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"Throw" of Bass From a Cabinet (Long Summary)

Discussion in 'Amps and Cabs [BG]' started by MikeyD, Dec 29, 2000.


  1. MikeyD

    MikeyD

    Sep 9, 2000
    Hi, Everyone,
    In an earlier thread (see http://www.talkbass.com/forum/showthread.php?threadid=8346&pagenumber=2), a question came up about how certain speakers seem to project (throw) bass out into a large room better than others. I promised to do some reading and see if I could find out more. I also asked people to contribute ideas and observations, but did not get much response. However, I think I can summarize a few leading ideas:

    __ 1. Member "Spacegoat" (Talkbass, 12/9/00) said: "Maybe it's because 10's produce more mid freqs than 15s or 18s and thus appear to be louder at the same distance near field." I think this is a good point: 10's more easily produce harmonics than 15's or 18's, which may make them seem louder - especially when we take Fletcher-Munson (hearing sensitivity) curves into account. Since electric bass signals are rarely without at least some harmonic content, I agree that this could be a factor.

    __ 2. I note that most bassists tend to put the bigger speakers on the very bottom (next to the floor), whereas smaller speakers (e.g., 10") are often placed up higher, away from the floor, and closer to ear level so that higher frequencies can be heard. Two related points:

    ___ (a) the sound from the big speaker near the floor will be more readily augmented by reflections from the floor boundary - (see Comment 4 about "virtual horn");

    ___ (b) the smaller speaker placed higher will be more readily heard by the player because of simple proximity to the ears (and, referring to Comment 1 above, they more readily emit harmonic content). I have noticed this with my own stack. The 18" bottom on the floor does not seem to be very audible when I stand near it (though I can certainly "feel" it), whereas the 2x10 on top is what I'm hearing more readily on stage.

    __ 3. For a given near-field sound pressure level (SPL), larger diaphragm speakers generate more _acoustic_ power than smaller ones [1],[2]*. I would think that the higher power radiated from larger speakers interacts more readily with room boundaries to produce higher SPLs farther out.

    __ 4. In effect, room boundaries act like a horn at very low frequencies; consequently the effective "mouth" of the horn may actually be well beyond the speaker and perhaps even the stage! In this situation, the speaker - and even the bassist - would be located inside this "virtual horn". The SPLs at points inside a horn may be less than those of points at or beyond its mouth, for certain frequencies.

    __ 5. I have not analyzed the radiation of 4x10 vs. 1x18 mathematically (can you say "Bessel Functions"?); however, the 4x10 array is likely to be somewhat more directional in the near field than the 1x18, at a given low frequency. If so, perhaps the near field SPL is higher for the 4x10, without augmentation by lateral reflections; whereas, since the 1x18 is more omnidirectional, reflections from nearby boundaries augment the SPL in the far field.

    __ 6. Folded horns, in particular, tend to couple with the room boundaries to extend the effective horn out into the room. A pertinent post on TalkBass (December 29, 2000), by member ROCKBOBMEL: "Stay away from the Acoustic 301 Cabinet. I had the 360 with the 301 cab. It is a great sounding rig but, the problem with 18s, and especially the folded horn 18 is the sound does not develop until about 15-20 feet out (past where you stand). You can't hear the notes well enough, so you turn up the deep bass and it is killing people in the back of the room. You probably can get one for cheap, but only good for stadiums (like John Paul Jones played)."

    In conclusion, to date I have not found any strong arguments to refute the claim that bass from certain types of speakers seems to carry (throw) better than bass from other types. It is really interesting ("Fascinating," as Mr. Spock would say). I think I mentioned earlier that I read that Ampeg's big SVT 810 cabinet started to win players over because it sounded stronger in the music dealers' showrooms than the existing folded horn cabinets; however the folded horns tended to excel in their "throw" of bass in bigger spaces.

    I'd be interested in comments anyone might have about this.

    - Mike


    *References:
    __ [1] "Low-Frequency Loudspeaker Assessment by Nearfield Sound-Pressure Measurement", by D.B. Keele, Jr., Journal of the Audio Engineering Society (April 1974).
    __ [2] "Some Aspects of the Self and Mutual Radiation Impedance Concept with Respect to Loudspeakers", by Oluf Jacobsen, Journal of the Audio Engineering Society (March 1976).
     
  2. Well, that pretty much sums it up! I suspected that boundary loading probably had something to do with it. A 410 array is definately more directional than a single 18. Multiple speakers in an array exhibit better directional control than do single drivers. There are some great papers on line array theory in the archives of the AES and the Live Sound Intl. websites, the addresses of which escape me. There's really nothing else I can add to this discussion, excellent work MikeyD. Thanks for an informative and interesting discussion!
     
  3. Oh, and I glad I posted something that was of use!
     
  4. Hi Mike,

    Now we're getting somewhere. I think the most interesting remarks you made here are the ones about room/wall influence. Especially when a stage is somewhat elevated above the audience, the back wall and the stage itself will act as a horn. Not quite an exponential or tractrix horn, but just a widening space, which is likely to amplify certain very low frequencies, but not until 10-20 feet away from the stage.

    The third point you addressed confuses me. SPL and efficiency are not related to frequency issues. A 1x18 has exactly the same cone area as a 4x10, so their acoustic efficiencies are likely to be the same. The 10s do have a much higher resonant frequency, because they each have a suspension system, which makes the total suspension 4 times as tight, and the resonant frequency twice as high, and consequently the efficiency 4 times as high. But I'm drifting off topic here.

    Thought of something else: a related topic. If you look at the wave lengths of the lowest octave (31 Hz - 11 m wave length, 55 Hz - 6 m), and you consider the wave to be at maximum vibration right at the speaker cone, then 1.5 to 2.5 meters away from the cab (1/4 lambda) the wave has its minimum. Which is almost silence. Not completely, because room reflections will give you something back. I, personally, am always about 1.5 to 2.5 meters away from my rig, which has low end beyond belief, but large rooms eat away almost everything. In fact, some time ago when we did a gig, the amp (a Trace Elliot 4x10 cab w/ head for crying out loud) was at the side of the stage, about 5 meters away. Please note, that's twice as far as in the story above, thus putting me close to the maximum (out of phase) point of the wave. I was amazed. It sounded great. I usually hate every bass amp I am forced to play on. But I think by standing farther away the lowest octave gets a chance to develop. And maybe I was also closer to the "stage horn" mouth. I was standing up front (because I'm also the vocalist), as far out as possible. I had to watch out not to kick the mic stand over the edge.

    Conclusion: the lower the frequency, the larger the wave length, the worse the location of the minimum point, the farther away you have to stand from the sound source.

    All right this doesn't relate to the 10's vs. 18's throw issue, but nevertheless it's a real life story about distances and stages. Actually it seems to put things the other way round.

    Why (by the way) is it that no important books have been written about acoustics lately. Most of the literature about it was written before the mid 70s by Thiele, Small, Keele, Dickason, Bullock, and the like. Would it have anything to do with patents and copyrights? Companies that develop revolutionary new sound systems seem to effectively shield the know-how from the public and, of course, other companies. Acoustics used to be science, is it just a way of making money these days? Or am I not looking hard enough?
     
  5. MikeyD

    MikeyD

    Sep 9, 2000
    Thanks for the feedback and your earlier input, Space! I still have lots of questions in my mind about this, but it had been a month since we last discussed it, and I wanted to present what I found so far. You must have encountered stuff about phased arrays - you can "point" the sound (or radio wave) in various directions by altering the phase of various drivers in a large array. Cool stuff.
    - Mike
     
  6. MikeyD

    MikeyD

    Sep 9, 2000
    Hi, Joris, thanks much for your interesting reply.
    Okay, given two single radiators of different diameters, the math shows that if you measure their near-field SPLs at a fairly low frequency (i.e., wavelength much bigger than the driver diameter), and if they happen to measure the same SPL, the overall power emitted by the larger speaker will be higher - even with the same on-axis SPL. You do have a good point about 1x18 vs. 4x10 (although I'm not sure the cone areas are exactly the same). Again, I did not do a mathematical analysis of these two cases (it's very messy and time consuming), so the answer remains unclear to me. As you suggest, it is possible that a 4x10 may achieve an acoustic power output equal to that of the 1x18 for a given near-field SPL. If true (and I still have some reservations about this), then perhaps the directionality of the respective speakers is the more relevant issue here.

    The amplitude may or may not be maximum at the surface of the speaker; it seems possible that it could be amplified somewhat with horn loading or acoustic labyrinths, etc., and so would have a maximum amplitude elsewhere. Moreover, if the cabinet is vented, the full wave may be developed at some distance from the cone.

    Only if you have a standing wave; otherwise, the compressions and rarefactions are always propagating away from the speaker.

    I'm not clear on what you mean by this. If you are in a standing wave situation and happen to be at the node, then the direct and reflected waves will be canceling each other (called destructive interference), and it will be quiet there. If you a located at an anti-node, then the waves will be constructively interfering, so it will sound louder there. If you are not in a standing wave situation, then I need clarification on your point. For example, if you do a gig outside in a grassy field, there isn't much chance of reflections and their byproducts, standing waves.

    I don't think I can agree with this by itself. I can hear great bass when I put on a decent pair of headphones: the wavelengths are hundreds of times the distance between the diaphragms and my ear. Again, I think what's going on is you are dealing with hearing more bass farther from the speaker because it is there, at some distance from the cabinets, that the wavefronts coalesce and constructively interfere (read: reinforce each other - as in a horn). The other thing is: locations of maximum and minimum points (anti-nodes and nodes in a standing wave) are completely dependent on the pitch (frequency) of the note you're playing. And I assume you play more than one pitch! So, if your point is that your sound improves when you get about one wavelength from the cabinet, I interpret that to mean the wavelength of the lowest pitch. If it were a bad standing wave situation, then that one note might sound good and strong, but then lots of other notes might sound really weak (this I call "boominess", and IMO is one of the hardest things we bassists have to deal with to get a good sound in a room). My guess is that what you're really experiencing, with the sound improving at a distance, is the constructive interference of the direct and reflected sound at some distance from the speaker.

    Lots of good acoustics work was done long ago. Also check out books by Beranek, Kinsler & Frey, and Timoshenko (vibrations, mostly). There are others. I don't know what has been written in the past 20 years or so; I don't think "acoustics" as a science has changed that much, per se. I do think, however, that there has been some progress in loudspeaker and amplifier technology, acoustic measurement, and acoustic modeling (by computers).

    Well, there's tons of stuff (papers and books) available through AES, and you can also get into acoustics via the Acoustical Society of America (and, as I recall, they have counterparts in other countries). AES and ASA do lots of patent reviews, too, which might be of interest to you. If you go to a good university library, you should be able to find a lot of material. However, a lot of this stuff requires a strong background in mathematics (calculus, diff. equations, etc.) Bruel and Kjaer (the acoustics/vibration measurement company from Denmark) - used to publish a lot of good material, too. In terms of recent technological advances in loudspeakers, yes, perhaps in some cases the companies or individuals are not publishing much; in other cases, they've applied for patents to protect their ideas, and you can obtain copies to read (but if the patent is still in force, then you cannot use the idea without permission). The phenomenon of loudspeaker throw has probably been addressed in the literature, but I'm not ready to embark on a doctoral thesis right now! If you are ambitious, you could probably really get somewhere - but it ain't easy!

    Well, thanks for your reply, Joris. It's fun to discuss these things with you! :) However, given that this is a "bass" forum and not an "acoustics nerd" forum, we should try to keep our posts within the interest level of most bassists. So... no big calculus derivations! (When I was in grad school, we used to joke about "drinking and deriving"!)

    Regards,
    - Mike


    [Edited by MikeyD on 01-02-2001 at 09:50 AM]
     
  7. Oysterman

    Oysterman

    Mar 30, 2000
    Sweden
    If it's me you're afraid of (da big bad moderator), don't worry. :D This is really interesting.

    My high school biology teacher had hundreds of those... :rolleyes:
     
  8. MikeyD

    MikeyD

    Sep 9, 2000
    Hi, Oysterman!
    Thanks for your message. This acoustics stuff can get really involved, and I notice my posts tend to be 2-10 times as long as others, so I'm mindful of "cooling it"! (I think I can hear some snoring out there through my screen.) I'm glad *you* are digging this, though!
    - Mike
     
  9. gweimer

    gweimer

    Apr 6, 2000
    Columbus, OH
    Interesting thread. I'm not quite up on the scientific end of the discussion, but I do have some formal recording training. As a former Acoustic 360 owner, I'll absolutely agree with the posted comment, with one slight exception. When I play, I play for an audience, and not just for me. My sound was adjusted with me standing 15 feet off the stage to hear how the room handled the amp. What I learned in the recording class was very similar - low end freqs take a longer space to fully develop, and most rooms (whether it's your living room for the stereo, or a large barn of a club) will aid in the definition of most freqs under 100hz. It was recommended to keep those ranges flat, and I found that by suppressing the low end below 100hz, I actually got a very nice booming, but distinct, floor rumbling sound. I apply the same approach with my 1x15 combo now. What you sound like is entirely related to what the other instruments sound like; it's a MIX, and not individual sounds sitting side by side.
    The bottom line is this - you have a certain sound that you wish to use. Sometimes, in order to acheive that sound, you have to modify it around the other instruments. Ever wonder why old Precision basses seem to have that nice fat low end? It's because they are basically a dead bass - very flat and pure. Once you throw them through an amp, you find that the tones come out naturally with very little coaxing.
     
  10. MikeyD

    MikeyD

    Sep 9, 2000
    Hi, gweimer!
    Great comments! Funny you said what you did about the Precision, because while I was reading your post, I was jammin' and funkin' along with some Groove Collective in the background on my P-bass, plugged into - get this - a tiny Pignose Hog 20! :) No real fundamentals coming out below middle B (~120 Hz.), but it actually has a sweet "P" sound! Actually, I wouldn't describe the Precision as "dead", because I can hear a lot of harmonic content, which I believe is very much mechanically influenced by the shape of the body, the bolt-on neck, and the type of wood used. The pickup seems to be positioned at the perfect place to pick all that up. And I think I agree if you mean the P has a great balance between its lows and highs (flat sort of output).

    Anyway, when I recently played in a somewhat boomy, shoebox-shaped room, I had the same idea as you: during the sound check, my 18" sitting in the corner was giving people on the back wall bowel problems! I had to back off the lowest bass and the overall volume so much that I could hardly hear myself on stage - yet, it was MUCH more important to me that it sound good out in the room (as long as my bandmates could still hear me enough). It's definitely a challenge.

    Another place I played, the sound guy cranked up everything blastissimo. Now, my bandmates and I are used to hearing and balancing each other just fine, and we're loud enough to pretty much fill that room without a PA. I got upset and told the sound dude to turn it way down. The result: the blend out there was perfect, because we musicians on the stage retained control over the mix! Anyway - we're getting into a bigger tangent here, but maybe we could start another thread about "balance" and sound reinforcement from PAs.

    Regards,
    - Mike


     
  11. Here is something I have done several times when I use my 18 and 2-10 stack. My 18'' cabinet is a Music Man front loaded reflex with an Ampeg 2-10 cabinet on top. In rooms where the bottom is killing the people in the back all I do is just turn the 18 around and face it to the back of the stage. I leave the 2-10's still stacked on the 18 facing the front. I am able to hear the highs and the lows on stage just fine and the sound still gets out without killing the bartender in the back of the room. Don't know the technical reasons why this works for me but it does and the drummer just loves it. Give it a try, it may or may not work for you.
     
  12. I don't know much about the math/acoustics thing- You guys sound like rocket scientists. I read something at MTDbass.com - it was called "The quest for tone A to Z". It talks about tone woods and what makes a bass sound the way it sounds. Near the end it talks about bolt-on's, and how they appear punchier (I have an FBass, and George F. says bolt-ons are punchier)- I agree. Mike T. says that a bolt-on lacks some fundamentals because of the mechanical joint, but you can hear the fundamentals better because the harmonic overtones piece the sound together and your ear/brain fills in the rest- like when you talk on the phone, the other party sounds normal, but the sound of the phone lacks the fundamental tones of the real voice! Interesting huh? I wonder if that's why an Ampeg 8-10 cab sounds s good. These 10" CTS 50 watt speakers can't produce fundamental bass to 31Hz, can they? They are very effecient, warm, non-boomy cabs, but you HEAR the deep bass, maybe better then an Acoustic 301 (18" folded horn). Just a thought---- Bob M.
     
  13. The Keeper

    The Keeper

    Sep 2, 2000
    Hey, MikeyD, I've been following your conversation since it started back in Joris' thread and find it very interesting. I'm sorry that I did not post more but I felt I had little to contribute as I am just barely into getting into the bass world (only been playing for 6 months) and I am experiencing most of what you guys are talking about for the first time at my gigs. But I thank you for these great posts and read them with excitement for what knowledge I'm going to pick up next from them! Also, as I am still a student, it's great to see that I can actually use this Calculus for something other than the problems in the book! Thanks a bunch and keep 'em coming!
     
  14. Ty McNeely

    Ty McNeely

    Mar 27, 2000
    TX
    I don't understand half of what you are saying (i.e. the scientific lingo), however what I DO understand is very, very interesting. I for one am not bored with this stuff beacuse it gives me 1.) food for thought, and 2.) something for future reference!
     
  15. Science rocks.

    Chris
     
  16. MikeyD

    MikeyD

    Sep 9, 2000
    Hi Everyone,

    Thanks for your replies - and Happy New Year! Some comments:

    To jbplayer: Interesting experience you had with turning the speaker around. I've been pondering what might be going on there acoustically. I'm mystified right now. The only thing I can think of is the relationship between the phases of the direct and reflected sound changing between the two situations. If the speaker is, say, 1.5' deep, then when it is turned around, there is a difference of 3' of propagation distance for the reflected wave. It doesn't seem like much of a phase change for the lower frequencies, though. Hmmmm. I would've guessed that facing the speaker backwards would tend to couple the driver with the walls even more effectively, which would enhance the "horn effect" rather than reduce it. I'm *baffled* (pun intended).

    To ROCKBOBMEL: I have a feeling that the basses with a huge amount of sustain are those whose construction does not absorb much string energy, so the strings keep vibrating "forever" with whatever spectral content (fundamental + overtones) was introduced to them in the plucking. With other basses, I believe that the string vibration interacts more with the neck and the body - and sets up resonances in these components. While such resonances do absorb some of the string energy (resulting in less sustain and more "punchiness" - which I think of as a bigger emphasis on the attack portion of the note), I suspect that the neck's and body's vibrations then feed back into the strings (and possibly the pickups) to (a) reinforce some frequencies, (b) attenuate other frequencies, and (c) introduce some new spectral content that wasn't there in the initial plucking. In other words: the body vibrations add color to the sound. An extreme example of this is an acoustic bass: I don't think acoustics have nearly the sustain as electric solid-body basses, but their thin wood body parts are designed to vibrate and introduce their own character to the sound.

    On your point about Ampeg 810 vs. Acoustic 301: I suspect you are right in that the 10s produce harmonic content much better, and our ears work better at those frequencies - so the 810 probably sounds louder and more appealing overall in the near field (on stage, for example). But the more I think about it, the more I'm becoming convinced that a lot of people don't realize what a true fundamental sounds like. You pluck your low E or low B, and you think you hear that fundamental out of your speaker, but what you may be hearing is mostly the overtones. For example, the pulsations you hear from a pipe organ or synthesizer playing extremely low notes (say 16-24 Hz.) may actually be occurring at 16-24 times/second, but it is primarily the high frequency portion of the wave "spikes" that we hear (in fact, not many people can actually hear a pure tone below 20 Hz.). I did an experiment awhile ago with good stereo speakers (with 15" woofers) and a synthesizer. I got the synth output to approximate a sine wave. With a sine wave pure tone, it is VERY hard to hear notes below about 50 Hz. When I cranked them up loud enough to hear clearly - I noticed a profound vibration. I could feel the floor moving even before I got a good sense of the pitch - especially with lower frequencies. Notes around 30 Hz. rattled everything MUCH more than they were audible themselves (i.e., the rattling windows were making much more sound than the actual note out of the speakers; the way the floor heaved up and down, it seemed like someone had put a running engine on it)!

    I've experienced this with my Carvin rig. When I turn down the channel to the 1x18, I can hear all the "pitches" clearly out of my 2x10, but only realize something was missing when I turn up the 1x18 and suddenly feel the floor moving and stuff in the house rattling (and this with a 4-string bass!). That fundamental that was really missing out of the 2x10 is something that seems to be more felt than heard.

    You said, "These 10" CTS 50 watt speakers can't produce fundamental bass to 31Hz, can they? They are very efficient, warm, non-boomy cabs, but you HEAR the deep bass, maybe better then an Acoustic 301 (18" folded horn)." I agree that 31 Hz. will take a LOT of power to produce at any signficant volume with the 810 system. But I would counter that you're not hearing much of the *deep* bass - you're probably hearing the stuff an octave or more higher, but as you suggest, the psychoacoustics helps us hear the note. We can usually tell the difference between low E and middle E - even with this speaker. I'm not directly familiar with the Acoustic 301, but my guess is that it doesn't reach down to 31 Hz. very well either. However, if placed in the right room and fed with enough power - it could probably put out enough volume at 31 Hz. to give people a bellyache. Just a guess, though. My only direct experience with that type of cab was a Fender 18"-loaded folded horn that used to be sold with their 400-PS tube amp. A monster, for sure.

    To The Keeper and hunter585: Thanks for your kind replies and show of support! :) And you're welcome - this is fun! I agree about the calculus - sometimes it's hard to get enthused about it until you see how it can be applied to interesting problems. Some of this stuff is really difficult, but I'll try to keep it on a level that people can digest. Glad you're digging it.

    To throbbinnut: Yeah - science Rocks, but it doesn't Rule! (If it did, we'd all be replaced by robots by now. What a life that would be!) Ain't no science to *soul*, y'know?

    Regards,
    - Mike
     
  17. Hey folks!
    Just a few comments. On the turning the speaker around thing. I would normally expect that to accentuate the "horn" effect and in many cases it probably would. For example check out how much bottom end you get if you put a rear-ported cabinet 3 close to a wall! This is most likely a phase thing. Delays of less than 1 ms can produce profound acoustical effects... But as MikeyD said you wouldn't expect such a difference at very low frequencies. Maybe facing the 18 backwards produces phase cancellations with the lows from the 210?? Probably not, but you never know. I gotta say I'm a bit stumped by this, but if it works use it!!!
    The Ampeg 810 cab actually doesn't produce the fundamental frequencies of the low strings. the way it produces the harmonics helps to even out the sound between the low string and the higher ones. Previous cabinets produced the low frequencies of the low strings very well but the higher strings got lost because the cabs didn't produce the higher frequencies very well. It's a sealed box design, which limits cone excursion. This helped limit the production of the boomy muddy low end associated with reflex boxes. The sealed box made the cabinet sound "tighter" in the low end, and the natural frequency response of ten inch speakers gave more definition by accentuating the mids. Adding that to the fact that the lowest octave was filtered out gave the Ampeg 810 it's classic punch and clarity. Personally, I don't think you need a whole lot of that lower octave on stage. My experience as a soundman is that the lower octaves of the bass are better reproduced by the PA, and that having a lot of low end in a bass sound tends to make the stage sound muddy and causes me to eq out a lot of the low end and to add mids in order for the bass to be heard in the mix. But this only holds true if you have a PA with subs....
     
  18. I hated calc and thought it was pretty boring stuff in high school until I got into electricity in college. A capacitor is calculus in the real world. It's cool as hell. I can actually get excited talking about it now.

    Dig - Calculus is an excellent way to model how the real world acts.

    Word to your mother.

    Chris
     
  19. To MickyD- When I was in the Music store, I read some of "The Ampeg Book" Those CTS loaded cabinets were rated at 240 watts! Thats only 30 watts each. No wonder they were so efficient- especially in a sealed compartment. Ampeg recommended 2 of the 8-10 cabs- WOW! You could also get an upgraded cab loaded with Altec speakers, allowing the player to utilize only one cabinet.
     
  20. MikeyD

    MikeyD

    Sep 9, 2000
    It seems a bit like my old Kustom amp. The head would questionably put out 100 watts RMS - probably into 4 ohms. However, the usual speaker bottom was their 2x15 (two 16-ohm drivers in parallel for 8 ohms total). So - this means to me that Kustom intended people to run two 2x15" cabinets in order to get the full power output. Indeed, the manual with the amp shows the head sitting atop two 2x15's! Not only would more power be delivered by the amp, but the geometry of two cabinets together would generate more volume per watt. My conclusion: back then, amps did not put out that much power, so we lugged around (multiple) large speakers to get the volume needed.
    - Mike