Hi,
I have an old pair bigger sized bookshelf speakers, a pair of Infinity Reference i21. These are a two way design with a 8-inch woofer. They are made from chipboard and have a wood imitation wrap that have seen better days, but they sound quite alright. Not the best speakers I heard or owned, but good enough to motivate me into a project to take me mind from other things.
I'm creating this thread to get some help throwing ideas. Maybe it will turn into a build thread. My main goal here is to have have some fun woodworking. But I also want to get some practice in speaker building and do my best to get the best result.
Plan is to reuse drivers and crossover. Basically just build a new enclosure and move everything over. Ideally we would need the T/S-parameters for the woofer to properly design the enclosure, but I haven't had luck finding this. Instead, it going to be a bit a guessing game that I hope someone here will join me in.
I found an old catalog from 1996. From that I know that the same drivers is used in the i21 and the almost twice sized i31. Maybe this can provide some clues...
F3 was however just 4 Hz lower in the i31.
I took out the drivers and measured the cabinet. I estimate the volume to 22 liters, excluding drivers, brace and so on. Port is 49 mm in diameter and 165 mm of length. According to an online calculator I found, this would mean a tuning frequency of 36 Hz. Agree?
What is then best approach? Just aim on same volume and tuning? Or should I increase the volume and lower the tuning to try to get some more bass? If I do lower the tuning, I believe that a risk is that the bass rolling of earlier, meaning deeper but weaker bass? Am I wrong?
Much thankful for any input 🙂
I have an old pair bigger sized bookshelf speakers, a pair of Infinity Reference i21. These are a two way design with a 8-inch woofer. They are made from chipboard and have a wood imitation wrap that have seen better days, but they sound quite alright. Not the best speakers I heard or owned, but good enough to motivate me into a project to take me mind from other things.
I'm creating this thread to get some help throwing ideas. Maybe it will turn into a build thread. My main goal here is to have have some fun woodworking. But I also want to get some practice in speaker building and do my best to get the best result.
Plan is to reuse drivers and crossover. Basically just build a new enclosure and move everything over. Ideally we would need the T/S-parameters for the woofer to properly design the enclosure, but I haven't had luck finding this. Instead, it going to be a bit a guessing game that I hope someone here will join me in.
I found an old catalog from 1996. From that I know that the same drivers is used in the i21 and the almost twice sized i31. Maybe this can provide some clues...
F3 was however just 4 Hz lower in the i31.
I took out the drivers and measured the cabinet. I estimate the volume to 22 liters, excluding drivers, brace and so on. Port is 49 mm in diameter and 165 mm of length. According to an online calculator I found, this would mean a tuning frequency of 36 Hz. Agree?
What is then best approach? Just aim on same volume and tuning? Or should I increase the volume and lower the tuning to try to get some more bass? If I do lower the tuning, I believe that a risk is that the bass rolling of earlier, meaning deeper but weaker bass? Am I wrong?
Much thankful for any input 🙂
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Trying to extend the response of a vented enclosure is always tempting, but it becomes a compromise. It's better to stay with reasonable values. Tuning too low results in a subdued bass response with a peak in it near the tuning frequency, with group delay inconsistencies.
It can be worthwhile trying to manage bass problems with subs, and the ability to choose room placement away from the mains.
It can be worthwhile trying to manage bass problems with subs, and the ability to choose room placement away from the mains.
I quite often advise to perform a basic and fairly simple impedance measurements which will be used to derive T/S parameters. That way we can decide on optimal route. Any software suite capable of doing such measurement will suffice, usually I recommend ARTA labs limp and/or R.E.W. Check these out first before you proceed.
I wish someday to test measuring parameters (I have some saved drivers this would be useful for) but for this project I want to move forward without buying new equipment. I was hoping that having some knowledge about another cabinet the same drivers is used in would help, but the guessing is still difficult as I understand. If we knew the volume and tuning of the bigger that might help, but just outer dimensions is not enough.
Per now I'm thinking I'm going to build with same volume and port dimension. Cabinet will be bit a more shallow and higher, and port will probably change direction. My guess is that this will be ok.
Like I said, main goal with this particular project is the woodworking. Covid and isolation has taken a toll on my mental health. Hoping some sawdust can help me with this.
Per now I'm thinking I'm going to build with same volume and port dimension. Cabinet will be bit a more shallow and higher, and port will probably change direction. My guess is that this will be ok.
Like I said, main goal with this particular project is the woodworking. Covid and isolation has taken a toll on my mental health. Hoping some sawdust can help me with this.
No, you can succesfully build a larger cabinet as i31 is, which will be roughly 35 litres internally. Port you can adjust by listening, use the same diameter as original. 8" units are normally deployed like that. In regard to measuring impedance, a working sound card with one line IN and one line OUT, a resistor, some hook-up wire and alligator clips or similar coupled to ARTA labs limp module or R.E.W. software as an alternative is basically it. But, no rush there. Whatever suits you better at the moment.
Good luck and take care of yourself while working on the cabinets.
Good luck and take care of yourself while working on the cabinets.
Based on this, the i31's Fb = 35 Hz and presume is just a bigger box plus implies it's a somewhat under damped alignment and/or just not enough internal damping and/or just 'critically' damping the vent*: Infinity Reference 31i Floor standing speakers review and test
*Click test: Click Test | GM210 | Flickr
GM
*Click test: Click Test | GM210 | Flickr
GM
Hi,
This project isn't moving that fast, but still moving some and now I have an issue I want to discuss. This is regarding to the port placement.
I'm going to build a new enclosure where I'm aiming at the same volume and tuning, but I'm changing the geometri. The i21s have a port facing backwards (sketch 1). I realize that if I would keep the port diameter and length I'll probably getting to close to the front wall (sketch 2). Further on, the port diameter is rather small so I'm considering building with larger. The port would then be even longer and harder to fit. So therefore I'll probably ending up using a bent port.
Any difference in pointing "inwards" or "outwards", inside of the enclosure? (inwards being up in sketch 4, outwards being down in sketch 3)
Would it make a big difference in moving the port from backside to front? I'm considering this, since I'm feeling that I'm then would be more free to place the speakers very close to a wall? But I'll think I like the estetics of backside port better...
This project isn't moving that fast, but still moving some and now I have an issue I want to discuss. This is regarding to the port placement.
I'm going to build a new enclosure where I'm aiming at the same volume and tuning, but I'm changing the geometri. The i21s have a port facing backwards (sketch 1). I realize that if I would keep the port diameter and length I'll probably getting to close to the front wall (sketch 2). Further on, the port diameter is rather small so I'm considering building with larger. The port would then be even longer and harder to fit. So therefore I'll probably ending up using a bent port.
Any difference in pointing "inwards" or "outwards", inside of the enclosure? (inwards being up in sketch 4, outwards being down in sketch 3)
Would it make a big difference in moving the port from backside to front? I'm considering this, since I'm feeling that I'm then would be more free to place the speakers very close to a wall? But I'll think I like the estetics of backside port better...
