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[Craig Leerman]

Quote:

The live sound RTA analysis puzzles me for a couple of reasons. The lack of bass program below 60 Hz could be from several causes: 1) Bass player doesn't play down low 2) Cabs don't produce much below 60 Hz 3) Power amp 50 Hz filters in place

Another reason could be  the style of music. Some live bands like Reggae, Dancehall, or Rap/Hip Hop are going to have way more bottom than say a Country or Pop act. If the live venue Bill measured mainly did mainstream acts like Pop, Rock, or Country, that would explain the lack of some bottom end.

In addition, acts with keyboard players or Synth players may generate more bottom end that a 4 or 5 string bass player will. I did sound for a Prog Rock band a few years ago that used a synth bass all night.  4 MT-4 Manifold quad 18s per side had a hard time keeping up with that guy!  He would do sweeps down into the 20Hz region.

Last, I was thinking that if this was a place with a house engineer, that the FOH person themselves could be the cause of the lack of bass.  I know a FOH engineer who doesn't like a lot of  bass (He comes from a country and bluegrass backround).  It could be that the FOH engineer simply didn't push the low end like many folks do. (right or wrong)

Either way, my vote is for a PA that can handle at least 40Hz before sloping off. I would rather have the bandwidth available and not use it, than be limited by the PA.

Craig

[bgavin (Bruce Gavin)]

One theory for lack of information below 60 Hz is the 2nd-harmonic-is-louder characteristic attributed to electric bass.  

IMO, where this theory falls flat is a Fender bass in the studio (DI) has far more low content than the same bass in a live situation (standalone or miced cab + PA cabs).  The bass harmonics are unchanged between studio and stage, and only the reproducing medium is changed.

Degradation is cumulative between stages.  If the electric bass is weak in the fundamental, reproducing this signal through a PA designed to be weak below 60 Hz compounds the problem.  Micing a bottomless bass cabinet, then reproducing it through this bottomless PA seriously exacerbates the problem.  RTA analysis done on this example shows no bass content, but does not say why.  Failure of the reproducing chain is the cause, not lack of content.

Half-space measurements of the Tuba24,  with its conical design and 56 Hz horn length, show significant roll off below 80 Hz.  The Tuba24 meets its design goals, so I do not fault the line of thinking in this case.  However, anybody expecting to realize a full 41 Hz out of this box will be disappointed.  

Full horn loading to 41 Hz requires a minimum 6.88 foot hyperbolic horn, or longer exponential/conical type, and a mouth area of 30 square feet in half space.  Measurements show exponential horns are useful down to about 125% of design Fc, and conical horns roll off even higher.  Multiple LAB subs or multiple larger Tubas are required for sufficient mouth area and horn length to get down this low.

Due to the faceless nature of the internet, this post is not intended to be belligerent in any way.  That said, I remain unconvinced as to "why" the RTA analysis shows little content below 60 Hz.    

[raj]

bgavin,
In your post dt 17th instant you have written "The Tuba36 Slim at 7.5 feet has an Fc of 37 Hz."
I think you have posted the horn length of the Tuba 30 instead of the tuba 36 ,
after reading your post I had doubts of the length written by you and did the following measurements of the horn leanth my tuba 36 slim ,
Horn length inner side of the horn 9ft,
Horn length centre       of the horn 9ft 10inches,
Horn length outer side of the horn 10ft 6inches,
I do not know how to measure a horn , I just took a nylon rope and spread it along the path and then measured the rope , I may be +/- 1 inch in my measurements ,  I hope I am right ??

[Johan Rademakers]

From the man himself:

Quote:

Traditionally the path is measured down the center. You normally would start the measurement at the leading edge of the driver hole in plate 1. My estimate is about 8.5 feet, starting at the junctions of plate 1 and 2 to be conservative

[ edit] Eeerrr...Seems you already knew [/edit]

Mvg Johan

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[peter.golde]

Simple intuition tells me that you are an idiot.
What is the point of your post? Your failed attempts at horn design qualify you as an expert? Or is it your experience with your buddies Tuba24 that doesnt play as low as you would like. How many horn designs have you built and tested? How much experience do you have with horns in live sound apps?
Ask raj how he likes the Tuba36S. Ask anyone who built the Tuba24, and are using it for what it was designed for, if they are happy with it. The Tuba24 was designed for backline, low frequency for bass guitar in a two way bass guitar rig, using a Beta10. It was found to work well enough for use with the HL10a in higher power applications. Although the HL10a is not the best driver for the horn, Bill F. will be the first to tell you this. Eminence (according to Bill F.)is seriously looking at designing a new version of the HL10a for use specifically in the Tuba24 horn.

[Dave Rickard]

BHFProfessional wrote on Sun, 22 May 2005 00:28

My own experience with the Crusher project taught me what the HL10 likes and doesn't like.

Ummmm.....Please elaborate on your *experience* with the Crusher/HL10.  As a student of science you know that hypotheses and simulations do not qualify as experience. Sawdust, trials, applications, and measurements do.

Dave

[efreak]

I would have to say the Lab. If anyone is interested in picking up an extra Tuba24 please let me know. I have one with a HL-1OA that i am looking to get rid of.

efreak@efreaked.com

[cmqt9]

Simple intuition tells me that you are an idiot.

Well, I wouldn't go that far, but Rory, there is a lot more to being a professional than just calling yourself one. We've been anxiously awaiting the arrival of your promised designs for about a year now, and it somehow never happens. I could give some credence to your opinions if you'd ever built a single speaker, but so far as I can tell you never have. I'm not dismissive of your academic endeavors, but being a student doesn't make you a pro. I have my degree and I don't call myself a professional loudspeaker designer. You can assume that mantle after you've done the deed. Perhaps a change in your moniker to 'aspiring professional' would be more appropriate.

I have a Tuba 24 and can't fault it in any way, it does exactly what it's supposed to do. It's advertised as a cabinet for backline bass and small to medium venue PA and when so employed works as well or better than any other 8 cubic foot cabinet I've ever heard. That's quite a few cabs too, because while I may have an engineering degree I make far too much money as a working musician to take a cut in pay and do anything with it.

My experience with my own Tuba 24 aside I prefer Fitzmaurice's approach from an engineering standpoint because they are goal-specific designs. Will Labs outperfrom T30s and T36s? Yes, if you use enough of them and you require flat response below 35 Hz. Does live music program require flat response below 35 Hz? Mounting evidence from a number of sources indicate that the answer is decidedly no, so there is little point in hauling about cabinetry large enough to do so. Fitzmaurice used horn loading to get to a desired fc at a desired SPL and then from the same cabinet direct radiation to extend response below fc at reduced SPL, in so delivering a response curve actually required by the program material from the minimum cabinet volume and at the lowest possible cost. That was his goal and he achieved it. The Lab goal was flat to 22Hz or thereabouts and Tom achieved that. I'm curious as to what Tom thinks now about that goal, since the majority of his new designs don't appear to attempt that.

Rory, I'm sure that you mean well, but until you actually get around to building a speaker perhaps you should do a lot less talking and a lot more listening to guys like Peter who have.

Bob Russell