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Old 9th January 2005, 05:56 PM   #1
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Default Designing Home Theater towers, advice????

I'm going to do a little modding and reconstruction on a set of home theater towers I have and I'd like a little advice.

First off, I'm a college student and these will most likely be going in a dorm room. I know space is normally a premium, but I'm willing to sacrifice floor space for sound. I love my music!

These towers weren't stunning by any means to begin with. They sounded nice, but probably only ran a few hundred at most when they were new. (I don't know for sure, they were given to me)

I want to pull the mid/tweet out and chop the top off leaving the 12" woofer and pasive radiator in tact. Where the mid/tweet was (top half of the tower) I want to build a pannel that rises up a few feet for a dipole midrange set up and a place for the tweet.

before I go any farther, is this a good idea? I'm not looking for top quality sound here. I just want something that will sound/look good for dorm room music listening and movie watching.

I'll be using a pair of Vifa/Infinity 4" mids for each tower. I've already mounted them on a baffle board along with a tweet from my Bose system in my car (long since removed in favor of WAY better stuff) and they sounded pretty good. They were better than the mid/tweet combo in the tower anyway. The 4" mids didn't have crossover on them and the tweets had the cap that was built into them from the factory. I would like to put a high pass xover on the mids because they sounded stressed during heavy bass lines.

The Bose tweets will be replaced with a pair of Morel MT10's most likely. I run those tweets with a pair of those same VIfa 4" mids as part of my 3way set up in my car and I love them. I'm pretty set on those tweets.


My main concern is the woofer/PR's performance. Will chopping half the box off and sealing it up drastically alter the woofer's performance? The towers stand almost 5' tall right now, and they'll be losing a little less than half that. I know from my car audio ventures when you put a woofer/sub in a box that's too small you get nasty peaks in the upper end and lose a whole lot of your bottom end. I know the principals are the same in home audio, but the volumes are quite a bit different, so I'm wondering if the changes are quite as drastic.
Let's say I have a 12" sub in a 2cu ft box. (car audio) If I put that same 12 in a 1cu ft box it woudl sound like ***, but if I went to a 1.75 cu ft box it wouldn't be very different.
now, if these home boxes are 5 cu ft (let's say, I havent' measured them) and I cut them down to a 3 cu ft box would the woofer's performance change drastically? I know the ratios are damned near the same, but you're working with more air to begin with in a home audio box, so it leave more room for change?

Also, a little advice on mounting the mids/tweet woudl be nice. Should I mount them, from the bottom up, mid-mid-tweet, or mid-tweet-mid, or tweet-mid-mid? Does it matter?
I don't want to build a whole xover network for mid tweet, I just want to wire in a couple of caps and be done with it. Would any decently priced cap from Parts Express work well enough? I'm not going to low pass the woofer unless I get some nasty peaks from the box change because it rolls off nicely up top (no xover from the factory).

Should I let the 4" mids do most of the work up top and just use the tweets for the highest highs, or woudl I be better off with a xover point of around 3-4kHz? In my car they're crossed at 3kHz and the 4" mids play to their natural roll off. The blend is really nice, but that's in a car. I know in the house it could be totally different.

How wide should I make my baffels for my mids? Right now they're on a board that's about 10" wide or so, should I go wider? I'm also thinking about building some side peices for the baffels. I remember reading that sides help for low end response and block more of the back waves than just a flat baffel.

Am I off to a good start or should I really reconsider some things? I don't want top notch quality out of this, just something better than I have, and somethign done by me.

I'm open for anything assuming it's cheap. What do you think about the mid choice? For $4 each they're pretty damned hard to beat, but I"m open to suggestions.

these mids:
http://www.partsexpress.com/pe/showd...number=299-492
these tweets:
http://www.partsexpress.com/pe/pshow...number=277-025
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Old 9th January 2005, 07:37 PM   #2
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Unfortunately changing the volume in a tuned enclosure will change things dramatically.

Ported and passive radiator boxes are much more sensitive to volume changes than sealed alignments. not a good idea in my opinion, at least not without running some sims (which assumes you have or can measure the parameters of the woofers.).

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Old 9th January 2005, 07:42 PM   #3
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Default Some random answers

Sorry, I didn't read all of that.

I saw that you're asking how it would affect the setup to chop off the top of the tower, leaving a smaller box with the same 12" woofer and passive radiator. In this case, you might be able to counteract the problems that introduces by adding mass to the PR cone.

About quality of caps from PE- yeah, they sound good. Just pay attention to the design, and use a cap that's intended for a crossover. Same with coils. Use caps and coils within their intended voltage and power ratings- if they're slightly oversized, you will have less trouble from pushing them too far.

About going dipole- you might want to read linkwitzlab.com in the phoenix and orion design sections. It's not always a simple matter to slap a driver onto a board and get decent response- if you don't have the right driver Q to get a low frequency bump to counteract the low frequency rolloff, then you'll need some filters to do it.

My advice to you would be:

1) Read Linkwitz's description to decide if you really want to go for dipoles.

2) Consider bi-amping or tri-amping. Bi-amping would help the most, because then you can cross between the 12 and the mids actively, and not need to use enormous inductors. You might gain a lot of good sound with the existing speakers just by tri-amping and playing with an active crossover.

3) Before chopping up these boxes, try reducing the volume first to see if the altered bass response is still OK. The way you do this is sticking solid objects of known volume (bricks, bowling balls, cans of beer, etc) into the cabinet, and seeing how it sounds with reduced volume. This might be easier for you than measuring T/S parameters and modeling the new box- though that would be the idea case.

4) I've used the Morel MDT20s and I love them. If you're happy with the MT10s, more power to ya! My next design will likely have some Seas 27mm tweets, or some Ushers.

5) About bi/tri-amping- I know you're going to be in a dorm room, and you're posting online right now.. so I'm 90% sure you're going to have a computer in your dorm. If it's a desktop, I'd really recommend looking at something like KX project, and other sound card based active crossovers.

Hopefully I said something helpful..

Joe
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Old 9th January 2005, 07:52 PM   #4
morbo is offline morbo  Canada
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IMO, you are much better off taking out the woofer and PR and building a new box for them with the same internal volume, but different shape. This way you could even measure their T/S params if you have the capability, and perhaps design a more appropriate alignment for them - in inexpensive commercial speakers you often see less than optimal box tuning. You would also most likely be able to build a far stiffer and deader box than they are in right now.
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Old 9th January 2005, 08:19 PM   #5
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Default Q

I've considered building new boxes, but if I do that I'm going to want to go all out and build a curved, painted fiberglass front. I just finished my fiberglass sub box for my car and my dad is getting pretty ****ed about the mess in the garage. I don't know if I want to make another, bigger mess I don't have a problem ditching the PR and going with a true sealed encosure (much more simple, I know) if you guys would recomend that.



Quote:
About going dipole- you might want to read linkwitzlab.com in the phoenix and orion design sections. It's not always a simple matter to slap a driver onto a board and get decent response- if you don't have the right driver Q to get a low frequency bump to counteract the low frequency rolloff, then you'll need some filters to do it
I've read a little on there, but it's been a while. I'll check it out again.
What Q am I looking for? I know in the car audio world I would look for a driver with a QTS as close to .7 if I wanted them to run IB in the doors. Am I correct in assuming this is the same? These drivers have a QTS of .4x. I've already tried running them on a board and they sounded pretty decent (other than material below 150hz or so but the woofer can take care of that). Are there some little tricks I can use to get a little more low end safely out of them? I know in my car, in sealed kick pannels, they don't like anything below 200hz when I'm playing them REALLY loud (levels way louder than a home stereo will ever see, also with a lot more power....150x2 between the mid and morel mt10)



Quote:
Consider bi-amping or tri-amping
I'd love to, but I already have the amp I'm going to use. It's a Technics 5.1 head. It's rated at 80x5, but the center and rear are heavily processed and never see the power the front 2 see. It was free, so it stays.
NOW, I do have a couple book shelf systems that have RCA inputs on them. Back in the day (Jr. High era ) I had about 4 different bookshelf systems tied into this head via RCA inputs running a wall of different cabinets. (hey, it was cool back before I knew better!). I'm thinking "no," but would it be a good idea to bring another one along and use it as a second amp? There are enough inputs and outputs on both units to tie them together, I'd just have to tune the volume knob on the second system like the gain on a car audio amp woudl be tuned. Ghetto? yes, would it work well? I"m asking you guys
That's really my only option for biamping, so should it be considered?

Quote:
Before chopping up these boxes, try reducing the volume first to see if the altered bass response is still OK. The way you do this is sticking solid objects of known volume (bricks, bowling balls, cans of beer, etc) into the cabinet, and seeing how it sounds with reduced volume. This might be easier for you than measuring T/S parameters and modeling the new box- though that would be the idea case.
good idea, I'll have to give that a shot.

Quote:
I've used the Morel MDT20s and I love them. If you're happy with the MT10s, more power to ya! My next design will likely have some Seas 27mm tweets, or some Ushers.
If I buy a higher end pair of Morel tweets they're going in the car, so it'll be the mt10's either way. The car is my #1 priority, the room is #2.

Quote:
About bi/tri-amping- I know you're going to be in a dorm room, and you're posting online right now.. so I'm 90% sure you're going to have a computer in your dorm. If it's a desktop, I'd really recommend looking at something like KX project, and other sound card based active crossovers.
most likely it'll be my laptop, but I may bring my desktop in for music and the like. Movies will be done through my Pioneer Elite DVD player though.

BTW, Center channel will most likely be a pair of Bose cubes (they were free) and the rears (if I have room, unlikely though) will be Bose cubes as well)
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Old 10th January 2005, 04:36 PM   #6
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