Thoughts on modding Klein+Hummel O300 monitors

[monx]

Hey. I picked up a pair of KH O300 monitors a few months ago, and the previous owner had hotrodded them by replacing the woofer driver with a Dayton audio speaker of similar Thiele/Small parameters, stuffing the cabinets with batting, and affixing some thick sound damping foam inside the cabinet walls.

I'm in the process of reversing the modifications (I have the original KH drivers) but I wonder if there is some benefit from keeping the damping material. The cabinet is pretty loud when you knock on it, but I just wonder if that's all "priced in" to the factory calibration.

I took some casual measurements comparing the original cabinet vs. the hotrod cabinet and saw a significant difference, but take these with a grain of salt. The dayton mod has a 5 dB attenuation centered around 200 hz (extending between 80 and 400 hz), relative to the stock. (attached)

 

[AnalogSteph]

I imagine the damping material would slightly reduce the low end. Given that the O300 is a closed speaker, it should not have any dramatic issues with internal resonances to begin with. Instead of going overboard with foam and wadding, I'd think that getting more mass onto the walls (e.g. butyl mat) would be more effective if in doubt. But yeah, these Dayton drivers have to go, they are clearly detrimental (lower sensitivity and dip below crossover). You really have to wonder what some people are thinking. It's not like the O300 was built by amateurs.

BTW, your phase curves look funny because zero time calibration is off and needs an offset.

 

[dfuller]

I wonder if maybe a Purifi PTT8 would fit? If so, you will have basically as much SPL capability as the amp can provide. Expensive, though...

 

[monx]

I went ahead and reversed all the mods and removed the damping material. One of the issues was that the damping foam adhesive (sticky tape backing) wasn't really sticking to the rough interior walls and it caused some minor rattling at low frequencies. In order to remedy, it would have to be smeared with a more permanent adhesive. But I don't intend to keep them forever and want them to be close to factory as possible for resale. They still sound great, of course.

 

[bremusound]

Which Dayton woofers were installed? I‘m in need for spare woofers, tried some old Peerless but there‘s a dip at 250hz compared to the original ones… Thanks!

 

[monx]

RS225-8 8" Reference Woofer 8 Ohm​

Dayton Audio - RS225-8 8" Reference Woofer 8 Ohm

RS225-8 8" Reference Woofer 8 Ohm

www.daytonaudio.com

 

[bremusound]

Thank you!

 

[monx]

Happy to send these over if you pay shipping, but note that the previous owner shaved down the circumference of the basket to make them fit in the O 300 cabinets.

 

[bremusound]

That would be great! I‘m located in Germany, though. If that‘s not a problem, i will happily pay for shipping
Thanks again

 

[AnalogSteph]

Do note that the reason they are available in the first place is that they weren't a super great fit acoustically. The originals must be a fair bit more sensitive at the very least. I'm kind of not surprised, the RS225-8 has a fairly low fs of 28.3 Hz and its 86.8 dB/2.83 V sensitivity is a bit below average, kind of more of a subwoofery driver. Compare this to, say, the Peerless P22WO03-08 with a 46.7 Hz fs and consequently higher sensitivity of 90.34dB 2.83V/1m.

 

[bremusound]

Yes, i‘m aware they aren‘t perfect. Unfortunately i don‘t have the parameters of the original Peerless 830947 woofer

 

[AnalogSteph]

I mean, if @monx could be motivated to try and measure the TSPs of the originals, that would definitely give some clues... AFAIK it's not that hard.

 

[dfuller]

I mean, if @monx could be motivated to try and measure the TSPs of the originals, that would definitely give some clues... AFAIK it's not that hard.

Remind me at some point to measure the drivers in my 420s.

(I might also do something silly like see how the tweeter behaves sans integrated grille... More on that later)

 

[bremusound]

Thanks for the Youtube link - I could try to measure the one original woofer i have

 

[AnalogSteph]

Thanks for the Youtube link - I could try to measure the one original woofer i have

That's another option, of course. Note that this is just pretty much the first video I found, I hope it's decent. Here's what the "effing manual" for REW has to say:

Impedance Measurement

Thiele Small Parameters

 

[bremusound]

Thanks again! Will try it and post the results!