Location: Goa, India
Posts: 143
I'm Denzil.
Location: Goa, India
Posts: 143
I'm Denzil.
Location: cheltenham
Posts: 746
I'm matt.
Scanspeak aperiodic vents have tightly packed fibreglass inside. I'm sure it would be a lot easier/safer for them to use some kind of fabric, so I can only think that Scanspeak believe fibreglass works well in this application. We know fibreglass works very well at converting sound into heat (so does wool).
An aperiodic shelf is usually there to add some resistance to air movement for high Q speakers to reduce the hump in the bass (Tannoy are VERY low Q so shouldn't need the resistance), but it's also going to help filter away high frequencies (you don't want high frequencies coming out your ports). Obviously If you use something too dense, it's not going to allow low frequencies to pass, but if you use a material like wool, that filters high frequencies by converting sound into heat, your aperiodic shelf will work even more efficiently at filtering high frequencies, and won't need to be as dense as it would if you used an inferior material.
Location: Goa, India
Posts: 143
I'm Denzil.
Thank you Matt !
I've been reading about Aperiodic vents :
http://techtalk.parts-express.com/fo...periodic-vents
https://www.diyaudio.com/forums/mult...c-vents-2.html
...and also about Scanspeak vents. I believe what they use is glass wool (not fiberglass, which is slightly different). I'm in the process of trying to figure out the correct resistance for the Aperiodic shelf (material will be glasswool or rock wool). I do believe the resistance of the shelf I was using earlier was way too much. I'm in the process of making a shelf with less resistance now using the right material. It appears there isn't really any formula (unlike port tuning which has a formula) for Aperiodic vent resistance. Tuning is to be done with varying the resistance and then using measuring equipment to check results.
I'll give you a full report about my observations without the shelf (just ported bass reflex) and (hopefully) corrected resistance Aperiodic shelf, once I'm done.
Thanks again !!!
Denzil
Last edited by Denzil; 22-06-2020 at 06:40.
https://www.instagram.com/elsewheregoa
Location: cheltenham
Posts: 746
I'm matt.
In my earlier post I should have said the aperiodic vent is there to add leakage to a sealed enclosure, to reduce the bass hump. In the Tannoy it's adding a bit of resistance. I realised my mistake when I got in to bed, but couldn't be bothered to get up to edit my post.
Location: cheltenham
Posts: 746
I'm matt.
I noticed in the diyaudio thread that you linked to that they measure for the flattest impedance peak (I only read the page you linked too). I wouldn't do that. All I'd care about is what it does to the low frequency response (how much of the peak I'd want to reduce). So if it were me, I'd measure Qtc.
Location: Goa, India
Posts: 143
I'm Denzil.
Okay, understood Matt.
I've found at the moment (with the aperiodic shelf removed), the tightness of bass has reduced which is probably due to lack of back pressure as you have just mentioned. Some other changes in the sound too which I'll talk about later as things evolve.
Denzil
https://www.instagram.com/elsewheregoa
Location: Goa, India
Posts: 143
I'm Denzil.
Location: cheltenham
Posts: 746
I'm matt.
Please do. I'm expecting the ported version to have a nasty peak at the tuning frequency. As I said previously, introducing a leak (loosening the back panel) should remove the peak. If you feel they lack midbass punch, shorten the ports. I usually keep a selection of ports at various lengths because modelling doesn't always match reality, and it's very easy to swap port in and out of the cabinets (assuming the port hole isn't too tight).
Location: Seaford UK
Posts: 1,861
I'm Dennis.
I think that study of Richard Small's analysis, and synthesis of ported enclosures could help.