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Help with subwoofer design


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22 replies to this topic

#1 of 23 Bud Huey

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Posted April 06 2006 - 04:32 PM

After reading some of the posts on this board I have decided that most of you have forgotten more about subwoofers than I will ever know, so I am just going to throw my situation out here to see what the experts suggest.

I am building a platform/stage in the front of my HT. It is going to be @ 24" high and 24" deep across the front of the room (15'-6" wide). It will have a semicircle in front that will extend into the room adding some depth in the middle of the platform.

Here are my questions:

1) How much subwoofer (or subwoofers) do I really need for my room (15'-6" wide x 28'-0" long x 10'-0" high)? I don't want my HT to sound like a 16 year old driving down the street with to much bass in the trunk, but I want my audience to feel their chest rattle during LFE extreames in a movie.

2) Since the platform is only going to be 24" high could I get away with using two or three 8", 10", or 12" subwoofers instead of one 15" subwoofer? The 15" subs will not fit well once I add base boards, and spacing for molding.

3) What is the best way to power multiple subs - one big amp with multiple speakers or several smaller amps, one per speaker? How should I wire the speakers in a multiple speaker/amp set-up?

4) I am trying to stay under a $750 budget, but if I can get a set-up that is a lot better for $1000-1500 I will spend the money. I just don't want to end up with a $5000 subwoofer system that is 50% of my HT budget.

5) I am using Klisph for the rest of my HT speakers in case that makes a difference. They offer good base response themselves, so the subwoofers are mostly going to be for LFE.

6) Should I build a custom box for the subs in the stage or just place the subs in the front panel (facing the audience) and leave the back open? If I build a box what are the best dimensions? What do I need to do to "tune" the box to a certain frequency?

7) Any suggestions on the best "bang for your buck" in a subwoofer speaker and subwoofer amp keeping in mind my goals for the system and budget?

Thanks for your help!
Bud

#2 of 23 MikeLi

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Posted April 07 2006 - 05:45 AM

Call SVS and ask those questions and let them advise you on what sub or subs you should get. Probably cheaper than DIY and they make quality subs. They love to talk and will not oversell you!

#3 of 23 Bud Huey

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Posted April 07 2006 - 07:47 AM

Thanks! Do you have a contact number or website for SVS?

Thanks,
Bud

#4 of 23 Robert_J

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Posted April 08 2006 - 12:37 AM

Quote:
Thanks! Do you have a contact number or website for SVS?
SVS or you could have clicked the advertisment at the top of the speaker section.

1. Your room is a little bigger than mine. Right now, I'm running a pair of 15's in sealed boxes. My next upgrade will be to four 15's in an IB. The "boom" sound is a product of your sub's frequency response not being flat not the size/number of subs that you have. The larger/more that you have, the more headroom you get. You can get a flat response with proper sub placement and the right EQ.

2. With a room that size and your goal of "chest rattling bass", the minimim I would go with would be multiple 12's. Multiple 15's would be better. Since you are already building the stage, why don't you you go ahead and build enclosures in there as well?

3. I like to use multiple subs and a large amp. Wiring depends on the subs you pick out.

4. You can get a nice SVS for $750. You can build a massive sub for the same price.

5. Subs don't care what your main speakers are.

6. We could spend days discussing this and it could better be answered in the DIY section of this forum. If you have the tools to build it, we can help with the design.

7. My suggestion - A pair of Soundsplinter RL-p 15's powered by a Behringer EP-2500 and a Behringer DSP1124P as the EQ. You are a little over budget but still under a grand.

-Robert

#5 of 23 Bud Huey

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Posted April 08 2006 - 01:19 AM

Robert,
Thanks for the great information! This setup sounds like exactly what I am looking for. I have a couple more questions if you will indulge me....

1) Would you recommend placing both 15" subs in the front of the room? Do I need to add a third sub in the back of the room just to make sure I get the extra "umph" I am looking for?

2) Since my stage will be @ 24" deep on the left and right side and 60" deep in the center would you recommend placing the subs on the left and right or in the center closer to the audience?

3) Since I am going to build them into the stage what size/type of enclosure do you recommend? Do I need a specific sized box? Sealed or vented? Do I need to put anything inside the box to control the frequency response?

4) If I put both subs in the center of the stage right next to each other would you build them into one enclosure or two seperate enclosures?

Thanks for taking the time to help me out!

Thanks,
Bud

#6 of 23 Ryan Schnacke

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Posted April 08 2006 - 03:43 AM

If you're already building a large box for the platform, it doesn't take that much more effort to make it a proper subwoofer enclosure. I say forget the SVS.

Right now the Assassin woofers from www.ascendantaudio.com are an absolute steal. $75 for the 12 incher. You could get 6 of these for $450 + shipping = ~$500.

Then get a pro amplifier like the Nady XA-900. Wire the woofers for a mono 6ohm load (3 woofers in series, other 3 woofers in series, parallel the 2 series chains).

Use the money leftover for building materials. Add a parametric EQ later on if you think it could use it.

This plan keeps you on budget at ~$750, uses 12 inch woofers (so you can still do the baseboards and molding as you had planned) and actually gives you a litte more displacement capability than a pair of the SoundSplinters.

1) All woofers go in the platform enclosure at the front of the room.

2) With my 6 woofer proposal you'll probably have to put them across the front. If you're concerned about the acoustical effects you could build a small test box and try different locations

3) Use the entire volume of the platform as one big subwoofer enclosure and build it like a sealed box. If the platform is going to be 2 seperate enclosures choose the largest or split the woofers up between the 2 enclosures. A very large sealed enclosure like this will be similar to an infinite baffle, which is regarded by most to be the ideal enclosure if you have enough woofers to take advantage of it. You could line the inside with batting or insulation but its not necessary.

4) Answered already.

#7 of 23 Robert_J

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Posted April 08 2006 - 05:14 AM

Quote:
Right now the Assassin woofers from www.ascendantaudio.com are an absolute steal. $75 for the 12 incher. You could get 6 of these for $450 + shipping = ~$500.
There have been a lot of good reviews of the Assassins. Or 8 surplus Image Dynamics for $520 shipped. Has even more displacement than the Assassins.

As you can see, there are hundreds of options in your price range. Find out how much space you have to work with inside your stage. That will give us an idea of what will work. I still recommend the Soundsplinter subs but I have a thing for subs built by TC Sounds. They must be good since they supply SVS.

-Robert

#8 of 23 Mark Seaton

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Posted April 08 2006 - 05:44 AM

As others have said, just put a little extra effort in making the platform structure the subwoofer enclosure. This basically means sealing it up and making sure it can't rattle or vibrate too much. You might want to add a couple crossmembers along the joist/stud cavities to screw the top sheet into to keep the un-braced panel area a bit smaller.

I would say that your best value option with that much useful volume would be in finding a way to make 15" drivers fit. If not, 12" drivers can do just fine as well. My suggestion would be a bare minimum of 4 12", preferrably 6-8. For the 15" option, 4 should be about perfect. The 15" DVC or IB drivers from Parts Express would be a good value, and of course there are others. Also shoot John Janowitz of AE Speakers a message to see if he has some IB15s or something similar available at a reasonable price.

If you search the home theater construction forum at AVS I think there are some similar projects to what you describe in there.
Mark Seaton
Seaton Sound, Inc.

#9 of 23 SteveCallas

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Posted April 08 2006 - 08:36 AM

Six AA Assassin 12" drivers sounds like it would be perfect. The only potential problem I see is that you mentioned the front of your stage will be rounded - how would you mount a driver to a rounded surface?

One idea would be to build a removable grill that is arched, and make the actual front of the stage into three flat, angled sections. The very front of it would be parallel to the back wall and you would mount two drivers on that surface - then there would be an angled wall on each side of it, each holding another two drivers. When the grill is in place, the stage will appear rounded.

Hard to explain in words - I drew this up real quick to show you what I am talking about:
http://gallery.avsfo....ppuser/7456874

#10 of 23 Bud Huey

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Posted April 08 2006 - 09:31 AM

You guys are great! Thanks for all of the great advice. OK - I will build the front part of the enclosure as the entire subwoofer box and line it with either 12" or 15" subs. Here is my next batch of questions.

1) Would 6 12" subs be better than 4 15" subs? The 12" would fit better with my baseboard and mouldings, but I could make the 15's work if they would sound better.

2) How much space do I need to allow in front of the sub for travel? I plan to wrap the entire stage in some type of fabric to give it a finished appearance and I need to know how much travel to allow for the subs before they touch the fabric.

3) What type of fabric would you recommend to minimize acoustic effects?

4) Per Steve's comments above, how much arc can I put in the front of the stage and still get the subs to mount flush? Do I need to build it with the flat surfaces and a grill to give the stage the curve I am looking for? Using a grill would also make my secopnd question a mute point, so maybe that is the way to go.

5) Just so I am on the right track from an amplier standpoint - is two (15") or three (12") subs in series a good configuration? The Behringer EP-2500 that Robert recommended would power two sets of speakers for a total of 4 or 6 subs.

5) Do I need any subs in the back of the room? I have built a cabinet for one, but I could potentially add two more if they are beneficial. It would be difficult from a contruction point of view, so the benefits would have to outweigh the construction hassels.

Thanks,
Bud

#11 of 23 Robert_J

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Posted April 08 2006 - 11:12 AM

1. It's mostly about displacement. Find the driver's Sd. That's the surface area of the cone in square centimeters. Multiply that by the xmax (the driver's one-way maximum excursion) times 2 (convert to centimeters if needed). That's the amount of air a single driver will move. Then multiply that times the number of drivers you will use.

I said "mostly" because the Soundsplinter RL-p drivers are a step up in quality over anything else that has been listed. Will there be a difference in sound quality between 2 SS 15's and 6 Assassin 12's? Probably not.

2. With the SS's, I'd give at least 1.5". The cone will move out 24mm. The Assassin's will only move 15mm.

3. Speaker grill fabric from Parts Express. They also have mechanical and magnetic grill fasteners as well.

4. Each driver needs a flat surface to mount on. Use the grill to make it look more rounded.

5. I'm using the EP-2500 right now to power multiple subs. The wiring will be the easiest part of this.

6. A sub at the back of the room may cause more problems with cancellation than not having one at all. It will be much easier to configure the system with all the subs in the front.

-Robert

#12 of 23 Ryan Schnacke

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Posted April 08 2006 - 02:13 PM

Concentrate first on deciding which woofers you want to use and how many. Then we can help you determine your amplification needs and help you wire them up since this will be specific to your woofers.

6 Assassin 12's should be about equal in performance to 4 of the Parts Express DVC 15's or IB15's. But 4 SoundSplinter 15's would be a big step up ... and a big step up in price.

The IB15's really want an infinitely large enclosure. If you decide you want to use 4 of these, I'd recommend calculating the enclosure volume. If its less than 70cuft then you'll get a pretty high-Q (generally undesirable) alignment even if you stuff it with batting/insulation. In this case go with 2 IB15's and live with less output or switch to any of the other woofers mentioned.

#13 of 23 Ryan Schnacke

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Posted April 08 2006 - 02:17 PM

Quote:
I will build the front part of the enclosure as the entire subwoofer box


I just re-read this and want to clarify. We're actually suggesting that you use the ENTIRE platform volume as the subwoofer box. Enclose and brace the whole thing to get as much air space inside the box as possible. That's what will get you closest to an (ideal) infinite baffle.

#14 of 23 Bud Huey

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Posted April 08 2006 - 02:25 PM

Thanks for all of the help. If I build the front part of my stage as the enclosure I calculate approximately 76 cubit feet of volume in the enclosure.

I am going to go with the square front design and grills to give the curved appearance. That seems to be the easiest thing to do all things considered.

I was hoping to use a fabric a little more decorative than speaker grill cover. Would other fabric types cause problems?

Thanks,
Bud

#15 of 23 Bud Huey

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Posted April 24 2006 - 12:48 AM

One more quick question - should I plan to fill the enclosure with some type of baffle material or should I just leave it empty?

Thanks,
Bud

#16 of 23 Ryan Schnacke

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Posted April 25 2006 - 10:19 AM

Filling won't be necessary with a 76 cu ft enclosure. If you decide to use 4 of the Dayton IB15's then you might want to stuff if to lower the system Q. With the other woofers you're considering, this won't be necessary.

#17 of 23 jamesIS

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Posted May 07 2006 - 05:23 PM

One possibility, if you are determined to go for the 15 inch option, would be to mount the drivers on a slanted panel--say something like 45 degress to the floor behind your covers. This would allow you to fit the entire driver in your set-up without sacrificing your asthetic goals.

Remember to secure everything well--the only thing you want vibrating in their is the air.

Personally, I'm likely to opt for a sealed enclosure for my theater. It seems to be the best option for accuracy and detail. However, I'm new to subs so you may want to keep that in mind as you consider the relative value of my opinion on the matter.

#18 of 23 Bud Huey

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Posted June 19 2006 - 06:17 AM

I apologize for the delay in my HT project, but my daughters Spring Soccer season really cut into my HT contruction time. Now that the 'dog days' of Summer are here, I am back in the basement trying to stay cool and get some work done. The platform in front on my screen is almost complete, so here are my next round of questions.

1) The total volume of the subwoofer enclosure is @ 56 cubic feet. The front of the sub will be 5-6' from the front of the first row of seats. Is this enough space to create an IB? Do I need to do anything special inside the enclosure?

2) I am still planning to use four 15" Sound Splinter subs per Robert's suggestion. Has something better come on the market in the last 4 months that offers a better price vs. perfomance ratio?

3) My subwoofer will double as a stage for my kids to play on while they are imitating "American Idol". Are there any special precautions I need to take to insure the sub is not damaged? The framing is 2 x 4's and the top and bottom decking are 3/4" plywood and will have another 3/4" of hardwood flooring on top of that. All seams are glued and screwed.

4) I saw a couple of 15" grill protectors on Ebay that were designed for automotive applications. Could I use these on my system without having to worry about damaging the subs or diminishing the peformance? I would like to protect the subs in the front of the stage from damage from feet or anything else that could damage the cone.

Thanks,
Bud

#19 of 23 Ryan Schnacke

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Posted June 19 2006 - 03:44 PM

1) Technically its too small to be considered an IB. Ideal would be 10x the summed Vas of the drivers or larger - that's 210 cu ft. Minimum to be considered an IB is somewhere around 4x the summed Vas or about 84 cu ft. Still, your plan falls into the realm of "really large sealed sub with tons of displacement" and that's not a bad place to be.

2) The only recent introduction is the Dayton RS 15's from Parts Express. They can't compete with the displacement of the SS RLP but they should be very nice woofers if the RS 12's are any indication.

3) A well braced subwoofer enclosure will easily stand up to kids or even adults dancing on them. If you're concerned about this, you probably should be doing more bracing.

4) Review Robert J's post above where he talks about allowing enough clearance for woofer excursion.

#20 of 23 Robert_J

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Posted June 20 2006 - 03:11 AM

1. I agree with Ryan. Big and sealed will work out great. Maybe add a little EQ if necessary.

2. There have been recent additions besides the new Daytons. TC Sounds has started selling direct to the public. I just modeled 4 of the the TC-2000's (similar to the Soundsplinter RL-p) in a 56cf sealed box with 500w per sub. Absolutely scary output levels.

3. I would feel comfortable with some of my smaller enclosures being used as a jack stand when changing a car tire. Build it strong or you will have unwanted vibrations.

4. This in black or chrome should work.

-Robert





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