Interesting. Was the enclosure somehow not symmetric that could have caused this behaviour ?
(Emphasis mine)
Back when I was building my Ariels ('95 MkIIs) I spent some time in correspondence with a "Jackius" (sp?) who was trying to write a paper on TLs (IIRC).
Long story short: keep them separate. Vastly goes to zero, at least until you hit the room itself
(Anyone tried the door experiment yet? Or do we just theorise here?)
Dunno who this is. Did a search without result.
As to theorizing, I didn't except for the TL comment.
Sorry this was many eons ago so no data to backup my statement.
BTW I hate harddrives from back in the day, ask the wife about the 5 she killed in ONE week, back in '93. That killed me with the data loss and the $6500 invested. Thank heavens shes' not one of those people that when they walk into a room, kill electronics by meer proximity. U know the type As to the door experiment, Instead of mounting a single driver in a door. Mount two, with one isolated by a box. Music (test signals etc) played through the enclosed driver. Measure the other (unboxed) driver from the box side. I didn't sacrifice a door for my experiment, but a large flat baffle outdoors.
My apologies, I got this mixed up with another thing. All this took place quire some years ago. The correct situation is this:
Different cable lengths to two drivers in parallel caused the drivers to not move together. The drivers were each in their individual enclosures.
Concerning two drivers in a single enclosure, if the drivers are different, then they need their individual enclosures. If the drivers are the same, depending on how you stuff the enclosure, you may still want to have individual enclosures. I would use individual enclosures just to avoid the uncertainty. But I can't be sure if it was actually tested or not.
Sorry if my previously post created confusion.
I can see a time difference with cable length. Of course this would be in the microwave band and the cables had to be matched in length due to frequencies the differential preamp used. BNC to BNC tip to tip had to be less than 0.01mm in overall length matched. This was using doppler shift for radar jamming. I was in ECM USAF.... Ya we jam further, penetrate deeper yada yada yada
Mate, you engaged your brain for precisely 8 minutes there on a terrifically difficult problem.
I really don't care what you think of D'Appolito's and comb filtering. You imply the Ariel is a pile of poo, which I would doubt. Lobing is a mess with two ways and the D'Appolito addresses it.
Answer the question and learn something: "Which is better in a common enclosure, 16 ohm series or 4 ohm parallel wired D'Appolito bass units?"
It's a good question.
So, I guess we aren't going to see his answer to this question?
When building a line there seems to be a school that does parallel/series to get back to 8 ohm, and a school that goes all out parallel due to "back emf" effects in series. No one ever has explained that satifactrily to me though.
Greebster,
Agreed that at the microwave application this would be something to consider and would make differences, but at audio frequencies this is a non issue. We are not hunting for B2 bombers with our audio systems. but it would be nice if it did indeed track mother-in-laws.......
flg,
You just answered the question yourself. What you also have besides the back emf waveform is the modulating inductor, the first voice coil in series with the second device. Yes it is a small factor but it is still there.
Agreed that at the microwave application this would be something to consider and would make differences, but at audio frequencies this is a non issue. We are not hunting for B2 bombers with our audio systems. but it would be nice if it did indeed track mother-in-laws.......
flg,
You just answered the question yourself. What you also have besides the back emf waveform is the modulating inductor, the first voice coil in series with the second device. Yes it is a small factor but it is still there.
Entirely possible to build a 2.5 system with a 416 and 515, especially considering the two drivers have the same surround, spider, and cone (at least for the current GPA models, don't know about earlier Altec production).
The 515 will have the tipped-up response characteristic of very low Q drivers (I believe it is below 0.2), so some sort of mid-to-low assist would be necessary if you don't want the system to be bass-thin. Since the 515 is underhung and has fairly short linear excursion, EQ'ing the 515 isn't a great idea, since deep-bass program content will move the driver out of the linear region. EQ also has the downside of not being all that compatible with low to moderate power tube amplifiers.
A 416 (in a separate enclosure) operating in parallel but with a moderate-value series inductor acting as a shelf filter could complement the 515 response tilt ... however, the 416 is typically about 3 dB less efficient than the 515. One way around this might be to use an 8-ohm 416 and a 16-ohm 515 (wired in parallel). Each driver would need its own lowpass filter, with an extra pole for the 416 (the response-shaping thing).
My original thought on this was a separate transistor amplifier for the 416, which would get its input signal sampled from the terminals of the 515. That way, the level of the 416 relative to the 515 is adjustable with a knob, and the appropriate EQ function is simple to add to the input of the transistor power amp (lots of inexpensive analog EQs on the market).
The reason I set the 2.5 system aside was the complexity factor, but there's no reason it wouldn't work. There's the one-time level and EQ adjustment to create an idealized woofer from the two drivers, but once set, it's left alone.
I was (very) satisfied with the sound of the single 416. Some of the best bass I've ever heard. The combination of the well-damped cone, underhung VC, and Alnico magnet really gives the sound sparkle and vivid tonality, very different than the flat tonality of low-efficiency audiophile drivers. Very good match for what direct-heated triodes do well ... Big Tone.
Pairing up the 416's moves them in the direction of horn bass ... more snap, more immediacy, without changing the tonal character of the direct-radiator 416.
Soongsc, although I'm more of a subjectivist than other posters, wire should have very low to zero audibility when "tuning" a speaker for subjectively flat response. I routinely test my crossovers with the thing in my lap, flipping switches while listening to pink-noise or music, at the listening position. There's plenty of extra wire going to and from the speaker as I make adjustments in the 3 dB to 0.5 dB range (starting with coarse adjustments and working down to fine). If anything, resistors are more audible ... I like precision Ohmite wirewounds for crossovers, a tiny amount of inductance doesn't matter at these impedances and frequencies.
My dial-in procedure is fairly crude: I get the speaker as flat as I can, optimizing time response as I go, and when it's looking fairly decent then move to subjective adjustments, making sure the frequency and time measurements don't start going in the wrong direction. If subjective and objective start to oppose each other, that means I've made a mistake somewhere, and need to see what I'm measuring wrong, or determine if the system has a conceptual problem at the design level.
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...A 416 (in a separate enclosure) operating in parallel but with a moderate-value series inductor acting as a shelf filter could complement the 515 response tilt ... however, the 416 is typically about 3 dB less efficient than the 515. One way around this might be to use an 8-ohm 416 and a 16-ohm 515 (wired in parallel). Each driver would need its own lowpass filter, with an extra pole for the 416 (the response-shaping thing)....
A-HA I'm hoarding drivers for so long that I have that option too. Thank you for taking time to respond !
A-HA
I'm hoarding drivers for so long that I have that option too. Thank you for taking time to respond !
I'm still far from being an Altec expert, but I have found that Altec had a habit of making small to fairly big changes in the their bass drivers as the years went by. That's why the T/S measurements jump around, as well as the efficiency. From what I can tell, in the early, pre-Theile/Small days, Altec went for all-out efficiency and low IM distortion at the center of travel, while JBL explored increasing excursion with their overhung "LE" series (which I think really stood for "long excursion").
So I'm not sure there really is one 416 and one 515. I suspect there are many ... not just the famous changeover from Alnico to ceramic (which is easy to see), but internal changes as well. If you have a bunch of oldies, make sure the magnets are fully charged and cross-check to see if the T/S numbers match up.
P.S. When I dial-in a loudspeaker, I use both transistor and tube amps. The kind of gross changes that crossover adjustments make overshadow amplifier differences, but it's always a good thing to make sure the EQ structure isn't compensating for an amplifier coloration.
So I'm not sure there really is one 416 and one 515. I suspect there are many ... not just the famous changeover from Alnico to ceramic (which is easy to see), but internal changes as well. If you have a bunch of oldies, make sure the magnets are fully charged and cross-check to see if the T/S numbers match up.
P.S. When I dial-in a loudspeaker, I use both transistor and tube amps. The kind of gross changes that crossover adjustments make overshadow amplifier differences, but it's always a good thing to make sure the EQ structure isn't compensating for an amplifier coloration.
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I'm sure Sheldon would approve of the use of a radioactive isotope on the mother in law. Then hijack oakridge's computers and link that to the military satelites Wolowitz has access to which gives you txt updates. Leonard and Raj haven't finished the android app yet, go figure