DIY: SI T Amp Boombox, FR Speaker Selection

[dellaseppes]

Maybe I'm crazy, I was about to buy a vintage Ghetto Blaster off of Ebay, yes the big heavy ones (some up to 20 lbs) because I want a good sounding portable radio for the pool in my apmartment complex, going to the park etc ...

Instead I decided to try to build my own, and I didn't want to go the car audio headunit approach which would necessitate a car or motorcycle battery b/c it would be way too heavy. I decided to try this using the SI T Amp which runs off of i think 8 AA batteries.

What i am planning on doing, and please offer advice, is building a mold of the unit out of light balsa wood, then putting fiberglass cloth and epoxy on both sides for strengh, I would think that would be much stronger than the plastic that ghetto blasters were made out of anyway. From all of my reading on t amps, they prefer driving a single high efficiency speaker rather than using a cross over etc ...

I was thinking about using full range speakers anywhere in the 5-10" range ... I would like this thing to have a very full sound, and If I have to bi-amp the thing, running 2 t amps .. that's ok too ... So if you could point me in the right direction in terms of speaker selection, and the type of enclosures (sealed, vented, etc) that would be great!

Thanks in advance!

[westend]

Interesting project. I'm listening to my Tamp through a set of Advent L. at the moment. So no worry about the Tamp driving a couple of fullrange drivers.I would definitely go with a sealed box as the application kind of warrants it, IMO. If Ebay isn't your way then a pick from Madisound like this might work:http://www.madisound.com/cgi-bin/ind....26597&pid=100 or a larger woofer with a coaxial tweeter. Possibilities are really endless. Good luck with this and keep us posted.

[RtV]

This is an interesting project. I know that I typically carry around a t-amp, some small speakers (old Panasonics), an ipod and a cigarette lighter power cable in my car. Sometimes I use the rig in a high school classroom (I'm a teacher) hooked up to a computer. I'd love to have something with a handle on it that easily carries the speakers for both sides.

I'm surprised you haven't had better response on this forum yet, but you haven't specified your price limits and weight & size limits for the enclosures. Once you do, you'll be sure to tweak the curiosity of those who are more knowledgable about drivers than I.

Most say that the t-amps are a natural match to Fostex drivers. But my impression is that many of the Fostex drivers are fairly fragile, and might not stand up under the abuse that portable speakers get. Also, for ultimate sound quality, the drivers normally need quite large enclosures.

Randy

[gus900]

Coolest portible system I ever saw was housed in an aluminium flight case. Something like this perhaps: http://www.maplin.co.uk/Module.aspx?...0case&doy=10m5

[Taperwood]

Fascinating project. One idea is to study the technology behind the Bose wave radio. It would be difficult to build, but you might just get away with making something that sounds pretty good with small drivers that are fully protected inside the box.

I see this as a project that definitely needs mockups in cardboard and plastic first. Keep us posted. I would like to know what you figure out.

Doug

[DocLorren]

Definately interesting. I would suggest coupling the T-amp to a pair of Fostex FE126s, in their recommended bass reflex enclosures, modified to be carried as a light-weight frugile HiFi stereo blaster. What kind of source are you planning to use?

[dellaseppes]

To answer some of you guys questions ...

I don't mind using a ported enclosure. I plan on making this think look like a guitar amp, shaped in the typical horizontal layout of a boombox, with a fabric "slide in" that will cover the entire front of the box which protects the speakers.

I would like Qtc to be as close to 1 as appropriate. I do want bass response, but i want it to be natural. Boom when it should, and only then. I would like it to be a little Hifi wonder, fit for classical, and/or capable of playing the latest from Kayne West Nothing like listening to a little "Gold Digger" here in dallas ...

I was prepared to use up 10" driver, but now that i think about it, it is obviously not wise, given the enclosure size needed to get a decent Qtc. Plus the weight factor.

The Fostex FE126E 4.5" full range driver recommended by DocLorren, and available from Madisound at around $37, is pretty compelling. The factory spec sheet says the recommended bass refex enclosure would be 265mm or 10.43 high (inside measurements), 150mm or 5.9" wide, and 265mm or 265mm or 10.4" deep. Internal Volume is 10.5 litres, and the port tube is tuned to 61hz. All of which would be very "do-able."

The budget, can't say, for sure less than $300, would rather it be less than $200 but we'll see. Weight budget? trying to keep it less than 20 pounds -- The fostex FE126E's are 2.22 lbs each. Given that the T Amp is around 1 pound, and batteries likely to be another, I should be well under the weight requirement If i used those.

Source? I was planning on using my ipod. They sell interesting little IPOD docking stations with line outs that have a simple IR controller that you can use to change tracks, and increase or decrease volume ... perhaps I could use that as my volume device. You can find these on ebay for around $20. Otherwise a simple steel volume nob on the top front of the unit could work.

I did a quick check on the bose acoustic wave, and the type of lLabyrinth enclosures look pretty complicated, and from what people tell me they don't have a flat freq response. The base is boomey, but missing large chunks of the spectrum.

I don't know guys, but it seems for less than $200 we should be able to design a pretty awsome sounding hifi boombox. Even if you modded the T Amp with better capacitors and perhaps a heat sink, or even bi-amped it if we found the output to be too low, we would still be underbudget and underweight. The sensativity of those 4.5" fostex drives are impressive at 93 db/W.

What do you guys think? Open to any ideas .. and for others to build along

[RtV]

Originally posted by dellaseppes
To answer some of you guys questions ...

I don't mind using a ported enclosure. I plan on making this think look like a guitar amp, shaped in the typical horizontal layout of a boombox, with a fabric "slide in" that will cover the entire front of the box which protects the speakers.

A nice feature to consider: making the speakers detachable. Maybe you could put a more solid grill over them to protect the paper cone drivers.

The Fostex FE126E 4.5" full range driver recommended by DocLorren, and available from Madisound at around $37, is pretty compelling. The factory spec sheet says the recommended bass refex enclosure would be 265mm or 10.43 high (inside measurements), 150mm or 5.9" wide, and 265mm or 265mm or 10.4" deep. Internal Volume is 10.5 litres, and the port tube is tuned to 61hz. All of which would be very "do-able."
...
Weight budget? trying to keep it less than 20 pounds -- The fostex FE126E's are 2.22 lbs each. Given that the T Amp is around 1 pound, and batteries likely to be another, I should be well under the weight requirement If i used those.

Although I have not heard this driver, it is universally liked by those who have paired it with t-amps.

The weight of this enclosure could become significant, determining whether you bother to lug it around sometimes. You might consider optimizing the dimensions of the boxes for least amount of material (for same internal volume), making them wider, less deep, and shorter. The shape of the front baffle is less relevant anyway, since the center of the box will be on the same plane as the baffle.

Choice of enclosure material is critical here also. MDF weighs more than plywood, which weighs more than hardwood. Are you considering higher tech alternatives? Plastics? Fiberglass?

I assume that BR type enclosures are more subject to resonances than larger boxes. The heavier materials are less subject to resonance. Anyone know what would be the best compromise here?

Source? I was planning on using my ipod. They sell interesting little IPOD docking stations with line outs that have a simple IR controller that you can use to change tracks, and increase or decrease volume ... perhaps I could use that as my volume device. You can find these on ebay for around $20. Otherwise a simple steel volume nob on the top front of the unit could work.

No doubt the electronically controlled pots are a pretty serious compromise of sound quality. Personally, I wouldn't see enough convenience from the IR control to go that route.

Randy

[ervington]

I have been working out how to solve this exact "problem"...i would like a boombox to take with me to ultimate frisbee tournaments (all day long outdoor affairs played with teams). Lots of people bring music to the field, but they bring it in the form of a walmart cdp boombox...you can't even hear the thing when you're sitting next to it...as if you would want to anyway.

My question on these lines...how big a deal is it to run the speakers on the same front baffle? Would your enclosure have two separate chambers? Maybe the discussion hasn't gotten here yet, or maybe I'm a moron for not knowing the answers. What about a box in which you made two separate front baffles by angling them slightly outwards? That would have the benefit of giving you non-paralell sides, too....

Excited to be reading everyone's ideas on this. My project is not the hifi adventure delaseppes is taking on...I'm doing it the free way using 5-1/4" car speakers that used to be in my girlfriend's car and some leftover MDF...heavy, I know, but free. Not trying to hijack this thread, though...just trying to learn from other's projects.

[el`Ol]

Spectrumaudio have a 5" Altec-Lansing for really small enclosures, good sensitivity, but not much bass. Price is low, even in Germany, probably you get them for an apple and an egg in the US.