aarothepharo

Huge SubWoofer for Organ Speaker

7 posts in this topic

In actual pipe organs the 32' notes are very low frequency notes. The lowest note is 16Hz. Our ears \ hearing range start to lose the musical note. You feel that note more as a sensation than a note heard. The pipe gets a huge mass of air moving back and forth which causes that sensation.

 

In a digital organ a very high quality, HiFi recording is made of the organ pipe. How could this sensation be recreated? A rule of thumb in audio engineering is that you need a speaker diameter that is a quarter of the wavelength you are trying to recreate. at 16 HZ that is a 5.4 meter speaker. How would this be accomplished in the speaker world?

 

Lets bring some discussion to this.

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I think Meyer Sound would disagree with that "rule of thumb". 

 

You can recreate 20Hz efficiently with in ear headphones. why is that? Probably because the amount of energy required to move the 20Hz frequency and make it audible is quite low when something is already stuffed next to your eardrum - as is the displacement required in the stroke of the speaker due to the sensitivity at that close range. If you want to make more noise, yes you generally need a larger area. It will certainly help with efficiency of moving air to create the sound wave. But it's not essential and not the only factor. If you increase the excursion of the speaker, you can increase the frequency response. The trade of being that you may find the sound is muddy and unintelligible if you're trying to produce more than a 16Hz frequency, for example, at one time.

 

To compensate for the speaker driver deficiencies, one can also tune the enclosure to smooth out or emphasise frequencies. So, if you put a speaker that has free air resonance of 60Hz in the right enclosure, for example, you could produce a fairly efficient 16Hz frequency without requiring a 5.4m wide speaker.

 

You also need to account for the environment. Indoors you're going to need treatment and could also design around the resonance of the structure you're in. Outside, you're going to need to rely on power.

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It's been so long since I did the math that I'm very vague when it comes to that side of it, but yes of course low frequencies can be generated with speakers smaller than wavelength/4. Speaker enclosure size and design have a profound impact, as do excursion distance as Jester points out.

 

Quick experiment to try at home - get a small speaker, like one inside a headphone or from inside a PC desktop system, get some cardboard boxes of different size, cut a hole in them nearly as large as the speaker, place speaker over the hole and play music. You'll notice an instant increase in bottom end no matter what the box. Thee larger the box, the more bottom end.

 

Isn't it also a fundamental principle of the old W-bin used for subwoofers? The W-shaped chamber inside the box effectively lowered the resonance of the box by increasing the effective wavelength it could produce.

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Thank you to all who has replied. I'd like to keep this discussion moving. It is important to have the flattest response possible in organ recreation. Would it be possible to tune a closed sealed enclosure to the low notes?

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Isn't it also a fundamental principle of the old W-bin used for subwoofers? The W-shaped chamber inside the box effectively lowered the resonance of the box by increasing the effective wavelength it could produce.

Yes, it is. The limitation with the W design being it is ultra resonant and ends up with a very limited frequency response and can be quite problematic if the desired result involves any form of fidelity. IMO, W bins are best left to the very low end where there's no need for any fast attack or short decay as they don't perform well in that area.

 

Thank you to all who has replied. I'd like to keep this discussion moving. It is important to have the flattest response possible in organ recreation. Would it be possible to tune a closed sealed enclosure to the low notes?

Including 16Hz? I think you'll struggle. The nice thing about an organ is that it has long attack and long decay in most cases. So, something like the W bin design RB was talking about can lend itself well to the low frequency side for organ sound re-enforcement. I've not heard of any W bin designs claiming sub 28Hz frequency response, though. Depending on how large the room will depend on how big and how many woofers and bass bins you'll want. Ideally you'll want some sort of cross over system (probably active) to try and split the sound between boxes that handle the entire frequency range. I'd also recommend, if the organ mainly lives in one place, to do a spectrum analysis on the room - this will give you an idea of the room resonant frequencies and can help in thing the final low frequency enclosure design to actually take advantage of the rooms natural characteristics as well. Sounds like a fun project!!

Human hearing can't really detect 16Hz. It's going to be more about the harmonics the organ generates for the low notes and vibrations being detected by skin more than ears. If you have processing gear that can handle 16Hz (i.e. crossover and mixer) then you're more likely to get all of the harmonics from second order up. That'll certainly help with the authenticity and clarity of the sound. Actually producing the 16Hz is going to take some effort, big amps and a really nicely tuned enclosure - but i think you'll find once you've got the enclosure sorted, it'll have limited frequency range (not much bandwidth) and you'll need to add other subs and top boxes to get the harmonics and the rest of the organ frequencies.

BTW - Pipe Organs would have to be one of my favourite instruments. The shear power from the sound they produce in the pipes and the complexity/skill to play one. I always end up as an organ groupie!! A friend of mine years ago had me in his bridal party for the wedding and the church had a 120 year old restored pipe organ. I got in trouble for spending pretty much the entire rehearsal chatting to the organist and quizzing her on how she learned to play and generally admiring her instrument. Simply awe inspiring. I was almost converted to become a church goer!!

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^ I remember being in Notre Dame cathedral in Paris many years ago, when they were doing maintenance on the organ, testing each pipe one by one. After hearing a range of notes being played, suddenly it went very quiet, but the air around my body felt thick and it was like my chest and stomach were being massaged gently. I turned to my friend and said "that's the low notes!" What an awesome feeling, something I've never felt with a speaker system, and I've encountered kick drums pushing out of subs that have made me feel like I literally wanted to vomit they were so low and powerful. But nothing compares to an acoustic instrument producing that movement of air mass in a such a natural way.

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