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In the Forum: Horn-Loaded Speakers
In the Thread: Problems with horns: upper bass

Post Subject: On The Pursuit Of A Mid/Upper Bass DesignPosted by Dresden on: 11/14/2008

The throat diameter of 7" is what I first approximated as an acceptable size, with the 4" being an alternative (should some unwanted effects arise, I may then experiment with the 4" throat). I can't simply assume 7" will be correct (though that's my assumption), thus the idea of using a 4" alternative should a different approach be warranted. As you may have deduced, using a 4" will force me to have a portion of the horn curved behind in order to allow accommodation of the additional length (not necessarily something I'm interested in doing).

In relation to the size of the mouth, though it easily merits a size of approximately 6' x 4', I'm aiming to reduce that. (This is the reason I had inquired as to the positive [or negative] potential difficulties in obtaining a balanced horn loading arrangement using the acoustic energy from both the front and rear radiating surfaces of the driver. [This is also the reason for my deciding on that particular JBL driver--a compression driver will not allow me that flexibility.].) Should the initial design look (sound) promising, the end design would consist of both front and rear horn loading, the mouth of the horn being considerably less than normally seen in many current designs.

As to the cost, I will construct the main body of the horn myself--everything except for a considerable area of the front section (mouth) of the horn, given that said part of the horn will be cast, preferably using an acoustically 'dead' compound. (High-Density Polypropylene is one I've considered--the same material used to make kitchen cutting boards. However, a thermosetting compound is what I desire, cost being the detriment. Nevertheless, a thermosetting compound will most likely be the end material, given it's great quality against scuffs, and of course, it's strength.) The cost I'm really concerned about is the manufacture of the molds, which will have to be machined if modeled in SolidWorks. I could alternately approximate the shape of the horn by modeling the shape in clay, later to be glazed and 'fired', and ultimately used as the mold to build upon with a polymer. I may have to take that path if the cost of having the molds machined is dreadfully prohibitive. (However, that path is unforgiving in terms of time and potential frustration, thus my wanting to have the molds machined. One other personal impediment in that approach is that I have a hyper adversity to chemicals.)
for starters.)

Understand, I'm not trying to build something that is out of the reach of most people. I've seen systems (and corresponding designers/retailers) that demand what I would consider a nice down payment on a home for their creation. Good sound should only cost so much. On that same note, I will first look to schools for any portion of the horn I have manufactured--anything that will keep the cost of the project very low. I'm willing to sacrifice innumerable hours in place of what would normally be relayed to outsourcing. The bulk of the cost may go into the casting of the horn mouth, as well as another couple of areas I consider condidates for the process. One very important component I'm leaving out of the cost of the horn is amplification (the horns will be active, using class-D amps). The reason for my choosing class-D amplification is that the modules and various components for building what I consider very capable amplifiers can be purchased at low cost and assembled by me (again, the mantra is to save money for the purpose of appropriating it toward the casting of the horn mouth, said cost as of this date undetermined). I have found two manufacturers which offer class-D amplification at reasonable costs, said amplification capable of delivering the target power and sustainable performance (one is located in Germany, the other in England).

Past experiences have taught me that setting a specific deadline on certain projects yields only frustration and stress. Thus, once I begin building the horn I expect to complete it in a few months (most likely the length of one season). The unknown factor at the time is the cost of the casting. More importantly, if I cannot model the horn in SolidWorks (I acquired the training for the program recently), I will have to contract someone I can trust with that part of the project. (One motivation for doing so is that I know the modeling of the parts made for casting will require no more than approximately seven hours of work, which will keep the cost low.)

In terms of overall costs, again, the modeling/casting of the horn mouth section is a large, yet undetermined, contribution to the overall cost. As it pertains to the section of the horn I will build (which in reality, is most of the horn, which includes the entire body of the horn along with the rear facing horn mouth), it amounts to numerous sheets of plywood (I'm estimating seven at last count), along with portions made of Maple hardwood. All put together with minimal use of a router, a biscuit machine, and screws. I'm seriously considering using inserts and machine screws, along with a silicone seal, should I decide to build the horn out of sections, to be assembled once all sections are completed. (This explains the large, almost disproportionate amount of wood invested.) Implementing inserts and machine screws will undoutedly raise the cost of the project, but I completed a project this past summer using inserts and machine screws and am very satisfied with the finished results (it is a folding Japanese table [approx. 4' x 3'], with the ability to tilt the top up to 90 degrees for use as a painting or display table. I used a large amount of stainless steel screws, given that I wanted the table to be of Japanese influence in design with a modernist edge).

The cost of furniture-grade Maple plywood doubled in a single month this past summer. Perhaps it'll double again by Spring? All of a sudden, structural foam looks attractive.

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