I was pleasantly surprised by the internal speaker in the FTDX101D. It was pretty good for a built in speaker. Why do you need an external speaker at all?

I wanted to take advantage of the dual receive, especially on CW. You can set the receivers to track each other; then set one for 300 Hz (You did buy that accessory filter, right? It works great!) Then set the second receiver for 3 KHz (or 1.2 KHz). Place the speakers widely separated on either side of the radio. This makes a sort of stereo effect on your run frequency. You can still pick out the rare one you want, while hearing any off frequency calls you might want to focus on. Also, in any mode working split, you can easily adapt to the spatial separation of transmit and receive frequencies. You lose the spatial separation adbantage with only the one internal speaker. I don't like headphones, they mess up my hair, and can get sweaty in hot weather. This hack fixes all that, without spending a lot of money. I got hooked on dual receivers with my beloved Ten Tec Corsair with external VFO and its blend feature to receive both VFO A and B.

I found this speaker recommended on the forums for the FTDX101MP. This speaker mounts without modification in the external SPS-101 Separate External Speaker and Power Supply for the 200 watt MP model. It seems a little crazy to pay $220 for the SP-101 accessory speaker and immediately gut it and put in a new speaker for $11 that is better than the original, but this one fits there too. The eham reviews confirm this. https://www.eham.net/reviews/view-product?id=14965
NOTE: It will not fit inside the FTDX101D transceiver cabinet. However, if you go to the thrift store and get a wooden speaker box or cheap boom box speaker cabinet with the same size speaker inside, you can install this one in that external enclosure or build your own box. Get two, for both receivers in the FTDX101.
NOTE: The manual for the FTDX101 specifies a 4 to 8 ohm load. The one recommended on the forums is 8 ohms. The one I am recommending here is 4 ohms, and will give you higher volume output, with the other specs identical.

I bought mine from Parts Express, about the same price as Mouser, but cheaper than Amazon. The Amazon version is 8 ohms and has less output because of the FTDX101 audio stage design. The FTDX101 has only 2.5 watts maximum into 4 ohms @ 10% THD, and requires a speaker of above average efficiency to be loud enough. 8 or 16 ohms is less volume.

Places to buy the Visaton R10S 4" Full-Range Speaker 4 Ohm:   (from Parts Express)   (from Mouser)

 

This speaker has exceptional specs for its price. It is popular for small guitar amps and PA systems. It has a big magnet, 20 watt power rating, and an efficient 90 dB sound output. The frequency response is quite flat, with a little boost in the speech/presence rise range at 3 KHz. It should be great for most SSB, CW, and AM, if you don't expect anything below 150 Hz. This speaker is less than $11 plus shipping. The wiring lugs on this model may not fit the existing Yaesu plugs on one side. You can change the Yaesu plugs on the wires to match the speaker if needed. Here is a complete how to install video with a demo of the improved sound: Yaesu FTDX101MP Speaker Upgrade by K9KJ

View the nice flat frequency response for yourself, and decide:   (R 10 S - 4 Ohm Page at Visatron)   (Data Sheet)

Here's a cheaper ($190) speaker/enclosure option to the Yaesu SP-101 that DX Engineering sells that comes highly recommended for SSB: Phonema Miranda S Speakers MIRANDA-S

The bhi is only $73 and gets good reviews. 4 inch driver with 1 inch tweeter. Same design as the one which has the amplifier in it. bhi Extension Speakers EXTSPK25

If you want an ACTIVE speaker with electronics like filters and a DSP noise reduction and 50-4,300 Hz response, bhi has this one for $310. bhi Ltd DSP Speakers DESKTOP-MKII
But your radio already has pretty good DSP and filters you can adjust.

Most amateur signals will not be below 150 Hz, unless you are doing ESSB or real hi fi AM. If you need more, you will need a more expensive, sophisticated studio monitor speaker, which won't fit in either the Yaesu SP-101 matching speaker ($220) or the FTDX101MP SPS-101 power supply/speaker. If you opt for an audiophile stereo speaker, try to keep it 4 ohms for more sound, and be aware that inefficient stereo speakers may require an active speaker or audio amplifier. The FTDX101 has only 2.5 watts into 4 ohms @ 10% THD. Good computer speakers might work, but beware of RF getting into them.

Damon, KJ7E, also recommended using an external speaker/enclosure for the FTDX-101MP. You can see his YouTube video about the subject. He chose to use the Yamaha MSP5 Studio Monitor ($275), which is available from Amazon.

Often you can score a cheap stereo at a garage sale or thrift store with an EQ and an amplifier. The FTDX101 does not have an EQ for receive. This hack will allow you to fine tune your receive sound for much less than the expensive SP101, which has no EQ. I like to shop at thrift stores for speakers, and I get pretty good deals sometimes. See my Best Speakers for Ham Radio article.

This is an example of a thrift store enclosure I bought for $20 a pair; it shows the R 10 S 4 ohm Visation speaker (about $10) with some standard fibreglass house insulation to damp resonances. It is a much cheaper alternative to the Yaesu SP-101. I built two of these for the dual receive of the Yaesu FTDX101D. They have a bright presence rise which makes for very intelligible SSB reception, and really sparkles on wider band ESSB. Even wider AM signals sound less muffled than the internal speaker. CW is crisp and clean, with no unwanted resonances. I had intended to use an external equalizer and amplifier, but this project has made that unnecessary. As I said earlier, the low end may not have boomy bass, but neither does the internal speaker or the SP-101. If that is what you want, you will need a more expensive studio monitor style speaker.

My other articles about the FTDX101D