Hegeman style subwoofer Q

[weinstro]

Hi,

I'm in the design process for a Hegeman style subwoofer.

For a refresher, this style is a sealed box, but uses a series of quarter-wave tuned pipes to flatten the resonance peak of the driver/box combo.

An article was published in December 2003 edition of AudioXpress by C. Morton. A loudspeaker based on the same principles is commercially available from Morrison Audio. Read all about it here:

http://www.morrisonaudio.com/morrison_loudspeakers.htm

In the AudioXpress article, 4 quarter-wave pipes are shown, each with the same cross sectional area. Each pipe has a different resonant frequency, i.e., the initial Q's for each pipe vary from 6 to 15. Tuning amounts to inserting sponges into each tunnel opening to get the target Q to about 3. Getting this right doesn't look like it will be a walk in the park.

1st Question. The AudioXpress article indicates that the original, original design (by Hegeman), actually used 6 tuned pipes. Using 6 pipes would smooth the impedance out to ~120 Hz, rather than 60 Hz or so, as published. But, is this a good idea or not? I will probably be crossing over to the sub around 100 - 120 Hz. However, the spread of initial Q's gets worse in this case (~3 to 19), which brings us back to the next question.

2nd Question: What if I were to contruct the cabinet such that each tuned pipe had a different cross sectional area? That way, the initial Q's would be spread over a much narrower range, say about 12 +/- 1. But, does this buy me anything? I'm thinking this might make tuning much easier....

Thanks for your thoughts.

[weinstro]

Wow, 145 views and not one reply. I'll take that as a sign that the original post was too dense. Please let me simplify.

Here's a depiction (see attached file), looking into the enclosure, of how the tunnels are configured. This depiction covers the design authored by C. Morton and published in AudioXprees, Dec 2003.

It has 4 tunnels, the last of which is tuned to 64 Hz. Initial Q's for the tunnels vary from 5.5 to 15.6. These are supposed to be tuned to 2-4.

[weinstro]

This iteration of the Hegeman uses 6-tunnels (please see attached file). The last tunnel is tuned to 126 Hz.

The cross sectional area of the tunnels are all the same size and constant, for ease of construction. However, the initial Q's of the tunnels varies between 3.9 and 21.8, by my estimate. These are supposed to be tuned back to 2 to 4.

[weinstro]

And last, I have this iteration (please see attached file).

In the interest of tuning ease, I've played with the idea of adjusting the cross-sectional area.

The tuning frequencies are the same as before, with the final tunnel tuned to 126 Hz. However, Q's now range from 10.9 to 11.9 - much narrower, by my estimate.

Construction of this box is more challenging.

So here's the question - is this worth pursuing?

[forr]

Hi Weinstro,
I have been quite fascinated by Hegeman's sub idea which is as original as it is little known. That's probably why feedback is missing. No reply yet. But don't be discouraged, you have one interested reader at least. It will be nice to read more about your experiments.
Regards.

[weinstro]

Originally posted by forr
Hi Weinstro,
I have been quite fascinated by Hegeman's sub idea which is as original as it is little known. That's probably why feedback is missing. No reply yet. But don't be discouraged, you have one interested reader at least. It will be nice to read more about your experiments.
Regards.

There should be more to write about in ~2-3 weeks. Sounds like I'm going to have to build a box and give it a try.

[planet10]

I took the drivers out of a set of Hegemans in the 70s... there were way more than 6 tunnels... probably 30 or more.

dave