Speakerplans.com Homepage
Forum Home Forum Home > Plans > Other plans
  New Posts New Posts RSS Feed - 2x15" front loaded horn F2B
  FAQ FAQ  Forum Search   Events   Register Register  Login Login

2x15" front loaded horn F2B

 Post Reply Post Reply Page  <1 789
Author
Message
Sonic the hedge View Drop Down
Registered User
Registered User


Joined: 12 May 2020
Status: Offline
Points: 146
Post Options Post Options   Thanks (0) Thanks(0)   Quote Sonic the hedge Quote  Post ReplyReply Direct Link To This Post Posted: 23 October 2021 at 6:07am
Originally posted by toastyghost toastyghost wrote:

Have a look at the Loudspeaker Rocking Modes papers here:
https://www.klippel.de/know-how/literature/papers.html

That’s a term for one form of what you’re describing on the cone motion.

Throat compression is pretty well understood in the theory; Kolbrek & Dunker’s book is the best one-stop resource for this (and most other horn things). What hasn’t been analysed in detail as yet is the non-adiabatic effects of non-linear distortion of the air itself when horn throats are driven to high levels. I’ve seen one study that built an example setup to test this properly, but further work hasn’t been done.

Contrary to what many seem to think, inverse distance law applies inside the horn too!

As an example, I (shoddily) built some poplar scale model horns recently. I measured 137 dB linear peak at the throat, driven with a 2 Volts peak log sine sweep. That’s bloody loud, but more importantly, a 30 dB increase in level is well into the point where the air itself is distorting even if the driver or amp isn’t.

However, we seem to tolerate - or even prefer - some types of distortion much more than others.

Thanks - some good resources!

From what you and Snowflake have said, it does seem possible, that a basic principal behind F2B is to deliberately induce distortion in the throat, which is then acoustically filtered, by the horn, to produce a full and pleasing tone. It is a warm sounding cabinet, and I guess that well-tuned acoustic filtering just sounds natural, because it is.

Interesting too, that there seems to be a bit of a gap in the underlying theory here - it does make you wonder, if MA have some secret unpublished formulae, or if 215/F2B was developed and refined by experimentation. 


Edited by Sonic the hedge - 23 October 2021 at 6:16am
Back to Top
toastyghost View Drop Down
The 10,000 Points Club
The 10,000 Points Club
Avatar

Joined: 09 January 2007
Location: Manchester
Status: Offline
Points: 10464
Post Options Post Options   Thanks (0) Thanks(0)   Quote toastyghost Quote  Post ReplyReply Direct Link To This Post Posted: 23 October 2021 at 2:26pm
Well, the theory is sound. It hasn't been experimentally verified much in low-frequency horns for PA applications partly because research is expensive, time-consuming, and you need mics and interfaces capable of measuring >165 dB linear average without distortion.

They do exist but are not cheap.

Here's the 2019 paper on this topic that I was referring to:
https://pub.dega-akustik.de/ICA2019/data/articles/000129.pdf



HF horns are another matter. The same principles should apply.

Here's Klippel with a model and a method to cancel out nonlinear throat distortions with processing, and a model by Holland for HF horns. Both from 1996:
https://www.aes.org/e-lib/browse.cfm?elib=7878
https://www.aes.org/e-lib/browse.cfm?elib=7891
Found those when I was looking at DIY 'Guinness focusing' aka Fulcrum's tQ.

Most of this work is in the field of vocal range horns. They're just used much more often, and we are more sensitive to distortion in those ranges. Voishvillo has a good one here:
https://www.aes.org/e-lib/online/browse.cfm?elib=11243

And here's one that's a bit more heavy on the theory:
https://asa.scitation.org/doi/abs/10.1121/1.1362688?casa_token=KZpJYrlKKr0AAAAA:glJBpmp-iaouCiDLWBbQR5li5DnRFb6e2IuZtLpB3NY2kX6x_kpIdvoDrySEPLBAHIc7XJPy3k7I

These all rely on one parameter models though, which don't predict the full modal response of the horn. Kolbrek published a Matlab toolbox for a semi-analytical modal propagation method s while back, but the more advanced version lives in his HornCAD software which is unreleased.

If you want to do it 'properly' like the big boys, then you just need a monster PC or server farm, a license for COMSOL with the appropriate add on models, and lots of free time and experience:
https://www.comsol.com/blogs/simulating-nonlinear-sound-propagation-in-an-acoustic-horn/

Edited by toastyghost - 23 October 2021 at 2:29pm
Back to Top
snowflake View Drop Down
Old Croc
Old Croc


Joined: 29 December 2004
Location: Bristol
Status: Offline
Points: 2767
Post Options Post Options   Thanks (0) Thanks(0)   Quote snowflake Quote  Post ReplyReply Direct Link To This Post Posted: 23 October 2021 at 3:37pm
Originally posted by toastyghost toastyghost wrote:

Well, the theory is sound. It hasn't been experimentally verified much in low-frequency horns for PA applications partly because research is expensive, time-consuming, and you need mics and interfaces capable of measuring >165 dB linear average without distortion.

They do exist but are not cheap.

Here's the 2019 paper on this topic that I was referring to:
https://pub.dega-akustik.de/ICA2019/data/articles/000129.pdf




couple of surprising things in that paper:
compression ration of 3.66 is a lot higher than recommended in most bass horn design guides. A lot of people believe over 2:1 risks destroying high excursion drivers.
they seem to detect a lot of 3rd harmonic. Could this be due to driver suspension non linearity? The throat distortion and chamber volume variation would create mostly 2nd harmonics wouldn't they?

if the front chamber volume is changing drastically then the LPF of the chamber will change. is this why the fourth and fifth harmonic levels are almost as high as the second and third?
Back to Top
toastyghost View Drop Down
The 10,000 Points Club
The 10,000 Points Club
Avatar

Joined: 09 January 2007
Location: Manchester
Status: Offline
Points: 10464
Post Options Post Options   Thanks (0) Thanks(0)   Quote toastyghost Quote  Post ReplyReply Direct Link To This Post Posted: 23 October 2021 at 4:09pm
It’s a cut-down version of a presentation, so I think some things are missing or glossed over. I have questions about their calculation of the throat adapter’s contribution since the simple equation used isn’t accounting for the actual SPL offset.

The concept is justified. A high compression ratio is fine, if the rear chamber is suitably large. The modern drivers available play well to the parameters which horns are most sensitive to - BL, Mmd, etc.

I’d like to see a comparison of the relative distortion levels at the same throat SPL, for example. That would make answering your questions much easier.

There is one level matched in both setups; 109.8 and 109.7 dB at -1 dBFS and -3 dBFS input respectively. But it looks like they don't use those two different drive levels to determine the contribution of the throat adapter alone    

An increased level should increase the distortion anyway, as can be seen in the tables. It isn't fully intuitive, since the effect is non-linear.

You can kind of do it yourself though. Looking at the fifth-order harmonic, it goes up by 13.3 dB with the throat adapter for that 109.7 dB level. There's not enough other info to make predictions as to *why* though. No diagram or photos of how they inserted mics at the throat while changing the throat adapter and rear chamber for example. Is the horn a straight one, or folded?

I've looked but can't find the presentation recording, and they've not published follow-up papers yet.

There’s also the issue of the anechoic chamber used. There’s no documentation of the cutoff frequency, so an increased level might be increasing the reflection contribution - which would show up as distortion.

If we had more details about the construction of the horn and driver used, it could be recreated in a coupled non-linear model within COMSOL, including the effects of/on driver suspension and the like.

Again this is something I wanted to do myself, but I've spent the summer looking into other things first. Which unfortunately became a very big rabbit hole of their own
Back to Top
Sonic the hedge View Drop Down
Registered User
Registered User


Joined: 12 May 2020
Status: Offline
Points: 146
Post Options Post Options   Thanks (0) Thanks(0)   Quote Sonic the hedge Quote  Post ReplyReply Direct Link To This Post Posted: 23 October 2021 at 9:03pm
Thanks both for your replies

Most of this stuff is way over my head, but it's nice to know that these things are still actively being researched, albeit on a limited scale. 

Especially since the trend for BPH 'one note wonders' seems to have given FLH a bit of a bad rap these days!
Back to Top
madboffin View Drop Down
Young Croc
Young Croc


Joined: 03 July 2009
Location: Milton Keynes
Status: Offline
Points: 1459
Post Options Post Options   Thanks (0) Thanks(0)   Quote madboffin Quote  Post ReplyReply Direct Link To This Post Posted: 23 October 2021 at 10:33pm
Originally posted by Sonic the hedge Sonic the hedge wrote:

Thanks - some good resources!

From what you and Snowflake have said, it does seem possible, that a basic principal behind F2B is to deliberately induce distortion in the throat, which is then acoustically filtered, by the horn, to produce a full and pleasing tone. It is a warm sounding cabinet, and I guess that well-tuned acoustic filtering just sounds natural, because it is.

Interesting too, that there seems to be a bit of a gap in the underlying theory here - it does make you wonder, if MA have some secret unpublished formulae, or if 215/F2B was developed and refined by experimentation. 


I can assure you that it was developed and refined by experimentation. It followed on from the bass horns used in the 215Mk3 and RS1200 cabinets. There was also the ergonomic and economic imperative of making it fit in a standard semi-trailer, which dictated one of the mouth dimensions (570mm or 22-1/2" to pack four across).

You need to understand that when we were developing this in the late 1980's there were no computer simulations and the main measuring instrumentation was B&K 2010's and chart recorders. We had just acquired a TEF-10 (a piece of transformatively innovative technology, look it up) and were beginning to learn how to use it, but it played almost no part in the F2B's development.






Edited by madboffin - 23 October 2021 at 10:41pm
Back to Top
toastyghost View Drop Down
The 10,000 Points Club
The 10,000 Points Club
Avatar

Joined: 09 January 2007
Location: Manchester
Status: Offline
Points: 10464
Post Options Post Options   Thanks (0) Thanks(0)   Quote toastyghost Quote  Post ReplyReply Direct Link To This Post Posted: 23 October 2021 at 11:27pm
Originally posted by madboffin madboffin wrote:



I can assure you that it was developed and refined by experimentation. It followed on from the bass horns used in the 215Mk3 and RS1200 cabinets. There was also the ergonomic and economic imperative of making it fit in a standard semi-trailer, which dictated one of the mouth dimensions (570mm or 22-1/2" to pack four across).




And a damn good bit of experience and long-learned theory, I would think! While Dave never published any ‘proper’ papers, he, Tony(s) and Czerwinski pioneered the use of bass horns for PA as I see it. Considering the Shearer horn was 40 years old when those companies made their first boxes, the fundamentals were known. The genius was making them transportable, arrayable and the transducers made for the occasion.

Frankly older horn subs hold up way better today than the reflex boxes of the era. It’s sterling work.
Quote
You need to understand that when we were developing this in the late 1980's there were no computer simulations and the main measuring instrumentation was B&K 2010's and chart recorders. We had just acquired a TEF-10 (a piece of transformatively innovative technology, look it up) and were beginning to learn how to use it, but it played almost no part in the F2B's development.








Not strictly true. Hornresp existed then, albeit on punch cards lumped elements and equivalent circuits also seem to be well understood by certain parties. Of course, Heyser’s own work was already a decade old then too, but I’m not surprised it took a while to become affordable and accepted.

It's really telling how closely the empirical design methods from these boxes hold up when simulated in the most complex modern multiphysics models. It doesn't mean there isn't big room for improvement, but given how much of the focus has been on just throwing watts at the problem for 30 years, it's going to take a step change to drive that shift back to innovation on efficient designs.

Something like the world fluctuating between blazing inferno and mini ice ages, perhaps?

The Heyser lecture videos uploaded last year on the AES from the late 70s and early 80s are truly mind-blowing stuff. Audio wasn't even his bloody job! I wish I was so good at my 'hobby' that I changed the entire industry who do rocket scientists think they are, eh?

https://www.aes.org/technical/heyser/
Open access, so dig in. Bring a big bag of popcorn, a pot of coffee, and a notepad cos you’re gonna do some learnin’

Edited by toastyghost - 23 October 2021 at 11:31pm
Back to Top
Sonic the hedge View Drop Down
Registered User
Registered User


Joined: 12 May 2020
Status: Offline
Points: 146
Post Options Post Options   Thanks (0) Thanks(0)   Quote Sonic the hedge Quote  Post ReplyReply Direct Link To This Post Posted: 27 October 2021 at 7:44pm
Originally posted by madboffin madboffin wrote:

I can assure you that it was developed and refined by experimentation. It followed on from the bass horns used in the 215Mk3 and RS1200 cabinets. There was also the ergonomic and economic imperative of making it fit in a standard semi-trailer, which dictated one of the mouth dimensions (570mm or 22-1/2" to pack four across).

You need to understand that when we were developing this in the late 1980's there were no computer simulations and the main measuring instrumentation was B&K 2010's and chart recorders. We had just acquired a TEF-10 (a piece of transformatively innovative technology, look it up) and were beginning to learn how to use it, but it played almost no part in the F2B's development.

Thanks for clarification, I did wonder if you might comment!

I don't think there is anything at all wrong with developing by experimentation. It's by no means easy and I think you guys did a great job, using what was available at the time. Computer modeling tools should make iterative development a lot quicker and cheaper, and drivers have certainly improved, but it doesn't seem to have worked out like that with cabinet designs.

I do find it a bit ironic, that with all of today's focus on even coverage and noise control, the excellent sound and directivity available, from well designed, properly arrayed, compact bass horns, seems to have been forgotten by many. I think it's a shame, that most manufacturers have now gone in a very different direction with their products. 

But the fact that F2B still commands such respect after all these years shows what's possible, so I hope at some point a few more designers besides e.g. Tom Danley, see this as an opportunity.


Edited by Sonic the hedge - 28 October 2021 at 11:40am
Back to Top
bob4 View Drop Down
Old Croc
Old Croc
Avatar

Joined: 29 February 2004
Location: Finland/Germany
Status: Offline
Points: 1633
Post Options Post Options   Thanks (0) Thanks(0)   Quote bob4 Quote  Post ReplyReply Direct Link To This Post Posted: 30 October 2021 at 7:11pm
Originally posted by toastyghost toastyghost wrote:

 
The Heyser lecture videos uploaded last year on the AES from the late 70s and early 80s are truly mind-blowing stuff. Audio wasn't even his bloody job! I wish I was so good at my 'hobby' that I changed the entire industry who do rocket scientists think they are, eh?

https://www.aes.org/technical/heyser/
Open access, so dig in. Bring a big bag of popcorn, a pot of coffee, and a notepad cos you’re gonna do some learnin’


Kyle, I can't see any links or videos on that page, does it require one to be lo gged in, and being an aes member?

Regards, Bob
Back to Top
toastyghost View Drop Down
The 10,000 Points Club
The 10,000 Points Club
Avatar

Joined: 09 January 2007
Location: Manchester
Status: Offline
Points: 10464
Post Options Post Options   Thanks (0) Thanks(0)   Quote toastyghost Quote  Post ReplyReply Direct Link To This Post Posted: 30 October 2021 at 7:30pm
Don’t think so, I see the links when I’m logged out (which is often because the new login system for the AES hates me).

But the really good one is also available here:
https://www.prosoundtraining.com/2021/02/04/heyser-videos/
Back to Top
 Post Reply Post Reply Page  <1 789
  Share Topic   

Forum Jump Forum Permissions View Drop Down

Forum Software by Web Wiz Forums® version 12.03
Copyright ©2001-2019 Web Wiz Ltd.

This page was generated in 0.152 seconds.