speaker assemble?

Question

hi so i have been working on a pair of speakers which are made of solid pine around 1\2 to a inch thick and i need to know how big should the port or vent be
bass 18 in ,8 ohm ,4 inch coil ,109ounce ,25-600hz, 8.5 cubic feet ,1250 watt
mid bass 300 watt, 200-6000hz ,1 cubic feet
9 cubic feet total, h45 l24 d17
box resonance in hz?
my email is [e-mail]
please help i have worked very hard on these speakers and i dont want to make a mistake after all that money and time spent

Answer 1

Successful DIY loudspeaker construction requires a very basic knowledge of loudspeaker theory combined with good woodworking skills.

From the information you've posted it appears that you're using a good quality 18-inch low frequency driver however your midrange driver is not sufficient for pairing directly with your 18-inch driver other than perhaps for a professional sound application. That said I'm sorry to say that you will be better served by starting over. You will need to obtain the proper Theile-Small parameters [1][2] for your drivers in order to determine the best enclosure alignments for each driver size as well as to design a proper crossover. You will also need to use much better, more appropriate materials (solid wood, let alone pine, is not an appropriate choice of material for constructing a loudspeaker enclosure other than perhaps in the form of a decorative veneer; see below for material recommendations.)

Fundamental Theile-Small Parameters required for loudspeaker enclosure design:
   • Qms and Qes (or Qts)
   • Vas (or Cas; or Sd and Cms)
   • fs
   • Mms
   • Xmax
   • Bl
   • Re

These and other design parameters are often published by loudspeaker transducer manufacturers for each of their individual models of midrange, mid-low frequency, and low frequency transducers (aka drivers.) The alternative is to individually measure each of your mid-low (or midrange) frequency and low frequency loudspeaker drivers in order to obtain the necessary Theile-Small parameters. Failing either of these your only remaining option is to use the trial and error method combined with a closed box enclosure design.

What follows are a few loudspeaker construction notes based on my personal experience.

One of the basic loudspeaker design considerations that I advocate for LOW FREQUENCY enclosures – and long favored by B&W Loudspeakers [3][4] – is the low mass, high modulus (high material stiffness) approach to LOW FREQUENCY enclosure design. (Low mass reduces the ability of an enclosure wall to store energy and high modulus allows the applied damping material to much more effectively control enclosure resonances. All things being equal a mechanically inert, non-resonant enclosure is a good enclosure.)

The best approach to building quality loudspeakers is using loudspeaker design software [5][6][7] along with related test and measurement equipment [8][9]; unfortunately this can result in quite a hefty investment and may be overkill for many. However, you will find that using the appropriate software and a computer will make the process of crossover design and optimization more accurate and much, much easier. Nevertheless, THE FIRST STEP FOR THE DO-IT-YOURSELFER IS TO START BY OBTAINING A COPY OF A GOOD BOOK ON LOUDSPEAKER (ENCLOSURE) DESIGN such as the Loudspeaker Design Cookbook by Vance Dickason [10].

Some materials and components with which I and others have had success building custom loudspeaker enclosures are as follows:

   • ½" and ¾" medium density fiberboard (MDF) for overall ease of working and cost [11]. Using the epoxy listed below consider laminating three ½" layers or two ¾" layers of MDF for constructing satellite enclosures; (for professional sound reinforcement applications use ¾" to 1" AA-grade marine plywood or ¾" Baltic Birch plywood);
   • ½" 9-ply or ⅝" 12-ply, void-free, Baltic Birch plywood for all internal bracing;
   • West System two-part epoxy from Gougeon Brothers;
   • Dacron polyester fiberfill or batting or Acousta-Stuff™ fiberfill;
   • Air core inductors;
   • Non-inductive wire wound and metal film resistors;
   • Low ESR and ESL metalized polypropylene or PTFE capacitors;
   • Speaker sealing gasket tape or non-hardening (elastomeric) caulk;
   • Heavy duty, gold plated, brass 5-way binding posts; (or Neutrik Speakon® Lockable Loudspeaker Connectors [12] for professional sound applications);
   • Textron TORX PLUS Fillister, Pan Head, or Socket Head cap screws paired with self-tapping, self-locking, threaded brass inserts for wood or fiber composite for fastening drivers and other hardware.

The best method for mechanically joining the individual enclosure panels is to use finger-joints (similar to dove tail joints but without taper) or better yet lock-miter joints; both require special woodworking equipment. ALL enclosures, including satellite enclosures, should be heavily braced internally using void-free, Baltic Birch plywood and all bracing should be dadoed and glued. (Screws or other metal fasteners are generally discouraged when assembling loudspeaker enclosures.)
 

Answer 2

You did not list some important parameters. To optimally speaker tune the enclosure you need to know the driver free air resonance usually listed as Fz in the dats sheet and the speaker Q. Q is the tendancy for the output to increase at the resonance frequency. I have built several speaker systems but that was 20 yr. ago and can't find the formula. I do know they are available online. Search for speaker building. I am guessing the speakers did not come with recomended cabinet sizes etc.
1/2" pine will probably not be stiff enough for an enclosure of this size though unless you have installed braces. Also do not forget to subtract the volume used by the damping material. Radio shack still carried hobiest books as recently as last year that had the formulae for enclosure volume and crossover design. Their older books by Forrest Weems were not the most in depth but were easy to understand and had all the basic info. Later edditions als came with design and performance prediction.

Answer 3

First off you need a budget to start with, also you do want satellite or floor standing speaker. When purchasing a speaker it is highly recommended that you demo any speakers with your own source of material and only listen to one item on each speaker you are interested in. Go online to Home Theater Magazine and read the reviews on speakers. Stay with name brands like Definitive Technology, Energy, JBL, Infinity, Klipsch, Paradigm and Polk Audio to name a few. Hope this will help you out.