I'm looking to upgrade the piezo tweeters in my 30+ year old tops with compression drivers. The tops are (Japanese) TOA SL-15 cabinets with 15" woofers, and piezo tweeters attached to a horn. I'm looking to replace the tweeter/horn with a modern compression driver and a 1-3/8 threaded horn. The woofer is rated for 250 watts @ 8 ohm and ~95dB sensitivity.
Here's my question:
Should I be looking for a compression driver with identical specs to the woofer? (250 watts @ 8 ohm; 95dB sensitivity) My understanding is that if I had a compression driver that had <250 watts handling that I would blow it at peak volumes if that's what I'm supplying to the woofer (using a passive crossover). My understanding is that if I had a compression driver that was more or less sensitive than the woofer then the high end would be either too loud or too quiet.
Thanks in advance for your help!
Here's my question:
Should I be looking for a compression driver with identical specs to the woofer? (250 watts @ 8 ohm; 95dB sensitivity) My understanding is that if I had a compression driver that had <250 watts handling that I would blow it at peak volumes if that's what I'm supplying to the woofer (using a passive crossover). My understanding is that if I had a compression driver that was more or less sensitive than the woofer then the high end would be either too loud or too quiet.
Thanks in advance for your help!
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Hello,
You can change the driver easily for example:
Drivers | Eminence Speaker
I used the 2002, I think there is bolt-on and screw-on version from it.
You should change the crossover, because the piezo needs a little different type.
S
You can change the driver easily for example:
Drivers | Eminence Speaker
I used the 2002, I think there is bolt-on and screw-on version from it.
You should change the crossover, because the piezo needs a little different type.
S
Similar speakers to your current ones have 80 W power handling, a 5 kHz crossover frequency and ~97 dB midrange sensitivity http://www.toacanada.com/assets/files/sl_series.pdf
How much are you willing to spend? Properly mating a 15" woofer to a 1" compression driver requires an expensive compression driver, as is has to play down to ~ 1 kHz if you want their dispersions to match. There are however many low budget 15" / 1" speakers that use a higher crossover around 2 - 2.5 kHz, allowing for a cheaper driver at the expense of a worse off-axis response.
Selecting a driver based on power handling is difficult, as it also depends on crossover frequency and efficiency. It is easier to look at comparable speakers and see whether a large high power driver is used or that a small one also suffices.
As an example, a Selenium D220Ti is a popular driver for $50, known from the 'Econowave' Selenium D220Ti 1" Titanium Horn Driver 8 Ohm 1-3/8"-18 . You can cross is at ~2 kHz.
How much are you willing to spend? Properly mating a 15" woofer to a 1" compression driver requires an expensive compression driver, as is has to play down to ~ 1 kHz if you want their dispersions to match. There are however many low budget 15" / 1" speakers that use a higher crossover around 2 - 2.5 kHz, allowing for a cheaper driver at the expense of a worse off-axis response.
Selecting a driver based on power handling is difficult, as it also depends on crossover frequency and efficiency. It is easier to look at comparable speakers and see whether a large high power driver is used or that a small one also suffices.
As an example, a Selenium D220Ti is a popular driver for $50, known from the 'Econowave' Selenium D220Ti 1" Titanium Horn Driver 8 Ohm 1-3/8"-18 . You can cross is at ~2 kHz.
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I appreciate the detailed response! I'd like to keep the cost to less than $100 per cabinet. I'll get new crossovers for each cabinet when I order drivers. That's a good point that the RMS power rating of the TOA is only 80W. Since I run them ~250 watts each I thought I needed a 250 watt compression driver, but I see my error there. Thank you.
I've looked at the D220. It's cheap enough and well reviewed, it seems. I'm concerned about the sensitivity though. If the 15" woofer has a 97 dB sensitivity, and the compression driver has a 109 dB sensitivity, wouldn't the high end be very much too loud?
(I realize that I can use an L-pad to soak extra power, but if I could pick a driver that didn't require that, I think I would prefer that.)
I've looked at the D220. It's cheap enough and well reviewed, it seems. I'm concerned about the sensitivity though. If the 15" woofer has a 97 dB sensitivity, and the compression driver has a 109 dB sensitivity, wouldn't the high end be very much too loud?
(I realize that I can use an L-pad to soak extra power, but if I could pick a driver that didn't require that, I think I would prefer that.)
Yes without L-pad it will be too loud. All compression drivers have a sensitivity above 97 dB so you'll need to use padding anyway. I understand that wasting power in resistor is not a pleasant concept. However, an efficient driver + L-pad together do not soak more power than a low efficiency driver without L-pad.
Other than that, compression drivers on constant directivity horns have a drooping response, which must be corrected for in the crossover.
Do you how to design the crossover?
Other than that, compression drivers on constant directivity horns have a drooping response, which must be corrected for in the crossover.
Do you how to design the crossover?
I see that the L-pad is going to be a feature. I can accept that.
Wouldn't it make more sense to use a 16 ohm compression driver with the 8 ohm woofer? Seems like I would be able to build a smaller L-pad if I was only dumping half as much power.
Although I have some background in EE, I have never designed a crossover and I'm entirely unfamiliar with the drooping response that you mentioned. I'm all ears if you can explain that or point me to more info. I had thought I would just buy high pass and low pass boards from Parts Express, but I'd rather do it as well as I can.
Interestingly, my SL15 cabinets have no crossover at all. The woofer is run full range and the 140-ohm piezo tweeter just has a 68-ohm resistor in series with it.
I really appreciate all your help.
Wouldn't it make more sense to use a 16 ohm compression driver with the 8 ohm woofer? Seems like I would be able to build a smaller L-pad if I was only dumping half as much power.
Although I have some background in EE, I have never designed a crossover and I'm entirely unfamiliar with the drooping response that you mentioned. I'm all ears if you can explain that or point me to more info. I had thought I would just buy high pass and low pass boards from Parts Express, but I'd rather do it as well as I can.
Interestingly, my SL15 cabinets have no crossover at all. The woofer is run full range and the 140-ohm piezo tweeter just has a 68-ohm resistor in series with it.
I really appreciate all your help.
Using a 16 ohms compression driver also is fine.
Designing a crossover has got a steep learning curve. It usually is done with simulation software (free ones exist) which require at least the amplitude and impedance response of the woofer and compression driver + horn as input data. This response depends on the horn you use, so you would have to measure this yourself. Learning how to do measurements and how to design a crossover takes time. Whether this is worth it depends on whether you enjoy learning or you just want a good result.
Thinking a different route..
A piezo driver and no crossover both indicate that the SL15 speaker is a low budget one. So woofer sound output is limited, so a compression driver might not struggle to be crossed over at a lower frequency. Then you could borrow the crossover from the Econowave design, if you also use both its $50 driver and $14 horn. You'll need the 'high-efficiency' version of the crossover. It will sound good, though I am not sure whether it will hold up to PA abuse. Maybe others can comment. Link to Econowave description: Zilch's AK Design Collaborative - Econowave Speaker | Page 12 | Audiokarma Home Audio Stereo Discussion Forums
Designing a crossover has got a steep learning curve. It usually is done with simulation software (free ones exist) which require at least the amplitude and impedance response of the woofer and compression driver + horn as input data. This response depends on the horn you use, so you would have to measure this yourself. Learning how to do measurements and how to design a crossover takes time. Whether this is worth it depends on whether you enjoy learning or you just want a good result.
Thinking a different route..
A piezo driver and no crossover both indicate that the SL15 speaker is a low budget one. So woofer sound output is limited, so a compression driver might not struggle to be crossed over at a lower frequency. Then you could borrow the crossover from the Econowave design, if you also use both its $50 driver and $14 horn. You'll need the 'high-efficiency' version of the crossover. It will sound good, though I am not sure whether it will hold up to PA abuse. Maybe others can comment. Link to Econowave description: Zilch's AK Design Collaborative - Econowave Speaker | Page 12 | Audiokarma Home Audio Stereo Discussion Forums
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I can see this is more complicated than I had hoped for, though I am not surprised.
I can't use any of the horns used in the Econowave as my cabinet is vertically challenged. Also most of the links on that page are dead, including all the crossover links, unfortunately.What do you think of these ideas:
1). Use a passive 12dB LR crossover to low pass the woofer, and another passive 12dB LR crossover to highpass the compression driver. Run them off the same amp. Use an L pad if needed to attenuate the signal to the compression driver. Use a DSP on the line-level to tweak the sound of both the woofer and compression driver (using an RTA mic, PC and pink noise for SPL/frequency data).
...or...
2). Biamp the woofers and compression drivers. Use DSP to band limit the woofers as well as tweeters, and also to tweak the sound (using an RTA mic, PC and pink noise for SPL/frequency data). Omit any passive crossovers and L-pad.
Once again, thank you for bringing your wisdom to bear on this.
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Ooh you have an RTA mic and DSP! Then it's no problem to design a crossover. The possibility to adjust it based on measurements is valuable.
Both of your ideas sound good. The first one is a bit safer / more reliable as the compression driver won't be blown if someone forgets to set a high pass filter. With the second one it is easier to make the individual drivers amplitude response match a target crossover curve and to time align woofer and horn.
The possibility to adjust it based on measurements is valuable.Both of your ideas sound good. The first one is a bit safer / more reliable as the compression driver won't be blown if someone forgets to set a high pass filter. With the second one it is easier to make the individual drivers amplitude response match a target crossover curve and to time align woofer and horn.
Technically I don't have an RTA mic yet, but it's been on my shopping list forever, so I'll bite the bullet. I do have a 2x4 DSP already. I'm glad to have not only one, but TWO acceptable paths to success now. Now I just have to decide whether to spend money on the 12 passive boards (8 crossovers and four L-pads), or spend money on a small amp to drive the compression drivers. Decisions decisions. Do you have any suggestions for free software for audio analysis? (For PC or Linux.)
Many thanks again for your invaluable input.
Many thanks again for your invaluable input.
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The crossover FD250 has jumpers for setting attenuation. Mine are at set at the lowest level. -7.5 dB Earlier I had them set with no attenuation and the sound was a bit trebled and from time to time (1 year wedding party every week) I had to replace coils. Now they don't burn. I also have some Eighteensound ND series drivers, but I think they give lower sound compared to the Seleniums, with the same jumper position. I Use the Eighteensound XT1086 Horn but I think I should use a larger one. I use this one because it makes the speaker smaller in height. Others need at least 20cm height. When I compare the horn opening to Yamaha or Turbosound speakers, they are indeed smaller. Every amp rack has an equalizer, so I can correct minor response changes, but I usually swap speakers and amps and don't touch the wave curve shape of the equalizer.
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I might just build new tops for the mids and highs
I'm thinking that I might go with a 4-way PA instaed of 3-way. The more I learn about "beaming", the more I think I shouldn't give my 15" tops anything over a few hundred Hz. I'd use my current subs and 15" low-mid tops, and then build tops that will cover the mids and highs using two compression drivers per side. I have a new topic on this idea here.
I'm thinking that I might go with a 4-way PA instaed of 3-way. The more I learn about "beaming", the more I think I shouldn't give my 15" tops anything over a few hundred Hz. I'd use my current subs and 15" low-mid tops, and then build tops that will cover the mids and highs using two compression drivers per side. I have a new topic on this idea here.
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