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PA 15" and built in amps?

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Rorut

Member
Hi,
I just got a couple of 15" passive PA subs for free.
Would like to get them running. Im offered to buy a pair of:
15" Celestion K15-H200
or 15"Celestion G15-150.
Price is about £70 for each pair. Dont know if thoose are good speakers...
I also would like to have built in amplifiers.
Class D, would be nice to keep weight as low as possible.
Any suggestions on a low budget solution?
Spekaers boxes looks like this:
IMG_7747.JPG
Would something like this work in each box?
http://store3.sure-electronics.com/1-x-500-watt-class-d-audio-amplifier-board-compact-t-amp
 
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dr pepper

Well-Known Member
Most Helpful Member
You know both those speakers k15 and g15 are for guitar, they will of course work with music but might not give great sound.
Celestion used to make good speakers, not sure these days I havent been in the bizz for 20 years.
Second hand price for good speakers without tears or loose coils is about right.
If you can have them for an hour or so to play with and make sure they are good that might be a deal.
 

Rorut

Member
Did not know about this, thanks. Maybe better go for other speakers for music. 4 ohms also seems more common on class d amps? Any suggestions on ok speakers not to expensive?
 

Nigel Goodwin

Super Moderator
Most Helpful Member
Did not know about this, thanks. Maybe better go for other speakers for music. 4 ohms also seems more common on class d amps? Any suggestions on ok speakers not to expensive?
You seem a little confused about impedances?.

Pretty well all PA amps are designed to feed 4 ohms - but most speakers are 8 ohms - the idea being that you can connect two speakers to the amp, to give 4 ohms total. Likewise, with a two channel amp, you can usually bridge it to give maximum power to a single 8 ohm load.

So it's nothing to do with class-D, it's a general design feature.
 

audioguru

Well-Known Member
Most Helpful Member
The size and tuning of the enclosure should match the detailed spec's of the woofer or the recommended enclosure designed by the woofer manufacturer should be used.
Oh, you want cheep, cluck, cluck? Then detailed spec's and a recommended enclosure design might not be available then the sub-woofer might sound boomy or have no bass.
 

Rorut

Member
Nothing that say what brand the enclosure is. Ok so there is no solution that is not very expensive? I understand, thanks
 

dr pepper

Well-Known Member
Most Helpful Member
Nope thats a music speaker, its resonance is quite low so it'll give good bass in a proper enclosure.
4 ohm is popular for car audio as it means you can get more power without a boost inverter for the power supply.
 

Rorut

Member
Nope thats a music speaker, its resonance is quite low so it'll give good bass in a proper enclosure.
4 ohm is popular for car audio as it means you can get more power without a boost inverter for the power supply.
That sounds great! So finding a set of original speakers seems difficult. Any suggestions on a similiar replacement?
 

tomizett

Active Member
As AG says (#6 above), in an ideal world you'd want drivers matched to the originals so that they interact with the box in the way that the designer intended.

However, we don't live in an ideal world - we live in a world where you've been given a pair of boxes and want to make a gig happen (it's ok, that's the world I live in, too). With this in mind, I wouldn't worry too much about what drivers you fit; in reality they cant be too far wrong. The most important factor is the free-air resonance - this should match that of the cabinet for what they call a "maximum power alignment". The problem is that we don't know the resonance of the cabinet, but looking at the data sheet (figure 8, assuming that's measured with the driver fitted in a cabinet like yours) it's around 50Hz. I think that many 15" drivers may be a bit below this, but not too far.

Personally I'd prefer an 8-ohm driver to a 4, as many amplifiers rated for 4-ohm seem to struggle rather more than I'm happy with at this impedance. This also gives you the option of slaving another passive 8-ohm box from each active one in future (in case anyone gives you another pair of cabs!). Also bear in mind that many of the amplifier modules that can be fitted to subs are run in a bridged configuration, which effectively halves the impedance, so many of them are only rated for 8-ohm in this context.

Essentially I'd look for a pair of used 15's in good condition and fit them. Good luck - don't forget to post pictures of the finished boxers!
 

tomizett

Active Member
Quick postscript - while I said "any" driver, I really wouldn't recommend you choose an "instrument" speaker - they are likely to be under-damped and excessively coloured (as per DrP in #3). Choose a speaker designed for PA if you possibly can!
 

Rorut

Member
Quick postscript - while I said "any" driver, I really wouldn't recommend you choose an "instrument" speaker - they are likely to be under-damped and excessively coloured (as per DrP in #3). Choose a speaker designed for PA if you possibly can!
Thanks Tomizett!
I think one box is about 85-90 litre.
So looking for a PA, 8ohms 3-400w with high sensitivity?
Do you think an amp line this one will work in each box?
http://m.ebay.com/itm/TAS5630-Subwo...3D361434980539&_trksid=p2056116.c100408.m2460
 

audioguru

Well-Known Member
Most Helpful Member
What will the speaker play? The 15" speaker is huge and powerful. It is made for very loud PA (Public Address) which is mainly voices, not music. Its resonance at 50Hz is much too high for it to be a good sub-woofer. Its response above 4kHz is almost nothing like most huge woofers.
An amplifier in the high power enclosure might be vibrated to death or ceramic capacitors in the amplifier might cause feedback (ceramic is microphonic).
 

Rorut

Member
I play mostly reggae and soul. Im not planning to use it in my home, would like to extend a active PA that I bring to clubs. If vibrations is a problem for the amp I can isolate it in a box outside the sub.
But you say this box or original woofer is not good for bass?
 

tomizett

Active Member
I'm not sure about that amplifier (in #13) - if it it only takes a 48V input then it can only deliver 140W into an 8R speaker, and you could certainly use more power than that.
More importantly, if you're interested in cutting down the weight then you want an amplifier with a built-in power supply (that takes mains electricity directly) otherwise you'll have to build a power supply, which will probably be large and heavy.

Vibration is an issue with inbuilt amplifiers, but I don't think I've ever seen one killed by it. Simply sticking everything that looks "wobbly" with some silicone rubber will almost certainly be adequate. I've certainly never come across feedback due to ceramic caps - if there was going to be a mic input then maybe, but in this case it won't be a problem.
 

Nigel Goodwin

Super Moderator
Most Helpful Member
What will the speaker play? The 15" speaker is huge and powerful. It is made for very loud PA (Public Address) which is mainly voices, not music.
PA is mainly music these days, and fairly little in the way of voices (and has been for decades) - voice only type PA systems use pressure horns, and make no pretence at providing low frequencies.
 

audioguru

Well-Known Member
Most Helpful Member
The ebay class-D amplifier is said to produce 600 Whats at a horrible 10% clipping distortion, when powered from 48VDC. 600 Watts into 4 ohms with no clipping is a sinewave that is 49V RMS which is 139V peak-to peak. The amplifier is probably bridged so each half of the bridge produces 139V/2= 69.5V RMS. But not when powered from only 48V! If the amplifier has low voltage losses then its output is 92V peak-to-peak which is 32.5V RMS that produces 265 Watts into 4 ohms or 135 Watts into 8 ohms without clipping. Then the true amount of power matches the low price.

Your speaker enclosures look like 50 years old ones in large hockey arenas. The "music" that is played is from an awful electronic organ with no bass. The speakers in local clubs are modern and the sub-woofers produce frequencies so low that you feel them. The old PA speakers wont doo dat. What will play ordinary high audio frequencies?
 
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