What is the Barefaced hybrid resonator design?

[martyy]

I've been following @stevie and @Phil Starr's adventures in cabinet design for a while now and it has gotten me very interested in the subject. The most recent lockdown cab build got me thinking about what it it is technically that makes some of the most popular cabs special. The Barefaced one10 is a firm favourite and by some claims you would think it defies physics

I understand that "hybrid resonator" is a marketing term, but what is it really? Having done some digging through ancient forum posts it seems like it is a double chamber reflex design, specifically a fostex double bass reflex design. Am I close? As I understand it, the difference between this and the typical bass reflex design is that it reduces cone excursion at certain frequencies? And some extra bracing as a side-effect?

I would like to be able to come up with own designs but I feel like I need to read a few books on this topic first...

[Bill Fitzmaurice]

I've yet to see a technical description or a picture of the innards that shows what it is. It may be a double bass reflex with a passive radiator connecting the two rear chambers as opposed to a port, but that's purely a guess without any evidence to back it up. There's no defying physics, nor much new under the sun for that matter. All reflex cabs reduce cone excursion. While most do so only at the tuned frequency of the box it's possible to have more than one tuning frequency, as in a double bass reflex, to reduce excursion at more than one frequency.

[martyy]

Based on an old post here, an internal slot port can be spotted by looking through the external round port. So maybe not a passive radiator.

[Phil Starr]

There are a lot of manufacturers claims that seem to defy the laws of physics. There's also very little new under the sun when it comes to speaker design. There were a lot of designs in the 60's and 70's which claimed to be hybrid resonators, resonating at more than one frequency. That's the earliest mention I know of the term but I haven't had a chance to look at the Barefaced design in detail so I can't really comment.

As to books there's a couple I like: The Loudspeaker Design Cookbook by Vance Dickason is great but can be expensive unless you find an early version secondhand. The other I like but it's a bit technical is High Performance Loudspeakers by Martin Colloms. It'll be fine if you have A Level Physics or Maths. I hope they are both still in print

Most of the actual design work is done by software nowadays. Most of us amateurs use WinISD which is a bit of freeware. It helps if you know a bit of theory when you are driving the software but it works pretty well if you follow the recipes.

[martyy]

Thanks Phil. I actually do have A level physics and maths funny enough, so maybe I will see if  I can actually remember any of it and seek out those books. 

I have tinkered with winISD but I don't understand a lot of it, I think I need to get some more of the theory first.

[Phil Starr]

3 hours ago, Bill Fitzmaurice said:

I've yet to see a technical description or a picture of the innards that shows what it is. It may be a double bass reflex with a passive radiator connecting the two rear chambers as opposed to a port, but that's purely a guess without any evidence to back it up. There's no defying physics, nor much new under the sun for that matter. All reflex cabs reduce cone excursion. While most do so only at the tuned frequency of the box it's possible to have more than one tuning frequency, as in a double bass reflex, to reduce excursion at more than one frequency.

 

Just now, Phil Starr said:

There are a lot of manufacturers claims that seem to defy the laws of physics. There's also very little new under the sun when it comes to speaker design. There were a lot of designs in the 60's and 70's which claimed to be hybrid resonators, resonating at more than one frequency. That's the earliest mention I know of the term but I haven't had a chance to look at the Barefaced design in detail so I can't really comment.

 

Spooky, I actually typed this up a few hours ago and forgot to 'submit reply'. Anyway it must be true then

 

[Bill Fitzmaurice]

If you want to see how little there is in the way of new speaker technology read 'Elements of Acoustical Engineering' by Harry Olson, 1957. http://cyrille.pinton.free.fr/electroac/lectures_utiles/son/Olson.pdf

The only major item missing is the use of Thiele/Small parameters, which came along eight years later. Most of what's contained in the 1957 printing was contained in the 1940 first edition. The math (or maths, if you prefer) hasn't changed. What has changed is the hardware, which has allowed significant reductions in enclosure size and increases in output, although much of the alteration in driver technology is tied to amplifier technology. When 20 watts was the largest amp available speaker power handling mattered little, while speaker sensitivity mattered a lot.

Edited March 20, 2021 by Bill Fitzmaurice

[MOSCOWBASS]

This from Alex on Talkbass:

"A port has one tuning frequency and the effect is very much like moving the lowest slider on a 12 band graphic EQ up by a fair few dB.

The hybrid resonator has two tuning frequencies, one lower than a typical port tuning frequency, one higher. Its effect is more like turning up the bass knob on a 3 band EQ by about two dB."

 

[Bill Fitzmaurice]

That pretty much describes a double chamber bass reflex box. The oldest example of that design that I recall was in 'Designing, Building and Testing Your Own Speaker System', by David B, Weems, first edition 1981. I doubt that Weems invented that alignment, so it probably dates back further than that.  

[martyy]

The Weems design has two external ports (one from each chamber) and one internal port, whereas the barefaced (I think) has one internal and one external. There is info out there on how to tune the Weems design, but I couldn't find anything on calculating the alternative double chamber designs.

Edited March 20, 2021 by martyy

[Phil Starr]

Hi Marty, this was all before Thiele and Small who developed the theories behind the current computer modelling. Over simplifying they treated the elements of a speaker as electrical elements of a tuned circuit. Before that we understood Helmholtz resonators and that was how they calculated the frequencies of tuned cabinets. The rest was little more than guesswork guided by experience. There were even designs with two different sized inside the same space, treating the ports as being independent of each other. these were the designs I first saw described as hybrid resonators from memory but I couldn't find a reference going that far back. The conventional double cavity speaker is so well known WinISD will model it for you.

[Bill Fitzmaurice]

There's more than one way to make a dual chamber bass reflex. For that matter there's more than one way to make just about any alignment.