Port Loading technique in bass of speaker

[midrange]

I was reading a review of the Wharfedale Diamond 122 and came across the following description.

The reflex port has received attention too, lnstead of being on the front or rear, as with previous models, the tube terminates centrally in the base of the cabinet. The latter sits on an integrated Plinth, a narrow gap separating the two; the slot port airflow is thus effectively distributed around the perimeter of the base. This arrangement, derived from the Jade research effort and known as a 'slot-loaded distributed port'. aims to smooth the transition in air-pressure between the room and speaker cabinet. Claimed benefits include a reduction of low-frequency distortion, improved efficiency and easier Positioning-

Does anyone know about this technique, and if the port is calculated differently?

 

[eriksquires]

Hi Midrange,

I ran across that too. I don't know about the math, but as far as I know it's not a unique idea, except they seem to be the first to do it in a speaker that can be turned sideways.

It's a very similar idea to speakers with bottom ports, of which there are several examples. The B&W 802 diamonds among the most famous of them. They probably use another name for the idea. I forget the reasoning behind it, but any time you can energize a room boundary directly by using a port or driver facing the floor tends to avoid energizing room modes in the same way as when you have a driver radiating into the room directly.

Best,


Erik

 

[eriksquires]

With subwoofers you often see this idea, only they use the floor as the bottom of the slot. Let's see, I seem to remember similar ideas from Polk since way back as well. The point is, the bottom of the slot does not have to necessarily be integral to the speaker. It could be a bookshelf, or the floor or a wall, though in that case you don't have gravity maintaining the distance.

 

[zach6532]

With subwoofers you often see this idea, only they use the floor as the bottom of the slot.

Are there problems with this? Seems like it would make it really easy to adjust tuning...just replace a 1/4inch piece of foam to seal to the floor with a 1/8inch piece.

 

[eriksquires]

Zach,

I'm not sure what you mean? There's no problem at all. Imagine the subwoofer has 4 feet instead of a sheet of plywood, with the woofer pointing down.

My experience, and desire however is to minimize the movement of the cabinets in free space. The drivers generate a tremendous amount of reactive energy (as in, for every action there is an equal and opposite reaction) so the better the cabinets are fixed in space, the more of the driver energy has to go into the air than the cabinet.

And all of that is off-topic from the slot loading.

Best,


Erik

 

[Cal Weldon]

30 years ago WEB Speakers used something similar in that a round port bottom fired into a slot port. Nothing revolutionary there. What they may be pulling your leg a bit on though is that the 'all around slot' will have better sound distribution. It might, but the sound from a port is pretty close to omnidirectional to begin with so there may be a little up-selling there.

 

[planet10]

This is a common technique. You add a resistance the vent which can help mmto adjust the character & amount of bass output from the vent.

The high aspect ratio vents in our miniOnken do similar things but in a different way.

A R in the vent helps make the speaker less affected by the dynamic changes in the bass drivers T/S parameters.

dave

 

[midrange]

Can anyone tell me if "loading" the port exit in this way with a very close boundary effects the tuning of the port?

 

[TBTL]

The port effectively becomes longer as the air gap below the speaker becomes part of the port.

 

[zach6532]

Zach,

I'm not sure what you mean? There's no problem at all. Imagine the subwoofer has 4 feet instead of a sheet of plywood, with the woofer pointing down.

Erik

I was thinking of a normal slot port, just without the bottom piece of plywood, so 3 sides instead of 4 feet (wouldn't need to worry about sealing to the floor with the 4 feet). Either way, seems it would make adjusting the tuning easy, just extend or lower the feet by a mm or so.

The port effectively becomes longer as the air gap below the speaker becomes part of the port.

How is this usually implemented? Is it a normal port, that exits into the air gap? Making it longer and flared? Or is it just a hole in the bottom of the cabinet into the air gap which is the entire port?