Hello
This is my first post to the DiyAudio Forum so don't mind if I do some unusual stuff🙂
Here's my problem: I've decided to build a 2-way speaker system for my room with the VISATON W130S 8ohm drivers (see : http://www.visaton.com/english/artikel/art_452.htm), didn't decide which tweeter to use yet. My main goal is to build a cheap speaker system that will have a reasonable amount of bass (may sound a little funny). I used WinISD and an excel worksheet (see: http://www.diysubwoofers.org/prt/ported.zip) to calculate the optimum box volume. Since it is really small (18.5 -19 liters) the problem is how to design the box to fit in the port. I've read somewhere that the distance between the port and anything in the box should be min 7cm. Knowing this I thought of a few solutions:
1.) To have the port outside the box (ugly, don't want this)
2.) To have the base of the box small so the height would be large (tower, Could be nice but not for that (small) volume)
3.) To build a square port using the width of the box (hard to build, I don't think I can be so precise, only 1mm change in port height changes the port length by 0.5mm and more)
4.) To add a lot of braces to increase the outer dimensions of the box (I guess it would be pretty hard to stuff this kind of a box)
5.) To build a 2 driver box and double the volume (don't have the money for this, higher SPL, larger vent, same problem again)
...oh, and I forgot to mention that this is my first DIY speaker I plan on building...
Greetz
This is my first post to the DiyAudio Forum so don't mind if I do some unusual stuff🙂
Here's my problem: I've decided to build a 2-way speaker system for my room with the VISATON W130S 8ohm drivers (see : http://www.visaton.com/english/artikel/art_452.htm), didn't decide which tweeter to use yet. My main goal is to build a cheap speaker system that will have a reasonable amount of bass (may sound a little funny). I used WinISD and an excel worksheet (see: http://www.diysubwoofers.org/prt/ported.zip) to calculate the optimum box volume. Since it is really small (18.5 -19 liters) the problem is how to design the box to fit in the port. I've read somewhere that the distance between the port and anything in the box should be min 7cm. Knowing this I thought of a few solutions:
1.) To have the port outside the box (ugly, don't want this)
2.) To have the base of the box small so the height would be large (tower, Could be nice but not for that (small) volume)
3.) To build a square port using the width of the box (hard to build, I don't think I can be so precise, only 1mm change in port height changes the port length by 0.5mm and more)
4.) To add a lot of braces to increase the outer dimensions of the box (I guess it would be pretty hard to stuff this kind of a box)
5.) To build a 2 driver box and double the volume (don't have the money for this, higher SPL, larger vent, same problem again)
...oh, and I forgot to mention that this is my first DIY speaker I plan on building...
Greetz
Do you have the means to measure the impedance curve of the speaker + box to see if you've hit your desired alignment? If not, stop right here, do not even consider building a ported box of your own design.
If so, your comment about stuffing should be examined. Stuffing a reflex is generally not a good idea unless you already know that it will change QL in a non-predictable way. Normally, the T-S equations assume some wall damping, but a basically empty enclosure. Again, if you can measure what you're doing, fine, you can hit any alignment you want if you're aware that the QL will not be the assumed figure.
I'd think strongly about oversizing the box, using the square or shelf port, then tuning the enclosure by altering box volume. Bricks or rocks are very nice for that application. Otherwise, it's closed-box time.
If so, your comment about stuffing should be examined. Stuffing a reflex is generally not a good idea unless you already know that it will change QL in a non-predictable way. Normally, the T-S equations assume some wall damping, but a basically empty enclosure. Again, if you can measure what you're doing, fine, you can hit any alignment you want if you're aware that the QL will not be the assumed figure.
I'd think strongly about oversizing the box, using the square or shelf port, then tuning the enclosure by altering box volume. Bricks or rocks are very nice for that application. Otherwise, it's closed-box time.
Sorry but I have a "little" lack of knowledge in theory (of speakerbuilding) and english so I'm not sure what you meant. The only thing that I know that is called the "impedance curve" has ohms on the vertical axis and freq. on the horizontal axis. If that's the case I can measure it with Boxplot and LspCAD Lite but even then I don't know what to do with the data, I don't know how should a perfect box "react".See the attachment for the diagram.
What I meant by "dumping", was putting a thin layer of carpet or smtn like that, not the closed box kind of damping - my english problem again, sorry.
And What's QL?
Do you know a good website with theory explained?
What I meant by "dumping", was putting a thin layer of carpet or smtn like that, not the closed box kind of damping - my english problem again, sorry.
And What's QL?
Do you know a good website with theory explained?
Attachments
tibor,
You could elbow the port inside the box to make it fit. Or... if you plan for the speaker to be 3 inches from the rear wall, elbow the port outside the box, so the port runs parallel to the wall (eg. vertically)
SY is correct about impedance peak measurement. That is the most accurate way to correctly tune a port for a box at a given frequency (eg. the peak impedance is where the driver is giving the most resistance to current flow from the amp, because it is being as damped by the port as possible). A cruder measure of tuning is to do a sine wave sweep around the tuning frequency (using WinISD for example) and look for minimum cone displacement. Easier for a sub - harder for a two way. To be honest I've never done this for a 2 way....
If you aren't sure - I'd stick with a closed box and get your bass by other means
Dave.
You could elbow the port inside the box to make it fit. Or... if you plan for the speaker to be 3 inches from the rear wall, elbow the port outside the box, so the port runs parallel to the wall (eg. vertically)
SY is correct about impedance peak measurement. That is the most accurate way to correctly tune a port for a box at a given frequency (eg. the peak impedance is where the driver is giving the most resistance to current flow from the amp, because it is being as damped by the port as possible). A cruder measure of tuning is to do a sine wave sweep around the tuning frequency (using WinISD for example) and look for minimum cone displacement. Easier for a sub - harder for a two way. To be honest I've never done this for a 2 way....
If you aren't sure - I'd stick with a closed box and get your bass by other means
Dave.
Now you got me confused. Take a look at the image sent before. The peak is somewhere around 70-80Hz. Winisd thinks the tuning frequency is 46Hz. So tuning the port to 46Hz would give the highest impedance at 70-80Hz? I dont' get it...
OK, you just tell me how to measure the impedance (and with what) and I'll do it. I thought the winisd values would be
sufficient and that I could make a perfect box just by cutting the right size pieces and putting them togeher, guess I
was wrong, Whatever, I won't give up on this easily.
OK, you just tell me how to measure the impedance (and with what) and I'll do it. I thought the winisd values would be
sufficient and that I could make a perfect box just by cutting the right size pieces and putting them togeher, guess I
was wrong, Whatever, I won't give up on this easily.
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