I have been working on an MLTL cabinet for the Alpair 10.2 Here is the result. The first picture is my new M10-A10. The second picture is the M10-A10 next to the Pensil 10.2, both in raw plywood. The FR plot is a comparison of the performance of two cabinets. A bit of explanation:
Because I don’t have access to an anechoic chamber, the bottom ends of the graphs are created by combining the driver and port nearfield responses. The top end is a gated 1/2m response. I am now thinking that I spiced the plots slightly wrong and the actual bass response of both cabinets is probably ~2dB less than indicated here. The M10-A10 is the black trace, the Pensil 10.2 is the red trace. The green trace is a crude representation of the published Alpair 10.2 response.
The M10-A10 and the Pensil 10.2 perform pretty much the same, other than the unbraced sides of the Pensil produce enough noise to screw up imaging. (This was a short cut that I took to get the boxes together quickly – I had them running in two days. I will probably run some dowels through the sides and veneer them for sale sometime in the future.) So why do a new design? It is a matter of design philosophy. I suspect that Scott’s design was driven by ultimate ease of construction. The cabinet is highly resonant and uses a LOT of stuffing to produce a reasonable output. My approach uses all of the tools to reduce all resonances except the fundamental with a minimum of stuffing – the cabinet is lined with fiberglass but uses no stuffing per se. The result is a cabinet that is somewhat taller and much less bulky.
The end result of either approach is a very fine sounding speaker. Which is better? Well, if you are asking me….
Because I don’t have access to an anechoic chamber, the bottom ends of the graphs are created by combining the driver and port nearfield responses. The top end is a gated 1/2m response. I am now thinking that I spiced the plots slightly wrong and the actual bass response of both cabinets is probably ~2dB less than indicated here. The M10-A10 is the black trace, the Pensil 10.2 is the red trace. The green trace is a crude representation of the published Alpair 10.2 response.
The M10-A10 and the Pensil 10.2 perform pretty much the same, other than the unbraced sides of the Pensil produce enough noise to screw up imaging. (This was a short cut that I took to get the boxes together quickly – I had them running in two days. I will probably run some dowels through the sides and veneer them for sale sometime in the future.) So why do a new design? It is a matter of design philosophy. I suspect that Scott’s design was driven by ultimate ease of construction. The cabinet is highly resonant and uses a LOT of stuffing to produce a reasonable output. My approach uses all of the tools to reduce all resonances except the fundamental with a minimum of stuffing – the cabinet is lined with fiberglass but uses no stuffing per se. The result is a cabinet that is somewhat taller and much less bulky.
The end result of either approach is a very fine sounding speaker. Which is better? Well, if you are asking me….
Attachments
Happy New Year Bob!
Those are handsome looking speakers (as usual from you!). Is the supra baffle a must or that is mainly an aesthetic function?
Some listening impressions on different genres and in comparison to your A 7.3 and TB W8 design would be welcome.
-Zia
p.s. OT - Maybe too early to ask, but would you be designing a cab for the upcoming Alp 12.3?
Those are handsome looking speakers (as usual from you!). Is the supra baffle a must or that is mainly an aesthetic function?
Some listening impressions on different genres and in comparison to your A 7.3 and TB W8 design would be welcome.
-Zia
p.s. OT - Maybe too early to ask, but would you be designing a cab for the upcoming Alp 12.3?
Last edited:
Interesting, Mark. The gold driver does look good against the dark wood. Of course, assuming that I can sell some of these, I’ll use whatever the customer wants!
The veneer I used will not be repeated. It is beech, which I had from a customer who changed his mind about veneers. I don’t particularly like the broad and prominent grain. On top of that, it blotched somewhat when I applied the stain. If I need a dark brown wood, I’ll use either natural walnut or teak.
I redid the FR chart for the M10-A10. Here is the result:
Graph 1:
Gray=ungated 1/2m.
Black=combined nearfield + gated 1/2m.
Red=10*.
Blue=15*.
Green=20*.
Graph 2:
Gray=ungated 1/2m.
Black=combined nearfield + gated 1/2m.
Red=15*.
Blue=30*.
Green=45*.
Brown=60*
Graph 3:
Impedance.
Bob
The veneer I used will not be repeated. It is beech, which I had from a customer who changed his mind about veneers. I don’t particularly like the broad and prominent grain. On top of that, it blotched somewhat when I applied the stain. If I need a dark brown wood, I’ll use either natural walnut or teak.
I redid the FR chart for the M10-A10. Here is the result:
Graph 1:
Gray=ungated 1/2m.
Black=combined nearfield + gated 1/2m.
Red=10*.
Blue=15*.
Green=20*.
Graph 2:
Gray=ungated 1/2m.
Black=combined nearfield + gated 1/2m.
Red=15*.
Blue=30*.
Green=45*.
Brown=60*
Graph 3:
Impedance.
Bob
Attachments
Thanks, Larry. Bass is very good, but these speakers may need a bit of BSC. I suppose it depends on how close to the wall you have them, but @3', I wind up with some 3dB of bass boost. I use DSP for my EQ, so it is not an issue. I may have to add a BSC filter for those who can't/won't to digital EQ.
I have the plans available now, but the new page will not be on the web site for a few days. PM me.
Bob
Well, sort of both. With the 3/4" round-over on the supra baffle added to the 3/4" round-over on the main cabinet, you get an effective 1 1/2" round-over. Theoretically, this is good. Whether you can hear it is another matter. The supra baffle is attached with double-sided foam tape. This forms a constrained layer sandwich. Theoretically, this reduces vibration transfer from the driver to the cabinet. Again, whether you can here it.... Finally, the black oval is my signature. I am sure you can hear that!!
Each of these drivers present an entirely different challenge. The 7.3 is definitely a mid/tweet. My T7-A7 is turned to 45Hz and the F3 is near 50Hz. It can be EQ'd to do much deeper bass, but this is not a good idea if you intend to run much rock through them. The M10-A10 is tuned to 38Hz and the F3 is near 40Hz. If you can keep the SLP below 85dB at 8', then you can play just about anything. Remember that the max excursion is going to be at ~80Hz -- right where the kick drum slap will be. BTW, I brickwall high pass these at 30Hz. The TB W8-1772 is an 8" driver with fair excursion. It has lots of guts and with care, might be used as (small) party speakers. As you go up is size, you trade finesse for guts. It you are going to use a sub or do a FAST, then the 7.3 would be the choice, probably crossed at the floor bounce. For general polite listening, the 10.2. For stuff that requires guts, the TB.
-Zia
I have not immediate plans for the 12.3. However, if you would like to have a pair delivered to me, I might see what can be done.
Bob
Pensil Vibration
That should work, on my pensils I had a lot of side to side braces except for where the holey brace was in the upper half of the cabinet. Had to go back and glue a few braces in that pass through the holey brace holes. Problem solved, no vibration.
What kind of DSP do you use Bob?
That should work, on my pensils I had a lot of side to side braces except for where the holey brace was in the upper half of the cabinet. Had to go back and glue a few braces in that pass through the holey brace holes. Problem solved, no vibration.
What kind of DSP do you use Bob?
Perhaps my choice of words was not the best. Lets look at the modeled FR traces. The first is is the M10-A10 with no stuffing. Next, the M10-A10 with moderate stuffing (this was at 10 watts, sorry). The third is the Pensil 10.2 without stuffing. Finally the Pensil 10.2 with heavy stuffing. Use your own adjectives. Different design philosophy, roughly the same final result as verified by actual builds -- see post#1.
Bob
Attachments
Bob, I'm not much of a spec or modeling expert, but do the 2 graphs depict a 10dB difference in reference SPL for the same driver
As I said in the post you quoted the M10-A10 plots were at 10w. The Pensil 10.2 is at 1w -- 10dB different.
Bob
As long as you don't overpower these speakers, they won't change much with power levels. But your ears hear different at different power levels. I have 3,6,and 12dB loudness EQ's for each of my speakers. This allows me to listen at very low levels and still have some sense of sonic balance in the music. I would recommend that you adjust your stuffing for the SPL level you will use most often.
Bob
Stuffing
Much like you I am already using my DSP to provide a dynamicEQ function that boosts the bass depending on the listening level for the percieved appropriate response. This is critical in a system that is calibrated flat IMHO to avoid that boring plain sound.
To find what I was looking for I removed the stuffing and ran the calibration. I found that even though the system was able to work out some of the issues with the response, the blending of the front and rear output was not pleasant to me. Overstuffing yeilded better results but actually restricted the low end a fair amount.
Your soultion of lining the walls and using the cabinet geometry to tune out the rear output in the upper frequency ranges may be ideal. Your design really seems efficient in the low end.
Do you have a way to measure the impedance of your new speaker?
Much like you I am already using my DSP to provide a dynamicEQ function that boosts the bass depending on the listening level for the percieved appropriate response. This is critical in a system that is calibrated flat IMHO to avoid that boring plain sound.
To find what I was looking for I removed the stuffing and ran the calibration. I found that even though the system was able to work out some of the issues with the response, the blending of the front and rear output was not pleasant to me. Overstuffing yeilded better results but actually restricted the low end a fair amount.
Your soultion of lining the walls and using the cabinet geometry to tune out the rear output in the upper frequency ranges may be ideal. Your design really seems efficient in the low end.
Do you have a way to measure the impedance of your new speaker?
Nice one Bob, those look great. 
Hope they do well for you, they deserve to.
You're spot on BTW; the pensils are far from being the last word in MLTLs; they were intended to be simple to build cabinets providing reasonable performance & a degree of adjustability via the damping for people to experiment should they wish. I did have an ulterior motive too; the high damping requirements should in theory produce a relatively unreactive load, which I thought could be useful for boxes at the simpler construction end that often end up being used with a wide variety of amplifers. For the sake of interest the 10.2 box has a different Vb alignment to the other pensils, purely to keep the size reasonable (since the vertical dimension is fixed in these boxes). Bit of a compromise, but it still works acceptably.
Hope they do well for you, they deserve to. You're spot on BTW; the pensils are far from being the last word in MLTLs; they were intended to be simple to build cabinets providing reasonable performance & a degree of adjustability via the damping for people to experiment should they wish. I did have an ulterior motive too; the high damping requirements should in theory produce a relatively unreactive load, which I thought could be useful for boxes at the simpler construction end that often end up being used with a wide variety of amplifers. For the sake of interest the 10.2 box has a different Vb alignment to the other pensils, purely to keep the size reasonable (since the vertical dimension is fixed in these boxes). Bit of a compromise, but it still works acceptably.
Last edited:
- Status
- This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.