Speaker positioning - hight

..or quite possibly....maybe he's even got something no-one here's considered before

 

I give up :banghead: I do try, but well, hey it's sunday and mellow day, and I was being polite too

 

I'm not a regular visitor to the forum, and i'm absolutely not an regular poster. I'd assume that's why i'm now failing to follow the last few posts. Hasn't this thread been 'done', so to speak?. There not necessarily being conclusions, rather there being several strongly voiced opinions. Followed by myself and LiloLee with a couple of amiable posts regarding some wall diffusors.

Cable performance perhaps?. I haven't thought about that for years, since I stopped designing and researching them. In fact, it would be fair to say that i've thought nothing of cable performance since.

 

Lee...mission said in some literature it was to do with time alignment.....but it will obviously change the distance the bass unit is from the floor with all those attendant effects...

for the question as to how tweeter top or bottom makes any difference, imagine you have a 2 way with the tweeter on top at ear level....draw a line on paper from your ear to a blob....this blob is the tweeter....put another blob direct below...this is woofer ...draw a line from the tweet blob to woof...now there is a space from your ear to the woofer, draw a line...this is a diagonal of a triangle..remember pythagoras that the hypotenuse...is the longest side...this is the diagonal...ie ear to the woofer and is longer than the ear to tweeter...
..so if you reverse it and the woofer is at ear height and the tweeter below, you are making the tweeter further away...
now the tweeter is less deep than the woofer, so time takes less to arrive...now if tweet is on top, then its nearer via your line, and the sound centre is nearer, too as the voice coil is further forward...
but if you make it below, hopefully the time from tweeter to ear will be same as from woofer, as tweeter is made further away...if this makes sense!!

most speakers these days are designed time aligned( one would hope) I have found tho' it does make speakers more open if they are tilted up slightly...that is assuming tweeter on top...

crossover design is complicated..you can make many different values and they all measure flat..at higher frequencies, the baffle reinforces the bass drivers output, and this has to be accounted for, too...its called the baffle step effect...I don't think your average man in the street has any idea about the intricacies..

refraction is bending of a wave passing thro a different medium...

eg air/water..

relection is obviously that..but won't putting a table in between still reflect the sound up to you..effectively raising the floor height....

the listening room is a big problem, and I have not got an ideal one...i haven't done anything to it....soft surfaces are for hf absorbtion, as these get absorbed quick due to low energy...imagine an empty room and it is reflective....reverberation...
breaking up room modes is another thing and is to do with bass reinforcement and booms....this is where you need to scatter to reflections, not absorb them.....tho that would help..I don't know much about this...and havne't xperimented yet...

 

Gotcha!!!

OK, I appreciate that hf will get to you faster than lf, and that the non perpendicular driver will take longer to reach the listner than if it was perp'. But with the average gap between the two drivers being so small, surely the gap would unnoticable? I'm not aware of any sorts of distance/time figures, but surely that gap isn't audible? Or is it?

 

Well this depends on the frequency. Low Frequency signals have a wavelength of several metres so adifference of a few mm is not going to be noticable. Let's calculate a bit...

for a signal of 100 Hz:
Sound travels at 300 Metres a second. 100 Hz means 100 waves a second so a wave is 300/100 = 3 metres long.

now for a 10000 Hz sound:
again at 300 m/s this signal has a wavelength of 300/10000= 0.03 metres. Three centimetres which means a distance difference of 15 mm will now result in a phase shift of half a wave or 180 degrees. This could be audible.

 

Most tweeters are designed to be at ear height, however, it is not a fixed rule. Some sound better above or below ear level, a little experimentation is required.

As for room acoustics, this is highly complicated issue. It is the interactions with the room which provide a sense of space which is pleasing to the ear/brain. Reflections are important in music but they must be managed.

A hard floor can create some problems but can be minimised by speaker hight and placement, it is the same for hard ceilings. Domestic considerations do play a part, how many rooms apply diffusers or other devices to a ceiling? My guess is very few. In most rooms the interaction with the ceiling is quite low compared to wall reflections which tend to dominate reflected sounds.

Overkill on reflection control will kill the acoustics in a room and consequently the sound quality as well.

 

Yes, at frequencies whose wavelength equates to the size of said table. Those frequencies whose wavelength is greater than the table will not 'see' it (although these are likely to be of a size considered modal, rather than reflective in terms of first reflection points). Naturally, the table surface may be absorptive and/or diffuse, depending on any covering.

In terms of providing enough absorption to satisfy T60 (reverberation time - time taken for a sound to decay by 60dB), most (unless one follows a minimalist ideal) rooms probably have enough (defined by the number of Sabins - as in Sabine, the fellow responsible for much pioneering acoustical work, including the T60 formulae). The primary use of additional absorbents, then, comes from treating primary reflections. Hence, being generally additional, the need to control their use in order that the room does not become overly 'dead'.

Modal response is a given - relative to a room's dimensions - and impossible to treat with spot diffusion. Much better, then, to negate the influence of modal response with careful speaker/listening position set-up, perhaps allied to a bass trap or two.

Please do - the potential is very real.

I have a diffusor at the primary ceiling reflection point. Depending on room dimensions and speaker location, the ceiling maybe the second primary reflection, after the floor, to reach the listening position. It's treatment, therefore, should be given due consideration.

Very true, and the reason why; after calculating room absorption, I chose a diffusor for the ceiling - much more complex to build and install, but ultimately worthwhile.

 

Audiophile grade artex?

 

Yes, from Russ Andrews, £500/bag.

Has hyper-pure (natch) copper strands in the mix to combat any devious RFI that may emit from the rooms above. Most useful if one uses a radio alarm clock in the bedroom.

Comes complete with a reflection-phase-grating stippler