Hey Guys, first post here, excluding my intro post.
I recently came across a pair of JVC G-Max boombox speakers. They're 3-way bass-reflex type speakers. I'm working on converting them into a pair of bookcase speakers with separate sub. I used them last year at school with an old home theater reciever and very much liked the sound, although the dual 120W subs were overpowering, so I had to cut the bass way down.
Here's some specs of the speakers from the user manual:
Because the drivers are from a boombox, I've been unable to find the original driver specs, so designing a proper speaker cabinet from scratch is difficult, if not impossible. I decided to reverse engineer the existing cabinets by measuring the internal volume, and recreate it in a smaller bookshelf sized speaker. While using only one of the subs in the old cabinet as my subwoofer.
So here's my problem:
I calculated the volume of the mid/tweeter part of the original cabinet, which came out to about 300 in^3. Because the mid is 6" the best box dimension I've come up with is 8"x12"x3". The depth is what worries me. Am I doing something wrong?
The original cabinet had an internal wall separating the mid from the woofer. I measured only the mid side of the cabinet. Does the larger void on the sub side effect the mid, and do I need to account for it in the new cabinet?
I can post pictures if it helps.
I recently came across a pair of JVC G-Max boombox speakers. They're 3-way bass-reflex type speakers. I'm working on converting them into a pair of bookcase speakers with separate sub. I used them last year at school with an old home theater reciever and very much liked the sound, although the dual 120W subs were overpowering, so I had to cut the bass way down.
Here's some specs of the speakers from the user manual:
Code:
Speaker: SP-MXGA77
Type: 3-way bass-reflex
Speaker units:
Subwoofer: 13.5 cm (5 3/8 in.)
Main Woofer: 16 cm (6 5/16 in.)
Tweeter: 5 cm (2 in.)
Power handling capacity:
Subwoofer: 120 W
Main speaker: 60 W
Impedance:
Subwoofer: 6 Ω
Main speaker: 4 Ω
Frequency range:
Subwoofer: 30 Hz — 70 Hz
Main speaker: 70 Hz — 20 000 Hz
Sound pressure level:
Subwoofer: 73 dB/W•m
Main speaker: 86 dB/W•m
Dimensions (approx.):
290 mm x 317 mm x 336 mm (W/H/D)
(11 7/16 in. x 12 1/2 in. x 13 1/4 in.)
Mass (approx.):
5.5 kg (12.2 lbs) eachSo here's my problem:
I calculated the volume of the mid/tweeter part of the original cabinet, which came out to about 300 in^3. Because the mid is 6" the best box dimension I've come up with is 8"x12"x3". The depth is what worries me. Am I doing something wrong?
The original cabinet had an internal wall separating the mid from the woofer. I measured only the mid side of the cabinet. Does the larger void on the sub side effect the mid, and do I need to account for it in the new cabinet?
I can post pictures if it helps.
Hi,
You have the active biamping c/o specs ?
You cannot simply remove half the subwoofer because "its too loud",
That is irrelevant with active bi-amping. Your chucking away 6dB
of bass capability, and with a 5" driver that is inevitably limited.
rgds, sreten.
You have the active biamping c/o specs ?
You cannot simply remove half the subwoofer because "its too loud",
That is irrelevant with active bi-amping. Your chucking away 6dB
of bass capability, and with a 5" driver that is inevitably limited.
rgds, sreten.
Hi ,
It is better to keep as is, a 3 ways. A 2.1 gives less good sonic result.
The problem it is an active system. if you go to passive you need to add a new subwoofer which can do 86dB...
I think it's better to built or to buy a new speaker. There are a lot of nice projects on the internet.
See Speaker Kits: Madisound Speaker Store
Regards.
It is better to keep as is, a 3 ways. A 2.1 gives less good sonic result.
The problem it is an active system. if you go to passive you need to add a new subwoofer which can do 86dB...
I think it's better to built or to buy a new speaker. There are a lot of nice projects on the internet.
See Speaker Kits: Madisound Speaker Store
Regards.
Sorry, I should have mentioned that the original amp is dead, the boombox was rescued from a flooded basement.
Each of the 2 cabinets has 2 sets of wires, 1 for for the mid/tweeter, and 1 for the sub. I had the 2 sets of wires wired in parallel into the audio receiver, as it didn't have a sub output. Because of that setup the sub was receiving full spectrum audio, and was "too loud" (I had it plugged into a TV for awhile, and you could here it thumping from across the street). I ran the audio through a 3-band EQ and cut the bass down almost completely to compensate.
I'm planning on getting a cheap t-amp to power the speakers this fall, because the receiver is to big to drive down to college with (don't worry, once I have an actual income again I'll buy a decent amp). Which is also why I want to rebuild the cabinets, as an attempt to make then a little more compact.
Each of the 2 cabinets has 2 sets of wires, 1 for for the mid/tweeter, and 1 for the sub. I had the 2 sets of wires wired in parallel into the audio receiver, as it didn't have a sub output. Because of that setup the sub was receiving full spectrum audio, and was "too loud" (I had it plugged into a TV for awhile, and you could here it thumping from across the street). I ran the audio through a 3-band EQ and cut the bass down almost completely to compensate.
I'm planning on getting a cheap t-amp to power the speakers this fall, because the receiver is to big to drive down to college with (don't worry, once I have an actual income again I'll buy a decent amp). Which is also why I want to rebuild the cabinets, as an attempt to make then a little more compact.
One simple solution i see is to add a simple inductor on the woofer to lower high frequency output. for a 4ohms woofer L=10mH.
10mH 18 AWG I Core Inductor
10mH 18 AWG I Core Inductor
Yes, thank you, I've looked into using an inductor as a low pass filter for the sub.
However may I move us back to my original question:
However may I move us back to my original question:
Also I think I may have posted in the wrong section as my setup doesn't really have a physical crossover. Mods feel free to move it if you wish.
It is the good section. Ok i have some problems with your unit, not SI. 300in^3 ~ 5Liter is not a lot for a 6" but sufficient when use as a midrange. A 6-7" usually works in 15-35Liter BR box. I don't think you can reduce the volume of the box easily. 5 Liter is good for a 4".
Second we don't know what are the active corrections ? In active you can reduce a lot volume of speakers because equalizations are easy.
I think to make a complete reverse engineer, it will better to measure T/S parameters and to know active corrections.
Hope this helps.
Second we don't know what are the active corrections ? In active you can reduce a lot volume of speakers because equalizations are easy.
I think to make a complete reverse engineer, it will better to measure T/S parameters and to know active corrections.
Hope this helps.
Hi,
The "thump" is caused by allowing the the sub to overlap the bass mid,
it has nothing to do with how "loud" the sub is, because it isn't, its
sensitivity is a lot lower than the bass/mid.
The bass mid may be booming on its own if the actual design calls
for it to be high pass filtered. Seems you are not using the sub well.
Get an AV amplifier that somehow you can connect the sub out
to two spare channels for driving the subs and play with set up.
http://resources.jvc.com/Resources/00/00/97/22048ien.pdf
rgds, sreten.
The "thump" is caused by allowing the the sub to overlap the bass mid,
it has nothing to do with how "loud" the sub is, because it isn't, its
sensitivity is a lot lower than the bass/mid.
The bass mid may be booming on its own if the actual design calls
for it to be high pass filtered. Seems you are not using the sub well.
Get an AV amplifier that somehow you can connect the sub out
to two spare channels for driving the subs and play with set up.
http://resources.jvc.com/Resources/00/00/97/22048ien.pdf
rgds, sreten.
I'm thinking of getting another amp for the sub an plugging it into the sub-out of my soundcard, I can do internal EQ to cut out the high end.
I'm working on measuring the T/S parameters of my speakers, from this website: T-S Parameter Calculator
I still need to go back and get a more accurate measurement of the resonant frequencies.
An externally hosted image should be here but it was not working when we last tested it.
Also, to apologize, I realize that a lot of what I've talked about here would make any decent Audiophile cringe. But money is very tight at the moment, and I'm leaving for college in 4 weeks, so I'm just trying to do a quick project before I leave. And don't worry, I'm not modifying the original cabinet in any way. So if after I build new cabinets, and realize "wow these suck", I can always go back to the original 3-way speaker cabinet.
well this is annoying, I came back today to finish working on the t/s parameters, and all my ohm measurements don't match anymore. Yesterday I was able to go back to any frequency and receive the same measurement every time. I'm also not convinced my setup is outputting constant voltage (outputting from my sound card) across the entire spectrum, which may also be skewing my results.
T-S Parameter Calculator
While writing this I found some posts about AudioTester, so I'm looking into building the wiring harness for it. Hopefully it will yield more accurate results.
T-S Parameter Calculator
While writing this I found some posts about AudioTester, so I'm looking into building the wiring harness for it. Hopefully it will yield more accurate results.
Hi,
One of the issues is how the speakers are built. The front has two ports.
These are either both for the sub, making it a 6th order bandpass, or
the smaller one is for the bass/mid, making that a vented box and
the sub a 4th order bandpass, it is not clear from pictures.
Whatever, for the sub you should use both cabinets.
You could glue them back to back for force cancelling.
(A fair quantity of blutack is a reversible solution.)
Connecting them in series will drop levels from parallel.
If the sub is 6th order and really is boomy, close off the high pass port.
(You can't close off the low pass port, that will stop it working.)
rgds, sreten.
One of the issues is how the speakers are built. The front has two ports.
These are either both for the sub, making it a 6th order bandpass, or
the smaller one is for the bass/mid, making that a vented box and
the sub a 4th order bandpass, it is not clear from pictures.
Whatever, for the sub you should use both cabinets.
You could glue them back to back for force cancelling.
(A fair quantity of blutack is a reversible solution.)
Connecting them in series will drop levels from parallel.
If the sub is 6th order and really is boomy, close off the high pass port.
(You can't close off the low pass port, that will stop it working.)
rgds, sreten.
An externally hosted image should be here but it was not working when we last tested it.
Last edited:
Thanks for the info,
I had a write-up of the cabinets in detail, then I decided it's about time I posted pictures:
The speaker I haven't taken apart, with the wires shown, currently wired in series. The top left port is the sub port and the top right is the tweeter.
http://i55.tinypic.com/2qxc3k3.jpg
The other speaker with all plastic removed, showing the raised bass/mid driver, the sub port without the plastic riser, and the placement of the sub driver. The tweeter is free floating on the plastic front.
http://i54.tinypic.com/2100isk.jpg
The empty cabinet with all plastic pieces shown.
http://i53.tinypic.com/258cv48.jpg
All three drivers, right to left: sub, bass/mid, tweeter.
http://i56.tinypic.com/2sbjoxu.jpg
The backs of the drivers, showing the useless serial numbers.
http://i52.tinypic.com/mt15e0.jpg
The interior of the bass/mid compartment. It's a sealed cabinet, the sub port passes through it to the sub compartment behind it. The bass/mid and tweeter are wired in parallel, with a 2.2 uF cap wired into the tweeter.
http://i53.tinypic.com/1zdyhc3.jpg
The interior of the sub compartment. With the other end of the sub port shown.
http://i51.tinypic.com/1zgclt3.jpg
Another idea I had was to replace the ugly plastic front with a hardwood front, molded around the preexisting riser for the bass/mid, with a hole extending the sub port to it's proper length (although now I might try covering it up).
I had a write-up of the cabinets in detail, then I decided it's about time I posted pictures:
The speaker I haven't taken apart, with the wires shown, currently wired in series. The top left port is the sub port and the top right is the tweeter.
http://i55.tinypic.com/2qxc3k3.jpg
The other speaker with all plastic removed, showing the raised bass/mid driver, the sub port without the plastic riser, and the placement of the sub driver. The tweeter is free floating on the plastic front.
http://i54.tinypic.com/2100isk.jpg
The empty cabinet with all plastic pieces shown.
http://i53.tinypic.com/258cv48.jpg
All three drivers, right to left: sub, bass/mid, tweeter.
http://i56.tinypic.com/2sbjoxu.jpg
The backs of the drivers, showing the useless serial numbers.
http://i52.tinypic.com/mt15e0.jpg
The interior of the bass/mid compartment. It's a sealed cabinet, the sub port passes through it to the sub compartment behind it. The bass/mid and tweeter are wired in parallel, with a 2.2 uF cap wired into the tweeter.
http://i53.tinypic.com/1zdyhc3.jpg
The interior of the sub compartment. With the other end of the sub port shown.
http://i51.tinypic.com/1zgclt3.jpg
Another idea I had was to replace the ugly plastic front with a hardwood front, molded around the preexisting riser for the bass/mid, with a hole extending the sub port to it's proper length (although now I might try covering it up).
Hmmm ......
Somebody could not resist mangling the tweeter dome ....
Main thing to note is the tiny sealed bass/mid volume. This means
almost certainly without active bass roll-off it will boom like crazy.
It appears the front of the sub is not a bandpass AFAICT.
What you can do for the two sub boxes :
Blutack them back to back.
Line the ports with some thin open cell foam. 3xdia x length.
This will allow you to not need the extra moulded port extension.
The bass/mid drivers very likely need a larger box not to boom.
rgds, sreten.
Quite frankly it seems to me your chasing your tail. The c/o
is typical minimal garbage. I'd never ever make the effort
to build boxes for such basic stuff. Consult your local
small ads, buy a pair of real hifi speakers for peanuts.
Somebody could not resist mangling the tweeter dome ....
Main thing to note is the tiny sealed bass/mid volume. This means
almost certainly without active bass roll-off it will boom like crazy.
It appears the front of the sub is not a bandpass AFAICT.
What you can do for the two sub boxes :
Blutack them back to back.
Line the ports with some thin open cell foam. 3xdia x length.
This will allow you to not need the extra moulded port extension.
The bass/mid drivers very likely need a larger box not to boom.
rgds, sreten.
Quite frankly it seems to me your chasing your tail. The c/o
is typical minimal garbage. I'd never ever make the effort
to build boxes for such basic stuff. Consult your local
small ads, buy a pair of real hifi speakers for peanuts.
Last edited:
Hi, Or then again don't, it seems to me some form of mass loading, rgds, sreten.
Yeah, they came that way. It was one of the first things I noticed about the speakers.
Thanks a lot for all your info and suggestions, I'll keep my eye out for some used speakers. But for now, I'll make the final decision on these speakers when I'm finished measuring them. To see how annoying it would be to build cabinets for them.
Ultimately I'm using them this fall, as I don't have the time or money right now to go looking for new speakers.
I wrote something, how to measure T/S with SW
Thanks for the photos. These drivers are old technology. DIY is only for educational purpose. I know you money is short but making a box will cost more than the drivers. I had a special offer with similar drivers, sub + satellites in a box for 20$.
Thank you very much! That's exactly what I needed, I made the wiring harness last night based on that thread. It works great with Speaker Workshop, and AudioTester for that matter.
And I think you guys finally convinced me, I'm not going to go build a new cabinet. 😛
But I am at least going to look into making it look a little better by replacing the front. I think I've got some scrap hardwood lying around at home And I'll also look into making a passive LP filter or something for the sub out of parts I already have.
And I think you guys finally convinced me, I'm not going to go build a new cabinet. 😛
But I am at least going to look into making it look a little better by replacing the front. I think I've got some scrap hardwood lying around at home And I'll also look into making a passive LP filter or something for the sub out of parts I already have.
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