Open Baffle Subwoofer Advice Requested

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Ormy

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Open Baffle Subwoofer Advice Requested
« on: 5 Nov 2019, 07:49 pm »
Hello everybody, I'm new to the forum, I would like some advice and opinions from open baffle enthusiasts because of a recent purchase I made.  I have no prior experience or knowledge of open baffle speakers beyond the loose definition.

I was in the market for bigger and better sub-woofers for a 5.1 system but I'm on a tight budget.  I got an amazing second hand (originally manufactured and sold in 2015) deal on some 18" Stereo Integrity drivers (see pics and parameters below), they are an American manufacturer and I am in the UK so the shipping alone usually puts their gear well out of my budget.

The previous owner had them mounted in open baffles, four drivers in two 'cabinets', they certainly made the drivers easy to transport as the drivers are mounted securely in quite a compact space given their size and weight (each cabinet is around 100lbs).  My intention all along was to put each driver in a sealed or ported enclosure, but after listening to them for a while in their open baffle configuration I'm very intrigued indeed about how good they sound.  And because they take up so little floor space compared to huge ported boxes, plus the drivers are easily visible and they look good, I'm more and more inclined to keep them open baffle.  I searched the internet for a place I could get some advice on how to get the best out of my new subs and found this forum.  So here are my questions...

Extra info: They will be used to handle frequencies 80Hz and below only.  I have input-filtering, meaning I can apply EQ to the sub-woofers separately to counteract dipole rolloff. My listening space is 1500cuft.  If there is any other info that would be helpful please ask.

1.) Are these drivers appropriate for open baffle usage?

2.) How can I get the most out of them? 

3.) The drivers are rated for 600Wrms, is that enough for good output in the lowest octaves?

4.) Anything else I should be aware of or careful of whilst using them?








Thanks in advance.

Tyson

Re: Open Baffle Subwoofer Advice Requested
« Reply #1 on: 5 Nov 2019, 10:18 pm »
The W frames they are in are fine.  If you wanted to put in some extra effort, you could build some H frames and line the H frames with NoRez.  I'm a fan of no-void baltic birch for sub cabinets, that stuff is really quite rigid. 

OB subs will roll off a bit in the lowest octaves, but you also have to understand that you'll get room gain in those same frequencies.  So my best advice is to build it and amp it straight, no EQ at all.  Take some measurements and then add EQ based on what your measurements say.

JohnR

Re: Open Baffle Subwoofer Advice Requested
« Reply #2 on: 6 Nov 2019, 03:22 am »
Looks like a great find!! Vas is missing from your list of specifications, but I'd suggest you put the parameters into a box modeling program (eg Unibox), that will tell you how much power you need to get them to full excursion and should tell you whether they are suitable for downfiring (which those are, sortof). Set the box volume to a very large number.

If your situation allows for it, try putting them close to you (with added delay).

Ormy

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Re: Open Baffle Subwoofer Advice Requested
« Reply #3 on: 7 Nov 2019, 12:13 pm »
The W frames they are in are fine.  If you wanted to put in some extra effort, you could build some H frames and line the H frames with NoRez.  I'm a fan of no-void baltic birch for sub cabinets, that stuff is really quite rigid. 

OB subs will roll off a bit in the lowest octaves, but you also have to understand that you'll get room gain in those same frequencies.  So my best advice is to build it and amp it straight, no EQ at all.  Take some measurements and then add EQ based on what your measurements say.

The current cabinets are 1" thick MDF, all panels are screwed AND glued together and they're very solid and heavy.  Thanks for the advice regarding H frames but I think if I were to go to the trouble of building new cabinets (I don't have space to build, no garden or garage, would have to borrow a friends garage or something) I would almost certainly build sealed.  One of the many reasons I'm inclined to stay with open baffles is simple laziness.

I can't perform measurements yet, buying a calibrated mic soon.  Someone in another forum pointed me to an equation for dipole vs mono-pole output from the work of Mr Linkwitz; f = 0.17*v/D, v being speed of sound and D being path length from front to rear of woofer, f is the frequency where dipole and monopole have equal output with 6dB/octave loss of output below that.  Using estimated values I get a frequency of around 60Hz.  So I'm down 12dB at 15Hz vs sealed.  I've applied EQ boosts to these low frequencies to counteract this estimated roll off and it sounds great. 

Of course I will take proper measurements so I can apply EQ more accurately once I get hold of a calibrated measurement mic.


Looks like a great find!! Vas is missing from your list of specifications, but I'd suggest you put the parameters into a box modeling program (eg Unibox), that will tell you how much power you need to get them to full excursion and should tell you whether they are suitable for downfiring (which those are, sortof). Set the box volume to a very large number.

If your situation allows for it, try putting them close to you (with added delay).

Vas is 490 Litres.  Winisd is the modelling software of choice on my regular forum, not heard of unibox, would it be better for this application?  The problem I was having is winisd cannot model open baffles, I hadn't thought of just setting it to sealed with a huge volume, thanks!  I will have a play around with both softwares this weekend.

My room is quite small so I'm already pretty close, its impossible to be more than 2 meters from a subwoofer  8) .  I have one cab in the centre of the front wall, and the other in one of the rear corners, my main listening position is approx 1m from front cab and 2.5m from rear cab.  Is that close enough? Or are you just making a generalisation and saying 'closer is better'? Either way thanks very much for the advice! 

mcgsxr

Re: Open Baffle Subwoofer Advice Requested
« Reply #4 on: 7 Nov 2019, 03:20 pm »
In my experience the combination of QTS, FS and XMAX on those looks fantastic for OB use.

If you like the sound, I'd be leaving well enough alone.

You have TONS of swept area there with 4x18.  Should be a great experience!

bladesmith

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Re: Open Baffle Subwoofer Advice Requested
« Reply #5 on: 7 Nov 2019, 08:34 pm »
 :popcorn:.....

JohnR

Re: Open Baffle Subwoofer Advice Requested
« Reply #6 on: 8 Nov 2019, 12:15 pm »
Vas is 490 Litres.  Winisd is the modelling software of choice on my regular forum, not heard of unibox, would it be better for this application?

I don't use WinISD but I expect it would be fine.

Considering the box sizes involved, I'm thinking the builder of these did the right thing ;)

Quote
Or are you just making a generalisation and saying 'closer is better'?

No, I'm saying you might want to try putting them close to you. I'm not quite following your explanation of the geometry but if you can get the other one to a meter away (say on either side of you) you might find that "interesting"...  :D

AJinFLA

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Re: Open Baffle Subwoofer Advice Requested
« Reply #7 on: 8 Nov 2019, 07:02 pm »
1.) Are these drivers appropriate for open baffle usage?

2.) How can I get the most out of them? 

3.) The drivers are rated for 600Wrms, is that enough for good output in the lowest octaves?

4.) Anything else I should be aware of or careful of whilst using them?
Yes.
As is.
Yes.
Yes,don't piss off the neighbors.

Regarding placement, is it possible to place them each against both side walls, 1m out from front wall?

Ormy

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Re: Open Baffle Subwoofer Advice Requested
« Reply #8 on: 13 Nov 2019, 09:49 am »
In my experience the combination of QTS, FS and XMAX on those looks fantastic for OB use.

If you like the sound, I'd be leaving well enough alone.

You have TONS of swept area there with 4x18.  Should be a great experience!

This comment put a huge smile on my face.  Much appreciated!


I don't use WinISD but I expect it would be fine.

Considering the box sizes involved, I'm thinking the builder of these did the right thing ;)

No, I'm saying you might want to try putting them close to you. I'm not quite following your explanation of the geometry but if you can get the other one to a meter away (say on either side of you) you might find that "interesting"...  :D

I modelled in WinISD, at the lowest frequencies (30Hz and below) I'm heavily limited by the excursion of the drivers, but I also get a significant amount of room gain in those frequencies which these programs do not model, so I've learned some things but it wasn't as enlightening as I had hoped.

I'm very restricted for placement, but I will be moving house in the summer and sub placement will take priority when I'm mentally laying out the new room.


Yes.
As is.
Yes.
Yes,don't piss off the neighbors.

Regarding placement, is it possible to place them each against both side walls, 1m out from front wall?

Thanks for concise answers!  Regarding placement, see my reply to JohnR above.

Dmason

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Re: Open Baffle Subwoofer Advice Requested
« Reply #9 on: 13 Nov 2019, 07:40 pm »
Technically, those appear to be textbook perfect OB bass machines.   Set everything up, play 'Black Dog' loudly; if it is pleasing, then all is well.