Sub: sonotube, siting, EQ, delay?

[ro9397]

Questions concern siting & enclosure material for a custom sub for a very high-end music reproduction system. Sub source is a mono signal from a proprietary pure-analog processor. Will start w/ one sub; depending on results may add a second sub.

Room Dimensions & Volume

Approximately 26.6’ x 16.6’ x 8’, 3575 cu ft; unknown whether speakers are going on 27’ or 17’ wall.

Main Speakers

Will be actively &/or mechanically high-pass filtered @ 70 Hz.

Proposed Sub

Internal displacement approximately 4.4 cu ft
Reflex-loaded
Active heavy duty 15”
15” passive radiator, tunable mass loading
1000 WRMS amp, active low-pass XO, single-band parametric EQ

Sonotube Enclosure

Sonotube (cylinder-shaped treated-pulp cement former) is the proposed enclosure material because it is light, it’s affordable, it’s easy to finish, it has a relatively small footprint, & it fits in a corner or freestanding.

The active 15 would fire upward toward the ceiling, the PR15 would fire downward & spaced appropriately off the floor a few inches. (The vertical orientation of two subs can be inverted, i.e. one active fires up/PR down while the other sub does the opposite; would likely smooth room modes.)

Below 60 Hz how much will the ST’s “organ pipe” resonance (diameter repeats for entire length) contribute to one-note bass?

What about stiffness & anti-resonant qualities of the pulp? It could be internally lined w/ cork, Black Hole, &/or borosilicate.

What is recommended method to attach the driver baffles to the ST? Will Liquid Nails properly secure the outer perimeter of the baffles to the inner walls of the ST?

Is cloth or veneer best to finish the appearance of ST?

Other comments regarding ST?

EQ & Delay vs. Room Siting?

Corner siting increases bass output but can decrease smoothness & delay sub output relative to the main channels.

In my previous room a Sunfire sub was crossed similar to the proposed frequency. The sub was sited in a front wall corner R of & behind the R main speaker. No delay was applied to the main channels to time-align the sub & mains. There were no audible timing problems. Others predict time alignment problems. What say members?

The above Sunfire sub had 5-bands of digital automated EQ. The proposed sub will have single-band parametric eq. In the room described below 60 Hz, will single-band parametric EQ be enough to smooth the corner-loaded response?

Thanks for your consideration!

[ThomasW]

Below 60 Hz how much will the ST’s “organ pipe” resonance (diameter repeats for entire length) contribute to one-note bass?

Pipe resonances aren't an issue.

What about stiffness & anti-resonant qualities of the pulp? It could be internally lined w/ cork, Black Hole, &/or borosilicate.

Unnecessary

What is recommended method to attach the driver baffles to the ST? Will Liquid Nails properly secure the outer perimeter of the baffles to the inner walls of the ST?

Liquid nails works fine

Is cloth or veneer best to finish the appearance of ST?

The seam of the paper will show through veneer

Corner siting increases bass output but can decrease smoothness & delay sub output relative to the main channels.

Corner placement boosts output at certain frequencies.

The proposed sub will have single-band parametric eq. In the room described below 60 Hz, will single-band parametric EQ be enough to smooth the corner-loaded response?

Doubtful

[ro9397]

Thanks Thomas, I very much appreciate it.

Concerning my idea of smoothing room modes by inverting the vertical driver orientation of one sub vs. the other: The top-firing PR may emit high-frequency hash (as PRs are reputed to do) unless the noise is mechanically filtered via a slot. Is this made moot by the 60 Hz low-pass XO pole? Ideal slot dimensions if advised?

What is ideal spacing above the floor for the PR & also same for the active 15" (in the case of an inverted sub)?

Will the light weight of the ST tend to cause the sub to lift upward from the floor (subsequently dulling transients) when the down-firing driver moves toward the floor? Does the inverted relationship of the two drivers cancel this effect? Recommendations to add mass if advised?

Should a method be incorporated to direct the output toward particular areas of the room? For the downfiring driver, this could be accomplished by making a 180-degree-wide cutout a few inches tall, rather than just a straight cut across the ST; legs would be installed to support the cutout area. The output of the top-firing driver could be directed similarly, but requires an additional flat horizontal surface (a top) vs. the feet on the base.

I'm thinking it would be good to direct the PR output toward the L/R front wall corners (providing the subs are sited on approximately the same plane as the front speakers). The goal in this case would be to increase lowbass output.

Thanks for everyone's consideration.

Thomas your avatar is interesting. It's hard to stop staring at it!

[warnerwh]

Being as this is very high end I'd use a sealed sub. I've read where people claim a good ported sub can sound as good but haven't heard one. My experience is limited but found good success using sealed outboard subs with my speakers which happen to have passive radiators. The Dayton Reference Series subs had been recommended to me by other forums besides this one as the drivers I wanted to use.

My question to others in the beginning had been to build a sub that had the highest quality bass reproduction for my stereo. The RS series Hifi is what I was told and they are truly excellent. If the sub you're going to build happens to be for an integrated music/ht system the Reference Series HO drivers is probably what I'd use but I'd ask here first as it may also depend on your budget.

For the best bass quality one band of equalization can't do the job unless you're lucky enough to win the lottery all year. Otherwise I'd highly recommend a Behringer DEQ 2496 and the ECM 8000 microphone. The device will do all you need to fix bass peaks in your room. It will also create an LT circuit if you need it if you decide to go sealed offering you a low Q. For the money it's the best thing going for room correction, this is especially true with bass where the problems can easily be substantial.

If you run only the subs with the Behringer you can probably even time align the subs to your mains. In my system I've not tried it that way as the upper bands are too important to be able to adjust. Just a thought. For 250 I've seen the DEQ 2496 selling on Audiogon for around 250.

[ThomasW]

Normal PR's aren't suited for ST since they can't be used in horizontal positions due to their weight. Also one needs 2-3 times more Vd with the PR than with the driver. This means 2-18" or 3-15" PRs for one 15" driver.

What you see with the VMPS designs is a very atypical alignment. There's low excursion lightweight PR resistively loaded against the floor. The pressure supports the lightweight PR cone. That's not something I recommend the DIYer try to duplicate.

If you want a high sound quality tube, I'd recommend dual woofers (sealed alignment). One on the top the other on the bottom. Use a L-T circuit to lower the Qtc and boost the bottom-end output.

My avatar was chosen for the very reason you mention..

[warnerwh]

Rather than one tube with two drivers wouldn't the OP be better off with two tubes, one driver each placed in opposite corners? I can't say for sure as I haven't measured yet but adding my second sub recently made the response smoother to my ear. I'm suspecting having bass reproduced in the opposite corner is the reason.

Hopefully this week I'll have a chance to dial in my bass again so I can say for sure what happened after adding the second sub.

I believe the Dayton RS series drivers can be used in this configuration as they meet the 5% rule just barely. If you really need alot of output then four 15s will do the trick in your room. My room is only 12x17 but I have way more output capability with two 15" RS drivers than I need.

The sound quality improvement with these subs had been more than I expected improving the entire sonic presentation considerably. Everything that low bass does, below 60hz, is better than my mains with passive radiators could do. This is especially true at higher volume where I tend to listen alot of the time. I'm talking peaks in the mid to high 90s.