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Old 27th October 2011
  #9
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Quote:
Originally Posted by DAH View Post
1) 8" speakers are a horror in a small room due to standing waves - 5-6'' are preferred.
I propose 8" for rooms from 15 m2 and larger due to less constrained and deeper bass (the audeince there is a hip-hop crowd). My reasons are that 5-6'' will still excite midbass modes so one extra 40-60 Hz mode from 8" is not such a horror considering the horror that will most probably exist in the midbass range already form 5-6'' speakers.
I would have to say (first) to define "small rooms"......

I don't define room size by area as much as by volume.

That being said - speaker size has less to do with frequency response (within reason) than it does with the amount of air it moves.

For (just) one example - the PMC Ltd DB1S-AII only has a 140mm (5 1/2") bass - but it's useable freq response is rated at 50Hz-25kHz Peak SPL @ 1M: 108dB, by the way - this is not to say it will not produce lower frequencies than 50Hz - simply that they will not be apparent enough to be usable. You could prove this with any speaker by simply playing sine waves through the speaker beginning at it's rated lowest usable frequency and moving down one step at a time to see what the lowest transmitted frequency really was.

However - You'll always get more of a "thump in your chest" with a larger speaker.

Quote:
2) some room is required for bass to develope.
My "busting myth" reasons - take any headphones - there is bass. It is a different matter that small rooms with massive rigid walls do not support enogh low modes. A local guru disputed this by:" read Newell and google Missing Fumdamental effect" for bass in headphones, which is obviously stupid since the bass fundamentals such low as 40-30 Hz can be and are measured in headphones.
You can't necessarily equate headphones with rooms - so we won't bother going there....... BUT - they are wrong one the face of it with their statement.

First of all - let's look at a very small room......... 13' x 12.38' with 8' ceilings.
(this equates to your 15m2 small room)

Room modes dominate from 43hz to 132hz - but, what happens below that 43Hz?

The fact that room modes aren't supported in the above room below 43Hz does not mean they are not heard.

Heck - the wavelength itself (of the lowest mode) is longer than the largest dimension of the room, 43.5Hz has a wavelength of 26' - yet not only does it have plenty of room to generate - it also creates modal activity (it's an axial mode).

What does they suppose happens with the energy from lower frequencies - does it just go into a magical place and vanish into a huge void?

Tell them to stick a huge woofer in the trunk of a car and run some rap music through it - and then tell you there is not enough room in the car to generate those low frequencies.......

Quote:
3) foam pyramides\carpet\eggcraves are good to treat the room as general absorbers\ for early reflections.
My reasons - they are not good at least, and rather harmful.
They only absorb some (narrow) High\Mids ranges though leave low-mids and bass untouched - the room gets imbalanced more than it was before the "treatment" - a dull booming\nulling room will be what we will get as a result.
Eggcrates (meaning the cartons that contain eggs in stores) are useless for anything other than putting eggs in.

Eggcrate foam (on the other hand) can have some uses, the same goes for foam pyramids - carpet is great for walking on - lousy room treatment.

So, what you say they say is true (with the exception of carpet) - that, is if they are saying what you say they are saying. For general absorption/early reflections these products are fine. There are plenty of things they would not be good for - but those 2 items would not be on that list.

There are also some (very expensive) foams that have properties that can compete with rigid fiberglass or rockwool products pretty much even up.

Carpet sucks on walls unless one like the idea of the potential for runaway fires (should something bad happen).

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4) One can evaluate different speakers in different rooms or in one room in different placements.
My reason is that room\speaker in a given spot in a room is a system, and moving speakers a step in any direction in a room will yield a unique response highly affected by the room.
It would not be possible to evaluate different speakers by comparing in different rooms - however - the sweet spot in a room may well be vastly different for different speakers.

The true test for different speakers would be to find the sweet spot in the room for both pairs of speakers and (which could be the same spot - just doesn't have to be) then do "A/B" comparisons.

Quote:
5) rear-ported speakers cannot be placed relatively close to a wall.
My reasons - as long as some decent distance (like 4-8'') for free air travelling from the port is left between the wall and a port - it does not matter whether it is a rear-ported or a front-ported speaker in terms of time alignment\resonances\spectral balance since the wave length of the frequencies at which port works is well above 3 meters long.
This would be totally dependent on the speaker I would imagine - always work within the distances recommended by the manufacturer - however - the blanket statement is wrong.

Take the Genelec 8240A - which is a rear ported speaker........ the manufacturer indicates that this speaker can be placed within 2" of a wall surface - within 2" of a corner. They also indicate a maximum distance from the wall for that speaker. Understand that the closer to a surface a speaker is (regardless of the port location) raises the frequency level of SBIR - thus making it less problematic because it is much easier to treat.

I would consider 2" from a surface "relatively close".


I hope this helped,

Rod