My ideal Sub plans

[mashaffer]

I have been considering my ultimate sub and had narrowed it down to either IB or built in horn. The back wall of my listening room abuts the two car attached garage and has about 15 square feet of wall space that I can use for the system mouth. It boils down to spending a lot on drivers and power and very little on construction (IB) or a little on power and drivers and comparatively more on construction (horn).

Right now I am leaning toward a horn. A first pass on design is a 15" driver with straight mock hypex horn of about 10 square feet mouth opening. The actual implementation would be to approximate the taper using several conical sections. When playing with a 12" design it appeared that this approximation has very little negative consequence.

The horn response simulation done with a Dayton 15" Quatro sub is shown below. 1 Watt input gives about 105 dB but the plots shown are for 20W input. At this level we are still far from exceeding the 10mm Xmax of the driver. I would need to put in over 100 Watts (for 125+ dB at 16Hz to exceed Xmax.

I also did a simulation with an Eminence Beta 15 and it worked very well too (maybe even a little smoother and certainly much more efficient) but it has only about 4mm Xmax. It might however be an easier load for a tube amp.

Eventually I would like to drive it with a dedicated 6CA7 PP tube amp with a wee bit of negative feedback so the Pro driver might be a better bet in the long run.

Thoughts?

[carpenter]

A ten square foot mouth is too small. Even with corner loading, the response will be ragged. You didn't say how long the horn will be. Then there's the time delay to deal with. It is noticable.

I built a fifteen foot horn with a 10.8 square foot mouth, corner loaded. The bass fell off at 40hz. It ran at 105db 1w1m, but gave me problems with resonance peaks.

If you want to run a sub-bass horn, plan on much larger dimensions! If possible, keep it straight to eleminate resonance peaks.

The I.B. is a sweet proposition if you can afford the drivers. This is my next adventure. I'll use 8 Dayton Titanic Mkll drivers and load them into the garage below my media room.

No matter what you do, have fun

John Inlow

[RobWells]

Length is shown on the attatchment as 1227.79cm.

About 40.3 foot

wow thats a big horn I think my labhorns are about 9 foot long.

The mouth is nearer 8 square foot btw.

Rob.

[carpenter]

Good luck...

The mouth--where it enters at the corner of the room--should be considerably larger than what you've designed--36 sq.ft. seems like a minimum figure. 100 sq. ft. would be my choice. Otherwise, what you have is a horn with a section removed from the middle.

With a length exceeding forty feet, you'll most certainly want a time-delay unit in the signal path.

John

[mashaffer]

Great input guys. Yes at 40' length I would need one fold. I hadn't thought much about the delay. That could be a major factor. This "design" was just the raw output of the Hypex Designer of "Horn Response" with no adjustments at all. I was kind of surprised that it suggested such a small mouth size as well.

Would using two drivers (thus increasing the mouth area) shorten the length needed?

mike

[mashaffer]

BTW what would you think is the maximum length where delay will not be a problem?

mike

[zobsky]

Originally posted by mashaffer
BTW what would you think is the maximum length where delay will not be a problem?

mike

you should easily be able to correct for delay using some active circuitry (i think behringer, amongst others, made something up to the task)

[carpenter]

You can correct the delay electronically, but it kills the sparkle on the top end. Maybe you can find an expensive DSP. My QSC DSP-30 is noticable when I insert it into the audio chain. It sounds like mid-fi, not hi-fi.

Two drivers will make the throat larger, thus shorten the horn.

I haven't finished my first cup of coffee, but let's play with some numbers: To be practical, what you want is a horn that is at least 1/4 wave length of the lowest frequency you wish to reproduce. 1100 (speed of sound) divided by 20 (low frequency cutoff) = 55 feet between pulses at 20hz. 55 divided by 4 (1/4 of the 20hz wavelength) = 13.75 feet minimum length of horn. When I design a 20hz horn, I start at the throat and create multiples of expansion every 36" thereafter. In the case of a hyperbolic design, you must go for more length between expansions points, hence the unusual length of your design. But, more length = more distortion.

So, using the more practical exponential, 20hz expansion: let's say your throat is 100 sq.in. (10" x 10")--thirty-six inches down the road it becomes 200 square inches--seventy two inches from the throat, it becomes 400 square inches. At 108" it has grown to 800 sq.in. At 144" it's 1600 sq.in. Then comes 180" with 3200 sq.in. mouth. Now, 180" divided by 12 = 15 feet of horn length. The sq.root of 3200 = 56.5" per side of mouth. This is rather truncated, but may work. I'd grow the horn another section or two to be safe. I.e., 216" at 6400 sq.in. mouth = 18 foot length with an 80 inch x 80 inch mouth. That's almost 7 feet by 7 feet. Now we're getting somewhere. place this in the corner of your room and let the natural wall expansion take over. The final mouth perimeter should add up to the length of the wavelength at cutoff. In your case, 20hz = 55 foot perimeter, or 7.4 feet per side.

This is pragmatic, will fit in your garage, and will sound so much better than a folded horn. I've learned from experience that a folded horn does not sound like hi-fi. It sounds like a P.A. system. P.A. is designed to run hard and is impressive sounding in that capacity. At home, no way. Build this horn and blow your mind!

John

[paulspencer]

The comments I've heard from others is that folded bass horns are very hifi, but I can't yet comment from my own experience on that.

It's a good idea to play with numbers, and use hypex as a starting point. I believe the compression ratio is too high. The throat area should be no less than half the SD. A higher compression ratio than 2 means the driver must be very strong, or it will not ever be pushed.

Keep in mind that it may be bigger than you think, and you need to look at the foldings and geometry to see if you can actually fit it in!

Will this be built in?

It's a good idea to fire it into a corner and run it floor to ceiling. You might make two of them with a single 12" driver in each, stack them on top of each other. Get hornresp to calculate with two drivers, then make each box with the length specified, but half the mouth area each.

I've played around with a lot of designs, and what I found to work well was two horns with a 12" sub driver each (lab12 or similar) with 2 x 0.5m footprint running floor to ceiling. You can get it to 20 Hz and hit 120db easily at 20 Hz with 12.5w and not a lot of excursion is required for a sub driver.

When it comes to bass horns, I'm a bit of a beginner, but hope this helps.

[carpenter]

When it comes to hi-fi, everyone's entitled to their opinion, Paul. I think the sound wave at very low frequencies sound like pressure against my ears. Anything that can make them is fine. But when you go up into the second octave, my ears notice the lack of bass detail in a folded horn. That's why I'll never build another folded horn. Mind you, my gooseneck bass horn is very large and certainly efficient. It doesn't sound nearly as good as my higher frequency straight horns. The warmth/character is stripped away.

From what I read, most everyone who builds an enclosure says it sounds hifi, I'm no exception. But as time wears on, I allow my pride and memories of the effort exerted to move aside and truly examine what I've created. Straight always sounds better.

If I remember correctly, you submitted drawings to this forum, so I realize that when it comes to folded horns you've got a horse in this race...

John