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Old 23rd July 2014, 03:21 PM   #11
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Join Date: Apr 2010
Here is a hand written diagram of my ideas - hopefully you can read this.
Passive solution would use attenuators. Active would use mixer vol control.
Another option I am thinking of these days is: Go the passive solution but replace only the old beaten-up 15"s in both RCFs by a better new woofer (similar T/S plus much higher power rating). Maybe up the power amp a bit (like D-Power 3 or the like) and push the 15"s way harder through gentle EQ boost at 100 - 300Hz. That solution would be WAY below 5000 EUROS but depends on the lifetime of the old 8"s and the tweeters (do those speakers tend to wear out too over the years?). anyway those could be replaced later on too - would not be so expensive.
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File Type: jpg Sound system block diagram.jpg (251.7 KB, 173 views)

Last edited by ViennaTom; 23rd July 2014 at 03:35 PM.
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Old 24th July 2014, 01:30 AM   #12
RJF is offline RJF  Australia
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Join Date: Dec 2013
Location: Sydney,
Originally Posted by ViennaTom View Post
There is no problem - just high expectations: Since it is a home discotheque, I want to be able to listen at "room levels" without hiss, even at "sleep" levels,
Fair enough, and understanding your application does actually explain a lot.

So you are effectively running a home stereo type set-up that can also be used as a Disco (or probably more accurately, a Disco that you wish to use as home stereo).
So while In a traditional PA/Sound reinforcement application, any minor noise levels these speakers have, would usually be well and truly buried in the venue/background noise, even just half a room full of people breathing, I can see your application is slightly more sensitive in this regard.

It is probably worth mentioning here, that many modern D class type amplifiers tend to be slightly noisy inherently, so if you are happy with your Camco I would not rush to replace it.

Compression drivers (the tweeters in most PA boxes) do start to distort when driven harder (although being horn loaded, in theory they should not NEED to be pushed as hard) and I wonder if this could be the cause of some of your concern about the sound of your current set-up.
Even if not being pushed too hard, the tighter pattern control of a horn loaded compression driver may make it unsuitable for a home stereo type application as at the very least you will probably find that your top end changes as you move your head (an effect common on "less expensive" fold-back wedges, which I personally find annoying, but which many other folk do not notice) .

Most "Punch" is usually considered to be 50-100Hz which would be from your Sub-woofer, (although some of it can be up to 150Hz or so), once you approach 200-300Hz this is usually described as warmth (or mud, if you have too much)

Looking at your diagram you have the two 18" Subs in series giving a 16 ohm load to the amplifier, while I note that the XTI6002 is rated down to 4 ohms in bridged mode. running the subs in parallel will effectively give you another 6dB on your bottom end.

Then think about your sub location, one of the biggest mistakes with Sub-woofers in PA usage is to run stereo Subs (that is one sub-woofer each side of the stage), at best this results in uneven bottom end across the room.
Ideally as a simple rule of thumb is locate both Subs together in one corner of a room (or at least tight into a wall) and see how that goes.

Of course this could just be a semantics thing, and what you call "punch" is what I call "warmth".

speakers don't usually wear out as such, however abuse and physical damage, or less commonly, deterioration over time (such as the infamous foam surrounds of the 70es and 80es) can cause some change.
While many faults are buried deep in a driver (such as coil damage or misalignment) others can be picked up by a visual examination.
One potential issue (in an older driver) which can cause odd distortion, is if the surround becomes detached from the frame gently poke the edge of the cone from behind and look for any lifting of the surround.

This is presuming that your boxes are faulty, rather than merely just not suitable for your application and offhand nothing springs immediately to mind to recommend in your case....

Which does not solve your immediate quandary, but may give you something to ponder.

If I get time over the weekend I will try the remote volume control option on my K10es and see how that affects the inherent background hiss (as with the EV modules the same amplifier module is used across the QSC range with different firmware loaded into each) in theory at least, that may work, but then that assumes the noise is on the front end rather than elsewhere after the DSP....
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Old 24th July 2014, 10:20 AM   #13
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Thanks for your considerations.
Camco is great and has been chosen for S/N being really good, but they have more powerful ones too.
Running the subs in parallel would give 1. much less damping. 2. absolutely no benefit, since I cannot clip this amp even into 16 Ohms. It can cook my 2 x 18sound 18NLW9400 even in series. Currently I have an rms limiter at 58VRMS, e. g. 116VRMS for series bridge. the 18s could eat a little more, but I am not going to play with their actual limit and then be 5% above and -- smoke....
Subs are close to each other to gain max. efficiency through coupling.
Thanks for the effort to check out QSC remote gain - its just one potentiometer to be connected, I think.
If the EV ETX-35P really uses 2 way amplification plus passive mid/hi filter, I d consider that as a sound solution (like PRX735) , assuming they are able to implement this well. Still, the noise of ETX is too high. I want to be able to sleep in front of the speaker at night (as long as no one puts up some tunes ;-)
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Old 24th July 2014, 12:35 PM   #14
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Join Date: Apr 2010
a disco to double as home stereo - right.

"speakers don't usually wear out as such, however abuse and physical damage, or less commonly, deterioration over time (such as the infamous foam surrounds of the 70es and 80es) can cause some change.
While many faults are buried deep in a driver (such as coil damage or misalignment) others can be picked up by a visual examination.
One potential issue (in an older driver) which can cause odd distortion, is if the surround becomes detached from the frame gently poke the edge of the cone from behind and look for any lifting of the surround."

the RCFs are not dead, but approaching 20 years. foam surrounds still fairly good, but I am thinking of replacing them because: They will die anyway latest within the next 10 years AND I need more of the good P's

Plenty of Headroom

but less of the bad S's:


Maybe it is "warmth" what I am lacking ("mud"???, or is it just an overdose of ear-killing 2kHz - 10kHz screaming frequency area? I don't know. At medium listening levels the RCFs sound just good!! That again points to the concept of Headroom can only be replaced by ... guess what......more Headroom.
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Old 27th July 2014, 01:40 PM   #15
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From today's investigation (opening the speakers) I have found out the following:
The LF speaker of RCF Event 4000 is L15P530. It has about 93liter net volume to operate into plus 2 round ports, each 10cm in diameter and 8 cm long (effective length would be like 10 cm or so). Any RCF expert here to confirm that?
RCF states the tuning frequ. = 45Hz. Need to start the simulator to see if that fits.
Next step would be to find a possible speaker replacement. No electrolytics in the X-Over, only foil caps, resistors, a 24V light bulb to protect the tweeter and a big iron core choke, which I could replace by a higher current-capable self-built one....

Last edited by ViennaTom; 27th July 2014 at 01:56 PM.
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Old 17th August 2014, 07:04 AM   #16
RJF is offline RJF  Australia
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...So that shows it takes me over three weeks to get around to a simple test....
using the remote volume control on my QSC K10es significantly reduces the residual background hiss from the speakers,
At minimum level on the remote volume control, during daytime (so some background noise) but with doors closed I could not discern background hiss at arms length at least not clearly, I could just sense a change as I moved off axis but not enough to say I was clearly hearing hiss.

with an RCF L15P530 with a 93 litre cabinet and two ports 10cm dia 8cm deep WinISD gives me a tuning frequency of 67Hz and an expected frequency response of:
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Old 17th August 2014, 11:25 AM   #17
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thank you so much for your help. looks like qsc kw is some decent speaker. however, now it looks i ve decided to go the cheap way: continue using the rcfs, just swapping out all 3 transducers per speaker during winter time .it is less than usd 1000. the screaming i can improve by dcx input eq and with all transducers replaced i ll get like new sound. using the attenuators and always "full" signal like 4dbu within dcx2r96 really gives very low noise. the thing i am starting to get worried now is the sound of the amps fans as well as the noise of my disco light sphere turning... but thats another story....
the rcf 15 speaker plus the 93liters plus ports as described has about 47hz reso according to basscad what i use. the datasheet of rcf speaker shows impedance minimum at around 45hz. so you might have some parameter wrong. anyway i am not going to change much with thiele small just replace the same speaker by a new one or by a different one with similar thiele small paras. any suggestion of a good 15 inch speaker?
i set up the dcx at 110 hz linkwitz 4th order both lowpass and highpass pluss some input boost at 93hz for punch. not so bad any more if i pull some db around 2-10 khz.
reason for the lowercase letters is that i got myself a galaxy note pro 12.2 and the screen keyboard makes me not use the shift key. otherwise it is a great tablet.
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Old 17th August 2014, 12:31 PM   #18
RJF is offline RJF  Australia
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I would always recommend the cheaper option first ;-)
and since you had asked I was wondering, so it has satisfied my curiosity anyway.....
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Old 17th August 2014, 09:56 PM   #19
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so now i got into more troubles.
1.the xti6002 during startup will pass about .5secs of audio completely unattenuated and un-dsp'd before booting into the current setup which causes me to change the startup process to have the amp fully ON and booted into the dsp program running and attenuated before i can startup the mp3 player or the dcx coz otherwise i risk killing my 18s with unfiltered unattenuated maximum signal.
2. i ve spent bout 8 hours setting the right delay to match the xover phase between subs and rcfs. now i ve "good" phase between bout 75 hz and 175hz. i do this by placing a spl meter between subs and rcfs and using a sine generator find the delay that gives best cancellation then adding or cutting half a wave period for the setting -depend son what setting gives best overall result over the range of bout .7 - 1.5 x fxover.
to not in any case hurt this perfect setting, i cannot use the amp's dsp's internal subsynth to fatten the bass, since i then risk that the perfect crossover phase gets hurt by subsynth's harmonics. so i d have 2 buy dbx120a for use be4 the xovr that no phase imbalance can occur. the xti subsynth if enabled will place an additional lowpass into the dry signal chain as well. not good for the phase match. i raised that to crowns technical field engineering they said well thats life. i really would need that subsynth to only affect the sub 60 hz area otherwise i cannot use it.
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Old 2nd November 2014, 06:20 PM   #20
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So turn on problem solved by 4 speaker switches between amp and speaker,
Disassembled the RCFs today and found the midrange 8" transducer is operating into about 4.3liters plus 2 ports, total port area ca. 18cm^3, port length ca 2 cm. I also disassembled the passive X over and will report the schematic here once analyzed (don't think the LCR circuit is a trade secret). Problem is that the midrange has just one marking that says "8L7" plus a sticker that says "4Ohm". Could not find any info on RCF 8L7 on the internet. At least I would like to find out the TS parameters in order to find a suitable replacement.
Is it risky in this arrangement (BR 15" LF section plus BR 8" mid section) to screw up the phase at the crossover (300Hz) if I use another transducer with different TS parameters? It looks btw, that the tuning of the mid range resonator is set to only 145Hz, one octave below the crossover. So its use is actually mostly cooling of the voice coil, not port resonance, right?
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