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[bgavin (Bruce Gavin)]

The correct path length of the Tuba36 is 300cm / 9.84 feet.

The length question was raised on Bill's board, and he posted the following:

For the record, T36 is 300cm (9.84'), T30 250cm (8.2'), T24 170cm (5.57') , T18 and AT both 210cm (6.89').

The imperial values in parenthesis are mine, derived by calculator at 2.54cm per inch.  Bill's values are those he inputs to McBean as part of his design process.

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[cmqt9]

Rory, after you actually build that first horn, and a dozen or so more, and after your proposed business has been around for ten years or so, without going bankrupt, you may be qualified to pass judgement on someone else's work. In the meanwhile your opinion is worth no more than anyone else's.
Everyone who's anyone in the world of speaker design read the Tuba 24 article in Audioxpress. That magazine might not be what it was during the heyday of Speaker Builder in the '80s, but it's still the only magazine published in the US that has the likes of Vance Dickason, Reg Williamson, Joe D'Appolito and Nelson Pass listed as regular contributors, along with Bill Fitzmaurice. Please don't try to impress us because you read his article when anyone can log into his forum and ask questions of the guy who actually wrote it.
Word has it that Eminence is coming out with an improved version of the HL10a, improved in part from suggestions made by, guess who? Bill Fitzmaurice. That should come as no surprise, they're already recommending the Tuba 24 for the HL10a.
As to the stepped response curves of all the Tubas, they're there because they're supposed to be. Live music has a stepped response curve, and it only makes sense that speakers for live music should be designed for the requirements of the program material. Flat response below 35 Hz for live music sound reinforcement applications just isn't necessary.
Since the bulk of your knowledge on the subject seems restricted to textbooks, and since textbooks are at least 5 years behind the curve, your missing the point is understandable. But please, drop the moniker and call a spade a spade. Call yourself a pro after you actually become one.    

Bob Russell, BS EE/AE

[Michael_Elliston¶]

Now that weve established its yet another apples vs oranges debate,choose your fruit.

cmqt9:

Quote:

The only theoretical advantage for the Lab is extension below 20 Hz and then only if at least 8 cabs are clustered to get the necessary mouth area.

I doubt extension will reach that low,but 4 cabs to 32hz is said to be solid.

When I see 'direct radiator mode' I shudder because what it means its low power input and high excursion. For guitar perhaps useful but not big reinforcement.

Quote:

I am only analyzing and relaying what I thought was common knowledge: The HL10 doesn't like oversized rear chambers

When using modeling software this is easily apparent ~10litres vs ~50litres on the typical tuba drivers,obviuosly this is a result of the driver electromechnical specifications,and achieving a rear chamber of this tiny volume can be difficult as you point out.

We should all conclude that the tubas have a use and we all have different aims and preferences-its as simple as that.

Tom is being quite the gentleman regarding tuba vs labhorn(suggesting a shootout),I mean this is his forum,based on his design.

Mike.e

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The AudioXPress article didn't say that the stepped response is there because it's supposed to be. It's there because it seems like it doesn't really matter to many people if it's there or not, and so for a design where small size while maintaining usable performance was the main issue, having a stepped response was an acceptable tradeoff to make. My point is that in the larger Tuba horns, the tradeoff does not need to be made, yet it still is. And in the horns where the mouth is large enough to provide horn-loading to a low frequency, the Tuba principles extend the low frequency response to frequencies where reproduction at any significant level would shred the driver's suspension and bash the voice coil into unrecognizability due to the extremely large excursions that would be required to produce the needed displacement. It's a textbook principle, I'll admit, but I had figured it safe to assume that the laws of physics have not changed appreciably since the textbooks were published. There really is no replacement for displacement, and so in the larger Tubas the extra bass extension really can't be used without putting the driver in jeopardy. What I'm getting at is that if a larger horn can be accomodated, then there is no need to make the tradeoff of a stepped response, so why make it? Fitz and others have not yet made a convincing case to answer that question. That's what my point is.


I sense a lot of ad hominem and unjustifiable appeal to lack of authority argumentation here when there are real, abstract principles involved in finding the actual answer. I have never experienced what it feels like to be a cone loudspeaker driver being ripped apart, so appeals to experience don't really fly here. Instead, explain to me and the rest of us why the Eminence Magnum 15 cone in the Tuba 36 will survive 25 Hz in direct radiator mode, and if it won't survive that treatment, explain why the Tuba 36 has any business in extending the driver Fs to such a low frequency. I and the rest of us on here will learn a lot more if we address the specific issue of the argument and not dismiss the argument out of hand just because I don't have a Ph.D in electrical engineering from Georgia Tech and 10+ years of experience in designing speakers professionally.

[fernand]

Rory, I think I got your point.

You state that in the Tuba 36, the magnum 15 will be ripped apart quickly at 25 Hz.
Can you explain on what model and which simulator you base your statement ?
I guess you have a model that generates with the magnum 95 dB at 25 Hz.
Could you predict a maximum spl or excursion ?

[Michael_Elliston¶]

BHFProfessional: I partially agree with you,apart from the issue about below resonance loading,because it simply cant happen from what Ive read.
By loading I mean a meaningful airload applied to the cone of the driver thus providing output as opposed to below cutoff out of control excursion due to normal horn unloading...No magic that I know of. I dont see the point in extending the cutoff down low where its no use,a higher cutoff with same mouth area could result in a much nicer flat response to say 42hz but again its not how this design is for whatever reason.

I and the rest of us on here will learn a lot more if we address the specific issue of the argument and not dismiss the argument out of hand just because I don't have a Ph.D in electrical engineering from Georgia Tech and 10+ years of experience in designing speakers professionally
Too true.But then 'direct radiatior loading' saves the day so no proof is needed.

I hope this is a debate over design choices and not personal attacks.

Mike.e

[Gareth James]

Rory, i think your still missing the point the others were trying to make. Current thinking seems to reveal that although extension to the lower frequencies is desirable in live sound, a flat response to those frequencies is not absolutely necessary in real-world applications.

Not knowing enough about the subject, and not being an experienced sound professional however i can't really comment.

Gareth James
Student of Sound

P.S. i just finished building a rough clone of the AG-Audio TS-118H, im using the Precision Devices PD186 driver. sounds pretty sweet to me, loud and reasonable extension.

LABsub vs. Tuba36 shootout sounds good to me!

[fernand]

kaisersoze wrote on Tue, 24 May 2005 09:26

snip ... Current thinking seems to reveal that although extension to the lower frequencies is desirable in live sound, a flat response to those frequencies is not absolutely necessary in real-world applications.

To be more precise:
* a flat maximum SPL level to the lowest frequencies is not (always) needed because the source level at those frequencies tend to be some 10 dB lower than the main contents

* a flat overall response is always preferred, but can nowadays be solved with EQ

This is combined with the fact that the dB's at those very low frequencies are by far the most expensive in terms of equipment, volume, power and cost, so correct dimensioning of that aspect is crucial for obtaining the optimal configuration.

[cmqt9]

Rory, read it again.
From Audioxpress April 2004 'The Tuba 24 Horn', Bill Fitzmaurice, page 36: "The resulting stepped response curve is not necessarily what you'd want for your hi-fi or home theatre, but for live sound it fits the bill perfectly."
Again, I'm not trying to belittle your status as a student at all, but your lack of practical experience is insurmountable. Your concern about system capabilites at 25 Hz shows this clearly. The answer to why a Magnum 15 in a Tuba 36 won't tear itself apart at 25 Hz at full power is an easy one: because with music program input it will never see full power at 25 Hz. Both rock concert and dance club RTAs show that at an average broadband SPL of 100dB the level at 25 Hz averages 60dB, some 30dB down from 50-60 Hz where the peak demand lies. At -30dB from full power not only is the Magnum 15 in no danger of tearing the cone apart, I daresay that an Alpha 8 would be equally safe.  

Bob Russell