Fostex FF105WK 4" full range have very high impedance, would an amp w/o load dependency be good?

[ampguy]

At one of my desks I use, as a roon endpoint, and for computer audio, some 4" Fostex FF105WK full range drivers in a Kanspea enclosure. They work great, and I'm driving them with a Fosi v3, sound is good to great. However, I know the Fosi v3 has a load dependency, and we now have relatively inexpensive Class D amps w/o load dependence, one that I found is the SMSL D6, which while old, and less power, and lesser specs in other areas than the Fosi, apparently doesn't have load dependency.

I am not chasing super high S/N as either my music or tastes generally favor Class A/B amps or some class D amps that have reviewed very poorly in that area (SMSL A300). Curious as to what others thoughts are on what I might hear from a Class D amp with no load dependency with speakers that are ver high impedance, min 8 ohm, up to 85 ohms at 70Hz or so. ?

Fostex FF105WK 4" Full Range

Fostex FF105WK 4" Paper Cone Full Range. Full range driver available. Single driver solution, no crossover needed. Contact Madisound.

www.madisoundspeakerstore.com

 

[DanielT]

Until someone else answers, a bit OT:

Add a (small?) subwoofer instead. That Fostex FF105WK full range doesn't like reproducing low bass frequencies. Fostex FF105WK has only 10 watts RMS / power handling. Stroke, x- max ....what does it say 1.7 mm? That can't be right? It should be at least 17 mm x-max. I think so but I could be wrong.
Fostex FF105WK technical data:


A small subwoofer, if you have the opportunity to place it near the speakers so they mask the sound of the sub (mask the direction of where the bass is coming from) and if you find a sub that can operate up to around 200 Hz should be a yummy solution.
HP- LP filter. A 24 dB LP filter if you are going to crossover as high as 200 Hz is good to have.
I have been using exactly that type of desktop setup with a pair of small Audio Pro Avanti A.1 satellite speakers plus a Yamaha YST-SW150 sub placed between them, crossover via active crossover set at 200 Hz (24 dB filter) plus WiiM RoomFit(automatic room correction) for a few days now. Works perfectly.

The subwoofer rolls off at 200 Hz, I have checked that it works and set it that way, via my active crossover.

Since your Fostex FF105WK has 10 watts RMS, if I were you, I would have chosen a cheap low power class D amp. BUT with one with PFFB filter. That's mostly because I could never imagine a class D amp without PFFB filter. I want to be on the safe side. However, in your specific case, someone else will have to help you with that.

Do you want a small, physically small, class D amp or can you imagine a class AB? Which usually is physically larger, even those with little power.

Edit:
I'll give my opinion on your question anyway. The combination of your amp and your speakers. IF your speakers have the impedance curve shown in this graph:

At 70 Hz, the Fosi Audio V3 does not show any load dependence, so there's nothing to worry about then. Around 10 kHz with your speakers then around 10-12 Ohm. What can it give with your Fosi v3...about 0.5 dB extra boost from what I can see. Barely audible, super good hearing to detect it is needed.
If your speakers had a peak of let's say 30 Ohm or more around 6kHz-10 kHz then maybe but they don't.
Fosi Audio V3:

 

[ampguy]

Thanks. I do have some subwoofers, but my goal here isn't full range at the low end, I have other systems and monitoring headphones if needed. I want nice mid/high accuracy. The bass from this is not from the driver, but the cabinet it's in. There's a whole design ecosystem around that to get usable frequencies down to 150Hz or so with the cabinet the Fostex is housed in.

Until someone else answers, a bit OT:

Add a (small?) subwoofer instead. That Fostex FF105WK full range doesn't like reproducing low bass frequencies. Fostex FF105WK has only 10 watts RMS / power handling. Stroke, x- max ....what does it say 1.7 mm? That can't be right? It should be at least 17 mm x-max. I think so but I could be wrong.
Fostex FF105WK technical data:
View attachment 479576View attachment 479577

A small subwoofer, if you have the opportunity to place it near the speakers so they mask the sound of the sub and if you find a sub that can operate up to around 200 Hz should be a yummy solution.
HP- LP filter. A 24 dB LP filter if you are going to crossover as high as 200 Hz is good to have.
I have been using exactly that type of desktop setup with a pair of small Audio Pro Avanti A.1 satellite speakers plus a Yamaha YST-SW150 sub placed between them, crossover via active crossover set at 200 Hz (24 dB filter) plus WiiM RoomFit(automatic room correction) for a few days now. Works perfectly.
View attachment 479575
The subwoofer rolls off at 200 Hz, I have checked that it works and set it that way, via my active crossover.

Since your Fostex FF105WK has 10 watts RMS, if I were you, I would have chosen a cheap low power class D amp. BUT with one with PFFB filter. That's mostly because I could never imagine a class D amp without PFFB filter. I want to be on the safe side. However, in your specific case, someone else will have to help you with that.

Do you want a small, physically small, class D amp or can you imagine a class AB? Which usually is physically larger, even those with little power.

Edit:
I'll give my opinion on your question anyway. The combination of your amp and your speakers. IF your speakers have the impedance curve shown in this graph:
View attachment 479586
At 70 Hz, the Fosi Audio V3 does not show any load dependence, so there's nothing to worry about then. Around 10 kHz with your speakers then around 10-12 Ohm. What can it give with your Fosi v3...about 0.5 dB extra boost from what I can see. Barely audible, super good hearing to detect it is needed.
If your speakers had a peak of let's say 30 Ohm or more around 6kHz-10 kHz then maybe but they don't.
Fosi Audio V3:
View attachment 479585

 

[DVDdoug]

Higher speaker impedance usually isn't a problem. Impedance and resistance are "the resistance to current flow" so higher impedance means less current and less stress on the amplifier.

If the voltage remains constant with varying load impedance (which it usually does), current and power are inversely proportional to impedance. At 8 Ohms you typically get half the power as 4-Ohms. If not, it means the amplifier is current-limited with a 4-ohm load.

Speakers are tested with "constant voltage" so although a speaker might be "pulling" less power at frequencies where the impedance is higher, the frequency response is not affected. At frequencies where the impedance is low a current-starved amplifier might clip sooner (lower) than expected but it doesn't affect frequency response.




...With higher impedance headphones, you sometimes can't get enough current & power to go as loud as you want, and in that case you need a headphone amp with more voltage-output.

 

[burkm]

Until someone else answers, a bit OT:

Add a (small?) subwoofer instead. That Fostex FF105WK full range doesn't like reproducing low bass frequencies. Fostex FF105WK has only 10 watts RMS / power handling. Stroke, x- max ....what does it say 1.7 mm? That can't be right? It should be at least 17 mm x-max. I think so but I could be wrong.
Fostex FF105WK technical data:
View attachment 479576View attachment 479577

A small subwoofer, if you have the opportunity to place it near the speakers so they mask the sound of the sub (mask the direction of where the bass is coming from) and if you find a sub that can operate up to around 200 Hz should be a yummy solution.
HP- LP filter. A 24 dB LP filter if you are going to crossover as high as 200 Hz is good to have.
I have been using exactly that type of desktop setup with a pair of small Audio Pro Avanti A.1 satellite speakers plus a Yamaha YST-SW150 sub placed between them, crossover via active crossover set at 200 Hz (24 dB filter) plus WiiM RoomFit(automatic room correction) for a few days now. Works perfectly.
View attachment 479575
The subwoofer rolls off at 200 Hz, I have checked that it works and set it that way, via my active crossover.

Since your Fostex FF105WK has 10 watts RMS, if I were you, I would have chosen a cheap low power class D amp. BUT with one with PFFB filter. That's mostly because I could never imagine a class D amp without PFFB filter. I want to be on the safe side. However, in your specific case, someone else will have to help you with that.

Do you want a small, physically small, class D amp or can you imagine a class AB? Which usually is physically larger, even those with little power.

Edit:
I'll give my opinion on your question anyway. The combination of your amp and your speakers. IF your speakers have the impedance curve shown in this graph:
View attachment 479586
At 70 Hz, the Fosi Audio V3 does not show any load dependence, so there's nothing to worry about then. Around 10 kHz with your speakers then around 10-12 Ohm. What can it give with your Fosi v3...about 0.5 dB extra boost from what I can see. Barely audible, super good hearing to detect it is needed.
If your speakers had a peak of let's say 30 Ohm or more around 6kHz-10 kHz then maybe but they don't.
Fosi Audio V3:
View attachment 479585

The mentioned frequency response stems from an early example of the V3 Monos, as measured by Amir. Production samples are much more constant in frequency response due to a different PFFB, which had been adapted lateron for "normal" production as mentioned by a Fosi Audio employee.

 

[ampguy]

The mentioned frequency response stems from an early example of the V3 Monos, as measured by Amir. Production samples are much more constant in frequency response due to a different PFFB, which had been adapted lateron for "normal" production as mentioned by a Fosi Audio employee.

Are you sure? It looks like he reviewed the original V3 stereo unit, the V3 mono is a different beast - https://www.audiosciencereview.com/forum/index.php?threads/fosi-audio-v3-amplifier-review.45757/

 

[DanielT]

The mentioned frequency response stems from an early example of the V3 Monos, as measured by Amir. Production samples are much more constant in frequency response due to a different PFFB, which had been adapted lateron for "normal" production as mentioned by a Fosi Audio employee.

In any case, it seems to be a general trend that more and more small class D amplifiers are getting sensible PFFB. At least the brands Amir tests. This one, for example, seems to be excellent:

3e Audio A5 Stereo Amplifier Review

This is a review and detailed measurements of the 3e Audio A5 Stereo class D amplifier. It was sent to me by the company and costs US $229.99. Despite its simplicity, the A5 has very well thought out features. Clipping indicators are provided for each channel. And selection of inputs is made...

www.audiosciencereview.com

In addition, acceptable, in my eyes, low distortion in the higher frequencies, which can otherwise be an Achilles heel for class D amplifiers.

I could easily consider buying the 3e Audio A5 if I were in need of a new amplifier, so I have nothing against class D amplifiers as such.

 

[KL....]

At one of my desks I use, as a roon endpoint, and for computer audio, some 4" Fostex FF105WK full range drivers in a Kanspea enclosure. They work great, and I'm driving them with a Fosi v3, sound is good to great. However, I know the Fosi v3 has a load dependency, and we now have relatively inexpensive Class D amps w/o load dependence, one that I found is the SMSL D6, which while old, and less power, and lesser specs in other areas than the Fosi, apparently doesn't have load dependency.

I am not chasing super high S/N as either my music or tastes generally favor Class A/B amps or some class D amps that have reviewed very poorly in that area (SMSL A300). Curious as to what others thoughts are on what I might hear from a Class D amp with no load dependency with speakers that are ver high impedance, min 8 ohm, up to 85 ohms at 70Hz or so. ?

Fostex FF105WK 4" Full Range

Fostex FF105WK 4" Paper Cone Full Range. Full range driver available. Single driver solution, no crossover needed. Contact Madisound.

www.madisoundspeakerstore.com

Thank you, the Fostex FF105WK full range driver is a nice driver, Fs= 75Hz, Qts=0.41, Re=6.7R, SPL=90dB (rather than 88dB, especially with that bump at 7-7.5Khz)

• Bookshelf.... with a well designed Vented Enclosure, without crossover, some quick maths (15L Box, Vent/50Hz/2.5x3.5cm), the Bass could extend down to about 50hz, couldn't it, perhaps even 45hz....
• or Floor Stander/Large Bookshelf.... make a nice Mid/Treble Driver at 100hz and use the natural Mechanical roll off (no crossover) and a simple 1st order crossover for the Woofer (150-200mm/8R, with a 90dB SPL to match). As a Mid/Treble Driver its power handleing would increase to about 35/40watts and an easy =>8R load.

 

[JeffS7444]

It's been awhile since I've had them, but IIRC I had the exact same drivers + Kanspea P1000E enclosures + Fostex mini-amp as depicted on Madisound's web site. Wish I had kept the amplifier, as it was really tiny, but I don't think there was anything special about it which would make it a better match with those speakers than any number of other small Class D amplifiers. I thought the sound was "peaky" with good voice intelligibility, but it could've benefitted a lot from some equalization.

 

[Vladimir Filevski]

Fosi v3 has a load dependency

No load dependency if you add Zobel RC, to get 8 ohms impedance above 10 kHz.

 

[burkm]

Are you sure? It looks like he reviewed the original V3 stereo unit, the V3 mono is a different beast - https://www.audiosciencereview.com/forum/index.php?threads/fosi-audio-v3-amplifier-review.45757/

The original V3 Stereo amp was without PFFB, the newer V3 Mono with PFFB and additionally somewhat higher output (same power supply).
I might have been irritated, because I thought that you mentioned V3 Monos. If it was V3 Stereo I surely made a mistake...

 

[ampguy]

The original V3 Stereo amp was without PFFB, the newer V3 Mono with PFFB and additionally somewhat higher output (same power supply).
I might have been irritated, because I thought that you mentioned V3 Monos. If it was V3 Stereo I surely made a mistake...

No problem, I’ll clarify Original stereo Fosi v3 next time.