Adding Tweeters - should everyone? wiring/crossover?

[Wild Turkey]

(Update: Added, they sound great, and everyone should do this!)

I've got some tweeters that go in the front "sails" of the doors that I want to install. Unfortunately I don't have the specs on the tweeters other than that they sound great when I connect a sound source to them. I'm hoping this will help with the lack of the high end in my NSX. I'm figuring to this in the winter while I have the door apart doing the Hugo window fix.

My search turned up empty. I'm wondering how to wire the tweeters in? Do I need specific crossovers coming out of the BOSE amps? I assume I need more than just a capacitor in series? Have there been any threads on this, preferably with pictures? Or is the strong recommendation to add smaller tweeters to the stock BOSE units? I've seen some older threads on this, but looking at it, it seems it would make more sense to have the tweeters in the door sails pointing at the occupants than down by my knees.

Thanks in advance for input on it.

 

[Heineken]

I assume your speakers are still original? In that case you would have to attach them to the actual speaker pins inside the speaker box. The Bose system utilizes active speakers that are supplied with line level signals and power - compared to passive speakers used in most vehicles.

A capacitor in series (to create a high pass) is a good idea - you'll probably have to experiment a little and check how it sounds.
The actual speakers in the box are 2 Ohm, which is unusually low - just to keep in mind when calculating filters.

 

[Old Guy]

You are entering terra incognito! The Bose amp is a class D switching amplifier that uses internal feedback for signal conditioning which is not really conducive to having its output circuits messed with.

On a class D, the speaker impedance can be a critical component of the switching circuit on the H bridge output. This may be less of an issue with the Bose because it is an older design and still has those external inductor coils on the board in series in the speaker circuit. I have a class D guitar amplifier with no inductors in the output bridge and relies totally on the inductance of the speaker voice coil. Mess with the speaker and you are seriously messing with the amps output circuit.

If the Bose amp feedback circuit is tolerant of changes to the impedance - frequency profile of the speaker, you need (or should have) a crossover and speaker combination that still presents the same impedance to the amplifier as a single speaker. That is one of the functions of the crossover. If the original Bose speaker is 2 ohms you want the crossover to look like 2 ohms when both speakers are connected to it. If the Bose speaker is 2 ohms and the tweeter is 2 ohms and you just connect them in parallel it will look like 1 ohm which can create problems for the amp (dead output FETs). A properly designed crossover will allow you to attach 2 speakers of the same or different impedances and present a 2 ohm impedance to the amplifier.

A tweeter connected in series with a capacitor is just a low pass blocking (oops - meant high pass ) filter (a filter that you don't know the crossover point on). If you connect that in parallel with the existing speaker you still run into the total impedance miss match problem. To connect a proper crossover, you need to disconnect the Bose speaker from the amp terminals and run the amp output directly into the crossover input. Then one output of the crossover goes to the Bose speaker and the other goes to the tweeter. If you scrounge around on the web you can find guides on how to design a passive crossover to get your impedance matches and desired frequency roll off. Be aware that passive crossovers are not efficient. Because you are starting with a very low impedance Bose speaker you will need to add parasitic elements in the cross over to get the total impedance back into the acceptable range so you may experience a slight loss in volume.

All that said, there may be one easy out if you can find a high impedance tweeter such as 8 ohms (16 ohms would be even better). If you connect a 16 ohm speaker directly across the terminals of the existing Bose speaker the net impedance to the amp is 1.78 ohms. The Bose amp may be OK with that as long as you don't crank the volume up to max. You can add a capacitor in series with the tweeter as a high pass filter to block low frequencies to the speaker; but, unless you have the impedance versus frequency profile for the tweeter you cannot calculate the 3 db roll off for the tweeter circuit.

 

[Heineken]

Thanks @Oldguy, that was much more elaborated than my response

As far as I can tell, the central speaker is attached via a capacitor onto basically the same amplifier design and output coils, therefore I wouldn't be too concerned about the Bose amps getting damaged - but I might be wrong.

 

[Old Guy]

I agree that as long as the tweeter is not really low impedance the risk of damage to the amp is probably minimal.

I see that some automotive tweeters are sold pre packaged with what they call a cross over network. However, since it is a single input and output device it cannot be a crossover and is likely a high pass filter. If you get a tweeter with an included 'cross over' the vendor has likely matched the 3db point on the filter to the response of the tweeter which eliminates the guess work associated with trying to specify an input filter capacitor. A tweeter with a matched high pass input filter increases the impedance (of the tweeter) as seen by the amplifier at low frequencies. Since high power at low frequencies is usually when the amp output stage takes it on the chin, that probably reduces the risk of cooking the output FETs to a couple of places on the right side of the decimal point.

So, if @Wild Turkey has tweeters with matched crossovers / input filters then he is probably good to go. As you note, just connect the tweeters to the actual amp output terminals inside the enclosure.

 

[Wild Turkey]

No crossovers, so perhaps I need to abandon the idea of using these old tweeters, which were used in an NSX before (thus being built in to front "sails",) since I don't know how they were hooked up to the stock NSX speaker enclosures.

Suggestions welcome for kits to add tweeters either to some stock front sails, or mount behind the material with the stock speaker enclosures in the door when I do the Hugo window repairs.

 

[Old Guy]

Are they built in as in 'that sucker is never coming out' or can the tweeter actually be removed from the housing? If the tweeter can be removed, the safe would way be to find a new tweeter of the same dimensions sold with a matching filter. If that is a no-go, audio vendors do sell input filters for tweeters. Crutchfield has some which they more accurately refer to as 'blockers'

Bass Blockers at Crutchfield Canada

Shopping for Bass Blockers? Our Virginia-based experts love helping folks find the right gear. Get free shipping and free lifetime tech support with your order.

www.crutchfield.ca

The Crutchfield things look suspiciously like a capacitor covered with heat shrink. Search around and you may be able to find something a little more sophisticated.

 

[Wild Turkey]

Following up - should everyone add accessory tweeters if they have the OEM stereo? Probably yes.

SPECTACULAR! I can hardly believe how much better the stereo sounds with much clearer high midrange and high end. The difference is less dramatic with FM, but with the bluetooth from the GROM, what a difference!

I had a look at the way the tweeters were wired originally. The tweeters seem to be higher impedance, so less effect on the total impedance if added in parallel, as @Heineken thought. I measured 6 Ohms, for a total of 1.5 Ohms in parallel using Ohm's law, but I don't know how to add the (unknown) capacitor into the equation. The tweeters were previously wired in parallel inside the Bose speaker enclosure, as you both hypothesised, with a capacitor in series with the tweeter, 1/2 way between the Bose enclosure and the tweeter. No dedicated crossover. 6 Ohms seems to be in the ball park. Much higher and they would put out much lower sound levels than the Bose drivers.

I wired them the same way, but with the Crutchfield capacitors located inside the Bose enclosures. (As @Old Guy surmised, it's just a capacitor in series on one of the wires.)

Looking back, old news. (There was also another thread about tweeters added to the interior door panel but I can't seem to find it any more):

component tweeters added to stock bose setup

this is just a note for anyone considering adding component tweeters to the stock bose setup. I just had a set of jl's put in and it really sounds good (wont compete with aftermarket systems) but for anyone that prefers to keep the stock bose system in tact, adding components w/crossovers helped...

www.nsxprime.com

Some jewels here:

NSX OEM Stereo System - 101

Over time, there have been many threads about the NSX sound system; why isn't it working?; how can I fix it?; how can I upgrade it; etc. There is some content in the Wiki about it but some of it is dated and doesn't deal with some of the things that are available today so I had intended to...

www.nsxprime.com

 

[whh333]

I took the panels off the passenger door of my 1992 to fix the window regulator and this is what I found

I think the speaker is the original and here is a detail of what seems to be the crossover


The setup measures 4ohms on both doors and sounds good to me.

I see a lot of OEM speakers on the classifieds, the prices indicate they have value and it seems they would still be serviceable, should I just leave this the way it is or should I consider some sort of upgrade? My concern is whether the OEM speakers are generally OK after 32 years?

I am just trying to do whatever seems needed while the doors are apart.

Thanks for any ideas!

 

[Wild Turkey]

Zoiks! Have a good read of the OEM stereo 101 link that I referenced in post #8 as this looks nothing like OEM to me. I'll defer to the stereo experts, but in terms of whether you need to upgrade the stereo, are you happy with it? (other than the "novel" install under the door trim) I generally subscribe to the "If it ain't broke, don't fix it." strategy. (The speakers offered for sale on Prime would usually include the original Bose Amps in the original enclosure to function with the OEM head unit.)

1. My 1995 OEM speakers are still working great after 29 years, but that's probably moot since your pictures don't look like the OEM setup to me. My OEM speaker didn't have that protuberance in the middle. Is it Co-ax?
2. Does that clear plastic box even include an amp like the OEM speaker box? It looks like a cross-over to me as you've hypothesised.
3. Speaker impedance should be 2 Ohms to work with the OEM amp, but you don't seem to have the OEM amp anyway, or at least it's not in the pics. Do you even have an amp out by the speaker, or has the head unit been changed to one with passive speakers?

It seems more info is required. For a picture of what it should look like, see post #15 in this thread:

Post in thread 'Door seal (aka vapor barrier) part number mystery'

23 April 2024

Thought I'd update this thread since I just changed my door seals, which I found to be hardened and cracked when I went to install the @whrdnsx window fix-it kit.

I was able to just reuse the old Honda 08712-0003 sealant that @Old Guy mentioned on my driver's door, but the sealant on my passenger door was no longer sticky in spots. 3M windo-weld per @MotorMouth93 above worked great to fill in the gaps. Probably would have been nicer looking to pull all of the old white Honda sealant, but it's hidden, so functional will be adequate.

With respect to using the JDM door...

• Wild Turkey

 

[whh333]

@Wild Turkey, thanks, you have answered my questions.

I thought someone had removed the original speaker from the original enclosure and mounted it directly to the door, but since this is not the case, I can handle this as an aftermarket situation.

There is no other amplifier outside of the radio, so this is purely a crossover box driving what must be a coaxial speaker with separate inputs for the upper and lower ranges.

Yes, I have an aftermarket radio needing 4 ohms, I thought the crossover box was performing crossover and ohm adjustment when I was thinking these were the original 2-ohm speakers.

My reason for considering change is that the setup and speakers look old and it seemed I could eliminate the crossover and get more recent speaker design by mounting new 6" coaxial speakers, which is what I will probably do.

Thanks!