Carpe Diem System Spec by fjzhxb

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									Prosonics
System appraisal and upgrade recommendations for;Carpe diem, rossington street, leeds

Introduction
This report is on the critical appraisal of Carpe Diem in Leeds city centre. Carpe is a pub/live venue with a capacity of 550 (whole bar) and serves to entertain a varied crowd of dance, rap, acoustic and band style of music lovers in both live and jukebox formats. For the sake of the report we will just be concentrating on the system used for the live entertainment side of the venues audio entourage. The system is a fairly common format of backline, PA and monitor setup with only forward facing speaker to the audience who stand in front of the stage opposite the bar. The mix position is close to the stage off centre behind the bar where all mixing and CD DJ control takes place. This layout invites large bands (acoustic and electric) and DJ/MC acts to the open mic nights held. This report is to critically appraise the system Carpe use covering the following test and deductions: 1. System specification covering all areas of the equipment including mixer type, amplification equipment, cable and connectors (quality, lengths and distortion properties), loudspeaker choices and outboard equipment facilities.

2.

Full exploration in to quality of equipment in relation to added distortion/noise, frequency analysis of system (hot and cold) and graphical representation of our findings.

3.

Reverberant qualities of the room including a rough RT60 test, reflective properties of the room and a mode table showing the first set of tangential room modes of the live area with highlighted problem modes.

4.

Listening positions including that of the mix position, stage position and audience.

5.

System and positioning improvements for carpe diem including possible acoustic treatments and tips for improved sound.

System Spec Front of house Amplification and Speaker Configuration
The amplification system comprises of a QSC CX1102 amplifier driving the mid/high speaker running in stereo mode. The amplifier delivers 1100 Watts of continuous power into 4ohms to each speaker. The speakers in question are two Martin Audio „Blackline‟ F12‟s with a frequencies response of 65 Hz - 16 KHz. The 12” drivers are capable of receiving 400 to 1000 Watts of power into 4 ohms. The two subs are driven by a QSC CX902 amplifier; again in stereo mode it delivers 900 watts of power into 4 ohms to each sub. The amplifiers have a frequency response of 20Hz to 20 KHz. The subs

the venue uses are two Martin Audio Blackline S15‟s. These have 15” drivers with a frequency response of 45 - 120 Hz and can receive 600 -500 Watts of power into 4 ohms. These have an active/passive low pass filter at 120Hz to which cuts any signal above this frequency. The amplifiers have a distortion rating of 0.01% THD at 20Hz to 20 KHz. This is at 10db below rated power. Also the damping factor is acceptable rated more than 500, (anything over 100 is good), and this shows the amplifiers are more than capable of controlling voice coil excursions of the drivers attached to them effectively. Below are diagrams of the sound projection from the speakers. As you can see the crossover point is over the centre of the audience. Sub projection has been left off as sound is less directional with bass frequencies.

Figure 1: Overhead view of speaker projection

Figure 2: Side view of speaker projection

Sound Distribution System
The pub also runs a „sound web‟ system which is capable of distributing the sound to different areas of the pub as well as to the PA. The speakers for each area of the pub have a separate amplifier. Multiple inputs on the sound distribution system mean that as well as audio coming from the mixer a CD changer, TV audio and a networked computer for playing music can be played. Each of these streams can be routed to any of the areas of the pub.

Mixer
Carpe Diem uses an Allen and Heath „Mix Wizard‟ WZ3 16:2 desk. This has 16 analogue mic/line input channels and two sub-groups. Allen and Heath is a well recognised name in the music industry and considered to be a very high quality desk. One of the main features of this desk is its routing flexibility. Each channel has an insert point in which external effects can be added if

needed and there are six auxiliary sends. In this system aux 1 is used for the monitor mix. A master Aux 1 pot controls the overall level of the mix whilst individual channels can be mixed by adjusting the aux 1 pot on each channel. Each channel has a signal and a clipping LED, 100mm faders and a 4 band EQ with two sweepable mids. There is also a pre-faded listen button which means that elements of the mix can be monitored through headphones whilst the main mix is still playing from the front of house.

Signal Processing
Under normal circumstances a compressor/expander and limiter/gate are wired to the insert points of track 10 to 14 of the desk. These are used for kick, snare, and toms respectively. If these signal processors are needed on other channels patch wires could be changed over to different insert points relatively easily. There is a Beringer Multigate Pro (XR4400) quad expander/gate. The two compressors are Beringer composer XL (MDX2600) and Beringer Multicom Pro-XL (MDX4600).

Effects
A TC electronic multi-effects processor connected to auxiliary 4 is used to add effects to channels as required.

Monitoring System
The monitoring system comprises of two „Electro-Voice S15-ME‟ floor monitors connected to a Crest Audio amplifier. The monitor mix is sent from auxiliary 1 on the mixing desk through a Behringer 32 segment graphic EQ and a „Cloud CX335‟ limiter to the amplifier which is located on stage.

Mixer to amp Cables
The cabling used to wire between the mixer and the amplifier are Kelsey Uni-1 analogue/digital cables. At first sight of these cables they look to be reasonably old. Another factor to consider when measuring the quality of the cable is the thickness and these cables seemed to be fairly thin. This would suggest that they are not of a good quality and to achieve a better signal better, thicker cables would have to be installed. The fact that the Kelsey cables are manufactured for analogue and digital signals suggests that they are compensating to work fairly well in each field. However, as only analogue audio signals will be flowing through them it would be far more suitable to purchase a better quality cable that specialises in carrying analogue signals. The fact that these cables connecting the mixer and the amplifier have to travel approximately 22.8 meters tells us that the resistance of the cable will be far higher than is required. As with all electrical conductors the resistance increases with length. So although resistance will always play a part in reducing the performance, if the two connected pieces of equipment were situated closer to each other, the resistance could be kept to a minimum.

Speaker cables
The speaker cables which travel between the amplifier and the speakers are made by Nohalflex. These contain 2 cores of 2.5mm OSC copper speaker wire. These cables, like the Kelsey cables, have got a very long distance to travel, far longer than is ideal in an audio performance environment. From the amplifier to the left speaker the signal travels through 23.3 meters of wire while from the amplifier to the right speaker it has to travel through 27.8 meters.

Signal flow diagram

Above you can see a system diagram. This shows how Carpe diem is wired and shows the independent components in succession and the signal flow paths. As can be seen from the system diagram the signal comes off the stage via the stage box into the mixer, this is connected with a high quality Van Damme cable snake into an Allan & Heath mixer. The signal then goes to the outboard (hardwired) signal processors and also though an effects loop for reverbs and delays. The combined signal is then sent to the amplifiers where the signal is sent into 2 amplifiers. The output signal from the amps is set and the volume control is dictated by the mix output on the mixer which increases the line level sent to the amplifiers.

The stage mix (monitor) however is sent through a separate EQ rack mountable and sent to the monitor amp which then distributes the signal to the 2 monitor amps on stage so the band can hear themselves, this is useful because the band can have a completely different mix and mix level compared to what is sent to the audience to be heard. All in all a simple system that works well and can only be improved on a minor level.

Room Characteristics

To investigate if there were any problem areas for certain frequencies or room modes we decided to undertake a sweeping tone test. This involved using a test tone generator borrowed from the university. By connecting the instrument via an XLR cable into the mixer we could then control a sweeping- stepped set of pure tones being played into the venue. We then set up a flat response microphone in an area where an audience member would ideally want to be situated when watching a live act. This microphone was connected to the portable flash recorder with which we could then record the sweeping tone and later examine visually and audibly. While the tones were sweeping through from 20Hz to 20kHz (human hearing range) there were a couple of certain frequency tones that were audibly louder, more resonant, and especially for the higher frequency more piercing. While the volume of the sweep was kept constant throughout, this showed that there were a couple

of problematic frequency areas that would have to be identified when looking back at the results. We later uploaded the files onto the computer and were able to listen to the recorded frequency sweep. As well as this we could examine the image of the audio wave captured. The two main problematic frequencies were found to be at 100Hz and 500Hz. The wave can be seen above with the two areas highlighted. It is relatively clear to see that the two areas stand out more than the rest.

Frequency analysis
An experiment we decided to conduct was to place a flat response microphone in many different areas of the venue and record a track being played out of the main-stage speakers. We would then take all the recordings taken from the most relevant points in the venue and compare their frequency properties with those of the actual track. The song we chose to carry out this test with was The Cure- “close to me”. We chose this track because we all agreed that it was a very good quality recording of a rock/pop song which features many instruments playing in different frequency ranges. This song was also relevant because it fits well within what would commonly be performed at the venue. The picture below shows a roughly to scale birds-eye view of the venue and also includes the positions at which the most relevant recordings were taken.

Positions 1 and 2 are where the majority of the audience would be standing during a performance. Position 1 is 4 meters from the stage and position 2 is 10 meters from the stage. Position 3 is situated 17 meters from the stage and is possibly where some people would be standing if congregated at the bar. Position 4 is situated at the mix point and is where the engineer would be in control of the desk. Position 5 is situated in the side room where people would be sat down at tables.

The graphs below analyse the frequency responses of the song when played at the different points in the venue 1,2,3,4 and 5. Also included first is the graph showing the frequency response of the track on the original CD.

What the graphs show is what frequencies are being played and at what decibel level. The same flat response microphone was used each time and the song was played at the same volume each time. The main problems we noticed here are that at the mix position (position 4) we did not get results which matched them of the audience listening area (position 1 and 2). Ideally the engineer controlling the desk should be able to hear exactly what is heard in the audience area because he/she wants to produce a sound which is best for the audience‟s perception. If the engineer is producing sound levels which suit a different area then the audience will hear something totally different. In this case the engineer either has to know the difference in sound and compensate, or keep having to wonder out into the main area and back to the desk to modify the levels, which is a quite a hindrance on his/her job. It is visible on the graph and was audible to us when taking the tests, that there is a slight loss in bass response around the 100Hz and 250 Hz points at the mix position. This is a problem for the reasons stated above. The engineer wants to get the correct levels

for the audience and must take this loss in bass response into consideration. Another thing which was noticed within the graphs for the different positions is the obvious sink when reaching the higher frequencies (above 2 kHz). We originally thought a reason for this could just be the acoustics of a specific area of the room, but as all the graphs show this trend in low response for high frequencies it must be down to something else. The next possible cause of this we came across was poor quality cable because when cabling is not of good quality the signal tends to drop frequencies, especially towards the higher end. As we have already learnt that the cabling between the mixer and amplification is of poor quality this is what we are certain is the cause of this problem. Something that surprised us from the results was the fact that there does not seem to be a noticeable difference between the results from the main area and those of the side area (position 5). This shows that the members of audience who decide to sit in this area are not going to experience too much of a different sound than those in the main audience area. The only difference being a slight increase in low frequencies around the 60- 100Hz point.

Sound pressure Levels.
Below is a table which shows the difference in decibel level at each of the 5 positions in the room.

Position 1 2 3 4 5

Max dB 96.1 93.4 87.9 88.4 84.3

dB range 84.5- 96.1 81.8- 93.4 86.7- 87.9 85.4- 88.4 81.2- 84.3

These levels were recorded using a decibel level meter. The meter was recording the range in sound pressure levels and thus calculating the maximum level during the songs play time at each of the 5 positions. As expected the levels got lower the further we travelled from the speakers on stage. We noticed in the results that the further we got from the stage and the lower the max level got, the smaller the range got. This is due to fact that the further you stand from the source, the more the rooms reflective and reverberant properties dominate your perception of sound.

Reverb and reflective properties of Carpe.
The reverberant qualities of Carpe at first listen seem to be clean and no clear problems can be detected by ear. This is probably due to the huge surface are the sound has to diffuse and refract off. Inside carpe diem is a solid stone floor (uneven) with a hardwood varnished ceiling with a concrete roof (Carpe is situated in a basement location). All this is surrounded by varnished hardwood fixed furnishings. A nightmare for reverb you might think but the shape of Carpe seems to be more problematic than the reverb issues.

As you can see from the RT60 test below (carried out using a burst balloon for the transience) the reverb decays fairly quickly (unacceptable for a dry recording environment or control room however) resulting in very few problems with a critical distance, or reverb infected sound sources.

The resulting reverb time is 0.32secs, anything up to and including 0.5 secs is acceptable in an area the size of Carpe.

There seems to be only a problem with a volume critical distance by where the length of carpe is a problem for anyone at the back of the pub. After testing this by going to the club on a gig night we decided it wasn‟t the reverberant qualities causing the problem but the diffusion qualities of the club. The vast surface area was scattering the sound so much that all volume seems to be lost.

From the dB test we did you can see nearly a 10dB decrease in volume (dBA) and that was in an empty pub. Also to take into consideration is the absorption coefficients of the human body, 500 people are a dense material to penetrate and so some volume loss is expected. We also noticed that the club height reduces near the back of the club this could also have had a in the volume problems. This problem could be easily rectified with backup monitor speakers for the back of the room, this would reinforce the source sound and anywhere in the pub the band/performer could be heard properly. 2 more of the mid/high Martin Audio speakers would be fine for the job. We did notice some problem modes being around 100 and 500 Hz which really cut through the system and were hugely increased in volume and resonated over the initial mix. This was note in the song “close to me” by the Cure which we used to test the system. Below is a mode table of the first few modes of the room. These modes were calculated on the basis of the room being a whole and do not take into account slight dimension changes in the stage area being slightly wider and a little less in height). These were negligible and would not affect the audience listening position which is the area being calculated in the mode tables.

28.75

Hz Hz Hz Hz Hz

65.62

Hz Hz Hz Hz Hz

70.77

Hz Hz Hz Hz Hz

57.50

Hz Hz Hz Hz

131.2

Hz Hz Hz Hz

141.5

Hz Hz Hz Hz

86.26

196.8

212.3

115.0

262.5

283.1

143.7

328.1

353.8

172.5

393.7

424.6

201.2

459.3

495.4

230.0

525.0

566.2

258.7

590.6

636.9

Tangential mode table above

7.882

Hz Hz Hz Hz Hz

27.65

Hz Hz Hz Hz Hz

65.15

Hz Hz Hz Hz Hz

15.76

Hz Hz Hz Hz

55.30

Hz Hz Hz Hz

130.3

Hz Hz Hz Hz

23.64

82.95

195.4

31.53

110.6

260.6

39.41

138.2

325.7

47.29

165.9

390.9

55.17

193.5

456.0

63.06

221.2

521.2

70.94

248.8

586.3

Axial mode table above

From these tables you can see problem modes at the following frequencies: 27-28Hz, 65Hz, 55-57Hz, 586-590, 195-196. (There are others but these are ones we experienced).

These are the most noticeable problem modes and the easiest way to get rid of these would be to change the shape of the flat ceiling by hanging absorptive panels from it. This will cut energy from the mode and reflect the sound into the room off axis to when is arose.

Obviously

to

create

a

perfect

environment

is

difficult

near

impossible but for little expense these modes could be severely reduced if not solved.

Critical Analysis and Suggested upgrades

The first point to mention is the mix position. As can be seen from the above diagram is off to the side of the stage. This is a bad place for a number of reasons. Firstly as for a live performance the mix should be engineered to sound best where the audience stand. To do this the person mixing needs to be able to hear what the audience can. As the system is currently set up the sound engineer must stand in the audience position, return to the mixing console adjust and repeat to check their mix. This is very impractical.

Upon experimenting on frequency response at different locations we found there to be an increased bass response at the mix position. This reinforces the fact that the sound is heard differently in different areas of the pub, so if the engineer was to mix from the desk they would add more low frequency to the mix than is necessary from the perspective of the audience. The final point is that the sound engineer should be able to physically see the all of the performers in order to solve any problems that may occur on stage. As there is a column towards the stage from the mix position the engineer will be unable to see anyone on the left hand side of the stage. Ideally the mix position should be on a raised platform directly in front and to the centre of the stage, behind where the audience stand, in order for the engineer to get the best representation of what the audience hear. In the instance of Carpe Diem as the venue is relatively small, putting the mix position where the audience stand would significantly reduce the capacity of people who can watch the band. Baring this in mind there does not seem to be a solution to this problem. Another arrangement problem is the number of people who can watch the band at close proximity. This is caused by the seating booths directly in front of the stage to the right. For the band to have a good interaction with the crowd they should be straight in front of them. This makes the right hand of the stage redundant on many occasions. There is not a problem with bands which only have about three members, but any more than this bands find themselves crushed to the left of the stage. Where space is a problem it must be frustrating that they cannot utilise the extra section of stage. A possibility would be to remove at least the first booth in order to maximise the area of the stage.

The next point to make is the power amplifier location. It can be seen in the above diagram that the amplifiers that drive the front of house PA are located right across the other side of the bar. This decision has been made in order for alternative audio streams to be routed to the sound distribution such as TV signal or CD‟s. The amplifier location is not desirable as long cable runs will cause impedance loss and directly affect the amount of power and the frequency range which reaches the speakers. Members of staff advise that the PA is only ever used for amplifying bands. Therefore it would be suitable to remove the PA entirely from the distribution system. We suggest re-locating the amplifiers either to the mix position or on stage; ideally anywhere close to the speakers out of the way, but can be accessed easily will be suitable. If pub management did still want to be able to route alternative signals through the PA a connection between the distribution board and the amplifier in its new location could then be made. If the decision was made that the amps were to be moved this would be an ideal time to clean the amps as they are covered in dust, especially the fan ports. Dust build up will cause the fans to work less effectively which could cause the amplifiers to overheat. Even though the cable length will be less once the amplifiers have been relocated, replacing the cabling should significantly enhance the frequency response of the system, particularly in the mid to high areas where there are problems. Suggested speaker cable would be Van Damme or similar quality. In terms of speaker configuration, the speakers are of good quality, correctly matched to the amplifiers and generally positioned well,

however there are a couple of points to improve the overall sound to the audience. Firstly half way down the audience area the roof is lowered. This has a negative effect on the sound reaching the back half of the room which is by means of dispersal. The further back a member of the audience is the more likely they are to hear direct sound and more likely to hear reverberant sound which has been bounced around the walls. As the speakers currently angled as best possible for the front half of the room the addition of side fills would help the quality and level of sound to the rear half of the room. A suggested addition would be speakers similar to existing mid/high speakers. Secondly an active crossover could be connected between the amplifier and the mid/high speakers as there are subwoofers already in the current system the mid/high speakers do not need to be sent the full range. In doing this the speakers are being asked to do two things. Firstly reproduced low frequencies which require lots of energy and movement from the driver and secondly to reproduce mids and highs which require less movement and energy. In adding a crossover the all of the speakers will achieve their full potential, which hopefully a more flatting sound to the audience. A suggested crossover would be the Martin Audio M3 or DXI digital controller. There are also a couple of changes which could be made to the mixer set up. First if any outboard signal processors need to be routed to different channels the insert cables would have to be directly changed around the back of the desk. A more suitable option would be to connect all the insert points and the processors to a patch bay, that way changing routing would simply be moving a patch lead to a different insert point.

We would also suggest the addition at least one more compressor and gate, as in a normal live application you would always compress and gate the snare, high-hats and any toms which a drummer has as part of their kit. As there are only four compressors and gates and drummers often have three (sometimes more) toms there are not enough. It has also been noticed that the brand of the current outboard gear is that of a low grade. As they are hardwired to some of the channels even if they are not in use the signal will always pass through them, which could degrade it. A suitable upgrades would be DBX Quadgate and DBX 266XL compressor/limiter.

Overview of suggested upgrades
1. Removal of booth/s to right of stage to increase viewing capacity 2. Removal of power amplifiers from sound distribution system 3. Relocation of power amplifiers to more suitable place (mix position or stage suggested) 4. Cleaning of power amplifiers to remove build-up of dirt and dust 5. Addition of active crossover to mid/high speaker circuit (Suggested Martin Audio M3 or DXI digital controller) 6. Addition of side-fills to rear of main audience area (Suggested speakers should be similar to existing mid/highs) 7. Replacement of cabling from mixer to amplifiers ( Van Damme cables suggested) 8. Addition of a patch bay to connect mixing desk insert desk and outboard signal processors. 9. Addition of extra signal processors. 10. Addition of ceiling absorption tiles and diffusion panels.


								
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