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Sub design using Monacor/Dayton Audio kit

Rustyrocker

Well-Known Member
Hi, this is only my 2nd post here. In the 1st I made the decision to add a sub to my existing system.
I already had a Monacor Sam-2 amp and decided to go with Dayton Audios RSS315 HF-4 driver for the bass driver.

I'm a pretty good cabinet maker but tend to work trial and error with an eye on manf recommendations when it comes to sizing speakers.
The plan is a tall unit of around 36 x 36 x 82cms, giving a sealed box volume of around 84 litres. I read from the specs that this would be the target.

I'd welcome any advice on the proposal, it is an odd size for a sub but the room dictates I keep it fairly slim rather than cubic.
Given it's a sealed box, unless you guys advise differently, would the driver be best placed near the top or the bottom. Just realised I could actually turn it over if I kept the design simple and put the amp on centre the idea is to slant of the top at 45* from middle to back to improve looks.

Do's or don't does equally welcome, cheers in advance.
 
Where has the 84 litres volume come from? The product description here states 20 litres (0.71 ft^3) as the optimum sealed cabinet size.

My preference for large subs in a room is for them to look and function like tables.
 
And just to confuse things a bit more. It says 1.7ft3 (48ltr) on the partsexpress website :)

I think the best bet would be to model It In software.
 
No reason you can't make it 84 litres. It will be 5dB down at 34 Hz which is very gentle for a sealed box, and would be fairly flat in a UK domestic room. Just alter the amp low pass filter until it blends with the main speakers. Blending subs is known to be very tricky, but that would apply whatever box you used.
 
The Vas is 84 litres and I guess the OP has perhaps misunderstood what this means. The driver parameters look nicely chosen for a sealed box of around 35 litres with a reasonable level of stuffing. If the OP is keen to keep his original box size then a vented box volume would be around 75 litres which when you add volume for bracing, displacement by the driver, the vents, the amplifier,... will get close to 84 litres.
 
Where has the 84 litres volume come from? The product description here states 20 litres (0.71 ft^3) as the optimum sealed cabinet size.

My preference for large subs in a room is for them to look and function like tables.
20 litres just means a box size with a Q of sqrt0.5 which gives a flat upper bass. This is for a main speaker/irrelevant for a sub. Note it also says next to 20 litres that it is -3dB at 70 Hz [and therefore falling at 6-12dB octave].
 
Sorry for the delay. I'll try to answer each contribution in turn.
#2 Yes, that's probably the case, as said my understanding is limited. My previous sub was about 420 cubed with a 10" Volt driver, it never felt fully integrated and I listened without most of the time Design was simply following a given design.
Another option I had was to use an extremely heavy solid Oak coffee table I have add boxing to the underside and have the sub firing downwards but adjusting the amp and cables to the otherside of the room seem to rule it out, according to "er indoors"

#3 I found confusing advice, found post from someone who had gone for 60 ltrs and said it successful. Have no idea what was is or why it matters.

#4 Are you saying it will go deeper in a 20 ltr box than one of 80? . I have no means other than the 2 meters, one each side of my head to tell what I'm getting now, but having had deeper speakers in the past I think I just want to boost sub 40hz-50hz

#5 Probably, but i have no idea what was is or why it matters. Size is now totally flexible, just would sooned not create a square box, but given a 12" driver it may be tricky.

#6 As above really. (in other words I don't have much of an idea how to determine size.

These are the main speakers in use at present and shows why replacing with ATC like floor standers is awkward. Size is 560h x 310w x 560h and sit on very substantial 700 high stands, made when I was in engineering. Not entirely clear in the pics but the stands are 3 x 110mm 5mm wall thickness S/S tube with 10mm alloy plates top and bottom. Hopefully this shows the mechanical aspect isn't an issue to me, but theoretical acoustics? fraid not.

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Given your answers and my total misunderstanding of how to get the best from the units mentioned. Given only volumes are quoted actual shape seems less important, being just largely aesthetic?
In a nutshell just what volume cabinet would bet that speaker performing well in the area I mention?, and vented or sealed.

Just to add the best lowest of bass performance I've ever owned were the 1st set of speakers I built using the old Kef kit 3, hence I got B139's when I thought about this project a few years ago, they did however have the advantage of being mounted into a solid stone fireplace with probably a 4 cubic ft capacity each.

Sorry for all the naivety, but when I don't know I ask.:)
 
The shape of the volume for a subwoofer is largely unimportant in terms of loading the driver but it can be relevant for strength, configuration of the parts, how it fits into the room,...

The sealed volume given on the Dayton Audio website looks to be a mistake. Possibly typed 0.71 instead of 1.7 into their computer. The values on the Parts Express site look sensible (Dayton Audio is the house brand of Parts Express). Typing the driver parameters into one of the free box simulation programs I get roughly 35 litres for sealed and 75 litres vented. The output from the vent enables the response to extend about 20 Hz deeper in free space. The response in a room will be different and if you don't equalise the response the sealed is likely to be preferable whereas if you do the vented is likely to be preferable.

The optimum cabinet size changes with how one weights low frequency extension, SPL, distortion, cabinet volume and one or two other factors. The volumes recommended by Parts Express are larger than my particular simulation program is suggesting (Parts Express use a different one). In moderation this can extend the response a bit lower but often people favour smaller cabinets more. The driver parameters look to have been chosen to optimise a sealed sub more than a vented sub but it should work well with both.
 
If we assume you are building a closed box sub not a ported one, then the size really is not critical. The size of a main closed box speaker determines how flat the bass is before it starts rolling off. Flat is fashionable, so software suggests an optimum size for full range speakers. You are using your box for low bass only. Presumably the main box covers all of the main bass. If the box is small at 20 litres it will be 12dB down at 35 Hz. An 84 litre box is 7dB louder at 35Hz for the same amp output. You will turn the controls up a bit more to get your bass, and it will take about 4 times the voltage from your amp and a lot more power to play at 35Hz [hard to say how much because the impedance curve moves with the box size]. A larger box like 84 litres will require a lot less amp drive to play at 35 Hz. The max limit might be amp power, amp volts, driver cone travel or driver electrical power handling. A closed box needs filling with a few pillows to sound tighter. A small box may be easier to fit in different room locations if you are struggling to get the sound to blend.
 
The shape of the volume for a subwoofer is largely unimportant in terms of loading the driver but it can be relevant for strength, configuration of the parts, how it fits into the room,...

The sealed volume given on the Dayton Audio website looks to be a mistake. Possibly typed 0.71 instead of 1.7 into their computer. The values on the Parts Express site look sensible (Dayton Audio is the house brand of Parts Express). Typing the driver parameters into one of the free box simulation programs I get roughly 35 litres for sealed and 75 litres vented. The output from the vent enables the response to extend about 20 Hz deeper in free space. The response in a room will be different and if you don't equalise the response the sealed is likely to be preferable whereas if you do the vented is likely to be preferable.

The optimum cabinet size changes with how one weights low frequency extension, SPL, distortion, cabinet volume and one or two other factors. The volumes recommended by Parts Express are larger than my particular simulation program is suggesting (Parts Express use a different one). In moderation this can extend the response a bit lower but often people favour smaller cabinets more. The driver parameters look to have been chosen to optimise a sealed sub more than a vented sub but it should work well with both.

Ignorance strikes again, o_O, are you talking a simple adjustment on the amp or.........?
 
Ignorance strikes again, o_O, are you talking a simple adjustment on the amp or.........?
No. I am talking equalization to knock down the large booms due to the lowest room modes and to compensate for boundary reinforcement and room gain. It cannot address everything (e.g. the dips in response) but it can bring large improvements if wisely applied.
 
Sotty hg, but it's over my head.


If we assume you are building a closed box sub not a ported one, then the size really is not critical. The size of a main closed box speaker determines how flat the bass is before it starts rolling off. Flat is fashionable, so software suggests an optimum size for full range speakers. You are using your box for low bass only. Presumably the main box covers all of the main bass. If the box is small at 20 litres it will be 12dB down at 35 Hz. An 84 litre box is 7dB louder at 35Hz for the same amp output. You will turn the controls up a bit more to get your bass, and it will take about 4 times the voltage from your amp and a lot more power to play at 35Hz [hard to say how much because the impedance curve moves with the box size]. A larger box like 84 litres will require a lot less amp drive to play at 35 Hz. The max limit might be amp power, amp volts, driver cone travel or driver electrical power handling. A closed box needs filling with a few pillows to sound tighter. A small box may be easier to fit in different room locations if you are struggling to get the sound to blend.

Which is why I was going as big as practical. Main speakers are amazingly tight and detailed in both bass and upper bass. Top end is tunable to my ears given no tone controls on Naim kit and am more than happy as tried 3 different tweeter arrangements before settling on on present units. Just the lower 1/2 octave I'm trying to address.

Given I really don't understand all the theories here in spite of you guys trying to help, the obvious thing to do is simply build as big a sealed box as I can justify, then if not happy install small to large ports until it sounds right.

Confused as ever, but about 2 to 2.5 cubic ft seems a reasonable compromise taking in all the info here and what I've read others have tried, but it's still an utter finger in the air guess on my part.

Just another thought, given the bass driver of the main speakers, Volt BM2500-4 http://www.voltloudspeakers.co.uk/loudspeakers/bm25004-10/ is it possible the WA crossovers are limiting/rolling off of the lower end??. I will get in touch as I can't find the crossover drawing they supplied me with, (and couldn't understand it if I had it)

Thanks again.
 
Hello Rusty,
if I were you I would read a little about subwoofers and how they integrate with other speakers by going to:
http://www.troelsgravesen.dk/26W-4558T00.htm
Have you actually bought the Dayton 315 driver? or, are you still in the pondering phase?
One of the problems you most probably will have, irrespective of the cabinet size, is what are the main "drone" frequencies in your room. My listening room has the first drone frequency at 37- 40Hz and in spite of using very very speakers, similar to LS3/5As, the 40Hz drone is always apparent.
Have a quick look at amroc
//amcoustics.com/tools/amroc?l=575&w=430&h=245&r60=0.6
and type the numbers of your room in and see where the "drone" frequencies will be.
(if you can hold of a test CD, or somewhere in the internet, that allows you to play low frequencies in steps of 3Hz from about 16Hz to 70Hz give this a try and find out where you room booms, it should confirm the amroc results)
What you need to do after building the sub-woofer is to use a modern mini-dsp, I don't think your Monacor SAM2 can do this, to "draw" using the software the frequency response you think you want. You would lower the gain at the first 3 "drone" frequenicies by about 4dB while lifting the other frequencies to get more bass.
If you just use the Monacor you will always have "drones" due to the size and shape of your room.
You should also think a little about room gain, Troels Gravensens website also has various examples of his homemade "room gain" spreadsheet, for example
http://www.troelsgravesen.dk/8008-CORNER.htm
You should now see that it is quite easy to have too much bass at some frequencies.
If you decide to make a reflex port subwoofer, or passive membrane version, you will get more bass but make sure you don't choose the reflex port tuning frequency to one of the room "drone" frequencies. (you may also find your main speaker with benefit from changing the length of your relex port with a bit the waste pipe from B&Q)
I suggest playing about with unibox softeware
http://audio.claub.net/software/kougaard/ubmodel.html
a spreadsheet which allow you to "play" and understand the how quickly you run out of driver travel in a closed box subwoofer at very low frequencies and how if you use a reflex port or passive radiator tuned to the driver frequency (in the case of the Dayton 315, 24Hz) you can extend the low frequency range and have less problems with driver travel.
I recently bought a second hand subwoofer with the Seas Roy driver and a vented port, it is amazing how much air goes through the port at 25Hz, I now understand the term "port chuffing" much better. I am still having problems getting the subwoofer integrated, so you are not alone!

I hope I haven't bored you too much!
 
Not boring at all will check out those links shortly.
I do have a good stepped audio test cd, it's difficult to follow exactly as has no Number system or audible signal on the cd just a printed test list, very easy to lose position but still usable. My listening room has french doors into the dining room between the speakers and directly opposite the bay window where I sit. I listen with those doors open as preferable and checked with the disc which did show a boost at one frequency, don't recall which as was just confirming what I was hearing.

yPort chuffing I'm familiar with, though not sure why it occurs. Mt suck it and see method when I was working and had access to lathes was to make my own port from solid nylon bored out in stages until it sounded best, if I went too far I simply chopped down the length or started over again, so exactly as you say, just not supported by any theories.

Finally yes, I have bought in the Dayton driver, is actually being delivered today. Since I posted this I have found links to quite a few designs that use it, I don't think I've exhausted these yet so will try to find common ground in as many as poss after checking out your previous info.

PS scuppered in most software charts I've tried as I don't have Excell plus some don't seem to like windows 10.
 
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if you haven't got Excel then try:
http://sbp.softica.dk/2.0/en/?id=
Look at how your current speaker works, you can add the data of your Volt driver into the boxes (choose custom), measure the length and diameter of your port, calculate the box volume (take away about 2 or 3 litres for the ports and stiffeners), you then "play" with the tuning frequency (choose custom) of the vented box calculator until the approximate length of your actual port is shown after the calculation.
I expect you will get about 40Hz to 45Hz as the speaker tuning frequency (-3dB).
(most speakers are not tuned to much lower than 40Hz as the lowest note you can play on a bass guitar is about 40Hz)
You can then look at the frequency response at the top of the screen and you will see (perhaps) that your speaker probably has "fast" smooth bass but is about 3db "light" between 40Hz and 150Hz. (I had a quick "play" with the Volt driver in the softica programme)
You cannot change this with the speaker crossover as your have a 2 way speaker which will probably cross over at about 2000Hz and even if you have a first order filter (don't think too much about this) the crossover stops changing the frequency response at about 250Hz.
Hopefully you can now understand your existing speaker better.

Adding a subwoofer can help a (little) bit to reduce the upper bass lightness from 60 -150Hz but as your know is mainly there is give you bass slam and level below 40Hz.
You can now add the Dayton driver numbers into the link above and you will find somewhere between 35l and 50l cabinet volume (make the cabinet really stiff) will get you good results, 50l if you want to try a port out, 35l if you want "faster" bass.
After you have built the subwoofer and are trying to intergrate it with your existing speakers try the old "sock" trick. If you put a sock (as we are talking high end hifi the sock must be pure wool, no synthetic fibres here please, ha ha) loosely in the port of your existing speaker you can reduce the output from the port at 40Hz. This will allow you to adjust the subwoofer low pass cut off frequency slightly higher to fill in the upper bass.
You can take the "sock" idea to extremes by closing the port of your existing speaker (probably not a good idea) and then you get the sealed box response in the softica software above. This would allow you to set the subwoofer cut off even higher.

I hope I have given you food for thought, as I said in an earlier post, integrating subwoofers is very difficult.
 
That's very helpful, I have made a decision, or rather my good lady has. I'm going to create a sub within part of the old stone fireplace we have. Somewhere around 2-2.5 cu ft but not measured yet. Picture as is below, intention being to take out the central stone section, frame up, reinforce floor within then fit a ported arrangement in a front 25mm mdf board. Top is already 35mm solid oak. Won't attempt to create a sealed enclosure due to a very irregular interior. Amp will be sited in it's own frome adjacent to the other gear and speaker cable run through the existing fireplace.
I mentioned in an earlier post that the bass detail from the existing Volts is superb, just sub about 40-50 hertz needs a little help. Mike Oldfields Tubular Bells from the vinyl box set has incredible depth, I'm just missing the absolute bottom so cut off is likely to be quite low on the sub amp. Thanks for a more simpleton friendly reply, I think a few brain cells have disappeared with the passing of time and this old dog doesn't find learning new tricks easy.

Excuse the clutter in the pic, I need to do some rearranging

 
Hi, finally finished this little project, been held up waiting for the truck bed paint for the sub grill surround which got stuck in the post.

Just a few pics and a short explanation of my experience;

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I was wrong about the sub amp, it was a Monacor Sam1 not 2, hidden away for years so forgot. Because of the nature of the sub enclosure the amp is remotely mounted a a solid 20 oak "open back box" alongside the rest of the electronics
The speaker front baffle is 18mm + 15mm laminated MDF, 15mm of which is set back into the void itself. Had to do that for both rigidity and to allow a sandwich to be made of the speaker grill/front to step it out to clear the rubber surround of the Dayton unit which even though it's fully recessed still stands well proud of the front baffle.
Just added a pic of the Stax headphone stand I made a few years back for anyone interested. I didn't like the aftermarket stands offered for Stax so, probably as can be seen, I have a love of all things oak and made this from 100mm solid oak with a 50mm solid base.

So, it cost around £160 to import the driver from the states, the amp was sat around, so was most of the finishes and veneer used plus cable and some fixings. Had to buy the oak for the amp, glue and a sheet of 18mm mdf. Total cost under £210 spent. Was it worth it? Absolutely, I would have spent over a grand to achieve what I now hear, (more actually) It does sound exactly as I had hoped and just adds that extra depth. I have the crossover set at only 65/70hz and for the first time I have a sub that actually seems to fit in seamlessly with the main Volt/Scanspeak speakers, I'm well chuffed, and it hasn't ruined domestic harmony which anything more obtrusive may have :)

There is a plan for the future, the amp is underpowered and runs very warm and I did notice when I was setting things up that there is some clipping if I set the crossover to high and ramp the volume past about 75%, but for know it works perfectly as set, I have actually notched down the volume levels form the main speakers and reduced the attenuation to the tweeters for to lift the top a little for perfect balance.

Thanks for the help and advice.
 
Goes back to an early venture into hifi 1975ish, Kefkit 3's built into fireplace alcoves. A very old terraced house, neighbour used to come round and ask me to play his favourites as it sounded as good in his house as mine, :D;)
 


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