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Old 10th September 2012, 10:25 PM   #1
HiZ is offline HiZ
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Join Date: Sep 2012
Default Lack of bass

Hi, I've recently upgraded a lovely old bakelite radio with modern amp and two way speaker. Trouble is the lack of bass. I guess there are lots of reasons for this and id like to try and resolve it.

Its a table top radio with a 4" driver and due to the buttons and knobs the cabinet is not sealed.

How do i go about finding a solution?

Packing, sealing it up, different driver, ports etc all seem like options.

I realise this is a very open question but your help is much appreciated.

Thanks
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Old 10th September 2012, 11:22 PM   #2
tvrgeek is offline tvrgeek  United States
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The glib answer would be to add a sub.

What you have in an OB. Open Baffle. You will not get any frequency out lower that the distance from the front to the rear of the driver unless you can design some sort of enclosure inside the box. I'll let the full range experts suggest a driver. Stuffing is only going to buy a Hz or two.
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Old 11th September 2012, 12:07 AM   #3
sreten is offline sreten  United Kingdom
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Hi,

Open backed radios tended to use high Q drivers to compensate for
the open baffle off. They have poor efficiency higher up but are better
than using a higher efficiency driver that needs bass boost depending
on the power from the amplifier available.

The amplifiers in most old radios and TV's are not nominally flat, and
they are not suited to nominally flat speaker arrangements, they
were optimised to work best together, and the best versions
also compensated for for treble roll-off at the top end.

There is also the possibility it never did do bass and it can't.

rgds, sreten.

I'd recommend shelving EQ in the new amps feedback loop. Add
a series cap and resistor parallel to the lower feedback resistor.
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Last edited by sreten; 11th September 2012 at 12:21 AM.
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Old 11th September 2012, 10:24 AM   #4
HiZ is offline HiZ
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Quote:
Originally Posted by tvrgeek View Post
The glib answer would be to add a sub.

What you have in an OB. Open Baffle. You will not get any frequency out lower that the distance from the front to the rear of the driver unless you can design some sort of enclosure inside the box. I'll let the full range experts suggest a driver. Stuffing is only going to buy a Hz or two.
OK, thanks. The openings are at the font, near the knobs. The rear is sealed as I replaced the old hardboard stuff with a 5mm perspex sheet... maybe MDF would have suited more?

The cabinet is 6" deep. B3X95U 00F Radio Philips; Eindhoven tubes international!;, b and I have used this driver Visaton - Lautsprecher und Zubehör, Loudspeakers and Accessories fastended to a MDF adaptor ring needed to mount it correctly.
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Old 11th September 2012, 10:33 AM   #5
HiZ is offline HiZ
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Quote:
Originally Posted by sreten View Post
.........I'd recommend shelving EQ in the new amps feedback loop. Add
a series cap and resistor parallel to the lower feedback resistor.
Thank you. Im using this simple TDA2003 amplifier and have a circuit very similar to this (without the optional RC components shown dotted) 10W audio amplifier with TDA2003

I have swapped the 2R2 for 56R, to reduce the gain, allowing it to handle line level audio input. What values R and C would you suggest for this modification?

Thanks!
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Old 11th September 2012, 09:35 PM   #6
tvrgeek is offline tvrgeek  United States
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I am with Sreten on this one. A little EQ is about all you can do. A LITTLE. You need to be able to measure what it is doing to see where you can add just a tad. Past that, you are asking to do something that just won't work out. Do be careful messing with the feedback to be sure you don't effect the stability.
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Old 14th September 2012, 10:46 PM   #7
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The damping of TDA2003 is too high...try whit a series resistor near 10 ohms...it will improve the low end...
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Old 14th September 2012, 11:24 PM   #8
tvrgeek is offline tvrgeek  United States
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Again? Series resisters do not magically produce bass. The make a better load for the amp, but you are now making your 10W amp a 4W amp. Try it, no harm.
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Old 15th September 2012, 12:21 AM   #9
zobsky is offline zobsky  India
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Quote:
Originally Posted by HiZ View Post
Hi, I've recently upgraded a lovely old bakelite radio with modern amp and two way speaker. Trouble is the lack of bass. I guess there are lots of reasons for this and id like to try and resolve it.

Its a table top radio with a 4" driver and due to the buttons and knobs the cabinet is not sealed.

How do i go about finding a solution?

Packing, sealing it up, different driver, ports etc all seem like options.

I realise this is a very open question but your help is much appreciated.

Thanks
+1 on what Sreten said. You might have better luck with a Higher Qts speaker, such as a car audio speaker. I wouldn't recommend sealing up the back of this radio if those holes are meant for ventilation
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Last edited by zobsky; 15th September 2012 at 12:25 AM.
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Old 15th September 2012, 10:53 AM   #10
HiZ is offline HiZ
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I've tried a reasonable car speaker but still could do with more oomph. Can i not add some capacitance to the negative feedback loop to reduce the upper frequency gain? Or... add an RC network to the line input to reduce the upper frequency gain..

The overall gain then be lifted.
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