Modding the Kenwood SP 820 speaker

[Justme]

So, as might be known, i got a new radio in the shack, the FT 991A added to the others.
I use the Kenwood SP820 speaker, must have cost a bundle in the good times, with 2 high off filters and a low cut filter and A/B input.

The 991A has the world of QRM/QRN noise fighting tools on board and a very good audio settable in bandwidth in each mode through the menu.
Never was happy with the low tones from the speaker, so i pulled it apart last weekend.
Very large metal box empty bar a el cheapo japan made 3 watt 5" speaker and some decent filtering.

I remembered i had a visatone broadband speaker bought new, 20 watt with large magnet 20 times the size of the original speaker magnet of the SP820 speaker and also 5 "
The Visatone speaker was quite expensive when i bought it, high efficiency and ultra low distortion speaker so that paid off after 4 years kept on the parts shelf.

So, replaced the el cheapo original speaker with the visatone ( straight from 80 to 10.000Hz), added acoustic foam to the empty steel cabinet, and tested things out, first by going to some stations on the Am broadcast band, and yes, less audio drive needed, clean crisp audio with body, and then tested it on several bands on ham stations from strong to weak ones, and what an improvement.
audio level input was 1/2 needed of the original speaker and the sound is very clean and a joy to listen too.
It was a bit of a bummer to see the original low quality speaker in that large cabinet though, they easily could have used a better speaker for a few bucks more.

I admit the visatone speaker might be overkill, but it sounds a dream, on the broadcast band i have deep lows and bass, easily filtered out for speech just using the low cut filter or internal settings in the 991A.
Just proves any chain is as strong as the weakest link....

 

[Captain Kilowatt]

That speaker was designed for communications and not fidelity. The two are not necessarily the same thing. I have the same speaker on my actual Kenwood TS-820S and have no complaints with it.

 

[Justme]

I accept that, problem is i want to hear the lows as well, if not needed i can simply by a push of the button filter that out.
Secondly having an more effective speaker you don't have to turn up the volume that high, and have spare volume not overdriving the audio chain.
Having an ultra low distortion speaker also makes the listening less tiring, and will be better in producing the natural voice clearly.
Some on SSB have real good audio with also not to pronounced low, with the original speaker not audible.

The FT991A has enough tools to set the receive audio as i please with a good speaker.
Point is that the speaker must have that whole range without distortion and high efficiency.
It is not so the coffee cups are dancing on the table when i use it with bass
For what it is, I'm satisfied with the change.
My radio comes on when i get up, and put off when i go to bed, used on all modes including FM where it certainly is a lot better as the original speaker.
listening to the radio most of the day i get less tired listening to the new speaker, and that is what counts.

Remember that the audio amps in our transceivers have 10% THD distortion on full blast, add 10% distortion of an el cheapo speaker as used original in the Sp 820 and you have a lot of distortion, with that speaker i have low distortion from the speaker, less needed drive from the audio amp = lower distortion as well.
It is not just Kenwood skimping on their speakers all brands do it, we mostly don't see it, so they get away with it and pay 100+ bucks for them.
Mine was a given one from an silent key, nothing lost there and the original speaker is still here.

You are satisfied with the original, also good.

 

[Captain Kilowatt]

I'm just speaking about using it the Kenwood TS-820S and there is NO problem driving it to a good volume with distortion as the audio in the Kenwood has plenty of headroom to drive it without running into distortion. I understand what you are saying but I am just pointing out what it was designed for versus what you want it for.

 

[Justme]

I understand your way of thinking.
It still is a communications speaker, when receiving amateur bands, just with much less loudspeaker distortion that can run 20 watts, and loafs with 1 watt in.

The TS 820 audio response was 400 to 2600 Hz, my FT 991 A will do from 100 to 3200HZ
That old speaker was matched to that, and now 30 years old.
The audiio amp in the TS 820 was 1.5 watt at 10% distortion my FT 991a is 2.5 watt at 10% distortion.
In the hybrid times audio might have not played such a big role looking at the audio response now it does and if possible with the least distortion possible.

Secondly the broadbanded speaker is not a bass speaker, and the limited bandwidth determined by the settings of the FT 991A will just do fine.
I build my own speakers in the good old Hi-Fi times, and know how much distortion a cheap speaker gives,
That wil make you tired listening to that speaker over longer times.

Not adding acoustic foam to the metal cabinet lets that same cabinet reverberate with the speaker output, causing more distortion, that is gone as well.

In Hi Fi amplifiers are good with 0.05% distortion, but adding a speaker with 10% distortion is not a good case , so that as the choice for the ultra low distortion broadbanded speaker meant for my own loudspeaker cabinet for the radio.

The SP 820 just came in handy to do the job after some audio tweaks to get the best in speaker performance and lower needed drive frrom the 2.5 watt amplifier in the FT 991 a, less output is less distortion there as well.

As stated above, if you are happy with your standard speaker, fine.
i just know my refurbished speaker sounds lot better now, even after 10+ hour listening to it on the busy HF bands.
and that I don't miss any details from high to low, be it in any mode.