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Multi-Way Conventional loudspeakers with crossovers

What to use in the middle?
What to use in the middle?
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Old 4th October 2003, 09:46 PM   #1
Duck-Twacy is offline Duck-Twacy
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Default What to use in the middle?

Hi, yet another guy seeking some advice

I am building my ultimate 3-way speaker system (or shoud I say 2.5?)

The bass is handled by a pair of Lambda SB12 drivers in a 125 liter sealed enclosure (build from 32 mm MDF, with a double baffle and matrix ).
It will be crossed over at 150 Hz (24 dB/octave LR) by an active crossover (Marchand XM44). A lower crossover is possible.

The mid and high unit will be in a separate enclosure on top of the bass box.
For the tweeter I was able to buy a pair of Accuton C23-6 ceramic domes for a reasonable price.

Now what mid unit to use in between?? What parameters are important here? Of course there is the sensitivity of the Accuton (89.5 dB/watt). I guess the mid unit shoud be equal or lower.
But are there any other important factors.

My short list consists of the following units:

Accuton C94-8 89.1 dB/watt
Scan Speak 18W/8545 88 dB/watt
PHL 1230 93 dB/watt @ 16 ohm => 90 dB/w @ 8 ohm!!!

Now the Lambda SB12 has a rather high Mms (145 gr). Is this important?? The SS is rather heavy too with an Mms of 20 gr, the PHL is quite light Mms 12 gr, the Accuton about 15 gr.
It is rather obvious the C94-6 will go well with the C23-6, but is it a good match with the Lambda?

Of course it would be best just to try them, but Im afraid thats not an option. There is no shop around here that sells them all.

Another question. What is a sensible cross over frequency? I was thinking of around 2500 Hz, maybe with a 12 dB series filter. Any advice on this is welcome too.

By the way I like all kind of music (classic2hard rock, female vocals I listen to a lot).

Amplifier for mid/high will be a DIY Aleph5. Low end will be driven by a Crown K2 (eventually).

Well hope this wasnt to boring, any advice is welcome.
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Old 4th October 2003, 11:13 PM   #2
Salas is offline Salas  Greece
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What to use in the middle?
Cross below 100Hz to avoid boomy voices. The change from the PHL to the heavy woofer will be obvious on timbre too. The PHL can go down to 50Hz. I would cross as low as I could go.
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Old 4th October 2003, 11:19 PM   #3
rho is offline rho  Belgium
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A higher Mms takes the Fs down. Also the efficiency goes down.
Look at the Cms. If this is high the Fs goes up agian and efficiency goes down again. (You need more force to move the cone)

A driver with high Mms and low Cms has higher efficiency but can sound boomy.
In this case I think it's best tu use an amp with higher DF.
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Old 5th October 2003, 12:52 AM   #4
roddyama is offline roddyama  United States
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As Salas suggests, I too would lower the xover to the subs below 100Hz. WRT the mid-bass, you might think about an MTM arrangment. Many here have had good sucess with their MTM's and it gives you double the cone area (half the excursion) for the low mid-bass region.
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Old 5th October 2003, 08:09 AM   #5
Duck-Twacy is offline Duck-Twacy
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Okay, lowering the bass/mid crossover might me better. Lets say 100 Hz (if I set it to 50 Hz, the Lambda wil hardly be used I think )
The Cms of the Lambda is 0.4 mm/N, don't know if thats high or low.

The Crown amp I want to use for the sub has a DF of 3000 (10-400 Hz), so no problem there I think. Also it has lots of power ( see http://www.crownaudio.com/pdf/amps/136713.pdf). Probably a 350 watt@8 ohm K1 will be enough if I drop to 100 Hz. Fortunately the amps are very efficient (>90% or so, not a lot of heat here)

The PLH will not be a good choice I understand. So the Acouton and SS are the remaining competitors. Both can do 60 Hz in a appropriate BR housing.

A MTM setup is nice, buT I have a few problems with that:
- The efficiency will double I guess so probably exceed the 89.5 dB/w of the Accuton tweeter.
- I always see that using 2 woofers (or mids) results in low impedances ( < 4 ohm) and more irregular curves. A SE Aleph5 is not that fond on this. Impedance should remain above 5 or 6 ohm.
- costs, not that much of an issue if its good (I will use the speakers for 10 years or more).
Or do I see things wrong here??

What about the 2500Hz crossover point, does that make sense or should I aim higher?

Thanks for the answers so far,
Ronald
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Old 5th October 2003, 03:15 PM   #6
Salas is offline Salas  Greece
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What to use in the middle?
The 16 Ohm PHL 1230 you mentioned will go 8 Ohm if doubled. 96dB will be the midband sensitivity of the pair. If you correct -4dB for 4pi to 2pi step compensation you will get 92dB. Use one PHL 1220 8 Ohm instead. Half the pair's money, same impedance, 89dB when corrected, single point source. Fair enough?
Keep in mind that the PHL steps allover many well respected High-End brands when it comes to sound quality. Nexo, L-Acoustics, Stage Accompany etc. have reasons using PHL.
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Old 5th October 2003, 03:31 PM   #7
Bill Fitzpatrick is offline Bill Fitzpatrick  United States
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You may want to consider putting the mid in a sealed box with a Q of .7. This will determine F3. Then use a 2nd order high pass module in the Marchand with with the same F3.

The combined rolloff of the enclosed mid and the high pass module will provide a fourth order high pass with an F6 equal to the aforementioned F3.

With a low pass 4th order module with F6 set to the same frequency as F6 of the high pass, you will then have a perfect LR
fourth order network.

You may also want to consider a more efficient mid as you will need to compensate for the baffle step roll-off unless the Marchand can do this for you.
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Old 5th October 2003, 04:17 PM   #8
Duck-Twacy is offline Duck-Twacy
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More intersring ideas.

Btw WinISD gave for a sealed box with Qtc = 0.71 for the 1220 a volume of 4.21 liter and Fb of 135.8 Hz. Maybe I did something wrong, but is seems a little high.

Will have to do some reading how to calculate baffle step roll-off

Marchand XM44 does have an option for baffle step correction. Didnt purchase that (yet)
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Old 6th October 2003, 05:11 AM   #9
navin is offline navin  India
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what about a 4 way with a PHL 1220 as a lower midbass and the 94-8 as a upper mid.
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Old 6th October 2003, 09:31 AM   #10
Duck-Twacy is offline Duck-Twacy
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Actually I don't like 4 ways. Most of the time you will crossing over somewhere between 300-1500. I always understood thats a rather critical area.

Using a (stereo) sub to support a 3 way system is perhaps more sensible, eg crossover freqs of 60, 250 and 3000 Hz with 12, 8, 4, 1 " units or so. Still I would end up with too much speaker, even for my taste (a bassbox of 90*47*60 cm and a 3 way system of say 60*30*40 on top of that....)
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