Concrete Bass Horn Design Question - diyAudio
Go Back   Home > Forums > Loudspeakers > Subwoofers
Home Forums Rules Articles diyAudio Store Gallery Wiki Blogs Register Donations FAQ Calendar Search Today's Posts Mark Forums Read

Please consider donating to help us continue to serve you.

Ads on/off / Custom Title / More PMs / More album space / Advanced printing & mass image saving
Reply
 
Thread Tools Search this Thread
Old 14th October 2016, 04:32 AM   #1
diyAudio Member
 
Join Date: Sep 2016
Location: Washington State
Default Concrete Bass Horn Design Question

One of my bucket list items is to build an outdoor stereo system - i.e. a pair of reinforced concrete straight horns.

The tentative driver I’ve selected is a B&C 12NW76
BL = 25.5 Tesla-meters
Xmax = 8 mm
SD = 522 cm^2
MMS = 77 grams
Qts = 0.16

Click the image to open in full size.

Using a single driver per horn (20 Hz & 160 Hz cutoff frequencies) Hornresp (see above) recommends a 33.5 foot long hyperbolic-exponential horn, with a mouth that’s roughly 16 feet x 16 feet (assuming square mouth). The flair parameter is 1.03, and the horn will supposedly crank out 125 dB down to 20 Hz, without exceeding the 8 mm Xmax. This is good – I can live with that.

Click the image to open in full size.

But I was tinkering with adding additional drivers (the same B&C 12NW76) – for (qty 5 total) per horn (see above). My thought was a square chamber, with drivers on five of the six sides, all feeding the horn’s throat/chamber. In this configuration (with the same 20 Hz & 160 Hz cutoff frequencies), Hornresp recommends shortening the horn down to 26.7 ft, and increasing the throat area by a factor of five, while keeping the same mouth area - this makes perfect sense to me. What I don’t understand is why the recommended flair parameter changes from 1.03 to 0.93 by simply adding more of the same drivers? Nonetheless, increasing the drivers to (qty 5 total), will increase horn output to about 132 dB, without exceeding the 8 mm Xmax. I can live with that.

Conceptually, am I on the right track here? I've selected a driver with a low Qts, low MMS, and high BL - which is what the old design texts say to do. . . .

Last edited by Entropy455; 14th October 2016 at 05:21 AM.
  Reply With Quote
Old 14th October 2016, 06:38 AM   #2
diyAudio Member
 
Join Date: Jun 2007
Quote:
Originally Posted by Entropy455 View Post
What I donít understand is why the recommended flair parameter changes from 1.03 to 0.93 by simply adding more of the same drivers?
The horn throat area S1 automatically changes in the calculations because of the changed driver configuration. The calculated value of T is a function of throat area.

Quote:
Originally Posted by Entropy455 View Post
Conceptually, am I on the right track here?
You could probably get away with assuming 2 Pi rather than 4 Pi radiation, which would reduce the overall size of the horn somewhat.
__________________
www.hornresp.net
  Reply With Quote
Old 14th October 2016, 06:42 AM   #3
diyAudio Member
 
weltersys's Avatar
 
Join Date: Jan 2008
Quote:
Originally Posted by Entropy455 View Post
1)One of my bucket list items is to build an outdoor stereo system - i.e. a pair of reinforced concrete straight horns. The flair parameter is 1.03, and the horn will supposedly crank out 125 dB down to 20 Hz, without exceeding the 8 mm Xmax. This is good Ė I can live with that.
2)What I donít understand is why the recommended flair parameter changes from 1.03 to 0.93 by simply adding more of the same drivers?
3)Nonetheless, increasing the drivers to (qty 5 total), will increase horn output to about 132 dB, without exceeding the 8 mm Xmax. I can live with that.
4)Conceptually, am I on the right track here? I've selected a driver with a low Qts, low MMS, and high BL - which is what the old design texts say to do. . . .
Entropy455,

There are a welter of paths that lead to entropy, you appear to be on several ;^).
A single driver tapped horn of only 15.5 cubic feet will exceed the SPL of your design, though won't have much response below 32 Hz, generally not a concern unless you want to reproduce earthquakes, mortar blasts, or Osprey helicopter wash at original levels.
1) Concrete is a cheap, but very work intensive medium to work with, the reinforcement needed to keep it intact should not be underestimated. Building a stem wall a fraction of the size of the horn you propose stands out in my memory as a more negative use of time than two of the four airplane crashes I have experienced. Your mileage may vary..
2) When "thinking big", relatively small changes effect differences "down wind". A flair parameter difference of less than 10% is like not shaving for 90 minutes, who cares?
3) It is good to be able to live with the laws of physics, life becomes intolerable otherwise
4) Whether you are on the right track depends on what your goal concept is, building a concrete "statement", or producing a given SPL to a given frequency with minimal effort and maximal effect.

For better or worse, am far too familiar with using maximal effort to produce effects that few notice, much less appreciate, so I do appreciate where you are coming from, and wish you the best, whatever "track" you get stuck in/on.

Cheers,

Art
  Reply With Quote
Old 14th October 2016, 12:25 PM   #4
diyAudio Member
 
Join Date: May 2006
Quote:
Originally Posted by Entropy455 View Post
Conceptually, am I on the right track here? I've selected a driver with a low Qts, low MMS, and high BL - which is what the old design texts say to do. . . .
While the driver you chose obviously works you can forget about what the ancient texts say about low q, low mms, high bl drivers. That's just a first best guess at getting a decent driver to work in an ancient midrange horn.

If you want to know the truly best specs for your intended application, use Leach's math, specifically the System Design - From Specifications tool. That will design your horn and driver all at once in one fell swoop.

At that point the issue becomes finding a driver with the same specs that Leach's math suggests - in the case of the Labhorn, Tom Danley had to have one specially made by Eminence, hence the new Lab 12 driver specifically designed for the Labhorn.

That doesn't mean that you can't get fantastic results from wildly inappropriate drivers, but the point here is that the optimal driver specs for a low tuned bass horn very likely are not going to have low q, low mms or high bl.
  Reply With Quote
Old 14th October 2016, 03:25 PM   #5
diyAudio Member
 
weltersys's Avatar
 
Join Date: Jan 2008
Quote:
Originally Posted by just a guy View Post
At that point the issue becomes finding a driver with the same specs that Leach's math suggests - in the case of the Labhorn, Tom Danley had to have one specially made by Eminence, hence the new Lab 12 driver specifically designed for the Labhorn.

That doesn't mean that you can't get fantastic results from wildly inappropriate drivers, but the point here is that the optimal driver specs for a low tuned bass horn very likely are not going to have low q, low mms or high bl.
The "new" LAB 12 was designed around the turn of the century, I was late to the party and got my first units July of 2003, my first purchase of a horn driver with such a low FS and super stiff, heavy cone.

Prior to that, Tom Danley's servo-motor belt drive units had far more displacement potential than professional drivers, though by the mid 1990s they had been rendered obsolete by drivers such as AuraSound's 1808, the 1997 spec sheet copy below. Funny, (in retrospect) I was so caught up in driver "sensitivity" specifications back then that I paid little attention to their displacement- the AuraSound 1808 had considerably more than a pair of LAB 12", though the LAB 12 had more displacement per dollar.

I had mostly forgot about how advanced the 1808 was until 2015 when I started scanning old documents to eliminate hundreds of pounds of paper before moving cross country. Although the 1808 has great displacement capability, the mms is/was too low for low distortion in high compression ratio applications, something that does not show up in simulations, but can also result in ripped or kinked cones when pushed to Xmax.

Eminence has not made much advancement in LF horn drivers since the introduction of the LAB 12, but B&C and many smaller companies have, sold off my last (spare) LAB 12 last year.

I was contacted by PM several years ago on this forum by a man who wrote he had purchased the old Aura neo magnet structures, and was planning to re-issue drivers. I was unable to get a response back, and could find no web presence of his enterprise, a shame, as the 1808 magnet structure is still one of the best designs.

Art
Attached Images
File Type: jpg Aura 1808 P1.jpg (557.6 KB, 920 views)
File Type: jpg Aura 1808 P2.jpg (604.7 KB, 871 views)

Last edited by weltersys; 14th October 2016 at 03:31 PM.
  Reply With Quote
Old 14th October 2016, 04:03 PM   #6
bjorno is offline bjorno  Sweden
diyAudio Member
 
Join Date: Mar 2005
Location: Jacobsmountain
Send a message via MSN to bjorno
FYI:

b
Attached Images
File Type: jpg 5x_B&C-12NW76.jpg (844.1 KB, 864 views)
  Reply With Quote
Old 14th October 2016, 05:57 PM   #7
diyAudio Member
 
Join Date: May 2006
Quote:
Originally Posted by weltersys View Post
The "new" LAB 12 was designed around the turn of the century ...
Yes, of course, I meant it was new (created for) for that application. There are other options available now with much higher power handling.
  Reply With Quote
Old 14th October 2016, 09:37 PM   #8
diyAudio Member
 
Join Date: Nov 2007
Quote:
Originally Posted by weltersys View Post
I had mostly forgot about how advanced the 1808 was until 2015 when I started scanning old documents to eliminate hundreds of pounds of paper before moving cross country. Although the 1808 has great displacement capability, the mms is/was too low for low distortion in high compression ratio applications, something that does not show up in simulations, but can also result in ripped or kinked cones when pushed to Xmax.
I remember when those came out. 18" drivers with huge Xmax and very low Qes. But yes, light cones.

Didn't someone try filling the cones with foam at one point in an attempt to stiffen them up for heavy duty use?
__________________
www.diysubwoofers.org
  Reply With Quote
Old 15th October 2016, 02:24 AM   #9
diyAudio Member
 
Join Date: Sep 2016
Location: Washington State
Bjorno, I have been looking over your calculations. Please remember that I am still a beginner/novice at using Hornresp. I omitted adding dampening material to the driver’s box, because until about five minutes ago, I didn’t know how to do it. . . I am trying to draw conclusions from what you’ve posted. Please let me know if I’m interpreting your intent correctly?

A large horn mouth equates to a high electro-mechanical energy conversion (horn efficiency), however the horn’s off-axis response suffers at higher frequencies.

A smaller mouth horn is capable of extending to lower frequencies, and achieving decent sound pressure levels – and with what appears to be superior off-axis response – however the electrical input power requirements are higher, due to the decreased horn efficiency. Are the colored graphs and off-axis plots you posted from Hornresp, or are they from another software?

Please remember that I am not constrained by space. I’ve got 5 acres of land, surrounded by 700 acres of vacant State land to the north – thus I won’t have any complaints about the sound. I’m not the slightest bit discouraged at the thought of constructing 16, or even 20 foot diameter horns. They are going to be outdoors. I am just trying to understand why you would recommend such a drastic reduction in mouth area. Doesn’t this increase harmonic distortion? If you could type out a brief explanation as to the rationale behind your suggestion/calculations, it would be greatly appreciated!

Just-a-Guy, I’m a bit confused. Are you suggesting that a Lab-12 driver is better suited for a full-size strait 20 Hz exponential horn, than a driver with a lower MMS, lower Qts, and higher BL? Which driver would you specifically recommend for my application?

Last edited by Entropy455; 15th October 2016 at 02:27 AM.
  Reply With Quote
Old 15th October 2016, 02:38 AM   #10
diyAudio Member
 
Join Date: Sep 2016
Location: Washington State
From the engineering papers Iíve read regarding horn design, the throat of a horn is as close to a purely resistive load on the driver, as one could ever hope to obtain. In an equivalent spring-mass system, the hornís throat impedance is simply a damper Ė in which case you need raw & blunt applied-force to overcome the damper (i.e. a high BL). You specifically do not need extra mass (MMS), nor do you need additional spring-K (high Vas), to overcome the damper. The ideal horn driver has a low Qts, mainly due to the high BL, and low MMS. Or am I completely out-to-lunch on my understanding of horn driver selection???
  Reply With Quote

Reply


Hide this!Advertise here!
Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
Bass Horn Design Question (throat) Entropy455 Subwoofers 23 22nd September 2016 03:39 AM
Ciare 18 bass horn design soundhead Subwoofers 6 22nd September 2015 11:32 PM
Mid bass horn design Yasuo Kanda Multi-Way 18 5th May 2014 01:23 AM
how to go from horn response to a folded bass horn design? paulspencer Subwoofers 8 4th November 2005 10:44 PM
The best BASS HORN Design . darkm4n Multi-Way 14 27th March 2004 08:14 PM


New To Site? Need Help?

All times are GMT. The time now is 11:15 PM.


vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2017 DragonByte Technologies Ltd.
Copyright ©1999-2017 diyAudio

Content Relevant URLs by vBSEO 3.3.2
Wiki