Lack of bass

HiZ · 10th September 2012, 09:25 PM

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

tvrgeek · 10th September 2012, 10:22 PM

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.

sreten · 11:21 PM

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.

HiZ · 11th September 2012, 09:24 AM

Quote:

Originally Posted by tvrgeek

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.

HiZ · 11th September 2012, 09:33 AM

Quote:

Originally Posted by sreten

.........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!

tvrgeek · 11th September 2012, 08:35 PM

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.

0feedback · 14th September 2012, 09:46 PM

The damping of TDA2003 is too high...try whit a series resistor near 10 ohms...it will improve the low end...

tvrgeek · 14th September 2012, 10:24 PM

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.

zobsky · 11:25 PM

Quote:

Originally Posted by HiZ

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

HiZ · 15th September 2012, 09:53 AM

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.

10th September 2012, 09:25 PM	#1
HiZ diyAudio Member Join Date: Sep 2012	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

10th September 2012, 11:07 PM	#3
sreten diyAudio Member Join Date: Nov 2003 Location: Brighton UK	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. __________________ There is nothing so practical as a really good theory - Ludwig Boltzmann When your only tool is a hammer, every problem looks like a nail - Abraham Maslow Last edited by sreten; 10th September 2012 at 11:21 PM.

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10th September 2012, 10:22 PM	#2
tvrgeek diyAudio Member Join Date: Dec 2009 Location: Md	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.

11th September 2012, 08:35 PM	#6
tvrgeek diyAudio Member Join Date: Dec 2009 Location: Md	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.

14th September 2012, 09:46 PM	#7
0feedback diyAudio Member Join Date: Feb 2010	The damping of TDA2003 is too high...try whit a series resistor near 10 ohms...it will improve the low end...

14th September 2012, 10:24 PM	#8
tvrgeek diyAudio Member Join Date: Dec 2009 Location: Md	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.

15th September 2012, 09:53 AM	#10
HiZ diyAudio Member Join Date: Sep 2012	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.