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Multi-Way Conventional loudspeakers with crossovers

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Old 28th October 2018, 05:52 AM   #14941
Joe Rasmussen is offline Joe Rasmussen  Australia
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Originally Posted by Lynn Olson View Post
But they actually sound quite different (well, at least that's what I heard, and repeatably so). Why?

Well, the magnetic systems are different. The modern 2235 has an overhung voice coil, while the Altec and GPA have an underhung voice coil. The 2235 voice coil is partially in a region where the flux lines are not straight, while the voice coil of the 416 or 515 is in a region where the line are straight (inside the gap)... The onset of magnetic distortion is much more abrupt with an underhung VC, which is an indirect pointer against using them in a vented box without an external low-level highpass filter that creates a B5 or B6 response curve.

Hi Lynn

My apologies not getting back to you, going to ETF18 in Normandy and the last week has been crazy getting things done and leaving tomorrow. Will be seeing a number of people before ETF starts on 15th.

Your overhung versus underhung comments interest me. And I agree with the points you make because they are obvious. The best driver should be underhung, but if only it was that easy. This story indicates why:

Last year I went visiting SB Acoustics in DK and the topic came up when conversing with their designer Ulrik Schmidt - because I had noted that he only designed overhung voice coils (but highly symmetrical drive) and I made the point that underhung drivers has noticeable lower sensitivity for the same respective impedance (4 or 8 Ohm) and that it must be because of the magnetics in a long gap makes for weaker concentrated magnetic circuit. He confirmed that. So for a given dB-SPL the voice coil gets hotter. The low sensitivity, this is why he stuck with overhung, and he said you can only go so far in getting a strong magnetic circuit in underhung. I suppose we all do with what we are comfortable with.

But with underhung, the heat will also be distributed more evenly, as heat convection along the entire length of the coil across gap. I consider that a good thing, even if there is more heat to dissipate. So this is swings and round-abouts. But I like voice coils to run cool, I like a lot of surface area, so that excursions are OK at my listening levels. I do prefer a Bessel like vented alignment, interfaces well with the room, keeps excursions down, I tune low 30s Hertz and OK down to 25 Hertz. so sub 25 Hertz? Well, you have a point about that limitation. But still way fuller range than 99.9% of speakers out there.

Cheers, Joe
"Elsinore Project" DIY Speaker System
- "Don't take anything I say as an affirmation, but as a question." Niels Bohr [Subtext is about Humility]

Last edited by Joe Rasmussen; 28th October 2018 at 06:19 AM.
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Old 29th October 2018, 12:04 AM   #14942
soongsc is offline soongsc  Taiwan
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I kind of had the same perception. But had not got the amplifier part and enclosure design quite optimized yet.
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Old 11th November 2018, 08:30 PM   #14943
Moderation Team is offline Moderation Team
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Recent OT posts about amplier back-emf and load impeadnce have been moved here:
Back-EMF and flat impedance
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Old 11th November 2018, 11:39 PM   #14944
zbig001 is offline zbig001  Poland
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In case of amplifiers, THD levels are so low that they almost never get above the average level of noise in listening room (which is usually 20-30 dB)...

I noticed that for loudspeakers THD measurements are always made in relation to frequency.
But I wonder, what results could bring measurement of THD vs power?
That is, if you measure like for an amplifier...

I can hardly find such measurements of tweeters, but but I have never come across such a measurement of midrange or bass speaker.

Perhaps there would sometimes be interesting results that would help in the selection of a transducer for DIY project?
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Old 12th November 2018, 03:22 AM   #14945
AllenB is offline AllenB  Australia
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The siren song of the driver with compression issues is that there is a sweet spot volume level at which to listen. Even woofers can have trouble keeping up when the going gets loud. I just find something better.
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