8" + Waveguide MT

[Timbo]

Thinking of trying a small monitor with a 8" mid and a MCM Waveguide tweet. These will sit on bass bins, either a push-pull 10" or a single sealed LT 15".

I do not know which way to go with the drivers though, W22, M8a, RS 225.....It seems that the Seas TDFC will be the tweet of choice, I have not heard any comment as to benefits of using a higher cost (Millineum, Accuton) in this application.

This system will be Bi-amped with active XO between the Bass and the MT. I think the end result will probably loo like this

[JoshK]

Excellent idea! I think the project has merit. These would make nice shop monitors for me too. I'd been thinking along the same lines for a while now. MCM WG + Seas H1212 + RS225 in sealed cab with a modified xo from Jon or one of the other big boys.

[mazurek]

My latest thoughts are that the new peerless hds would be interesting to try, it is fairly reasonably priced and the flange is removeable.

[EspenE]

I have built a system very much like what you plan:

- Seas W22 mid and Seas 27TDFC in MCM waveguide
- closed box of 14 litres internal volume
- passive 8th order crossover at 1220 Hz
- Peerless 12" XLS subwoofers in 18 litres closed boxes
- electronic crossover 4th order at 80 Hz with room correction and eq built in

The system is just finished. I'm quite pleased with the result. Measured outdoors, the frequency response of the MT unit +/- 2dB from 100-20000 Hz.
Electronic EQ corrects for room resonances at 32, 110 and 180 Hz, and in-room response is reasonable flat down to 28 Hz.

My camera is not very good, but I attached a couple of photos anyway.

Espen

[EspenE]

Crossover

The passive crossover is at 1220 Hz. Inspired by various projects on these pages, I tried an 8th order Cauer-topology.

With 8th order slopes, the W22 4,5 kHz resonance is more than 60 dB down.

The 27TDFC in waveguide exhibit two small peaks (at 3,7 and 13 kHz) that needed additional notch filtering. The 27TDFC seems to handle the low crossover frequency well. The wavegude helps about 4-6 dB, and the steep slope helps a bit as well.

See attached frequency response and network schematics.
I'm also working on an electronic crossover. This will be fun to compare with the passive.

[jdybnis]

Very nice. I like how you kept the inductor values within reason (copper prices being what they are). Do you have any off-axis measurements?

[EspenE]

Controlled off axis and power response was one of my design criteria. My reasoning was:

The MCM waveguide should cover about 90 degrees (+/- 45) relatively uniform.
The 8" should cover 90 degrees up to at least 1300 Hz.
The crossover frequency was placed at that point where the W22 was down to 90 degrees to get uniform 90 degrees coverage from that point upwards.

Actually, I now think that 1220 Hz probably is a litte bit too low. The waveguide does not adequately load the tweeter down that low, and the 8" also covers 90 degrees a little bit higher. On the other hand, the W22 has some irregularities aroud 1400 Hz I would like to avoid.

My actual outdoors off-axis measurements seem to have gone missing. I made some new (a bit crude) measurements from my living room on axis and (about) 45 degrees off axis horizontally and vertically. The black one is on axis, the green one is 45 off axis horizontally, the red vertically.

The vertical shows an expected dip aroud the crossover frequency. Otherwise, the off-axis response is quite uniform.

[Timbo]

Thank you EspenE, That was what is was thinking about. I was unsure that I could sucessfully crossover for the Tweet to the 8".

For a time I thought a TMM with dual 7" and the waveguide may give me more output / lower distortion than a single 8" (like Zaph's towers, but put in smaller boxes since they will sit on the subs and I will not need the extension that the larger towers give him)

As far as the Subs will the single 15" deliver better than dual 10"?

[EspenE]

2 mid units will of course give lower distortion and higher max output compared to only one. But I only had room for MT units of 15-16 litres volume.

2 10" Peerless XLS gives about 5dB more max output at 100Hz compared with one 12". Again: I only had room for a small box.

Espen

[capslock]

Nice work! Did you source the MCM waveguide in Europe or order directly?

PE and Mad are quite good with foreign credit cards and international shipping, but most others in my experience either are a pain or flatly refuse to ship outside NA.

[EspenE]

I sourced 4 of those it directly from MCM:

http://www.mcminone.com/product.asp?catalog%5Fname=MCMProducts&product%5Fid=54%2D580&info=details

I paid by credit card, and the transaction and delicery was smooth and fast.

Another possible source for tweeter/waveguides in Europe, is Monacor. I used their tweeter DT-300 with waveguide WG-300 in another project. This waveguide is made for this specific tweeter, is bolt-on and fits perfectly without modifications. The tweeter is 1,5 inch, and handles low crossover points very good. If you google Monacor DT-300, I'm sure you'll find an outlet near you. I used www.monacor.no, here in Norway.

The DT-300/WG-300 combinations measures and sounds very good. If I had been aware of this Monacors when I started building my W22 project, I would have considered using this combination instead of the 27TDFC/MCM combo.

See attacted frequency graph. This is the Monacor DT-300/WG-300 with a JBL LE10A woofer/mid. Crossover is 1440 Hz, 4th order. This is a quite simplistic crossover. I could have put in a notch circuit to deal with the slight 14kHz bump, but I did not bother, as the crossover sounds pretty good as it is. The response is within +/- 2 dB from 100 to 16000 Hz.

Another good tweeter/waveguide combination.

[capslock]

Espen, did MCM agree to use regular USPS air mail parcel post? In my experience, most vendors insist on EMS or UPS, so you end up with $40 shipping and €20 brokerage fees.

Yes, the DT-300 (which is a 30 mm tweeter - strange size) received a favorable review in Klang & Ton a while ago. Still, the Seas is better on nonlinear distortion. If you have a XO for the Monacor/Excel combo, some guys here in Europe might still be interested.

[EspenE]

Espen, did MCM agree to use regular USPS air mail parcel post? In my experience, most vendors insist on EMS or UPS, so you end up with $40 shipping and €20 brokerage fees.

I'm sorry - I don't really remember that excactly. All I can recall is that the delivery time was good - so I presume they used air mail. And I don't recall paying too much shipping either.

Yes, the DT-300 (which is a 30 mm tweeter - strange size) received a favorable review in Klang & Ton a while ago. Still, the Seas is better on nonlinear distortion. If you have a XO for the Monacor/Excel combo, some guys here in Europe might still be interested.

Yes, the Seas/MCM is better on distortion. In my (crude) THD measurements (at 96dB/1 meter SPL), the Seas/MCM measures 0,44% at 1200 Hz (worst case), sinking to less than 0,2% at 2200 Hz and above. In the same measuring setup the Monacor combo gives 0,7% at 1500 Hz (worst case) sinking to less that 0,2% at 2800 Hz, with a new distortion peak (0,8%) at 4800 Hz, then sinking to 0,2% again.

I have not made a XO for the Monacor/W22 combo. I imagine that I would use about the same topology though.

[capslock]

Espen, did you grind down the throat of the MCM waveguide until the opening was 38 mm, as described by Zaph?

[EspenE]

Yes. The MCM is intended for compression tweeters, and has a metal 1 3/8" threaded portion. It cannot be used for dome tweeters without this mod.

I sawed off the threaded portion with a hacksaw.

Then I used a plunge router. I made a simple jig (of surplus MDF). The waveguide is bolted face down, some MDF spacers to the correct height and at the top a MDF "table" with an appropriate opening for the router. I carefully routed down in small increments, measuring the opening at each increment.

Actually, it was not a difficult process.

I did not bother with backplates etc to clamp the tweeter to the waveguide. I just glued the 27TDFC to the waveguides with expoxy glue and mounted the whole assembly to the baffle with ordinary screws.

[EspenE]

I did not get a frequency response from the 27TDFC/MCM combo quite like Zaph did.

I got the efficiency increase between 1kHz and 6kHz of about 5dB. Then I got a small bump at 4kHz (+2dB) and a bigger at 14kHz (+4dB). See attachment. Both of these are addressed by notch filters in the crossover.