Has anyone ever dealt with the issue of minimum floor clearance on a downwards firing subwoofer? I'm building a pair of low profile subs for a local church - most of the seniors there hate the look of any visible speakers (LOL) so I'm trying to help them out with a compromise. The design is just a simple ported enclosure with a downwards facing 18" driver and ports. I was planning on having 3.5 inches of clearance from driver face to the carpeted concrete floor. Is this sufficient clearance to not affect performance at higher SPL?
Edit - just realized I should have put this in the subwoofer section.
Edit - just realized I should have put this in the subwoofer section.
So you're saying the box tuning will be affected if the port diameter is greater than the floor distance? Port diameter is 4.5 inches ID x 2.
Since you ask there's much speculating that could be done.. will there be reflection, is the port modal..
Naturally tuning will be as it is but no, I was not trying to imply anything that couldn't be said generally. I like to note the way the valves in a 4 stroke engine operate. They don't necessarily open as far as their own diameter, and this is wanted as far as accelerations are concerned, and for clearance purposes. However the cross sectional area can be larger than the port when taken radially around their periphery.
Naturally tuning will be as it is but no, I was not trying to imply anything that couldn't be said generally. I like to note the way the valves in a 4 stroke engine operate. They don't necessarily open as far as their own diameter, and this is wanted as far as accelerations are concerned, and for clearance purposes. However the cross sectional area can be larger than the port when taken radially around their periphery.
Another (long term) performance issue is cone sag on horizontal loudspeakers.
Perhaps the speaker could be faced against the wall, which would also avoid the visual gap at the bottom of a down firing cabinet.
The performance won't change at higher SPL any more than it would front or rear firing, but there will be a cavity resonance associated with the enclosed area, as well as Fb may be slightly lowered depending on the proximity of the ports to the exit.
It's at 1/4 lift that it will have the same mantel area as the valve area, flow is still usually limited a bit further due to the obstruction, but it gives and indication on when the flow is controlled by the port. 🙂
For a speaker, I really don't know at all... 🤷♂️😂
The drivers used in this project are Lavoce SAF183.03. They have a dual spider setup and fairly large stiff suspension, so I'm not concerned about cone sag too much. It would be a different story with a high compliance single spider driver with a heavy cone.
Placing subs near a wall is not going to work because the only locations available close to a wall have hand rails for the steps leading up to the stage and must remain free of any obstacles. The subs will sit spread across the steps leading up to the stage and the steps span across the entire stage front. Placement behind the stage won't work either due to drum set proximity and potential feedback from kickdrum mic.
There isn't any boundary other than the concrete floor around the subs, so they operate in 2 pi field.
Placing subs near a wall is not going to work because the only locations available close to a wall have hand rails for the steps leading up to the stage and must remain free of any obstacles. The subs will sit spread across the steps leading up to the stage and the steps span across the entire stage front. Placement behind the stage won't work either due to drum set proximity and potential feedback from kickdrum mic.
There isn't any boundary other than the concrete floor around the subs, so they operate in 2 pi field.
Looks like a nice driver.
Cone sag will eventually happen to any horizontal speaker, just a matter of time.
Here is a recent example posted on Pro Sound Web of cone sag from the bottom 10" mid speaker in an EV cabinet, the stiff suspension and lightweight cone still sagged enough over time (appears to be about 4mm) for the driver to be ruined hitting the phase plug. Craig had the problem with multiple speakers, probably had sat idle during the Covid age...
Nothing a noise gate and a bit of EQ can't cure- I remember Rocky Holman's glee in using a pair of MTL-4 (manifold quad 18") cabinets for drum fill bass, "Texas Headphone" style, one either side of the kit.
My old friend Steve Raitt (RIP) built a sub that doubled as a drum riser- the horn exit was within a few feet of the kick drum mic.
Of course, that still might not be loud enough for most of the seniors in church 😉
Art
I appreciate the warning about the cone sag and I can see how it will eventually become an issue, but due to the majority of people involved with the decision (too many opinions) and the pressure from leadership not budging with proposed sub placement, I've decided to give this a shot and see what happens with longevity. I opted for a 4 inch floor spacing which should be more than enough to avoid skewing free air tuning or restrict output. I will be keeping a close eye on cone sag and report back about it in some time.
The bass heavy youth will definitely push this setup hard and I doubt any amount of limiting and LF high pass will fully idiot proof the subs from their predicted eventual demise. When it does go south maybe they will learn to not ignore my advice which is similar to what you gave me here. This will obviously be an interim setup until they have the funds to build something bigger ie. tapped horns with several smaller drivers that wont be pushed as close to their limits for desired output levels.
The bass heavy youth will definitely push this setup hard and I doubt any amount of limiting and LF high pass will fully idiot proof the subs from their predicted eventual demise. When it does go south maybe they will learn to not ignore my advice which is similar to what you gave me here. This will obviously be an interim setup until they have the funds to build something bigger ie. tapped horns with several smaller drivers that wont be pushed as close to their limits for desired output levels.
This is part of a small PA that I put together for them. Its a small room with very limited speaker placement options, mainly due to seniors not wanting to see any "big black boxes" lol. They unfortunately are the ones who donate the most money and therfor have most of the say so. Its a pretty sad situation.
The mains I designed for them consist of 4 x dual 8" cabs with Eminence Beta 8As and B&C DE250 drivers on ME20 horns crossed at 2.2k. The Lavoce 18" LF drivers are in 155L tuned to 35Hz.
The mains I designed for them consist of 4 x dual 8" cabs with Eminence Beta 8As and B&C DE250 drivers on ME20 horns crossed at 2.2k. The Lavoce 18" LF drivers are in 155L tuned to 35Hz.
Attachments
I did propose a drum riser with subs, but the band director didn't want the subs right behind him. Also, i was trying to keep the subs closer to the mains for tighter integration. Gating would definitely work to avoid FB, but its not a setup that can be left unattended with less qualified sound techs who dont know how to dial that in. Dealing with techs like that is frustrating but that's usually what you find in smaller churches. Its bad enough that the older techs dont know their way around a digital console, even a simple one ie. Allen Heath QU32.
I sure wish they could be persuaded to using a quad of TH118s - that would definitely be enough for the "kids".
Hahaha yeah, when dealing with the WW2 post generation, its hard to get any modern attitude towards audio. They should be used to bigger speakers being they're from the pre-Bose are. Alot of smaller churches in this area are made up of these people and they are the ones with the deepest pockets who give the most, so they're catered to.
I did paint them gray just to take that argument away from them. Lol - I don't really care since I'm not attending there. I'm burned out on ignorant old people, some of which are downright mean and overly opinionated.
I did paint them gray just to take that argument away from them. Lol - I don't really care since I'm not attending there. I'm burned out on ignorant old people, some of which are downright mean and overly opinionated.
All will soon be complaining
" There is too much Bass"
Guess non of them have ever seen
A Hammond church organ with a big leslie speaker.
My church would have 2 of them.
All n All on a positive note your build efforts seem straight forward and should work well
" There is too much Bass"
Guess non of them have ever seen
A Hammond church organ with a big leslie speaker.
My church would have 2 of them.
All n All on a positive note your build efforts seem straight forward and should work well