DIY Sub Advice please

[warnerwh]

Greetings: I've been directed to this forum as I understand there are world class sub builders here.

I just ordered the Dayton RS Hifi 15" woofer. I'm planning on using a sealed box 2' square. This will be heavily braced as well as using some granite I have inside. Then I will fill it with fiberglass.

It will be powered by a spare channel of a Cinenova 3 power amp I'm using in a biamp configuration.

This is the most important consideration: I want the fastest most accurate sound I can get from this driver. I learned of this driver from the people at the Partsexpress board. I'd been willing to spend more and had been apprehensive about buying a Dayton brand driver but have been assured this is an excellent driver.

I want a sealed box as I want the tightest bass possible. An excellent transient response is necessary due to the fact my main speakers are hybrids with planars for mids and a ribbon tweeter. They're VMPS RM 40's.

This sub will only be used for music so the lowest lows aren't necessary. I do want however excellence to 25hz and have been assured with this driver I can do it.

If you see any way to improve what I've got in mind I'd appreciate the advice as I've never done this.

Thank You

[---k---]

Sounds like you are off to a good start. You didn't say it, but I'm guessing that sense you've seen other's build, that you are planning on using double layer of 3/4" MDF for the walls.

Also, I wouldn't say "fill it with fibreglass" is quite right. Start with a little fibre lining the walls, listen, add some more, listen, continue this until it sounds right to you. SteveNN and I both ended up removing fibre from our first sealed projects, because we overdid it a little.

Just post pictures as you go. We'll try and be helpful as possible.

Oh and welcome to the guide. (I'm thinking you came here from Hometheatertalk???)

[ThomasW]

Hi and welcome... :T

RM40's are large speakers designed for high output and usually matched with larger rooms. So I question the choice of a single relatively modest Xmax driver as a 'match' for them

The 15" HF driver is indeed very good driver. However it's limited Xmax could prove problematic if one is wanting or needing higher output levels.

If you can provide a bit more data regarding the size of the room, distance to the listening position, expected output levels, etc, it would be easier to discuss design options.

[cjd]

I thought the plan was to use two of the 15" subs?

C

[warnerwh]

My original plan had been to use two of the subs but the box size would be too large. I also will be using a Vmps sub. This way I'll have a left and right sub.

The sub will only be augmenting the RM 40's. That's what I'm doing now and bass power and sound quality is outstanding by all counts.

My room is 12'2"x17'1"x7'2". This is near the ideal ratio but had just happened that way as I built the room as large as I could get away with down here.

My room is also treated with 3-4" acoustic wedge foam. This covers the entire wall behind the system and 5 feet out on the ceiling and sidewalls. There's a bass trap in each corner. First reflection points are treated in all four spots.

My goal has always been to recreate a live performance as nearly as possible with a home system. To power the low and mid/upper woofers I use a Cinenova Grande 3. The extra channel will be used to power the sub I build.

The midrange panels and ribbon tweeter are powered by a Van Alstine 550exr hybrid amp so I've got plenty of power to use. I believe in having way more power than you'll ever use so you can never clip unless the sound is so loud it's unbearable. I listen commonly at a level that produces mid to upper 90db peaks.

At my listening seat a measured 105db is very loud and I rarely listen at this level and if I do it's only for short periods. Hitting 100db though I may listen for a while so please remember to speak LOUDLY so I can hear you

I did come over here from HTT as a link had been posted for me of the pics of subs you guys have built. Actually I had been a member as I stumbled across this forum a while back but didn't realize what is here.

So in the end I believe one 15" sub must be plenty. I barely have the Vmps sub turned up. I do however plan to use the built in crossovers in the Cinenova which has both high and low pass filters. This way I can take the bass from 45hz and below away from my RM 40's and let the subs do that work.

Presently I'm crossing at 45hz and running the RM 40's full range. If I turn up the sub just a tad more it's way too much.

Thank for the advice regarding the fiberglass. I should have realized that myself as I've done tweaking before and too much fiberglass will muffle the bass.

I forgot to add that I've got a piece of 3/4" granite left over from a recent kitchen remodel of my rental that is about 2'x3'. I'll use it to help brace the cabinet. I'll also add cross braces. I hadn't plan on using two thicknesses of mdf on the sidewalls but that's probably a good idea. The front baffle I'd planned on using a triple layer though.

Is there a Lpad that's heavy duty enough to adjust volume to the sub?

I should mention also that I use a Behringer DEQ 2496 so bass problems are very controllable in my room but not perfect. Using Ethan's cd with bass tones in 1hz increments I'll use next time.

My parts won't get here until maybe next week sometime as I just ordered them last night. When I buy the mdf I will have Home Depot cut it up for me. I bring this up because please make sure I don't make any mistakes. If I do it's your guys' fault :E

Of course all of the advice you guys supply is greatly appreciated. I've wanted to do this for a very long time and now have the time to do so. Perfection in the bass region is my only goal although I do realize is like the pot of gold at the end of the rainbow.

[warnerwh]

My other post was pretty long so here's a change I made last night due to space restraints.

I'd like to build the sub 20" wide by 24" tall by 26" deep. This will obviously reduce my cabinet volume to maybe 7cu ft. What I'm curious about is what latitude do I have on cabinet size from say minimum to maximum? Also what changes does this make to the performance changing from smaller to larger etc.

Thanks

[ThomasW]

I'm heading out to run some errands, but here's a quick comment.

Save the granite for something else. No one can't use an L-pad on a sub.

What's your crossover for the sub? The subout from a prepro or receiver?

[warnerwh]

There's a low/high pass filter built into the cinenova amp so I'll use it. It's adjustable from 20hz to 5khz. My system is made up of separates. My music system is not part of my home theater but a dedicated 2 channel stereo for music only.

[ThomasW]

You need a way to set the relative output levels of the various speakers. This is usually done with the 'pots' on a outboard active crossover when one is using separates in a 2 channel system.

I looked at the Cinenova Grande 3 webpage and can find no info regarding the slopes of their filters. Do you know what they are?

[warnerwh]

In one of the test reports on one of their amps they printed graphs. I didn't analyze them but should. It seems like they were 4th order.

[ThomasW]

Unless you plan on somekind of a line-level outboard box placed before the power amp, there's no way to set the relative output levels of the mains and the sub.

[warnerwh]

I may use a passive preamp there.

I've got another couple of questions:

I've never used a router and don't own one. Is a fixed router sufficient to use with the Jasper Jig I'm getting or do I need a plunge router?

What kind of a bit do you use to cut a hole?

Thank You

[ThomasW]

Might consider an active crossover instead of a passive preamp.

It's possible to use a fixed base router, but it's more dangerous.

1/4" solid carbide upcut spiral twist bit.

[chasw98]

Just a thought. I own a Grande 3 and a Grande 5 with the High & Lo pass filters on them. They are not really an electronic crossover. If you have a signal generator and a frequency counter with a scope you might be able to adjust them properly, otherwise it is all by ear. A CX2310 crossover is relatively inexpensive, much more accurate, and will give you the level control needed to adjust the levels between hi & lo. You might also look into a unit from Marchand for the crossover. Just a thought.

Chuck

[warnerwh]

I figure I can adjust them by setting the crossovers on the amp all at the exact same spot and taking measurements with a mike which I'll have to do anyway. The crossover on the amp on my sub now had been done that way and it worked well. If you move the crossover up just a very small amount it can be heard.

It's possible that running my RM 40's full range may still be the best idea. Then I'd have 4 different low bass woofers firing in different directions. Don't know if that will work out better or not though.

[ThomasW]

Per Chuck's suggestion I recommend you consider using something like the Behringer CX2310. It's very reasonably priced (lower that a good passive pre-amp) and it's operation is virtually transparent.

One benefit to rolling off the mains is taking the workload off the woofers, doing that provides better sound quality.

[warnerwh]

I just finished checking this crossover out. Great idea and thank you again! I hadn't been aware something so inexpensive existed. I'm very pleased with the Behringer DEQ 2496 I use presently too.

Maybe I could use this crossover with my other sub also. Could I turn up the crossover and volume on the plate amp of my other sub all the way and just use the crossover and volume control on this crossover?

[ThomasW]

There's a missing = sign here. Why are you supplementing a VMPS sub with another sub, when you say you barely have the VMPS sub turned up?

Seems like the logical thing to do if you want more output, is to turn up the VMPS.....

[Brendan_L]

I can't beat Thomas' input, but about the Jasper Jig; I used it with a fixed router for several years. It works, but it's not as nice as a plunge router.
I also lost the center pin and use a nail with it's head cut off.

I found a plunge router for $20 at the Dewalt outlet and gave up on the fixed base router for the Jasper Jig. Now I use the fixed router for the roundover bit. Now I'd like a 1/2" collet router to get the really big roundovers.

Definitely get an upcut bit, I used the 1/4" straight bit for too long, and it burns the wood and bit.

[ThomasW]

but about the Jasper Jig; I used it with a fixed router for several years. It works, but it's not as nice as a plunge router.
I also lost the center pin and use a nail with it's head cut off.

Now I'd like a 1/2" collet router to get the really big roundovers.

Definitely get an upcut bit, I used the 1/4" straight bit for too long, and it burns the wood and bit.

I too have used a fixed base router with circle cutting jigs for a very long time. So yes it can certainly be done. But it's just SO much easier and safer when done with a plunge unit.

Using a 1/4" bit with a 1/2" collet adapter is nice when routing multiple layers of thicker material. The adapter allows one to extend the 1/4" bit further out increasing the cutting depth compared with using the 1/4" collet. Don't go overboard with this idea since there's less supporting the bit in the machine..

[warnerwh]

Thomas: This is my favorite hobby. At one point I had wanted to build a pair of world class speakers. That would have been my first attempt. Bad idea. Bought the Loudspeaker Cookbook and talked to the guys at partsexpress' forum. Very bad idea for a novice. A sub however is doable by a beginner like myself.

This is a project more for enjoyment than anything else. Will it improve my system? It may make things worse I don't know yet. Performance of my system is exemplary imo. I've not heard better including in the bass region. (room acoustics are huge!)

So in the end it may just end up as a box in my listening room. I will try however to do a good job. The whole cost is only a few hundred dollars which is very affordable to me considering the enjoyment and satisfaction I'll get out of this project.

At least in theory with all these subwoofers in my room bass distortion would be less. I know another guy with four Vmps Larger Subs in his room. These are huge subs with an active 15" and 12" as well as a passive 15". I can assure you that two of those should be enough for anybody in any normal size room in a house under any circumstances including using them for the bass drivers of an electric bass.

Apparently you can conclude my ability to reason objectively may be skewed at times. I'm well aware of it everytime something like this comes up and my wife just rolls her eyes, lol. Over the years I've said "well I'm done" referring to upgrading my stereo. You should see the look I get from my wife

Thanks for the info on routers too. Now I know I'll need a plunge router.

[ThomasW]

Yep Vance's book is a little 'daunting' for the complete n00b....

I'm familar with the VMPS subs, they're a rather 'unique' design, so there maybe issues 'integrating' them with the types of subs we tend to design.

Here's a Unibox sim for your driver, figuring a 21" internal dimension from a 24" OD cube.

The plot shows the anechoic output with 300 watts input. Where the red line crosses the dark blue line the driver runs out of Xmax. So as you can see it's difficult to get much output from a single one of these drivers.

If you want the 'tightest' bass, the box needs to be larger so we can get the Qtc down to 0.5

[warnerwh]

Appreciate your effort Thomas. How much larger does the box need to be? I can make it taller and deeper without a problem. I just want to make sure the width leaves room to move it forward and backward next to my left main speaker. It's exactly 20" from the edge of the acoustic foam to the rear corner of my speaker so there's not alot of room to make it any wider.

My driver and the Jasper Jig will be here by the end of next week. By that time I plan on having the box ready to build.

If this sub will actually hit 106db that should be plenty as it will be in or near the corner. I usually like to do overkill but I may be running it with the mains full range. It's entirely possible I'll like this sub better than my present sub and will end up still running only 1 sub.

If it's not enough I can always build a second and just stack them.

Another question entered my mind. Being as the front baffle will be fairly large does it matter where the driver is positioned? What I wonder is if putting it near an edge would make it less likely to cause vibration to the baffle. And what about if I put the driver closer to the floor? Thanks

[ThomasW]

It would take a 360L box to obtain a 'critically damped' Qtc 0.50 with that driver.

If you get something like the Behringer DEQQ2496, you can create a LT (Linkwitz-Transform circuit). Using that it's possible to electronically lower the Qtc of a driver in a small box.

Given the wavelengths involved, driver placement on the baffle isn't critical

[Paul H]

...
Apparently you can conclude my ability to reason objectively may be skewed at times. I'm well aware of it everytime something like this comes up and my wife just rolls her eyes, lol. ....

Just hang around here for a while and you may find a whole new world of extreme audio and upgraditis - my next sub will likely be an infinite baffle with 4-18" drivers or 8-15" drivers, and I used to be normal ...

[ThomasW]

The "Wretched Excess Motto"....

If some's good,
More's better,
And too much,
Is just enough...... :B

[warnerwh]

Just hang around here for a while and you may find a whole new world of extreme audio and upgraditis - my next sub will likely be an infinite baffle with 4-18" drivers or 8-15" drivers, and I used to be normal ...

Thanks I needed that :T By the way that's ridiculous!

Already if I turn up my sub much I can feel my eardrums being pushed rather hard so another sub is not a necessity.

If there's anything I haven't thought of please let me know. The dimensions seem to be my main priority. 20" width is necessary but height and depth to get 360 liters. I could probably do this myself but don't want to make any mistakes. That way if it's wrong I'll have someone to blame it on :huh:

I wondered if anybody has designed these so you can remove the back easily or maybe hinge it so you can add and remove stuffing easily. It seems like the foam rolls at Home Depot may work for this but I'm concerned about leaks.

[ThomasW]

It's really much more practical to use an LT circuit than trying to move around a 360L box (think 250-300lbs when properly constructed).

If the driver is mounted with t-nuts or threaded inserts, it's easy to use it's opening to adjust the damping. And the reality is that once optimized, there's no reason to play around with the amount of damping.

BTW the damping material of choice is regular old fiberglass insulation (yep the same stuff used for insulating a house)

[warnerwh]

What is an LT circuit? I do have a Behringer DEQ 2496.

Moving a heavy box on carpet is actually pretty easy. My speakers weight 250 each and they're easy to move around. They weren't easy to get down the stairs however.

How many cubic feet is 360 liters? I came up with 12.7 cu feet. Now if I put in fiberglass how much larger will the fiberglass make the box act?

According to Vance Dickason's measurements it appears good ole fiberglass is about as good or better than other fillers. Cheap too.

[Bent]

28.31685 liters / ft^3

12.71 ft^3

really big

[warnerwh]

Yes that is big. If I'm at 20" wide it would have to be about 42" tall and 24" or 26" deep.

What happens if I made it a bit smaller? I need to know how much the fiberglass affects the internal volume. I know it makes it act larger but by what percentage.

[ThomasW]

What is an LT circuit? I do have a Behringer DEQ 2496.

http://home.comcast.net/~thomasw-2/S...EQ2496-LT.html

Now if I put in fiberglass how much larger will the fiberglass make the box act?

Depends on how much is added, but it's not the best idea to plan on using the damping to fool the driver. It's better to use it to fine tune the performance of the sub.

[warnerwh]

That LT circuit is apparently simple enough. The DEQ 2496 is a wonderful tool. It should be required in all systems to have something like it.

I'll recalculate what will work out well as to dimensions. It seems that I'll be wanting two sheets of mdf.

Any extra mdf I'll use for bracing. Someone said I shouldn't use the 3/4" granite. I'm not sure I understand why. I'd think that gluing a nice sized piece to both side walls would help alot. Plus this stuff is heavy which must help also.

[ThomasW]

There's no need for granite inside the box, so use it for a fancy top or something. If you feel the need to mass load the inside of the cabinet, go the a home center store and buy a 1/2" sheet of Durock concrete tile board. Glue it to the walls...

As long as the cabinet Fs is higher or lower than the passband of the sub, and the walls don't flex that's all it takes to have a good cabinet.

[warnerwh]

What happens if I go with a 9 cubic foot box? This is the VAS of the driver.

It appears you can go above or below it by what I've learned thus far. What happens if you go below the VAS and above the VAS?

Thomas that's a good idea of using the granite for the top. I plan on painting this sub piano black. Trying to get a perfectly smooth surface on something I built though has me worried and with piano black it will stick out like a sore thumb.

I just found a program called AJ Sealed Designer. Is this an accurate program? The reason I ask is because it came up with 157 liters. Then again I've no doubt entered a wrong number.

If any of you guys live near Portland, OR that have helped me let me know and I'll buy you a nice dinner.

[ThomasW]

9 cu ft gives a Qtc of 0.53.

Never heard of AJ sealed designer.

The sims you're seeing me post are from the freeware program Unibox. It's very accurate

[warnerwh]

Thank you again Thomas. If I can return the favor in any way please let me know. You've been a great help and I sincerely appreciate it.

It looks like I will go with a 9 cu ft box. Hopefully I can do this next week. I'll go ahead and get the box built while I'm waiting for my parts.

[ThomasW]

As long as you already have a DEQ2496, there's no problem going with your original idea of the 24" cube, and creating an LT lower the Qtc. That 24" cube will be movable by mear mortals, and not a big deal to stack a second on top when you realize you want more output.

[warnerwh]

I will be making the box 18w x 36h x 26d. Yes I thought about the weight as I only weigh 155 but am fairly strong and as long as it weighs under 150 I'll be ok. I will just put the driver in when I get it down here in case I need to let it go 8O

I'm somewhat disturbed by the fact that I'm reading that no fiberglass is necessary. It seems that damping the rear wave would help. I donated my book by Vance Dickason to pass around for Audiocircle members so if there's another place where I can read up on this I'd appreciate it.

[ThomasW]

I'm somewhat disturbed by the fact that I'm reading that no fiberglass is necessary

You haven't read or been told that on this forum. What's been said here is that it's better to appropriately size the box instead of trying to use very high amounts of damping to force the box to look bigger.

All the Unibox sims I posted have used "heavy fill' as the criteria for the boxes performance. I just haven't cut and pasted screen shots of every part of the main Unibox sim page.

[warnerwh]

Yes it wasn't here I read about not using filler. I've been all over doing research. There's more to learn than I would have guessed just regarding subs as I've spent quite a few hours and feel like I know almost nothing.

[Dennis H]

Stuffing changes the Qa parameter in the box sims. It doesn't really change Fb like using a bigger box would but it does change the overall Q of the driver + box. I'm not sure what Unibox assumes (can't run it on my antique Excel) but typical values are:

No fill : Qa = 100
Minimal : Qa = 50
Normal : Qa = 10
Heavy : Qa = 5

[warnerwh]

Dennis: Would you please define

"No fill :Qa = 100
Minimal : Qa = 50
Normal : Qa = 10
Heavy : Qa = 5

How much fiberglass would you start with in an 8.5 cu ft sealed box with the Dayton 15" Hi Fi driver?

Thank You

[Dennis H]

Dennis: Would you please define

"No fill :Qa = 100
Minimal : Qa = 50
Normal : Qa = 10
Heavy : Qa = 5

How much fiberglass would you start with in an 8.5 cu ft sealed box with the Dayton 15" Hi Fi driver?

Thank You

Minimal, line the walls.
Normal, fill more than half of the enclosure with the stuffing fully fluffed up.
Heavy, pack it in so it's compressed a bit.

Thomas has a FAQ about how to adjust the stuffing but I don't remember where it is. Maybe he'll chime in. Basically, start light, say half full fully fluffed, and keep adding some as long as it keeps sounding better. If you add so much it starts sounding muffled, pull some out.

[ThomasW]

It's not a FAQ, just a post somewhere.

Start off with 0.5lbs/cu ft. Then add in amounts 2-4oz at a time. Each time the bass should 'tighten'. Continue adding until the last amount added simply decreases the overall output. Remove that last amount added and you're done.

Ken Kantor who's forgotten more about subs than I'll ever know says....

Exact enclosure volume is not critical, and stuffing can be added or subtracted to fine tune the response. I recommend adjusting the stuffing by monitoring the impedance versus frequency of the sealed box system. Add stuffing to lower the frequency where the impedance is highest. When that impedance peak starts to rise in frequency, you have added too much.