My first Tuba

I have been inspired lately to build the autotuba by billfitzmaurice. It all started in "The Maximum bang for your buck" thread where many have suggested that the autotuba not only gives an amazing amount of bang for your buck, but also is of high sound quality.

So I went to Billfitzmaurice.com and ordered the plans. It took a while to get them, but for good things we must be patient.

So I ordered the MCM driver and I will start construction on the enclosure tomarrow.

My questions for those of you who have built this in the past(or Bill himself)

1. how well does 3/4" MDF work?
2. Is the only differnce between the 8" autotuba and 10" the width?
3. Will increasing the width of the 8" autotuba give performance beneifits?
4. How exact must the construction be?(I can get down to <1mm tolerences, but not a whole lot better than that with my skills)
5. How much wood will the entire enclosure take to build(how many 4'x8' sheets)

I would post on the forum at billfitzmaurice... but I like this one MUCH better
 
BassAwdyO said:
I have been inspired lately to build the autotuba by billfitzmaurice. It all started in "The Maximum bang for your buck" thread where many have suggested that the autotuba not only gives an amazing amount of bang for your buck, but also is of high sound quality.

So I went to Billfitzmaurice.com and ordered the plans. It took a while to get them, but for good things we must be patient.

So I ordered the MCM driver and I will start construction on the enclosure tomarrow.

My questions for those of you who have built this in the past(or Bill himself)

1. how well does 3/4" MDF work?
2. Is the only differnce between the 8" autotuba and 10" the width?
3. Will increasing the width of the 8" autotuba give performance beneifits?
4. How exact must the construction be?(I can get down to <1mm tolerences, but not a whole lot better than that with my skills)
5. How much wood will the entire enclosure take to build(how many 4'x8' sheets)

I would post on the forum at billfitzmaurice... but I like this one MUCH better


as the plan suggests, use 1/2" material, else all the other proportions will be inaccurate

a 4 x 8 of 1/2" plywood will suffice (and is only slightly more expensive than 3/4" MDF)

1mm tolerance is sufficient :)

in my opinion, the one thing that i would suggest would be to make 2 of the sides 4 - 6 " longer so you dont have to deal with making feet for upright placement later on
 
I do plan to use this for Auto purposes.... so I wont be needing the legs as it will surely be placed sideways...

I think I can make adjustments to accomodate 3/4 inch wood. I already have a few sheets of MDF and thats what I normally used to build with.

I will do some home comparisons though.. and hopefully some measurements for simon5
 
If you build with 3/4 material, make absolutely sure that the added dimension is added to the OUTSIDE of the scroll as you go. In other words, there will be real problems with the sound quality if you make the speaker chamber any smaller... the speaker will not fit! It needs all the clearance it can get.

Mount the speaker on the baffle before you start assembly.
 
I have one more suggestion. If you do build the cabinet from 3/4 inch material, don't make the assumption that you can leave out the center brace. It is critical. If I were to build this basshorn, and I purchased the plans so maybe one day I will, I also would build it out of 3/4 inch stock for the improved stiffness.

I can't answer the question about MDF or plywood. MDF is more accoustically dead and is less likely to have resonances in the midrange frequencies, but I have heard no complaints about this when reading posts about the quality of this bass horn. MDF is less stiff, but building the box out of 3/4 inch material with the center brace should compensate.

Retsel
 
Thanks for all the advice guys...

I plan to increase the dimensions by 1.25"- H .75"-D and .5"-W to make the 3/4" material work. I will brace exactly as the plans have specified except maybe at the mouth I was thinking of making the brace come out a bit farther so it ends up ~6 inches.

I'll be starting on the enclosure in a few minutes, but it will be a while until I get the driver. I havent even recieved an invoice from MCM so it could be a while...

I was thinking of putting an extremis in there and trying it out though
 
Well.... after about a half a day's work the enclosure is basically finished. Once my digital cam battery charges I'll post some pictures, and after that I'll hook it up for a listen!

I'm using one of my extremis6 midwoofers in it right now, so I dont know how good of an assesment it will be considering that it was not designed for this speaker, but a horn is a horn and the speaker in question shouldnt have too dramatic of an effect on it's function... right?
 
Here's a side view with one side removed....

I know the woodworking isnt perfect, but what can I say. That angled peice that forms the mouth is the most horrid. My table saw only goes to 45degrees though so thats the best I could do with it. Oh well.... I'm filling all the gaps with hot glue(for now) to seal it up and hear how it sounds. Once I get the MCM I'll take it apart and liquid nails everything and finish it off.
 
oops... forgot to attach the pic
 

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After hooking it up and listening I'd say the in room usable response ends at ~40hz. However comparing to a sealed box its got to be at least 10db more efficient. I havent done any measurements yet, but its more than twice as loud. Amazing....

Now I REALLY want to horn load my Tumult.... a 30hz horn would be insanely loud.
 
Indeed... I could use the tempest horn plans, but bill informs me that the tuba 36 will work well...

decisions decisions.... one free, one $10....

I think i'll buy bill's design and see what differences there are between that and the tempest horn. Mostly I'm looking for high efficiency(well it doesnt have to be insanely high, just better than the 88db that the tumult has in a normal enclosure) and a low cutoff.

Bill suggested the 20" slim horizontal baffle slim version (which has less extension but a higher cutoff

I figure though, if you're gonna go, why not go all out... Couldnt I just do the 36^3 version? I guess that would mess with the compression ratio possibly since the 36^3 version is recomended for 2 15's..... the Vertical baffle configuration is also supposed to give extension to 15hz which I personally would love. I guess that wouldnt work so well with the low FS of the tumult, but I dont see why just using a smaller rear chamber to raise the effective resonance up to where it would work well. HMMMMMM

I'm no horn expert... looks like I'll have some learning to do
 
Horn loaded tumult? Is that going to be put in a bomb shelter or do you have bullet proof glass? :smash:

I'd be very interested to hear what you think of the AutoTuba and how it compares with a cheap 8" to your Tumult in terms of SQ. Probably difficult to compare since the response would be so different.

One possibility with horns would be to use some "compact" midbass horns like the AutoTuba to get down to 40 Hz, then cover the bottom end with a pair of vented Tumults. If you have the best quality of driver you can get for the midbass horns, you could have very accurate low distortion bass where the ear is more sensitive. I suspect the extremis would not have the chance to use all of its excursion and from that point of view it might not have any significant advantage over a typical midbass except for the linearity of the motor design combining an XBL2 motor with shorting rings.
 
BassAwdyO

I figure though, if you're gonna go, why not go all out... Couldnt I just do the 36^3 version? I guess that would mess with the compression ratio possibly since the 36^3 version is recomended for 2 15's..... the Vertical baffle configuration is also supposed to give extension to 15hz which I personally would love. I guess that wouldnt work so well with the low FS of the tumult, but I dont see why just using a smaller rear chamber to raise the effective resonance up to where it would work well. HMMMMMM

If you have the plans you find that there is indeed good low end response with the tuba 36. THat is at the expense of efficiency. With a good low end eq you could indeed have some truly thundering bass.

I downloaded the plans a couple weeks back. Going to put some 15" to work in a different configuration. THe boxes will be setup with dual 15's.

Just a note on timber between driver loading. You may have already noticed that there is a difference between the bass that comes out of the autotuba and what would come out of a normally loaded 8". It's basically a much cleaner sound. If you go with a different driver loading at to high a frequency you will definitely notice the difference. That will have have to be determined by you and some carefull listening.

I'd love to build them and listen along with you. But unfortunately I'm moving in two months and have enough stuff stuff do move as is. In the new place!

MArk
 
Greets!

Drivers like the Tumult are best suited for BHL to take advantage of the super low Fs/high Xmax, so a conical expansion cornerhorn should yield the best 'bang'/floorspace. Obviously, the longer you can make it the lower it will go with gain, but with a conical flare and sufficient length it should have >100 dB sens. to Fs if the corner construction is rigid enough.

That said, I ~agree with Paul, use midbass horns down to ~40 Hz and a Tumult BP (or two) for sub duty.

GM
 
GM, I'm not exactly sure what you are suggesting ... bandpass, horn for the Tumult?

What do you mean by BHL?

Horns seem a curious thing to design for using typical sub drivers. I've tried out my AV12s in hornresp, and it seems that they don't get quite as much output as I'd expect considering their power handling and excursion. I get very little cone movement, then suddenly the excursion shoots up at the tuning point.
 
Greets!

I said I agreed with you, with the caveat of putting the Tumult(s) in a bandpass cab(s) and if a Tumult or similar sub driver is horn loaded, that it be a back horn, preferably corner loaded.

WRT the horns unloading too soon, I assume it's because you're making the length a 1/4WL long rather than an acoustic 1/4 WL, which will be somewhat longer based on its 'M' factor. Of course, just like any other vented or sealed design, it unloads/compresses based on the alignment below Fc.

GM