# EQing my main sub (HSU VTF3 MKII) and a mid-bass module (hsu mbm-12)



## lexx2004

I just got a BFD 1124P and was wondering if it would be difficult to integrate a mid-bass module. From reading on this forum, the idea doesn’t appear to be that popular. There are a lot of positive feedbacks over on the HSU forum. Individuals who’ve tried it seem to have been blown away. The concept equates to two subs running as one but, focusing on frequencies that they handle the best. For example, the VTF3 MKII will handle 50 Hz and down. And the MBM-12 mid bass module will handle 50 Hz to 80 Hz. The MBM-12 has a very light driver and according to all accounts I’ve read, handle the mid range of 50-80 Hz with authority (spls of 110db and up). HSU’s concept of splitting the bass frequencies involve positioning your main sub (VTF3 MKII in my case) farfield (e.g. in a corner) and the MBM-12 nearfield (e.g. behind your couch or close to your sitting area). Supposedly, mid-bass is better when the woofer is next to the listener. 

My current set-up includes a HSU VTF3 MKII (with Turbo attachment) but I’m thinking of adding the MBM-12 or another VTF3 MKII. I’m thinking that the MBM-12 would be much harder to integrate and EQ since there would be two crossover points (the receiver will send signals from 80 hz to 50 hz to the MBM-12) and the crossover on the VTF3 MKII will kick in from 50 Hz down to approx. 16 Hz. Another problem might be delay times as the mid-bass module would be significantly closer to where I sit. Users, on the HSU forum, haven’t found these to be problems but I thought I pose this question on a non HSU forum. 

Has anyone tried this? Most people on this forum seem fond of having 2 of the same sub so I assume most have little to no experience with this concept of bass splitting (which seems to be novel approach by Dr. HSU). Do you foresee any problems with this integration? As I’ve mentioned, there are a lot of “awed” users at the HSU forum. Here is the link on the MBM-12 mid bass module approach…(http://www.hsuresearch.com/products/mbm-12.html). 

It’ll take me a while to get some graphs because there is a lot of reading that I have to do on using REW and the BFD.

Thanks for your help,


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## Wayne A. Pflughaupt

Hi lexx,

I don’t see why it should be a problem. The BFD has two channels. Just dedicate one channel to each sub. Or, if they’re both fed by the same sub out from the receiver, just insert the BFD in front of them, just like you would do with a single sub.

If the delay becomes an issue, you could switch to another equalizer. My Yamaha YDP2006 has independent delay for both channels; I believe some of the Behringer processors do, too.

Regards,
Wayne


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## lexx2004

Thanks Wayne,

Given what I've stated, would go buy the mid bass module or buy another of the same sub?

Thanks,


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## dieselpower1966

why have a mid bass module?

it makes more sense to have 2 identical subs for the system.


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## Wayne A. Pflughaupt

Lexx,


> Most people on this forum seem fond of having 2 of the same sub so I assume most have little to no experience with this concept of bass splitting (which seems to be novel approach by Dr. HSU).


The common reasoning for having two identical subs is because they’re typically both operating full-range (full-range bass, that is), and if one is a poor performer, that one will “dumb down” overall bass performance. 

That’s not the same as what you’re talking about. As you noted, with the “bass splitting” arrangement you’re using two subs to cover the same frequency range that one sub would normally. So the “identical” mantra doesn’t apply.

As to whether or not you should try it, it sounds interesting. Can’t hurt to give it a shot, since I assume Hsu has a generous return policy. I guess the deciding factor would be, is your current VTF3 MKII meeting your needs – i.e., playing loud and low enough with headroom to spare (which you’ll need if you equalize with the BFD)? If so, no reason not to try the MBM12. If not, I’d opt for getting the “grunt” factor addressed first with a second VTF, and then maybe the MBM later.

Regards,
Wayne


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## brucek

> I thought I pose this question on a non HSU forum.


Yeah, I remember when that mid bass module first came out, I read the manual and the article and decided it had some built in problems that most users wouldn't likely overcome so as to realize the claimed advantages. There is positive anecdotal evidence from the forum, but then they have an ownership bias that I tend to ignore.

The advantage I guess is that power requirements are reduced as a result of the near-field situation, and so the light driver cone and close direct signal offer a real visceral (in your face) slam for gunshots and all the other effects that are resident in that mid-bass bandwidth. Then the low bass gets the usual advantage of corner effects etc.

Nice idea, but most people won't take the manuals advice and get a digital delay unit to compensate for the fact that the processor/receiver has set a distance time delay for the low sub and that delay is also 'enjoyed' by the mid bass unit that is sitting a couple feet away. 

Additionally, most people may not understand the extra work they should go to in measuring the overall 15Hz - 200Hz bandwidth and then applying equalization to two crossovers (the first between two mis-timed subs and the second between the near-field sub and mains). Not that difficult, but I can see the delay anomaly causing some horrible cancellation problems in some installations.

If it was done right, I think it would be kinda cool. I wouldn't recommend it myself. Regular subwoofers are quite capable of handling the 0Hz-80Hz range. If you have headroom problems, add an additional identical subwoofer. If you don't, don't.... 



> the receiver will send signals from 80 hz to 50 hz to the MBM-12


No, the receiver has a single crossover that when set to 80Hz transmits a low pass signal below 80Hz (at a given slope). This signal is split with a Y-splitter (from the manual) and sent to the low-sub and mid-sub. The mid-sub has a 50Hz 4th order high pass filter that limits the range from 50Hz up to crossover of the processor sub signal. The low bass unit must have its low pass set to ~50Hz.

brucek


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## Wayne A. Pflughaupt

brucek said:


> Nice idea, but most people won't take the manuals advice and get a digital delay unit to compensate for the fact that the processor/receiver has set a distance time delay for the low sub and that delay is also 'enjoyed' by the mid bass unit that is sitting a couple feet away.


Yup. It was probably short-sighted of them not to just include a delay function in the amp module, especially if near-field is their recommended placement...

Regards,
Wayne


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## lexx2004

I have plenty of headroom with my VTF3 MKII but, I think that adding a 2nd of the same sub is the path I'll take for now. I like the idea of evenly distributed bass from both sides of my room. Like Wayne said, I can always add an MBM-12 later. 

Thanks Wayne and Bruce for your thoughts.


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