Considerations for Peerless 830452 Multiple Compact Ported Subwoofer Build

[Mandroid]

Looking at the other subwoofer threads going right now, I am under the impression this is one of the few places to go for sensible input on subwoofer designs. I have been slowly selling off my larger speakers and subwoofers in favor of more modest equipment to put in the living room. Dedicated theater room in the basement just doesn't get used enough.

Thought process here was that summed low frequency output from four subs should allow the use of smaller and lower tuned enclosures than would typically be used. The small enclosures can then be placed wherever they perform best without being confined to a couple spots where a large sub would fit.

RSS265HO-4, SB29SWNRX-S75, and 830452 were the three drivers I thought looked most promising. Saw there were still a few of the Peerless left at pre-price-explosion prices and bought four.

Trying to decide which set of compromises to go with. Modeled up three options in sketchup. Figure all three should be roughly 40 liters after driver and bracing, tuned hopefully 20-23Hz-ish:

First was the passive radiator. Model suggests the 830452 and RSS265-PR would run out of excursion at about the same time. Not sure if it's worth the extra cabinet width, wait time, and money to go with the RSS315-PR. Suppose the only downsides to the passive radiator option is the extra $400 in parts and having cones on two sides of the box.

Second was a conventional downfiring round port. Really no way to fit anything larger than a 3". Model suggests it is significantly undersized to take advantage of the full output of a single sub. I still wonder if this alignment wouldn't work just fine, though.

Third was a slot port. Utilizing the entire depth and height of the cabinet, the slot port allows for area equivalent of a 4" round port. I have concerns about the right angle bends negating most of the performance benefit of the larger port, but such designs seem to be widespread throughout the diy and car audio communities. Also slightly larger cabinet.

I would be interested to hear folk's thoughts on the matter.

[xandresen]

Couple of thoughts

A slot port has enormous surface area.
Air next to any port inside surface does not move, reducing the effective port area. The drawing also shows two 90 degree angles, one at the port entry and the second at the bend. When sizing forced-air boiler exhausts, there is a strict limit on the number of 90 degree bends due to resistance to flow. This suggests to me that a slot port, as shown, is much more lossy than the other options.

conventional port
In my 3-way with 8" woofer I do not have enough room for a straight port (unless it exited the top of the cabinet).
I used a 3" shop vacuum hose elbow to put a 90 degree bend in the 3" port port. This works well for me. I don't have measurements on the loss.
Would using a 4" hose elbow let you fit a 4" port that exits under the woofer?

Try for as large a diameter in the elbow bend as you can. Some port bends sold to DIY are just as abrupt a turn as the slot port.
You can also use common PVC plumbing 90 degree elbows - however these are very heavy.

Also be sure to use large port flares at both ends of the port. These vastly reduce audible airflow noise - which is another indicator of loss.

The published simulations I have seen show an under-size port works fine at low amplitudes (low flow rates) but acts more like a closed box at very high output.

Edit: since you have four subwoofers, you may never drive them anywhere near full output during actual listening. In that case a 3" port might work just fine.

[Evil Twin]

"realistic tradeoffs" is a concept not often explored well before embarking on a project. The points brought up in your second post are quite valid... unless you get to the point that you do want to enjoy a more unbridled experience.

In my usual role of telling people things they do not truly wish to hear, I would point out the Fs and other aspects of the Peerless driver do not suggest a role as a subwoofer, but as a woofer. I might also question the veracity of the rated Xmax, given the sensitivity for an 8 ohm nominal part. It seems hopelessly optimistic. However, the price, as currently shown on Parts Express, is quite reasonable.

Your 40L target volume is quite reasonable for a compact subwoofer, but were I pursuing the same goals as you, I would be inclined to consider the Dayton RSS210HF-4 with a 10" passive radiator such as the Dayton RSS265PR. Unibox is an easy to use Excel based tool which makes working with passive radiators and evaluating performance and tuning very straightforward, if you have a grasp of the physical basics at hand. You will quickly find that PR configurations require careful cone mass tuning for the box volume and PR Qms, and will usually work best with significantly higher Sd than the main driver- it's not unusual to pair a 10" PR with a 7" woofer.


Here, an example relevant to your design overview with the RSS215HF-4 and an RSS265PR with 350g total Mms, and 75W drive (relative to 4 ohms), which will push the RSS210HF to Xmax at 30Hz, the excursion peak frequency before the PR contributions dominate. This is not considering room boundary load as regards output level, this will contribute around 6 dB at the low frequencies, and having 4 cabinets would bring it up another 6 dB. So, as analysis for another design in progress shows, a quad array can hit 110dB with some headroom.

[Mandroid]

I suspect you're looking at the specs for a different driver, spec sheet attached.

It was also brought to my attention that choosing a single passive radiator instead of a port may be trading likely port compression for likely cabinet movement at high excursion.

Dual opposed passive radiators would certainly move the project into unreasonable price territory for what is effectively an experiment to see if I can be happy with smallish subs.

[technodanvan]

I'm not so sure my build is all that sensible, but it's a heckuva lot smaller than the subs discussed at some other forums for sure!

First was the passive radiator. Model suggests the 830452 and RSS265-PR would run out of excursion at about the same time. Not sure if it's worth the extra cabinet width, wait time, and money to go with the RSS315-PR. Suppose the only downsides to the passive radiator option is the extra $400 in parts and having cones on two sides of the box.

Thoughts/questions in no particular order:

Jon has stated in the past that using a PR to its xmech is probably not a great idea through the usable bandwidth due to rising distortion, however much like was stated previously about using a 3" port possibly being okay given the four separate subs, I would think the RSS265-PR may be fine as well. Really depends on how low and loud you like to go with things. Note that if you go with the RSS265-PR I think you could put this on the same face as the driver itself, you may have enough room for it. That said, in my brief modeling of the subwoofer/PR combo I don't believe it would be a great fit - I think ported is probably the way to go.

How are you planning on powering the subs? Do you have any way of applying EQ/DSP via your receiver or some other methodology?

Are the external dimensions a result of constraints set by other factors? I do think a smaller ported subwoofer could work pretty okay, something with a tune of 30Hz in 40L may be ideal. I want to stress this really was brief though, maybe 5 minutes of playing around once I entered all the parameters in UniBox. Note that a 3.5" ID port would still push boundaries, but retain much of the shorter length and reduce chuffing. I believe this size is available in electrical PVC sections at home improvement stores.

What sort of bracing are you planning, just using carefully placed dowels?

Jon might be referring to the relatively modest xmax of the driver coupled with the lowish power rating. I think four of them will still move a fair bit of air and make for an above average home theater/music experience. I just wouldn't expect a lot of really deep (<30Hz) bass out of them. That said, I haven't explored sealed options where you could opt to use EQ to bring up that low end. You'd probably run out of xmax fairly quickly doing it that way, but with four of them that may not be a problem depending on your listening habits.

[Evil Twin]

I suspect you're looking at the specs for a different driver, spec sheet attached.

It was also brought to my attention that choosing a single passive radiator instead of a port may be trading likely port compression for likely cabinet movement at high excursion.

Dual opposed passive radiators would certainly move the project into unreasonable price territory for what is effectively an experiment to see if I can be happy with smallish subs.

You are correct about having viewed the "wrong" data sheet. Checking again and finding the parameters, I would say it has a combination of design characteristics probably better suited or targeting a bandpass enclosure, due to the very low Qts from high BL factor.

Tuning for a ported system at 40L and for the driver Fs, the response is what would usually be termed an EBS alignment. In practice this means that the lower bass is extended, but shelved down. As Danny notes, a shelving EQ might well be desirable. Note the calculated response curve.

[Mandroid]

Going to be powered with a pair of rackmount amps with dsp, since that's what I already have. Using dsp for high pass and delay. They'll be getting their signal from an avr with crossover set around 80Hz. The Audyssey multeq-x program will likely end up handling eq.

This is mostly for movie purposes. I value my hearing though, so I don't subscribe to the reference volume level commonly quoted by the internets. Audyssey is supposed to calibrate to that level, and I generally watch loud movies at -18 to -12db. Maybe -6 for a few minutes if it's a particularly good part of a concert bluray.

Box dimensions were selected for small footprint without being overly tall for my sensibilities whilst accommodating the estimated 3" port length. Downfiring to get a bit more effective length and push the tune just a bit lower. Really going for an alignment that probably wouldn't well suit a single unit. I do get some low frequency reinforcement, since my room isn't very large.

Bracing is yet to be determined.