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Offline Simon Briggs  
#21 Posted : 03 November 2013 14:38:02(UTC)
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My project is simple, no active EQ or compensation, just a large sealed box system with a lowish overall system 'Q' approx 0.5 - 0.6 about 200 litres, a fairly rigid brief though.

I have built several of these before but not above 8" based and around 50 - 70 litres.

I have now broadened this project brief to consider other drivers and have found two 13" units from SB acoustics which look ideal for this project, one providing an ideal system Q ~ 0.5 in a box of 150 litres.

This 13" model will provide near 20Hz extension in room -3dbs (-6dbs @ 30Hz raw response) with some rear wall boundary assistance, I could EQ to get deeper but from plenty of experiments I have made from my teenage years to about 5 years ago I have never been truly happy with any equalised alignments I have tried, and I have tried about a dozen.

The 15" SB acoustics driver is the best I have found thus far but one of the other models from SB acoustics and provides very close to 20 Hz -3dbs with higher output but in 230 litres.

It appears that excepting the audiotech drivers which can be customised at a price but alas are priced outside of this brief; that there are few suitable 15" drivers with the raw parameters that match my design brief around.

This thread was just asking simply has anyone had experience or knows of a suitable 15" driver suitable for a box around 200 litres and so mounted in such an enclosure with a resultant system Q approx 0.5 - 0.6

Edited by user 03 November 2013 15:06:54(UTC)  | Reason: Not specified

Offline ashleym  
#22 Posted : 03 November 2013 20:55:43(UTC)
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Thanks for that. Nice to have some flesh put around the idea.

An obvious one I forgot (mainly because they appear to go in and out of distribution to the general public)- ATC

ATC 15"

Did you ever think about isobaric loading? Here you could use a 12" pair per side and gain with the root2 lowering of Fs. Or with some less expensive two pairs a side and roll them off early a la TRK? The extra bracing for the double drivers will help with the large cabinet.
Offline Simon Briggs  
#23 Posted : 03 November 2013 21:06:37(UTC)
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Yes the DBL used an ATC unit IIRC they are good but as you say not easy to get hold of.

Considered Isobaric loading as I have 4 Focal 13V7511 drivers not used so that is a possibility.
Offline Simon Briggs  
#24 Posted : 03 November 2013 21:12:08(UTC)
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Focal 13V7511 Sealed Isobaric Q=0.5

VB = 90 litres

FB = 45 Hz

QTc = 0.5

F3 = 70 Hz!!

F10 = 30 Hz

F15 = 20 Hz

Though I recon the software did not reduce the effective Fs ~ Root 2

so by modifying the TL parameters in the software

We have

VB = 90 litres (rear chamber)

F3 = 50 Hz

F6 = 32 Hz

Probable in room response with boundary loading around 22 Hz or so

Edited by user 03 November 2013 21:26:15(UTC)  | Reason: Not specified

Offline kengale  
#25 Posted : 04 November 2013 11:26:26(UTC)
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Originally Posted by: darkmatter Go to Quoted Post
Focal 13V7511 Sealed Isobaric Q=0.5

VB = 90 litres

FB = 45 Hz

QTc = 0.5

F3 = 70 Hz!!

F10 = 30 Hz

F15 = 20 Hz

Though I recon the software did not reduce the effective Fs ~ Root 2

so by modifying the TL parameters in the software

We have

VB = 90 litres (rear chamber)

F3 = 50 Hz

F6 = 32 Hz

Probable in room response with boundary loading around 22 Hz or so


Fs only goes down by rt2 as the suspension stiffness becomes completely negligible compared with the cabinet stiffness. You'll get somewhere in between nothing at all (free air or infinite cabinet) and rt2 (infinitely compliant suspension).

Offline Simon Briggs  
#26 Posted : 04 November 2013 17:47:43(UTC)
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Originally Posted by: kengale Go to Quoted Post
Originally Posted by: darkmatter Go to Quoted Post
Focal 13V7511 Sealed Isobaric Q=0.5

VB = 90 litres

FB = 45 Hz

QTc = 0.5

F3 = 70 Hz!!

F10 = 30 Hz

F15 = 20 Hz

Though I recon the software did not reduce the effective Fs ~ Root 2

so by modifying the TL parameters in the software

We have

VB = 90 litres (rear chamber)

F3 = 50 Hz

F6 = 32 Hz

Probable in room response with boundary loading around 22 Hz or so


Fs only goes down by rt2 as the suspension stiffness becomes completely negligible compared with the cabinet stiffness. You'll get somewhere in between nothing at all (free air or infinite cabinet) and rt2 (infinitely compliant suspension).



Yep know that, I proved this to myself when I was 13!! Interestingly the above is what some LS software put out Mellow , I did my 'Isobaric' modelling with a simple HP 34C calculator whilst still at high school.

Edited by user 02 December 2013 23:09:57(UTC)  | Reason: Not specified

Offline Simon Briggs  
#27 Posted : 02 December 2013 23:13:34(UTC)
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2 x 10" Seas L26RFX/P units can provide 20Hz in room in around 200 litres, this is a large enclosure but would likely time quite well.
Offline Simon Briggs  
#28 Posted : 02 December 2013 23:48:11(UTC)
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From another thread

Originally Posted by: Martin Colloms Go to Quoted Post
DM will have to work hard to define the design and try to exclude the noise from all our suggestions.

Thiel and KEF have been working towards coincident, time aligned driver systems with proprietary drivers. The Quad gets there as of right.

Avalon is more time coherent than most with low diffraction narrow enclosure forms , tilted back to align the bass mid and treble start positions relative to the listener.

The resulting system CSD is particularly good, thanks to careful control of the effective driver working ranges. With these designs it is the attention to such detail which impresses.


My instinct for an enthusiast is a sealed box three way with a form narrowing with height, a true 8ohm impedance, , ie two of the '5ohm' bass drivers in series probably 220mm SEAS , .

probably the 160 mm Scan pulp cone wide range mid and a DXT soft dome tweeter.

We could try and firm up device type numbers from this broad suggestion.

Martin C


Interesting looking back at older posts

My idea of using two Seas bass may not be so crazy after all!! I have some Scan mids and the tweeters purchased for another project some time ago!!
Offline Simon Briggs  
#29 Posted : 21 December 2013 18:31:55(UTC)
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Originally Posted by: darkmatter Go to Quoted Post
2 x 10" Seas L26RFX/P units can provide 20Hz in room in around 200 litres, this is a large enclosure but would likely time quite well.


Originally Posted by: darkmatter Go to Quoted Post
From another thread

Originally Posted by: Martin Colloms Go to Quoted Post
DM will have to work hard to define the design and try to exclude the noise from all our suggestions.

Thiel and KEF have been working towards coincident, time aligned driver systems with proprietary drivers. The Quad gets there as of right.

Avalon is more time coherent than most with low diffraction narrow enclosure forms , tilted back to align the bass mid and treble start positions relative to the listener.

The resulting system CSD is particularly good, thanks to careful control of the effective driver working ranges. With these designs it is the attention to such detail which impresses.


My instinct for an enthusiast is a sealed box three way with a form narrowing with height, a true 8ohm impedance, , ie two of the '5ohm' bass drivers in series probably 220mm SEAS , .

probably the 160 mm Scan pulp cone wide range mid and a DXT soft dome tweeter.

We could try and firm up device type numbers from this broad suggestion.

Martin C


Interesting looking back at older posts

My idea of using two Seas bass may not be so crazy after all!! I have some Scan mids and the tweeters purchased for another project some time ago!!



With a load tolerant amp and suitable backup I have decided on three of the Seas 10" drivers some vol stuffing in a 250 litre sealed enclosure for a serious project for 14.

I have revelator mids and a few tweeters to play with as well; Birch or HDF is the next question?

Perhaps I'll write up the iterative process I have gone through in arriving at where I am and the design process as it is progressed next year


Offline ashleym  
#30 Posted : 21 December 2013 19:47:37(UTC)
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One large box or separate enclosures for each driver? Open baffle for the mid and highs? If by chance you haven't tried an open baffle it is worth a go. If you cross over high enough you won't miss the lack of box.

If the 10"s don't give you enough bass and you cabinet needs some strength you could always add some internal baffles in the shape of once transmission line..........then the wood type will matter less.
Offline Simon Briggs  
#31 Posted : 21 December 2013 19:54:13(UTC)
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Originally Posted by: ashleym Go to Quoted Post
One large box or separate enclosures for each driver? Open baffle for the mid and highs? If by chance you haven't tried an open baffle it is worth a go. If you cross over high enough you won't miss the lack of box.

If the 10"s don't give you enough bass and you cabinet needs some strength you could always add some internal baffles in the shape of once transmission line..........then the wood type will matter less.


One large low 'Q' sealed enclosure is envisaged the drivers that will likely be used for my project are totally unsuitable for OB use.

Great drivers for OB use include a model from Eminence
Offline Martin Colloms  
#32 Posted : 22 December 2013 14:05:52(UTC)
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Another thought 120litres

4xSeas 10inch side firing in opposition , each pair in separately sealed sections for enclosure rigidity, and if possible force canclelled coupled internally.

You need some mass loading on the diaphragm to bring down the overall sensitivity and to lower the in-cabinet resonance

Also like the sound of an elevated 6inch mid location, in the Focal Scala it solved the floor bounce reflection very well.

Give the tweeter enough baffle area for a smooth response and also a gentle horizontal radius to the baffle, it works wonders for lateral edge diffraction.


MartinC
Offline ashleym  
#33 Posted : 22 December 2013 15:32:55(UTC)
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Originally Posted by: darkmatter Go to Quoted Post


One large low 'Q' sealed enclosure is envisaged the drivers that will likely be used for my project are totally unsuitable for OB use.

Great drivers for OB use include a model from Eminence



I was only thinking of the mid and top to be OB for this project
Offline Simon Briggs  
#34 Posted : 22 December 2013 19:32:02(UTC)
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Originally Posted by: ashleym Go to Quoted Post
Originally Posted by: darkmatter Go to Quoted Post


One large low 'Q' sealed enclosure is envisaged the drivers that will likely be used for my project are totally unsuitable for OB use.

Great drivers for OB use include a model from Eminence



I was only thinking of the mid and top to be OB for this project


Gotcha!

Quite possible that I could consider this Smile
Offline Simon Briggs  
#35 Posted : 22 December 2013 19:39:11(UTC)
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Originally Posted by: Martin Colloms Go to Quoted Post
Another thought 120litres

4xSeas 10inch side firing in opposition , each pair in separately sealed sections for enclosure rigidity, and if possible force canclelled coupled internally.

You need some mass loading on the diaphragm to bring down the overall sensitivity and to lower the in-cabinet resonance

Also like the sound of an elevated 6inch mid location, in the Focal Scala it solved the floor bounce reflection very well.

Give the tweeter enough baffle area for a smooth response and also a gentle horizontal radius to the baffle, it works wonders for lateral edge diffraction.


MartinC



Like it was an idea I was going to try on a future project but could easily adapt this one to suit series parallel means I can retain an 'easy' load; the Seas units are amenable to this meaning I could create a really solid enclosure with this arrangement together with some fancy coupling and system/cabinet wall tunability as well.

Could play with theoretical modelling to see how varying mass load will affect other parameters before I commit to actual mass loading requirements.

14 could be a fun year BigGrin
Offline mat  
#36 Posted : 25 December 2013 14:16:40(UTC)
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For three woofers i would split the cab into three parts. I'm pretty sure i've done this test and found the q to be high when sharing a single volume, all the units see each other as well as the box. You could check this out if you have modeling software.

As for the enclosure, ply supposidly sounds better, should be thick and braced for the lf and damped for the mf. Steel plates are an effective way to increase mass and stffness without making the box too big.

mat.
Offline ashleym  
#37 Posted : 26 December 2013 12:49:37(UTC)
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I remembered this from somewhere. Look how the idea develops rather than specifics.

cyclop
Offline frank23  
#38 Posted : 26 December 2013 13:27:37(UTC)
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I have found this at an acoustic shop a few weeks ago. It has amazing damping properties, but is about 4 times as expensive as MDF. At that shop it is called Merfoplex. I am thinking of building some cabinets using this:

UserPostedImage
Offline ashleym  
#39 Posted : 26 December 2013 17:41:13(UTC)
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That looks similar to the construction method recommended by Ken and others. Two layers of ply with a lossy layer. But having it prebuilt will make everything about 100 times easier.

Do you know what thickness each layer is?
Offline kengale  
#40 Posted : 26 December 2013 18:32:21(UTC)
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Originally Posted by: ashleym Go to Quoted Post
That looks similar to the construction method recommended by Ken and others. Two layers of ply with a lossy layer. But having it prebuilt will make everything about 100 times easier.

Do you know what thickness each layer is?


Surprised to see a symetrical construction. For constrained-layer damping you usually get best results using a notably assymetric structure with a very thin visco-elastic layer, so that flexing of the sheet causes maximum shear stresses in the damping layer. From their ads they seem to be advocating use in soundproofing, relying heavily on the bulk mass for the majority of the proofing, rather than construction of mechanical assemblies. Not easy to use when building speakers either: if you use fillets on the inside of the cabinet then it's hard to get a nice join on the outside of the cabinet. For our speakers, and other (DIY) projects I've seen published, the cabinets were built using conventional methods and thin layers of ply or hardboard internally bonded with visco-elastic glue afterwards.

By the way, anybody know why posts have suddenly become two screens wide? Makes them very hard to read and edit.


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