"Slot-loaded" sub designs?

[SE-Raider]

I've seen several "slot loaded" subs lately, or at least designs described as slot loaded. An example is the 8-inch offering from av123. Many of these designs are down firing, and a partition is placed a few inches away from the face of the sub, loading the front wave; an opening around the perimeter of the plate vents the energy to the room. I have never seen design parameters in regard to such enclosures. For instance, how far should the partition be from the face of the driver and what are the tradeoffs of closer/farther away; is there an optimum distance? Is there a minimum size opening that should be maintained? An associated question, can the perimeter opening be closed on 1, 2 or 3 sides? Again what are the inevitable tradeoffs? How is a plate any different from just a subwoofer downfiring the same distance into a floor?

Another design (and also seen on the AV123, Velo DD18, etc) is to slot load the rear wave of the driver. In this design, a rectangular port the width of the enclosure is used, and usually folds back on itself within the enclosure one or more times? What makes this "slot-loaded" as opposed to being just another variation of the bass reflex or transmssion line enclosure, marketing hype? (By the way while on the subject, what diffentiates TL from a long ported enclosure?) Is such a "slot-loaded" design essentially a ported design, and therefore port area and volume would be calculated accordingly?

Essentially I was curious as to the design parameters for the front loaded slotted design, and what are the design parameters for a rear loaded slotted design? Any reference sites or reference data appreciated.

thanks for any input.

[Rudy Jakubin]

Interesting question. Even the guru Martin J. King doesn't really know where a TL begins and a Bass Reflex ends.
If the bass reflex box gets long or tall.
I've built test boxes for both as you can see in the pictures.
The TL's bottom baffle could be called a slot port, since it lost most of it's taper and the Bass Reflex baffles resemble the TL's....
The TL's sound and measure great.
The slot port in my opinion sounds better than a round port.

[Hdale85]

well in car audio they call it a vented box idk if there is any difference between it and a transmission line...i know the parameters are different then a standard round port though and programs like bassbox give you options to calculate a vent or slot rather then a round port

[JonMarsh]

A true slot loaded sub (front loaded) is a variation on a bandbass reflex design. I designed and built some of those in the 70's. The front slot load configuration, if done right, can dramatically lower the box tuning of the driver (for example, 15" driver in same simpled sealed volume goes from box Fb of 65 Hz to 28 Hz), but as the enclosure raises the system Q dramatically also, I normally started with a very low Q prosound type driver (Qts=0.2 or less), then that would result in a box Q in the range of 0.6 to 0.65. Built some using JPL and Audax Pro drivers.

If you put a more conventional driver in this type of configuration, you're qoing to windup with a very high Q mess at the box tuning, but the car sound guys would probably like that. Since it's basically a sealed box, power output is still a function/limited by Xmax and Sd.

[SE-Raider]

Jon:

If I understand you, the frontloaded slotted design is then just a variation of a 4th order bandpass? Your observation is that the design lowers the Fb at the expense of Q, then is this true of the 4th order bandpass in general. Thinking conversely, could this be an effective tool for obtaining the lowest possible FB for a given Q. Say starting with a Q of .5 would you be able to use an udjustable plate to obtain a lower fb than normal, and possibly help with power handling as well?

Since the TL box as I understand it helps with a flatter response and lower Q, might this be the reason that some designers are using the front-loaded plate/slot and rear-loaded slot/tl in combination. That is, use the rear-loade design to maintain the lower fb of the front loaded design but mitigate is undesirable tendencies?

Further, some designs are complemetary to others. In using two different designs for the same driver within the same box (one on each side of the driver), changing any parameter on one side of the driver would affect the other side as well. Does any of the commonly used software allow experimentation with juggling these designs against each other. It might be possible to acheive a synergy in doing so. Dare I say it, I have often marveled at the amount of calcultion that must have gone into the Bose acoutimass modules to acheive the output they do from such small drivers.
It seems to me that similar gains could be made with larger more sophisticated drivers toward a more accurate design goal as opposed to the mass market appeal targeted, I think by Bose. (This is the point at which my intelligence and my manhood will begin to be challenged for having mentioned this brand in a positive light :lol: . But IMHO they do a very good job of applying specific engineering toward a very specific market as targeted by their business plan.)

[SE-Raider]

Rudy:

Do you prefer these designs over any others. What driver was the drawing modelled for? The size of this box is barely larger than a small sealed box. Did you ever experiment with these enclosures in combination with a front slotted design?

Dougie085: Does basbox treat this differently or is it just a different shape of the same area to volume ratio of the port?

[Rudy Jakubin]

For the TL Sub (9" baffle) I had;
Dayton 8" Classics
Dayton 8" RS
Goldwood 8" OEM
Than on to a 11" baffle - same TL box (style & length) I had;
Dayton 10" Classics
MCM 10" Aluminum 55-1300
MCM 10" Professional 55-1740

The best sounding were the
Dayton 8" RS and the 10" MCM Aluminums. The RS 8's will pair up with the RS7's RS 28a MTM (NatalieP's)... :W
The 10" MCM Aluminums will pair up with a 2.5 TMM in a Labyrinth TL which I'm listening to now and tuning the crossover.
They all sounded good but Xmax and SPL had to be considered. Sometimes I like it loud.
Surprisingly as a test I put in one 8" Classic with one 8" Goldwood OEM. It sounded better than pairing them with the same drivers...Alas, no Xmax.

The 0.5 cu. ft. Bass Reflex with the MCM 8" High Excursion woofer with a Qts. of .18 and 16mm Xmax 55-2421 sounds really good and handles "Laurie Andersons - Life On A String" really well. That's my test piece for bass boxes.
After reading Jon's take on higher Qts woofers in a bass reflex box has me rethinking about a higher Qts drivers to try in them.

Oh, on the TL's I did model those drivers in MJK's MLTL worksheet to see if they would match...
I didn't have to angle them, I did it because I was tired of Monoliths...

Comparing the TL with the BR;
The TL's sounded cleaner but the BR had it's own style or voice that sounded good also. A change of pace sort of.... Like music. Somedays Jazz, somedays Disco...

As for size, they model slightly larger than a sealed box and maybe smaller than ported box...

Great Fun!!! :lol:

[SE-Raider]

Rudy:

According to Jon's comments, wouldn't you be better staying with the low QTS driver in the bass reflex application?

How did you model the BR design?

Since you have used a variety of drivers in the TL design, did you design a generic enclosure and experiment with different drivers or were the T/S parameters close? Then again you may have been experimenting - nothing wrong wtih that :W

[Rudy Jakubin]

That was a low Qts driver I used. It was 0.18....
I used WinIsd beta and alpha versions to get the port length.
Mine was a bit shorter than what's in the graph above.
Since Jon mentioned the problems about higher Qts drivers I think I'll stay clear.

Yeah, I love to experiment. When I didn't care for Xmax problems with the Dayton Classic's I went back to MJK's worksheet and plugged in different drivers. The T/S parameters didn't match or even come close on some drivers, but putting them in the worksheet they seemed to match or come close to MJK's infinte baffle slope.
I could play it safe and build other peoples designs, which I do, but when I see pictures of commercial speakers I get some crazy ideas.
Like this one the other day;

http://www.innersound.net/kaya.html

See the back on this speaker. Now if I use a high Qts midbass drivers and replace the back grill on this KAYA speaker with open-celled foam and painted it black, gold or what ever or go dipole in some fashion or add a backfiring tweeter etc... Hee Hee...