Why though? 18inch has more area than 12inch? So therefore it has more grunt no?
One of the grunt specs is how much volume of air will be moved. Surface area times x-max. Surface area alone tells you nothing about grunt!
Terry
Should be a very fun project!
Bass from an 18'' will cause trauma to the guts !
Do post some build pics.
1. Trying to tune to music frequencies makes sense for an instrument, not a reproducer. That design issue should start with you watching your music collection on a spectrum analyzer and determining what the bottom should reach. I've posted several times recently on my low-note favorite recordings and you might find that, albeit classical and organ, informative. While I can't speak for tom-foolery in HT, serious music doesn't have a whole lot of super low content reallly, as nice as it is when it does occur, and your ear is filling-in all the nearly-sub-sonic bass notes you have pretty well most of the time.
2. Presenting design theory to a decimal place reflects the great faith on this forum in the accuracy of models and/or published specs. Particularly for someone with limited measurement capabilities, lotsa luck getting close to the model when the sawdust settles.
3. I am always surprised when people talk of modeling sealed enclosures. Since there's only one humanly audible parameter much in play (loudness spectrum), there's only one design parameter (box volume). You pays your money and you gets your low extension. "Q"... whazzat in a sub? In other words, can't go wrong with a sealed box. With a tuned box you get a bunch of notes. My recent trial with a very large open baffle sub has inclined me even further towards untuned boxes in untuned rooms.
4. Inherently "paradoxical" to favor a 12 inch over an 18 inch when, ceteris paribus, we are talking 2-3 times the cone area. My old-guy view is that when you run to 18 inches, very hard to make a quality speaker with such a big hunk of cardboard and floppy suspension. Is it any easier to make a 12 inch driver with an enormous excursion? That makes 15 inches the Goldilocks solution. Maybe also I am too concerned about Doppler distortion, something rarely mentioned on this forum and I wish somebody would tell me if that is a real concern with all the 8 inch TL woofers being touted around here.
2. Presenting design theory to a decimal place reflects the great faith on this forum in the accuracy of models and/or published specs. Particularly for someone with limited measurement capabilities, lotsa luck getting close to the model when the sawdust settles.
3. I am always surprised when people talk of modeling sealed enclosures. Since there's only one humanly audible parameter much in play (loudness spectrum), there's only one design parameter (box volume). You pays your money and you gets your low extension. "Q"... whazzat in a sub? In other words, can't go wrong with a sealed box. With a tuned box you get a bunch of notes. My recent trial with a very large open baffle sub has inclined me even further towards untuned boxes in untuned rooms.
4. Inherently "paradoxical" to favor a 12 inch over an 18 inch when, ceteris paribus, we are talking 2-3 times the cone area. My old-guy view is that when you run to 18 inches, very hard to make a quality speaker with such a big hunk of cardboard and floppy suspension. Is it any easier to make a 12 inch driver with an enormous excursion? That makes 15 inches the Goldilocks solution. Maybe also I am too concerned about Doppler distortion, something rarely mentioned on this forum and I wish somebody would tell me if that is a real concern with all the 8 inch TL woofers being touted around here.
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Doppler distortion? You mean the high frequencies shifting when the low frequencies are moving the cone? I'm sure it exists. Wouldn't the higher freq be FM modulated by the lower freq? If there was concern with doppler then the smaller the distance the driver has to move the lesser the effect. Seems a large driver would be a better choice in minimizing doppler distortion.
Here's an article on it. Stereophile: Red Shift: Doppler distortion in loudspeakers
Here's an article on it. Stereophile: Red Shift: Doppler distortion in loudspeakers
When it comes to subwoofer use, the Doppler effect will have a tiny effect. For either a full-range, or wideband driver, the movement of the cone will affect higher frequencies.
The article linked above seems to confirm this: it talks of th effect of 100Hz on 1kHz. Using 20Hz-100Hz will give minimal effect.
Chris
The article linked above seems to confirm this: it talks of th effect of 100Hz on 1kHz. Using 20Hz-100Hz will give minimal effect.
Chris
Thanks for great Stereophile link.
Chris - I don't have the smarts to add much here but...
100 to 1k is 1:10 and 20 to 100 is 1:5. So we are not talking apples-and-oranges.
Moreover, the monumental excursions needed at low frequencies are monumental, again bringing the two situation into close comparison.
Finally, the distortion products arising from 20-100 Doppler, maybe be vastly more hearable than the bass notes themselves and worse yet, may reveal the sub location in the room and spoil the stereo illusion, a real no-no.
Chris - I don't have the smarts to add much here but...
100 to 1k is 1:10 and 20 to 100 is 1:5. So we are not talking apples-and-oranges.
Moreover, the monumental excursions needed at low frequencies are monumental, again bringing the two situation into close comparison.
Finally, the distortion products arising from 20-100 Doppler, maybe be vastly more hearable than the bass notes themselves and worse yet, may reveal the sub location in the room and spoil the stereo illusion, a real no-no.
Your welcome. I thought it was interesting to see some math crunched on the subject.
One thing to consider. Take 1000hz for example. +/- 50hz on 1000hz isn't much. 50hz on 100hz on the other hand is half an octive. Interesting topic though. I've never really thought about it but now that I do, speakers suck. Thank god we have our brains to sort it out.
Do cracks in the drywall (revealing the subs location) count? Having to paint the livingroom is no illusion.
One thing to consider. Take 1000hz for example. +/- 50hz on 1000hz isn't much. 50hz on 100hz on the other hand is half an octive.
Interesting topic though. I've never really thought about it but now that I do, speakers suck. Thank god we have our brains to sort it out.Do cracks in the drywall (revealing the subs location) count? Having to paint the livingroom is no illusion.
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So, looking at the numbers they give...
You'd get (with 100Hz on top of 20Hz) 20Hz output, 100Hz, 80Hz, and 120Hz, the level of the latter two being affected by exactly how fast the cone is moving. Being 20Hz, the cone is likely to be moving much slower than 100Hz (really long wavelengths involved, and the excursion won't be huge for an 18" driver - we already know it's 8mm Xmax).
I don't think there will be a problem here.
Chris
You'd get (with 100Hz on top of 20Hz) 20Hz output, 100Hz, 80Hz, and 120Hz, the level of the latter two being affected by exactly how fast the cone is moving. Being 20Hz, the cone is likely to be moving much slower than 100Hz (really long wavelengths involved, and the excursion won't be huge for an 18" driver - we already know it's 8mm Xmax).
I don't think there will be a problem here.
Chris
I think this may be a good reason for endorsing the larger size drivers like OP has in his hands. And avoiding big-movement-in-hearing-range boxes - like tuned boxes. And avoiding 8 inch subs with enormous movements.
BTW, if concerned about Doppler distortion, TRUE horns and ESLs are the way to go.
BTW, if concerned about Doppler distortion, TRUE horns and ESLs are the way to go.
Speaking of ESLs I LOVED mine. LOVED LOVED LOVED LOVED.
They were Acoustats. I powered them with a Carver. They were big but close your eyes and they vanished. Acoustically speaking. Had to sell them when I moved. What's a "true" horn? Do you mean folded horn subwoofers? On that note this 18" would be unreal in a horn. I'd need a longer house to enjoy it.
I think a smaller port sounds better. Large enough not to huff air of course. If the port is too large I find that the reflections inside the enclosure escape right out the port and I get a "shoe-box" sound even if it's tuned correctly. In a PA or automotive system I'd be all for it but not for a home theater. Maybe because of how close the listener is. Across the yard you'd never hear it.
I had a chance to build a couple of enclosures to test this speaker. One is a 6.6 cubic ft. 24" cube with two 4" diameter ports 6" long (34hz). The other enclosure is 4.72 cubic ft. 24" tall, 13" wide, with 33" depth. One 6" port 10" long in front (34hz). Speaker in the side.
The cube box is ungodly loud. @.@ 100w rattles everything in the livingroom. It would be great for sound reinforcement but lacks deap bass. It's very "punchy" and kick drums slam your chest. I ran out of 4" pipe to try longer ports.
The second enclosure is sort of strange. If I use a shorter 4" long port (44hz) the deep bass extends lower then with the 10" port (34hz). I'm not sure why. I haven't had a chance to drive it hard yet. The kids went to bed.
The cube box is ungodly loud. @.@ 100w rattles everything in the livingroom. It would be great for sound reinforcement but lacks deap bass. It's very "punchy" and kick drums slam your chest. I ran out of 4" pipe to try longer ports.
The second enclosure is sort of strange. If I use a shorter 4" long port (44hz) the deep bass extends lower then with the 10" port (34hz). I'm not sure why. I haven't had a chance to drive it hard yet. The kids went to bed.
Wow. If you're thinking about a port that big why not consider a PR and avoid the majority of the fluid losses associated with a port the size of Texas?
Are we talking about ESL's and subwoofer frequencies? I thought they had trouble with bass let alone sub-bass...
An 8", or even some 6" subs, can out perform most ESLs when it comes to bass. ESLs can't move a large volume of air so the bass will seem lacking but they are playing it. I had a set that didn't have a seperate subwoofer and although the bass from the panel couldn't shake walls, they were so smooth and pleasing that I didn't bother to turn on my powered 12" unless I was watching movies. Funny thing was more bass from behind the panel then in front and if you stuck your head back there it was incredible. Better then any sub I've heard. Too bad nobody makes an enclosureless ESL subwoofer.
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