Trying to get more kick from my Bose MB-4

[chieftfac]

Trying to get little more punch from a pair of MB-4 subs. System is as follows:

Mackie Onyx 32 Chan. Mixer; Left and Right Main outs input the Panaray controller; Controller is set for 402 tops and MB-4 Subs; (I have 402's in pairs as stereo tops with a EQ between controller and amp for RTA'ing the room... not relevant, just FYI) Amps are QSC RMX 1450's one amp on tops, one amp on subs, the sub amp is switched for low pass and is set at max level of output.

Everything I've read so far in the manual/online says the MB-4 is rated for 200w continuous, so is the 1450 enough amp for this set-up? Should I bridge the amp and wire the MB-4's together? I do have a old Crown Power Base 1 at home that I could take in and bridge, or a QSC GX3 I could take in and use.

We are in transition and trying to do things a little over our head, with no rental budget.
(Trying to make this work for a band consisting of Drums, Keys, Sax, Bass and Guitar, Going to add some yamaha side fills at the very least and maybe even the 20 year old bose 802's)

Oh, should mention space... Proscenium stage, 31' wide x 23 deep from plaster line, House rear wall is 46 ft from the plaster line, stage has 4' lip in front of plaster line, We seats 335 with a small balcony,

I want to do this as best as it can be with what I have, but wouldn't be totally devastated if this really shows that we need different equipment for these presentation.

Sorry, stressed and rambling, as I'm not sure I can even do this moderately well.

Also, just curious, if the MB-4 is 200w continuous, what is peak?

Manual said Long-Term Power Handling 200W continuous, Band-limited noise, meeting the IEC Standard #268-5 is applied to the MB4 speaker and amplified to a level at the loudspeaker terminals corresponding to the power handling of the loudspeaker. The loudspeaker must show no visible damage or measurable loss of performance after 100 hours of continuous testing.

 

[FMEng]

The problem is the EQ is in the wrong place. It belongs between the console and the Panaray controller. It is changing the gain structure in the system, making the 402 tops too loud in comparison with the MB4 subs. Turn OFF all filters in the 1450 amps as the Panaray controller should do all of that by itself, if properly configured. You should not have to apply much EQ, if any, and forget the RTA.

 

[neotrotsky]

The problem is the EQ is in the wrong place. It belongs between the console and the Panaray controller. It is changing the gain structure in the system, making the 402 tops too loud in comparison with the MB4 subs. Turn OFF all filters in the 1450 amps as the Panaray controller should do all of that by itself, if properly configured. You should not have to apply much EQ, if any, and forget the RTA.

Agreed. The best progression for your gain structure should be as follows:

Signal>console>Crossover>EQ>Controller>Amplifier>Speaker

Another factor to consider is are you using a crossover? If you can isolate the set of frequencies you will have a better chance of getting a clean signal to the EQ and thus a better sound. It won't improve the "kick" simply because it's only a 200w speaker (Now, is that 200w peak or continuous?). In the room you have, one bass driver may not be enough for what you want to do. It would help to get an idea of what kind of effect/sound you are trying to achieve. More power doesn't always equate to more sound. Sometimes you have to use less power in more speakers to get a cleaner, more effective sound.

 

[chieftfac]

The problem is the EQ is in the wrong place. It belongs between the console and the Panaray controller. It is changing the gain structure in the system, making the 402 tops too loud in comparison with the MB4 subs. Turn OFF all filters in the 1450 amps as the Panaray controller should do all of that by itself, if properly configured. You should not have to apply much EQ, if any, and forget the RTA.

That is exactly the problem... I will try the correct config and let you know how it works out... No crossover though... Need the EQ in the chain, The room has two consistant feedback points, one around 630-800 and the other around 8k... real bad in the spring summer... A lot depends on humidity... not near as bad in the winter and both points drift up in frequency in December - February...

Thanks to you both...

 

[museav]

The Bose controller includes a crossover and the standard configuration for a system like yours would be mixer outputs to equalizer to Panaray processor inputs with the processor Channel 1 and 2 outputs to the mains amp and the Channel 3 and 4 outputs to the subwoofer amp. If that is not the signal flow you currently have that might be a good place to start.

The RMX1450 does not have a low pass filter, it has a high pass/low cut filter to help filter out very low frequencies. That filter can be set on or off as well as for either 30Hz or 50Hz, Bose recommends a 30Hz high pass for the MB-4 so I would turn that filter on and set it for 30Hz on both sub amplifier channels. FYI, according to the product data on their web site the Bose MB-4 is rated 200W continuous and 800W peak.

It also sounds like you have two 402 Series II speakers and one MB4 sub per channel. The 402 Series II is a nominal 120 degree horizontal pattern so it's not clear why you have two per channel or how they are arranged, but I don't think the Panaray processor has a preset for that configuration so you may have to choose the closest preset and then make some other adjustments to address having two mains per channel. Related to that, where are the mains and 'subs' located and how are they mounted? Are all the speakers for each channel located together? Are the MB-4s on the floor or flown?

Since there apparently could be a number of factors involved, it seems useful to try to clarify the setup and conditions before offering suggestions, but...

Have you considered that the while I don't know the crossover the Bose procesor applies for the preset, the crossover point could be anywhere from 100Hz to 300Hz, potentially making the MB-4 more a bass speaker than a true subwoofer? Or that the maximum output of a MB-4 is 116dB at 1m and with the RMX1450 the maximum output is probably around 111dB at 1m? For a room like yours a single MB-4 per channel may simply not be able to provide the 'kick' or 'punch' desired for some applications. So while you may be able to get some improvement from the current conditions and that may be an acceptable result, you may also have to match your expectations to what is practical with that system.

 

[FMEng]

The RMX1450 does not have a low pass filter, it has a high pass/low cut filter to help filter out very low frequencies. That filter can be set on or off as well as for either 30Hz or 50Hz, Bose recommends a 30Hz high pass for the MB-4 so I would turn that filter on and set it for 30Hz on both sub amplifier channels. FYI, according to the product data on their web site the Bose MB-4 is rated 200W continuous and 800W peak..

Brad,
I could be be wrong, but I would think that the Panaray controller would apply a 30 Hz high pass to the sub output. If the filter is also turned on in the power amp, the additive effect would result in the roll-off starting at a higher frequency than desired. Unfortunately, the Panaray spec sheet from Bose doesn't say, but the MB4 spec sheet shows the Panaray driving amps with no high pass filter.

 

[museav]

I could be be wrong, but I would think that the Panaray controller would apply a 30 Hz high pass to the sub output. If the filter is also turned on in the power amp, the additive effect would result in the roll-off starting at a higher frequency than desired. Unfortunately, the Panaray spec sheet from Bose doesn't say, but the MB4 spec sheet shows the Panaray driving amps with no high pass filter.

The MB-4 product data is no more help, stating the specified response is with the recommended processing but also stating that a 30Hz high pass is recommended, which I interpret to thus mean it would be in addition to the "recommended" equalization. But in any case, I doubt that the very bottom end response is directly relevant to 'kick' and 'punch', that is typically referencing more up around 125Hz or so.

 

[chieftfac]

Here is the layout, 402's in pairs for tops and MB-4's down in the unused return air chase behind the grates under the stage. To explain how this all got here is a long story of horror, politics and board members "just trying to be helpful" saying "I know the guys at X sound company, I know what we need" Considering I got this much in late 2009, I really do consider myself lucky, but still think I got better sound from the pair of 802's I had, without subs. At the time I said we should go with an M7 and full JBL rig for bands but grant money didn't even cover 25% of that.

"Helpful" board member is now gone so I can touch (ie, move and reconfigure) the system but no money available this budget cycle to improve.

Did some checking and found filters on both amps turned on. Turned them off. Tried to put the EQ (a dbx 231) between the console and the Panaray and got a very bad hiss, around the 4k mark... Tried the system without the EQ, hiss gone but using a 58 on stage fed back when at the lip, EQ'ed the channel, feedback gone but the 58 sounded "hollow". Tried PCC-160's (theater set-up) no usable gain before feedback. so put EQ back after the Panaray before the amp for the 402's, RTA'ed the room and sound is better. I'm thinking the one MB-4 per side is just not enough for this room. Any suggestion are welcome, and I have to thank everyone who has posted so far, this has got me thinking more clearly and the suggestions are helping...

Thanks

 

[museav]

Unless the MB-4s are in much smaller enclosures within the chase then a lot of their energy may be going into the cavity rather than out into the room. And if the chase space is untreated, you may be getting some resonances and cancellations that could make the lows a bit muddy and/or missing some frequencies. I'd also verify the 'unused' aspect as if that cavity is used for return air then it is probably considered a plenum space, which means both the cable and speakers would have to be rated for use in plenums (and the speakers are definitely not so rated).

With the MB-4s on the floor and the 402s flown you might have some interesting issues through crossover and varying coverage through crossover, for example those in front who are greatly out of the pattern of the flown mains but right in front of the subs likely hear a very low frequency biased response compared to people seated in the balcony. And speaking of crossover, on the Bose processor did you verify that Channels 1 and 2 out feed the 402s and Channels 3 and 4 out feed the MB-4s? That is apparently how the stereo 402 + MB-4 processor preset is expecting the system to be configured and if the system is configured using only outputs 1 and 2 on the processor then it might give a whole new twist to the old "no highs, no lows, must be Bose" phrase as there would truly be no lows.

It is definitely not clear why there are two 402s per side. With them flown side by side facing the same direction and the relatively broad nominal horizontal coverage of the 402 it does not seem to be an attempt to address coverage or to really have any benefit. I would consider trying disconnecting one of the 402s on each side and listening to what that does to the coverage and overall sound, it might actually clear things up a bit and perhaps even help with gain before feedback.

 

[chieftfac]

Did confirm correct set up on the processor. They even used star quad cables with speak-on connectors. When I have time I am going to verify if the speak-on's are correctly wired. You mentioned one of the on going issues a few knowledgable people (patron's) have with the tops near the ceiling and the subs down at the floor. Front row is a problem with being out of the pattern from the flown 402's. One of the hardest things to explain to board members is that the sound system needs to be moved around a bit for different uses. One size does not fit everyone. Subs and side fills work great for bands but for theater type presentations groups need the stage space.

I will move the subs out of their hiding space and put them on stage near the side fills. The return air chase they are in was used a long time ago but is dampened off, don't know if that is good enough for code or not. (let's just say we are a bit off the map inspection wise) and they are not treated, so yes, the chase is probably eating up power and reverberating/canceling. I will try the 402 disconnect as soon as I can.

Thanks again for the help everyone...

 

[FMEng]

The system should work fine with the EQ ahead of the Panaray. The fact that it doesn't suggests an underlying problem. The noise problem with the EQ moved suggests a problem with either the EQ or the interconnection. The EQ may be self-oscillating and the placement after all A/D conversions may just be hiding the problem. I trust all cables between console, EQ, and Panaray are balanced XLR, and the wiring tests OK?

 

[chieftfac]

The system should work fine with the EQ ahead of the Panaray. The fact that it doesn't suggests an underlying problem. The noise problem with the EQ moved suggests a problem with either the EQ or the interconnection. The EQ may be self-oscillating and the placement after all A/D conversions may just be hiding the problem. I trust all cables between console, EQ, and Panaray are balanced XLR, and the wiring tests OK?

All connection wires are 1' XLR... I will test them first... Then I can swap in a different EQ to check that... (an Art 355) Tuesday is shaping up to be a long day...

 

[derekleffew]

...I trust all cables between console, EQ, and Panaray are balanced XLR, and the wiring tests OK?

...They even used star quad cables with speak-on connectors. ...

I hope this is a misspeak/misuse of terminology--as Star Quad is a type of mic/line level construction and SpeakON is an amplifier output/speaker connector. The two simply don't go together.

 

[chieftfac]

All of the speaker lines are this: Canare 4S11 Star Quad Stereo Speaker Cables, wire runs are about 85'. They are wired with the two Reds being + and the two Whites being -, Canare's specifications say that results in a effective 11 gauge wire size. The math sounds/looks correct, but not sure if that really is the case. (Engineering classes were a long time ago)

 

[derekleffew]

Learn something new everyday. I'd never heard of Star Quad speaker cable before.

 

[chieftfac]

I think it's used more on consumer installs... And in movie house settings... Got the impression that company didn't do many live theater installs...

 

[museav]

All of the speaker lines are this: Canare 4S11 Star Quad Stereo Speaker Cables, wire runs are about 85'. They are wired with the two Reds being + and the two Whites being -, Canare's specifications say that results in a effective 11 gauge wire size. The math sounds/looks correct, but not sure if that really is the case. (Engineering classes were a long time ago)

Yes, using two identical size conductors in parallel results in an effective net reduction of 3 to the equivalent AWG, so two 14AWG conductors together is comparable to a single 11AWG conductor. However, in your application you almost certainly have used what would probably be considerably less expensive speaker cable with little or no compromises.

I think it's used more on consumer installs... And in movie house settings... Got the impression that company didn't do many live theater installs...

And that may explain many things including a major concern regarding the speaker cable. Canare does not show a rating for the 4S11 cable and I eventually found Speaker Cable at Blue Jeans Cable that points out that the Canare 4S11 cable has no UL or NEC ratings. This means that cable is not intended for install applications and is likely not permitted to be installed in walls or above ceilings, much less in plenum spaces, unless it is run in conduit for the entire relevant run length. So unless the speaker cable is run in conduit wherever the cable is in walls, above ceilings or in plenum spaces, then it probably needs to be replaced with properly rated cable. If that is the case, you might want to contact the company that installed the cable and ask them what they plan to do about it.

 

[ejsandstrom]

Has anybody considered that those subs are woefully undersized? 116db MAX to me that is the biggest limitation rather than any eq or crossover.

 

[neotrotsky]

This is what I was mentioning before. Given their dispersion angle and the power rating, I just don't think one sub is going to give enough coverage. Amplitude is only one factor and one should NEVER run their cabs at the max level at any time. If you have to crank it up, it's not a matter of not having enough power but not having enough speakers to disperse the power evenly. And, you have to take into consideration the angle of dispersion when placing your bass cabs in order to cover the most of the house area being used.

 

[museav]

This is what I was mentioning before. Given their dispersion angle and the power rating, I just don't think one sub is going to give enough coverage. Amplitude is only one factor and one should NEVER run their cabs at the max level at any time. If you have to crank it up, it's not a matter of not having enough power but not having enough speakers to disperse the power evenly. And, you have to take into consideration the angle of dispersion when placing your bass cabs in order to cover the most of the house area being used.

While the directionality of full range or MF/HF speakers is typically a significant factor, subwoofers usually have very limited directionality and the specifications for the Bose MB-4 state that it is omnidirectional under 200Hz. That is why my concern with the MB-4 boxes being located under the stage in a large cavity as much of the radiated energy from the subs is likely being radiated into the area under the stage rather than out to the audience.

"Coverage" usually refers to the variation in level and/or response over a listener area. Poor coverage can result in insufficient levels at some listener locations, but you can also have poor coverage combined with more than sufficient level or you could have good coverage along with insufficient level. They are potentially related but different considerations. I think the point was that poor coverage can result in needing greater maximum output levels while good coverage may reduce the maximum output level required. Sometimes an insufficient level issue is best addressed not by increasing the maximum output but rather by reducing how the level varies throughout the listener area.

The subwoofers or low frequency speakers that they have may indeed not be able to provide all the 'punch' and 'kick' that one would like for the application, but they apparently have no budget to replace them so trying to get the most from what they have seems to be the only viable option.