jessie.dazzle wrote:

I didn't know rigid (hard) foam was available in a spray can. Be careful; if you're using proper rigid foam, it expands with great force and would likely push through any tape protecting the cone of the driver. However, the only really rigid foam I know of is a 2-part product that must be mixed in proper proportions. If high density is desired, the reaction must take place in a confining (volume-limiting) and very strong container. http://www.uscomposites.com/foam.html

Romy wrote:

"...Let pretend that you play a normal some kind of horn with a lot of air in it. The air drives the driver impedance down..."

I'd like to understand this; correct me if I'm wrong:

As soon as the membrane of a horn-loaded driver starts to move, that membrane sees the air mass located in the horn as a load. Because the air inside a horn is confined by the walls of the horn, this load will be greater than what the membrane would see if operating in free air or as a direct radiator. The result is a pressure inside the horn fluctuating between greater and lesser than normal atmospheric pressure outside the horn; the difference being most pronounced at the throat of the horn. 

It would seem fair to say that this load physically "impedes" movement of the membrane, and that a horn-loaded driver will experience greater resistance to movement, or greater physical impedance than would an identical but non-horn-loaded driver.

Are these conclusions correct? If they are, then does that increase in physical impedance equate to an increase in electrical impedance as seen by the amplifier? If so, can it not be said that "driver impedance" has in effect been increased by the load (the air in the horn)?

jd* 

jessie.dazzle wrote:

Romy wrote: "...Let pretend that you play a normal some kind of horn with a lot of air in it. The air drives the driver impedance down..." I'd like to understand this; correct me if I'm wrong: As soon as the membrane of a horn-loaded driver starts to move, that membrane sees the air mass located in the horn as a load. Because the air inside a horn is confined by the walls of the horn, this load will be greater than what the membrane would see if operating in free air or as a direct radiator. The result is a pressure inside the horn fluctuating between greater and lesser than normal atmospheric pressure outside the horn; the difference being most pronounced at the throat of the horn.  It would seem fair to say that this load physically "impedes" movement of the membrane, and that a horn-loaded driver will experience greater resistance to movement, or greater physical impedance than would an identical but non-horn-loaded driver. Are these conclusions correct? If they are, then does that increase in physical impedance equate to an increase in electrical impedance as seen by the amplifier? If so, can it not be said that "driver impedance" has in effect been increased by the load (the air in the horn)? jd*

unicon wrote:

Roman,  first of all I feel good about your bass horn that's what i have always bin dreaming and if i get the space for it wont even waste a minute I think you already know it or using it ... You mentioned using a foam in  back chamber so it adds a mass in driver and then the Fs goes down. thats a great idea and it works.and besides coupling your driver to horn you can simply measure how much is the added mass of it. I suggest that you do add the mass in driver like coins in driver cone(and measure the coin weight too) and do added mass free air impedance test then you can see where it can bring another low resonance .then when it reaches 20% lower the free air you are getting the most out of your driver  .so in loaded horn you can be sure how much foam to add and having the goal impedance you can be almost sure everything is right. and i suggest not to try more than 20%

Romy the Cat wrote:

If you do add mass to driver then you get exactly opposite effect as you will be dropping the Fs even lower, so I do not see your logic. The Cat

Romy the Cat wrote:

I also do not see a need to wary about the actual mass. We worry about mass ONLY in context of resonance frequency. So if we measure the resonance frequency and set it where it hall be then why do we worry about the actual mass? The Cat

I think my carpenter got another job as he is kind of working lastly 3-4 hours per day. I would like to finish the project ASAP therefore I have built a simple project plan and the following check points:

Sunday, August 12

Construction is finished. All primary and secondary elements are glued. Horns are sanded and primed. Back chambers are built. Horns are lifted to listening room and positioned for final assembly.

Friday, August 16

Horns are assembled. Final finish appalled. The back chambers are tune to the 42Hz. The lifting up mechanism is devised and horns are positioned to be lifted. The attic aria is prepared and cleaned up to accept the horns. The center poll beam is installed.

Saturday, Sunday August 18, 19

The horns are lifted up to the default position in the attic.

Friday, August 24

The horns are attached to the house frame. The attic support beams are installed. The horn supporting framed are built and installed. The horns are connected and tested at max pressure. The resonating framing joins are identified and taken care of. The drywall around the horns mouth and around the center poll beam re-built. The wall plaster is applied and sanded.

Thursday, August 30

The horns are spot-re-painted where necessary. The walls are painted. The final touch up and cleans up. End of the project.

Romy the Cat wrote:

I feel that we deal with damping resonances that are not necessary directly related to solidity or to strength. The Cat

Romy the Cat wrote:

Talking about the resonances. I have no idea how to deal with it. Yes, I monitor what need to be monitored and have/developed tools, skills and knowledge to deal with it but I have no way to predict how the existing or none-existing resonances will impact the harmonics of the future sound. I have a very clear idea what harmonics I would like to get but I have no idea how resonance at this or that surface would impact it. So, it is like bringing up a child – you do what you hypothetically feel to be the beast and parry that it would turn out all right. Meanwhile, I spend in basement in dirty clothes most of my time nowadays and I do pray that this episode of my life will be over. The Cat

unicon wrote:

If I were you I would set up all things so that when the mid bass is in his place i can reconfigure the baffle tightness by using a huge DIY made screwdriver from the opening mouth...or wherever it can be reachable then monitoring the impulse results .you already know what a good result should be.

Unicon,

those horns that I working on now are much larger than any imaginable DIY made screwdriver, even if you propose the “screwdriver” as a hypothetical device. The horns are huge and in a way overbuilt. It is as now is over 1000 pounds each and it has a very solid frame. The horn is made with plywood of good quality and plywood has no directional tension. The plywood attached to frame with Gorilla glue that itself is a bit dumping type of glue. The last few days, when the sections become too heavy to rotate for one person, the sections were accidently dropped during rotation. They were falling like a single brick – very heavy, solid and firm – there is absolutely nothing in there loose and to the best of my knowledge there are no two wood surfaces that touch each other and have no glue between each other. Why do you think I spend 6-7 hours per day after my work working on this thing? There is another aspect that I feel will work out. The horn mouth is the most resonating thing in horns but in my horn the very edge of the mouths will be the surface that will tight the horn to the house frame. A horn will be lying with mouth own upon 14 beam truss and will be attached to the trusses with 6” screws.  In fact it will be attached to the frame in 6 locations: