Scientific and real-world design

[NickA1976]

As I continue to read and learn as much as I can about speakers I seem to have questions that don't jive with what I'm learning. In a 2-way (TW) design for example, it seems that woofers no larger than 8" are used. From what I can tell, it seems even a 8" woofer is pushing the limits of a 2-way design. Most 8" woofers (with the exception of very few) tend to break up before 2khz. That makes sense to me. However, what confuses me is a pair of speakers I grew up listening to in the early 80's, a pair of Advents. They were a medium sized floor standing 2-way design with a big 10" woofer. I don't have golden audiophile ears or claim they sounded amazing; however, I thought they sounded pretty darn good. I'm trying to wrap my head around how Advent (and other companies) pulled it off. Or was speaker design still in its "black magic" state back then without scientific knowledge? That or there is a big gap missing between the massive 10" woofer and the tweeter and Advent didn't koow (or even care). This is not a discussin or bash about Advent, just an example

This kind of falls into my next question(s). In terms of all the graphs and scientific calculations used to create a speaker design. If we go against what the graphs and calculations tell us (weather slightly or in a big way) the design is not worthy of good sound? Does every little dip or peak need to be corrected and flat as a pancake? I guess what I'm saying is should we build a speaker/crossover EXACTLY to the calculations generated from graphs and design programs? Or is it just a way to get us "close"

[Chris Roemer]

Most modern (non-"pro") designs today will use a (maybe "soft") dome tweeter - about 1" in dia.
Your ADVE\TS used the "fried egg" tweeter, which was kinda like a "hybrid" between a small dome (was it about 5/8" ?) and an old-fashioned "cone" tweeter - due to its large half-roll (paper?) surround - giving it the area of maybe a 3" cone?
That tweeter was crossed much lower than almost any dome can be crossed today (I think they claimed 1500Hz, maybe even as low as 1000?).

Today, most 8" woofers (which are not even very common for a 2-way) find it hard to reach up to 2k cleanly, where many 1" domes can cross.
Also, smaller domes (like today's - compared to an old-fashioned 3" cone tweeter, say) can have wider dispersion, which match up off-axis better with smaller woofers (which "beam" more severely as their dia. increases).

[billfitzmaurice]

The off-axis response issues of large drivers are just that, off-axis, so for the most part they won't be noticed. That said, one of the reasons for use of the MTM is that a pair of smaller woofers will have better off-axis response than a single larger woofer of equivalent displacement.

[Sydney]

... I grew up listening to in the early 80's, a pair of Advents. They were a medium sized floor standing 2-way design with a big 10" woofer. I don't have golden audiophile ears or claim they sounded amazing; however, I thought they sounded pretty darn good. I'm trying to wrap my head around how Advent (and other companies) pulled it off. Or was speaker design still in its "black magic" state back then without scientific knowledge? ...

No - The ubiquitous EM loudspeaker has been around since 1927. A lot of fundamental research and implementation happened in the decades after, including the Physics behind the EM "piston".
Material Science, Manufacturing Advancement and Analysis/Diagnostic tools improved of course along the way, especially since the 60s and later.
I'd opine that your "bar of expectation" raises through experience; what dazzled you then is an early experience.
Compare against today's offering and implementation options.

[philthien]

The woofers in my Advent speakers had a weird frame with a wide rim and more like an 8in cone.

They did sound very good.

Many designs back then were basically 8” two-ways. I think the shift to 6.5” two-ways came when people wanted smaller speakers at about the same time manufacturers were getting better at ported designs.

[Chris Roemer]

12" frame w/a 10" cone and a masonite 1" wide "ring" to make up the diff. Henry used the larger frame to get more Xmax.

[djg]

They were very good for listening to LPs and FM radio. I had a pair.

[philthien]

12" frame w/a 10" cone and a masonite 1" wide "ring" to make up the diff. Henry used the larger frame to get more Xmax.

https://www.midwestspeakerrepair.com/shop/speaker-repair-kits/advent-10-inch-wood-masonite-ring-refoam-kit-f10-15/

Is the measurement from the peak of the surround to the peak of the surround?

What constitutes an 8", 10", or 12" driver?

[dlr]

The off-axis response issues of large drivers are just that, off-axis, so for the most part they won't be noticed. That said, one of the reasons for use of the MTM is that a pair of smaller woofers will have better off-axis response than a single larger woofer of equivalent displacement.

I have to disagree with this, although you seem to contradict yourself a bit. Were this true, tweeter off-axis "flare" would be a non-issue. Off-axis relates to in-room power response and is certainly a significant consideration as well as better response for anyone not in the "sweet spot".

dlr

[Sydney]

... as well as better response for anyone not in the "sweet spot".

Never get anything done if I was always stuck in a "sweet spot"

[billfitzmaurice]

I have to disagree with this

That's your right. But where the beaming of a too large woofer for the pass band is concerned it will only be obvious if you're far enough off-axis. The average living room isn't going to have a large enough audience sitting far enough off axis for it to matter that much, within reason of course. How tweeter flare figures into the OP's question regarding the use of larger woofers I can't imagine.

[Pete Schumacher]

That's your right. But where the beaming of a too large woofer for the pass band is concerned it will only be obvious if you're far enough off-axis. The average living room isn't going to have a large enough audience sitting far enough off axis for it to matter that much, within reason of course. How tweeter flare figures into the OP's question regarding the use of larger woofers I can't imagine.

Bill, the off axis response does matter if you're in a room. The dip from the beaming of the woofer to the crossover with the tweeter will "color" the reflected sound and change the perceived balance of the presentation.

[dlr]

That's your right. But where the beaming of a too large woofer for the pass band is concerned it will only be obvious if you're far enough off-axis. The average living room isn't going to have a large enough audience sitting far enough off axis for it to matter that much, within reason of course. How tweeter flare figures into the OP's question regarding the use of larger woofers I can't imagine.

Tweeter flare is almost always an issue with largish midwoofers. The off-axis droop of the midwoofer coupled with the strong off-axis at the low end of a tweeter has to be considered. There are too many variables with rooms to ignore the off-axis, listening position and room response. I'm actually a bit surprised with your position on this.

dlr

[ernperkins]

Bill, the off axis response does matter if you're in a room. The dip from the beaming of the woofer to the crossover with the tweeter will "color" the reflected sound and change the perceived balance of the presentation.

+1. Look at the work of Toole and Olive on this importance.

[billfitzmaurice]

There's importance, and there's importance. I deal with this all the time in pro-sound, and if you think that crossing over from an eight to an one inch dome at 3kHz or so is bad consider going from a fifteen to a horn loaded tweeter at 4kHz, which isn't at all uncommon. Not that I'd ever put my name on a speaker of that sort, but I've designed more than a few for companies because that's what they wanted, and the one who signs the check has the final say. As I already said I'd rather a pair of 6.5s in an MTM to one eight, but one eight will still sound pretty good, and the off-axis dip at the upper end of the eight's range will look far worse on a chart than it will sound.