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When I bought a secondhand FT-7800R at Field Day 2017, I received an MLS-100 external speaker with it. I installed it recently and having the speaker more than an inch away from the radio's mounting surface is great.

I'd like to buy more external speakers, but the MLS-100 seems absurdly expensive (about \$45) for what it is: a 12W 4-ohm, unpowered mono speaker. I expected to be able to find a bulk pack of similar speakers for $10 on Amazon or ebay, but this is proving not to be the case.

  • Is there something that makes amateur radio speakers better or different than any other kind of unpowered speaker of equivalent wattage and impedance?
  • Is there a common term for such speakers? I've tried searching for "4-ohm mono speaker", but all I've been able to find are guides on how to get pick or install stereo speakers.
  • Is there a good reason I couldn't purchase something like this and expect it to work if I attach a mono audio cable to it?
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3 Answers 3

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Is there something that makes amateur radio speakers better or different than any other kind of unpowered speaker of equivalent wattage and impedance?

Some may have audio filters, headphone jacks, or other such application-specific features.

They could be somehow designed to be best at reproducing the frequencies important to intelligible speech, as opposed to a broader but overall lower frequency response or dynamic range for music, and you will see such claims but I don't know how true they are.

Is there a common term for such speakers? I've tried searching for "4-ohm mono speaker", but all I've been able to find are guides on how to get pick or install stereo speakers.

"Communications speaker".

Is there a good reason I couldn't purchase something like this and expect it to work if I attach a mono audio cable to it?

No, you should feel free to use any speaker of suitable impedance. Of course, that is just a driver without an enclosure, so technically it is not a complete speaker.

Note that in a mobile installation an important characteristic is whether you can get it loud enough to be heard over road noise without causing distortion. This will be affected by the impedance and efficiency of the speakers. A speaker that is poorly designed may not get loud enough without distorting (or rattling!)

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  • $\begingroup$ My 3D printer says that anything that makes sound is a complete speaker if I want it to be, but just searching for "communications speaker" came back with exactly what I was looking for and is less work than wiring up my own and printing/building an enclosure. Thanks! $\endgroup$
    – William
    Commented Oct 31, 2017 at 18:14
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    $\begingroup$ @William-Rem The enclosure can make a big difference in the sound quality, since every driver produces waves out the front and the back. You might want to read up on DIY speaker design before making an enclosure. Not my field so I don't know how much it will matter for this application. $\endgroup$
    – Kevin Reid AG6YO ♦
    Commented Oct 31, 2017 at 18:34
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    $\begingroup$ @William-Rem — the purpose of most enclosures is to get the waves that come out of the back of the speaker to head toward the front so that you get more sound. A sock would give you less. $\endgroup$
    – Pete NU9W
    Commented Nov 1, 2017 at 12:28
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    $\begingroup$ I suspect the sock would do almost nothing, actually. And a problem in general is the phase of the rear-pointing wave (which starts out inverted) — if you do redirect it forward you don't want cancellation at important frequencies. $\endgroup$
    – Kevin Reid AG6YO ♦
    Commented Nov 1, 2017 at 15:03
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    $\begingroup$ @William-Rem I suggest you get some with bass and treble controls, which are useful on mine (1 and 2 in the photo). Having said that, I have some really cheap ones without any, that might even be better than those old Altec-Lansings (which I bought years ago at a yard sale) that came with a subwoofer (not needed!). Nothing beats headphones. Mine are military surplus, and are perfect for communications, much better than hi-fi stereo music phones, earbuds, etc. $\endgroup$
    – Mike Waters
    Commented Nov 1, 2017 at 22:28
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Our choice of speakers are important.

They can make the difference between either hearing the other station clearly or straining to hear and missing part of the conversation.

But we don't need "special" speakers, that may be expensive and not even be very good.

The sound from the small tinny-sounding speaker in the top cover of that IC-765 under the monitor kept me from hearing the people that I was ragchewing with on HF SSB. So, I added those speakers, 1, 2, and 3. They are all connected to my transceiver. Tuning to any SSB signal on the HF bands, the sound from them is very clear and easy to understand. The same would be true for narrow-band FM signals.

W0BTU speakers

Speakers 1 and 2 are older Altec Lansing computer speakers. Even though they were not intended for amateur radio, they sound great and I highly recommend them! Get some computer speakers and try them.

Speaker 3 is an older Am-Comm Inc. digital ClearSpeech™ speaker. Most of the time, the digital noise filter is off, but it still adds a few highs that the computer speakers lack. Am-Com has since been acquired by another company which added several adjustable levels of digital noise filtering that made it an even better speaker (so others have told me).

This page on one of my websites explains the frequency ranges that are important for us to hear weak voice signals that are almost buried in the noise.

But good communications-style headphones are better than any speakers for hearing the weak ones!

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There are already two answers posted with good information but here is a little bit more information to help with your selection process.

Impedance

Matching the impedance of the speaker to the speaker impedance range specified for the audio amplifier (the transceiver in your case) is important in order to ensure a maximum power transfer from your radio to your ear. An improper impedance can also introduce distortion and potentially instability in a marginally designed amplifier.

SPL

Most speakers have a Sound Pressure Level (SPL) rating. This is an indication of how efficiently the speaker converts electrical power to acoustic power. It specifically is the sound pressure level measured at 1 meter from the speaker with 1 watt of excitation applied. The result is generally expressed in dB form. In general for a common speaker design, the larger the speaker, the greater the SPL.

A higher SPL indicates a more efficient speaker. This can be important for hearing the subtleties within the sound source as a lower SPL can render low level sounds as imperceptible.

Frequency Range

The frequency range of the speaker indicates what frequencies the speaker will reasonably reproduce. This area of characterization lacks standardization so often a close inspection of data sheets are in order to make comparisons. The general bass, mid range, and tweeter components used in audiophile systems are examples of speakers that are optimized for specific frequency ranges. The frequency range required for a specific amateur radio application depends upon the modulation mode. An standard SSB voice will be faithfully reproduced in a 200 to 2500 Hertz range. A CW signal can be used with a much narrower frequency range signal based on the preferred side tone frequency of the operator. An FM signal often has a wider response than standard SSB. Some deficiencies in frequency response can be overcome with a parametric equalizer added to the amplifier chain.

It should also be noted that a speaker with too large of a frequency range may prove annoying as it will be more prone to reproduce noise that is accompanying the desired signal.

Enclosure Design

The speaker enclosure can have a dramatic effect on the frequency response and in some cases, the effective SPL of the speaker. A common example of this is acoustic dampening within the enclosure. Wool will generally modify the mid range frequencies while felt will modify the low end frequencies. Other methods effectively alter the geometry of the enclosure for certain frequencies. Examples of this includes porting and acoustic foam. You will find a great deal of subjective and objective information on this topic on various audiophile sites.

From an amateur radio perspective, the enclosure may also play a role in keeping RFI out of the amplifier chain.

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    $\begingroup$ Modern audio amplifiers are not intended to be used in a matched impedance configuration but a bridged one. You should not use a speaker of matched impedance (such a system would see greater variations in frequency response), but one whose impedance is no lower than the amplifier's documented minimum load impedance (typically 4 or 8 Ω). The actual output impedance of the amplifier will be much lower than that. $\endgroup$
    – Kevin Reid AG6YO ♦
    Commented Nov 1, 2017 at 15:16
  • $\begingroup$ @KevinReidAG6YO Good point, Kevin. I will edit my answer to clarify. $\endgroup$
    – Glenn W9IQ
    Commented Nov 1, 2017 at 15:18
  • $\begingroup$ Thanks @KevinReidAG6YO. I actually thought you were supposed to match impedences of speakers, too. $\endgroup$
    – William
    Commented Nov 1, 2017 at 16:43
  • $\begingroup$ @GlennW9IQ - The Sound Pressure Level measurement isn't one I've seen before, but I suspect that's a result of always buying cheap speakers. Thanks for the answer. $\endgroup$
    – William
    Commented Nov 1, 2017 at 16:44
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    $\begingroup$ P.S. to the above -- I actually do not use cheap computer speakers anymore but rather a nice (and, relatively expensive) speaker from Elecraft as well as the Comms speaker from West Mountain Radio. $\endgroup$
    – K7PEH
    Commented Nov 2, 2017 at 17:01

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