Coming up: RFL-21L

[lasse]

Hello,

next system in the famous (!?) RFL-XXL series of speakers is the RFL-21L, a system intended for my wifes music-teaching colleague.

My view has been that is it very important to have a good sound-system in the classroom when giving music-classes and the school has agreed to the deal that I build the speakers and the school buys the amp/CD-combo.

I have decided to use some drivers laying around and build a vented two-way crossed at abt 3000 Hz, perhaps 3rd order Tw and 2nd order Wo.

Drivers: Woofer/mid Peerless CSX 217H, Tw Peerless KO10 DT

I have measured the woofers and after 24h of in-breaking, I came to these average figures:

Re, Le, fs, Qms, Qes, Rts, Mms, Cms, VAS
5.9, 2.6, 35, 4.3, 0.32, 0.29, 40, 0.51, 40

I have decided to use pre-built boxes of abt 21L and a vent of standard-diameter of 69 mm could be good. The max lenght would be abt 250 mm (>2" from back-wall)

Now, a few different design-programs and spread-sheet suggests a portlenght of ca 22-23 cm to reach a Fb of 41-42 hz.

These are my thoughts now. Do you think that this makes any sense??

More coming soon, with pictures.

Regards//lasse
Stockholm, Sweden

[brianpowers27]

That seems like a high xo point for such a large (8"?) woofer. The off axis might suffer. If you can, try crossing lower.

[lasse]

That seems like a high xo point for such a large (8"?) woofer. The off axis might suffer. If you can, try crossing lower.

Hello and thanks for the feedback.

Yes, the high XO-point could be a problem, but Peerless suggests just that, a two-way crossed at 3000, in their data-sheet.

I think that my intended tweeter is hard to cross lower and perhaps it is good to have all the voice-part of the spectrum (300-3000) in the same driver.

BUT 3000 sounds a bit on the high side for an 8", doesn´t it?

Regards//Lasse

[brianpowers27]

Hello and thanks for the feedback.

Yes, the high XO-point could be a problem, but Peerless suggests just that, a two-way crossed at 3000, in their data-sheet.

I think that my intended tweeter is hard to cross lower and perhaps it is good to have all the voice-part of the spectrum (300-3000) in the same driver.

BUT 3000 sounds a bit on the high side for an 8", doesn´t it?

Regards//Lasse

The rule of thumb for beaming is just that, a rule of thumb. But it does provide a good guideline.

11500 (in/sec) / driver diameter = beaming frequency
11500 / 8 = 1437hz


I would suggest that this arrangement will lend itself to a narrow sweetspot. I think that a classroom setting would benefit from wider dispersion. Perhaps a three way is called for? Or perhaps a different tweeter?

[lasse]

The rule of thumb for beaming is just that, a rule of thumb. But it does provide a good guideline.

11500 (in/sec) / driver diameter = beaming frequency
11500 / 8 = 1437hz


I would suggest that this arrangement will lend itself to a narrow sweetspot. I think that a classroom setting would benefit from wider dispersion. Perhaps a three way is called for? Or perhaps a different tweeter?

Yes, probably adding a midrange would result in a very nice speaker but, being on a learning curve, I want to isolate the next challenge to me (the vented cabinet) and make the basic alignment as "easy" as possible. I think that the KO 10 DT could be made to work from abt 2500 Hz, but this is probably the limit. I do not want to buy more drivers at this point so I will install and take the measurements and see what happens.

By the way, has anyone of you out there any measurements of the Peerless KO 10 DT ?? I would be very greatful for some info.

Regards//lasse