Deep End DIY - My first speaker project

[almikel]

On 23/03/2023 at 6:06 PM, acg said:

look at this...

 

 

...that is a MASSIVE suckout from say 40Hz to 120Hz.

the deep suckout between say 65 Hz and 90 Hz looks terrible - but is it audible? the human ear is not very susceptible to high Q changes in the frequency response (ie sharp dips).

Mike

[almikel]

On 23/03/2023 at 6:20 PM, acg said:

 

Mike, Ive done a bit more research into the BAD panels and they only start diffusing from about 2kHz.  Research indicates better sound quality results when diffusion is circa 500Hz to 5kHz with high frequency diffusion not necessarily sounding great nor diffusion into the bass frequencies.  Even got a quote for RPG BAD wall panels but that was definitely out of reach.

 

My speakers are very narrow dispersion and thus don't engage the room nearly as much as conventional speakers (high ratio of direct to reflected sound) so I think the first thing to sort out after bass are the early reflections within the room which I can decide individually to absorb or diffuse.  There will be diffusion in my room, but I'm not yet sure just where and how much.

 

Also read some more recent research on traditional QRD diffusion that used the equivalent of the "spin-o-rama" to measure scattering and diffusion which really mapped out how non-neutral that form of diffusion can be...hence how it is often described to have a "sound".  This has made me to not want to build my own diffusors instead relying on newer, more neutral QRD variants and/or the scattering/reflector types.

Agreed - IMHO BAD masks (1D or 2D) are best used over existing corner placed absorption if the absorption has soaked up too much treble getting the room's bass under control.

The BAD panel reflects treble back into the room with "some" diffusion, which is much better than the treble being absorbed.

 

On 23/03/2023 at 6:20 PM, acg said:

also read some more recent research on traditional QRD diffusion that used the equivalent of the "spin-o-rama" to measure scattering and diffusion which really mapped out how non-neutral that form of diffusion can be...hence how it is often described to have a "sound". 

Cox and D'Antonio discuss the minimum listening distance to QRDs as 3 x the lowest wavelength diffused, otherwise you'll hear "artefacts"...

On 23/03/2023 at 6:20 PM, acg said:

instead relying on newer, more neutral QRD variants and/or the scattering/reflector types.

Diffusion technology is changing rapidly - of course the QRD will be improved upon - I'm happy to learn from you and others.

 

Mike

[acg]

6 hours ago, almikel said:

the deep suckout between say 65 Hz and 90 Hz looks terrible - but is it audible? the human ear is not very susceptible to high Q changes in the frequency response (ie sharp dips).

Mike

 

Oh yeah, it is very audible.  Currently  I am listening further away from the speakers until this dip is sorted...sounds much better where the ceiling is lower and the dip is higher in frequency.   The ceilings are sloped, and the one above the listening position is at something like 45 degrees so is a big first reflector and the only thing that will change with listening position is where the dip occurs within the frequency response....so the ceiling treatment needs to absorb everything from as low as possible to as high as possible.

[davewantsmoore]

7 hours ago, almikel said:

the deep suckout between say 65 Hz and 90 Hz

It's ~ half an octave (is not high Q)

 

Or even wider if you call it as 40 to 120.    Probably more than just the "lone mode" going on.

[acg]

50 minutes ago, davewantsmoore said:

Probably more than just the "lone mode" going on.

 

For sure.  The REW simulated room modes are shown at the bottom of that graph.

 

 

 

But the rooms sloped ceilings cannot be  simulated by REW and I am sure to have more than just "normal" ceiling issues given the angle at which it dangles

 

 

 

 

 

 

There is one last thing to try for the wall bass treatments.  Below is one of the VPR's that straddles a front corner.  Note that I retain the wall mounted VPR's behind it, so three in each corner in total.  The wall mounted VPR's were much more effective than the equivalent sized superchunk trap that was initially there, and they still bring something with the VPR straddling the corner as well, but there is now a large space in that corner (a triangle roughly 1.5m x 1.2m x 1.2m) that I can backfill with the soft and fluffy batts which are still in the garage (much to my wifes chagrin). 

 

Also note that you should not get your 15yo son to help hang these VPR's because in his spare moments he will draw cocknballs on every dusty exposed surface on your speakers.

 

 

[BioBrian]

10 hours ago, almikel said:

the deep suckout between say 65 Hz and 90 Hz looks terrible - but is it audible? the human ear is not very susceptible to high Q changes in the frequency response (ie sharp dips).

 

 

 

But how relevant is that statement, compared with musical reality?

 

Half an octave might not rate highly in The Clever Caveman's Manual of Survival, but for those of us who appreciate the middle section of Chopin's Raindrop Prelude, those missing notes (including C# up to F# in the left hand) could be a serious concern!

[acg]

2 hours ago, acg said:

There is one last thing to try for the wall bass treatments.  Below is one of the VPR's that straddles a front corner.  Note that I retain the wall mounted VPR's behind it, so three in each corner in total.  The wall mounted VPR's were much more effective than the equivalent sized superchunk trap that was initially there, and they still bring something with the VPR straddling the corner as well, but there is now a large space in that corner (a triangle roughly 1.5m x 1.2m x 1.2m) that I can backfill with the soft and fluffy batts which are still in the garage (much to my wifes chagrin). 

 

So, I brought up the soft n fluffy poly insulation batts and filled the corner void in one of the VPR corners.  This time I compared the frequency response with the trapdoor down...

 

 

 

So the superchunk filling makes a difference (of course) with much of that 50Hz-100Hz octave filling in a little.  Although not shown here, addition of one superchunk filling made quite the difference to the room RT60 Decay time which is now < 500ms all the way to 20Hz.  The RT60 Decay is basically 0.35s from 20kHz down to 50Hz and stays below 0.5s to 20Hz.  That is killer!

 

I also measured the bass response in front and behind the sweet spot and it is more or less identical in those three locations which is fantastic.  However, if I move the microphone toward the left or right wall the bass response changes dramatically which is at least in part due to the equipment rack blocking the VPR on the right wall...I wish my room was deeper!

 

Next step is to build the superchunk framework for the VPR trio at the left-front corner of the room, re-measure, then probably put up the first of the ceiling absorption.

[davewantsmoore]

20 hours ago, acg said:

The RT60 Decay

This chart is the RT60 (time), not the "RT60 Decay" chart (frequency).   Is completely meaninless when the SPL is caused by modal behaviour.

 

The decay chart, or the RT60 Decay chart is more betterer, or just like a spectrogram or watterfal is fine.

 

20 hours ago, acg said:

However, if I move the microphone toward the left or right wall the bass response changes dramatically which is at least in part due to the equipment rack blocking the VPR on the right wall

I'd be surprised if it wasn't purely due to moving (modal), and (little to) nothing to do with "blocking" given size of the waves.

 

Are you planning to change the general downwards slope (between 20 and 200)? .... not necessarily relevant for now

[acg]

2 hours ago, davewantsmoore said:

This chart is the RT60 (time), not the "RT60 Decay" chart (frequency).   Is completely meaninless when the SPL is caused by modal behaviour.

 

The decay chart, or the RT60 Decay chart is more betterer, or just like a spectrogram or watterfal is fine.

 

Yes, that is the chart I have been talking about....RT60 Decay.  I've produced it below plus have highlighted that pesky 32Hz ringing that seems most difficult to control...

 

 

EDIT:  Not the listening postition but a random location about half a metre away.  see next post for correct graph for listening position

 

There is a 200Hz ringing slightly hidden in that graph above which is the fans in my work computer so can be disregarded.

 

 

2 hours ago, davewantsmoore said:

I'd be surprised if it wasn't purely due to moving (modal), and (little to) nothing to do with "blocking" given size of the waves.

 

Up at 60Hz and 90Hz is right in the sweet spot of the VPR's and I would hope they would be able to "nuke" those lateral wall reverberations...but apparently not.  Was at another audiophiles house yesterday and we were playing with speaker and listening positions with REW and a mic and what astounded me was that a back wall one-third open (i.e. open doors) still had strong 30Hz/60Hz modal behaviour.  Those wavelengths are so long that perhaps much more than one-third of the back wall would need to be open so that the effects of the standing waves are reduced.  Makes me wonder just how useful my rear wall length of windows are as bass traps considering they do not extend ceiling to floor. 

 

 

2 hours ago, davewantsmoore said:

Are you planning to change the general downwards slope (between 20 and 200)? .... not necessarily relevant for now

 

Yes, that needs to be addressed, likely with another sub channel.  Am having trouble finding sub implementations that fit within my stupid design imperitives. 

 

My two immediate concerns are the one octave or wider suckout below 150Hz and the general lack of bass sensitivity as I do not wish to attenuate the Upperbass Horns to match.

 

Edited March 26, 2023 by acg

[acg]

So, pressed "submit" and realised that the graph in the post above was not for the listening position, but for a random spot about half a meter away.  I'll leave it there, just for interests sake, but the listening position graph is this one...

 

 

[davewantsmoore]

1 hour ago, acg said:

one octave or wider suckout below 150Hz

Can we see the SPL chart again, with the individual (bass, and midbass) SPLs overlaid?

[acg]

1 minute ago, davewantsmoore said:

Can we see the SPL chart again, with the individual (bass, and midbass) SPLs overlaid?

 

Yes, I was considering measuring this again today to make sure I've not left a "gap" between channels.  Got a bit of work to finish then I'll be into it.

[acg]

1 hour ago, davewantsmoore said:

Can we see the SPL chart again, with the individual (bass, and midbass) SPLs overlaid?

 

Measured from the listening position with the room in current state of bass absorption (no smoothing)...

 

 

Looks to me 

[almikel]

On 25/03/2023 at 7:36 AM, davewantsmoore said:

It's ~ half an octave (is not high Q)

 

Or even wider if you call it as 40 to 120.    Probably more than just the "lone mode" going on.

oops  - agreed

 

On 24/03/2023 at 11:44 PM, almikel said:

the deep suckout between say 65 Hz and 90 Hz looks terrible - but is it audible? the human ear is not very susceptible to high Q changes in the frequency response (ie sharp dips).

Mike

My BAD ~ 1/2 an octave would be audible

 

On 25/03/2023 at 9:56 AM, BioBrian said:

But how relevant is that statement, compared with musical reality?

 

Half an octave might not rate highly in The Clever Caveman's Manual of Survival, but for those of us who appreciate the middle section of Chopin's Raindrop Prelude, those missing notes (including C# up to F# in the left hand) could be a serious concern!

Of course 1/2 an octave is significant, and as Dave points out it's not a high Q dip.

 

The musical reality is that high Q dips aren't audible - if you shifted that 40 to 120Hz (80Hz wide) dip up multiple octaves to say 4 kHz to 4.080 kHz it would be 0.03 octave wide, high Q, and inaudible....

...but yes, I was wrong about the dip in @acg's response to suggest it may not be audible.

 

Mike 

[acg]

Thanks to @ylioAugustin for his Room Eigenmodes Simulator which can be used to model standing waves in odd shaped rooms such as mine.  Check out the image below for the oddly shaped pressure regions at 61Hz in my simulated room thanks to the ceiling shape...

 

 

I'm a bit unsure of a few things in setup of the model but I have used it this afternoon to try to in advance get an idea of the effects ceiling absorption on room response.  A lot of standing waves should be minimised due to the listening position, which is great.  The simulation of the circa 70Hz floor-to-ceiling mode is not behaving exactly as simulated, but it is pretty close, see below...

 

 

 

There are plenty of oddly shaped nodes generated due to the ceiling in the 60Hz-150Hz range which seem most likely to be the root cause of the suckout in that region.  It may pay to treat part of the peak of the ceiling as well as the wall ceiling junctions with something effective in that same range.

 

First things first though, finish that other VPR Superchunk filling and put some VPR's on the ceiling above the listening position.

 

 

[almikel]

49 minutes ago, acg said:

 

 

 

Why is the left back corner red, but the left front corner blue?

 

Is your gable ceiling lightly constructed? (eg Gyprock/fluffy/sisolation/colourbond sheeting)?

If it is, it's likely you won't have strong floor/ceiling modes <100Hz or so as the sound will leak out through the ceiling rather than be reflected, but the gabled ceiling will spread the floor/ceiling modes in frequency (lots of modes instead of 1 mode)

 

Mike

 

 

[andyr]

2 hours ago, acg said:

Thanks to @ylioAugustin for his Room Eigenmodes Simulator which can be used to model standing waves in odd shaped rooms such as mine.

 

Indeed.  I wish I had access to that software, 35 years ago - when I was designing my last "listening room"!  

 

Your ceiling angle - as per your below pic - looks like about 130 degrees.  As such, it should be a very good roof-slope - as, if you draw the reflection rays between floor and ceiling planes ... they do not repeat themselves (as a 90 deg angle would do).

 

I chose 110 deg for the same ceiling type, in my last house.

 

 

 

However, you may find you get better sonics by firing the spkrs down the length of the room, rather than across the roof-slopes.

 

[acg]

On 26/03/2023 at 8:08 PM, almikel said:

Why is the left back corner red, but the left front corner blue?

 

Is your gable ceiling lightly constructed? (eg Gyprock/fluffy/sisolation/colourbond sheeting)?

If it is, it's likely you won't have strong floor/ceiling modes <100Hz or so as the sound will leak out through the ceiling rather than be reflected, but the gabled ceiling will spread the floor/ceiling modes in frequency (lots of modes instead of 1 mode)

 

Mike

 

 

 

Blue and red in this situation are just like the Amroc calculator where they are areas of high pressure.  the colouring is supposed to make it easier for layersons to read.

 

Celiing is double fyrcheck with greenglue, so not that light.  The aim when building was soundproofing.  70Hz at the listening spot is measured 36dB below what is measured coming from the speakers so that mode is well and truly excited.  The gabled ceiling will tend to spread a few modes, but it also seems to make plenty more of its own which appear to be one of the triggers for the 60Hz-120Hz suckout.  Surely the horizontal room dimensions do not help in that frequency range either, but there is little more I can do with the walls to soak up that modal behaviour, it will need to predominantly be a ceiling treatment effort from here.

[davewantsmoore]

On 26/03/2023 at 1:58 PM, acg said:

Looks to me 

Did you ever record an "anechoic" SPL from the bass cannons, driven by its amp?

 

That would be very helpful, to validate how much of the "hole" is being caused by the room..... entertaining the possibility that it is not (wholy) the cause, then it may be more that the overall SPL curve of the bass channel is just "off"  (eg. in super rough terms, the level too low, and the LPF too shallow).

[acg]

1 hour ago, davewantsmoore said:

Did you ever record an "anechoic" SPL from the bass cannons, driven by its amp?

 

That would be very helpful, to validate how much of the "hole" is being caused by the room..... entertaining the possibility that it is not (wholy) the cause, then it may be more that the overall SPL curve of the bass channel is just "off"  (eg. in super rough terms, the level too low, and the LPF too shallow).

 

No anechoic or outside measurement, but I do get what you are saying.  When I put the mic up to one of the Bass Cannon drivers while it is playing 70Hz, for example, the mic reads 90dB (like it should) but put the mic at the listening position it reads 54dB which indicates high output at that frequency and a large cancellation.  I can easily check other frequencies like that, say 80Hz and 90Hz but would be surprised if the Cannons are short on output at any of those frequencies.

[davewantsmoore]

59 minutes ago, acg said:

When I put the mic up to one of the Bass Cannon drivers while it is playing 70Hz, for example, the mic reads 90dB (like it should) but put the mic at the listening position it reads 54dB

Ok.  Probbaly.

 

When you put the mic close to a bass driver, and do a sweep what do you see?

 

Of course, this "nearfield" measurement is also affected by the modes in that position, but....

[acg]

1 hour ago, davewantsmoore said:

When you put the mic close to a bass driver, and do a sweep what do you see?

 

Attached is a gated measurement from 100mm when they were first finished a while back...

 

 

Will try to see if that can be replicated when I have a moment.

[acg]

Interestingly, this is the empty room response two years later in 2019.  That 60Hz - 110Hz suckout was there are that point too.

 

[frednork]

Does look reminiscent of that room we visited with similar dimensions

 

 

[acg]

Not too different @frednork