Speakerplans.com Homepage
Forum Home Forum Home > General > Newbie Discussion
  New Posts New Posts RSS Feed - room effects
  FAQ FAQ  Forum Search   Events   Register Register  Login Login

room effects

 Post Reply Post Reply Page  <123>
Author
Message
5toes View Drop Down
New Member
New Member


Joined: 09 April 2018
Location: Seattle
Status: Offline
Points: 7
Post Options Post Options   Thanks (1) Thanks(1)   Quote 5toes Quote  Post ReplyReply Direct Link To This Post Posted: 09 April 2018 at 6:51pm
Hello,

Longitme lurker here, and this is my 1st post so take with a grain of salt... I do not claim to be an expert.

I am in the same position as you. I throw events very similar to yours... always having a new venue, with my own DIY speakers, etc. I think you need to take a step back and realize something:

1. any DIY speakers that you make yourself and are generally content with or find "OK" or "Good" are going to be "amazing" and "incredible" to 98% of the audience. DIY designs you are proud of are going to be alot better than any guitar center type crap others in your area likely use.

2. your rig does not need to be flat to 30hz to truly impact your audience. You said yourself that most tracks that will be played do not go that low, and even then, very few basslines touch those frequencies. To be +/- 3db down to 30hz is asking a hell of ALOT for a BR speaker. You need alot more "rig" for the gig to achieve that... you will need twice as many subs as a system that can hit +/- 3db at 35hz. does not make sense. 

3. DISPERSION. Horn loaded subwoofers have a coverage pattern just like horn loaded compression drivers... say 90hz horizontal by 45 vertical, etc. If your crowd members are going to be standing around the dance floor all over, then having two giant stacks of speakers one on each side will not have very much bass in the middle. Even worse, with these narrow dispersion patterns you will have that bass "in the carpark" and not on the floor. Think like a flashlight beam... for these kinds of parties a FLOODLIGHT style is better than a focused beam. Bass reflex, sealed, open baffle etc. speakers will provide more "spread-out" coverage on the dance floor.

4. LOGISTICS LOGISTICS LOGISTICS. Giant horn loaded boxes are very bulky and hard to transport. I just picked up a gig myself because the other guy had Bill-Fitz-Maurice (BFM TUBA 60s I believe) that are too big to be carried up stairs and into the venue. If you are on the move, always using a new venue (like me), then high-power bass reflex designs are likely the best for you. They can be ran as singles, fit easier into transport vehicles, and some can be carried by one person. 

My own rig, subwoofer wise, is 8 single 18 inch boxes loaded with B&C 18TBX100's. The cabs are built in my backyard out of 33/4 MDF, and heavily braced and painted with duratex. 9 cubic feet gross and tuned to 35hz... the final Vb is roughly 8.2 cubic feet. I power all 8 with 2 QSC PL380s in stereo. I have under $5000 in this whole rig and it is bonkers the output per $$$. My subs play very nicely and I love the warm tone of them. The sim'd F3 is 34hz at 125db continuous (half space). So with 8 of them center-clustered it is about 134db at 34hz.

That said, one of the venues I frequent is an empty 7,000 sq. ft metal building. The walls vibrate so much that it steals alot of the bass response... you can hear the building rattle in the parking lot with windows up LOL. It sounds like you hit a plateau sort of... you push the speakers harder but the gains are not linear, as if the venue is compressing the output for you in a way. In venues like this the best you can do is just put the show on and deal with the consequences. This place rattled like crazy, but the rig still sounded good with no peaks in the response from the room, and the crowd thought it was great how much the place rattled LOL. Rig placement, as said, is much more important.

might of gotten off topic.. but my main point of this post was to help you realize what you REALLY NEED :)
Back to Top
gen0me View Drop Down
Young Croc
Young Croc
Avatar

Joined: 20 February 2016
Location: UK
Status: Offline
Points: 999
Post Options Post Options   Thanks (0) Thanks(0)   Quote gen0me Quote  Post ReplyReply Direct Link To This Post Posted: 09 April 2018 at 7:11pm
Originally posted by 5toes 5toes wrote:

3. DISPERSION. ...
No they dont have pattern like cd drivers. Only thing that controls directivity here is mouth shape. Its ofc bigger than just membrane in reflex box. But more important is shape of a stack.

Originally posted by Teunos Teunos wrote:

Read up on Huygens theory and imagine how it would affect sound.
If the source is small compared to the wavelength, the source will become omnidirectional. If the source is much larger than the wavelength, it will automatically be directional.

Typically you have 3 regimes that control directivity.
  1. Low frequencies where the wavelength is much lower than the size of the horn in the measurement plane. In this area directivity is primarily controlled by horn size and efficiency/frequency response by expansion profile. Since your horn is wider than it is tall, it will be more directive down low in the horizontal plane than it will be in the vertical plane. This is contradictive to what you want if you for instance want a 60Hx40V horn. Below a certain frequency, the horn will become more directive in the plane with the bigger size, in this case the horizontal plane. This is a phenomenon commonly refered to as pattern flip.
  2. Midband frequencies where the wavelength of the sound is roughly equal to the size of the horn. In this area, both directivity and and frequency response are HEAVILY influenced by horn geometry more than it is influenced by the size. Since the wavelength is roughly equal to the horn dimensions, you can get all sorts of reflections and therefor standing waves inside your horn if the mouth does not perfectly terminate in a smooth transition towards the open space. This is because the sound undergoes a change in acoustic impedance and if this change is abrupt, it will cause the sound to be reflected. Usually in this area is where you see edge effects that cause comb filter like effects in the frequency response, and long, slow decaying trails in a waterfall plot. The effects you see in a directivity graph are what is commonly known as midrange waste-banding. 
  3. High frequencies where the wavelength is bigger than the sound. In this region, size does not matter anymore. The primary effects that affect the dispersion is simply the angle of the horn walls, and how well the sound can follow these walls. If you have a horn with a rapid expansion profile, the higher frequencies will ''break'' free from the walls very soon which means that for increasing frequency, the directivity increases and dispersion angles decrease. 
    To make sure that even the highest of frequencies are ''dispersed'' throughout the intented coverage angle, many horn designs use a diffraction slot. If the width of this slot is small enough compared to the wavelength, the slot will be omnidirectional. If the horn angle after that is for instance 90 degrees, the sound will be dispersed throughtout the full 90 degrees. (again, read up on Huygens). The diffraction slot however is a distortion generating beast since like i said in 2, it offers a HUGE abrupt change in acoustics impedance > reflected sound > standing waves > resonances> high distortion. (This is why i love my JABO KH53 horns on the BMS horns, no diffraction slot. These horns sound leagues better than the JBL 2385A i also sometimes use. (See the topic : http://forum.speakerplans.com/2-tractrix-horn-any-interest_topic97925_page1.html ) 
Point 1

Read Rog Mogale guide of bass arrays.

There was topic on diyaudio full sized vs undersized horns about dispersion.
I appreciate every like :)) https//www.facebook.com/genomesoundsystems
Mixes: https://www.mixcloud.com/gen-ome/
Back to Top
Hemisphere View Drop Down
Old Croc
Old Croc


Joined: 21 April 2008
Status: Offline
Points: 2272
Post Options Post Options   Thanks (0) Thanks(0)   Quote Hemisphere Quote  Post ReplyReply Direct Link To This Post Posted: 09 April 2018 at 7:27pm
The bit about needing more subs to reach 30Hz than 35Hz with a reflex system is also untrue. Bigger, but not more, and as my suggestions illustrated, not even necessarily bigger! Just pick the right driver for a small 30Hz reflex bin.
Phase 1: Post on Speakerplans
Phase 2: ?????
Phase 3: Profit!
Back to Top
toastyghost View Drop Down
The 10,000 Points Club
The 10,000 Points Club
Avatar

Joined: 09 January 2007
Location: Manchester
Status: Offline
Points: 10920
Post Options Post Options   Thanks (0) Thanks(0)   Quote toastyghost Quote  Post ReplyReply Direct Link To This Post Posted: 09 April 2018 at 10:39pm
So much misinformation in this thread.

The bass in the car park effect is caused by the fact that absolutely no subwoofer has its acoustic centre at the mouth, let alone an array. Even for a reflex it’s in front of the box by several inches to feet. A fully horn loaded bass system has a ‘phantom horn’ effect caused by the impedance match to the air in front of the array, and often loads smaller rooms as part of the system meaning you’re technically inside the box.

https://www.merlijnvanveen.nl/en/study-hall/145-low-frequency-acoustic-center-calculator

Used correctly they can be way better in almost all aspects than reflex, but it takes more skill to deploy and design them properly. Hence hybrid or reflex being more common.

Edited by toastyghost - 09 April 2018 at 10:40pm
Back to Top
5toes View Drop Down
New Member
New Member


Joined: 09 April 2018
Location: Seattle
Status: Offline
Points: 7
Post Options Post Options   Thanks (0) Thanks(0)   Quote 5toes Quote  Post ReplyReply Direct Link To This Post Posted: 10 April 2018 at 4:46pm
I didnt claim to be an expert, but I just learned something new too.

First off, I didn't say that compression drivers have a pattern... I said that horn-loaded compression drivers have a pattern. The pattern being established by the THE HORN... just like a horn-loaded subwoofer. We are in agreement that the horn's mouth/shape is what controls pattern. My point was basically that horn-loaded subwoofers have a narrower pattern than bass-reflex type, and that on small + wide dance floors a wider pattern is more even coverage... agreed? I now am beginning to udnerstand how arrays change the pattern, I am reading this resource (thank you for the tip)

https://www.electrovoice.com/binary/wp%20-%20Subwoofer%20Arrays%20v04%20.pdf

As far as reaching 30hz with BR boxes, there are not any budget drivers I know of out there that can do that at high SPL. Sometimes at my shows I bring all my subs and lower my highpass from 35hz to 25hz. I add 5db boost @ Q2.0 @ 30hz to extend the low end since I have all the subs working together. At high output my speakers exceed xmax below the tuning freq. very easily but if running them at lower power levels I enjoy extending the low end in this way (thus more subwoofers at less XMAX each to have a usable 30hz). That was what I meant by bringing more subwoofers... that if your standard box is f10 at 30hz, using 4 of them gets you F4 at 30hz (just have to reduce the standard operating range, say 40hz-80hz).

TOASTYGHOST - are you saying with large arrays the acoustic center is in the center of the dance floor, making the bass somehow go outside the venue..? please elaborate I am very interested.
Back to Top
gen0me View Drop Down
Young Croc
Young Croc
Avatar

Joined: 20 February 2016
Location: UK
Status: Offline
Points: 999
Post Options Post Options   Thanks (0) Thanks(0)   Quote gen0me Quote  Post ReplyReply Direct Link To This Post Posted: 11 April 2018 at 8:14am
You dont have to capital letter words instead you could read once more.

Why acoustic centre is in front?
Basses group delay has positive value. So it should be behind them.

Basses stacked in line will have more cylindrical wave than spherical so less disappearing with distance but it wont work anyway on parking distances.

Heard this 2 months ago. On reflexes. On dancefloor was very weak :( side wall was being demolished.
                                                                               PARKING


Edited by gen0me - 11 April 2018 at 8:25am
I appreciate every like :)) https//www.facebook.com/genomesoundsystems
Mixes: https://www.mixcloud.com/gen-ome/
Back to Top
toastyghost View Drop Down
The 10,000 Points Club
The 10,000 Points Club
Avatar

Joined: 09 January 2007
Location: Manchester
Status: Offline
Points: 10920
Post Options Post Options   Thanks (0) Thanks(0)   Quote toastyghost Quote  Post ReplyReply Direct Link To This Post Posted: 11 April 2018 at 9:54am
Originally posted by gen0me gen0me wrote:

Why acoustic centre is in front?
Basses group delay has positive value. So it should be behind them.


What? You think that the lag in time domain means that the box physically starts radiating sound behind the cabinet?

The AES paper is here if you want to read it:
https://secure.aes.org/forum/pubs/conventions/?elib=15289

Edited by toastyghost - 11 April 2018 at 9:54am
Back to Top
gen0me View Drop Down
Young Croc
Young Croc
Avatar

Joined: 20 February 2016
Location: UK
Status: Offline
Points: 999
Post Options Post Options   Thanks (0) Thanks(0)   Quote gen0me Quote  Post ReplyReply Direct Link To This Post Posted: 12 April 2018 at 7:27am
Ofc Im wrong.
So the virtual acoustic source is a line in front of the stack?
I appreciate every like :)) https//www.facebook.com/genomesoundsystems
Mixes: https://www.mixcloud.com/gen-ome/
Back to Top
toastyghost View Drop Down
The 10,000 Points Club
The 10,000 Points Club
Avatar

Joined: 09 January 2007
Location: Manchester
Status: Offline
Points: 10920
Post Options Post Options   Thanks (0) Thanks(0)   Quote toastyghost Quote  Post ReplyReply Direct Link To This Post Posted: 12 April 2018 at 1:57pm
It's not a line, no. But yes, for all subs, it is in front of the box / stack and the position varies dependent on design type / box shape as shown in the paper. There isn't full data for fully horn loaded boxes, presumably due to test time constraints or access, but I am working on doing some testing of horn loaded boxes alongside some other people at some point this year.

As an example, for a DAS Event 218A, the acoustic centre was over a foot in front of the boxes.
Back to Top
gen0me View Drop Down
Young Croc
Young Croc
Avatar

Joined: 20 February 2016
Location: UK
Status: Offline
Points: 999
Post Options Post Options   Thanks (0) Thanks(0)   Quote gen0me Quote  Post ReplyReply Direct Link To This Post Posted: 13 April 2018 at 4:30pm
So do you want to place mics, take measurements and check how the wave decreses with distance? For stack you cant just cant check how the spl decreses 6db. The wave will be cylindrical on smaller distances and spherical in far field. You need to figure out the hole physics behind it. Can take a shoot and hypotheticaly assume that virtual acoustic source would be a face like this:
Than you could treat the face as the sum of points: Ex=a to b(Ey=g to h   f(A(x,y))

Than for every of those points + mic use classic spherical decrease, add some reflection from ground. And you need to figure out the phase summation... (all together is f(x))
This is 3 dimensional integral math :(.
Edit:
Actually 3rd dimension will probably hide in the function so probably 2 dimension integral.


Edited by gen0me - 13 April 2018 at 4:47pm
I appreciate every like :)) https//www.facebook.com/genomesoundsystems
Mixes: https://www.mixcloud.com/gen-ome/
Back to Top
toastyghost View Drop Down
The 10,000 Points Club
The 10,000 Points Club
Avatar

Joined: 09 January 2007
Location: Manchester
Status: Offline
Points: 10920
Post Options Post Options   Thanks (0) Thanks(0)   Quote toastyghost Quote  Post ReplyReply Direct Link To This Post Posted: 13 April 2018 at 7:06pm
I’d recommend reading the paper before you get theoretical.
Back to Top
MattStolton View Drop Down
Old Croc
Old Croc
Avatar

Joined: 04 September 2010
Location: Walthamstow
Status: Offline
Points: 4234
Post Options Post Options   Thanks (0) Thanks(0)   Quote MattStolton Quote  Post ReplyReply Direct Link To This Post Posted: 14 April 2018 at 9:13am
FFS.

+3dB is "electrically double", so 100W to 200W is +3dB, 200W to 400W is +3dB.
+6dB is "perceived" as being twice as loud.

Standing waves will happen with 2 or more parallel reflective surfaces. The fundamental frequency of this standing wave between two surfaces, is a function of distance of the two surfaces.

Quite simply, a wave hits a wall. Depending on surface, some of the wave will be reflected. When peaks of incident wave match with peaks of reflected wave, you get summation to one big off wave, i.e. loud. When nodes of incident and reflected happen together, you get summation to silence.

If you excuse the attempt to sell you multiple subs to combat above, nice diagrams here

The first standing wave frequency is given by:

F1=C/2L

where L is the distance between the two walls.

C is the speed of sound

Harmonics will occur at 2F1, 3F1, etc.

If you put (wave) energy, i.e. sound, into that system, at some frequency, related to the dimension, you will create a standing wave.

For that particular standing wave, as you listen along its length, it will have loud areas, and silent areas, for that particular frequency.

Now the fun. You have all these nodes (silence) and anti-nodes (loud bits) of standing waves between any two particular walls, and their harmonics. And between floor and ceiling. And between the back of the stage and it's opposite wall. And that little alcove around the corner works like a closed pipe, so its fundamental resonance is given by the formula F1=C/4L, with harmonics at at odd harmonics, i.e 3F1, 5F1, etc.

In effect wherever you lay your ear, you are going to be hearing a mix of direct from speaker membrane sound, mixed with standing wave effects at the exact micromillimeter of your ear. When I say mix, the direct and local waves will sum/cancel at any one particular frequency, in or about your timpanic membrane.

Move, and the room Vs direct sound mix to timpanic mebrane will change too.

We wont get into how the hall way works as an open pipe, and its fundamental frequencies.

A different effect, with nothing to do with standing waves, is whacking subs in corners of rooms.

We all wank on about measuring in 4Pi space, and how some HR predictions are BS "'cos it was done in 1/2Pi mode".

Bear With Me.

The surface area of a sphere is a function of its radius, A=4 Pi r^2.

A speaker is hanging in the middle of space. Because it is only a 8" driver, at 50Hz (7M ish wavelength), the emanating sound wave will tend to emanate omni-directionally. It does this spherically, or in Full space, AKA 4Pi.

Now attach same speaker to wall. The 50% of the sphere of radiated sound wave bounces off wall behind and now emanates forward with original, doubling output (+3dB!). This is 1/2 space AKA 2Pi.

Now stick it on the Floor, against a wall. 1/4 Space AKA 1Pi (another +3dB)
Now stick it right in a corner, 1/8 Space, 1/2Pi (Another +3dB)

So in going from hanging your speaker in free space to whacking it in a corner, you get 9dB more SPL, all other things being equal!

The rub. This is very true for low frequencies, which emanate from BR boxes omni-directionally. Horn loaded can be thought of as already having their BR reflex constrained in some form of 1/2Pi "Conductor", the exact dimensions of the horn create the exact form of this control, and size of horn will effect to how low this "1/2Pi ness" is applied, but, in short, a fully horn loaded sound source will not be affected by space changes as much as a BR speaker. Apart from frequencies lower than the horn is controlling, it effectively is putting itself in the corner already, to some extent, and to some low frequency, which is mouth size related.

So yes, some rooms sound having sex awful, get some drapes to absorb acoustic energy from hitting wall, and break up surfaces to make what standing waves are left as diffuse and even as possible.

Car park sub. That resonant hall way open pipe I skipped over, or the roof flexing, or any other tuned volume of air....
Matt Stolton - Technical Director (!!!) - Wilding Sound Ltd
"Sparkius metiretur vestra" - "Meter Your Mains"
Back to Top
 Post Reply Post Reply Page  <123>

Forum Jump Forum Permissions View Drop Down

Forum Software by Web Wiz Forums® version 12.06
Copyright ©2001-2023 Web Wiz Ltd.

This page was generated in 0.094 seconds.