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Not just another speaker build.

Here's a picture of my quick release back panel. It obviously means I don’t have to remove the woofer everytime I want to try a different stuffing arrangements. It also means I can keep the microphone in exactly the same position, for accurate comparisons.

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I took a measurement of the port output of the fully stuffed enclosure and then removed one bit of stuffing at a time whilst taking measurements. As you can see, the more stuffing, the lower the tuning. I did try raising the tuning frequency by fitting a shorter port, but it didn't sound right to me. I'm sure over stuffing does something bad, but I'm not sure what that is, it just doesn't sound right.

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For some reason not every curve is shown (LspCAD playing up), but it shows stuffing lowers the tuning frequency, and also reduced the 200hz standing wave.
 
Briggs used the same principle in the 60s with the wharfedale airdale, 15 bass driver in a semi ported / semi open baffle, ( there is a proper name that escapes me ) that looked like box, and the speakers above all in open baffle ..
Briggs loudspeakers book is worth reading the calculations may be primitive, but he has a good way of explaining the basic principles.. but i don't think your far off
Many people advocate the use of high Q loudspeakers for open baffles, it's easier to get a flat response. I've tried both ways and much prefer the sound of low q drivers and then a few tricks to help the bottom end.
Bi amping is an easy way out, but I prefer to use single amplification per channel.
 
Steve 57 said:
Briggs used the same principle in the 60s with the wharfedale airdale, 15 bass driver in a semi ported / semi open baffle, ( there is a proper name that escapes me ) that looked like box, and the speakers above all in open baffle ..
Briggs loudspeakers book is worth reading the calculations may be primitive, but he has a good way of explaining the basic principles.. but i don't think your far off
Many people advocate the use of high Q loudspeakers for open baffles, it's easier to get a flat response. I've tried both ways and much prefer the sound of low q drivers and then a few tricks to help the bottom end.
Bi amping is an easy way out, but I prefer to use single amplification per channel.
Click to expand...

It is sort of similar with the slots I suppose, but the drivers fire upward and have a back panel. I don't think copying his idea would work for me. His slots are right next to the drivers. I want the baffle to reinforce the sound right up to the baffle step, then the slot reduces the reflections around the problem area of 1khz, and as the wavelengths get longer and past the slot, they are then reinforced by the baffle again (but obviously the baffle is angles backwards after the slot, so it's not going to fully reinforce the lows). Hmmm - that's got me thinking...

I may have to buy his book though. Sounds interesting, and I've found it surprising what you can learn from old books. It's as though things get forgotten about or lost in time.
 
Yes I have a good collection of old books and wireless worlds going back to the 20s, they where very much hifi / music reproduction orientated.

Most of the things that are wrong with modern systems is described back then too.
I have a 4 watt amplifier from 1930 and its described as bring used for dance halls, so you can only be in awe of the efficiency of the field coil drivers used for professional installations back then.
 
martin clark said:
That, and the results - are a bloody brilliant bit of lateral thinking; I've not seen anything like that fine a study on stuffing alone!
Click to expand...

Thanks Martin. I've tried all sorts of materials for stuffing - including polystyrene S-shaped packing peanuts and bubble wrap. I'm going to try breaking up the standing waves with some odd shaped triangles cut out of 2" foam board next. Similar to the wedges they use in anechoic chambers, but solid, closed-cell foam of random lengths.

Sometimes you achieve a good result, but you don't know exactly why. An example of this is when I put triangle lengths of soft foam in all the corners of the cabinet, and then covered them in duct tape. This removed some peaks lower down in the port output, but was it because the corners were rounded? Or was it because there was a soft, flexible material in the corners?
 
Looks great, Matt. Way over my head, but great. There is something about larger drivers.
 
wd40addict said:
Is there any mileage in a modern version of the Hartley 'Boffle'?
Click to expand...

That's an interesting design, and similar to what I'm trying to achieve (lose the backwave). It looks quite similar to how a gun suppressor works.

The question is whether it would offer any benefit in my design over a fully stuffed enclosure? Because of the 2"x8 slots, the thiele/small parameters of my driver measure as it would in free-air, so as long as my stuffing material isn't dense enough to reflect back through the cone, I don't see any benefit for me. If I didn't have the slots, then this definitely would have been worth a try.

Just found this - "H. A. Hartley was the man who first coined the phrase 'high fidelity'"
 
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