Dance Club Sub Box Help!

[SMKSoundPro]

Dear Forum Members,

I am experiencing quite a few failures of McCauley 6256 18" drivers and changed the drivers to my personal favorites - 2240H. The DJ drives it hard, and I've got him squeezed down a bit with a DBX 2215 with peak stop limiting. The cabinets are homebrew boxes I built 15 years ago, modeled after a box we pulled out of a nightclub retrofit. The chief engineer I worked for at the time said these are good enough and to build three more of them. The JBL 2240's are not lasting any longer.

I just bought Harris BassBox Pro from Parts Express. The box is (outside dimensons) 32" high X 23.5" wide X 20" deep. It has a rectangular vent with the port opening of 5.125" X 15.875" on the lower half of the baffle board, with a total duct length of 13.875".

It seems as if the drivers are over-excurting, and burning up voice coils. There are three of these sub cabinets in a small 25' X 25' dance floor. They are powered by a Mackie 2600. The room is biamped with a homebrew Cerwin-vega box with a 12 and Peavey HT-94 tweeter using a Dayton 3.5K box-ready crossover from PartsExxpress. They work fine as a high-mid, powered by Mackie 1400i amps. Everything is a simple 8 ohm load.

I am running out of ideas and out of money for recones.

Has anybody ever had this problem before?

I read all of your posts, and live for and love my own JBL collection of pieces and parts!!!

Questions:
1. Do I rebuild the baffle board with a different size vents?
if so... what size should it be?

2. Do I look for 4520 scoops w/ 2225s?
3. Do I change to Crown Macro 2400 amps for subs?
4. Do I fire the DJ? ; or teach him how it works?

Please help as my wife, although an incredible understanding strong person, is kind of tired of listening to me talk about Q, free air resonance, box loading and tuning, torn surrounds....

Thank You.
Scott.

[duaneage]

The first thing I would do is run simulations on what the 2240H or even the McCauley drivers should be mounted in and tuned to. Then add about 20% box volume becuase as the drivers heat up the box requirements go up as well (Qts rises with hot voice coils).

Tune the box according to the simulation. Your going to need a signal generator and a voltmeter with frequency display to do this. Run the boxes hard with about 40 watts of power for about an hour or so and then retest quickly to see if the tuning frequency changed. Adjust the vent if needed.
Personally I would build a proper box and set the vent tuning a little higher than recommended. This will increase the loading on the drivers and maybe even give the speaker a bit more bump. If the DJ hears more thump he won't reach for the bass control as much,

Vents should be big. For 2 18s I would go with 2 x 6 inch tubes or my favorite : a shelf port of biblical proportions. It has been written that ultra high output systems need a port area almost equal to the driver area for maximum output with minimal power compression, At high power the port cannot move enough air and becomes restricted This means you have more of a sealed box than a vented box, and the drivers tend to move too much.

Watch a driver at resonant frequency in a tuned box. The cone hardly moves but the vent is really moving air. That is the vent damping the driver and limiting cone excursion.

In summary, design a proper box and tune it properly.

[SMKSoundPro]

Thanks for the advice.

I have put the box dimensions into bassboxpro and if I'm reading it right, the port opening is too large in area.

Maybe a new baffle board is in order. A single 2240 with the right port and duct length, I think, is ard to beat.

Using the external box dimensions of 32" x 23.5" x 20", with 3/4" x 3/4" internal bracing on all inside walls, and 1x3 side stiffeners, what results do you get for size of tuning ports?

Yes, I do have a older tube HP audio freq generator, and fluke 8060a bench meter. Please show me how to sweep for the impedance curves and tuning. I've never been confident about my hookups.

(I would never admit to anyone here at the club, what a newbie I am about some things)

Thank you all for your help!
Scotty.

[Zilch]

In each of your simulations, click down the plots at the left to check the acoustic power and cone excursion graphs, as well.

Get a high pass filter working on there to stop infrasonic frequencies the system can't handle. Set the frequency according to what the BB6P plots show is safe for your final alignment.

Consider 2241 and 2242 as potential upgrades. Run their sims to see how they'll play. It's not overexcursion that's smoking voice coils. :no:

Definitely teach your DJ what's up and how it does it. He buys all recones after that. :yes:

[moldyoldy]

Nothing personal, Scott, but I can't help but feel your question seems to be an unusual one to come from the representative of a company with "SoundPro" in its' name.:dont-know

[duaneage]

Thanks for the advice.

I have put the box dimensions into bassboxpro and if I'm reading it right, the port opening is too large in area.

Maybe a new baffle board is in order. A single 2240 with the right port and duct length, I think, is ard to beat.

Using the external box dimensions of 32" x 23.5" x 20", with 3/4" x 3/4" internal bracing on all inside walls, and 1x3 side stiffeners, what results do you get for size of tuning ports?

Yes, I do have a older tube HP audio freq generator, and fluke 8060a bench meter. Please show me how to sweep for the impedance curves and tuning. I've never been confident about my hookups.

(I would never admit to anyone here at the club, what a newbie I am about some things)

Thank you all for your help!
Scotty.

Based on your box dimensions I get 7.18 cu ft. If your running two drivers in this box that is too small, not enough volume to properly load the drivers. Tuning a small volume like that is impossible. A single 2240H works into about 8 cu ft tuned between 30 and 40 Hz, there is a lot of leeway there. When you factor in the bracing, your looking at less than 7 cu ft. Too small a box can cause bad transient response as well. It is hard to get proper low frequency response with a small volume, the port is usually lengthened to compensate and that just makes it worse.

Stuff fiberglass in the box. Put 6 inches of fiberglass along the back wall, one side wall and one more side wall. You should have three of the six "insulated". This will add about 15-20% of volume to the box by increasing the damping of the air.

Next set up the oscillator and run a sweep from 20 Hz to 100 hz. Don't use and amplifier, just connect it to the speaker directly and give it about 2 Volts of output. Observe where the speaker actually moves the LEAST and the sound from the vent is the loudest. This is the Fvb or vent tuning frequency. If it is above 40 hertz, measure the length of the tube and add 20 percent ( you can also sometime slip another tube inside for testing to make it longer) If the tuning is below 30 or close to it cut 10 % off and retest. I would shoot for 35-40 Hz.

Measuring the impedance with the meter is trickier but more accurate. Get a small 10 ohm resistor and ACCURATELY measure it. I have the same meter you have so first hit the rel button when measuring resistance and touch the leads together. Hit the rel again and this zero's the meter. measure to the tenth of an ohm what the 10 ohm resistor is.

Connect the resistor across the leads of the oscillator ( remove it from the speaker) and connect the 8060a across the resistor as well.

Set the 8060a to volts around 2 volts scale.

Turn on the oscillator and increase the output until you read 1 volt on the meter.

Now, if the resistor measured 9.9 ohms adjust the oscillator until you have .99 volts. If it measured 10.5 ohms adjust until you have 1.05.

Remove the resistor and do a sweep of the speaker. You connect the leads to the speaker just like the resistor. Now you have a precision impedance meter that you can use to measure the driver impedance and see where the speaker resonates. we here on the forum can then offer more advice and ask what you see when you test.

PM me if you want to take this offline or have other questions. If you were not half wy around the world I would come over and help you with it.

[duaneage]

Nothing personal, Scott, but I can't help but feel your question seems to be an unusual one to come from the representative of a company with "SoundPro" in its' name.:dont-know
nothing personal, but I can't help but feel your post contributes nothing to solving Scotts problem or educating him about something he admits to not understanding.

[louped garouv]

this forum is awesome....

between Scott and Duanage, you'll have the means to solve that woofer blowing issue....

[mikebake]

nothing personal, but I can't help but feel your post contributes nothing to solving Scotts problem or educating him about something he admits to not understanding.
It's still a good point.

[Zilch]

I'm seeing a decidedly professional approach here, a desire to figure this out and develop a considered solution to the problem based upon knowledge and experience through consultation with others.

It's all good.... :thmbsup:

[SMKSoundPro]

Thank you Duaneage and Scott for the helpful replies.

These are single 18 cabs. One 2240h per box in three corners of the room, the fourth corner being the dj booth.

I have four en8 cabs that I rebuilt with a 2240, e110 and 2404 cheek tweeter that I use for mobile dj work. I drive them with Crown macro 2400 and 1200, crossed at 250hz, and 3.5k. My rig just sounds and looks great. It has funded my lifestyle quite well, and I would never consider replacing this "tool" as it really stands tall.

That being said... I agree with you regarding the sometimes less than punchy sound of a single vented 18, but in this small dance floor, this is all I have room for. I have quite a few projects on my plate and was looking for some simple advice and help with this speaker problem. I did not mean to imply that I am incapable of hooking up my own test bench. I was asking for a simple refresher course.

I keep looking at the plans I have for JBL 4719s. I'd like a pair of those in our larger ballroom at the club. Dual 18s in those cabs are big and appropriate for the bigger room and in a few weeks, I am hoping that our loud dj will go into that room with the bigger rig. Its all a case of politics right now, and firing the resident dj in that big room.

There are a pair of 4520 scoops next door at the music store for sale. I don't think they are a real jbl cab, just a knock off. In my dealings with my next door neighbor music store, it seems as if the employees are just looking for their next hit on the proverbial bong of life, rather than having a serious discussion about pro sound. The pity is, they are the only game in town. I just can't see how I would build scoops into this room because of the drink rail at 39" off of the floor that rings the room that I built in there 8 years ago. In reading on this forum about 4520 single scoops, I recall someone posting that in the horzontal position this particular writer did not like them or their properties.

Please accept my apologies if I have offended any of you that feel my questions were too elementary for someone with soundpro in his name. It started out as sound productions, and got shortened along the way.

When I worked at Alaska Sound Labs for 17 years, I learned ALOT! The owner/eng was my mentor, sometimes father figure, and then my aa sponsor. When I took the fulltime maintenance man, builder, resident sound guy job at the newly reopened largescale gay bar/ nightclub, he thought I had sold my soul to the devil and we parted as business partners. We don't talk and I am learning on my own what he knew, one little piece at a time.

Way more than any of you care about, I'm sure.

Thank You!
Scotty.

[SMKSoundPro]

Oh and by the way,

I am using a Mackie 2600 to drive these three 8 ohm subs, and am using the 35hz low pass filter on the back of the amp.

A friend has two racks of older crown macros available. 6 -1200s, and 2 - 2400s, but money is tight. I am trying to work a deal with him, and change both dance floors to these crowns.

smk.

[johnaec]

These are single 18 cabs. One 2240h per box in three corners of the room, the fourth corner being the dj booth.

I have four en8 cabs that I rebuilt with a 2240, e110 and 2404 cheek tweeter...OK - 'first question - are the E110's in their own "doghouse", (inside cabinet)? What is the volume, (or at least the measurements), of this doghouse cabinet, (which must be subtracted from the total inside volume to get the true net volume the 2240 sees)? Four 2240's should be plenty for a 25x25 area! I'm thinking your port volume is way off, but we need the *net* inside volume before drawing any real conclusions.

John

[Zilch]

I am using a Mackie 2600 to drive these three 8 ohm subs, and am using the 35hz low pass filter on the back of the amp.You mean high pass, I presume. Low pass would be set consiberably higher, at the crossover frequency.

The subs are separate from the EN8s, right? I think there may be some confusion here, now....

[SMKSoundPro]

Dear Johnaec,

The single 18 cabs in question are:

(external Measurements)

32" tall x 23.5 wide x 20" deep

A single, simple sub cab with a 2240h.

A rectangular vent of (interior) 5.125h x 15.875w and 13.875 duct length.

.75 AB fir plywood. 1x3 braces on opposite sides. .75square bracing at all intersections.

filled with 1.5' fiberglass stapled all around interior sides and back. none on the baffle board.

braced baffle to back with a 1x2 attached also to the duct.

duct made from .75" plywood

2240 is face mounted to the baffle with t-nuts and allen head screws, not inset or rear mounted.

If I am using this new bandboxpro software correctly, it seems that the tuning is way off.

If I cut/bust out the plywood duct, and install round port tubes in a plywood cover plate to cover the rectangular vent cut-out...seems like a good fix.

What to you get for the recommended tuning length of 2 or 3 - 4" ports

by the way,
I saw Scott Fitlin's 2x18's on this forum for his bumper car ride and they look outstanding!

I would love the plans to build those for our larger ballroom/showroom/dancefloor.

Thank You.
Scotty.

[SMKSoundPro]

Yes, 35hz high pass filter on the back of the mackie 2600 amp.


My four En8 cabintes are in my personal mobile dj rig, and the reference to them is the fact that I have not chewed up any of the 2240s in over 20 years in them!

thank you,
smk.

[SMKSoundPro]

and yes, those e-110s are in their own 12" sonotube enclosures.

smk.

[SMKSoundPro]

its after noon, here in anchorage.

must go to work.

will check postings there.

Thank You!
scotty.

[Zilch]

I'm getting 6.841 cuft net.

BB6P suggests tuning to 31 Hz with two 4" ports @ 5.45" long.

Those'll generate 21 m/s vent air velocity @ rated max 300W; use three 4" ports @ 10.42" long to reduce that to 13.5 m/s if you want them quieter.

In either case, you're out of cone displacement at 26 Hz with rated 300 W, and it's rising fast. You need that highpass filter working correctly to protect the driver.

At 27.75 Hz, 2242H will handle an 800 W excursion limit, playing 5.7 dB higher SPL.

I'd put three 4" X 10.5" ports in one and measure what the tuning is, adjusting the port length to get between 30 and 32 Hz.

I'd also be investing in 2242H as opposed to more 2240H recones.

[johnaec]

and yes, those e-110s are in their own 12" sonotube enclosures.

smk.So are you saying the E110 sonotube enclusures are inside the big enclusures with the 2240's? If so, what diameter are they and how deep? That volume must be subtracted from the main internal voulme for calculations.

John

[SMKSoundPro]

Dear Mr. Zilch,

Can you continue to help me re-tune these single 18" sub boxes?

Using your advice, instead of tuning for 2240's; I scored 4 new JBL 2241h to fill these boxes.

I am trying to work through this project with BBP6.
To refresh your memory, the sub box in question is:

1. a single 18" driver, front mounted
2. made of .75" high density particle board
3. already has a rectangular vent cutout of 5.25h X 15.75W(82.6875 sq. in.)
4. Internal box dimensions (A)30.5"high X (B)22.125"wide X (C)18.125" deep.
5. Using thick, heavy fiberglass fill.
6. Using a single JBL 2241h.

Please help with duct tuning length, please.

I planned on mounting two or three 4" round tubes on a board that will plug the open rectangular duct, making it easy to remove and cut the dut lengths with a band saw, and then screw the whole plate and tubing assembly back on the front of the baffle.

Thank You for your time and help!!!

Scott M. Koeller
"SMKSoundPro"
[email protected]


I'm getting 6.841 cuft net.

BB6P suggests tuning to 31 Hz with two 4" ports @ 5.45" long.

Those'll generate 21 m/s vent air velocity @ rated max 300W; use three 4" ports @ 10.42" long to reduce that to 13.5 m/s if you want them quieter.

In either case, you're out of cone displacement at 26 Hz with rated 300 W, and it's rising fast. You need that highpass filter working correctly to protect the driver.

At 27.75 Hz, 2242H will handle an 800 W excursion limit, playing 5.7 dB higher SPL.

I'd put three 4" X 10.5" ports in one and measure what the tuning is, adjusting the port length to get between 30 and 32 Hz.

I'd also be investing in 2242H as opposed to more 2240H recones.

[Zilch]

Tune to 35 Hz.

4 X 4" ports 9.5" long.

You're out of cone excursion at 30 Hz.

35 Hz is good for the filter.

They'll give you 120 dB @ 35 Hz, 600 W.

[SMKSoundPro]

Tune to 35 Hz.

4 X 4" ports 9.5" long.

You're out of cone excursion at 30 Hz.

35 Hz is good for the filter.

They'll give you 120 dB @ 35 Hz, 600 W.

Thank you for the advice!!!

SMK.

[duaneage]

Cut them a bit long and then TEST THEM to see where the cones actually stop moving when you sweep them. That is the only way to properly tune a box, not just measure and cut.

[SMKSoundPro]

Cut them a bit long and then TEST THEM to see where the cones actually stop moving when you sweep them. That is the only way to properly tune a box, not just measure and cut.

Yes I agree. I just went to the carpet store and got 4" inside diameter cardboard tubing.

I would like to use three ports and mount them in the open rectangular cutout on the baffle, and make the whole port assembly removable to facilitate easier cutting on the bandsaw, or tablesaw.

Question: Can I divide the fourth tube length into three equal parts and add those lengths onto the three equal tubes? In other words, I need a certain length of 4" round duct divided into three equal lengths, right?
smk.

[Zilch]

I spec'd four ducts because the vent velocities get too high with three.

You'll hear the "chuffing" port noise at dance club volumes.

You can't make four fit?

Ooops, I see it's too tight, now. Hang on....

O.K., it's 3 x 4" @ 6" long. Vent velocity is ~22 m/sec.

You can play with the rectangular dimensions in BB6P, for example, 5.25" X 10" @ 9" deep gets you down to ~16 m/sec, much better. The 4 x 4" is 17.5 m/sec.

[SMKSoundPro]

I am making the rectangular baffle plug now, and will drill three 4.25" holes in it to mount the ducts.

I will cut them 6" per your recomendation.

Is that right?

If the plug is removable, tuning and cutting should be a snap?

[Zilch]

Correct.

Then measure the tuning frequency, like Duaneage suggests.

Shortening the ducts will raise the frequency.

BB6P usually gives longer than required....

[duaneage]

Another trick is to cut the tubes on a slight angle (inside portion) to prevent pipe resonances at the box frequency. Similar to a flared end but easier to do. You should be able to tune it by triming only one tube, provided it is close. If your off by 5 or 6 Hz cut all three a little and test again. Dial it in by trimming one tube. Do this at low power, less than 1 watt (2.83 volts) after warming them up with 20 watts of sine wave for a while.

All design simulations are done at low power, sophisticated software like LEAP can do high power thermal comparisons and determine power compression results.

Use large diameter speaker wire in runs as short as possible to keep the total Qts down and remained tuned. If your really particular check the tuning at the end of the speaker wire runs to see what effect the leads have

[ralphs99]

Am I missing something here?

It seems to me that the original post indicated a thermal failure due to voice-coils burning up.

If so, and the limiter is doing its job to limit the power to the driver, it could be an amplifier fault.

Can you provide some forensics information about the exact nature of the blown voice-coils Scott? Are they a little bit discoloured? Really black and cooked? Were the blown drivers always on the same amp?

Cheers, Ralph

[Mike Caldwell]

Hello
Getting properly tuned boxes is a must but double check the high pass filter on the amp. What is the cut off rate it will listed something like 12db per octave or 18db, the higher the better. Is there an eq in the system that has everything in the sub low frequencies boosted to max? Also check and double check the system polarity/phase if one of the cabinets is backwards from the rest or even a speaker in the cabinet is reversed from the other that will significantly reduced your low end output make you want to drive the system harder to make up for it. If your system is connected with balanced cabling a simple mis wiring flip of + to - in a connector can cause the same thing. A peak stop limiter of any kind will only protect the system so far if the operator is determined to keep pushing into the limiter.

Mike Caldwell

[Zilch]

Am I missing something here?

It seems to me that the original post indicated a thermal failure due to voice-coils burning up.Nope. Earlier observed at #4:

Consider 2241 and 2242 as potential upgrades. Run their sims to see how they'll play. It's not overexcursion that's smoking voice coils. :no:Get more powerful drivers running in a proper alignment and using an infrasonic filter.

DJ buys all recones after that.... :thmbsup:

[mech986]

Is there a consideration about how the room is set up? A 25 x 25 foot square room with 3 speakers in the corners and the DJ in the last corner doesn't sound like a place where the DJ would be able to hear accurately.

I'm thinking that there may be considerable room nodes and that the DJ placement and/or speaker placement could be a problem. I know it may be impractical to move the speakers but I would be concerned that the DJ is pushing the LF or VLF trying to compensate for poor room acoustics. Or the DJ is pushing the amp into clipping or hard current limiting with the setup that is in place. Or the DJ's hearing is already damaged severely and is unable to mix properly - I am not kidding here, the type of DB levels this system can put out will cause damage over time and can compromise any person's ability to make good choices based on what they hear.

I agree with Mike that the absolute polarity of the system should be checked, especially since the drivers have been taken in and out a number of times, very easy to get the crossover/driver wiring out of phase.

Seems to me (without the benefit of software) that 2 of these beastie subs should be real sufficient to drive that size room, properly tuned and placed. Has the original poster done any evaluations of the room acoustics and or run some RTA measurements from various points in the room?

DJ buys all recones after that.... :thmbsup: : AGREE, he who pushes the sliders, pays for the damage!

My 0.02.

Regards,

Bart

[GordonW]

Personally, I'd look at better amps.

I've seen a number of those Mackie 1400i and 2600i amps come in for service... and our service guy swears at them, regularly. Just not terribly stable, compared to stuff like QSC and such.

If you can't afford the Crowns, I'd look at something like QSC 4050HDs and such. Good, stable, easily-repaired amps.

Also, I'm still unclear on how the amps are wired to the subs... three sub cabinets on one amp? Is it bridged, or is there one sub on one channel, and two on the other? You DEFINITELY don't want to be bridging Mackie amps... PERIOD. Really makes them hot-headed, IME. I'd look at getting a 4th cabinet, and run two per channel... that'd be a safe, 4-ohm load. Get an amp that's big enough to run stereo into 4 ohms, and get the power you need per woofer. A QSC 4050HD would be just about right, for 4 2240s...

Regards,
Gordon.

[Mike Caldwell]

Hello
Is there a mix and match of drivers in different cabinets, McCauley and JBL? JBL's with the exception of the latest neo drivers move back wards with positive to the red terminal.
If your are bridging your amps are you connecting the speakers to the two red binding post on the amp. If you are connecting the speakers to the red and black terminals per channel while bridging an amp you will automatically have them inverted from one another and not gain any increased power.
Like was mentioned before I would look into a more professional power amp or amps with enough power to give you the headroom you need. As for the power rating of your Mackie 2600 and a Crown MA2400 they just about identical. While the Crown is definitely a pro solid amp and I would say will sound better you would still be a little short on power.
How are you connecting and driving the three cabinets you have.

Mike Caldwell

[scott fitlin]

Crown is no longer manufacturing the MA-2400. So, you are looking at buying used amps. I personally prefer buying new if you can.

Crown has the new XTI series, and the iTechs, go and have a listen to them.

But, you should also consider QSC! They are rock solid reliable, like Crown, and they sound very good, and are more cost effective.

If you can, get your local amp dealer to loan you two amps, one QSC, one Crown, of the size you need, and audition!

[Izzy Weird]

Perhaps you don’t have enough subs for the volume level and the dance floor size.

25’ by 25’ is not that small for a dance floor. In the past I have used a quantity of eight 18” vented box subs on dance floors that size, a pair of them in each corner for example. I often used cabinets custom made by EAW that were 12 cu ft internal. They had large removable ports so we could easily change the tuning. They were 42” tall so they could be used as drink rails, and had aluminum edges to keep the drinks from vibrating off.

At one club I remember, Studio West in San Francisco, it was almost impossible to get the DJ to run at less than insane volume levels. So I added a slow gain-riding limiter. The DJ’s absolutely hated it. At Studio West, the management was opposed to increasing the subs from eight to sixteen units, mainly because of the room they would have taken up. They kept a spare set of eight drivers, and were perfectly willing to have them re-coned frequently.

If the DJ is well out of the sound field then the problem can be worse. If the DJ cannot hear how loud it is for the customers, he may run the system too loud. Some tests have shown that the threshold of discomfort is about 6 dB lower for women than men. So an excessively loud system may drive the women out first.

Yes, do try to educate the DJs. No sound system has infinite headroom. Educate them as to where the limit is, especially for the sub channel. Put a level meter on the sub channel. Explain how a DJ’s temporary hearing loss can cause them to slowly raise the volume level over the course of an evening.

The typical high-pass filter we used was 25 Hz @ 18 dB/octave. The cabinet tuning was done by EAW and was a QB3 alignment with an f3 of 30 Hz. if I remember correctly. Most clubs that used these subs had systems that were very loud but did not have frequent failures.

http://IzzyWeird.com/images/eyes1.jpg

Izzy

[Mike Caldwell]

Hello
The MA2400 is now the 2402, the biggest change was being able
to accept the latest version PIP input cards. They went to the "02" version in every MA model except the 3600vz, from what I heard there was not enough space in the 3600's to so what was needed. I used the MA3600vz's with the EDCb PIP cards. The MA600 was dropped from production. As for the XTI amps, from what I have read them seem to suffer from various glitches in operation. I second what Scott said about QSC, all of my amps with the exception of the MA3600vz are QSC PL2 series.

Mike Caldwell