Hello, I have two 6x9 inch 4 ohm speakers that I want to build separate cabinets for. I think the the speakers are car speakers. Would these speakers require cabinets sealed or open back?

What would be a recommended program for designing speaker cabinets?

It depends on how discriminating the listener's ear is. To answer the question properly, you would need to determine the speaker parameters which can be done by building a 1 foot square test box and then taking some measurements. That will tell you whether a ported speaker would be appropriate for those cones or whether a sealed speaker would be more appropriate.

Generally speaking, a sealed speaker is better when one hasn't made measurements and calculations, as a ported speaker will introduce all kinds of resonances and artifacts unless it's tuned properly. A sealed speaker (aka acoustic suspension) often sounds tighter, where a ported speaker (aka bass reflex) gives a lot more bass. The problem comes when the bass is all in one or two notes, then it's very unsatisfactory. The sealed speaker mitigates this possibility substantially.

I definitely do not want to build a cabinet with bass reflex to save me the hassle, however I am debating an open back cabinet or a sealed one. What type of cabinets do car speakers generally have?

Many 6x9 car installations from the factory are in the rear deck which peers into the trunk. Thus most such installations can be considered a sealed enclosure.

Okay, will the size of the sealed cabinets matter for the speakers?

The size of the box does change the characteristics of the bass notes. But many many people have put 6x9 speakers in nominal noncalculated size cabinets without regard or complaint about the sound. It is a common way to DIY a set of shop or garage speakers. An example size would be 12 inch tall x 8 inch wide x 6 to 8 inches deep

+1

Please don't use an open back enclosure. You'll wonder why you even did the project. Any type of sealed enclosure will be better than that even if it's not much bigger than the speakers themselves. However I do recommend you use a size at least as big as what Dale is recommending to have decent sound at all. Those 6 x 9 auto speakers are capable of really good reproduction when implemented. correctly.

It's important to remember that good speakers are often referred to as a system. The driver is just one part of it but equally important if not more important are the components that cause the driver to work to its best advantage. This is why an open box is pretty much worthless except as a driver holdet.

Here's a suggestion. When you get your stereo pair built, temporarily leave the back off of one so you can compare the sound with the sealed box. Then let us know how satisfactory you think the open box sounds.

P S. If you're going to go to all that much trouble anyway, use as thick wood for the box walls as you can, use some internal bracing that is offset from midpoints, and fill the box with inexpensive pillow stuffing that you can get at the fabric store. Those three techniques can reduce unwanted and annoying resonances that tire the ears.

Most car trunks aren't perfectly sealed so that could be considered as more of an infinite baffle type of enclosure.