The problem is the property has to meet other needs as well… The house I had in mind (70s bungalow) has a room large enough to build a good size listening room within, apart from limited height unfortunately. COVID has resulted in changed plans, with house move postponed and uncertain, so whether that ever comes about I don’t know. And yes, solid walls needed - which makes going ahead a substantial decision (pun not intended) so much planning first…
In an ideal world I’d have a house built to my design - but there is simply no land of suitable size in the locations to which we would want to live out our years after retirement (the rare plots that do come up invariably have planning permission for multiple houses, pushing the land price up ridiculously).
Absorbing at 30 Hz, isn’t an easy task. Just forget the usual porous absorbers, they have literally no effect.
The only way to go is to precisely identify the frequency and build something targeting that specific frequency (Membrane based absorber, Helmholtz Resonator or diaphragmatic absorber).
There is another, but costly, option : active absorption, like the PSI AVAA C20.
Moving the listening position, if possible, is something to try. In fact, the listening position has massive impact on the perceived low end.
It is easy to try : just walk around the room while listening to low frequencies (under 250 Hz).
Just forget my previous answer. I fear my “techy answer” won’t be of any help.
My advice would be : just forget your 30 Hz issues. It’s no big deal really, unless you’re an organ or electronic music amateur. Even so 30Hz doesn’t happen so often.
I would worry a bit more about the upper part of the low end spectrum.
If you have a room mode at around 30Hz, it means you have it too at around 60Hz, 120Hz, 240Hz and so on.
You can deal with 60Hz, and up, with 6 inch (or more) porous absorbers. If you make them yourself it’ll cost you the price of two bottles of Islay single malt (and you can make a lot of them).
By the way my system sounds incredible…but i would hate to have it put thru a rew test…another can of worms. Even dealers, find it difficult to give a homely demo setting, and so called perfection.
I had my speakers toed in pointing directly at the listening position. I tried toeing them out so I could just see the inside face of each speaker. This widened the sound stage and definition of vocals and instruments improved a tad.
As a first attempt to tackle the slightly bloated low bass (from standing waves I presume), I tried inserting and then removing the speaker port foam bungs.
I used a Diana Krall track with a plucked double bass that displayed this bass overhang. Bungs removed had the deep bass resonating with a deep single note sitting on the presentation when a deep note appeared in the mix. The upper bass and mids however are a joy with wonderful definition and tone.
Inserting the bungs helped with the deep bass resonance but robbed the upper bass and mids of some definition with Diana’s voice being a tad less distinct and plucked upper/mid bass notes losing some leading edge.
So I have settled on putting the bungs very lightly into the ports with most of the bungs hanging out. Thanks for the tip @Gazza. Not perfect but I am getting almost the best of both worlds, although I will now test different seating and speaker positioning to continue to address the residual bass overhang.
Listening to Gregory Porter Liquid Spirit now and not noticing the deep bass issue so much (as there is less deep bass content) but better PRaT, and ‘boogie factor’. This album was always a challenging listen in the smaller room as it has a dense mix in places. Here in the bigger room things seem more in control, although I fear I am reaching the peak of the 250DR’s capability in this regard.
And there was kind me not earlier suggesting exactly that Nigel! ATB Peter
PS. You could always start an entire new thread: ‘… and now over to the 500’. Best Peter
Quite right Thomas. It is indeed seating position I was going try next. Once I have optimised listening position in terms of getting the best bass balance, I will move onto trying different speaker positions to optimise soundstage and balance. I am conscious however that if I try to push the speakers back too close to front and side walls, bass response could be adversely affected, so it will be incremental speaker movements. This is the bit I am not looking forward to in that it can become tedious and you can end up disappearing up your own rear end!
I only played with toe in and port bungs as I thought there could be some quick wins here, and lessen the problem that seating position will need to fix.
That’s not necessarily true. This is a myth peddled by companies that make large expensive blocks of foam and call them bass traps, promulgated by them to differentiate themselves from people who make the smaller and even more expensive tuned membrane traps.
The alternative is the damped membrane class of broadband absorbers; which, compared to tuned membrane absorbers are more bulky but cheaper to implement and easier to set up, and compared to foam blocks are of similar bulk (or slightly smaller), slightly more expensive to implement, work to much lower frequencies (typically >1 octave lower) and are just as easy to set up.
(Of course those who make the tuned membrane devices don’t mention the damped membrane absorbers either, as these would put a big dent into their lucrative main market of neater and very expensive custom designed solutions professionally tailored to the precise needs of the room!).
Even with a substantial understanding of the physics, so was I!
Essentially you need to understand the lowest frequency that you need to absorb…
That determines the combination of the thickness of the absorber and the area density of the membrane.
The thicker the absorber and the denser the membrane, the lower the absorption band starts (and stops!).
It’s a good idea to understand the highest frequency in the main (lower) absorption band that you can tolerate and the lowest frequency you can allow in the in the upper absorbance band that you can tolerate as these determine the surface materials available. For instance, plastics have more reflection at higher frequencies than does cloth, and inherently lossy materials have more absorption in the mid band than do more purely elastic (i.e. more ‘springy’) materials. This is a lot less important as it’s a secondary issue and the higher frequency absorption of a room can be adjusted in many other ways.
The other thing to consider is the area required; unfortunately, this is best left to experiment, but will typically be at least 10% of the surface area of the walls of the room in order to treat more severe resonances.
So after deciding on quantity and a membrane material, the construction:
In essence this is just a sealed bag (the membrane) containing two grades of elastic porous material (the storage and loss media and control of the air velocity inside the bag). The core of the bag is a set of higher density fibre (mineral or glass) slabs, surrounded a lowed density fibre ‘blanket’ to provide a lower density suspension and damping for the membrane.
That all there is to it!
It’s this simplicity that puts off commercial manufacturers as they can’t use complexity of structure or shape, or fancy "acoustic’ materials to justify a high cost.
As I have said before I hope to avoid the introduction of bespoke room treatment through my own ‘trial and error’ set up and positioning measures. The use of any kind of bass trap would be a last resort (that 10% min coverage puts me right off and they would need to be at least 6 inches thick), but it is good to have an idea of what would work best and what is practical.
I would never attempt to build my own damped membrane absorbers, so I would be at the mercy of the manufacturers getting the design right and recommending correctly (e.g. GIK and their monster bass traps with their range limiter, so-called ‘FlexRange’ technology, a fancy way of describing some glass fibre insulation in a bag!) Although the FlexRange models show better absorption at lower frequencies, they do not seem to be much more absorbent at the lowest of frequencies compared to their standard bass traps. What I do like about the GIK membrane (FlexRange) monster traps is they are less absorbent at mid and higher frequencies. The last thing I want to do is treat low bass and kill some of the life and vibrancy I am enjoying higher up the frequency range.
Do you have any thoughts on GIK bass traps and the efficacy of their FlexRange?
(and you can make a lot of them).
ATB Peter
Best Peter