Hi Everyone,
After just a bout 10 years im DIY'ing some audio again instead of buying and having fun. Now i know the topic is done to death so apologies in advance but i need to understand or at least confirm my understanding of basic tuning on a sub enclosure so i can puzzle out what i'm seeing.
some background: i saw some car audio DD speakers, a single driver and tweeter for sale in a pawn shop for a steal and thought i can make a fairly nice portable bluetooth speaker with that. The idea of course being that i'm not spending any real money on this.
i have a 4ch RF punch amplifier and i hacked into its guts a little BT5 receiver feeding the analog inputs inside and powered it by the remote input.
I've got some Headway 38120 cells with an active balancer from some other projects. I was worried the balancer was going to cause some noise but its ok. currently have 12v 20Ah capacity, planning another string as it only lasts about 4 hours.
Getting on to the sub itself and the reason for my post, Its the only thing i purchased new for this and its a DD 8 inch sub, tiny thing. The idea of course keeping it portable.
I used an online box design software that already had the TS parameters for the sub and after playing with that aimed for a 45L box and port tuning of 35Hz. proceeded to build the box but then had a clever idea turning out to be not so clever, to make it so that i can tune the port length by cutting away at the plank inside. apart from that being fairly difficult to do through an 8" hole it also violates a universal rule of not changing 2 things at the same time.
Of course shortening the port from the inside also increases the box volume, and by design i didn't make this a small port. its 40mm x 300mm and starting off at 1200mm long.
so box built i measured the impedance of the speaker on a scope with it being at its lowest on 28 hz, i promptly cut away a large piece of the port shortening it and the response changed to ~30hz.
this played really very nicely on my ears and i kept it like this for a while getting to know how it handles different songs at different power levels. The sub itself had a lot of movement and the amps gain has plenty headroom. thought if i tried to get to the 35hz as planned i would get more power handling, again i cut away a large piece at random and this is where i am now.
i definitely have more power handling and not nearly as much movement as i had before. The impedance is now lowest at ~32hz. but it sounds softer, and this is what i want to figure out. The amp is 400W 4 channel admittedly not big 2 x100W channels bridged for the sub which can supposedly handle 250W RMS. i can now almost max out the gain, but why is it softer?
My thoughts are coming back to the changing 2 things at once rule. I'm increasing the box volume substantially when i cut the port shorter. From ~35L initially to ~55L now and i think the 8" isn't raising the pressure in the box as much as it did in the previous cut? I've noted at low power levels i lost a lot of DB. id almost say this isn't as efficient as it was. if so would changing to a 10" driver compensate for the increased box volume and make it more efficient again and the frequency response would go up if i did that even if its the same box or am i wrong thinking that? should i just paste back a plank and call it quits. if someone has a bit more insight into the relationship between port tuning, box volume, speaker displacement and perhaps some unknown to me factor.
Thanks, have a great weekend.
After just a bout 10 years im DIY'ing some audio again instead of buying and having fun. Now i know the topic is done to death so apologies in advance but i need to understand or at least confirm my understanding of basic tuning on a sub enclosure so i can puzzle out what i'm seeing.
some background: i saw some car audio DD speakers, a single driver and tweeter for sale in a pawn shop for a steal and thought i can make a fairly nice portable bluetooth speaker with that. The idea of course being that i'm not spending any real money on this.
i have a 4ch RF punch amplifier and i hacked into its guts a little BT5 receiver feeding the analog inputs inside and powered it by the remote input.
I've got some Headway 38120 cells with an active balancer from some other projects. I was worried the balancer was going to cause some noise but its ok. currently have 12v 20Ah capacity, planning another string as it only lasts about 4 hours.
Getting on to the sub itself and the reason for my post, Its the only thing i purchased new for this and its a DD 8 inch sub, tiny thing. The idea of course keeping it portable.
I used an online box design software that already had the TS parameters for the sub and after playing with that aimed for a 45L box and port tuning of 35Hz. proceeded to build the box but then had a clever idea turning out to be not so clever, to make it so that i can tune the port length by cutting away at the plank inside. apart from that being fairly difficult to do through an 8" hole it also violates a universal rule of not changing 2 things at the same time.
Of course shortening the port from the inside also increases the box volume, and by design i didn't make this a small port. its 40mm x 300mm and starting off at 1200mm long.
so box built i measured the impedance of the speaker on a scope with it being at its lowest on 28 hz, i promptly cut away a large piece of the port shortening it and the response changed to ~30hz.
this played really very nicely on my ears and i kept it like this for a while getting to know how it handles different songs at different power levels. The sub itself had a lot of movement and the amps gain has plenty headroom. thought if i tried to get to the 35hz as planned i would get more power handling, again i cut away a large piece at random and this is where i am now.
i definitely have more power handling and not nearly as much movement as i had before. The impedance is now lowest at ~32hz. but it sounds softer, and this is what i want to figure out. The amp is 400W 4 channel admittedly not big 2 x100W channels bridged for the sub which can supposedly handle 250W RMS. i can now almost max out the gain, but why is it softer?
My thoughts are coming back to the changing 2 things at once rule. I'm increasing the box volume substantially when i cut the port shorter. From ~35L initially to ~55L now and i think the 8" isn't raising the pressure in the box as much as it did in the previous cut? I've noted at low power levels i lost a lot of DB. id almost say this isn't as efficient as it was. if so would changing to a 10" driver compensate for the increased box volume and make it more efficient again and the frequency response would go up if i did that even if its the same box or am i wrong thinking that? should i just paste back a plank and call it quits. if someone has a bit more insight into the relationship between port tuning, box volume, speaker displacement and perhaps some unknown to me factor.
Thanks, have a great weekend.
I would just use WinISD and input the data for both of the set ups you had/have. Alternatively you can grab Bassbox Pro 6 with all of its extras for free via the usual illegal means "me hearty!" (yes pirating from the same named website...).
Where you use your mobile set up has an impact on frequency also, I'm talking room gain... The same as a car has gain around 30-35hz ish (from memory), but if you are using it in the house then your previous port tuning may have excited a mode depending on your location.
As I said originally though I recommend that you add the two box volumes and port lengths with the TS Parameters from the sub into WinISD (or Bassbox) and overlay them both to see wha the differences are.
I'm assuming you have a PVC port so adding a slip joint you can easily extend it to be longer again so it's almost infinitely tuneable to a certain extent. The port just doesn't have to be inside the box either so if you can stick it out an inch or two you can then add the slip joint and make it longer externally...
You can also add a second port in WinISD to see the effects.
Have fun and hopefully someone more knowledgeable chimes in for detailed answers.
Where you use your mobile set up has an impact on frequency also, I'm talking room gain... The same as a car has gain around 30-35hz ish (from memory), but if you are using it in the house then your previous port tuning may have excited a mode depending on your location.
As I said originally though I recommend that you add the two box volumes and port lengths with the TS Parameters from the sub into WinISD (or Bassbox) and overlay them both to see wha the differences are.
I'm assuming you have a PVC port so adding a slip joint you can easily extend it to be longer again so it's almost infinitely tuneable to a certain extent. The port just doesn't have to be inside the box either so if you can stick it out an inch or two you can then add the slip joint and make it longer externally...
You can also add a second port in WinISD to see the effects.
Have fun and hopefully someone more knowledgeable chimes in for detailed answers.
Thank very much for the reply, appreciating the input.
Going back to simulations is probably the most sensible thing to do, there's really no harm in it is there? and your room gain considerations, playing a definite role. initially thought about it but i didn't know how id go about simulating it, that or box losses, materials etc. so that's why i opted for a more pragmatic approach in tuning.
I took today to properly listen to it, different locations and power levels as before, since the last cut made i just took a few minutes to be dissapointed and didn't/couldn't really listen. But after today i'm fairly pleased, i reset the gain levels on the amp and tuned it back in.
it is more responsive than before, the cone moves much less while being much louder. windows have started to rattle as well as cutlery in the kitchen sink.
I think i can explain what happened.. The port isn't a PVC pipe, its a dividing plank on the inside, cutting inside is every difficult and took me a lot of time with my head in a dusty hole, so as embarrassed as i may be to say it i got terrible sinus from the cutting and pretty much couldn't hear that well, i really think that's all. its sounds awesome now.. 😱😱
Going back to simulations is probably the most sensible thing to do, there's really no harm in it is there? and your room gain considerations, playing a definite role. initially thought about it but i didn't know how id go about simulating it, that or box losses, materials etc. so that's why i opted for a more pragmatic approach in tuning.
I took today to properly listen to it, different locations and power levels as before, since the last cut made i just took a few minutes to be dissapointed and didn't/couldn't really listen. But after today i'm fairly pleased, i reset the gain levels on the amp and tuned it back in.
it is more responsive than before, the cone moves much less while being much louder. windows have started to rattle as well as cutlery in the kitchen sink.
I think i can explain what happened.. The port isn't a PVC pipe, its a dividing plank on the inside, cutting inside is every difficult and took me a lot of time with my head in a dusty hole, so as embarrassed as i may be to say it i got terrible sinus from the cutting and pretty much couldn't hear that well, i really think that's all. its sounds awesome now.. 😱😱
