Speaker enclosure calculations

[cumesoftware]

I'm calculating a speaker enclosure for a multimedia speaker project of mine. However I want to do this in a decent manner. The speakers I'm using are Visaton models, the FR10 4OHM models, and have the following characteristics:
- Nominal impedance (Z): 4Ohm
- Frequency response: 80–20000Hz
- Maximum cone displacement: 8mm
- Resonance frequency (fs): 92Hz
- Diameter: 100mm
- Mechanical Q factor (Qms): 2,29
- Electrical Q factor (Qes): 0,7
- Total Q factor (Qts): 0,54
- Equivalent volume (Vas): 2,3l
- Effective piston area (Sd): 50cm²

I concluded that a ported enclosure would be better suited. Using the calculator (from ajdesigner.com) I came to the volume of 6.31 litres for a SC4 alignment. This alignment gave me the flattest frequency response and a reasonable enclosure volume. Indeed it enhances the bass, but only to the 0bD level (exacly what I want). The box should be suitable for all kinds of music, and therefore should have the flattest response possible. Besides SBB4 gave me a value of 3.14 litres, too small and QB3 gave me a value way too large. So far, SC4 is the most adequate alignment.

I double checked this values using the basic car audio electronics website. I need someone too see if anything is wrong, or if I'm choosing the wrong design.

Also, I don't know what SBB4, QB3 or SC4 means in terms of port alignment. Is there any website with examples on port alignments for ported designs? What are the main differences?

Plus, the software gave me several port lengths for several diameters, as such:
- 20mm diam.: 17mm
- 25mm: 31mm
- 30mm: 50mm
- 35mm: 72mm
- 40mm: 98mm
- 45mm: 128mm
- 50mm: 162mm
Is there any particular diameter and length I should use to fine tune the frequency, or the port diameter doesn't affect at all, as long as the port has the matching length?


Note: Please note that I'm aware that the efficiency of these particular speakers is low and that they "have no bass". Despite the charts, I've tried these speakers with a temporary open baffle made of expanded polystyrene and they sounded good. Even with no baffle they were better than some supposedly "Hi-Fi" speakers.
The point is, given the distortion of the TDA2003 amps, why using expensive speakers. With this project I wish to attain acceptable quality for low price.

[JLC7]

Well for the port diameters, the smaller the diameter it is, the shorter is can be. The drawback to that is you've got to deal with port turbulence due to the narrow opening. With a bigger diameter port, air doesn't have to move as fast, but you need a longer port overall which you might not have room for.

[cumesoftware]

Thanks. The software warned me for that for port diameters lower than 20mm.

What means SC4 in terms of alignment? Is it port alignment? Where should I locate the port?

Another question: Does the enclosure proportions affect sound? I'm using 14,8cm x 30,8cm x 15,8cm, which is a tall box. The box will have some wood pieces and a PC board inside, making the volume much closer to the ideal one.

[Ron E]

Originally posted by cumesoftware
Also, I don't know what SBB4, QB3 or SC4 means in terms of port alignment. Is there any website with examples on port alignments for ported designs? What are the main differences?

These alignments are simply known good starting points for enclosure design. They were once quite useful to reduce calculation requirements in the days before personal computers.
SBB4 is the so-called 4th order boombox alignment
QB3 is Quasi Butterworth 3rd order - for Q less than 0.4
SC4 is subChebychev 4th order - for Q less than 0.4
C4 is Chebychev 4th order - for Q greater than 0.4
B4 is Butterworth 4th order, for Q~=0.4
BE4 is Bessel 4th order - for Q~=0.33, IIRC

C4 is the most suitable for high Qts drivers like you have to attain flat response, but it can cause low excursion limited power handling if your driver doesn't have much excursion. Your software likely misnames C4 as SC4.

Originally posted by cumesoftware
Is there any particular diameter and length I should use to fine tune the frequency, or the port diameter doesn't affect at all, as long as the port has the matching length?

Use the largest diameter port whose matching length will fit in the box. Leave at least a port diameter between the inner end of the port and any wall. You can flare each end to reduce turbulence.

[cumesoftware]

Well, I find it difficult to find any ports suitable for my project (only can find 50mm diameter and up, and those won't fit.

To solve the problem I'm planning to make a port made of MDF, so it has 25mm diameter and 32mm long. Since I'm using 16mm thick MDF for the enclusure, I'm planning to glue a 40mm x 40mm piece to the back of the front panel and drill a hole with 25mm diameter. Thus, the thickness around the hole is 32mm. Is this reasonable?

[cumesoftware]

I've found a better solution. I will use the Monacor BR-30HP bass-reflex tube cut with 46mm (more mm or less mm). Its the only suitable tube I can find.

[PeteMcK]

try your local hardware store, buy some pvc plumbing pipe of the dia. you need and cut to length... much cheaper than from an electronics shop...

To get even lower, if you have bass tone controls available, you could consider tuning lower, around 50Hz, and boosting around 6dB to get a flat response. The only prob with this speaker is that tuning below Fs you'll probably run in distortion fairly quickly. To minimise this,I'd be inclinded to use a separate driver below say 150Hz.

Re: "they were better than some supposedly "Hi-Fi" speakers" - what did you compare them with? The FR10s are a bit hot in the upper region which may make them initially appealling, but would need to be tamed to make them approach "Hi-Fi".
http://www.soundlabsgroup.com.au/p/V.../FR+10+-+4+Ohm

[cumesoftware]

The separate driver option would be better than changing the bass indeed. This project is meant to be a cheapo, so I don't consider using a third driver. However, in the next project, a truly Hi-Fi one with integrated power suply, I'm planning to use 3" satellites (perhaps the FR8 or an high end proper satellite instead) along with a 8" woofer.

About the speaker, it is not truly Hi-Fi, but the quality is still suprising considering that it is a 4" midrange. And when compared with some other speakers of the same size that are claimed to be Hi-Fi, the sound seems warmer and a little better, although the middles are a bit harsh and tends to distort at frequencies below 100Hz. That means that the other speaker I've bought (I don't remember the brand) sucked and was not Hi-Fi at all.