Looking around diyaudio for example PPSL inspiration, I see some have a slot with a single open face (one big board on top & bottom spanning the slot), but I also saw a design where the top and bottom of the slot was open. I assume the former is more typical?
Does sealed PPSL require bracing like a traditional sealed box?
I assume also, I should lay out box dimensions in CAD due to my space constraints, then decide on drivers & model?
Yes,.. the first would be more typical
I use SketchUp for layouts . .. quick and relatively easy
Remember , bracing is more effective in the center of panels . if you are strapped for volume you could jam dowels and glue screw them in . Otherwise , you could create window braces .. which waste more wood / volume
I also use wedge braces sometimes to ensure a tight fit .. I'll try and draw up a pic .. it's simple but hard to explain in words
Finally, .. when designing / building ..Just be sure that you have a plan to actually get both the drivers in the slot and can access the mounting holes . Might require pre drilling the screw holes (if using screws) and a mini ratcheting driver / wrench of some sort . If using screw holes .. star or square head screws will be your friend as the bit won't tend to cam out like Philips head screws do without enough downward pressure applied (as can be the case in confined / restricted access scenarios)
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Is there a particular slot area that I should be targeting?
I realize it can only get as narrow such that cone at max excursion doesn't touch the inverted drivers magnet, but I imagine there is a sweet spot.
I realize it can only get as narrow such that cone at max excursion doesn't touch the inverted drivers magnet, but I imagine there is a sweet spot.
what drivers ?
Also, you should consider adding some 45 degree corners to fill the dead space between the drivers and the rear of the slots.
As I recall, the slot plenum should be as small as physically possible . I'll let the experts chime in 🙂
Remember, the smaller the plenum, the higher the sub will go (benefits in midbass / integration) .... at least in theory
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No drivers picked out yet, I could use guidance here. My experience with drivers is super limited.
Generally, the smaller the slot, the less problems it will cause, until too small. 2" would not be too small for 10" drivers.
The drivers need not be inverted, cone to cone will reduce the available cabinet volume considerably.
what is the max volume you have available .. are you limited to around 2 cu ft or can you go larger ? Dimensions would help .. is the first sketch you provided in one of your initial posts still valid ... that is closer to 3.x - 4 cuft ?
The initial sketch is still valid.
The cross section of the box I put together is 28 x 18" x 12" tall.
To get larger means having to build 45 degree angles to the corners of the enclosure. I also started with height at 12" overall as a starting point.
What effect does more internal volume have?
it's time to get reading about T/S Parameters, System Q and dampening
Speaker drivers seem to be expensive right now so wait for a sale
If you are looking to build a sealed subwoofer system , .. look for drivers with Qts above 0.45 and a Fs of about 30 Hz or lower .
Specifically, if you are looking to build a PPSL using 2 drivers .. the nominal impedance will be halved if wired in parallel (or doubled if wired in series) .. so using two 4 ohm drivers , your system impedance will be 2 ohm or 8 ohm depending on how they are wired. There are benefits to both wiring schemes but most folk prefer parallel. Bottom line, figure out a suitable driver / amp strategy ..
Here is an example of an 8 ohm sub that would likely work and present an easy load to a sub amplifier when wired in parallel.
Parts express has a reasonable filter to narrow down your Choices. Prices are high right now .. though
https://www.parts-express.com/Dayton-Audio-RSS265HF-8-10-Reference-Series-HF-Subwoofer-8-Ohm-295-442
For starters , .. start researching for drivers that work well in about 1 cu ft sealed ina home environment
And get familiar with winisd pro and / or the slightly buggy mobile app - speaker box lite
Play around with sample designs and you will learn a lot. Don't hesitate to ask for help
And get familiar with winisd pro and / or the slightly buggy mobile app - speaker box lite
Play around with sample designs and you will learn a lot. Don't hesitate to ask for help
Measurements can help to learn:
https://www.diyaudio.com/community/threads/push-pull-vs-normal-distortion-compared.191833/
Mark 100's observations are more current.
Art
Is there a practical benefit of dual 4-ohm drivers wired in parallel for a 2-ohm load paired with an amp capable of 2-ohm output, vs. dual 8-ohm drivers wired in parallel for a 4-ohm load paired with an amp capable of 4-ohm output?
It seems there are many more options for 8-ohm drivers vs. 4-ohm.
Also, if building PPSL I can fit dual 10" drivers due to the material needed to build the plenum. If building Dual Opposed, I can fit dual 12". Assuming both cabinets are sealed, seeing the same amount of power, am I gaining or losing much between the two?
It seems there are many more options for 8-ohm drivers vs. 4-ohm.
Also, if building PPSL I can fit dual 10" drivers due to the material needed to build the plenum. If building Dual Opposed, I can fit dual 12". Assuming both cabinets are sealed, seeing the same amount of power, am I gaining or losing much between the two?
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On the contrary, 4 ohm SUBWOOFER drivers are much more common than 8 ohm SUBWOOFER drivers.
Assume a pair of 4 ohm drivers connected in parallel vs series i.e. ( 2ohm vs 8 ohm as per your example)- and assuming the same enclosure.
- the parallel connected pair will be "louder . Without getting into efficiency, vs sensitivity explanation . More info on the www such as here https://www.diyaudio.com/community/...series-sensitivity-rules.117821/#post-1433789
- The amplifier will be more stressed driving the 2 ohm load . Many plate amplifiers will have a hard time driving this load long term
- Lower impedance loads are harder to dampen (control) - possibly looser bass
- I guess one approach would be to use a 2 channel amp (such as a pro-amp) and driver each driver off a separate channel.
- Dual opposed offers the benefits of vibration cancellation
- PPSL offers the benefits of vibration cancellation and even order harmonic cancellation
- 12" drivers typically go deeper and louder - better for larger rooms
- 10" drivers typically can go higher (not a critical factor for your application) but not as deep or loud
- A lot comes down to the quality of the drivers rather than raw-size
- My personal thoughts
- you are restricted in sub volume
- given a fixed volume, 10" driver will typically dig deeper than 12" drivers in the same volume (but not go as loud - but maybe still loud enough).
- play around with some drivers in winisd pro and you will figure out what works best for you -
I spent some time playing around with drivers in WinISD. My approach was to browse PE for drivers of a given size and compare a group of 10" drivers, then a group of 12" drivers. I limited my selection mostly by what drivers had pre-made winisd files from loudspeaker database due to lazyness. This resulted in a nice group of 26 drivers, twelve 10" and fourteen 12" across a few different brands. If there any additional sources I should consider, please let me know.
After importing all drivers, I changed the box volume to 2 cubic feet for all drivers. Given I plan to crossover between 60-80Hz, I truncated the plots to show 15-100Hz response. This is the plot of all drivers:
My assumption from looking at the transfer function plot is the driver that best fits my needs has the least amount of roll-off in the 15-100Hz window; where the SPL at 15 is closest to the SPL at 100Hz. Using this metric, I eliminated a few drivers which, by eye, had large difference in response between 15 and 100Hz. These happened to be mostly 12" drivers; seems (2) 12" drivers in a 2cuft box has a steeper roll-off.
Using the crosshairs in WinISD, I made a table of the response for each driver at 15Hz and 100Hz. Since I'm using Audyssey for DSP, I chose to compare drivers based on response at the frequency response extremes as I assume the least DB difference between 15Hz and 100Hz would be the easiest for DSP to compensate. It's my understanding that DSP only has so much "correction" ability, so the flatter the better. I also did not consider any frequency between 15-100Hz as I assumed DSP could more easily compensate in this middle area. These are the results, sorted by Diff (100Hz response - 15Hz response).
Based on this modeling, it seems to be a toss-up between the top 4 drivers. I'm sure the differences are very subtle for the top 12-ish drivers, but for simplicity's sake, I'll focus in on the top 4.
Next steps will be to compare cost, power requirements and practical considerations (specifically, SD12X due to 12" diameter cannot be built in PPSL due to my size constraints).
Am I on the right track so far and is there anything I may have missed?
After importing all drivers, I changed the box volume to 2 cubic feet for all drivers. Given I plan to crossover between 60-80Hz, I truncated the plots to show 15-100Hz response. This is the plot of all drivers:
My assumption from looking at the transfer function plot is the driver that best fits my needs has the least amount of roll-off in the 15-100Hz window; where the SPL at 15 is closest to the SPL at 100Hz. Using this metric, I eliminated a few drivers which, by eye, had large difference in response between 15 and 100Hz. These happened to be mostly 12" drivers; seems (2) 12" drivers in a 2cuft box has a steeper roll-off.
Using the crosshairs in WinISD, I made a table of the response for each driver at 15Hz and 100Hz. Since I'm using Audyssey for DSP, I chose to compare drivers based on response at the frequency response extremes as I assume the least DB difference between 15Hz and 100Hz would be the easiest for DSP to compensate. It's my understanding that DSP only has so much "correction" ability, so the flatter the better. I also did not consider any frequency between 15-100Hz as I assumed DSP could more easily compensate in this middle area. These are the results, sorted by Diff (100Hz response - 15Hz response).
Based on this modeling, it seems to be a toss-up between the top 4 drivers. I'm sure the differences are very subtle for the top 12-ish drivers, but for simplicity's sake, I'll focus in on the top 4.
Next steps will be to compare cost, power requirements and practical considerations (specifically, SD12X due to 12" diameter cannot be built in PPSL due to my size constraints).
Am I on the right track so far and is there anything I may have missed?
Couch subs rock. I picture dual or quad 8's. In a wide flat shallow (sealed) enclosure. Something like a Boston Acoustics A 200 speaker cabinet tipped over on its back. The baffle would also serve as the top. Such a shape wouldn't be difficult to build in to the underside of a sofa, not at all. The bigger the better.
Attachments
Here you can find a lot of info. It´quite long but with a lot of rubbish. (As normal...)
https://www.faktiskt.io/phpBB3/viewtopic.php?f=3&t=71680
It´s in Swedish, but with a lot af pictures and links so hopefulle you can manage it.
If you need some translation I can try to help you.
https://www.faktiskt.io/phpBB3/viewtopic.php?f=3&t=71680
It´s in Swedish, but with a lot af pictures and links so hopefulle you can manage it.
If you need some translation I can try to help you.
Have a think about what you want to hear. This assumption and your modelling of 10" vs 12" would be irrelevant for most.