Hi,
Having just completed my first build using an Alpair 7.3 I am very interested in building this speaker. I cannot seem to download the plans from post #51. Is there another way to get them or do I need to do something special?
Having just completed my first build using an Alpair 7.3 I am very interested in building this speaker. I cannot seem to download the plans from post #51. Is there another way to get them or do I need to do something special?
Thanks Dave,
I do not have any experience with crossovers. Am I correct if I say the baffle step frequency for this enclosure would be 435Hz with the baffle being 264 wide?
Would you have to damp the SPL of the one driver due to the sensitivity discrepancy?
I do not have any experience with crossovers. Am I correct if I say the baffle step frequency for this enclosure would be 435Hz with the baffle being 264 wide?
Would you have to damp the SPL of the one driver due to the sensitivity discrepancy?
That is a good 1st approximation. XO at that or a bit lower (as low as 0.7 of the BS frequency).
Biamping makes things easier to get good results, and XOing this low a good idea. Level matching can be done at the amps andrelative driver sensitivity is mostly a non-issue.
With a passive XO woofer typically needs to be 3-5 dB more sensitive. We have found that this low, with the broad overlap, 1st order series XO works well, but getting the parts right takes some work. Parts cost is fairly high and unless you are lucky it is going to take a selection to dial them in. Measuring kit is really, really helpful.
dave
I am in the process of building a A12PW/A7P combo speaker. It loosely follows the lines of the "simple 2-way", although there are some differences. I had to do something about the looks, because the color of the Alpair X(x)P cones is a bit awkward. It is a rather understated color, but at the same time it doesn't combine well with strong colors. Paint the box Ferrari red, Lamborghini yellow, or racing green and chances are that the final result will be rather ugly. But at the same time I did not want to make a speaker that would look so inconspicuous that one would just walk right into it and never notice...
The most obvious difference is of course the faceted front face, which will have its implications for the A7P baffle step frequency. The layers of the birch plywood on the facets will remain visible after painting, but the front and sides will be painted slightly off-white.
The port is an Intertechnik Jetset 70, with huge flares. It looks like something that will readily suck up the cat and transport her to another dimension. As a result, it looks totally out of place below an Alpair, so it went to the rear. Yesterday evening I finished tuning the vent, I arrived at 36 Hz, with an estimated box volume of 42 liters for the A12PW. The box is lined (not filled) with polyester wool mats with a density of 40 kg/m3.
Later this week I will finalize the cabinets, an then filter tweaking can start. I think I'll try a series filter first, but I only have vague ideas right now. I have already casually measured the response of the woofer and "tweeter", and nothing looks out of place, so I fully expect to be able to make the series crossover work. As an alternative, I will also try a 2nd order Linkwitz-Riley filter. The filter will go in a separate box, so it will stay accessible. The speaker has a 4 pole Speakon connector at the back, allowing a good connection without the possibility of mixing up wires, which is good when a 5 year old also haunts the house looking for screws to undo...
If anyone is interested, I will keep posting about my progress. Dave might want to make the decision which place is the most appropriate: this thread or a new one.
The most obvious difference is of course the faceted front face, which will have its implications for the A7P baffle step frequency. The layers of the birch plywood on the facets will remain visible after painting, but the front and sides will be painted slightly off-white.
The port is an Intertechnik Jetset 70, with huge flares. It looks like something that will readily suck up the cat and transport her to another dimension. As a result, it looks totally out of place below an Alpair, so it went to the rear. Yesterday evening I finished tuning the vent, I arrived at 36 Hz, with an estimated box volume of 42 liters for the A12PW. The box is lined (not filled) with polyester wool mats with a density of 40 kg/m3.
Later this week I will finalize the cabinets, an then filter tweaking can start. I think I'll try a series filter first, but I only have vague ideas right now. I have already casually measured the response of the woofer and "tweeter", and nothing looks out of place, so I fully expect to be able to make the series crossover work. As an alternative, I will also try a 2nd order Linkwitz-Riley filter. The filter will go in a separate box, so it will stay accessible. The speaker has a 4 pole Speakon connector at the back, allowing a good connection without the possibility of mixing up wires, which is good when a 5 year old also haunts the house looking for screws to undo...
If anyone is interested, I will keep posting about my progress. Dave might want to make the decision which place is the most appropriate: this thread or a new one.
Attachments
+2 on the nice work - as for colour of finish, if the face veneers are of decent enough grade, a thorough RO sanding to 220G and couple of coats of NC lacquer or post catalyzed conversion varnish would give a very mild amber tone that could work well with the blue cones.
Or you could get crazy with translucent / aniline stain, but the exposed edge grain of the plywood can yield a very distracting tiger-stripe effect.. Of course, if painted those edges can take a fair time to fill and seal for a seamless finish.
Or you could get crazy with translucent / aniline stain, but the exposed edge grain of the plywood can yield a very distracting tiger-stripe effect.. Of course, if painted those edges can take a fair time to fill and seal for a seamless finish.
Hi Chris,
Thanks for the suggestions! I am still open to ideas for the finishing, and there are two basic points that I will stick to. Firstly, I want the plywood at the facets to remain visible. Secondly, I am after a matte finish, or one with a very subtle luster. Plenty of options to choose from. I am not familiar with the English names of finishing products, but I'll figure them out so I can ask for the right stuff in our friendly local paint store.
The surface veneers look a bit rough from close by, but they clean up wonderfully with just a light pass with the orbital sander and a fine sheet of sandpaper.
@ Anton, I used three layers of 24 mm thick plywood in B/BB grade. I used a foldable table saw with a slide table to cut the bevels on the layers. First, I made an angle template from MDF, and when I got that right, I used the template to set the angle of the fence. I had to change the fence angle several times, and this method would give me the best reproduction of the angle. Then I joined the layers with PVA glue which I applied with a paint roller. I used a thick glass coffee table to keep the baffles flat. After the glue cured I used a low angle block plane to clean up the facets and make the layers flush. Using a plane was an eye opener to me. When properly set up (Google "set up a block plane") it is a joy to use, and it leaves a superb finish on the wood. I have a "Quangsheng" (sold here under the brand name Peaktool) plane, they have a very good price to quality ratio.
Thanks for the suggestions! I am still open to ideas for the finishing, and there are two basic points that I will stick to. Firstly, I want the plywood at the facets to remain visible. Secondly, I am after a matte finish, or one with a very subtle luster. Plenty of options to choose from. I am not familiar with the English names of finishing products, but I'll figure them out so I can ask for the right stuff in our friendly local paint store.
The surface veneers look a bit rough from close by, but they clean up wonderfully with just a light pass with the orbital sander and a fine sheet of sandpaper.
@ Anton, I used three layers of 24 mm thick plywood in B/BB grade. I used a foldable table saw with a slide table to cut the bevels on the layers. First, I made an angle template from MDF, and when I got that right, I used the template to set the angle of the fence. I had to change the fence angle several times, and this method would give me the best reproduction of the angle. Then I joined the layers with PVA glue which I applied with a paint roller. I used a thick glass coffee table to keep the baffles flat. After the glue cured I used a low angle block plane to clean up the facets and make the layers flush. Using a plane was an eye opener to me. When properly set up (Google "set up a block plane") it is a joy to use, and it leaves a superb finish on the wood. I have a "Quangsheng" (sold here under the brand name Peaktool) plane, they have a very good price to quality ratio.
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timpert - I'm blessed to work in a commercial cabinet shop with access to a full spray booth, so I tend to use industrial finishing products - specifically https://www.mlcampbell.com/products/categories/clear_topcoats/solvent_borne/postcatalyzed/krystal
the Dull (10% sheen is one of my personal favorites - it looks like a nice oil and satin waxed finish, but the 35% Satin is most commonly used on millwork and kitchen cabinets)
presumably there would be similar products available in your vicinity -
I've found tThe major issue with clear coat finish on exposed edge grain of the BB plywood is the open pores on end grain of each alternating core layer. There are paste fillers available, but my cheap and nasty approach has been to mask off the adjoining faces and give the exposed edges a couple of lightly fogged in spray coats, than spray the entire box. A cheap gravity feed HVLP gun and dry air make pretty quick work of the job.
the Dull (10% sheen is one of my personal favorites - it looks like a nice oil and satin waxed finish, but the 35% Satin is most commonly used on millwork and kitchen cabinets)
presumably there would be similar products available in your vicinity -
I've found tThe major issue with clear coat finish on exposed edge grain of the BB plywood is the open pores on end grain of each alternating core layer. There are paste fillers available, but my cheap and nasty approach has been to mask off the adjoining faces and give the exposed edges a couple of lightly fogged in spray coats, than spray the entire box. A cheap gravity feed HVLP gun and dry air make pretty quick work of the job.
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Thanks,
Have not done any crossovers yet so that might be something interesting to do.
Might just get the 7P to save some hassle otherwise.
Have not done any crossovers yet so that might be something interesting to do.
Might just get the 7P to save some hassle otherwise.
This weekend I have been trying to cobble up a filter for my speakers. It turned out that the A12PW takes care of BSC by itself reasonably well (something that Bob Brines also noted). The A7P does not, and needs correction to work with a basic first order series filter. My other alternative is to implement an acoustical LR2 filter, and account for the pole shifting that the BS causes.
My first attempt at a series filter is now at the point where both male and female voices sound natural. It needs some tuning still, but I have to take the speakers outside in order to be able to measure at a better resolution than what I am able to achieve in the basement. The LR2 variant is still on my agenda to try.
My first attempt at a series filter is now at the point where both male and female voices sound natural. It needs some tuning still, but I have to take the speakers outside in order to be able to measure at a better resolution than what I am able to achieve in the basement. The LR2 variant is still on my agenda to try.
It is a week later now, and I have been mucking extensively with the filters while listening to music and measuring responses. First I need to make a remark on the impedance plot in the A7P datasheet and on the Madisound website. It is not the plot for the A7P, as can be seen on the resonance peak at 40-something Hz. That is a tad unrealistic for such a small driver. My impedance measurements confirm this, they match with what can be expected based on the T/S parameters in the sheet, not with the curve. The characteristic "blip" in the impedance lies around 730 Hz. I measure 11 Ohms at the peak of this blip. It's not a big thing, but it should be noted for anyone wanting to make a traditional crossover for the A7P.
Due to the behavior around the baffle step frequency of the A12PW and the A7P being different, I couldn't really get the series filter working to my taste. I have had much better results with a normal first order filter consisting of a 1 mH inductor for the woofer, and a 24.2 (22 + 2.2 in parallel) uF capacitor for the "tweeter", with the tweeter padded down with a resistive L-pad to the right level. The resulting response has a slight "saddle" around 1500 Hz, and needs some further refinement (small steps will get me there), but it gives me an idea where things might be going.
The treble sounds a bit odd to my ears. It may be a matter of taste, but I can not make it sound lively and easy to listen to at the same time when attempting to correct it with the filter. My measurement of the response show a depression of roughly 5 dB between 6 kHz and 16 kHz. Any attempt to correct the depression brings back the liveliness, but it also makes me want to turn the volume down when playing music. I am now trying to find a clue about the cause of this depression, in order to (hopefully) find something I can do about it. Would anyone care to give a suggestion? My first experiment will be to fill the A7P compartment with sheep wool, in addition to the polyester wool plates that are now used to cover the compartment's walls.
Due to the behavior around the baffle step frequency of the A12PW and the A7P being different, I couldn't really get the series filter working to my taste. I have had much better results with a normal first order filter consisting of a 1 mH inductor for the woofer, and a 24.2 (22 + 2.2 in parallel) uF capacitor for the "tweeter", with the tweeter padded down with a resistive L-pad to the right level. The resulting response has a slight "saddle" around 1500 Hz, and needs some further refinement (small steps will get me there), but it gives me an idea where things might be going.
The treble sounds a bit odd to my ears. It may be a matter of taste, but I can not make it sound lively and easy to listen to at the same time when attempting to correct it with the filter. My measurement of the response show a depression of roughly 5 dB between 6 kHz and 16 kHz. Any attempt to correct the depression brings back the liveliness, but it also makes me want to turn the volume down when playing music. I am now trying to find a clue about the cause of this depression, in order to (hopefully) find something I can do about it. Would anyone care to give a suggestion? My first experiment will be to fill the A7P compartment with sheep wool, in addition to the polyester wool plates that are now used to cover the compartment's walls.
The first time I heard the 7p's up at Dave's house, I wasn't impressed at all. I've just recently heard them again at Chrisb's house in the big dual woofer MLTL's. The difference isn't subtle. They sound exactly like you'd expect a paper Alpair driver to sound, really good. Other than being in a different enclosure, the only difference is the number of hours on the drivers AFAIK.
jeff