth. Most larger speakers, like the ones that I use, break-up pretty badly once they become non-pistonic. A sharper filter helps this problem. The Abbey was first order LP for a long time, now its third. The extra slope makes for a slightly smoother crossover. The Nathan is still first order and will probably stay that way.

[anubisgrau]

just to confirm this project is now in the final phase. i've used a 2" MDF for the cab and in the end i opted for the bass from the original project so there was no need to adjust the crossover for that. it sounded surprisingly nice from the first moment everything was assembled. there was just some playing with the cab damping in the bass area left and that's it, or it is my brain reminding about different nature of the LF and MF/HF sounds.
the thing i was most surprised with was lack of coloration from the geddes horn. yes, it maybe ain't have the similar feeling of pressurizing the room like tractrix or lecleach do, however that's compensated with much wider sweet spot and lack of beaming. now i better understand the hype about OSWGs.
actually i'm now contemplating about selling the fiberglass waveguides and building the similar from the plywood or MDF, as it would just look nicer in the room.
also at a certain point i will need to upgrade the crossovers with premium parts at the critical positions on the MF/HF filter which is assembled from the cheaper parts, obviously too see how it works.
but it sounds very decent and not too far from my previous horns that were $$$$$.
even my wife who is always a very critical judge gave them a green light soundwise which is an amazing compliment. she's much more critical than me and very often confronts with my tolerance towards some models....the last one she complained about was audio note AN-J. actually the only two ever to get her blessing in our room were oris swing and this one.
thanks anyone who helped.

[454Casull]

Originally Posted by anubisgrau

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.

http://www.adireaudio.com/Files/WooferSpeed.pdf

[noah katz]

Originally Posted by anubisgrau

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?

First of all, mass affects efficiency, not necessarily speed; for a given freq and excursion, it will simply take more power.

If the mass is actually in the cone, it may very well play high better; if it's twice as thick, it's 8 times stiffer, allowing it to play higher before breakup modes.

That's other things equal, which they may not be, i.e. inductance.