Speaker box construction?

[ZmOz]

I have a pair of really nice Philips shelf speakers that had an unfortuneate incident with a forklift. I want to take the speakers out of the damaged casing and into a new portable box I can use in the boat.<br /><br />Problem is, I know nothing about speakers. Am I correct that the size of the air space inside the box has something to do with how they sound? How do I know how big of box to make, and what size "vent" hole to make? I want to keep it as small as possible...

 

[ZodFutMk2]

Re: Speaker box construction?

Google speaker enclosure<br /><br />good explanation here<br /><br /> http://electronics.howstuffworks.com/speaker9.htm <br /><br />Particle board or plywood works well.<br /><br />Under redneck projects here on the board, we saw ammo cans used as speaker boxes.<br /><br />Cheap plastic tool box would work well and would survive any environment.

 

[Pony]

Re: Speaker box construction?

ZmOz- typically air space and and vent holes apply more to sub woofers, and less to full range, 2-3 way speakers (still apply but less imprortant....asw in the volume isnt as big of a deal). If you stuff the box you put a speaker in, it essentially is "doubling" the volume. Or it will act as if the enclose is 2x as big. This is how you can get around the small box issue. I would say that the face of the box where the speaker should mount should be sized so that you have roughly an inch or so around the speaker. The depth of the box is up to you, but 5-8 inches should do the trick. I have made several Sub enclosers for my truck and car and have found MDF to be a good material, but water may give ya problems so plywood should work. I would also put silicone on all the seams from the inside to make it air tight.

 

[Andrew Leigh]

Re: Speaker box construction?

Hi,<br /><br />speaker design is fairly complex. To maximise your speakers the enclosure is critical as the cone size used in modern speakers is not large enough to produce the bass response required. This is artificially achieved by porting the box and "tuning" the port for the desired -3dB cutoff frequency.<br /><br />The response curve of the assembled speaker can then be plotted on log paper to illustrate where the speaker will become "boomy" or where the speaker will experience a cut in frequency. If the response curve does not follow the required shape then the size of the box and or the porting is altered until the curve shows a perfectly flat response. It is this box design that you will settle for.<br /><br />Three speaker parameters are needed to create an efficient design. If you do not have these it is possible to measure them by applying a sine wave through a signal generator through an apmlifier through a 1k0 resister and using the low range on a voltmeter.<br /><br />If you have access to software that will allow you to program in BASIC (an old ZX Spectrum or the likes) then I can fax you a copy of the program I wrote years ago as well as an article on design.<br /><br />If you dont won't to go to these lengths then calculate the INTERNAL volume of the box. See if you can find the port (if is has one) this may be a tube or round hole or slot in the speaker cab. Measure the are of the opening and the depth. Now by using the two to one principle make your box in the ratio 1,5 high x 1 wide x 1 deep. If it was ported replicate the port. Symmetrical speaker enclosures seldom work. <br /><br />For these ported designs you must seal all seams and where the speaker meets the box and where the cable come out. Good speakers reduce internal reflections of sound so be sure to line the insides of the box with ample felt or other suitable deadening material.<br /><br />A reflex speaker (no porting) has a much flatter response curve with undesirable rolloff of the bass.<br /><br />Remember the porting only helps the bass. All your mid tones tend to come directly from the speaker cone so you must have line of sight to the speaker for maximum effect.<br /><br />Lastly, if the background noise in your boat is loud then you will not hear any benefit. If you plan on using these when not under power, and you like good quality music then spend the time and effort.<br /><br />Hope this helps<br />Andrew

 

[Dave Abrahamson]

Re: Speaker box construction?

Aren't home speakers different from 12 volt car/boat audio speakers? I though there was an ohm difference.

 

[sangerwaker]

Re: Speaker box construction?

Yes there is Dave.<br /><br />Most car (and boat) audio amplifiers and speakers are 4 ohm while most home audio equipment is 8 ohm.<br /><br />You can use a higher impedence (ohm) speaker, but you will suffer output. It just plain ol won't be as loud as it would be with the correct (lower impedence) speaker. You shouldn't go the other direction. Using too low of an impedence will damage, and possibly melt down, your amplifier.

 

[ZmOz]

Re: Speaker box construction?

Alright, I'm still a little confused about how much volume the box has to have. I would imagine the volume of the box they are in right now is about perfect, so I could just copy that, but I want something smaller.<br /><br />If I put both speakers into the same box, does that effect the volume the box needs to be? If I line the inside of the box with something, how much smaller does that mean I can make it? (current boxes are unlined particle board)<br /><br />I believe these speakers are 6 ohm, and I'm hooking them up to an 80 watt car amp - I've already hooked them up to it and it sounds great.

 

[Andrew Leigh]

Re: Speaker box construction?

Hi<br /><br />If you want something smaller without going through the design then you will have to guess at the volume.<br /><br />If you put both speakers in one enclosure then the volume will need to be more. Be careful if you do that that you don't reverse connections and cause phase canncellation i.e. One speaker cone going the opposite direction to the other.<br /><br />The lining of the boxes is an issue for damping the internal reflections of the mid frequencies coming off the rear of the speaker cone, One therefor one can use lots of lining.<br /><br />Some enclosures use a polyester wool and stuff it into the cavity filling the entire cavity but without impeding the movement of the speaker. Low bass frequencies are omnidirectional and will go through most things whereas trebel is directional and will be absorbed.<br /><br />The key to audio is if it sounds good why change. If they sound good to you right now then don't change a thing. Most your sound is to be found in the range well above about 200hz and consequently one will often experience good sound without an adequate enclosure. Lots of guitar amps are open at the rear however most bass guitar amps have ported enclosures.<br /><br />I am willing to bet that the bass response is not what it should be unless the cone diameter is 8" or more.<br /><br /><br />Hope this helps<br />Andrew<br /><br />PS: I am seriously into HiFi and therefore may well offer opinions that will seek the perfect solution through design and experimentation. This tends to be over the top for most people who simply want to listen to music.<br /><br />Take you car speakers, they all go into different size doors with differing enclosure volumes!! Some speakers protrude into the trunk of the car which has a huge volume!! Yet they all sound good.<br /><br />If it sounds good it ain't broke, therefore don't try fix it.

 

[Triton II]

Re: Speaker box construction?

ZMOz, I used fibreglass house insulation matting (called bats here in Australia) to line my speaker boxes and sub. Works well, you can cut it with scissors and it's cheap. Wear rubber gloves when handling if you have sensitive skin. Good luck.