multiple driver HT sub ..how to design ?

[JinMTVT]

since i am considering a sub-bass HORN,
i want to also consider the other alternative ...

how could i simulate response of alot of bass drivers?
is there a simple sofware that would allow to see how would behave alot of bass drivers ???

i am maybe thinking about using alot of 18" or 21"
drivers, since i will have the space to do it ..

i am looking for ultimate HT sub bass here,
and since the rest of the system will be line arrays,
a good number of bass drivers could feel at home i believe


how exactly does a few drivers wired together behave?
i think i remember something like +3b for each doubling of the driver numbers ? ( efficiency )

what would be the best configuration ?
i could seal the back and absorb most of the rear wave somehow ...

i will have around 10 cubic meters available for each side
( front size of maximum 9' by 5'width )

thanks for ur time

 

[planet10]

With that much cabinet volume you have lots of options... a big sealed cabinet (IB) probably makes the most sense. And with 1/ such a big box prone to resonancem and 2/ multiple drivers it only makes sense to push-push them.

what drivers you have in mind?

dave

 

[Cloth Ears]

Regarding multiple drivers, 3dB is the ideal efficiency increase. And, according to this post, that is true up until efficiencies of around 20% or more. It's a good thread on efficiency and worth a read.

A sub-bass horn is really a waste of space, IMHO D), whereas you'll get better, deeper and probably louder sub-bass using a infinite baffle set-up. A few ideas - William Cowan's IB subwoofer, FAQ for IB Subs and another IB. The only problem is finding the extra room (or basement or attic) to be your enclosure. The more drivers, the better.

 

[JinMTVT]

hey dave

well i do not have choose any particular driver yet..
as always the 6174 from mcC interests me,
but my wallet doesn't allow for that crazy expense
( at 500$/piece )

probably a good 21" ..could get 10 to 16 of em

the reason why i want to look at simulation
is because i want to see what can be done with a few drivers like that ..
i'd like to be able to reach something interesting at 20hz and sub frequencies ... probably need 130db @ 1m
to be able to get decent output at seating places

still need to work on that room design,
and i'll study the one you have suggested in the past also ..


Infinite baffle ..could always be nice!
anyway you know to get rid of the waves in the ground ?

i don't mind digging 2 big holes in the ground and using some case with wool or something in it ...
though the water level in my land is pretty high..could have some problems ...could probably source some big plastic containers ...
what if one hangs big lumps of wool from the ceiling in the back box ,wouldn't that absorb alot of the waves by making all of the lump moves + heating up the fiber?


what are the difference in the end result at front output from a sealed, infinite, ported ???
i don't think that ported would do it ..since the backwave will be disturbing the output quite much in any config ..

 

[planet10]

probably a good 21" ..could get 10 to 16 of em

Some details would make it easier to answer your questions.

dave

 

[JinMTVT]

what kind of details do you need ??

i am 5' 7", brown hair, athletic body ...
ah nah ..not that kind of details i guess
hahaha


what i want to do, is use the space i have to get the best possible bass and power for my new HT room

so if i need to use 10 or 16 21"inchers, i'lll do it

i was considerin sub-bass horn alot lately, but the problems associated with the delay has me giving it almost up

and i am pretty sure that using alot of drivers will bring distortion to a very low level since they won't have to move that much for the same spl

so what should i do ???

i was thinking of a semi horn within wich a few 21" would be in a central enclosure going push-push together, firing within the horn wich would then point toward the seats ??
i'd have to do a 3d sketch for that ..

 

[planet10]

what kind of details do you need ??

pictures, link, T/S?

i was thinking of a semi horn within wich a few 21" would be in a central enclosure going push-push together, firing within the horn wich would then point toward the seats ??
i'd have to do a 3d sketch for that ..

I might already have sketches of that idea.

dave

 

[JinMTVT]

don't try and steal all my ideas here Dave
hahaha

so what would that give ??
would the horn be somewhat effective or not worth it?
could make it way further in ..

don't look at the pic's quality ..i did that in 5 minutes just to demonstrate ( not at scale either )

An externally hosted image should be here but it was not working when we last tested it.

An externally hosted image should be here but it was not working when we last tested it.

this could make a nice semi horn front fired
and would take care of the rear waves pretty good
also would lead to alot of surface for moving air

 

[JinMTVT]

how important is the volume of the enclosure for push push subwoofers ?
does it matter at all since the waves are cancelling out?

 

[planet10]

how important is the volume of the enclosure for push push subwoofers ?
does it matter at all since the waves are cancelling out?

That last statement indicates you have some misunderstanding of how push-push works. The woofers work together not against each other.

If 1 driver requires a volume of A, then n drivers need a volume of nA

dave

 

[planet10]

don't try and steal all my ideas here Dave

You would need to deal with the throat properly, you'll likely need more volume for the back of the driver, and the front of the driver box will need to be prow shaped (ie part of the horn flare, but otherwise that is the topology.

dave

 

[SpeakerBob]

Not mine, but an interesting pic I found on the web..

Rob.

 

[JinMTVT]

Rob,
this is somewhat i had in mind when i did the quick sketch, but using the push push line of woofers a the back ...

problem with this, still have a few ms of delay for the bass... is delay of a few ms a big concern for sub bass frequencies??

it would probably be easier to delay of a few ms all of the audio except the midbass...than delay also the video for longer horns to match ..

Please Dave explain better what happends inside box with push=push arrangement

i thought that the waves canceled each other compeltly...but thinking of it, this only happens right at the middle of the enclosure where they meet up ...
what eaxctly happens to waves and pressure inside the enclosure>?

 

[JRace]

High output is easily achieved with a single driver in the right box with the right amplification. Flat, even room response (meaning it sounds good all around the room) is much harder to achive and best delt with by using multiple subs in multiple locations throught then room.

Adding drivers will increase the output, which means nothing if there is a null in your seating position.

 

[SpeakerBob]

Hi,

Regarding the delay, if you're going for a setup where all the bass from all 5 speakers is redirected to the sub, then you can adjust for the horns delay in the speaker settings. You just tell the processor that your main 5 speakers are 'x' nearer than they really are, and the processor will add delay to them. 'x' being the length of the subhorns path.

I don't use any video delay and it looks in time to me btw.


Push push is where you use 2 drivers, both in phase (ie: when 1 moves away from the box, the other also moves away from the box) when placed on opposite sides of the enclosure the mechanical vibration from each will cancel the other. Its not about sound, but vibration cancellation. When a single driver moves it tries to push the enclosure in the opposite direction, causing vibration in the box. If you mount a second driver on the opposite side it will push the enclosure back, cancelling the vibration. The labhorn drivers are mounted this way.

-->[]<-- Drivers moving in, forces cancel each others vibration out.
<--[]--> Drivers moving out, forces cancel each other again.

<--[ Both drivers moving same way, no force cancellation
<--[ Box will have more vibration.

Cheers,
Rob.

 

[JinMTVT]

ok
i understand the part about the mechanical forces cancelling out ..

but what about the waves ?

i always thought that 2 waves of oposite phase and exact same amplitude should cancel themselves ??
isn't it the case here inside the enclosure?

 

[Brett]

i always thought that 2 waves of oposite phase and exact same amplitude should cancel themselves ??
isn't it the case here inside the enclosure?

They're in phase.

 

[JinMTVT]

They're in phase.

OMFG ...there must be something wrong going inside my head ...
since the begining of this thread.
i had the mental image of push-push cancellling the rear waves ....

i stand corrected !!!!

Sorry about all the stupid questions for 2-3 days,
i was in the thinking that the rear waves were out of phases, but on the contrary ..

so it behaves like a regular sealed subwoofer inside the enclosure except for a band at the center ???






so we get back to basics, this doesn't solve anything as far as removing the rear wave
and push-push is good for a box that has to fit in a limited "Regular" kinda sub enclosure

what are the other options?

infinite baffle?
dipole?

 

[Brett]

...there must be something wrong going inside my head ...

I know that feeling.

i had the mental image of push-push cancellling the rear waves ....

i stand corrected !!!!

Sorry about all the stupid questions for 2-3 days,
i was in the thinking that the rear waves were out of phases, but on the contrary ..

so it behaves like a regular sealed subwoofer inside the enclosure except for a band at the center ???

Visualise the box like Dave (planet 10) posted in another thread earlier today with a pair of drivers on each side, wired so that when a positive voltage is applied, they both move outwards, away from the enclosure. Now there's less pressure inside the box (assume sealed). As the waveform cycles back, the drivers move back inwards and now there's more pressure inside the box. The pressure changes are the same as they would be for a single driver in a box half the size. Because the wavelength is long compared to the box dimensions, it effectively radiates omnidirectionally, and at LF, the drivers acoustic outputs add (roughly) in phase, eg at 40Hz a wavelength is 8.6m and the encloure width seperating a pair of drivers (in my case 18's) will be about 50cm or 1/17th of a wavelength.

Where the advantage lies with this layout is that the mechanical forces that the drivers would ordinarily impart to the box, are cancelled out for the most part. The box will also be a hell of a lot stiffer across the axis where the resinforcing rods are too.

Clearer now?
Cheers

 

[JinMTVT]

YEs of course it is much clearer now with ur explanations
and my turning up of the driver movement and waves ..

so it can be said, that there is no advantage to this design if space, is not a factor ( limited , but not regular living room space )

Back to topic then ...



I'll ask it simply ...


What WOULD YOU DO , if you had some good budget,
and had to do your ULTIMATE HT subs ??

(i don't have 10 000$ ..but i don't mind spending a few 1000$ on the subs alone .. space is approx 10cubic meters per loudspeaker .. i want stereo bassssss )