Humble Homemade Hifi

Progress – construction

24-04-2003

Well, I’ve got all the Scanspeak drivers now! I have ordered the Seas sub-woofers; they should arrive in a few weeks. These Scanspeak drivers do look very promising, very well made and they all came in matched pairs. I have plugged the tweeters into my current reference system because I just couldn’t wait to try them out. They still need a bit of burn-in time but already I can say they are very, very good! They have a sort of “ease” with the production of the music. Clarity is exceptional without being exaggerated, detailing is good and the efficiency is high (in my current reference system they are running with only a very small series resistor). Furthermore they just look very cool.

A sight for sore eyes!

Regarding the cabinet: I have decided to leave the idea with the laminated panel technique for a later project. If I built the woofer cabinets using this technique then they would either be too large on the outside or the internal volume would be too small. The laminated panel technique is not the most efficient regarding the size / internal volume ratio. So here the compactness of the woofer cabinet won. The final version will use thick panels and internal matrix bracing with circular cut-outs to let the airflow freely in combination with mass loading of the internal walls. The woofer cabinet is constructed from two layers of mdf glued together as I did with the Auriga speaker. Basically it is a 22 mm internal cabinet and all the joints and ends will be finished so that it is nice and smooth. The bottom panel that incorporates the 26 cm sub-woofer is made extra thick and uses a double layer of 22mm mdf (44mm total). The 22mm thick cabinet is covered by a second layer of mdf with a thickness of 6 mm so the total wall thickness adds up to 28 mm. Due to the layered structure with varying density this is much more solid than one single layer of 28 mm mdf. The outer 6 mm mdf is then sanded to make a nice airtight cabinet. Then comes the trick to make the construction look very professional as if all panels were cut to the perfect angle and no panel thickness is visible: cut all edges with an 6 mm facette at a 45 degree angle or rounded off edge (the same as the thickness of the visible layer) using a router. Later on when the cabinets will be spray-painted there will be no small cracks in the paintwork due to the mdf reacting to changes in air humidity or temperature.

The cabinet drawings are finished in a preliminary manner. This means I will be building the cabinets according to this drawing and any alterations made during construction will lead to a final drawing that won’t be made until the whole system is finished. So if you can’t wait to start building the cabinets then use this drawing, if you don’t want to take any risks then wait a few more months for the final version. On the other hand this is a diary so my findings will be published as I go along.

A higher resolution drawing is available on request.

‗‗‗‗‗‗‗‗‗‗‗‗‗‗‗‗‗‗‗‗‗‗‗‗‗‗‗‗‗‗‗‗‗‗‗‗‗‗‗‗‗‗‗‗‗‗‗‗‗‗‗‗‗‗‗‗‗‗‗‗‗‗‗‗‗‗‗‗‗‗‗‗‗‗‗‗‗‗‗‗‗‗‗‗‗‗‗‗‗‗‗

06-06-2003

Well, at last I’ve got the Seas (sub) woofers! Now I have them in my hands I can get a “feel” about them and how to implement them. They seem to have a relatively soft suspension, which has got me thinking: should I go for the down-fire principle? I have been following several forums on the net about down-fire subs and many mention the woofer cone sagging after a while. I know that is with really heavy coned subs with over 100 grams of moving mass and the Seas L26RFX/P has a moving mass of “only” 58 grams, but still, I have a funny feeling about it. Maybe I will have to go for a side-firing woofer after all. I’ll have to think this one over for a while.

Another sight for sore eyes!

17-06-2003

Should I go for the down-fire principle? That question has been keeping me busy recently. I have checked the Adire Audio “sag” calculator. According to the calculations the Seas L26RFXP would have a sag of 0,63mm which is 9% of Xlin or 3,6% of Xmax. Yes or No?

Tapio Suonpera from Finland sent me an e-mail with the following interesting and promising information:

“ I talked about down-fire principle with Mr. Jorma Salmi. He owns Gradient Ltd Finland, which makes some very fine loudspeakers named Gradient Revolution. These loudspeakers are designed by Mr. Salmi and have been praised by The Absolute Sound and Stereophile among the others. He is also the main distributor of SEAS in Finland and has tested them a lot. He said that there would be no sagging problems or changes in parameters when using L26RFX/P in down-fire principle. He has used and measured down-fire elements for over 20 years period and sees no problems with the kind of L26RFX/P. ” – Yes!

I also mailed Seas directly and they had the following reply:

“ We do not recommend to mount the L26 firing downwards since we do not have a long term experience with this driver mounted this way. However, we have many customers that has used our old 25cm units mounted this way without any problems.” - Yes or No?

In the past I have built several speakers using Seas 25cm paper and polypropylene cones but all mounted the standard vertical way. Their suspension was stiffer than that of the L26 so I still have some concern about mounting them horizontally.

I have built a pair of trial sub-woofers (50 litre closed box) to determine what sounds “better” for my situation. The set-up was very crude but it was only to determine a difference in sonic signature between the down-fire principle and the standard front and side firing principle. The subs were connected parallel to my newly finished Mezzo Proteus speakers with a single high quality 12mH transformer type inductor. To create a height adjustable space between the bottom of the down-fire sub and the floor I placed three large screws per box.

The two sub’s next to the Solo-103 to give an idea of their size. Note the height adjustable “spike”.

To start off with: I couldn’t hear any audible difference between the standard front and side firing principle. Remember, using a 12mH inductor this gives a very crossover frequency so it was obvious that if the woofer were in the front or in the side there wouldn’t be much difference. Now for the difference between the down-fire principle and the standard front firing type: The down-firing principle seems to work as a sort of acoustic filter. From the front-firing woofer more lower midrange energy reached the listening spot and muddled up things a bit. The down-fire woofer sounded tighter and only added an extra sense of depth (in image and in bass) to the overall sound without changing any of the existing qualities of the Mezzo Proteus. The front firing woofer tended to “bloat” things up a bit.

Note that these statements are made without changing anything to the crossover. To get a similar result from the front-firing woofer it had to go 2^nd order with an extra capacitor added parallel. This means a more complex crossover with steeper and deeper swings in the impedance curve, I like to keep things simple where possible, so in this case I preferred the down-fire woofer.

07-08-2003

Its been a while since my last update, but I’ve been busy lately and not only with these speakers!

As you can see the lower cabinets are ready to go to the paint-sprayer. After all I decided to go for a side-firing sub-woofer, not because of the “sag” problem (I don’t think that would have been much of a problem in the end) but because I did some more listening tests and some more simulations and found out that I wanted to have the possibility to let the sub-woofers run a little higher into the bass region than possible with a down-fire woofer. The down-fire sub sounded great when only running up to about 80-100Hz (nice and dry, and strong) but if run any higher it tended to lose its tightness and became a little “thicker”. Still very nice bass but not good enough for me!

The photos also show some of the internal matrix construction and a separate open compartment in the bottom where I will be mounting the crossover when it is finished. If you look closely you can see that the edges of the circular matrix cutouts are nicely rounded-off. I don’t know if it will make any audible difference but at least it looks cool and was easy and quick to do. And I like to pay attention to every little detail! If you look at the bottom of the cabinet (middle photo) you can see that it is constructed from two layers of mdf glued together – like the Auriga speaker. Basically it’s 22mm internal cabinet with a second layer of mdf with a thickness of 6mm so the total wall thickness adds up to 28mm. Due to the layered structure with varying density this is much more solid than one single layer of 28mm mdf. Then comes the trick to make the construction look very professional as if all panels were cut to the perfect angle and no panel thickness is visible: round-off all edges with an 6mm radius (the same as the thickness of the visible layer) using a router. The side panel in which the sub-woofer is mounted is made extra thick and uses a double layer of 22mm mdf (44mm total). Finally you can see the good old trusty carpet-tile lining of the internal panels.

06-10-2003

I’ve finished the upper section of the cabinet. Its made from 7 layers of laminated finnish birch plywood of 3mm thickness built up to a total thickness of 21mm. The end product has been sprayed RAL 9006 metallic aluminium colour.

03-11-2003

Cabinets completed (except for the correct hieght of the nylon distance rings between the woofer enclosure and the top section). Here is a photo impression:

NOTE: This design is strictly for the home DIY enthusiast and not to be used professionally without my permission!

Tony Gee

The Netherlands