How to boost certain frequencies?

JapanDave

Member
2011-05-03 6:27 am
Is there a way to boost certain frequencies via circuitry? I am trying to boost frequencies as low as 5hz or lower if I can, is there a way to do this? What I am trying to do is apply a house curve down to single digits if I can.

Cheers
 
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tinitus

diyAudio Moderator R.I.P.
2005-11-24 1:47 am
there are special labs with such systems
very big, and complicated

used for different studies
basicly I think test objects or persons are literally placed inside a big speaker, which also happens to be a room

funny to see a hell lot of woofers moving, but nothing else happens
 
FYI - I build portable powered speakers, some of which are configured for studio type powered monitors. I run my input into an combination active opamp filter that shaves off everything below 40 hz to eliminate the sub-harmonics and everything above 30 khz. The next stage consists of several opamp buffers to break out the frequencies to specific opamp filters and then to the amps, some chip-amps, and the proper speaker(s): tweeter, mid-range, and woofer. The point - I have tested this arrangement with and without the sub-harmonic filter and you can HEAR the difference when you have the filter in place. Amplifying anything below a Bass Guitar, 40 Hz, is bad news sonically. When I apply the 40 Hz High Pass Filter, the Bass sounds even better and crisp; a lesson learned.

Now to dive deeper into your question? Yes. There are numerous opamp audio filter calculators and tutorials on the Net that discuss "active opamp audio filtering." Elliot Sound Products (ESP) has some great schooling, example, and projects that will help you in your quest. Personally, I like his site a great deal.
 
Dave,

I would not use parametric eq below 20Hz anyway. Not really a good idea. Use a shelf boost with a knee in the 15-20Hz range if you must. Basically an LT type filter. You must be very careful messing around with EQ that low or amps and speakers will get damaged. Most any unit with a shelf filter can produce this type of boost. You could always get a Marchand Bassis
 
Any amp worth it's salt will stand it.

I'd expect bass drivers to run out of headroom very very quickly, even something really big.

Mark, that's certainly an interesting opinion WRT bass reproduction. What're your thoughts on reproducing a double bass, where the lowest string is tuned down at 31Hz?

Chris
 
5Hz? Let me give you a hint. There is a reason a standard 33 band PA eq does not go that low. You should not. If you must prove why to yourself, You probably need to build a box as even the eq boxes you could modify have the DC servo higher that that or if not servo, will have blocking caps at much higher cutoff. For a house sound system, 25Hz HP is far more reasonable. If you succeed, about all you will do is find out that subsonics give people a horrible headache and can sometimes cause issues with bladder or bowel control.
 

JapanDave

Member
2011-05-03 6:27 am
What are you trying to achieve? Boosting such low frequencies could also boost offsets and create problems with DC if the cutting slope is not steep enough.
I am trying to get a house curve that does not stop @20hz. At the moment I can get a nice house curve down to about 18hz and after that it goes flat due to my receiver's EQ only applying filters down to 20hz.

Dave,

I would not use parametric eq below 20Hz anyway. Not really a good idea. Use a shelf boost with a knee in the 15-20Hz range if you must. Basically an LT type filter. You must be very careful messing around with EQ that low or amps and speakers will get damaged. Most any unit with a shelf filter can produce this type of boost. You could always get a Marchand Bassis
How would I go about doing a shelf boost at those frequencies? And what is a Marchand Bassis? (Off to see what google has to say)

5Hz? Let me give you a hint. There is a reason a standard 33 band PA eq does not go that low. You should not. If you must prove why to yourself, You probably need to build a box as even the eq boxes you could modify have the DC servo higher that that or if not servo, will have blocking caps at much higher cutoff. For a house sound system, 25Hz HP is far more reasonable. If you succeed, about all you will do is find out that subsonics give people a horrible headache and can sometimes cause issues with bladder or bowel control.
Prolonged subsonics may give 'some' people a headach, but bowel control? I was under the impression that that was an old wives tail???
 
Now to dive deeper into your question? Yes. There are numerous opamp audio filter calculators and tutorials on the Net that discuss "active opamp audio filtering." Elliot Sound Products (ESP) has some great schooling, example, and projects that will help you in your quest. Personally, I like his site a great deal.

Thanks , I will check it out.
 
JapanDave,
Something that you need to think about is that others may not appreciate your production of frequencies that low. I have developed some low frequency bass enclosures and one of the comments was that neighbors, and I am using that as a bit of a misnomer, have complained about the low frequency output. What I am talking about is not a direct neighbor but someone actually down the block, not even the same building! You can not stop those wavelengths from emanating over long distances. The US Army at one time had extremely large and powerful bass horns that were used to knock down buildings! No lie you can cause physical damage at such low frequencies. I once had some low frequency horns in a famous nightclub in Los Angeles and when we turned them on 30 plus years of dust high up on exposed ducting came raining down on everyone's head. Everything that could in the room resonated, it was a nice learning experience. I can believe the notion that some may get sick or toss their lunch with such low frequencies. This is not a myth, most times the output is just not sufficient to do that but if you have the db output you will soon find out that you don't want to do that. Very few direct radiator devices can or will do that without self destruction. There are electronic circuits that are designed to have a bass speaker work below it normal resonant frequency but the power requirements to work with them are extreme in themselves to drive a device this low.
 

JapanDave

Member
2011-05-03 6:27 am
I don't doubt that some people could be affected by ULF, such as headaches , nausea and disorientation, but bowel control or bladder control that is what I was saying was an old wives tale.

Keeping the thread on track, there certainly are devices that can reproduce ULF in the common home, take the rotary sub for example.

What I am talking about is boosting the lower frequencies to apply a house curve (And goes without saying if the sub/amp is capable doing doing this) . I not looking at playing silly SPL levels as I almost never play a movie at reference, which is probably a big reason why I want to be able to do this.
 
JapanDave,
If you are after just the sensation of ultra low bass like in a movie why not just go with some shakers that could be a simpler solution. Not like your going to hear anything this low, but you do feel the vibration in your body. I see in some of the latest movie theaters here they are putting individual shakers on each seat in the theater. Doesn't take up all the space of a low frequency enclosure either.
 

JapanDave

Member
2011-05-03 6:27 am
JapanDave,
If you are after just the sensation of ultra low bass like in a movie why not just go with some shakers that could be a simpler solution. Not like your going to hear anything this low, but you do feel the vibration in your body. I see in some of the latest movie theaters here they are putting individual shakers on each seat in the theater. Doesn't take up all the space of a low frequency enclosure either.

I have shakers, it is not the same unfortunately. I much prefer the effects of the ULF in a movie.
 
Dave,
A dcx, mini-dsp, bassis, dsp-30 or any number of other devices will do a shelf boost. Commonly used to extend the response of sealed systems. You seem to want a tailored house curve with rising response all the way down. This will be difficult to accomplish without dedicated hardware and I would not recommend it. Technically a mini-dsp will do it or a bassis. You will be fighting electronics roll off, and asking for huge amounts of current from the LG's using up a lot of their headroom for very little perceptible gain. Just shelve up the low stuff with a slope that kicks in in the 15-20Hz range. Adjust to taste and let your room acoustics and electronics respond how they do at the bottom without trying to force the response into a nice shape. Adjust a broad range of frequencies mildly instead of notching small ranges aggressively. That's what I do with mine and I only use enough boost or cut to get flat. Getting trustworthy measurements in that range is another big obstacle as well.

This might not be the best place for this discussion btw.
 

Mihkus

Member
2012-07-22 8:01 pm
I didnt want to create new thread so I write here...
I need +12dB boost at 28Hz, got 12" subwoofer with 150W amp.
Built a large enclosure tuned to 28Hz but theres smooth drop from 35Hz, I want to fill it up with extra power.

Got lots opamps, caps, resistors... pretty much everything i could need.
 
Do you need a peak or shelf (flat below 28Hz)? What shape do you need? A narrow peak, or compensation for driver roll off starting much higher?

That's a lot of boost with "only" 150W available. That gets you to about 10W on the rest of the program before you run out of amp at 28 Hz. Probably enough for home use but wanted to make you aware of the issue.

One of the best resources for active filters is Active Filters

Would a Linkwitz transform work for you? It's pretty much the stnadard way fo compensating for a driver's rolloff. Rod Elliot has boards available. Linkwitz Transform Subwoofer Equaliser You might consider not goig with the full boost your anechoic simulation recommends. You'll get some room gain and corner placement gets you a few dB, so if you use the anechoic boost you'll be bass heavy. Less boost also gives you a bit more headroom.

A 12" driver might have a tough time producing significant output down to 28 Hz. If your room is big you may find yourself wishing for more subwoofers. Multiple 12" subs would be nice if you can afford it.