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P. Audio PH-4525 horn and BM-D750 (aka. K69)


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I have both the k-69 and the d750's.

the d750s claim frequency response of 500 - 18khz with a recomended xover of 800hz

I think the MCM grand IV's uses this driver as a tweeter in a 4 way system.

If your going to use these other wise at a low volume, id cross them over using a steep crossover.

If you look at the plots for the driver, it look likes the impedance rises below 800hz quite a bit.

don't forget this is an 8 ohm driver, and not a direct replacement for the k-55.



Impedance

8 ohms

RMS Power Rating 100 Watts above 500Hz
Sensitivity (1W/1m) 108dB
Frequency Response

500Hz - 18kHz

Recommended Crossover 800Hz or higher
Voice Coil Diameter 2.84" / 72.1mm
Mount Type Bolt-on

speakerfritz - Thanks for the info. I'm trying to understand your comment about needing a steep crossover if using them at low volume (if I understood you correctly)?

I'll be biamping the Khorns and new center. Will be using a DCX-2496 for crossover and time alignment so hopefully will have enough flexibility with individual gain controls and crossover steepness.

I keep seeing the specs for frequency response and recommended crossover frequency and am a bit bewildered with the good results people seem to be getting with this horn'driver combination.

I'm open to suggestions for other combos, but can't go the expense or size of the big Jubilee horn. Said another way, I sure do like the price and size of the PH-4525 & BM-D750!

Rod

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"I'm trying to understand your comment about needing a steep crossover if using them at low volume "

reverse that...typo on my end.

here are some general comments

check out this link

http://www.diyaudio.com/forums/multi-way/58060-need-help-pa-crossover-please.html

for PA use, they are using 18db per octave at 1200hz.

it makes sense to me that if you are going to run these at high volume that the xover point needs to be set higher.

the manufacture says crossover at 800hz. but if you are ok with less power handling, i'm sure you can go lower. how much power can these things handle at 500hz, don't know, but it's certainly less than the rated power handling at 800hz.

don't forget the impedeance rises quite a bit below 800hz, why should we care?

above 800hz , the plot shows 8 ohms, a 24uf capcacitor will crossover at 800hz

below 800hz, the plot shows a big spike in impedeance, the same 24uf capacitor will now crossover at 400hz

so, it makes sense that the PA folks are crossing over at 1200hz, that will result in 600hz at the impedeance spike point.

400hz is below the manufactures idicated frequency response range.

I don't think the folks that are using these at home are really putting a lot of power thru them.

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The reason I started my search for a different bass bin was twofold. First, I was searching for a bass bin that gave me more of a chest thumping feel than the enveloping bass sound of the Khorn. More importantly however, I wanted a better match for the P. Audio driver in terms of crossover frequency. IIRC, I had taken some plots of the entire Khorn and could see that I had a bass dip between 400 and 500 Hz, right where I was crossing the drivers. I knew the P. Audio was being pushed at those levels and was below the recommended crossover point.

I also wanted to be able to use as steep a slope as I could get from my DCX2496 so as to isolate the drivers as much as possible.

The end result for me was my DBB build. As I have said in several other posts, the big surprise of the entire build was the fantastic soundstage I am getting from the P. Audio horn once I pulled the speaker away from the wall.

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here are some general comments

check out this link

http://www.diyaudio.com/forums/multi-way/58060-need-help-pa-crossover-please.html

for PA use, they are using 18db per octave at 1200hz.

it makes sense to me that if you are going to run these at high volume that the xover point needs to be set higher.

the manufacture says crossover at 800hz. but if you are ok with less power handling, i'm sure you can go lower. how much power can these things handle at 500hz, don't know, but it's certainly less than the rated power handling at 800hz.

don't forget the impedeance rises quite a bit below 800hz, why should we care?

above 800hz , the plot shows 8 ohms, a 24uf capcacitor will crossover at 800hz

below 800hz, the plot shows a big spike in impedeance, the same 24uf capacitor will now crossover at 400hz

so, it makes sense that the PA folks are crossing over at 1200hz, that will result in 600hz at the impedeance spike point.

400hz is below the manufactures idicated frequency response range.

I don't think the folks that are using these at home are really putting a lot of power thru them.

I do play things quite loud at times in our 19' x 13' x 7 room. Besides music we do a lot of movies.

I can understand your comments about the impedance changes affecting the crossovers. But since we will be using active crossovers with one amp per driver it seems that this should not be an issue. Or am I missing something?

If the above is a non issue, I'm still concerned about running them below their indicated frequency range. Rudy seemed pretty clear that he had a gap between 400-500. That is sure less than optimum. Also we don't know the power handling capability below 800 Hz.

As I mentioned earlier, I can't go the cost or large size of the huge Jubilee horns, but are there others that I should consider?

I wish I could do as Rudy did and build new bass bins. Unfortunately that's quite a ways down the road for both budget and time constraints. My compromise is to enclose the backs so I can pull them into the room.

I should also mentiion that my Khorns are 1958 vintage with the old wood mid range horns. Another option would be to keep the system as 3 way, but use the BM-D750s to replace the tweeters crossing over much higher than 400. This unfortunately would complicate the 'Active' crossover/amp system and would require a new cabinet for the new horns. This is not sounding like a very appealing approach.

Ugh!

Thanks everybody for all your input here.

Rod

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Rod:

If think the only way for you to know how it will sound and work out is to try it. I had to jump in myself and took a leap of faith. Very glad I did, BTW.

I originally just sat the P. Audio horn and driver on top of the bass bin. Hooked it all up and played around with the crossover points and EQ. I ran my crossover point near 450Hz IIRC. I EQ'd the low portion on the P. Audio driver a bit to better match the bass bin. I did not note any major detrimental issues. The 2" driver is plenty powerful for any home space as far as I'm concerned.

If you can find a decent price on them, get 'em and give it a try. Worst case, you go back to stock and sell the gear on eBay. I doubt you will have trouble selling the gear. You might take a litte bit of a hit, but consider it the price of admission.

If you can enclose the backs and pull the bins away from the wall, I really beleive you are going to like what you hear.

Good luck.

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  • 2 weeks later...

Update to my setup. Yesterday I had some time to work on various crossover settings on my DBBs. I started out trying to compare the Le Cleach method of setting up a crossover and really ended up just messing around with varous crossover types and slopes. It is so nice to be able to rapidly compare one setting with another WHILE music is playing.

My original setup had a L-R 48dB crossed at 600Hz. The Le Cleach method had me move the HF point much higher and that led me to see how a standard crossover setup would sound at a higher crossing point. I ended up liking the sound of the Butterworth 24dB crossed at 800Hz. I still need to do more listening, but so far I really like the sound with the crossover moved up a bit. The DBB's capability to go above 1kHz really helps in selecting various frequencies for the crossover.

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