BMS 4550 experience

[Gibsonian]

In a triamp arrangement in the garage (my main system), I recently removed the upper mid/high section which consisted of a Pioneer midrange from DSS-9 speaker system and a Morel tweeter, can't recall the model exactly but is one of their more affordable high power handling ones. I believe MDT-308. It did include a 12 dB high pass filter for the tweeter, nothing for the mid as the electronic crossover handled that.

Anyhow I replaced this with the BMS 4550 compression driver and settled in on a Altec 810 horn after trying a couple other CD waveguides. Am crossing over from 12" mid/bass driver at around 1400 Hz. I have a T-filter on the 4550 and with RTA looks pretty darn flat, maybe slightly up a couple dB at 20 KHz, which I kinda like. (old ears, worn)

It sounds nice and on some recordings maybe better than my cone mid/dome tweeter arrangement and definitely handles loud passages with zero compression (one of the goals of this exercise), but some of the airiness is gone from the highs, which I miss. Is there any compression drivers out there that can supply the airiness of the dome tweeter, or should I look at other options, like ribbons, or back to dome tweets? I want my cake and to eat it too.

 

[bowtie427ss]

It's not the driver, it's the horn, assuming you actually meant Altec 811.

I don't mean to beat up on the 811. But, in all fairness it's the worst sounding small format horn Altec made. See if you can borrow a pair of 32B/ or C, MR931-12(will need CD eq), or a pair of Emilar bowties and try the BMS drivers on any of those.

Also, those are really sensitive drivers. Are you sure 12 db is enough pad?

 

[Gibsonian]

It's not the driver, it's the horn, assuming you actually meant Altec 811.

I don't mean to beat up on the 811. But, in all fairness it's the worst sounding small format horn Altec made. See if you can borrow a pair of 32B/ or C, MR931-12(will need CD eq), or a pair of Emilar bowties and try the BMS drivers on any of those.

Also, those are really sensitive drivers. Are you sure 12 db is enough pad?

Thanks for response bowtie. I tried 2 waveguides before the 811's, and the 811's won out for sound. The two I tried were Parts Express waveguides, a rectangular one and a 12" cone shaped one. I think many use them for the E-wave projects. So I did do some comparison, but maybe I should try some of your recommendations. I am triamping with electronic crossover so pad amount doesn't matter, I dial in the output from 4550 with level control on the crossover. The 12 dB I referenced in original post was the slope of the crossover between the mid and dome tweeter in the pre-BMS4550 setup. In passive crossover you are right, the 12 dB would not be enough pad to even it with the other drivers.

 

[Gibsonian]

810, yeah, I meant 811. Was only one off!

 

[bowtie427ss]

Again, it's not my intention to talk down the 811, it's a good horn, and more than adequate in the majority of it's applications.

I just feel that this particular instance is a case where the OP is reaching the 811's limitations, and they are getting in the way.

If i were in the market for a horn that has all of the qualities that the 811 gets right without the distortion artifacts that get in the way for some of us, and i wasn't in a hurry.................

Madisound gets 700 bucks each for those. A little spendy for my end of town.

But, if a fella is handy...................

http://techtalk.parts-express.com/f...on-plans-for-fostex-type-of-h400-wooden-horns

 

[GordonW]

The BMS4550 on one of the SEOS waveguides should just about best all comers, in their price range...

It will probably resolve a lot of the "spaciousness" issues- most of those are caused by limited dispersion at higher frequencies (which the Altec 811 definitely suffers from-pattern narrowing at HF). The SEOS should carry the HF to a wider pattern than most.Once the response is contoured to flat (constant dispersion waveguides inherently have a response that drops with increasing frequency, that has to be countered), it should be quite good...

If you weren't contouring the response on the Parts Express waveguides- that may be why the Altec sounded better. The, Altec, due to the narrowing of the HF response pattern, "squeeze" more HF energy into the on-axis region- they're louder at HF on axis, and therefore, will give flatter un-equalized response on-axis. Off axis, though- they drop like a stone at HF.

IME, a properly response-compensated constant-dispersion waveguide (such as those used in E-wave setups), gets closer to the "best of both worlds"- they dynamics of a horn, but still having decent off-axis response at all frequencies- HF included. It does require proper EQ or other methods of compensation...

 

[Gibsonian]

Here's a pic of the garage setup. I may go back and try the Dayton Audio waveguide, (rectangular one) as I did not try it with the optimized T-filter. I had removed it for the cone style Dayton waveguide before finishing, so could be worth another listen. Do you think the SEOS waveguide would be an upgrade over it? Below is the one I have.


The compression driver/horn combo has attained the dynamics goal for sure, just miss a little sizzle at the top. No more dome tweet compression or fear of blowing tweets during the longer and louder listening sessions. Could be what I am hearing is more honest, and maybe I prefer little white lies within my high notes?

 

[Gibsonian]

Another thought is that maybe the DSS9 mid/morel tweet combo was a damned good sounding mid/high combination.............