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In Reply to: RE: An alternative to a 'tympani' would be a 20.7 size woofer! posted by josh358 on January 22, 2017 at 18:09:04
I should add that the midbass panel on the model 3 has no crossover, they just let it fall off acoustically.
OB bass idea is great - making it optional is even greater as no big box will ever have a strong WAF unless it is decorated elaborately.
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Makes sense, if you don't want to shift load to the subwoofers.
Someone with a WAF problem could just get a sealed sub - wouldn't sound quite as nice as an OB but would still be fine for most. Or use the smaller OB dipole with IIRC 2 GR drivers.
Have to wonder about that copper, though -- who wants to add mass to a driver? Unless they wanted to lower the resonance without reducing diaphragm tension or reduce breakup.
IIRC the midbass is rated to 40 hz. so the mid/tweeter panel would be a fine standalone speaker. but for IMD reasons they want to cut it off far higher than that.
I am a bit taken aback by the choice of copper. But they may have an issue etching the Al. That is far harder to do than copper. But what their dealer was saying was that it was more along the lines of the sound character of the conductor as a wire material driving the choice. Only JPS with their Al/Cu metallurgy have experience with the sound of it.
The problem isn't so much bass extension as it is the distribution of resonances -- the second lowest resonance isn't in the bass panel, but the midbass:
The low bass panel is tuned to 68 and 51 Hz, while the midbass panel is tuned to 91, 78, and 64 Hz. So the second-lowest resonance is actually in the midbass panel, while the third lowest is in the bass panel. This means that both drivers should really be active for optimal dipole equalization.
Ah well. Got half of the diffusers mounted with velcro so I can take them off the window and even with only one side mounted properly there was a major improvement in imaging. Then ran out of steam (and velcro) so will have to get the others mounted tomorrow. (Actually not steam, since the radiator is finally fixed.)
I really doubt that they were going for lower resonance freq in the speaker with weighting of the diaphragm. It would be a rather bad trade off.
Isn't the bottom freq of the bass panel in the high 30s hz? I think mine were marked up in crayon 1t 37hz for one channel and 34?? for the other? Or is the distribution hiked up on the TIVa vs the earlier model? IIRC Roger was saying his TIII started with a high 30s resonance and it fell lower over time towards 30hz.
Velcro is a good idea, but buy extra since it won't survive too many removals and reattachments .
Good on the radiator, did it yourself?
Well, the label on my other panel reads 62/48. But these would be the frequencies measured at time of manufacture, so presumably the numbers dropped as the drivers broke in and these are meaningful only as relative values. They appear to be tuned do (woofer) re (midwoofer) mi (woofer) fa sol la (all midwoofer). Then presumably you have the resonance of the unpartitioned diaphragm since the hold downs don't extend the full width. And that's going to be the lowest resonance, but it isn't marked on the label.
Thanks for the heads up on the Velcro. That being the case, it occurs to me that magnets might be better. Maybe I can steal a couple of strips out of the speakers . . .
I did fix the radiator myself. It's an unusual arrangement -- single ended steam and I didn't want it venting into the room since I'm sensitive to mold and it releases some steam/brings up musty air from the vent in the basement. So I enclosed the vent and ran vinyl tubing back down to the basement through the plumbing chase, but something blocked the tube over the summer. Fortunately, I was able to get to the bad section by removing an outlet box in the living room on the floor below and didn't have to cut into the wall.
Next step, getting the plumber back to move the radiator to the other wall so I can put the bass panels where I want them! Either that, or get a Class A amp and do away with the radiator entirely. :-)
Josh---I've been away for awhile, and am catching up on all the PSA posts. In the meantime, may I ask what are the diffusers I see in the pics of your room? I'll be getting some soon, and yours look about right for my situation. Thanks---Eric.
GIK Gridfusors -- they're lightweight EPS foam which makes them great if you're experimenting with position or can't mount a heavy wood diffuser. But they do dent if you drop them, like Styrofoam. They also have a Styrofoamy-sounding resonance when you tap them, so I suspect wood diffusers sound better, and they don't cover as wide a range as more elaborate QRD's like the Diffractals.
Ah, okay. Are they and those of PI Group basically the same?
Good question. The Pi Audios are a very different design -- they're also QRD's but they're somewhat shallower and more complicated. Should be better in the highs but they say they only diffuse down to 1 kHz or so. I don't know what they're made of, just that they're CNC.
Thanks Josh. The PI site doesn't say, but they look like styrofoam. Really cheap, like $160 for two pair of 2' x 4' diffusors.
Yeah, since they're CNC, I think EPS is a good bet (like styrofoam but about 3x as dense). It is a great price, isn't it.
Cheap yeah, but you're right, they are effective only down to 1k or so. The 6" GIK's work down to around 600Hz, muchas better. I'd love some RPG type---maybe I'll make one. I need to cover a 4' x 4' window dead center between my speakers. The window cavity is 5" deep. Now that I think of it, four of the GIK 2' x 2' x 6" GridFusors would be perfect!
Yeah, the RPG's would be nice, wouldn't they. :-)
I have a window too and I hate covering it because I lose so much light, so I was thinking that what I really need is a transparent polycylindrical diffuser. Unfortunately, as far as I know, no one makes one, so I'd have to bend the Plexiglas myself, which looks to be something of a chore. Maybe we should start a company called "Diffusers For Windows." :-)
Ha! I actually WANT to close off the window (the only one in the room), for two reasons: 1- Although I'm sure my Tympanis were restored with Magnepans new, anti-UV sensitive glue, why take a chance?; but more importantly 2- I want my room to feel like an isolated musical oasis, the outside world being non-existent. My neighborhood is very, very quiet (it seems like the Northwest in general is, in comparison with noisy, congested Southern California), but with no outside light coming into the room, I can actually forget it's out there. I don't know why some people consider me anti-social. ;-)
Heh. I like the sunlight and I got UV resistant windows to protect the Tympanis (as well as less important things like my eyes). Though mine may have the water-sensitive adhesive that came after, not sure.
Patched up my diffusers which had gotten bunged up in transit (for which I got a $50 credit) and from falling off the wall, now I have to paint them and hang them for the umpteenth time, having discovered that tape just doesn't want to stick to them. The paint apparently improves their performance by hardening and sealing the surface.
I think these frequences are right out of the production. After years of usage they are lower, at least the lowest ones. T-IIIA low bass have 46 and 55 Hz written on the frame of the driver. After 40 years it is 34 Hz for the lowest frequency even without being used for years. I have forgotten the values written on my T-IVa.
I am not sure the moving mass is that important for a dedicated bass driver. The old T-IIIA have a lot more moving mass (copper wires) than later models like T-I-D, T-IV and IVa.
The Apogee basses were not very low mass and did their job well.
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