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Ported? Not ported?

post #1 of 5
Thread Starter 
I am going to be building bookshelf speakers with Rockford Fosgate P165's. The wood I purchased is 3/4" MDF. I have subwoofers so bass is not extremely important. I am more worried about my mids and highs. So, ported or not ported. That's the question.

Max
post #2 of 5
I would just start off with a simple sealed enclosure. Fill up the inside with that foam stuff (search around on parts express and read the reviews before you buy). It's basically foam insulation, I just forget the name of it.

Anyway, also make sure your impedance matches up to whatever amplifier you plan to use. Those are obviously car speakers, so they're likely 4ohm or 2ohm. A lot of home equipment is only rated to handle 8ohm. If you have 8ohm power, and the speakers are 4ohm, just use 2 pairs of them in series for 8ohm per side. thumb.gif
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post #3 of 5
Quote:
Originally Posted by Fremish View Post

I am going to be building bookshelf speakers with Rockford Fosgate P165's. The wood I purchased is 3/4" MDF. I have subwoofers so bass is not extremely important. I am more worried about my mids and highs. So, ported or not ported. That's the question.

Max
As you're about to find out, there's a lot more to speaker cabinet design than ported or not ported.
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post #4 of 5
Thread Starter 
Quote:
Originally Posted by pioneerisloud View Post

I would just start off with a simple sealed enclosure. Fill up the inside with that foam stuff (search around on parts express and read the reviews before you buy). It's basically foam insulation, I just forget the name of it.

Anyway, also make sure your impedance matches up to whatever amplifier you plan to use. Those are obviously car speakers, so they're likely 4ohm or 2ohm. A lot of home equipment is only rated to handle 8ohm. If you have 8ohm power, and the speakers are 4ohm, just use 2 pairs of them in series for 8ohm per side. thumb.gif

Noted, cheers.

Quote:
Originally Posted by billbartuska View Post

As you're about to find out, there's a lot more to speaker cabinet design than ported or not ported.

Lol, yeah. I did, it's an infinite baffle speaker, so, I decided to allow the lows to go away, I'm more interested in the mids and highs. I have the back of the enclosure open. Two speakers per channel... The amplifier is only 8Ohm stable and the speakers are 4ohms, so I have two 4 ohms. They sound good. I'm happy...
post #5 of 5
Using more than 1 tweeter per channel will cause as much destructive interference as constructive coupling depending on listening position. The result typically manifests as increased non-linearity and and a loss of the top octave/s response almost entirely. More is not always more in the case of speakers but it's no big deal, they will still make sound wink.gif (as I'm sure you already know)


Car speakers are typically voiced for less-than-2pi space loading (that is, if they are "voiced" at all.) When moved onto baffle used in near-free-space the space-loading (diffraction) changes significantly. The speakers will undoubtedly suffer from uncorrected baffle step loss issues that will manifest as a "thin" sounding speaker (falling response somewhere below 1Khz, depending on baffle width).


In effect, I would expect the speakers you have created to play lows and highs more quietly than the ideal "flat" response (don't take this the wrong way, non-flat responses are normal in lots of consumer speaker products anyway). Correcting for this in the series wired configuration with passive components is not likely practical. Set your EQ to the "smiley-face" shape and they will actually be closer to playing flat. They will probably need about 4-6dB or more boost on both ends. If you found that you had already EQed this way to get them to sound to your liking then you have good ears wink.gif

Regards,
Eric

PS: The open-back box design will behave as a bi-pole to some extent, which may deliver some constructive effects but will mostly complicate things as it will produce a more pronounced and sudden low frequency drop-off in response just below a spike in response known as a dipole peak (the frequency at which the wave propagated from the rear of the driver diffracts around the baffle, and couples with the wave propagated from the front of the driver in phase). This drop-off below the peak can not be "recovered" via any reasonable amount of EQ as you will simply drive the speakers into over-extension before ever overcoming the destructive coupling losses. Placing a back on the box, and experimenting with an additional resonant system (a port) will give you some leverage to "tune out" some of the baffle step losses. Since you have a sub, I would suggest tinkering with tuning frequencies in the 60-120hz range for starters to see what sounds best in your application. (use a simple box simulation program like winISD to find port diameters/lengths required to achieve a specific tuning frequency in your box. You can use any driver for the simulation itself just ignore the simulated output as it won't apply to your situation.)
Edited by mdocod - 11/8/13 at 10:07pm
     
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