Unusual speaker cabinet design

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Hello all :) . I remember reading about an experimental enclosure which used many different length tubes inside of it, at least I think that was it. I believe it was produced and sold and was well regarded at the time.

I am interested in this concept, does anybody know of the design? Are there any guides for developing a DIY enclosure in a similar vein? What might the primary advatages be, I am assuming something like the tubes act as resonators and damp any peaks?

Any insight gratefully recieved :)
 
Thanks for your responses. It sounds like it acts a bit like a 1/2 wave closed end TL in terms of impedence at least. I was planning this type of enclosure but since the planned drivers has a low fs the pipe would need to be extremely long (5m or so!).

The AudioXpress article isn't up online so I don't know any more about the theory of it. Would the internal pipes need to be as long in the Hegeman cabinet?
 
Greetings, all. Mr. Morton, a retired engineer (if there is such a thing), is a member of our Phoenix, AZ audio club, EMAC, or Everything Matters Audio Club. He has built several versions of this subwoofer, and we have enjoyed the fruits of his labor. The sound is indeed well damped. If you'd like, I will contact him to see if he'd like to participate in this thread
 
Dr.EM said:
Thanks for your responses. It sounds like it acts a bit like a 1/2 wave closed end TL in terms of impedence at least. I was planning this type of enclosure but since the planned drivers has a low fs the pipe would need to be extremely long (5m or so!).

The AudioXpress article isn't up online so I don't know any more about the theory of it. Would the internal pipes need to be as long in the Hegeman cabinet?

I have one of these in the design phase. Very generally, the tubes lengths are selected to bracket Fs.
 
Thanks for the replies! I should be more clear on my application, the woofers in this system (Hi-Vi M8a) are being implemented with the expectation that subwoofers will be added. Deep bass response from them is not required especially. The bass response they give in sealed boxes is ideal.

I hope I'm right in assuming these boxes are closed and ultimately produce similar rolloff to a closed box and limit excursion naturally?

The aims of the box are mainly to give a very flat response up to 800hz or so where the driver is crossed over. I was attracted to the 1/2 wave TL as it would offer this and also impedence flattening which I would like. I realised a half wave pipe would be 5.2m long though for this driver and that was a bit off putting! I know it could be folded and tapered (perhaps even 20/1 since there's no vent noise to consider) but remembered this type of box and hoped it might be an alternative.

Any ideas on pipe diameters and numbers of pipes typically used?
 
Hegman subwoofer

Hi, I'm the writer of the AudioXpress sub article. The sub enclosure contains four 1/4 wave tubes closed at one end and opening into a small plemun that the driver sets in. At the tuned frequency of the tube the open end, mouth, exhibits a high resistive impedance to an incoming wave and is also the point at which the particle flow rate is maximium. By staggering the tube frequencies around Fs a bandpass filter can be constructed that reflects a resistive load upon the total area of the driver cone. As the particle velocity is maximium at the tube mouth the effective Q of each tube may be adjusted by stuffing the mouth with an open cell foam, such as the large sponges available at a local hardware store. Note that fiber glass and other stuffing fibers become transparent to sonic frequencies below 100 Hz. As the enclosure reflets a resistive load upon the driver around Fs instead of a reactive load, Fs does not change when the driver is mounted. I typically measure the Q of the sub by driving it with a three or four cycle sine wave at Fs and measuring the responce with a mike suspended a few inches above the cone. Attack amplitudes and decay time and overshoot. An attack amplitude of 90% and a decay overshoot of 10% are normally obtained indicating a Q of 0.5---Great sound. As the resulting cabinet structure resembles a honey combe, the longest tube is folded 7 times, resonances are subdued and above the operating range of the sub. The no free lunch part. They are heavy, my 8 in version comes in at 55 lb. They are complex, 70 individual pieces are used to build one. As the measured driver impedance does not exceed 12 ohms at any frequency, for an 8 ohm driver they will test the amplifier at low frequencies.

A note on TL speakers. The TL design ia a special case of a tuned port where the line is the port. Properly designed and tuned the TL will show a resistive load around the tuned frequency anf the typical reactive peaks above and below tha tuned frequiecy. The design resultes in the sonic value of the peaks being 2 to 3 db so they are rather benign. Tuning is rather tireing though as the line must be cut slightly short then lengthened by stuffing with the idea of reaching the proper length and Q at the same point in the stuffing process. Hope this helps......Con
 
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Re: Hegman subwoofer

ConM said:
I'm the writer of the AudioXpress sub article.

Good to see you chime in :)

I typically measure the Q of the sub by driving it with a three or four cycle sine wave at Fs

Could you rephrase what you mean so it makes sense? Do you mean 3-4 cycles at the Fs? As it sits i read 3-4 Hz at Fs which doesn't make sense unless Fs = 3-4 Hz

Tuning is rather tireing though as the line must be cut slightly short then lengthened by stuffing with the idea of reaching the proper length and Q at the same point in the stuffing process.

It is pretty well established that damping does not affect apparent line line. That the misnomer came about was that the affect of taper was assumed to be caused by damping. With modern TL modeling tools (MJK) one can get a pretty accurate idea of what a TL will do before ever building it.

dave
 
Hegman Sub

1. 3 or 4 cycles at the Fs frequency.

2. Line length has little effect on damping, however the stuffing material does at the Fs for most TL systems. The stuffing reduces the propogation velocity making the line appear longer and at the same time provides an impedance to the propogation lowering the Q. There may also be a several cycle variation of Fs between production units of the same model driver which also hinders tuning. And yes the newer design tools do make a difference in TL design.

Thanks.....Con
 
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Re: Re: Hegman Sub

planet10 said:


That has been shown to be untrue. Damping has almost no afeect on the time the signal takes to get to the end of the line.

dave


I think you have it wrong Dave. The stuffing does not have an effect on the speed of the sound wave. It will have an effect on the Q and provide impedance to the wave propagation as ConM says. Stuff any box full and it will lower the Q and change the apparent volume.
 
Speaking to the physics any damping has to slow the wave speed, but this isn't always significant especially if you are talking in terms of time delays in a short tube. But even with 8" of open cell foam I can measure a delay, but its certainly not even on the order of 1 ms. At LFs it might only be a small phase shift. But the point is that its always there.

The box size appearing to increase can also be explained by things other than a wave speed change. In fact the size increases are much larger than a speed change could account for.
 
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planet10 said:
At extreme stuffing density (the cabinet becomes aperiodic) there is a very small propagation delay.


As the stuffing density approaches solid, it will ever increase impedance to air movement - that is how a box or pipe is tuned - by reducing or increasing the volume (or apparent volume)., adding or subtracting damping material. It has little to do with the speed of sound.

Fill a guitar with fiberglass and pluck the strings.
 
Hello, For those of you wondering why this thread seems to have been left unfinished...
My father, Con Morton, went blind a couple of years ago. It has been very difficult for him to adapt. I have been studying his work and it is very interesting. As I sit hear listening to music through a set of loud speakers that he built based on the same design theory I can tell you that the guy is an amazing engineer. Some more of this design theory is explained in this article here.
Best wishes to all
Scott
 
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