Axiom Home Page Forums General Discussion Stereo Subwoofers

I would get the new 350 from Axiom, much better then the previous model, and not much more in price.

I have never seen an audio shop setup to perform an A/B test synchronously; that is to say, evaluate two speakers almost simultaneously. I have also heard from an audio salesman (who looked well-seasoned) that memory retention of music lasts only a few minutes, or is that seconds.

So the question remains, how do we perform the evaluation.

Thanks sirquack. I seem to be getting the overwhelming opinion that Velodyne is not well liked (or is it that particular model).

Velodyne makes nice subs, I was just saying if your considering the older version of the 350, you may want to look at the new enhanced 350 which has better performance.

Velodyne makes excellent subwoofers make no mistake about it. They have been making subs since the early 1980s, longer than any other audio company. Velo's DD series pretty well set the stage for DSP controlled subs. I own a couple of Velos and am very happy with them, then again I own quite a few subs including Axioms that I enjoy.

However, I would pass on that particular Velo for different reasons than indicated above. Slot ports, such as those on these subs are notoriously noisy because of air turbulence from their sharp angled corners. But they are cheap to make and do provide extra output. If you compare it to the rounded vents on the 350 the Axiom will have far less chuffing at higher SPLs than a Velo DSP-10 or DSP-12 for that matter. The extension is also much better with the 350. No contest stick with the 350.

The Polk PSW505's have a slot port too. Is this a trend, or just plain laziness in the manufacturing process. I'd hate to think that a company would "compromise their design over a couple round holes.

Slot ports generally have edges and that is the main reason why they contribute alot of noise relative to round vents. Slot ports with rounded internal joints (no edges) can be very effective in moving air with minimal turbulence, same as a flared cylinder but that is not the case with the DPS-10 and many other slot ported subs. I also suspect that if they didn't round the edges outside then the inside opening will also not be flared. If that slot is similar to many slot design it will be angled at 90 degrees inside the enclosure.

Here is another take on why that is not a good characteristic if you don't mind some of these fluid dynamics principles, so bear with me in the physics below.

There is huge pressure inside that big box during loud passages. Inside the enclosure, air tends to slow down along the four corners of the port causing the air flowing along the middle of it to become more unstable or gusty. The 90degree angle of that edged slot port will also create unlinear air velocity (more artifacts) which in turn adds to internal air turbulence. If that isn't enough as this unstable air exits it must flow over another edge creating eddys and more turbulence as it abruptly contacts the stable air boundary outside the opening. The net result is uneven FR, resonance at higher frequencies which colours the bass, and other noise/distortions. Chuffing may or may not be detected but at high output the effect of these unlinearities will be evident compared to a flared rounded slot or a flared cylindrical port.

The slot port design can be improved by adding flares at both ends but that is more expensive to accomplish with a slot than a round cylinder hence why the cylinder ports are so popular. Flares help by compressing air into the body of the port inside the sub and expanding it upon exit. Because of this compression/expansion of air the length of the port can handle higher inner-port velocities without increasing the mid-section diameter. The angle of the flare is important and it needs to be a minimum of 45Deg along a circular path to achieve this type of airflow. Some people would suggest the flare curve needs to be parabolic but that's another story we don't need to get into right now.

The problem of internal edges also needs to be addressed. It gets expensive but the slot can be made effective if its internal and external edges are rounded and flared. In effect it increase laminar flow causing it to behave much like a cylinder.

Bottom line is avoid slot ports and especially slot ports with edges. Notice how well designed the Axiom sub ports are. Its one of the many underappreciated features of these subs.

John: From Klaus audio http://www.klausaudio.com/subwoofer-box-articles/flared-ports-vs.-slot-ports.php

"Many people question what the difference is between flared ports and slot ports. There are fairly basic differences between the two, and depending on your situation, one might suit you better than the other. The common purpose of the two ports is that they must be the correct length for the particular subwoofer box to achieve the desired sub box tuning. There are a few differences that may help in your decision between flared and slot ports for your custom subwoofer box.
Flared ports are very good at virtually eliminating port noise. Port noise is the noise created by the friction of air moving through the port. If you have sharp edges on a port (as with standard round ports, which we do not use), you are going to have significantly more port noise than with a flared port. A flared port requires the smallest acceptable port area for a subwoofer box. Since the ends are flared, and the inside of the port is round (no sharp edges), it is unlikely you will be able to notice any port noise from the subwoofer enclosure. However, if you are running a large, high-powered subwoofer, you will want to use two flared ports. A single flared port is still capable of creating port noise when very large amounts of air pass through it.

With a slot port, you can use as much port area as needed for your application, which is especially helpful in SPL applications. A slot port requires more port area than a flared port to minimize port noise. We generally use a rule of 12 square inches of port area per cubic foot of internal volume of the custom sub box. You may go with a larger port area, but this will increase the total volume and length of the port. In turn, a large port area will mean an increase in the total size of your subwoofer box. Slot ports are the standard for our ported custom subwoofer boxes.

If you are not limited on space, we would recommend going with a slot port for your subwoofer box. If space is tight, and you have a few extra bucks, you'll probably want to use a flared port (or two, depending on your subwoofer size and power). It is possible to achieve the same result from both subwoofer boxes, so the decision between flared ports or slot ports depends on your specific needs for your custom subwoofer box."

John: Another question comes to mind in regards to ports. If the vendor elects to use a slot, why doesn't he just put a chamfer or bevel the on the inside and outside edge of the enclosure, which is easily done with a router.

Because it adds to the cost. Rounding the edges is highly desirable but I've found that cheaper subs have slots to keep the cost down and most have edges so you get more port noise. Also it isn't just the outside port opening that needs flaring, its also the internal opening.

The author of the above article is correct in saying ports and edges should be flared or rounded to minimize port noise. What he isn't saying is that most slot openings are edged or have a 90deg edged joint inside the sub which is never rounded. Relative to flared cylinder ports, edged slots are a very cheap albeit noisy way to get SPLs.

Ports are a necessary evil in a high powered sub and the best designs avoid edged slots for flared vents in order to keep noise and resonance as low as possible. The Axiom vortex ports are as good as I've seen or heard on any vented alignment.