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tomana 13th October 2012 04:06 AM

Please Help me chose the right speaker
 
1 Attachment(s)
I have a Crate Taxi 30 guitar amp (30W rms + boost switch) that uses a TDA-1560Q car radio output amplifier chip. Since this Crate is a battery powered street amp, I figured they opted for this chip so the amp could provide a decent volume level and long run time on a sealed lead-acid 12V battery. This it does extremely well. As for sound quality ... meh.

The amp is 14 years old and the original Crate speaker distorts at high volume when I play the low E string (82Hz) so I figured it might be time for a new speaker? This amp was originally intended for use with an electric guitar, not the electric acoustic I am using (Alvarez AD60SC with Yari 600TMk II Pre-Amp; I use the saddle piezo pickup blended with an Alvarez sound hole pickup). There's also an independent dedicated vocals channel on this amp. The cabinet is a sealed particle (pressed) board and has a small port cut out on the front speaker board. There is also a 2" piezo tweeter.

Woofer: Crate Custom Design 8, 8 ohm, 50 watt 1 voice coil

It's a small cabinet (approx 14" x 12" x 12"). It is said that a HiFi full range speaker system "reproduces" sound and a guitar speaker system "produces" sound. I'm guessing an acoustic guitar would want an amp that does reproduction but would the circuitry work well with a Full Range speaker (please see attachment)

Also, I play drop D tuning a lot (low E lowered to 41Hz)

What reliable replacement speaker would be the best choice for an acoustic guitar with pre-amp and a handheld Shure 57 mic setup?

picowallspeaker 13th October 2012 05:16 AM

An amplifier just amplifies ! The difference between a guitar amp and an hi-fi amp is that the second should follow the standard requirements that are :
linearity in the whole bandwidth 20-20000 Hz .
Instead, a guitar amp can be set to suit to your taste. In particular , the TDA-1560Q ,if you read the datasheet and watch the figures :) , hasn't
a very good behavior at low frequencies...but that's a particular chip that
works in H-class , that means that it switch to a higher voltage rail ( self-produced by an internal DC-DC converter, I guess ...) when the demand of power asks it for . Of course at high power it 'sags' -which is the same as 'distorts' - so the (electrical) waves at its input are not the same at the output.

Distortion from the amp is often searched, like the overdrive ...but that
characteristic is given by tube amplifiers , which behave different when saturated . So, maybe you're right about an acoustic guitar that would
need a 'more hifi' setup to play ,in the terms of no coloration of the sound.
Maybe...if you have 24 VDC for supply instead of 12 V , you have more headroom . A good amp starts from the supply side ;)

tomana 13th October 2012 07:22 AM

thank you for that great reply. I did read the data sheet, and saw how past a certain percent output power, the onboard power doubler kicks in. But the distortion I am getting is speaker break-up, and only on the lowest frequency (approx 80Hz - 100Hz).

picowallspeaker 13th October 2012 09:52 AM

I don't read any great reply :o

I once saw a portable amp and the speaker in the little box was
about 4" but with a huge magnet - that guarantees high efficiency, especially
in the mid frequencies .

A 1" voice coil means that it would have a good response at mid-hi frequencies
because the wavelenght corresponding to those happens to be emitted by the centre of the cone ,not by its peripherial area ( also : the higher the frequency, the stiff part of a loudspeaker is still in the centre ,as it doesn't deformate )

I don't understand the term 'break-up' : usually it is referred to as when the speaker looses linearity due to the mechanical limits, but this happens at mid-hi frequencies . It may be possible that the driver is not in good condition,
so a try with a good one would take any doubt away; from the pick-up to the transducer, it may be everything ...!

Enzo 13th October 2012 11:19 AM

Do yourself a favor and disconnect the existing speaker, and play this amp through some other speaker cab. That will show you how much of this distortion is really the speaker, and how much is a speaker reproducing the distorted output from the amp. You could find that the aging battery is no longer able to hold up under low frequency demands.

sreten 13th October 2012 03:05 PM

Hi,

Something like :

Celestion K8T-100 100W 8" 8 Ohm Loudspeaker Driver 22.58 IN STOCK (13 Oct 2012)

or

IMG Stage Line SPA-8PA 8" Loudspeaker Driver 22.63
http://monacor.co.uk/products/speake...-8/vnr/105260/
(Very nicely built driver for its price ....)

or

Celestion Truvox TF0818 8" 150W loudspeaker driver 8 Ohm from Celestion 33.88 IN STOCK (13 Oct 2012)
http://www.parts-express.com/pe/show...umber=294-2060

rgds, sreten.

tomana 13th October 2012 08:24 PM

thanks for all the info

sreten 13th October 2012 08:44 PM

Quote:

Originally Posted by tomana (Post 3200376)
I can get a Celestion TF0818MR for about $45 shipped, and they claim that
the sealed basket means it will work just as well in my 14 x 12 x 12 cab as
in a larger enclosure. Is this true? If so, this could be the ticket.

Hi,

Celestion Truvox TF0818MR 8" 100w loudspeaker driver 8 Ohm from Celestion 19.99+VAT IN STOCK (13 Oct 2012)

Whoever "they are" they are complete idiots, it will work just as badly as a
bass/mid in your cabinet as it would in any cabinet as its a sealedback mid.

http://celestion.com/product/111/tf0818mr

Utterly dreadful advice, its beyond being a bad choice, its a totally
wrong choice for the application and simply won't work at all.
No bass below 400Hz = a unmitigated disaster area.

rgds, sreten.

Drop D is about 37Hz on a bass, 74Hz on a guitar, fundamentals.
What really matters is output of the 2nd harmonic, 147Hz for guitar.

sreten 13th October 2012 09:23 PM

1 Attachment(s)
Hi, PDF of the mid, the link won't work, rgds, sreten.

tinitus 13th October 2012 10:15 PM

Quote:

Originally Posted by sreten (Post 3200073)
]IMG Stage Line SPA-8PA 8" Loudspeaker Driver
(Very nicely built driver for its price ....)

or a good look-alike

to suggest a good speaker for especially acoustic guitar, I would say you really should know the driver from personal experience
with acoustic guitar and not something else
its unpredictable without


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