Exotic CNC'd 100Hz-600Hz bass horn - help sim please

Status
This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.
Looking at a new design for Tractrix base horn, target 100hz to 600hz

Attached, see drawing showing:

Varying mouth sizes from 4032cm sq to 4608cm sq

Throat can be sized to suit driver/horn (notionally 110cm sq to 260cm sq)

Back chamber vol notionally at 22,800 cm cube (0.8 cubic foot)

Three driver specs shown of B&C 8, 10 and 12 inch.

Axial horn length 1.4m (55 inches)

My questions:

Which driver size to aim for given horn range?

What size throat once q1 decided?

What size throat?

What best/max width of can to increase mouth size to suit? (I wish to limit height to 120cm, and prefer to keep width under 42cm.

Any help greatly appreciated.

Andrew.
 

Attachments

  • image.jpg
    image.jpg
    520.9 KB · Views: 431

GM

Member
Joined 2003
Fs wise the 8PE is the best 'fit', but probably a poor choice for what you want to do. That said, setting an arbitrary length, then trying to 'fit' a driver to it to cover a specific BW is well beyond my math skills without access to my various Excel designer programs, so 'sounds' like you need to fire up Hornresp and let its designer help you.

GM
 
Fs wise the 8PE is the best 'fit', but probably a poor choice for what you want to do. That said, setting an arbitrary length, then trying to 'fit' a driver to it to cover a specific BW is well beyond my math skills without access to my various Excel designer programs, so 'sounds' like you need to fire up Hornresp and let its designer help you.

GM
Thanks Greg.

The 'arbitrary' setting of the horn length is just a starting point, as I have some cab size restrictions.

If the exercise yields a smooth horn profile, untruncated, and min 100hz, I'll be happy.

Thanks for the tip on the 8PE....I used this driver once before in a John Inlow horn.

Kind regards

Andrew.
 

GM

Member
Joined 2003
GM, one other question I firgot to post, why do you suggest the 8PE is not ideal for the mid bass application I'm looking at? Do you have another driver in mind? Kindly.

In general, the smaller the [prosound] driver, the higher its Fs, ergo the higher its lower and upper mass corners [Flm = Fs*Qts/2, Fhm = 2*Fs/Qts], so for a tractrix the throat size tends to be > driver Sd for an optimum alignment, ergo either dual [or even quad] drivers or a larger driver with different specs is required to keep the horn as short as practical.

In short, you theoretically want a driver with specs that has a ~600 Hz Fhm with a ~1:1 CR that when pre-loaded with a reasonably small rear chamber 'rings' at [~100-600 Hz]^0.5 = ~245 Hz.

At a glance then, an 8 - 10" driver is required since 600 Hz = a ~7.2" dia., though this will make for a long horn, but if we truncate it where the throat is ~1 WL across, then dual 12" or a single 15" with the right specs can be used. This was the 'breakthrough' solution in the '40s to get a low frequency horn in a short enough cab to also be physically time aligned with the HF horn, and why it's still in use today, though DSL's designs and its [illegal] variants are slowly, but surely, going to make them as obsolete as they deserve to be.

GM
 
Moderator
Joined 2008
Paid Member
With your indulgence, Andrew.
though DSL's designs and its [illegal] variants are slowly, but surely, going to make them as obsolete as they deserve to be.
Interesting point of view, but I see the co-entrant horn as a separate matter.

If a good way to guide a mid and a tweeter means their horns turn out to be similar, peoples discovery of this through the synergy may be pure coincidence. I may be missing your point.

Otherwise synergy profiles are considered under a more limiting set of constraints, not that that has to be a problem. Why don't you like tractrices in the lower mid band?
 
How so?

Whatever most accurately reproduces the signal over the best defined polar response at the lowest distortion, highest average/peak SPL supercedes all else in its category to my way of thinking. Due to my experiences with lightning strikes, my foremost criteria in a system is how well it can reproduce a recorded one WRT its 'hair raising' transient 'attack' and while some speakers have come reasonably close in some ways and my last system seemed the best overall, none before the SH50/DTS20 system could actually 'trigger' this involuntary response.

For serious listening, once I built my first conical horn I've been pretty much against using any 'rising on axis' horn above ~80 Hz. For other, less critical apps, might as well use an expo or hypex to get the extra power/BW.

GM
 
Moderator
Joined 2008
Paid Member
Thanks, my experiences also.. except I'm not convinced it is the co-entrant horn per se, but two indirectly related things. One is the profiles as you mention, how the sound enters the room more than how the driver is loaded.

The other is the crossover, which is like shooting fish in a barrel with a synergy horn. My method for dealing with crossing separate horns takes several dozen measurements and thousands of calculations and is similar to the way Dr Geddes does his. It also relies on careful acoustic design in the first place. The synergy obviates all this work.

I know that many of us (present company excluded ;)) jump a few rungs in each new design which is fine if we don't jump to conclusions about the results. I'm not convinced that many people can truly do a crossover right for physically displaced drivers so I'm reluctant to blame this unfairly.
 
In general, the smaller the [prosound] driver, the higher its Fs, ergo the higher its lower and upper mass corners [Flm = Fs*Qts/2, Fhm = 2*Fs/Qts], so for a tractrix the throat size tends to be > driver Sd for an optimum alignment, ergo either dual [or even quad] drivers or a larger driver with different specs is required to keep the horn as short as practical.

In short, you theoretically want a driver with specs that has a ~600 Hz Fhm with a ~1:1 CR that when pre-loaded with a reasonably small rear chamber 'rings' at [~100-600 Hz]^0.5 = ~245 Hz.

At a glance then, an 8 - 10" driver is required since 600 Hz = a ~7.2" dia., though this will make for a long horn, but if we truncate it where the throat is ~1 WL across, then dual 12" or a single 15" with the right specs can be used. This was the 'breakthrough' solution in the '40s to get a low frequency horn in a short enough cab to also be physically time aligned with the HF horn, and why it's still in use today, though DSL's designs and its [illegal] variants are slowly, but surely, going to make them as obsolete as they deserve to be.

GM
Thanks, I confess to not being to keep up with all of this.

Can I summarise your point by saying a quality 12 inch, eg 12PE32 or Faital Pro 3012 but make throat equal to SD of driver? This way, I retsin the horn length and mouth size. I'll still need to sim that to see if smooth enough in my target range 100-800hz.

Cheers.
 
Moderator
Joined 2008
Paid Member
I want GM to answer your question but in addition I'd like to add that the further out you place the throat, the more the normal wavefront is expected to bend outward. The correct throat angle will be greater. If you distort the wavefront by supplying closer to a plane wave this could make the profile incorrect and modify diffraction/HOM.
 

Attachments

  • a.png
    a.png
    71.6 KB · Views: 152
Thanks, I confess to not being to keep up with all of this.


You're welocme!

Yeah, I'm a tough read for horn neophytes, but don't want to spend the time rewriting what's already available in various books, JAES papers, etc..

Personally, I'd use a 15" mid-bass horn driver such as the Altec/GPA 515-8G or similar B&C/whatever with a 2:1 CR, but a 12" with a 1:1 CR works too, especially if you're bumping it up to 800 Hz.

GM
 
You're welocme!

Yeah, I'm a tough read for horn neophytes, but don't want to spend the time rewriting what's already available in various books, JAES papers, etc..

Personally, I'd use a 15" mid-bass horn driver such as the Altec/GPA 515-8G or similar B&C/whatever with a 2:1 CR, but a 12" with a 1:1 CR works too, especially if you're bumping it up to 800 Hz.

GM
Ok thanks. Altec I can happily live with....my current rig is a pristine 420a in a 6+ cubic foot cab and 340hz le leach Azura horn with Faital Pro HF200 CD. great overall sound.

The mid bass horn is just a bit of a dream for now, but I love building horns.

If 12 or 15 inch, should I am for throat size of driver SD?

Regards
 
Thanks, my experiences also.. except I'm not convinced it is the co-entrant horn per se, but two indirectly related things. One is the profiles as you mention, how the sound enters the room more than how the driver is loaded.

The other is the crossover, which is like shooting fish in a barrel with a synergy horn. My method for dealing with crossing separate horns takes several dozen measurements and thousands of calculations and is similar to the way Dr Geddes does his. It also relies on careful acoustic design in the first place. The synergy obviates all this work.

I know that many of us (present company excluded ;)) jump a few rungs in each new design which is fine if we don't jump to conclusions about the results. I'm not convinced that many people can truly do a crossover right for physically displaced drivers so I'm reluctant to blame this unfairly.

You're welcome!

Well, it's all part n' parcel of designing this or any other system to suit the needs of the app.

Thousands/horn system?! I haven't done anywhere near this much in my entire design/building 'career', but then I basically followed what the pioneers did, so doubt they would pass 'muster' with the high tech crowd around here.

Yeah, if one gets the acoustics right, the XO should be no harder than in a typical horn 3 way and for HIFI/HT apps where desired peak SPLs are much lower than for prosound apps, I assume that some design 'liberties' that I've taken to further reduce XO complexity in my late horn system will work with a uni-horn also.

Agree that even the simplest XO is the 'stumbling block' for most DIYers, though guessing that some of the software available these days makes it a trivial exercise to design if they can import actual measurements.

GM
 
Ok thanks.

The mid bass horn is just a bit of a dream for now, but I love building horns.

If 12 or 15 inch, should I am for throat size of driver SD?

You're welcome!

I use to also! Built enough different proven types/variants to figure this stuff out 'good enough' without much help/math skills.

Again: "I'd use a 15" mid-bass horn driver such as the Altec/GPA 515-8G or similar B&C/whatever with a 2:1 CR, but a 12" with a 1:1 CR works too, especially if you're bumping it up to 800 Hz."

GM
 
Moderator
Joined 2008
Paid Member
Thousands/horn system?!
Sound field and power calculations, the algorithms only need to be written once. It could be done by ear of course but maybe not mine, just yet :(

Regarding 1:1 compression ratio. In the subjectivists camp I've heard that a cone should always be under compression in a horn or it will sound bad. In the objectivists camp they say that cone size (implying CR) isn't as relevant to horn design as motor strength and the horn. And option C, the throat baffle acts as a phase plug.

Is it fair to ignore option A even when using a type of horn that loads?
 
Status
This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.