Sound up close vs. on the dance floor

[dwynsen]

You're absolutely right about the 18" having a much greater cone excursion. In typical bass guitar cab designs, the 10's do NOT have the excursion capabilities of an 18" -- usually. That's by design so the 10's can generate higher frequencies (less mass). My comments about a 4x10 having more area than a 1x18 make sense ONLY if the 4x10 was designed for subbass like the 1x18 -- which it wasn't. As for swept-volume, the 18" wins hands down. In my home, my two Hsu subs each have a single 12". Each is driven by a dedicated 250 watt amp. They can go to 17Hz flat at 112 db (felt, not heard). That's amazing. The cone excursion is spec'd at about 1.25"!!!! They really flop. The cones are stiff and hugely massive. Their upper end is rolled off at 12db/octave beginning at only 92 Hz. In my bass stack, my 18" has a useful upper end of only about 1500 Hz. From there, my amp crosses over to the 4x10 cab (in stereo mode). Sounds wonderful (to me) because the 18" adds the bottom to my growl (and ocassional slaps/pops).

Several sites I found for cab design:

http://www.kbapps.com (design calculator)
Invalid Link Removed (gen'l info)
Bad Link Removed (great article about tradeoffs in design)

To find addn'l sites, go to http://www.DOGPILE.com (GREAT search engine) and search using boolean logic like "bass AND guitar AND speaker AND cabinet AND design". You'll get many hits.

Best of luck!

DWynsen

 

[MikeyD]

Originally posted by throbbinnut
I was thinking about that, the fact that for low frequencies, the speaker has to throw a long way to keep from distorting at high volume levels.

Actually, the less excursion the better insofar as distortion is concerned. Paul Klipsch argued this point for his folded horn designs: that smaller speaker movement, amplified by the horn, yields lower distortion. I think I understand what you meant, though: lower frequencies physically require more cone movement than higher frequencies for the same sound level.

Originally posted by throbbinnut
I'm used to thinking in terms of sine waves with "side to side" travel like a guitar string vibrating, but sound is a compressive wave, so it can be represented by a sine wave, but it is really a longitudinal wave, if I remember correctly. Compression peak, rarification trough, etc. And I heard/read someone say that the speaker can only compress the air, not really rarify it, so you only get power on the push out. All sorts of gooey crazy stuff goes along with acoustics that I don't begin to fathom, it's really fluid dynamics on a micro scale in a container. That's messy

Yes, it can get very messy! Your point about sound being a longitudinal (compressive), rather than a transverse (like a guitar string), wave is correct. This is because particles of air do not transmit shear as do strings. I believe speakers *do* rarefy the air on their return stroke (back into the cabinet): how else would the air be able to return to the cone surface? The partial vacuum causes the nearby air to rush back in. Anyway - you are right on about acoustics being fluid dynamics in microcosm!

Originally posted by throbbinnut
Here's the speaker box designer I know and love:
http://www.linearteam.dk/
It does plots and has a driver database.

Interesting link. Thanks!
- Mike

 

[MikeyD]

DWynsen, thanks for the links and the description of your bass generators! I think we're in sync on these technical points.
- Mike

 

[dwynsen]

A speaker cone does generate pressure and rarifaction (vacuum). They can move so much air that this is actually a problem for subwoofers with long excursions. If the port isn't properly flared you can actually hear the air rushing in and out of the port!

I really appreciated the comment about Paul Klipsch! My dad had a pair of Klipschorns for decades -- always updating them. He's gone now and the Klipschorns sit in a garage -- saddly. These are 3-way speakers with a "horn" in front of each driver. The tweeter looks pretty normal. The midrange horn is big; it's about 18" wide, 6" tall, and 16" deep. However the bass horn is HUGE! It's designed as a folded horn, if you can imagine that. It's unfolded dimensions are enormous. I don't recall the exact measurements, but it's effectively something like 12 feet long! Imagine a cheerleader screaming thru something that large. The K-horns are designed to be placed in a corner so they use the walls as an extension of the horn. The K-horns are huge -- as big as a 5-sided refrigerator. Anyway, the Klipschorns are known for efficiency (something like 103 db/1 watt/1 meter). They were designed in the early-50's because wattage was expensive, and because speaker design hadn't yet solved the problem of IM distortion caused by "excessive" cone excursion. They can blow you out of the room at less than 5 watts. I know this! Regrettably, the K-horns sound like horns (megaphones), IMHO. You can STILL buy them new even though Paul sold the company in the 90's.

Thanks, all!

 

[Bryan_G]

What about square speakers? My friend bought 2 12inch solo-baric squares for his car, from kicker, they sound great. But is this really an option when dealing with higher than subwoofer frequencies. I mean could you get good tonal quality from a square speaker? They have like 20% more surface area than a circle. I don't really know that much about this stuff, but it just looks like the whole square thing should sound terrible.

 

[Mark Reccord]

Hey! The first PA I ever used was one of those old Klipsch folded horn monsters! The bottom end could knock you down!! Literally! Great rock n roll PA! A really impressive manipulation of acoustics, crazy efficiency!

 

[MikeyD]

According to info I have, the Klipschorn has sensitivity of 104 dB (1w, 1m), so with 100 watts input, that would give 124 dB. That is very LOUD! At 5 watts, the speaker would be about 111 dB - quite loud, but not deafening (if for a limited time).

Regarding square loudspeakers - it sounds like (pun?) another fad. Typical coils are wrapped around circular bobbins, so a cone or dome remains the best way to obtain stiffness without much mass - which is why cone-type loudspeakers still dominate. Besides, with a square "cone" how does one build a surround that can seal the "cone", yet flex uniformly? I understand the argument for radiating surface, but a square speaker seems to have so many other disadvantages...

- Mike

 

[dwynsen]

Thanks for the scoop on Khorns. The 111db figure sounds right for a single speaker. However, Khorns are usually set up in pairs with a third (nearly as efficient) middle channel (the Klipsch LaBelle??). The "5 watts per channel" then approaches 117db! Anyway you cut it, that's really loud in someone's family room! Using 100 watts, that figure jumps to nearly 130db. That'll do ear damage rather nicely. BTW, I'm using the rule-of-thumb of adding 3db each time you double the wattage. Is that correct? I think it's close.

I know absolutely nothing about those square speakers. Do they have a typical cylindrical voice coil/former? As you know, a number of manufacturers have marketed rectangular speaker-drivers for decades. Usually (if not always) these have been electrostatic or planar-magnetic (Magnaplaner)panels. They're known to be extremely inefficient, and they don't reproduce bass very well.

Thanks again!