almikel

anyone looking to DIY 2D QRD diffusers needs to check out QRDude https://www.subwoofer-builder.com/qrdude.htm QRD (Quadratic Residue Diffuser) designs rely on prime numbers to generate diffusion. If your QRD diffuser has 12 wells (12 is not prime), the best diffusion it can provide is it's lowest prime multiple (ie 3) Primary Root Diffusers (PRD) use different maths, resulting in different well counts. If DIYing, just make sure you're building a diffuser based on good maths/science - not copying a commercial design that may have compromised the science of diffusion to avoid patent issues! Mike

best use is to straddle corners if you want it to work at lower frequencies. IMHO XHD is wasted mounted flat on a wall. Mike

what a crock of BS! Who says your small bookshelf speakers have the right coloration to improve the sound of a double bass? How can your speaker enclosures (on their own) do anything to replicate the sound of a string quartet in a large room? If you had a grand piano in your listening room, and you turned the wick up, the piano would be resonating at lots of different frequencies not at all contributing to great "in room" sound. A great example of an opinion stated as fact, with no science behind it. Mike

Be careful of paying too much attention to Reverberation Times (RT60, T30, T20 etc) in our typical small rooms. The original science of reverb times was developed by Wallace Sabine > 100 years ago, measuring much larger spaces and assuming a diffuse sound field. I've got huge respect for Sabine - measuring reverb in an auditorium with a stopwatch, with his students bringing in more and more cushions.... then creating the science of architectural acoustics from there...but it was based on large spaces, eg auditoriums. Sabine went on using his science to design the acoustics of the Boston Symphony Hall - considered one of the best sounding halls in the world! Our small listening rooms don't have a diffuse sound field (our small rooms have reverberant modal lower frequencies and specular higher frequencies). The designers of REW know this - hence their multiple options for RT times - use them all as guides to compare different treatment approaches. Even though RT times aren't necessarily scientifically valid in our small rooms, IMHO they're entirely valid to compare before/after measurements when applying acoustic treatment (just don't move your mic or speakers throughout the process of adding treatment). cheers, Mike

if a single speaker each side can meet your SPL requirements with some headroom - why complicate your life with the myriad of issues that come with multiple speakers playing the same information? (constructive/destructive interference/lobing etc) Mike

LoL - almost everything I've learned about audio I learned from @davewantsmoore's posts on SNA! Mike

fair enough - and I agree definitions are important to clarify what we mean... ...and your question has made me ask myself, what do I mean by bass?... ...And can I justify my statement ?: I certainly don't think that bass is only 100Hz and below... ...we both know that absorption gets too big/too large to be effective <100Hz I don't care what the definition of the upper frequency of bass is, only how bass interacts with the room. ...I'm happy to run with Wikipedia's definition of what defines bass frequencies https://en.wikipedia.org/wiki/Bass_(sound) which is <250Hz are bass frequencies... But it doesn't matter what the upper frequency of bass is - absorption will happily absorb every frequency above the absorption's lowest design frequency - size/depth/air gap will determine how low the absorption can go - most people can't deploy large/deep/gapped enough absorption to work much below 150Hz or so, which is where below 150Hz or so IMHO EQ works well in conjunction with absorption. The target is reasonably even "in room" decay times at the listening position across the spectrum - typically this is hardest to achieve in the low end... ...and absorption applied for the low end will clean up resonant issues above. Other solutions are needed for room issues <150Hz In doing so, you may have pulled out too much top end, which may require a plastic membrane or slats or both over the absorption... ...but I stand by my comment other treatment is icing on top. Mike

The Schroeder frequency of the room is a reasonable starting point for managing "in room" bass. ie where the the room size dimensions start getting close to the longest sound wavelengths such that modal/resonant behavior takes over compared to sound waves bouncing off boundaries in a specular fashion (ie like light bouncing off a mirror). Of course this transition has no set frequency, and every room has it's own "transition zone" where this occurs. For larger rooms, the Schroeder/transition zone is lower than smaller rooms, eg for large auditoriums, this transition zone/resonant zone is not an issue as it's lower than we can hear. For our small domestic rooms we may get resonant behavior up to 500Hz or so... ...regardless of what frequency it is, if it's resonating within the room, you're hearing the room not the speakers. There's a big difference between allowing treble to bounce around the room to decay naturally against soft furnishings (which is good), compared to allowing lower frequencies to resonate off room boundaries (which is bad)... Ultimately you want even reverb/decay across the spectrum, with some allowance for increased decay times at lower frequencies. Mike

I implemented double DEQX in 2015 after I built my T20 sub for 4 way active X/O (single sub/stereo TD18s/PSE144 mids/PSE144 tweeters). More recently (2021) I wanted to simplify my life, and implemented Paul Spencer's passive crossover for his PSE144 (I bought the "standard" version of Paul's passive crossover), which meant I could run a single DEQX, and this remains my current setup: Paul's passive 2 way X/O within the PSE between tweeter and mids at 1.25kHz DEQX active X/O between PSE and TD18s at 350Hz - I'm pretty sure I just configured a Linkwitz Riley LR4 XO DEQX active low pass on the sub at 60Hz with LR4 (my T20 sub is a tapped horn so nasty resonances occur above the pass band I don't think I've applied a high pass filter/XO to the TD18s to cross to the sub...just allowing the TD18s to get as low as they can in their enclosure without a X/O taking anything away some global room EQ has been applied < 200Hz or so ...actually it's been so long since I made any changes, your question has made me question what configuration I setup back in 2021...the above may not be entirely accurate...just what I recall... Sort of relevant to this discussion, is that after I built my TD18s in their small sealed boxes (around 2013), and dialing in a bunch of EQ to push them lower, I thought I had reasonable low end extension in my room, because the bass sounded great, but I'd never actually measured it 2 things happened within a week of each other that convinced me I needed a sub operating below the TD18s: some friends came over and we played the Boston Philharmonic Orchestra's version of "Fanfare for the Common Man", and they said, "you're missing something in the bottom octave"! I listened to @Jiri's system and some of the low frequency content made the hairs on the back of my neck stand up ! I immediately commenced the build of my T20 sub...I'd had all the bits and the design for ages, but just hadn't made any sawdust. I was running single DEQX HDP3 active 3 way back then and adding a sub meant going double DEQX to remain fully active... ...Alan from DEQX sourced me a 2nd hand HDP3 unit with digital outputs to integrate with my existing DEQX, and actually came to my house to help me set it up! I'm a big fan of DEQX - I really hope they succeed with their next generation product! Mike

My experience with TD18s in sealed enclosures is they don't go anywhere near low enough to be called a "subwoofer" without seriously large EQ and amp power, even in a large sealed box. TD18s excel at mid bass - that's where I use them - in my tiny 60litre sealed enclosures they still have a Qtc < 0.7, and I push them down to 40Hz or so to crossover to my sub at 60Hz. Easily the best mid bass I've heard - amazing bass slam... ...but they're not sub drivers if mounted in a sealed enclosure.... ...maybe there's a ported alignment where they can get low...? My wife thinks my sealed TD18s sound so good she's taking them if we break up...she's dreaming...but they're not subs. Mike

First of all the S200w amp you linked to is safe for 4ohm loads, and you want to connect your "Krix seismix 3 mk5 with 11" 4ohm woofer" and your other passive sub to this amp...with the Krix already at the lower limit of impedance for your amp. Any parallel connection will always have a lower impedance than either sub - so you risk running the amp into overload trying to deliver the current required. Say each speaker is 4 ohms impedance - connected in parallel the amp will see an impedance of 2ohms. If your amp is only rated for a 4ohm load this could push your amp into current limiting (ie the amp can't deliver sufficient current into a 2ohm load whilst maintaining a constant voltage) Running them in series will be fine - the amp will see a higher impedance (both speaker impedances will add together) - you won't risk the amp trying to deliver more current than its able to... ...you'll likely have to crank up the volume on the S200w amp, but it won't go into current limiting! Mike

Hi npw, no mention of your room, how many hard surfaces, how much absorption (eg carpet, soft furnishings etc). By a long margin your room has the most impact on your "in room" sound, followed by your speakers - everything else has a much lower impact on your "in room" sound unless they're terrible, which yours aren't. Room treatment is the only upgrade I've done where there was actually a night and day difference between before/after. The next biggest upgrade I did was changing my speakers - from box speakers to Redspade PSE144 horns + Acoustic Elegance TD18 mid bass - this change was less significant than the room treatment, although the combination of stereo TD18's in a room with the bass under control is just glorious IMHO forget any electronics upgrades and focus on your room response. Get your room's bass response under control as the 1st priority using treatment and EQ. Again IMHO, once you have your room's bass under control, you're 80% done, and I'm fine with stopping at 80% solutions (I'm a big fan of the Pareto principle, but I get that most of HiFi likes to sit in the 20%...probably 1%) cheers Mike

Build cost for a room $50-100K? Things have clearly gone nuts - ignore my post! Mike

Looping back to the original topic - you do not need a dedicated phase for your audio room - a dedicated circuit is fine. If you can, keep motors away from the phase your stereo room is on (A/C, fridges, pool filter motors)...but don't worry overmuch...modern stereo kit typically has an excellent Power Supply Rejection Ratio (PSRR), ie noise from the mains supply doesn't get through to your speakers with good gear... ....and even if you take great pains to have no motors connected to the phase your stereo room is using, you have zero contol over how many motors are connected to that phase down your street! Absolutely - but there are hidden benefits in having a 3 phase connection to your house: a local transformer failure can result in losing a phase - if your house is single phase and you're on that phase you lose power If you have 3 phase power I would recommend having multiple power point circuits and light circuits spread across the phases, so if you lose a phase (or two) you still have power to some power points and some lights In a domestic setting, there's not too many devices that require/benefit from a 3 phase connection - and all can make do on a single phase: charging electric vehicles will be a growing use case, as will charging home batteries in extended cloudy days large home A/C and heat pump home heating/pool heating I still say if you have 3 phase connected to your house you need at least one 3 phase power point just for 'Ron (later on), and because you can! Mike

A 3 phase power point is just a power point leveraging all the 3 phases available in your home. They look like this: random interweb link here: https://www.sbx.biz/products/415V-30-Amp-3-phase-power-point-6413.html If you have 3 phase connected to your house you need one of these...just because you can!! Mike

In that case running your sub at low level from "pre-out" outputs, then you could run speakers of either A or B outputs mike

it can work very well - take a simple main speaker with a sealed woofer, which will have a 2nd order 12dB/octave high pass response - you can get reasonable summing with any sub (whether connected at high level or low level) so long as you have some control of the low pass Xover point on the sub (slope would be nice also). There's a lot to be said for simplicity! Mike

If all done by an external contractor - ballpark $30-$50K if done to regulations

I'm late to this thread, and the work is likely completed - but I agree with the above - you want a dedicated circuit for audio - but not a dedicated phase. What you do want is a 3 phase power outlet somewhere in your garage/shed...just for 'Ron (later on)...I installed 3 phase power in my last house, and asked my sparky to install a 3 phase power point in the garage, and he asked, "why?"...I replied, "because I can!"...if you have 3 phase to your house of course your need a 3 phase power point!!! Mike

two different subs is fine so long as no sub exceeds its amp power/driver excursion limits.

Rel have built their reputation on high level input to subs being superior to low level input- it isn't superior if you have the ability to manage the low pass response of your main speakers crossing to the high pass response of your sub. If a high level input to your sub is your only option, then look at the other recommendations in this thread. I like Rythmik and JL Audio. I run a Rythmik sub myself - low level connection with a crossover. I don't like Rel as they push the "high level connection is better" thing so hard. Mike

does your amp have a sub (low level) connection? If not, then having your sub connected at high level to your A terminals means there's no way to have the sub working on your B terminals. You could add a switch so that your sub could be connected to both A and B outputs of your amp, and you select which one is connected (A or B) Mike

Thanks heaps for that! - I'm very interested in the technical design aspects of all things audio!! Fascinating read...although I've also just skimmed...clearly I need to learn more about PRD diffusers! The key takeout from my quick read of the patent is that 2D PRD diffusers cannot be square...the "well count+1" needs to be prime, and each direction needs to be coprime (ie no common factors >1) - which is the case with your PRD diffusers - well count of 156 (+1 = 157 which is prime), and 12 and 13 have no common factors >1. I don't think there is any deficiency just based on my reading of the patent - PRDs may have better diffusion performance than QRDs, especially from a repeated pattern/lobing perspective. I totally get that - your PRD's are awesome and way beyond what I would DIY! I love the concept of BAD panels! For me, BAD panels are what you use as a mask over existing room absorption if while adding sufficient absorption to control your room's bass response you've made your room "too dead" and want to bring some treble back into the room, but with some diffusion. Unfortunately, it's hard to find good data on where diffusion starts and stops with BAD panels compared to say Quadratic Residue Diffusers (QRDs), and likely Primary Root Diffusers (PRDs). I have an old thread linked below attempting to clarify the diffusion specs of BAD panels: My takeout is that if you want "actual" diffusion use QRDs (or maybe PRDs?)... ...if you've managed to control your "in room" bass (yay!!), but through the process absorbed too much top end - adding BAD masks over existing absorption IMHO is an excellent way to bring treble back into the room, with some amount of diffusion. 1D BAD masks are very easy - just slats over absorption in a 1D BAD pattern (coin tossing works fine - heads=slat, tails=gap) The cheap 2D BAD panel approach is just adding another layer of slats in the other direction (90 degrees). The 2D BAD panel hole mask design like RPGs takes a bit more maths. @hochopeper wrote an algorithm to generate a 2D BAD pattern any size - refer page 5 but I haven't seen Chris ( @hochopeper ) here on SNA for a while cheers, Mike

Lot's of work there - well done! Your reference link goes to a site for calculating Primitive Root Diffusers (PRD). I'm more familiar with Quadratic Residue Diffusers (QRD)...commercialised by RPG (Cox and D'Antonio) ...both PRDs and QRDs diffuse, but I'm unsure of the technical differences between them. For QRDs, the N number is the prime number the diffuser is based on...ie the number of wells before repeating the pattern eg N3, N5, N7, N11, N13, N17, N19, N23, N29, N31, N37 ...I looked at your photos (clearly not that carefully) and didn't identify any obvious repeats, and came up with a well count of 37 on 1 side....again maybe not correct...but that's where I got N37 from. From your post, I'm guessing your diffusers are N13 in 1 direction and the pattern is repeated - which is fine. From my understanding of QRDs (not PRDs !), primes are important to achieve diffusion - I don't understand why the site you linked to gave a design of 12 x 13 instead of 13 x 13 ??? In the scheme of things, it likely makes no audible difference, but with QRDs theoretically 12 wells can only achieve diffusion based on the largest prime divisor ie 3 (N3). I'd be surprised If this doesn't apply to PRDs also - you likely have less "diffusion" in the direction with repeated 12 wells than you thought... Obviously too late now to change your existing diffusers, but if you decide to build more, I would recommend the free tool QRDude https://www.subwoofer-builder.com/qrdude.htm , an amazing free tool for designing/optimising QRD 1D and 2D diffusers. Both 1D and 2D QRD diffusers are always based on prime numbers to achieve diffusion... ...repeating patterns are fine...but can introduce "lobing"...ie strong peaks ...Cox and D'Antonio recommend using an "inverse" pattern panel...or just rotating a panel 90 degrees to reduce "lobing" effects. Mike

Obviously if only using absorption, 50mm thick is too thin to be effective down to 200Hz even if appropriately air gapped. @200Hz, max air particle velocity (wavelength/4) is 430mm from the boundary - which should be the mid point of your absorption...but you know all this already... Mike