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JBL A180 Tower Speaker Review

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    Votes: 35 17.8%
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    197

Dennis Murphy

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@Dennis Murphy

Since you have extensive experience with the BMRs, wouldn’t their unique size allow you to respect the D’appilito distances? Or is the distance not respected in your Philharmonic tower?
Close, but no banana. The tower is crossed at about 3700 Hz, which gives a wavelength of about 3.2" The Cente -to-Center distance between the BMR Mds and the RAAL tweet is 3.5". As usual, it's trade-off time. There's a limit to how close you can make the various routings without risking structural failure. And you don't want to cross the tweet much lower because distortion will rise.
 

abdo123

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Close, but no banana. The tower is crossed at about 3700 Hz, which gives a wavelength of about 3.2" The Cente -to-Center distance between the BMR Mds and the RAAL tweet is 3.5". As usual, it's trade-off time. There's a limit to how close you can make the various routings without risking structural failure. And you don't want to cross the tweet much lower because distortion will rise.
Do you happen to have some sort of measurements just to see what are we compromising?
 

cavedriver

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10.5 ft?? or I am confused how do you calculate the distance?

NVM thought it was a front 3 channel layout lol
I was ignoring the "10.5", it's from the other thread and presumably is the solution for d for another application that the poster copied the image from. I just estimated d by reading the note at the top and obtaining the wavelength for sound at 2 kHz. Without D'Appolito's book or paper or whatever I have no idea if this is correct. The comments I've read several places suggest it's fairly hard to build a speaker with the correct spacing because you basically have to squeeze the drivers so close together that you can't use off the shelf drivers. I don't get that from this image.
 

Dennis Murphy

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Do you happen to have some sort of measurements just to see what are we compromising?
You can check out the Audioholics measurements, which are quite extensive. Obviously nothing is sacrificed in the horizontal plane. The reviewer was only able to get to 15 degrees above the tweeter level for logistical reasons, but the response is very similar to the on-axis at that angle. Since I'm not sure what the "right" vertical dispersion pattern is, it would be hard for me to say what the compromise is.
 

MacCali

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I was ignoring the "10.5", it's from the other thread and presumably is the solution for d for another application that the poster copied the image from. I just estimated d by reading the note at the top and obtaining the wavelength for sound at 2 kHz. Without D'Appolito's book or paper or whatever I have no idea if this is correct. The comments I've read several places suggest it's fairly hard to build a speaker with the correct spacing because you basically have to squeeze the drivers so close together that you can't use off the shelf drivers. I don't get that from this image.
Kind of reminds me of the Arendal bookshelves which are massive, wonder if they followed this principle
 

abdo123

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There's a limit to how close you can make the various routings without risking structural failure.
I would love to hear more about this by the way, what is the minimum distance you think is necessary between two drivers (the two plastic rims)?

I've been exploring on paper some small 'satellite' designs focused on output from 100Hz and up (Like 4 liters sealed design) with MTM D'appilito distancing in mind and i would like to hear what you would consider a 'safe' distance between two drivers.
 
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sarumbear

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I would love to hear more about this by the way, what is the minimum distance you think is necessary between two drivers (the two plastic rims)?

I've been exploring on paper some small 'satellite' designs focused on output from 100Hz and up (Like 4 liters sealed design) with MTM D'appilito distancing in mind and i would like to hear what you would consider a 'safe' distance between two drivers.
According to d’Appolito the distance between low and high drivers should be less that half the wavelength at the crossover frequency and the voice-coils should be time aligned. At 2000Hz crossover drivers should be less than 9cm apart, which means you can’t use a low driver larger than around 4-5” in diameter.
 

abdo123

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According to d’Appolito the distance between low and high drivers should be less that half the wavelength at the crossover frequency and the voice-coils should be time aligned. At 2000Hz crossover drivers should be less than 9cm apart, which means you can’t use a low driver larger than around 4.5” in diameter.
the paper says one wavelength, not half. Can someone confirm which one it is? I was already thinking of using two 4' inch midwoofers. but ofcourse there will always be space needed between them for structural reasons, unless I 3D print a baffle.

index.php
 

sarumbear

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the paper says one wavelength, not half. Can someone confirm which one it is? I was already thinking of using two 4' inch midwoofers. but ofcourse there will always be space needed between them for structural reasons, unless I 3D print a baffle.

index.php
Then I’m wrong. It has been a long time ago that I read his paper. Why do you ask our advise then?
 

sarumbear

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I’m asking how much wood should there be between two drivers before it becomes a logistical nightmare or worse, fall apart.
That is always the problem with his design. You should have no “wood” between the drivers as you want the drivers as close as possible. One wavelength is the maximum distance. You also have to push the tweeter back (for time alignment), possibly using a short horn (or whatever you call them) and that will push the drivers further apart. It is a design nightmare indeed.
 
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abdo123

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That is always the problem with his design. You should have no “wood” between the drivers as you also have to push the tweeter back, possibly using a short horn (or whatever you call them) and that will push the drivers further apart. It is a design nightmare indeed.
I was kind of inspired by the work in progress ported tweeter Erin showed on his chanel, which should make these designs a reality (while remaining relatively simple) if you use a 1.5KHz crossover (with steep slopes) you would need the centers to be 9 inch apart, which is kind of reasonable.


Then I tried to go the other way around with a small 4" midrange with really high excursion (Purifi PTT4.0X08-NFC-01). The Driver is 5 inch in total in diameter.
Extension, sensitivity and output are all remarkable for a 4L cabinet, the distancing for a typical 2.7 KHz crossover (5 inch distancing required) becomes a little bit of a nightmare as you're looking at only 0.4 inch of wood between drivers.

1655680316257.png


The tweeter low frequency extension and output seems to be the biggest limitation, and when you job to a compression driver with a waveguide you're already way above the distancing requirements. The ported tweeter is aimed at car audio, but i really think decent horizontal centers would also be a great application.
 

sarumbear

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I was kind of inspired by the work in progress ported tweeter Erin showed on his chanel, which should make these designs a reality (while remaining relatively simple) if you use a 1.5KHz crossover (with steep slopes) you would need the centers to be 9 inch apart, which is kind of reasonable.


Then I tried to go the other way around with a small 4" midrange with really high excursion (Purifi PTT4.0X08-NFC-01). The Driver is 5 inch in total in diameter.
Extension, sensitivity and output are all remarkable for a 4L cabinet, the distancing for a typical 2.7 KHz crossover (5 inch distancing required) becomes a little bit of a nightmare as you're looking at only 0.4 inch of wood between drivers.

View attachment 213687

The tweeter low frequency extension and output seems to be the biggest limitation, and when you job to a compression driver with a waveguide you're already way above the distancing requirements. The ported tweeter is aimed at car audio, but i really think decent horizontal centers would also be a great application.
The question is what you gain with d’Appolito layout? Is that better than using a higher frequency crossover and using a midrange driver like in Revel Salon2?
 

abdo123

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The question is what you gain with d’Appolito layout? Is that better than using a higher frequency crossover and using a midrange driver like in Revel Salon2?
These are incredibly more complicated to model, design and measure in an amateur environment. Also better vertical dispersion is a plus for many reasons specially if you have seats at different heights.
 

hex168

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When spacing gets really tight, I've seen aluminum plates used for mounting. The Peerless GBS series midwoofers look interesting to help with the time alignment issue. Whether the whole D'Appolito thing is worth it, no idea.
 

Dennis Murphy

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That is always the problem with his design. You should have no “wood” between the drivers as you want the drivers as close as possible. One wavelength is the maximum distance. You also have to push the tweeter back (for time alignment), possibly using a short horn (or whatever you call them) and that will push the drivers further apart. It is a design nightmare indeed.
Now we're getting confused. First of all, the world doesn't end (although it might with current conditions) if you exceed the 1 wavelength rule. I've been researching this issue and have found almost nothing that really goes into the exact consequences. But I didn't quite make it with the tower, and so far there haven't been any complaints. Second, you don't have to time align the drivers. Look at the diagram. The drivers aren't time aligned, but you still get a straight forward lobe at the crossover point. That was one of the main objectives of the MTM design. In an MT, the forward lobe will tilt downard if the drivers aren't time aligned, or if you don't delay the tweeter electrically by adjusting its crossover slope so that it's steeper than the woofer's. If you mount the tweeter below the midwoofer in a TM, the frontal lobe will tilt upward. These two effects cancel in an MTM, and that's why you avoid the problem. As for the OP's question about front baffle structural integrity, my cabinet builder said 1/4" was as small as he was willing to go. I think that has more to do with the routing process than long-term rigidity, since the outer lip doesn't usually doesn't penetrate very far into the mdf.
 
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thewas

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I would love to hear more about this by the way, what is the minimum distance you think is necessary between two drivers (the two plastic rims)?

I've been exploring on paper some small 'satellite' designs focused on output from 100Hz and up (Like 4 liters sealed design) with MTM D'appilito distancing in mind and i would like to hear what you would consider a 'safe' distance between two drivers.
If you use Boxsim you can simulate and experiment with the directivity by using some similar sized drivers in their database.
 

sarumbear

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If you use Boxsim you can simulate and experiment with the directivity by using some similar sized drivers in their database.
Never heard of the software but I will try. Thank you for mentioning it.
 

thewas

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Never heard of the software but I will try. Thank you for mentioning it.
You are welcome, in its current version it gives quite close results for the included Visaton drivers, have designed a couple of loudspeakers for myself with it which didn't measure very differently.
 

sarumbear

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You are welcome, in its current version it gives quite close results for the included Visaton drivers, have designed a couple of loudspeakers for myself with it which didn't measure very differently.
Had a quick look. Very accomplished software and I think short of simulating it in MatLab or similar, it is the only such simulator.
 
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