help updating an old DIY sub

I built a really solid sub box many years ago to specs I found in a instruction book. I made sure the woofer I used (there were no specific sub drivers in those days which tells you how long ago I built it - about 17 years ago would be my guess) had a decent response curve down below 60 hz.. But I couldn't find any information on adding a port at the time which has always left me disappointed in the volume I got (remember this was before the net was popular for the public). I do get decent volume but with the front speakers I use the sub gets overpowered and can barely be heard. It doesn't help that I have been using only a 100 watt 4 ohm amp to power the sub (also 4 ohm) all this time. This was actually considered enough power in those days when used with a 101 spl 15 inch driver and it did improve my system back before I had the front speakers I have now.

At this point I'd like to add a port and change the driver. I think I would get substantially better response by doing this. Can anyone suggest information on how to add a port and what driver I might want to use. I'll upgrade the amp in the future. I'd really just like to try adding a port first so I wouldn't have to spend much money at all )Christmas is coming after all and I have 2 kids in college). My box dimensions are 17 1/4 deep, 21 1/2 wide and 12 inches tall on the exterior and I built the box out of 3/4 plywood. The woofer is downfiring and I have 2 inch legs (cut from the plywood). I have two layers of the plywood on the bottom where the driver is mounted and on the top so the interior dimensions are affected by this. I have a 100hz choke installed inside the box and I use an EQ to reduce any higher frequencies between the sub out of my receiver and the amp I use. This is probably overkill now but it was actually pretty important to do this with some of the older equipment I had. My HK pre-amp sent too much higher frequency stuff to the amp IMO. I haven't even tried hooking up my new Denon receiver without the EQ. It may work well without the 12db cut from the EQ for everything above 60 hz.. I could probably set the EQ a little higher at least but I don't want anything but low frequency stuff coming from this sub.

I actually use this sub as an end table. It's no flimsy piece of work. The plywood is all screwed and glued and I've never had any problems from it vibrating or rattling. I have it set against a side wall of my house so I figure a port pointing that direction would be my best bet. Also I don't have access to the wood working tools that I did when I built this box so a simple plan would be best. I don't want to tear the box apart either since it is put together so well. I don't want to risk causing problems. I can of course remove the driver for access to the interior of the box. The sound I do get from this sub is tight for what it is at this point. I know I may not be able to use the driver I have now since it probably wasn't designed for a ported enclosure but I'd like to give it a try before I commit to buying a new sub driver.

Any help at all would be appreciated. My dad helped me build this box so I really want to hang onto it. I don't doubt it might be better to start from scratch but I'd prefer not to.

Re: help updating an old DIY sub

Well like I said I built the box based on a space formula I found back at the time. It isn't so much that the efficiency is horrible as it is a function of the fact that my fronts are incredibly efficient. And the EQ boosts the signal going to the amp (by only about 4 db I think - I'd have to check to see how I have it set) so I can't see how that it would increase the sound by removing it. The choke was there to keep the driver from playing higher freq sounds. That was the main function of the EQ too but it does boost the signal which of course makes the amp put out more power. I don't get any distortion with the driver and the amp because the amp basically doesn't have the power to overpower the driver. I have experimented to see how to get the best response from this speaker. Remember this was not designed as a sub driver. I didn't install the choke or the EQ until I noticed I had voices coming from the speaker which wasn't good of course.

I don't really expect this box to produce massive amounts of bass. The design was just too early to accomplish that. To be honest I had pretty much written it off until I bought a newer receiver. That new receiver allows me to give the sub another 15db of boost and I reduce the front speakers by about 10db which actually makes it possible to hear the sub when playing video content. It's a lost cause for music still since I don't reduce the sound of my fronts for that. But at least I can hear it when I watch tv at times. That's what got me thinking I could add a better driver actually designed to be a sub and get better results. I could remove the choke (and possibly the EQ) then.

Besides all this I don't think my wife is going to go for adding another foot to the height of the box. I was hoping for a port design that would work. I'd still like to get a better driver just to see what I can get from the space it has. Like I said my father helped me build this thing and I don't want to replace it because my father passed away about 15 years ago. I'd rather just keep on using it as an end table and a minimal sub. I think I can improve it some which is my only real goal. I don't expect glass breaking bass from it.

I suppose I really don't even need a sub with the front speakers I have anyway. I'm running 300 watts RMS (480 peak) at 4 ohms (from a Kenwood Basic M2) into those speakers which have an spl of 106. They will rattle the walls all the way down to 25hz. They play pretty well at 20hz but I can't tell if my ears don't hear all the sound or the speakers just don't produce the sound. 20hz is very low for human ears. I have trouble with my CD players skipping when the bass is cranked up in the same room as those speakers anyway and I have a concrete floor. If I want to listen to them full volume (very rare for me) I generally have to play something from a hard drive on my computer. My DVD player does better than the CD player but it will skip too at full volume. Those speakers will make the concrete floor vibrate and the wooden floor upstairs practically acts like a passive radiator.

Re: help updating an old DIY sub

I'm not changing the box. I don't need a sub bad enough to change it and besides it performs pretty well at the size it is now.


Never heard of it and likely not interested in it.


I've known that for almost 40 years now.


I know how EQ's work too.


The formula I used contained all of that information. But it was 17 years ago or so. I don't believe you know whether it has changed from what I saw or not.


I realize there are far better drivers available but I actually updated the driver a long time after I built the box. It's probably only about 12 years old. It was after the time subs were starting to get popular in cars but not really in houses. The kind of drivers available now were not available back then but I doubt the driver I used is as bad as the drivers from 17 years ago.


Thank you. That's what I was looking for.


I really don't want to buy an amp at this point. I have 2 kids in college and Christmas is coming up. Besides I think 480 wpc plus a 100 watt sub is plenty loud enough especially considering my front speakers are 106 spl. Maybe sometime in the near future but most of my spare money goes into financing my video business at this point. I have about finished buying all the equipment I need for that for the time being so I was thinking about upgrading my sub mainly because my new receiver actually drove it enough so that I could actually hear it. I thought a driver update might make it audible when I play music too but it's not important enough to me to spend $500 to make it work better. Anyone who listens to my system for long at full volume will lose hearing quickly anyway so I don't really see a lot of point in spending money that could go elsewhere.

Thanks for the help but I think I'll just buy the driver for now and possibly update the amp later. BTW I do have a separate amp that isn't built into my sub now and I don't see any reason to change that design. I don't need an amp built into the sub for any reason.

Re: help updating an old DIY sub

My EQ is set to kill anything above 60 hz so extreme accuracy has never been a concern with my sub setup.


I just don't want to spend anything more than the minimal amount to try to get a true sub driver at this point.

That may be true but IMO I'll likely be able to find an amp that will push the sub when and if I decide to upgrade that part of my sub. I've got along with a sub amp sitting on a shelf in my cabinet for quite a while. I'm just looking for a little improvement at this point anyway and subs running as low as I have this one set up really don't require a high quality amp IMO. I don't think I want to put a Sound Design amp from 1972 in it or anything but I think I'll be able to find an amp that will push the driver well enough when I decide to upgrade which could be a long time. Like I said this is more of a sentimental project anyway. This sub worked fairly well when I was using far less efficient speakers on my fronts. I'm not expecting it to be my main source of low range sound now. It may turn out to cause more problems to be honest. The fronts I have were designed to work well as a set of drivers so adding a sub could actually screw things up IMO.


Yeah I know it was pretty much inaudible before I got my new receiver. Now because I can cut back the power to the mains enough and I can raise up the power to the sub enough that I can hear the sub with 5.1 content. I only thought I might improve that situation a little with a better driver. I know I could use a bigger amp (a lot bigger amp) to drive my sub but IMO I could buy an old Adcom or something and make it work very well. It's really overkill anyway so I don't want to spend a bunch of money when I could be spending it elsewhere if you know what I mean.


Well I've actually done most of what you say already. I've tried a dozen different EQ's with that sub to get it to sound right. It will likely all change of course when I get a different driver and it will change again when I get a different amp but spending time getting it tweaked isn't going to cost me anything and I still have most of those EQ's lying around somewhere. I only have 1 2/3 cubic feet inside my box so I'd really like to not cut that down any more. Yeah I know that isn't enough space inside but I used the only formula I could find when I built the thing. It's been a very long time since I built it and I basically remembered the forumula from a book in a store so I don't still have the formula I used. I just remember figuring it out the way the book said to do it.

Again I'm not afraid of some trial and error tweaking. That's how it was all done back in the days I started messing with audio equipment. Now my son is an electrical engineer and very much into audio equipment too so I'm sure I can get him to design a tuned port if I beg long enough (if you don't have kids you don't know what I mean ) but he's busy working on his phd in electo optical physics so I can't get his attention for a very long period at a time these days. I figure it's just easier to buy a good driver and try to tweak it myself. My son tells me my system sounds far better than the stuff his friends have that they have spent mega bucks on but that's probably more to do with my years as a roadie/sound guy for different bands etc.. I actually had intentions of becoming an engineer myself so I could design sound equipment at one time but I discovered I liked to do other things better. That was back in the 1970's though so I would have likely gotten in on the ground floor of the audiophile era if I had gone that route. But that's all water under the bridge. I still spend lots of time working with audio equipment in my video business (concert videos etc.) but that's generally more on the recording side rather than the playback side. I've been satisfied with the system I have for a long time though I know things have improved since I put it together. But I have a very good system and I didn't see a lot of reason to go messing around with it. It took me 15 years to get it the way I wanted it and I've probably kept it that way for about 10 years.

I appreciate the help but again I'm just looking for a simple upgrade at this point. Mainly I just want a better excuse to keep this box in my living room because me and my dad put it together.

Re: help updating an old DIY sub

I would have a hard time converting the box openning to 12 inches at this point. I might check out the Dayton Reference subs you mentioned.

Re: help updating an old DIY sub

Yeah Robert I've been very interested in getting one of those but I just spent way too much money going to an Ohio State football game (only to see them lose - arrgghh!!!) so until I round up some loose change I won't be able to buy anything soon. I saw that there was a limited supply of those so hopefully I can get while the getting's good.