I just purchased a Minidsp 2X4HD box so that I can play with delays and crossover slopes for the PPSL an main stereo speaker. My current chain is sources - PrimaLuna Prologue3 -Minidsp 2X4HD - XTZ AP-100/Hypex DS2 - speakers. XO is LR2@80Hz acoustic.
I ended with 2ms delay for the main speakers, after many tests (measuring and listening) and provocative settings. Mains and the sub also have some low-Q parametric EQ to make LR2 slopes smooth and to tame 3-4kHz power response of main speakers. The crap that are laying on the sub resonate when doing sweeps, but not when listening.
Room modes are terrible in this small room. The listening spot is very bad, but my butt gets very smooth response... I still haven't tested an auxiliary sub, because this does not sound as bad as it looks like
I ended with 2ms delay for the main speakers, after many tests (measuring and listening) and provocative settings. Mains and the sub also have some low-Q parametric EQ to make LR2 slopes smooth and to tame 3-4kHz power response of main speakers. The crap that are laying on the sub resonate when doing sweeps, but not when listening.
Room modes are terrible in this small room. The listening spot is very bad, but my butt gets very smooth response... I still haven't tested an auxiliary sub, because this does not sound as bad as it looks like
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Thank you, Allen!
In another thread discussion went to PPSL designs, and obvious cavity resonances. I checked my 10 years old subwoofer, and noticed that I still had a piece of cardboard in the slot, holding two pillows from touching cones. By common sense it will vibrate and cause distortion. As I happened to have a new project going on and my measuring system ready in the "lab" HT room, it was easy to check this.
The sub is a bench that holds HT main speakers, books, bongo drum, two guitars, printer etc. essentials, that easily resonate too. I removed most of them. Nearfield measurement is not sensitive to room resonances, so let's see. Typically as per my experience, mechanical resonanecs appear as 3rd harmonic distortion, and also this time. Other effects were disappearing of 480Hz cavity resonance and slight change in response above 300Hz. Measurements were done without eq or lowpass.
In another thread discussion went to PPSL designs, and obvious cavity resonances. I checked my 10 years old subwoofer, and noticed that I still had a piece of cardboard in the slot, holding two pillows from touching cones. By common sense it will vibrate and cause distortion. As I happened to have a new project going on and my measuring system ready in the "lab" HT room, it was easy to check this.
The sub is a bench that holds HT main speakers, books, bongo drum, two guitars, printer etc. essentials, that easily resonate too. I removed most of them. Nearfield measurement is not sensitive to room resonances, so let's see. Typically as per my experience, mechanical resonanecs appear as 3rd harmonic distortion, and also this time. Other effects were disappearing of 480Hz cavity resonance and slight change in response above 300Hz. Measurements were done without eq or lowpass.
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I'm planning a down firing 2x 18" sub posing as a coffee table. I'm using B&C 18PZB100 in a vented 220l per driver enclosure, critically damped. I'll be powering it with a QSC GXD8 amp with extensive built in dsp.
I know people have strong opinions on down firing arrangements, stating that cone sag is an issue, but I haven't had any problems with stiffer pro drivers which resist sag very well. I've built a few of these type subs and haven't so fat experienced any cone sag problems. I only use dual spider drivers for this but its not cheap.
I like your design concept Juhazi. The drivers you chose are decent for the money. The upgrade path is nice to have. In my case, I already have the drivers laying around, so its a no brainer. I'll have the option to plug the ports if I don't like the sound, but I've had good luck with critically dampened designs. They can sound close to a sealed box if done correctly.
I know people have strong opinions on down firing arrangements, stating that cone sag is an issue, but I haven't had any problems with stiffer pro drivers which resist sag very well. I've built a few of these type subs and haven't so fat experienced any cone sag problems. I only use dual spider drivers for this but its not cheap.
I like your design concept Juhazi. The drivers you chose are decent for the money. The upgrade path is nice to have. In my case, I already have the drivers laying around, so its a no brainer. I'll have the option to plug the ports if I don't like the sound, but I've had good luck with critically dampened designs. They can sound close to a sealed box if done correctly.
I agree.
I believe a 4th has the same group delay as a sealed at double its tuning.
I found 40hz tuning quite chunky sounding.
But 27hz sounded just fine.
Even a snobby buddy of mine with multiple sealed 10's was impressed with how "fast" and clean the 27hz tuned push pull double 12 sub was.
The phase/time wrap at 18-24db filters 80-120hz does far more damage to the sound.
I stuffed my double 15's port changing it to below a .7 sealed.
I didn't hear it as quicker bass, just less low bass.
You could do a m&k also.
Just be sure to have the drivers share the same enclosure (backspace).
I believe a 4th has the same group delay as a sealed at double its tuning.
I found 40hz tuning quite chunky sounding.
But 27hz sounded just fine.
Even a snobby buddy of mine with multiple sealed 10's was impressed with how "fast" and clean the 27hz tuned push pull double 12 sub was.
The phase/time wrap at 18-24db filters 80-120hz does far more damage to the sound.
I stuffed my double 15's port changing it to below a .7 sealed.
I didn't hear it as quicker bass, just less low bass.
You could do a m&k also.
Just be sure to have the drivers share the same enclosure (backspace).