Using Z-19 crossover with BMS 4550 drivers

Scott Becker

New Member
I have read several threads about Zilch and others liking the BMS 4550 drivers to replace the 802 on the 811b horn, but have not be able to find specific changes to his Z-19 crossover that may be required. Is there enough adjustment with the way his L-pads are set-up to run the higher sensitivity 4550 without additional padding? Haven't ordered them yet, but would want to order any other crossover components at the same time.
Some of those treads showed members also preferring the SEOS-15 horn to the 811b. SInce loading of the driver will be quite different, did they use an entirely different crossover than the Z-19? All the comment seem to be about sound vs. changes in crossovers that I can see.

Thanks for any links I've missed or insight.
 
If you currently have 811b horns ( & the M19 network ) I'd say just buy the 4550's and mount them to see what you think.

Here's what you can expect for response with that horn ( & M19 network );

811B M19 XO 4550 Flat.jpg

If needing to build a network from scratch, I'd build the Z19 ( since it's a bit more versatile ).

attachment.php


The Z19 is a nice evolution of the M19 ( Altec N1201a ) > actually ( IMO ) more closely resembling ( in its layout ) the network used with the Altec 604-8H .

altec_604-8h_crossover_sch.pdf_1.png


If you find the need for more horn attenuation ( when using the BMS driver ) you can always omit L3 + C5 ( which form a variable UHF lowpass/trim that I believe goes mostly unused by many ).
- Doing so ( omitting those components ) turns LP2 into a standard ( 8-ohm ) variable Lpad ( adjusting the complete horn/driver circuit, up & down in level ).
- I leave out R3 & LP1 ( as well as R7 , fwiw ) preferring a fixed amount of midband attenuation which is set by using a 6.2R resistor ( in the R3 position )

:)
 
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Scott,

If you end up going with the SEOS15 and BMS 4550 combo, then you'll need to rework the HP portion of the Z19 ( or M19 ).

Here's one way to do that rework ( this is a sim using other peoples actual measurements > so use at your own peril !! ).

This is an obvious HighPass take-off from the basic Z19 layout ( though, different values are used to hammer the response into something useful ) .

The most notable difference here ( IMO ) is the inclusion of a low-"Q" notch-filter to deal with a wide-band bump ( centered around 3K for this driver/horn combo ).
- The notch elements are formed by L4,C4 & R4 ( the red FR trace below shows the notch "out-of-circuit". .

I should mention that R6 & R7 represent a variable Lpad in this circuit.

BMS4550_onSEOS15_sim.png


Here's a copy of the file showing the raw response of a bms4550 on a SEOS15 ( I used the top trace to create my filter ).

4550_on_SEOS15_RAW.png

One can see the 3K bump needing some extra attenuation.

:)
 
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EarlK,

Excellent information and thanks for taking the time to show the schematics and charts! The Z19 crossover is build, but I appreciate knowing mod possibilities for the BMS 4550 and requirements for the SEOS-15. 3K Hz would have quite an impact on sound, so I will consider your recommendations if I go that route. While I have no test equipment myself, I see some online options with a decent mic, but having values to start with is much appreciated.

Given your working knowledge of these components, any chance you've had a chance to audition them yourself?

Thanks again for the useful information.

Scott
 
Hi Scott,

Happy to help with those X-over sims.

Unfortunately I have no "ears-on" experience with the BMS-4550 or the SEOS15 ( so I can't advise one-way or-another ).

I do know ( from monitoring the various forums for quite a while ) that those who have gone this route previously have stated many times their happiness with the BMS driver ( on an 811b ).
- JackGiff + friends, within the original "Look at my New Babies" / LHF thread ) .
- SpinMonster in this thread over at AVS ( though he eventually bought $$$ Radian Be diaphragmed drivers and put the 4550's up for sale ).

I listen to Altec 288-8Ks ( aluminum diaphragms ) on Emilar EH500 horns ( working over JBL woofers ), so what I like is quite a different kettle of fish than most.

:)
 
Hey EarlK,

Thanks for the thread references. I re-read some of the first link which was one that helped get me interested in the BMS 4550 (and noticed some of your contributions to the thread as well!). You also have a very nice HF combination for your two way. That get's me re-thinking about going to a 1.4" CD, but that would be down the road if I can some "ears-on" experience myself to hear how they sound vs. what I end up with using a 1" CD.

Since the reason most site for going to the 4550 was to extended the high frequency range beyond the Altec CD's, especially a 806, I did a frequency sweep test on myself using a high rez download and listened on a good pair of headphones and two speaker systems and have come to realize that my hearing is pretty much done by 13K Hz. With this in mind, my focus is now to maximize components in the range I can hear and that a 802 already covers.

I'm a fan of Emilar as well with EC-175's on the 811b right now and have read many positive comments about the smoother sound of the Emilar EH-800 horn vs. the 811b, so that will be my first change. I still appreciate your help and information, especially if I still decide to try the 4550.

If anyone has comments about what the 4550 does to possibly improve the midrange and lower high frequency that the Altec compression drivers already cover, I would still appreciate any feedback there. Otherwise, the general "improvements" in sound quality the 4550's provided, often referred to as smoother, better dynamics and/or sound stage, may be realized with the EH-800.
 
Have you tried the combo yet? I have a pair of BMS 4550 on the way home as I will replace the Altec 802 drivers.
 
ljungberg,

Since most said they made the switch for an increase in upper frequency response, I did not because I don't hear above 13k Hz and figured I would not be able to hear the difference others did. Hopefully you will be about to discern any changes, and I hope it is an improvement for you.

I would be interested to hear what your thoughts are on it once you compare them.
 
Thanks for the reply. I will test them on stock Z-19 crossover. Also have a customer that is crossed at 950 hz to test with.

I will also laboratate with adding the switch at the Z-19 crossover to see If I can hear any difference.
 
It's always nice to have different ways to test a new component and it sounds like you'll have another pair of ears to listen to the changes as well.

I look forward to hearing about what you heard.
 
I will built new ones. Will use Z-19 schematics for the LF and redesign the crossover as mentioned in this thread for HF. I tested with a 950 hz crossover without L pad and It was terrible :-D . I also tested the Z-19 original crossover and I did not like the HF at all, to honky. I have ordered new resistors and also some other Components to finnish the HF Circuit.
 
ljungberg,

Which horn or waveguide are you using ( with your BMS 4550 )?

:)

edit; OK, never mind my question, I found an older thread of yours outlining your system.
 
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